Nonlinear analysis of structural frame-wall system: infil wall with eccentric window opening

Abstract

Okvirni sustavi sa ispunom sastoje se od dva konstrukcijska elementa, okvira i ispune. Najčešće su to armiranobetonski okvir, te ispun zidan opečnim blokom. Ispunsko ziđe zbog svoje krutosti mijenja odziv ukupne konstrukcije na horizontalne sile, odnosno, na dominantnu horizontalnu silu koju izaziva potres. Utjecaj ispunskoga ziđa može biti pozitivan i negativan. U dosadašnjim propisima, uglavnom je uzet u obzir negativan utjecaj, tako štiteći dominantni konstrukcjski element, tj. armiranobetonski okvir. Pojednostavljenim postupcima određivanja međudjelovanja ispunskog ziđa i okvira najčešće se koristi zamjenjujuća tlačna dijagonala. Modeliranje samog ispunskog ziđa je teško, jer se i ono samo sastoji od više elemenata koji nemaju jednaka mehanička svojstva u svim smjerovima, te jako ovise o kvaliteti izvođenja. Dodatan problem predstavljaju otvori u ziđu koji su neizbježni. Pojednostavljeni postupci zanemaruju mnogo parametara, pa tako i postojanje otvora, dok neki i to uzimaju u obzir ali nedovoljno definirano s obzirom na veličinu, smještaj i vrstu otvora. Zamjenjujuća tlačna dijagonala u većini slučajeva ima širinu jednaku širini ziđa, te mehanička svojstva kao ziđe, a proračuni se uglavnom razlikuju po izrazima za određivanje visine poprečnog presjeka zamjenjujuće tlačne dijagonale. U ovom radu proveden je nelinearni proračun okvira ispunjenog ziđem sa otvorom za prozor postavljenim ekscentrično u računalnom programu Atena 3D Engineering. Ovakvi modeli, tzv. mikromodeli imaju mnogo parametara, stoga je model kalibriran s obzirom na eksperiment koji je proveo (Penava, 2012). Mikromodelom se simulira neelastično ponašanje svih elemenata u ispunskomu ziđu, te njihov međusobni utjecaj i utjecaj na armiranobetonski okvir. Proračun je proveden metodom konačnih elemenata. Na kraju su uspoređene otpornosti okvira ispunjenih ziđem u svojoj ravnini i okomito na svoju ravninu, dobivenih pomoću eksperimenta, mikromodela i pojednostavljenih postupaka .Infilled frames are made from two construction elements, frames and infills. The most common ones are reinforced concrete frames, and infills made from clay block masonry. Masonry infill due to its own stiffness, change construction response to the horizontal forces , primely to the dominant horizontal force caused by earthquake. The influence of infills can be positive and negative. In the current regulations, a negative impact was generally taken into account, thus protecting the dominant construction element, ie the reinforced concrete framework. Most often simplified analytical methods of determining interaction of infills and frames are using equivalent diagonal struts. Modeling masonry infills is challenge, because it consist several elements that do not have same mechanical properties in all directions, and quality of infills depends on workers building skills. An additional problem are the openings in the walls which are necesarily. Simplified methods ignore many parameters, thus, the existence of openings, while some also take into account but insufficiently defined with regard to size, position and type of openings. The equivalent diagonal strut in most cases has a width equal to the width of the wall, and the mechanical properties like the infill wall.Calculations are generally different in terms of determining the width of the cross-section of the equivalent diagonal strut. In this paper, the frame filled with walls with a window opening set eccentrically is calculated as nonlinear in the computer program Atena 3D Engineering. Such models, so called micromodels have many parameters, so the model is calibrated with respect to the experiment carried out by (Penava, 2012). The micromodels simulates the inelastic behavior of all elements in the infill walls, and their mutual influence , also their impact on the reinforced concrete frame. The resistances of the infilled frames in its plane and out of its plane, obtained by experiment, micromodel and simplified procedures are compared at the end