Ocenjevanje potresne odpornosti obstoječih armiranobetonskih objektov
| Autor: | Sinkovič, Klemen |
|---|---|
| Přispěvatelé: | Fajfar, Peter |
| Jazyk: | slovinština |
| Rok vydání: | 2016 |
| Předmět: |
potresna zahteva
armiranobetonski objekti structural capacity nelinearna analiza udc:624.012.45:624.042.7(043) reinforced concrete buildings building environment effective stiffness nonlinear analysis efektivna togost seismic resistance assessment ocena potresne odpornosti kapaciteta grajeno okolje seismic demand |
| Popis: | (AB) konstrukcij s postopki na različnih nivojih zahtevnosti. Najnižji nivo predstavlja preliminarna metoda za hitro oceno, ki predstavlja modifikacijo osnovne ameriške metode. Njej sledijo postopki na petih nivojih računa. Ti vsebujejo enostavna postopka, ki sta bila originalno razvita na Japonskem (nivo 1 in 2), N2 metodo z dvema variantama matematičnih modelov konstrukcije (nivo 3 in 4) in nelinearno dinamično analizo (nivo 5). Ločeno poglavje je namenjeno predstavitvi različnih modelov za ocenjevanje kapacitete posameznih elementov nosilne konstrukcije, ki jo je potrebno oceniti pri računih na različnih nivojih. Predstavljeni so modeli za oceno upogibnega in strižnega obnašanja, pri tem pa so rezultati posameznih modelov primerjani z eksperimentalnimi rezultati za preizkušance stebrov in sten, ki so bili povzeti iz baze podatkov SERIES. Za oceno upogibnega obnašanja so predstavljeni različni postopki določitve upogibne nosilnosti, efektivne rotacije na meji elastičnosti in mejne rotacije elementov. Ob upoštevanju baze podatkov SERIES so izbrane predpostavljene vrednosti mejnih napetosti stebrov, ki predstavljajo strižno in upogibno nosilnost stebrov pri računu na prvem nivoju zahtevnosti. Na najvišjih treh nivojih zahtevnosti je analiza potresne odpornosti izvedena na podlagi matematičnega modela konstrukcije. Pri tem je na tretjem nivoju uporabljen poenostavljen matematični model, potisna analiza pa je izvedena z nekoliko spremenjeno verzijo programa NEAVEK. Matematični model temelji tu na razširitvi pseudo-tri-dimenzionalnega modela v nelinearno območje. Standardno modeliranje konstrukcij je uporabljeno na četrtem in petem nivoju računa. Pri tem so vse nelinearne analize konstrukcij izvedene s programom OpenSees, ki pri uporabi v tej doktorski disertaciji deluje v povezavi s programskim paketom PBEE-toolbox. Ocenjevanje potresne odpornosti je izvedeno na dvanajstih variantah okvirnih konstrukcij, štirih variantah (konzolno) stenastih konstrukcij in petih variantah mešanih konstrukcij. Rezultati ocene potresne odpornosti obravnavanih konstrukcij kažejo majhno razliko med rezultati N2 metode in rezultati nelinearnih dinamičnih analiz, medtem ko so rezultati postopkov na prvih dveh nivojih manj natančni in veliko bolj konservativni. Po drugi strani se količina vhodnih podatkov in računski čas povečujeta s povečevanjem stopnje zahtevnosti izbrane metode. Razlogi za konservativnost postopkov na najnižjih dveh in na tretjem nivoju zahtevnosti so opisani s pomočjo ovrednotenja posameznih predpostavk. Rezultati vseh raziskav so pokazali, da bi bilo potrebno opraviti nadaljne raziskave, ki bi bile povezane predvsem z določanjem kapacitete, zlasti glede strižne nosilnosti konstrukcijskih elementov in glede kapacitete celotne konstrukcije. Ugotovljeno je bilo tudi, da so ocene potresnih zahtev močno odvisne od ocene začetne efektivne togosti konstrukcije, zato je izbira ustrezne efektivne togosti na nivoju elementa izredno pomembna. Enakomerno zmanjšanje togosti na polovično vrednost togosti nerazpokanih prerezov, ki jo predpisuje EC8, lahko zelo podceni potresne zahteve. Izbira začetne togosti ima lahko na potresno odpornost večji vpliv kot izbira postopka analize. The doctoral dissertation describes the methodology for the assessment of the seismic resistance of reinforced concrete (RC) structures at different levels of complexity. The methodolgy starts with a preliminary rapid visual screening method which is based on the American method. This is followed by procedures which operate at five different levels of complexity, including simple procedures which are based on methods that were originally developed in Japan (levels 1 and 2), the N2 method with two variants of the mathematical model (levels 3 and 4), and the non-linear dynamic analysis (level 5). A separate chapter deals with the assessment of the load-carrying capacity of structural members, which is assessed differently at the different level of complexity. Models for the assessment of flexural and shear behaviour are presented, and the results obtained when using the different models are compared with experimental results for column and wall specimens from the SERIES database. In the case of flexural behaviour, the assessment of flexural strength of the structural members is presented, together with the effective yield rotation and the ultimate rotation. Based on data given in the SERIES database, assumed values for the ultimate stresses are selected in the case of columns at the 1st level. In the case of the three highest levels of complexity the assessments of the seisimc resistance of the structures are performed by using a mathematical model of the structure. A simplified model is used at the 3rd level, where the pushover analyses are performed using a slightly modified version of the original NEAVEK program. Here the mathematical model is based on an extension of the pseudo-threedimensional mathematical model into the non-linear range. In contrast to the 3rd level, at the 4th and 5th levels standard mathematical modelling is applied. In this case the non-linear analyses are performed using the OpenSees software, together with the PBEE-toolbox. Seismic resistance assessment was performed on twelve variants of several frame structures, four variants of (cantilever) wall structures, and five variants of dual structures. The results of the performed seismic resistance assessments for all the investigated buildings indicate a small difference between the N2 method and the non-linear dynamic analysis, whereas the results of the procedures at the first two levels were less reliable, and are much more conservative. On the other hand, the amount of input data and the scope of computational work increases with the increasing level of complexity. The reasons for the observed conservatism of the lower two levels, and also of the 3rd level, are explained by an evaluation of the individual assumptions made. Research into the definition of load-carrying capacity is needed, especially with respect to the shear capacity of structural members and the capacity of the whole structure. It was found that the seismic demand depends strongly on the initial effective stiffness of the structure. For this reason the choice of an adequate initial stiffness at the element level is very important. A uniformly reduced stiffness to one half of that corresponding to the uncracked gross-sections, as allowed by EC8, may grossly underestimate the seismic demand. The choice of initial stiffness may have a larger influence on the seismic resistance than the choice of the analysis procedure. |
| Databáze: | OpenAIRE |
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