Vpliv modeliranja razpokanih prerezov pri potresnoodpornem projektiranju AB stavbe

diplomska naloga

Andraž Starc (Author), Matjaž Dolšek (Mentor), Janko Logar (Thesis defence commission member), Anže Babič (Co-mentor)

Abstract

Med močnim potresom s pridom izkoriščamo sposobnost plastičnega obnašanja duktilne armiranobetonske konstrukcije, ki jo projektiramo z uporabo metode načrtovanja nosilnosti, pri čemer projektne potresne sile določimo z upoštevanjem razpokanja armiranobetonskih konstrukcij. Način določitve togosti razpokanih prerezov se v predpisih razlikuje. Vpliv različnega modeliranja razpokanih prerezov smo v diplomski nalogi preučevali na primeru 6-etažne armiranobetonske okvirne konstrukcije. Definirali smo 9 računskih modelov. Razlike v modelih se nanašajo na modeliranje togosti razpokanih prerezov ali sodelujoče širine pasnice gred v skladu z različnimi standardi in smernicami za potresnoodporno projektiranje stavb. V dveh modelih smo upoštevali, da se efektivni vztrajnostni moment spreminja vzdolž konstrukcijskih elementov, zato smo po elementih upoštevali spremenljivo redukcijo togosti, ki je bila vezana na moment na meji tečenja armature, oziroma je bila izračunana na osnovi predvidene deformacijske linije prereza pri projektni potresni obremenitvi. Takšen pristop k modeliranju zahteva iteracije. Pri primerjavi razultatov analiz ugotovimo, da dobimo za modele, ki upoštevajo na poenostavljen način enotno redukcijo togosti po celotni konstrukciji, precej podobne rezultate. Za model v katerem izračunamo vztrajnostni moment razpokanega prereza na težišče nerazpokanega prereza, dobimo precej neuporabne rezultate, saj se redukcije togosti za zelo različno razpokane prereza veliko ne razlikujejo. V primeru izračuna efektivnega vztrajnostnega momenta na težišče razpokanega prereza, pa dobimo nižje efektivne togosti, ki se po konstrukciji spreminjajo. Tako dobimo podajnejši model, ki nam v primerjavi z modelom po EC8 daje manjše količine potrebne armature, saj je celotna potresna sila za 29 % nižja, izračunani pomiki konstrukcije pa so večji, saj je maksimalni zamik etaže za 24 % višji (celotni pomik na vrhu pa za 43 %). Ker je za dimenzioniranje okvirov običajno merodajna kontrola pomikov (MSU), daje ta model rezultate na varni strani, vendar so po drugi strani projektne potresne sile manjše. Kateri postopek je bolj primeren za projektiranje bi lahko ovrednotili le z oceno verjetnosti porušitve objekta, kar pa presega okvire te diplomske naloge.

Keywords

gradbeništvo;diplomska dela;potresnoodporno projektiranje;armiranobetonski okvir;modalna analiza;togost razpokanih prerezov;sodelujoča širina pasnic;SAP2000;

Data

Language:	Slovenian
Year of publishing:	2015
Typology:	2.11 - Undergraduate Thesis
Organization:	UL FGG - Faculty of Civil and Geodetic Engineering
Publisher:	[A. Starc]
UDC:	624.042.7(043.2)
COBISS:	7255393
Views:	1971
Downloads:	476
Average score:	0 (0 votes)
Metadata:

Other data

Secondary language:	English
Secondary title:	Influence of modeling of cracked sections on earthquake-resistant design of RC building
Secondary abstract:	In the case of strong earthquakes, the ability of inelastic response of ductile reinforced concrete buildings is of great importance in order to assure adequate collapse risk of structures, which are designed with consideration of the capacity design principles and the design force, which is obtained by taking into account post-cracking stiffness of structural elements. However, there is no uniform criteria for consideration of effective stiffness of structural elements. In this graduation thesis, several approaches for determination of effective shear and flexural stiffness are presented and demonstrated by means of an example of a six-storey reinforced concrete building. Nine different models of the structure were evaluated considering various seismic design codes, two of which reflected the fact that flexural cracking varies along the element length. In the later cases, the effective stiffness of the elements corresponded either to the initation of yielding of the reinforcement or to the estimated seismic response of the structure. Therefore, an iterative procedure was required. It is shown, that the results using uniform stiffness reduction throughout entire structure have small variation and that the results for model, where effective inertia is calculated relative to centroid of uncracked section, are not representative. Calculating effective stiffness relative to centroid of cracked sections reflects in higher stiffness reduction, thus the displacement demands are larger, although design forces are often smaller. In the case of the investigated building, the base shear was reduced by 29 % and the maximum drift was increased by 24 % in comparison to values obtained in the case of model proposed by EC8. Consequently, the required amount of reinforcement is also smaller. Which model of effective stiffness is more appropriate for earthquake-resistant design could only be evaluated by estimating seismic collapse risk for the buildings, which is beyond the scope of this thesis.
Secondary keywords:	civil engineering;graduation thesis;earthquake-resistant design;reinforced concrete frame;modal analysis;post-cracking stiffness;effective flange width;SAP2000;
File type:	application/pdf
Type (COBISS):	Bachelor thesis/paper
Thesis comment:	Univ. v Ljubljani, Fak. za gradbeništvo in geodezijo
Pages:	X, 38 str., [37] str. pril.
ID:	9058891