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Modification of partial safety factors for a semi-probabilistic evaluation of existing timber structures
The evaluation of the load-bearing capacity of existing structures is a central and important part in the work of structural engineers. Currently, engineers are confronted with the challenge of applying design rules developed for new structures in the evaluation of existing ones as no specific recommendations exist on a European level. As a contribution to this, a first step of this study is the evaluation of the reliability level of timber elements subjected to common limit states. Based on these analyses, modifications of the target reliability and of partial safety factors (PSF) for existing structures on the resistance side are studied. Considering a modification of the target reliability, the PSF for the material strength could be proposed with for compressive and flexural strength in limit states, where variable actions are present. Additionally, options for incorporating updated material parameters from a survey on site supported by technical devices are discussed and further need for research is identified. Subsequently, this paper provides a stepwise evaluation procedure including modified PSF considering both, an update of the target reliability and update of the material parameters obtained by a survey on site and is thus adaptive for different individual cases and level of information. First published online 10 February 2025
Copyright (c) 2022 The Author(s). Published by Vilnius Gediminas Technical University. http://creativecommons.org/licenses/by/4.0
Analysis for symmetrical and asymmetrical loading of a single-span combined string steel structure
The article consists of 3 parts. String analyzes with symmetrical loading, combined parametric analyzes of string structure with symmetrical loading and combined string structure analyzes with asymmetrical loading. Through various parameters, the influence of different parameters of the string on its behavior is revealed. The influence of prestressing in the combined string structure is also released. To assess the correctness of the results, an experimental study was carried out in the laboratory, after the structure was designed from steel elements. First published online 20 January 2023
Assessment of defects in masonry walls for the residential buildings in Lithuania
This paper presents the assessment of masonry wall defects in residential buildings in Lithuania. The created model is based on a multi-attribute evaluation of wall defects in residential buildings in Lithuania, the determination of their optimality criterion values calculated according to Laplace’o rule. The developed defect assessment algorithm has advantages to be used by repair contractors and people or companies performing building maintenance. First, the model allows planning the course of repair works properly. When carrying out repair work in a building with recurring defects that mainly occur at the building site, proper workflow and its planning are essential. The proposed model could be applied further to a building owner to select the most damaged walls. A background and a description of the proposed model are provided, and several key findings from the data analyses are presented. First published online 11 January 2023
Copyright (c) 2021 The Author(s). Published by Vilnius Gediminas Technical University. http://creativecommons.org/licenses/by/4.0
A simple approach for multi-criteria decision-making on basis of probability theory
In the present paper, a new concept of favorable probability is proposed first, and a simplified approach for multi-criteria decision-making is developed on basis of probability theory. It assumes that all the performance indexes of all alternatives can be divided into beneficial and unbeneficial types in the multi-criteria decision-making, and each performance index of all alternative makes its contribution to a partial favorable probability in positively or negatively correlative manners linearly upon its type of beneficial or unbeneficial; the partial favorable probability of each performance index with the same physical meaning is normalized in the alternative group; the product of all partial favorable probability of an alternative makes the total favorable probability of the alternative. As a consequence, all the alternatives can be ranked according to their total favorable probability comparatively in the multi-criteria decision-making. As application examples of the new method, the quantitative assessment of multi-criteria selection for effective dwelling house walls, project managers and contractor for construction works are given in detail, satisfied results are obtained. First published online 10 January 2023
Behavior of pre-stressed intersecting cable steel bridge
Cable-stayed bridges are known as one of the most effective and graceful forms of bridges. The main problem in the design of cable-stayed steel bridges is their deformability, especially under asymmetrical loads. Stabilization of the initial form of cable-stayed bridges can be achieved by selecting the appropriate cross-sectional area of the cables and their pre-stressing, as well as by increasing the cross-sectional height of the stiffness beam. However, a greater effect can be achieved by applying new forms of such bridges. Solutions for such bridges with an atypical arrangement of cables and additional pylons are already applied in practice. The article discusses an innovative pre-tensioned intersecting cable steel bridge structure system. The behavior of this bridge system under permanent and temporary loads is analyzed. Based on the performed numerical experiment, the efficiency of the innovative cable-stayed steel bridge system was determined. This newly designed bridge system is more effective in terms of stress and displacement distribution than a classic cable-stayed bridge system. First published online 10 January 2023
Techno-economic comparison of bifacial vs monofacial solar panels
A techno-economic analysis is performed for a solar farm with a 35 MWe installed capacity using bifacial solar panels and compared with standard monofacial solar panels at the same installed capacity level. The bifacial panel usage gain from total panel efficiency is identified from 4-year measurements to be within a range of 7.9–16.8% depending on monthly yield. A Monte Carlo simulation is carried out to forecast electricity prices under uncertainty. In terms of Net Present Value, it is found that the bifacial farm yields 12.6% higher values than the monofacial options under reference assumptions. An incremental internal rate of return (IRR) analysis is carried out yielding an IRR for the bifacial panels of 44% under various scenarios. The sensitivity analysis reveals that results are highly sensitive to discount rate and lifetime, and less sensitive to electricity prices. SWOT analysis performed to compare the bifacial with the monofacial panel and evaluate panels according to internal and external factors. The study was concluded with a summary of the technical specifications based on the test results. The results were used to identify that 12.2% added net present value corresponding to $186.7 – $214.5 per unit MW (under various electricity price trajectories) can be used as a reference for assessing the benefit for usage of bifacial PV for 35 MW type medium-size projects. In summary, it is suggested that bifacial solar PV with its outstanding techno-economic results can be the driving force of the growing solar PV market. First published online 08 July 2022
Experimental investigations on innovative crack repair methods and reinforcing steel structures with adhesivly bonded CFRP – lamellas
The paper describes some of the experiments carried out at the Chair of Steel and Timber Construction to reinforce steel with adhesively bonded CFRP lamellas. The first topic deals with the repair of cracks in steel structures exposed to fatigue. The aim was to extend the remaining service life of these components by means of adhesively bonded CFRP lamellas and then to compare the results obtained with established methods for repairing cracks. In order to improve the informative value of the investigations, several test parameters such as adhesive candidates, temperature, creep effects, degrees of prestressing, load levels and the position of the reinforcement measures were varied. The second set of topics examined the extent to which a typical steel beam-to-column connection can be reinforced with the help of adhesively bonded CFRP lamellas. First published online 08 July 2022
Modifying the composition of hollow-core slab concrete
The questions of the extruded concrete composition and the possibilities of modifying it are very important for the technology for the extruded concrete. The gained experience of working with the extruders of hollow core slabs shows that the operators of such equipment frequently choose an improper strategy for the production process. The main drawbacks are as follows: a) the use of fairly stiff mixture that is far above the necessary Vebe consistency class V2 for this technology; b) the over saturation of the mixture with coarse aggregates which determines a low compaction factor of the mixture; c) the rejection of using concrete admixtures which causes equipment overloads or led to its exploitation in the limitary conditions. Besides, the experience of using extruders proves that all parameters predicted by standards and other norms (for example, concrete strength class C40/50 or C50/60 including water cement ratio W/C<0,45) are obtainable without large efforts. Therefore, the main criteria for the suitability of such concrete modifi cation have rather technological character including the lowest energy consumption during shaping and the compaction of the semi manufacture of the reinforced article as well as the highest structural strength or stability of the fresh concrete slab. Whereas the mechanical properties (mainly strength) of such hardened concrete are mostly within acceptable values, it cannot be treated as the main criterion for optimizing the extruded concrete composition. Extruded concrete compositions used for producing hollow-core slab were chosen for technological and laboratory scale investigations. The amount of Portland cement in the concrete mixture was 335…370 kg/m3, sand made 0/2 mm grade – 330…440kg/m3 and 0/4 mm grade – 680…510 kg/m3; the amount of coarse aggregates 200…325 kg/m3 and 755…825 kg/m3 for grades 2/8 mm and 11/16 mm respectively; W/C ratio 0,34…0,39. The crushing strength of the extruded concrete was within 57…68 MPa and more (the results of technological trials). The character of the structure and the compaction level of the extruded mixture are the indicators of its technological suitability. Adding common lignosulfonate-based plasticizer (up to 1% of the cement mass) or a very small dose (0,2…0,3%) of the new generation super plasticizer with or without air entrainment agent could improve the structural and technological properties of such concrete. The experience obtained during laboratory scale investigations and on trials for the manufacturing lines of hollow core slabs shows that the main cause of such improvements is a better dispersion of cement particles in the stiff concrete mixture while the cohesion of the mixture of the freshly extruded article rests near unchanged. The effectiveness of such improvement was proven within the process of observing the level of the consumption of compaction energy – it was registered by the control console of extruders. After improvements in the concrete mixture were carried out, the consumption of compaction energy was reduced by 20…25 %. Investigations into concrete cores drilled-out from the hardened articles prove the apparently better structure of the modifi ed concrete while concrete strength and other physical properties rests rather unchanged (if the mixture W/C ratio rests unchanged). Improvements to concrete structure manifests by the absence of ‘air pockets’ (large pores of irregular form, air gaps trapped during mixture extrusion and compaction), more gradually distributed and comparatively small pores, the absence of internal concrete structure zones with cleft aggregates and loose sand particles and evenly coloured concrete (which proves a very good distribution of cement particles). The use of an air entrainment agent in the stiff concrete mixture allows reducing the dose of the plasticizer (super plasticizer) and reduces the density and crushing strength of the extruded concrete. Such was negligible during investigation and technological trials (up to 1,5 % of concrete density and about 3 % of strength), it was concluded that the air entrainment agent could be used in the extruded concrete for articles the exploitation conditions of which are severe, for example, for class XF2 etc. Article in Lithuanian. Tuštymėtųjų perdangos plokščių betono sudėties modifikavimas Santrauka. Straipsnyje aptariami ekstruziniu būdu formuojamų gelžbetoninių gaminių (tuštymėtųjų plokščių) betono sudėties parinkimo ir modifi kavimo klausimai, susiję su formavimo įrangą tausojančio darbo režimo taikymu (didelių energinių sąnaudų nereikalaujančiu betono mišinio sutankinimu, tuo pat metu išlaikant ekstruziniam formavimui būtiną mišinio koheziją) ir optimalios betono struktūros gavimo aspektais. Laboratoriniais tyrimais ir gamybiniais bandymais bei pagal specialią metodiką išpjautų betono kernų savybių tyrimais įrodyta, kad tinkamai modifi kavus ekstruzinio betono sudėtį, įmanoma išlaikyti visus šiems gelžbetoniniams gaminiams reikalaujamus betono parametrus: betono mišinio standumo (Vebe) klasę V2, betono gniuždomojo stiprio klases C40/50 ir C50/60, esant mažam V/C ir taupiai naudojant portlandcementį (330–360 kg/m3). Be to, gaunama tanki ir vienodai sutankinta betono struktūra. Toks modifi kavimas susijęs su stambiųjų ir smulkiųjų betono užpildų santykio parinkimu ir plastiklių (superplastiklių) naudojimu mišinyje. Įrodyta, kad nedidelio kiekio orą įtraukiančių įmaišų naudojimas standžiame betono mišinyje leidžia formuoti konstrukcijas, kurios gali būti eksploatuojamos agresyvesnėmis aplinkos poveikio sąlygomis (pvz., XD3 ir XF2). Reikšminiai žodžiai: ekstruderis, tuštymėtosios plokštės, Vebe konsistencija, betono mišinys, V/C santykis, plastiklis, betono kernai, poros. First Published Online: 16 May 2013
Copyright (c) 2009 The Author(s). Published by Vilnius Gediminas Technical University. https://creativecommons.org/licenses/by/4.0
The behaviour of axial compression timber elements at fire
This investigation is intended for an experimental assessment of the fire resistance of the axially loaded timber members aff ected by open flames and for comparing those with design results obtained in accordance wiTheC5-1-2:2005 provisions. Diff erently from metal or reinforced concrete structures, the longitudinal strains of timber at elevated temperature are negligible. A decrease in the bearing resistance of the timber member is associated with diminishing the cross section at the later stages of heat exposure. The process of diminishing the cross section leads to buckling an element or the other mode of fracture. The necessity of special equipment and a great quantity of smoke during an experiment are big problems for researching timber members under fire conditions. Therefore, practically it is impossible to use standard test equipment applied for testing steel or reinforced concrete members at elevated temperature. When researching the behaviour of axially loaded timber members under fire conditions, the furnace was specially designed to use a gas burner to provide the heating of specimen. The furnace was constructed from a special devise for loading the specimen and keeping it at required load level during the test. All timber specimens were of the same cross-section (50mm × 50mm) and length (1.2m). The compression specimens were pin-ended using spherical hinges. Fire resistance and the mode of failure were estimated during the test. The failure of axial compression specimens exposed to fire from one side is based upon diminishing the cross-section, a decrease in compression strength and the modulus of elasticity. In this case, the deflection of specimens follows flame direction. Design value fire resistance for timber elements was calculated using (EC 5-1-2:2005) provisions for the reduced cross-section. The calculation of load-bearing capacity was performed for axially loaded timber elements. The data required for design such as cross-sectional reduction due to charring and timber shrinkage was measured after testing fire. Article in Lithuanian. Medinių centriškai gniuždomų elementų elgsena ugnyje Santrauka. Šis tyrimas skirtas eksperimentiškai nustatyti medinių, pušies medienos centriškai gniuždomų elementų, veikiamų atviros liepsnos iš vieno šono, kai kiti šonai nėra apsaugoti, atsparumą ugniai ir palyginti su skaičiavimo rezultatais, gautais vadovaujantis EC5-1-2:2005 nuostatomis. Eksperimentiniams tyrimams vykdyti buvo sukonstruota kaitinimo krosnis, kurioje dujiniu degikliu buvo sukeliamas kaitros poveikis bandomiesiems elementams. Bandinių skerspjūvis kvadratinis (50×50 mm), o jų klumpamasis ilgis – 1,2 m. Galai įtvirtinti lankstais naudojant rutulinius lankstus. Bandymais nustatytas nedidelių skerspjūvio matmenų medinių elementų atsparumas ugniai, kai elementai apkrauti skirtingo dydžio gniuždymo apkrovomis. Pateikta gautų eksperimentinių rezultatų analizė, nustatyti veiksniai, turėję poveikį bandinių elgsenai ugnyje ir jų atsparumui ugniai, eksperimento duomenys sugretinti su skaičiuotiniais duomenimis. Reikšminiai žodžiai: mediena, gniuždymas, kaitra, anglėjimas, kaitinimo kamera, standartinė gaisro kreivė, atsparumas ugniai, klupumas. First Published Online: 16 May 2013
Application of uncertainty analysis to stability problems of steel-concrete structural members
The paper deals with the fuzzy analysis of the ultimate limit state of a steel strut with an encased web in compression. The first part of the paper lists presumptions required for the determination of the theoretical load carrying capacity for the column. Stresses in the concrete and steel sections are determined according to the principles of elasticity. The ultimate limit state is given as the limit stress attained in the most stressed section of either the steel or concrete section. A general extended principle, which takes into account the epistemic uncertainty of input parameters, was utilized for the conducted analysis. Neapibrėžtumo analizės taikymas plienbetonio konstrukcinių elementų stabilumo uždaviniuose Santrauka. Straipsnyje nagrinėjamas plienbetonio konstrukcinių elementų stipris remiantis fuzzy analize. Pirmoje straipsnio dalyje aprašomos prielaidos, reikalingos teoriniam kolonos laikomosios galios nustatymui. Itempiai plieniniuose ir betoniniuose skerspjūviuose nustatomi pagal tamprumo teorijos principus. Ribinis pavojingiausio pjūvio būvis pasiekiamas tada, kai įtempiai pasiekia ribinių įtempių reikšmes plieno apvalkale arba betono užpilde. Analizei buvo pasitelktas išplėstinis principas, kuris įvertina pradinių parametrų „epistematinį“ neapibrėžtuma. Reikšminiai žodžiai: plienas, betonas, konstrukcija, projektavimas, tvirtumas, fuzzy, yda. First Published Online: 16 May 2013
Strength evaluation of cold-formed steel columns using the results of finite strip and finite element linear stability analysis
Most cold-formed steel columns display open and rather thin-walled cross-sections which mean that their structural behaviour is strongly affected by local and global buckling. Th e local mode, that occurs for shorter profi les, is characterized by (i) the local plate mode (LPM) characterized by the simultaneous flexural buckling of the web and fl anges and (ii) by the distortional mode (DM) characterized by the displacements of flange-stiff ener edges (that remain plane). The global mode occurring for long profi les is characterized by (i) the fl exural mode (FM) characterized by the translation of the whole section in the direction of the major principal axis and (ii) by the fl exural-torsional mode (FTM) characterized by the simultaneous translation and rotation of the whole section. Th e possibility of using the results of linear stability analysis in the national codes of thin-walled cold-formed steel structural elements (for instance, European and Brazilian Codes) arises, i.e. local and global buckling instability modes and corresponding bifurcation stresses determining the ultimate strength of members. Two powerful numerical methods are chosen to perform a linear stability analysis of a cold-formed steel structural member: (i) the Finite Strip Method, (i1) the Semi-Analytical Finite Strip Method (trigonometric functions are used in the approximation of displacement) used for simply supported boundary conditions, (i2) the Spline Finite Strip Method (‘spline’ functions are used in the approximation of displacement) used other boundary conditions and (ii) the Finite Element Method. The linear local and global stability results of for Z, C and rack cold-formed columns are used to obtain ultimate strength through the procedures adopted in the Eurocode 3, Part 1.3 and in the Brazilian Code (NBR 14.762/2001). The obtained numerical estimates by specifi cations are compared with experimental results available in literature. Šaltai formuotų plieninių kolonų laikomosios galios įvertinimas naudojant baigtinių strypų ir elementų tiesinio pastovumo skaičiavimo rezultatus Santrauka. Dauguma šaltai formuotų plieninių kolonų turi atvirus arba plonasienius skerspjūvius, todėl jų konstrukcinė elgsena daugiausia priklauso nuo vietinio arba bendrojo klupumo. Vietinis klupumas, kuris būdingas (1) trumpesniems profi liuočiams, gali būti apibūdinamas vietinės plokštelės modeliu (LPM), pasižyminčiu vienalaikiu lenkiamuoju juostų ir sienelių klupumu ir (2) iškraipomuoju modeliu (DM), kurį apibūdina juostų ir sąstandų kraštų (kurie išlieka plokšti) poslinkiai. Bendrasis klupumas, kuris būdingas ilgiems profi liuočiams apibūdinamas (1) lenkiamuoju modeliu (FM). Jam būdingas viso skerspjūvio išilgai pagrindinės ašies pasislinkimas ir (2) lenkiamasis sukamasis (FTM) modelis, kuris pasižymi viso skerspjūvio pasislinkimu ir pasisukimu. Nacionalinėse šaltai formuotų plonasienių plieninių elementų normose (taip pat Europos ir Brazilijos) yra galimybė taikyti tiesinį pastovumo skaičiavimą, t. y. nustatant ribin elemento laikomąją galią naudoti vietinio ir bendrojo klumpamojo nepastovumo modelius bei atitinkamus išsišakojimo įtempiu. Šaltai formuotų plieninių elementų tiesiniam pastovumui skaičiuoti pasirinkti du veiksmingi skaičiavimo metodai: 1. Baigtinių strypų metodas: 1.1-pusiau analitinis baigtinių strypų metodas (trigonometrinės funkcijos naudojamos poslinkiui aproksimuoti), kuris taikomas lankstinio atrėmimo kraštinėmis sąlygomis; 1.2-kreivinių baigtinių strypų metodas („kreivinės” funkcijos naudojamos poslinkiui aproksimuoti), taikomas kitokiomis kraštinėmis sąlygomis. 2. Baigtinių elementų metodas. Z ir C skerspjūvių ir spragotųjų šaltai formuotų kolonų tiesinio vietinio ir bendrojo pastovumo rezultatai naudojami nustatyti ribine laikomąją galią remiantis Eurokodo 3 (1.3 dalies) ir Brazilijos normų (NBR 14.762/2001) priimtomis metodikomis. Pagal instrukcijas gautieji skaitiniai įverčiai palyginti su literatūroje randamais eksperimentinių tyrimų rezultatais. Reikšminiai žodžiai: šaltai formuotas, baigtinis strypas, baigtinis elementas, vietinio klumpamojo nepastovumo modelis, bendrojo klumpamojo nepastovumo modelis, normų reikalavimai. First Published Online: 16 May 2013
Analysis of methods for calculating the width of normal cracks in reinforced concrete structures
The width of normal cracks at the level of tensile reinforcement was calculated according to various methods using the data obtained from experimental tests on reinforced concrete beams (without reinforcement pre-stress), pre-cast reinforced concrete slabs and ribbed roof slabs. Th e numerical results were compared to actual crack widths measured during the experimental tests. Also, the crack widths of pre-stressed reinforced concrete beams were calculated according to various methods and compared with each other. Th e following conclusions were reached based on the analysis of numerical and experimental results: 1) Design stresses in tensile reinforcement calculated according to [STR] and [EC] design codes are very similar, although the calculation of such stresses is more logical and simple according to [EC]. Design stresses calculated according to [RU] are greater due to the estimation of the plastic deformations of concrete in the compressive zone. Th e method proposed by Rozenbliumas (Розенблюмас 1966) estimates tensile concrete above the crack peak, and thus allows a more accurate calculation of stresses in tensile reinforcement (Fig 3). Therefore, the latter stresses in pre-stressed RC beams may be decreased by 10–12 %, when height hct ≠ 0 (Fig 1, c) and ratio M/MRd varies between 0,65 and 0,75; 2) The widths of normal cracks in conventional RC beams (subjected to load that corresponds approx. 70 % of their carrying capacity) calculated according to [STR] and [EC] design codes are almost equal to the experimentally obtained crack widths. When beams and slabs are loaded by approximately 52 % of their carrying capacity, design crack widths wk [EC] are approximately 12 % less than wk [STR], although the design crack width wk [RU] is signifi cantly greater. Here, ratio β in the beams and slabs is equal to 2 and 3.3 respectively. Th erefore, the design code [RU] ensures higher probability that the crack width will not reach the limit value (for environmental class XO and XC1) equal in all design codes mentioned in this article; 3) In case of loaded prestressed reinforced concrete beams, the calculated increases of crack widths wk [EC], wk [RU] and w [5] are greater if compared to wk [STR] (Fig 6). Th e increased reinforcement ratio ρ has more signifi cant infl uence on the increases of crack widths calculated according to other design codes if compared to wk [STR]. Tensile concrete above the crack peak has signifi cant infl uence on the design crack width when pre-stressed RC beams are lightly reinforced (ρ ≤ 0,008); 4) During the evaluation of the state of fl exural RC members, expression (5) could be used for calculating the crack width or a position of the neutral axis when the heights of the crack and the tensile zone above the crack are known (calculated or measured experimentally). Design crack widths w (5) are very similar to the experimentally obtained results. Article in Lithuanian. Gelžbetoninių konstrukcijų normalinių plyšių pločio skaičiavimo metodų analizė Santrauka. Remiantis eksperimentinių gelžbetoninių sijų (be išankstinio armatures įtempimo) ir surenkamųjų gelžbetoninių perdangų bei stogo briaunotųjų plokščių tyrimų duomenimis, pagal skirtingas metodikas apskaičiuotas atsivėrusių normalinių plyšių plotis tempiamosios armatūros lygyje. Skaičiavimo rezultatai palyginti su tyrimų metu išmatuotais plyšių pločiais. Taip pat palyginti pagal įvairias metodikas apskaičiuoti įtemptojo gelžbetonio sijų plyšių pločiai. Atlikta analizė parodė, kad pagal Lietuvoje galiojantį statybos techninį reglamentą ir euronormas beveik vienodai įvertinamas normalinių plyšių atsivėrimas. Pagal Rusijos projektavimo normų metodiką apskaičiuotos paprastojo gelžbetonio sijų plyšių pločio vertės yra gerokai didesnės. Pateikta plyšio parametrų tarpusavio priklausomybė gali būti panaudota apskaičiuojant plyšių atsivėrimą ar nustatant neutraliosios ašies padėtį elemento skerspjūvyje, kai atliekami konstrukcijų būklės tyrimai ir vertinimas. Reikšminiai žodžiai: gelžbetoninės sijos, plokštės, armatūros įtempiai, plyšio plotis. First Published Online: 16 May 2013
The algorithm of the cross-section optimization of inelastic geometrical nonlinear steel frame structures
The purpose of the problem of optimization is introducing a project on the structure satisfying the limit requirements of the safety and usability conditions of the various eff ects of external actions. It can be provided by disposing comprehensive information about the real behaviour of construction under all working conditions and at any period of occurrence. Such problem cannot be solved applying the methods of the linear theory of structural mechanics because the form and dimensions of construction under assorted loads essentially change and the principle of small displacement becomes unreliable. In addition, starting from certain stress conditions, Hook’s law for majority materials is ineligible and changing by nonlinear relation. It is necessary to refuse the linear theory assumptions and change over to considerably wide and complex nonlinear theory generalizations. Abandoning calculation by unstrained condition tolerating small displacements allow changes in the infl uence of construction geometry on its defl ected mode, proceed to nonlinear tensions and relations with deformations and allow incipient plastic deformations because some materials of construction close to plastic collapse receive very large displacements and do not satisfy requirements for successful exploitation. Th ereby, the above mentioned causes must be allowed developing the mathematical models of solving the problems of construction optimization. A developed mathematical model and calculation algorithm with material inelastic properties as well as the evaluation of maintenance requirements are presented for the cross-sections optimization of geometrically nonlinear frames. Th e evaluation of dissipative features when employing inelastic steel stains results in a signifi cant reduction of reserve in carrying capacity in respect of the optimal elastic state of the structure. Maintenance requirements for the structure introduced to its operation time involve not only strength constraints but also stiff ness, stability and structural constraints defi ning minimal cross-section parameters and the ration of element slenderness. Th e aforementioned factors limit the free development of plastic stains, and therefore the optimal structure is considered in the state prior to plastic collapse. Th e used elastic response values are related to the optimal parameters of standard profi le cross-sections by nonlinear functional relation. Th erefore, this problem has to be solved using the iterative method. Th e procedure of forming a new beam element tangent stiff ness matrix considered by internal forces stimulated by diff erent element alterations is presented. Th e effi ciency of the developed algorithm exemplifi ed by calculating the optimal values of the cross-section involving 16-stroyed steel frame beam elements is obeyed by minimum volume requirements when node horizontal displacements are limited. Netamprių geometriškai netiesinių plieninių rėminių konstrukcijų skerspjūvių optimizavimo algoritmas Santrauka. Straipsnyje pateikiamas patobulintas plieninių rėmų kaip geometriškai netiesinių sistemų strypų skerspjūvių optimizacijos uždavinio matematinis modelis ir skaičiavimo algoritmas, įvertinantis medžiagos netampriąsias savybes bei eksploatacinius reikalavimus. Disipacinių savybių įvertinimas, naudojant netampriąsias plieno deformacijas, lemia reikšmingą laikomosios galios rezervo sumažinimą optimalios tamprios būklės konstrukcijos atžvilgiu. Eksploataciniai reikalavimai, keliami konstrukcijai jos naudojimo laikotarpiu, apima ne tik stiprumo, bet ir deformatyvumo, stabilumo ir konstrukcinius apribojimus. Jie apibrėžia minimalius skerspjūvių parametrus ir elementų ribinius liaunius. Visa tai riboja laisvą plastinių deformacijų plitimą, todėl optimali konstrukcija yra neyramoji tamprioji plastinė. Naudojami tampraus atsako dydžiai susieti netiesiniu funkciniu ryšiu su standartinių profi lių skerspjūvių optimizuojamais parametrais, todėl uždavinys sprendžiamas iteracijų būdu. Pateikta nauja rėminio strypinio elemento tangentinės standumo matricos sudarymo metodika. Atliktas 16 aukštų rėmo iš standartinių profi liuočių skerspjūvių optimizacijos uždavinio skaitinis eksperimentas. Reikšminiai žodžiai: optimizacija, tamprioji plastinė konstrukcija, geometrinis netiesiškumas, tangentinė standumo matrica, geometrinis standumas, plastiškoji irtis. First Published Online: 16 May 2013
Research on structures and technologies for sustainable development in constructions
“Research on structures and technologies for sustainable development in constructions”, Engineering Structures and Technologies, 1(1), p. 5–9. „Konstrukcijų ir technologijos tyrimai – darniosios statybos plėtrai“, Statybinės konstrukcijos ir technologijos, 1(1), p. 5–9. First Published Online: 16 May 2013
Copyright (c) 2010 The Author(s). Published by Vilnius Gediminas Technical University. https://creativecommons.org/licenses/by/4.0
Dangerous actions while installing building constructions and means to decrease their undesirable influence
Construction business is quite specific, that is why work safety management in construction companies is very specific too. Work safety management in construction companies and sites is difficult and much more complicated than in companies of other businesses. Analysis of work safety management systems in construction companies can be very diverse. It depends on the work quality and technological processes in construction sites (from the preparation for construction work to different extra processes). Because of the specific features of building, like its dynamic or diversity, it is very difficult to ensure safe work conditions constructing using traditional methods and especially new methods, processes, and technologies. There is practically always a risk of having an accident at work (while installing reinforced concrete, wooden or metal constructions or doing other construction technological processes) because it is almost inconceivable to decrease its possibility to the least level. Work safety in this article is analyzed in the light of dangerous actions doing installation or other construction work. There is also made a survey of scientific literature about dangerous actions and of experience of Lithuanian Work Inspection at construction sites, and report on observation of exact construction sites picking out the most dangerous factors, the most important of which is labors’ falling down from height. In the article there are data (about influence of dangerous actions on construction process) analyzed and systemized. All of them were picked out during forensic examination of work safety Summarizing made researches the author advises to use such preventions: it is advisable to pay attention not to all possible dangerous factors, but only to three of them – falling down from height, objects falling down on labors, and injuries made by working mechanisms. The author advises to use work safety assurance scheme (3rd picture) and while preparing technological projects to use 3S principle (principle of three schemes). Article in Lithuanian. Pavojingi statybos konstrukcijų įrengimo veiksniai ir priemonės nepageidaujamam jų poveikiui mažinti Santrauka. Straipsnyje aptariamos darbuotojų saugos ir sveikatos problemos, kylančios atliekant įvairius technologinius procesus statybvietėse, pasiūlyti realūs sprendiniai, padedantys užtikrinti statybos įmonių darbuotojų saugą. Atlikta naujausios mokslinės literatūros šaltinių apie pavojingų veiksnių statyboje tyrimus apžvalga, apibendrinta Lietuvos valstybinės darbo inspekcijos sukaupta patirtis, tiriant ir vertinant pavojingus veiksnius statybos procesuose, atliktas statybos darbų ir procesų stebėjimas konkrečiose statybvietėse, išskiriant pavojingiausius pagal poveikio dažnumą ir pasekmių sunkumą veiksnius, kurių svarbiausias – darbuotojų kritimas iš aukščio. Straipsnyje taip pat analizuojami duomenys (apie pavojingų veiksnių veikimą atliekant statybos procesus), kuriuos surinko autorius atlikdamas ekspertinius darbų saugos tyrimus. Minėti duomenys susisteminti, pateikiama konkrečių siūlymų, kaip mažinti nepageidaujamą pavojingų veiksnių poveikį. Reikšminiai žodžiai: statybos technologiniai procesai, nelaimingi atsitikimai darbe, pavojingi veiksniai statybvietėse, saugių statybos procesų projektavimas, saugos darbe sprendiniai, rizikos valdymas statybos procesuose. First Published Online: 16 May 2013
management of risk in construction processes
Copyright (c) 2009 The Author(s). Published by Vilnius Gediminas Technical University. http://creativecommons.org/licenses/by/4.0
Hydrotechnical concrete with local aggregates and them using for monolithic structures
The article discusses the technological peculiarities of construction monolithic hydrotechnical concrete structures, use of local aggregates for producing special concretes, methods of determining water impermeability of concretes as well as the evaluation of the methods mentioned above. The article presents the requirements for the granulometric composition of aggregate mixes for the production of flowing concrete mixes used for the construction of monolithic hydrotechnical structures. The possibilities and expediency of using local crushed gravel with increased amounts of weak particles for hydrotechnical structures are discussed. The mass loss of weak particles is slight compared with the whole mass of aggregates, and the total mass loss of crushed gravel it occurs due to micro-cracks present in particles. The frost resistance mark of crushed gravel and its suitability for hydrotechnical concretes should be determined by evaluating the amount of weak particles and their frost resistance. The article discusses concrete impermeability data received by means of two methods (according to LSTST 1974:2005 and LSTST EN 12390–8 requirements). Theoretical water penetration depths have been calculated. Determination of water impermeability according to LSTST 1974:2005 is recommended for C25/30 and lower compressive strength class concretes with W≤8. The LSTST EN 12390–8 water impermeability determina-tion method is recommended for C25/30 and higher compressive strength class concretes whose water impermea-bility mark is W≥8. For the construction of certain hydrotechnical structures water impermeable concretes whose water penetration depth should not exceed 20mm are recommended for use instead of the W6 and W8 concretes. Technological peculiarities and potential technological-organizational solutions for high walls of a water treatment plant have been discussed. The analysis of potential concreting methods of the reservoir’s high walls has been made as well as that of the key parameters of the continuous concreting process and their interaction. Dependences for the estimation of continuous concreting volumes and permissible concreted segment lengths have been proposed by evaluating the beginning of the intensive formation structure of concrete, number of layers in the height of the concreted wall and concreting intensity. Article in Lithuanian. Hidrotechninis betonas su vietiniais užpildais ir jo naudojimas monolitiniams statiniams Santrauka. Straipsnyje nagrinėjami hidrotechninių monolitinių betoninių statinių statybos technologijos ypatumai, vietinių užpildų naudojimo galimybės šių betonų gamybai, betonų nepralaidumo vandeniui nustatymo metodai bei jų vertinimas. Išnagrinėti vandens valymo įrenginių aukštų sienučių statybos technologijos ypatumai ir galimi technologiniai-organizaciniai sprendimai. Atlikta aukštų rezervuaro sienučių galimų betonavimo būdų ir nenutrūkstamos betonavimo technologijos procesų reguliuojančių parametrų bei jų sąveikos analizė. Pateiktos priklausomybės nenutrūkstamo betonavimo apimtims ir leistiniems betonuojamų segmentų ilgiams apskaičiuoti, įvertinant betono struktūros intensyvaus formavimosi pradžią, klodų skaičių betonuojamos sienutės aukštyje ir betonavimo intensyvumą. Reikšminiai žodžiai: hidrotechninis betonas, vietiniai užpildai, betono nepralaidumas vandeniui, betono struktūra, nenutrūkstamo betonavimo technologija, vandens valymo įrenginiai, aukštos rezervuaro sienutės. First Published Online: 16 May 2013
Investigating the protective properties of concrete containing ash from coal combustion in a fluidized bed
The article reports the results of research on the protective properties of concrete with the addition of ash from hard coal combustion in a fluidized bed at a power plant in Katowice. Research was carried out on concentrated water extracts from disintegrated concrete using a polarization technique. The results were compared with those obtained in a similar way from concrete extracts without additives and with criteria including the delimiting values of the parameters of the electrochemical process. The results have shown that concrete incorporating 15% and 30% ash as cement replacement correctly protect reinforcement against corrosion. Betono su skysto kuro krosnyje sudegintos anglies pelenais apsauginių savybių tyrimas Santrauka. Straipsnyje pateikti betono su Katowice gamykloje skysto kuro krosnyje sudegintos anglies pelenais apsauginių savybių tyrimų rezultatai. Taikant poliarizacijos technologiją buvo tiriamas vandens koncentratas, išskirtas iš suirusio betono. Rezultatai palyginti su panašių tyrimų rezultatais, kai taikant tokią pačią technologiją buvo tiriamas betonas be priemaišų. Rezultatai taip pat buvo palyginti pagal kriterijus, ivertinančius ribines elektrocheminio proceso parametrų reikšmes. Rezultatai parodė, kad, betone 15 ar 30 proc. cemento pakeitus pelenais, armatūra būna tinkamai apsaugota nuo korozijos. Reikšminiai žodžiai: apsauginės betono savybės, betono priedai, cementą pakeičiančios medžiagos, skysto kuro krosnyje sudegintos anglies pelenai, armatūros korozija, poliarizacijos kreivės, korozijos srovė, korozijos potencialas. First Published Online: 16 May 2013
Applying multi-user technology for modeling complex cad objects
Complex CAD modelling occurring in engineering design and construction processes relies upon the effective management of teamwork where a variety of specialists work together on the development of one compound object that leads to the following issues which have to be dealt with in order to make this process time- and cost-effective: i) difficulties in exchanging technical information (including drawings) due to modifications in the CAD model; ii) difficulties in tracking modifications performed by other project participants; iii) difficulties in working with elements connected to another element already used by other participants; iv) assessment of various object versions. To facilitate these processes and manage the flow of technical information between project partners, multi-user technology is considered. It operates with a complex CAD object in the same way as an electronic archive system in engineering document management systems and offers a level of control over the information flow within the construction process. “Multi-user” technologijos taikymas kompleksiniams statiniams projektuoti Santrauka. Modeliuojant didelius kompleksinius statinius, efektyvus projektavimo procesas priklauso nuo komandinio darbo suderinamumo. Tiek vienos projektinės grupės projektuotojai, tiek atskirų projektinių dalių inžineriai, dirbantys prie vieno didelio objekto, susiduria su tokiomis problemomis: 1) dėl CAD modelyje vysktančių pasikeitimų techninės dokumentacijos (brėžinių) apsikeitimo procesas tarp atskirų projektavimo grandžių yra sudėtingas; 2) projekto dalyvio ivesti taisymai laiku nerodo pasikeitimų; 3) sunku efektyviai projektuoti, jei vienas bendras konstrukcinis elementas arba objektas naudojamas atskirų projektuotojų; 4) versijų sekimas. Šio darbo tikslas – pateikti naujausią “multi-user” technologiją, kuri leidžia valdyti projektavimo procesą tarp projekto dalyvių, vykdant kompleksinių statinių CAD modeliavimą. Reikšminiai žodžiai: automatizuoto projektavimo sistemos, techninės dokumentacijos valdymas, “multi-user” technologija. First Published Online: 16 May 2013
techninės dokumentacijos valdymas, „multi-user“ technologija
Global optimization of grillages with a hybrid genetic algorithm
Aim of the article is to suggest technology for optimization of pile positions in a grillage-type foundations seeking for the minimum possible pile quantity. The objective function to be minimized is the largest reactive force that arises in any pile under the action of statical loading. When piles of the grillage have different characteristics, the alternative form of objective function may be employed: the largest difference between vertical reaction and allowable reaction at any pile. Several different allowable reactions with a given number of such piles may be intended for a grillage. The design parameters for the problem are positions of the piles. The feasible space of design parameters is determined by two constraints. First, during the optimization process piles can move only along the connecting beams. Therefore, the two-dimensional grillage is “unfolded” to a one-dimensional construct, and the supports are allowed to range through this space freely. Second, the minimum allowable distance between two adjacent piles is introduced due to the specific capacities of pile driver.The initial data for the problem are the following: the geometrical scheme of the grillage, the cross-section and material data of connecting beams, minimum possible distance between adjacent supports, characteristics of piles, and the loading data given in the form of concentrated loads or trapezoidal distributed loadings. The results of solution are the required number of piles and their positions.The entire optimization problem is solved in two steps. First, the grillage is transformed to a one-dimensional construct, and the optimizer decides about a routine solution (i.e. the positions of piles in this construct). Second, the backward transformation returns the pile positions into the two-dimensional grillage, and the “black-box” finite element program returns the corresponding objective function value. On the basis of this value the optimizer predicts the new positions of piles, etc. The finite element program idealizes the connecting beams as the beam elements and the piles – as the finite element mesh nodes with a given boundary conditions in form of vertical and rotational stiffnesses. The optimizing program is an elitist genetic algorithm or a random local search algorithm. At the beginning of problem solution the genetic algorithm is employed. In the optimization problems under consideration, the genetic algorithms usually demonstrate very fast convergence at the beginning of solution and slow non-monotonic convergence to a certain local solution point after some number of generations. When the further solution with a genetic algorithm refuses to improve the achieved answer, i.e. a certain local solution is obtained; the specific random search algorithm is used. The moment, at which the transition from genetic algorithm to the local search is optimal, is sought in the paper analyzing the experimental data. Thus, the hybrid genetic algorithm that combines the genetic algorithm itself and the local search is suggested for the optimization of grillages. Article in Lithuanian. Globalusis rostverkinių pamatų optimizavimas hibridiniu genetiniu algoritmu Santrauka. Straipsnio tikslas – sukurti technologiją polių padėtims rostverkiniuose pamatuose optimizuoti. Siekiama minimizuoti polių skaičių rostverke. Tikslo funkcija imama didžiausia atraminė poliaus reakcija, kuri optimizavimo metu yra minimizuojama. Iš pradžių uždavinys sprendžiamas genetiniu algoritmu, o kai toliau genetinį algoritmą naudoti tampa neefektyvu, gautas rezultatas gerinamas specifiniu atsitiktinės lokalios paieškos algoritmu. Analizuodami eksperimentinius duomenis autoriai bando nustatyti momentą, kada reikia pereiti nuo genetinio algoritmo naudojimo prie lokalios paieškos algoritmo, kad geresnis rezultatas būtų pasiekiamas per kuo trumpesnį laiką. Bendrą algoritmą, sujungiantį genetinį algoritmą su lokalios paieškos algoritmu, autoriai vadina hibridiniu genetiniu algoritmu. Reikšminiai žodžiai: globalusis optimizavimas, genetiniai algoritmai, poliniai pamatai. First Published Online: 16 May 2013
Influence of longitudinal reinforcement on the punching shear resistance of reinforced concrete slabs
This work presents the results of experimental tests on reinforced concrete slabs with different longitudinal reinforcement ratio ρ under concentrated load. Five series of specimen were made and tested, a total of ten slabs. The measurements of the specimens were 2135×2135×140 mm (Fig. 3). Longitudinal reinforcement ratio ρ = 0,449–1,90 %, the diameter of reinforcing bars was 8–16 mm, reinforcement bore yield stresses, spacing between bars was 100 mm. The protective concrete layer of the longitudinal reinforcement in all slabs was 20 mm. The cubic compressive strength of concrete fc,cube = 33,4–46,6 MPa. In the course of the experiment the measurements of the collapsing punching force, the radial and tangential deformations of the compression zone were made, the curves of their expansion were given, displacements of the column head were measured. The surface of the punching cone, irrespective of the longitudinal reinforcement ratio ρ, makes a ˜35° angle with the bottom (compression zone) surface of the slab. Deformations of radial and tangential directions in the compression zone during the course of cracking of the slab do not reach the ultimate compressive strains of concrete (3,50 ‰), the mean value of deformations in the radial direction is 1,6 ‰, the mean value of deformations in the tangential direction is 1,8 ‰, which allows to make a conclusion that the slab is punched-through under transverse collapsing force. The strength criterion of biaxial stress state proposed by Zalesov et al. (1973) and the expression of the resultant transverse force of the dowel action of the longitudinal reinforcement ratio ρ as proposed by Theodorakopoulos et al. (2002), were used to get the expression of the collapsing transverse force Vu which is given in equation (2). The factor of the influence of longitudinal reinforcement ratio ρ expressed through the resultant transverse force Vd of the dowel action makes 40–50 % of the collapsing force, Vd increases with increasing of the longitudinal reinforcement ratio ρ. The resultant transverse force Vc of the compression zone of concrete in the critical section makes 50–60 % of the collapsing force, Vc increases with increasing of the longitudinal reinforcement ratio ρ. Article in Lithuanian. Išilginio armavimo poveikis gelžbetoninės plokštės praspaudžiamajai laikomajai galiai Santrauka. Šiame darbe pateikti gelžbetoninių plokščių su skirtingu išilginio armavimo intensyvumu ρ, veikiant sutelktajai apkrovai, eksperimentinių tyrimų rezultatai. Išmatuota gelžbetoninių plokščių ardomoji pra spaudžiamoji jėga. Išmatuotos plokščių gniuždomosios zonos radialinės ir tangentinės krypties deformacijos, pateiktos šių deformacijų kreivės. Nustatyta, kad praspaudimo kūgio paviršius, nepriklausomai nuo išilginio armavimo intensyvumo ρ, sudaro su plokštės apatiniu (gniuždomu) paviršiumi ˜35° kampą. Išanalizavus radialinių ir tangentinių deformacijų kreives, siūloma faktinį kritinį pjūvį priimti ˜0,5d atstumu nuo kolonos paviršiaus. Išilginio armavimo intensyvumo ρ įtakos faktorius, išreikštas kaiščio efekto atstojamąja skersine jėga Vd, sudaro 40–50 % ardomosios jėgos. Reikšminiai žodžiai: gelžbetoninių plokščių praspaudimo stipris, kritinis pjūvis, kritinis perimetras, išilginio armavimo intensyvumas ρ, kaiščio efektas. First Published Online: 16 May 2013
punching shear resistance of reinforced concrete slabs
Development of mobile communications and their networks in Lithuania produced an essential influence on high telecommunications structures design activities. In its turn it has stimulates their research and innovations of such structural systems. One of the most efficient systems of telecommunication structures is guyed mast. It should be indicated that the behaviour of prestressed structures systems has been thoroughly examined in many investigations. But recently the increase of economical efficiency of guyed masts becomes undoubtedly actual. The development of such structures in many cases is directed to the selection in the mast elements scheme and their cross-sections. It should be underlined that geometric and physical parameters have a decisive moment on prestressed structures. An exact parameters choice allows to obtain in the mast rational distribution of bending moments, predetermining a project solution closely connected with the mass criteria. The diagram of bending moment’s distribution in guyed mast is considered rational when negative and positive moment values are absolutely equal. In the present research, analytical expressions for rational bending moments determining are presented. Above mentioned non-linear expressions estimate an influence of axial force for the bending moments. When solving the task of rational bending moments in a guyed mast, it is necessary to select suitable (i.e. rational) guyed mast bending spans. In the article is described the calculations of the guys fastening altitudes when guy level number is known. It should be noted that it is necessary to use the way of gradual approximation. The sequence of calculations is interrupted, when the sum of guyed mast spans corresponds to the exactness selected. The decisive part in mast behaviour is played by guys. The main parameters of them are pretension and cross-section area. In the article the equations are presented for determining the above-mentioned parameters. It should be stressed that after making uniform stresses of the guys on the different level of each of them it is possible to minimise some steel quantities. In the article a numerical experiment is presented for determining the technical-economical effectiveness of stress regulation. For the analysis, a standard three edged lattice guyed mast with cross-section parameters was selected in a usual way. By the suggested beam composition methods the design of the shaft was performed, and the results obtained were compared to a standard guyed mast shaft. For determining the stresses of beam elements Robot Millennium software was used; its reliability was demonstrated by earlier investigations. The results of numerical experiment that the maximal bending moment of composed guyed mast is three times less than that of a standard maximal one. An applied regulation of stresses has allowed to lessen much of the cross-section of guy rope. By applying the suggested methods it was possible to diminish the steel expenditure of shaft by more than 30%. Article in Lithuanian. Plieninių stiebų įrąžų reguliavimas Santrauka. Straipsnyje aptariama plieninių stiebų projektavimo metodika, paremta įrąžų reguliavimu. Pateikiamos analitinės išraiškos racionaliems lenkiamiesiems momentams bet kuriame kamieno tarpsnyje nustatyti. Šiose netiesinėse išraiškose vertinama ašinės jėgos, veikiančios kamiene, įtaka racionalių lenkiamųjų momentų reikšmėms. Straipsnyje aptariamas ir atotampų tvirtinimo prie kamieno racionalių koordinačių (altitudžių) apskaičiavimas, taip pat ir pačių atotampų išankstinio įtempimo bei jų skerspjūvio ploto nustatymas. Atliktas skaitinis tipinio tribriaunio spragotinio plieninio stiebo eksperimentas parodė, kad siūloma įrąžų reguliavimo metodika leido ne tik sumažinti atotampų skerspjūvio plotą, bet ir bendrąsias sąnaudas. Reikšminiai žodžiai: plieninis stiebas, racionalūs lenkiamieji momentai, įrąžų reguliavimas, geometriniai ir fizikiniai parametrai, elgsenos modeliavimas. First Published Online: 16 May 2013
Tensile, compressive and flexural strength reduction of timber in fire
The present research was dedicated to investigation into the strength of timber structures under fire conditions. Two kinds of timber specimens including oak and pine were used. The carried out investigation covered static tests on tensile strength, compressive strength along the grain, compressive strength perpendicular to the grain and flexural strength. The specimens were tested under the temperatures of 50°C, 100°C, 150°C, 200°C and 230°C. The obtained results show that pine specimens have better properties over the entire temperature range in case of tests on tensile and flexural strength. Also, as for these types of strength, oak specimens show a higher strength reduction rate than those of pine specimens, whereas oak specimens have better properties over the entire temperature ranges in case of compressive strength perpendicular to the grain. Based on statistical analysis, a linear expression of the strength reduction coefficient was proposed. Medienos tempiamojo, gniuždomojo ir lenkiamojo stiprio mažėjimas gaisro sąlygomis Santrauka. Straipsnyje nagrinėjami dviejų rūšių medienos stiprumo tyrinėjimo, veikiant aukštai temperatūrai, rezultatai. Tyrimams buvo naudojama ąžuolo ir pušies mediena. Ištirtas aukštos temperatūros poveikis šių medienos rūšių stiprio rodikliams. Tyrimų metu buvo taikyti tokie bandinių bandymo būdai: medienos tempimas išilgai pluošto, gniuždymas išilgai pluošto, gniuždymas skersai pluošto bei lenkimas. Statiniai tyrimai atlikti tokiose temperatūrose: 20°C, 50°C, 100°C, 150°C, 200°C ir 230°C. Tyrimų rezultatai rodo, kad tempiant ir lenkiant pušies mediena pasižymi geresnėmis stiprumo savybėmis visame temperatūrų diapazone. Taikant šiuos bandymo būdus ąžuolo bandinių atspario mažėjimo koeficientai yra didesni negu pušies bandinių. Kalbant apie gniuždymą išilgai pluošto, tai ąžuolo medienos atsparis visame temperatūrų diapazone yra didesnis už pušies. Remiantis statistine analize buvo pateiktas medienos stiprio mažėjimo koeficiento ir temperatūros sąryšis. Reikšminiai žodžiai: mediena, gniuždymas, tempimas, lenkimas, gaisras, temperatūra, stiprio mažėjimas. First Published Online: 16 May 2013
Modelling deformation behaviour of rc beams attributing tension-stiffening to tensile reinforcement
After cracking, the stiffness of the member along its length varies, which makes the calculation of deformations complicated. In a cracked member, stiffness is largest in the section within the uncracked region while remains smallest in the cracked section. This is because in the cracked section, tensile concrete does not contribute to the load carrying mechanism. However, at intermediate sections between adjacent cracks, concrete around reinforcement retains some tensile force due to the bond-action that effectively stiffens member response and reduces deflections. This effect is known as tension-stiffening. This paper discusses the tension-stiffening effect in reinforced concrete (RC) beams. Numerical modelling uses the approach based on tension-stiffening attributed to tensile reinforcement. A material model of reinforced steel has been developed by inverse analysis using the moment-curvature diagrams of RC beams. Total stresses in tensile reinforcement consist of actual stresses corresponding to the average strain of the steel and additional stresses due to tension-stiffening. The carried out analysis employed experimental data on RC beams tested by the authors. The beams had a constant cross section but a different amount of tensile reinforcement. It has been shown that additional (tension-stiffening) stresses in the steel depend on the area of reinforcement. However, the resulting internal forces are less dependent on the amount of reinforcement. Article in Lithuanian. Gelžbetoninių sijų tempiamosios zonos elgsenos modeliavimas armatūros diagrama Santrauka. Straipsnyje nagrinėjama supleišėjusios gelžbetoninės sijos tempiamojo betono elgsena. Skaičiavimo modelyje laikoma, kad, atsiradus plyšiams, dėl armatūros ir betono sąveikos atsiradę įtempiai betone priskiriami armatūrai. Sprendžiamas fizikinio modelio kūrimo uždavinys: taikant momentų ir kreivių diagramą, apskaičiuojamos suminių armatūros įtempių ir deformacijų priklausomybės. Suminius armatūros įtempius sudaro tikrieji įtempiai armatūroje ir papildomi įtempiai, sukelti armatūros ir betono sąveikos. Darbe naudojami autorių išbandytų skirtingų armavimo koeficientų sijų duomenys. Iš eksperimentinių momentų ir kreivių priklausomybių gautos tempiamosios armatūros įtempių ir deformacijų diagramos, kuriose įvertinta supleišėjusio betono įtaka. Parodyta, kad papildomų įtempių armatūroje dydis priklauso nuo armatūros skerspjūvio ploto, o papildomų įrąžų skirtumai nėra tokie dideli. Reikšminiai žodžiai: tempiamasis betonas, atvirkštinis uždavinys, fizikinis modelis, eksperimentiniai tyrimai, tempiamasis betonas. First Published Online: 16 May 2013
Applicability of fuzzy logic to the definition of the buckling length of steel plane frames
This paper presents a fuzzy-logic-based approach to the definition of buckling length evoked by the uncertainty of joint stiffness and boundary conditions for the member support. The example demonstrates a lucid and specific application of fuzzy sets in modelling uncertainties in design. To carry out analysis, the extension principle in the form of α-cuts was used. Buckling lengths were analysed utilizing stability solution according to the second-order theory. The beam finite element method with the shape functions of sin and sinh was utilized in the analysis taking into account valuable information on the uncertainties of input data. Formaliosios logikos analizės pritaikymas plokščių rėmų skaičiuojamųjų ilgių nustatymui Santrauka. Straipsnis pateikia siūlomą skaičiuojamojo ilgio nustatymo metodą, grįstą formaliąja logika, sukeltą esant nepastoviam jungčių standumui ir elemento atramų ribinėms sąlygoms. Pateiktas pavyzdys demonstruoja aiškų ir specifinį formaliosios aibės pritaikomumą modeliuojant nepastovumą projektavimo metu. Skaičiuojamasis ilgis buvo analizuojamas panaudojant stabilumo sprendinius taikant antros eilės teoriją. Sijos baigtinių elementų metodas su sinuso ir hiperbolinio sinuso formos funkcijomis buvo pritaikytas analizėje. Ivedamų duomenų nepastovumas taip pat buvo įvertintas analizėje. Reikšminiai žodžiai: plienas, betonas, konstrukcija, projektavimas, patikimumas, atsitiktinis, formalioji logika, trūkumas. First Published Online: 16 May 2013
Stress, strain and creep analysis of the layered composite structures under sustained loading
The paper proposes numerical and analytical models of the time-dependent analysis of a multilayered composite. These models enable us to predict the time-dependent behaviour of composite structures made of materials having age-variable properties. The proposed numerical model deals with a numerical solution of linear Volterra integral equation implying the validity of the principle of superposition for the layers. Meanwhile, the proposed analytical approach is based on the application of the age-adjusted effective modulus method for the composite. The validity of these models has been proven by a direct calculation of the time-dependent stresses and strains for the three-layered composite wall structure comparing the obtained theoretical values with those determined numerically. In particular, it was demonstrated that the analytical approach gave the identical values of the time-dependent stress strain state parameters. Relying on the results obtained, the concluding remarks have been summarized as follows: a) Despite the fact of sustained load, acting on the composite made of layers with different time-dependent deformational properties does not always hold time-invariant layer stress. In particular, the layers possessing a higher strain tend to produce relaxation while the layers with a lower strain are undergone the stress increase to maintain the equilibrium between internal and external forces (Fig. 4, b, e). Therefore, the failure should primarily be originated from the layer with a lower strain; b) Time variation in the elastic modulii of the layers is responsible for the increased stresses at time t in a higher strain layer due to a partial recovery of instantaneous strains. This effect is more progressive at a young age of the composite loaded (cf. Fig. 4, b and e); c) The ageing coefficient between the layers is different and is mainly subjected by the history of the ageing process of the layers. However, at the age of loading exceeding 28 days, the difference in the ageing coefficient of the layers is insignificant (Fig. 4, a). Moreover, it should be emphasized that the ageing coefficients of the layers are coincident with each other for the case of the time invariant elastic properties of the layers (Fig. 4, d). d) For the most practical purposes requiring long creep periods (exceeding 360 days), an approximate value of the ageing coefficient of the layers equal to 0.8 should be recommended predicting the stress-strain state of the layered composite using the proposed analytical method. More sophisticated functions for the ageing coefficients proposed by Lacidogna and Tarantino (1996), Ghali et al. (2002), ACI 209R-92 may be implemented for the sake of analysis accuracy. e) The values of the creep coefficient for the whole composite are mainly within the values of the creep coefficients of the layers. Article in Lithuanian. Sluoksniuotųjų konstrukcijų įtempių ir deformacijų būvio bei valkšnumo analizė, veikiant ilgalaikei apkrovai Santrauka. Sluoksniuotojo kompozito ilgalaikei įtempių ir deformacijų būvio analizei atlikti pasiūlyti skaitiniai ir analitiniai modeliai. Jie leidžia prognozuoti kompozitinių konstrukcijų, pagamintų iš bet kokio skaičiaus sluoksnių, kuriems būdingas ilgainiui pasireiškiantis senėjimas, tampriai valkšnios deformacijos savybes per laiką. Skaitinis modelis grindžiamas Volterra lygties skaitine formuluote, kai kintančių laike sluoksnių įtempių sukeltoms suminėms deformacijoms nustatyti taikomas poveikių superpozicijos principas, leidžiantis sumuoti šių sluoksnių įtempių prieaugių sukeltas deformacijas. Pasiūlyti analitiniai modeliai remiasi senėjančios medžiagos efektyviojo modulio metodo pritaikymu. Atlikta modelių verifikacija bei pateiktas nuoseklus trisluoksnės sienos skaičiavimo pavyzdys, kuris gali būti naudingas statybos inžinieriui, projektuojančiam kompozitines konstrukcijas. Tiesioginio skaičiavimo būdu taip pat parodyta, kad analitinis modelis duoda skaitiniu būdu gautus rezultatus. Sudalijus nagrinėjamą laiko intervalą į gana mažus laiko tarpsnius, skaitinis sprendimas yra laikytinas tiksliu. Taikant skaitinį ir analitinį modelius, nustatant jų privalumus ir galimybes, analizuoti įtempių ir deformacijų pasiskirstymo tarp sluoksnių dėsniai, apskaičiuoti valkšnumo parametrai. Reikšminiai žodžiai: sluoksniuotoji konstrukcija, įtempių persiskirtymas, senėjimo ir valkšnumo koeficientai, kompozito valkšnumo matas. First Published Online: 16 May 2013
creep coefficient for the whole composite
The engineering method for determining the settlement of point due adjacent constantly distributed circular load
The article considers linear half space subjected to the circular load of constant intensity. Point settlement is determined by integrating relation to an infinitesimally small area, as per the Bussinesque solution, for concentrated load. The authors propose to replace an integration technique with a summation technique aiming to reduce computational efforts. The application of the summation techniques developed by the authors and their subsequent employment to develop an engineering method ensures sufficient accuracy for engineering purposes for point settlement evaluation. An attractive feature of the proposed engineering method is its implementation via nomograms ready for fast usage. It is especially convenient for a design process that requires obtaining relatively rapid results for multi-variant geotechnical design situations. A calculation algorithm and computational program have been developed to perform the summation techniques. Thanks to the extensive numerical simulations of settlement evaluations under the developed method, variation in the loading surface radius has also been limited. When applying the engineering method, relative error does not exceed 2% for cases when the ratio of radii from the settlement point being investigated to the centre point of circular loading varies within the interval of 1.5 to 7 times. This degree of accuracy is sufficient for engineering design needs. In practice, this engineering method can be applied in case it is assumed that the circular load of constant intensity is the load that acts on the base at the point of contact between the foundation and the base. The point the settlement of which is calculated is the point of the base or the point at the centre of the foundation. It is recommended to apply the engineering method presented in the article when the distance between adjacent foundations is 10 times less than the diameter of the foundation. When the distance is 10 times more than the diameter, foundations almost do not affect each other. The engineering method is especially useful when differential settlements are being calculated, e.g. the impact of deformation seams on the foundations or the effects of a projected building that will be attached to an existing one. This method can be used for calculating both shallow and deep foundations. When deep foundations are calculated, it is necessary to evaluate the enlargement of the pile base occurring due to friction between the ground and the pile material. Article in Lithuanian. Inžinerinis metodas taško nuosėdžiui skaičiuoti nuo gretutinės apskritiminės tolygiai išskirstytos apkrovos Santrauka. Tiesiškai deformuojamo puserdvio, apkrauto apskritimine tolygiai išskirstyta apkrova, vertikalieji poslinkiai apskaičiuojami integruojant Businesko sprendinio vertikaliojo poslinkio išraišką apkrautame plote. Šis integralas apskaičiuojamas sumavimo metodu. Darbe pateiktas tiesiškai deformuojamo pagrindo, apkrauto apskritimine tolygiai išskirstyta apkrova, nuosėdžių skaičiavimo metodas yra gana tikslus. Šiuo metodu galima įvertinti puserdvio paviršiaus nuosėdį ne tik nuo apskritiminės tolygiai išskirstytos apkrovos, bet ir nuo kitų, greta esančių apskritiminių tolygiai išskirstytų apkrovų. Inžineriniam metodui realizuoti taikytas sumavimo principas, pakeičiantis tiesioginį integravimą reikiamu tikslumu. Tuo tikslu sukurtas sumavimo algoritmas, jį realizuojanti kompiuterinė programa. Inžinerinis poslinkio skaičiavimo metodas realizuotas laipsnine lygtimi ir jam taikyti patogia naudoti nomogramų forma. Taikant sukurtą inžinerinį metodą atliktas nuosėdžių apskaičiavimo skaitinis modeliavimas. Atlikus skaitinio eksperimento rezultatų analizę, identifikuoti nuosėdžių kitimo dėsningumai. Pasiūlyta analizinė išraiška nuosėdžiams skaičiuoti. Nuosėdžių, apskaičiuotų inžineriniu metodu, santykinė paklaida neviršija 2 %, kai apskritiminės tolygiai išskirstytos apkrovos centro taško atstumo iki taško, kurio skaičiuojamas nuosėdis, santykis su apskritiminės tolygiai išskirstytos apkrovos spinduliu kinta nuo 1,5 iki 7. Reikšminiai žodžiai: apkritiminė išskirstytoji apkrova, Bussinesque sprendiniai, sumavimo algoritmas, inžinerinis metodas taško nuosėdžiui skaičiuoti. First Published Online: 16 May 2013
engineering method for point settlement evaluation
A test of reinforcement corrosion progress in the presence of organic corrosion inhibitors
Test results for KCR and DME migrating inhibitor efficiency are presented. The method of linear polarization is used in the tests on loaded reinforced concrete elements. Various durations of inhibitor activity, cracked concrete cover and different levels of reinforcement corrosion development in test parts are taken into account. The inhibitors are only partly efficient at low levels of corrosion development at an early stage, however, after two years the protective work is not verifiable. In the case of intense reinforcement corrosion a reduction in its degree is not observed, even directly after inhibitors have been applied. Armatūros korozijos eksperimentiniai tyrimai naudojant organinės korozijos lėtiklius Santrauka. Straipsnyje pateikti lėtiklių KCR ir DME efektyvumo eksperimentinių tyrimų rezultatai. Eksperimentiniuose tyrimuose apkrautiems betoniniams elementams taikyti tiesinės poliarizacijos metodai. Ivairios lėtiklių aktyvumo trukmės, supleišėjusio betono apsauginio sluoksnio ir skirtingų armatūros korozijos laipsnių išsivystymas eksperimentų dalyse yra įvertintas. Lėtikliai tik iš dalies veiksmingi esant žemam korozijos išsivystimo lygiui pradinėse stadijose, tačiau po dvejų metų jų apsauginis darbas nėra įrodytas. Kai yra didelė armatūros korozija, nėra nustatyta jos laipsnio sumažėjimo, netgi tuoj pat panaudojus lėtiklius. Reikšminiai žodžiai: betonas, lėtiklis, korozija, efektyvumas, apsauga, armatūra, gelžbetonis. First Published Online: 16 May 2013
The strength of concrete with an elastic additive of tires rubber waste under cyclic loading
Concrete strength under cyclic loads is much lower compared to short-term loading strength because cyclic loads stimulate the growth of microcracks in the cement matrix, reduce the adherence of cement stone and aggregates and cause higher creep deformations. The paper presents the deformations of samples with or without a rubber waste additive subjected to cyclic loads and determined by the methods developed during research. The obtained results show that relative plastic strains under cyclic load and relative residual strains after the removal of the load depend on the rubber additive. Relative strains in the rubberized concrete samples loaded at 70% prism compressive strength are 63% higher and residual strains after the removal of the load are 234% higher. When the samples are loaded at 80% of prism compressive strength, relative strains and residual strains after the removal of the load in concrete with the rubber additive are respectively 56% and even 360% higher if compared to the samples without the rubber additive. When the samples are loaded at 90% of prism compressive strength, the obtained respective relative strains are 63% and 219% higher compared to the samples without rubber additives. An increase in relative plastic and residual strains shows the influence of the rubber additive on the stress-strain behaviour of concrete subjected to cyclic loads. The conducted investigation has revealed that concrete with rubber waste additive under cyclic loads changes ultimate strains. We can see a significant difference in the yield deformations leading to the ultimate failure of concrete with or without the rubber additive. When the samples of rubberized concrete are loaded at 70% of prism compressive strength, the longitudinal ultimate strains are 36% higher; loading at 80% results in 47% higher strains and that at 90% results in 42% higher strains compared to the non-rubberized concrete samples. The analysis of changes in deformation conducted by the created method does not give a precise forecast as to the number of cycles that one or another type of concrete will resist under a certain load. Nevertheless, the obtained changes in deformations enable to make rather precise decisions with regard to the ability of concrete to absorb cyclic stresses with the higher strains of the concrete matrix. A detailed analysis of the test results has revealed the following tendencies: concrete with rubber additives has better deformation abilities under cyclic loads because of bigger plastic (residual) strains and bigger ultimate strains. This leads to the presumption that rubber additives present in the concrete matrix are able to absorb cyclic-load-stimulated internal stresses driving the concrete fragmentation process. Article in Lithuanian. Betono su elastingu priedu iš gumos atliekų atsparumas ciklinių apkrovų poveikiui Santrauka. Nagrinėjama betono su elastingu priedu iš mechaniškai smulkintų naudotų padangų gumos atliekų priedo įtaka ciklinių apkrovų poveikiui. Skirtingos frakcijos ir skirtingas gumos atliekų priedo kiekis buvo naudojamas betonuose. Atlikti eksperimentai parodė, kad gumos atliekų priedas turi įtakos ciklinių apkrovų poveikiui. Gauta, kad to paties gniuždomojo stiprio betonuose su mechaniškai smulkintomis gumos atliekomis deformacijos po 20 ciklų 56–63 % didesnės, o liekamosios deformacijos nukrovus yra 219–360 % didesnės nei bandiniuose, kuriuose nebuvo naudojamas gumos atliekų priedas. Pastebėta, kad po ciklinių apkrovų poveikio bandiniai, kuriuose buvo naudojamos gumos atliekos, kur kas labiau deformavosi, susidarė daug didesnės ribinės deformacijos nei bandiniuose, kuriuose nebuvo naudojamas dempferuojantis gumos atliekų priedas. Iš atliktų eksperimentų matyti, kad gumos atliekas tikslinga naudoti betono konstrukcijose, veikiamose daugkartinėmis nuolat pasikartojančiomis apkrovomis. Reikšminiai žodžiai: betonas, gumos atliekų priedas, ciklinės apkrovos, liekamosios deformacijos, ribinės deformacijos. First Published Online: 16 May 2013
Discrete analysis for single-pylon suspension bridges
This paper presents calculation methods, developed at Tallinn University of Technology (Idnurm 2004; Kulbach 2007), for the single-pylon suspension bridges stiffened by a girder. Classical suspension bridge consists of a geometrically non-linear cable, connected by hangers with an elastic linear stiffening girder, pylons in both ends of the bridge and anchor cables. Alternate form of a suspension bridge is a bridge, with only one pylon on the middle of the span and suspension cable is connected to the abutments or the ends of the stiffening girder. In the calculation of suspension bridges, the geometrically non-linear behaviour of the parabolic cable is the main problem. The linear methods of analysis suit only for small spans. A geometrically non-linear continual model is especially useful for classical loading cases – a uniformly distributed load on the whole or half span. But the modern traffic models consist of concentrated and uniformly distributed loads. The discrete model of a suspension bridge allows us to apply all kinds of loads, such as distributed or concentrated ones. The assumptions of the discrete method described here are: linear elastic strain-stress dependence of the material and absence of horizontal displacements of hangers. Hanger elongation is taken into account. Kabamojo tilto su vienu pilonu diskrečioji analizė Santrauka. Straipsnyje pateikiamas skaičiavimo metodas, pasiūlytas Talino technikos universiteto mokslininkų (Idnurm 2004; Kulbach 2007) ir skirtas kabamųjų tiltų su vienu pilonu standumo sijai skaičiuoti. Klasikiniai kabamieji tiltai susideda iš geometriškai nietiesiško lyno, kuris tampriomis atotampomis sujungtas su standumo sija. Paprastai lynas būna pakabintas tarp dviejų pilonų, inkaruotų inkariniais lynais. Alternatyvi kabamųjų tiltų konstrukcija yra tokia, kai naudojamas tik vienas pilonas tilto viduryje, o pagrindinis geometriškai netiesiškas lynas yra inkaruojamas standumo sijos galuose. Skaičiuojant kabamuosius tiltus, pagrindinė problema yra parabolinio lyno geometrinio netiesiškumo elgsena. Tiesinė analizė tinkama tik mažiems tarpatramiams. Geometrinio netiesiškumo modelis ypač naudingas klasikinės apkrovos atveju – vienodai išskirstytai apkrovai visam arba pusei tarpatramio. Tačiau šiuolaikinius transporto modelius sudaro koncentruotos ir vienodai išskirstytos apkrovos. Diskretusis kabamojo tilto modelis leidžia mums taikyti visų tipų apkrovas, tokias kaip koncentruotos ir išskirstytos. Diskrečiojo modelio prielaidos yra tokios: taikoma medžiagų ir horizontalių atotampų poslinkių tiesinė įtempių ir deformacijų priklausomybė. Atotampų pailgėjimas taip pat yra įvertintas. Reikšminiai žodžiai: lynų konstrukcijos, standumo sijos, kabamasis lynas, didelių tarpatramių konstrukcijos, diskrečioji analizė, geometrinis netiesiškumas. First Published Online: 16 May 2013
Design and analysis of combined plane steel guyed tower-mast
One of the most effective and widely used high-rise telecommunication structures are steel towers and guyed masts. The behaviour, analysis and application fields are exhaustively discussed in a number of scientific publications. The main advantages of tower structures are low building area, however, from the point of view of steel consumptions, such structures are not effective enough. For technical-economic efficiency not only the rational types of cross sections for typical mast elements are selected, but also various combined structural systems are developed and implemented. Flat tower-masts are also known. They are combined from a single plain truss supported out of its plane by guys. In this case, such mixed system is able to carry acting loads and actions in one direction like a tower and in other direction – like a mast. From a technicaleconomic point of view, such system stands in the intermediate position between the guyed mast and the tower. The major weakness of such framework is relatively great depth and the cross sectional area of the chords of the tower truss which is caused by the relatively high values of the bending moment in the chord acting in the plane of guys and the large buckling length of the chord out of truss plane. It must be stressed that wind action on the investigated structure directly depends on the dimensions of the chord cross section. This paper deals with the new combined plain tower-mast structure the chords of which out of plane are stiffened by and inserted between the guys connecting joints and the double-sided strut members. These members are pre-stressed to avoid compression induced by transverse loading. The analysis of the behavior of a separate strut system under transversal loading is performed and analytical expressions for determining internal forces and displacements in its members with and without pre-stressing are provided. The minimum values of the required pre-stressing in ties of the strut system are described. It is proved that a proper choice of the parameters of structural components gives a possibility of obtaining a favorable distribution of bending moments in the chord. On the basis of numerical experiments, a comparison between the results defined analytically and ones determined by the means of the Autodesk Robot Structural Analysis program is performed. The accuracy of the proposed analytical method is discussed. For defining the behaviour peculiarities of the new combined structural system and for estimating its technical-economic efficiency, the numerical experiment by the means of FEM program (Autodesk Robot Structural Analysis) was carried out. Analysis was performed using 98 meter high ordinary and new guyed tower-mast structures with guys fixed at four levels. The member sections of the analyzed structures designed according to the values of the defined acting internal forces are presented. It is estimated that using strut members helps in considerably reducing (about 4,8 times) the maximum values of bending moments in the chords of tower truss. It was estimated that depth between the chords in a new combined system was 2 times lesser than that in the ordinary tower – mast system. It is shown that in case of the same cross section and value of the pre-stressing force, the value of the vertical reaction of the new strutted tower-mast system on foundation was 1,65 time lesser than that in the ordinary system. Conclusions and recommendations are provided. Article in Lithuanian. Kombinuoto plieninio plokščiojo bokšto-stiebo konstravimas ir skaičiavimas Santrauka. Straipsnyje aptariama nauja kombinuota plokščiojo bokšto-stiebo konstrukcijų sistema, kurios juostos sustandintos iš bokšto santvaros plokštumos dvipusiais paspyriniais iš anksto įtemptais elementais, išdėstytais tarp atotampų tvirtinimo mazgų. Analizuojama atskiros paspyrinės sistemos dalies elgsena veikiant skersinei apkrovai, pateikiama inžinerinė metodika jos elementų įrąžoms ir poslinkiams apskaičiuoti. Atlikto skaitinio eksperimento pagrindu nustatytas parengtos inžinerinės skaičiavimo metodikos tikslumas. Pasitelkus baigtinių elementų programą aptarti naujos kombinuotos konstrukcinės sistemos elgsenos ypatumai. Parodyta, kad paspyrinių elementų naudojimas leidžia gerokai sumažinti maksimalius lenkiamuosius momentus bokšto-stiebo santvaros juostose. Parodyta, kad siūloma nauja kombinuota paspyrinė bokšto-stiebo sistema pagal masės kriterijų yra kur kas efektyvesnė už analogišką tradicinę bokšto-stiebo sistemą. Reikšminiai žodžiai: plieninis bokštas-stiebas, paspyrinė sistema, išankstinis įtempimas, elgsenos modeliavimas. First Published Online: 16 May 2013