اثر استرس های عمودی و فلنج ها در رفتار لرزه ای ساختمان های آجری مسلح نشده Effects of vertical stresses and flanges on seismic behavior of unreinforced brick masonry

1. Introduction Brick masonry is one of the most widely used building material in construction industry throughout the world. For centuries, masonry construction has been preferred primarily due to plentiful and inexpensive availability of constituent materials and ease of construction. Historically, such type of construction is located in areas that are prone to seismic activity [1]. URBM offers a weak response when subjected to lateral loads such as earthquake. As witnessed in 2005 Kashmir, Pakistan earthquake, and November 2015 earthquake in Afghanistan and Pakistan, URBM suffered heavy damages [2–8]. Masonry structures (brick and stone) suffered yet again in the more recent earthquakes of 2009 and 2016 in Italy [9–12] and 2015 in Nepal [13,14]. These events have further strengthened the need of continuing research to understand and improve unreinforced masonry construction. It is evident, that such type of construction, although more economical and popular, pose high risk to the safety of masses during earthquakes. Extensive research has been carried out and more work is in progress to understand the behavior of masonry structures and to develop better design guidelines for the same. Seismic capacity of masonry structure is affected by a variety of parameters that include aspect ratio, level of vertical stress, mechanical properties of masonry and its constituents and flanges This paper investigates the effects of vertical stresses and boundary conditions (flanges) on the in-plane behavior of the URBM structures. Vertical stresses are inherently present in all load-bearing URBM structures. Vertical stresses resulting from the diaphragm, adjacent parts of the buildings and occupancy loads, constitute one of the important parameter which influence the behavior of URBM under the action of lateral loads. A number of researchers have studied vertical stresses for their effects on masonry behavior and response. Research work carried out by (Magenes, G., Calvi [15], Irimies & Bia [16]; Yi et al. [17]; Haach et al. [18]; Tomaževič & Weiss [19]; Salmanpour et al. [20]; Salmanpour et al. [21], Salmanpour et al. [22]; Javed et al. [23]) utilized both solid and hollow brick and block masonry to study the effects of vertical stresses. Quasi-static cyclic testing has been performed in most of these studies due to its advantages over other types of testing techniques [24]. Most of these researchers tested isolated masonry piers or walls either full scale or half scaled. However, Irimies & Bia [16] also incorporated flanges in the specimens.