EXPERIMENTAL STUDY ON SEISMIC BEHAVIOR OF MASONRY BUILDINGS RETROFITTED WITH SHOTCRETE

Unreinforced masonry is the most common form of building construction in Iran and many other countries. In developing countries, this type of building is being constructed for residential or educational uses, mostly regardless of engineering design schemes and principals. Previous observations indicate problems such as improper seismic resistant system, ill-suited structural detailing, and weak materials to leave masonry buildings vulnerable even to smallest lateral excitations; so that in the case of a major seismic event such as recent Kermanshah earthquake, there would be no guaranty for the safety of the residents [1]. As many Iranian buildings are masonry and because the occupants often have little financial affordability, replacing these structures cannot be concerned as an alternative, and further investigations are needed in order to develop low-cost, feasible and simple methods for retrofitting these structures and minimizing the damages; this requires fully understanding the seismic behavior of these structures by the means of experimental tests. Through many years of study, various methods are developed to improve the seismic performance of unreinforced masonry (URM) buildings and each method has its own advantages and disadvantages. Rigid belts, steel bar mesh, vertical and horizontal beams, horizontal tendons, PP bands, steel wires, L shape and vertical rebars, center core, and shotcrete are of the most noteworthy methods [2], amongst which, the application of steel mesh along with a shotcrete layer is commonly used by the Organization for Development, Renovation and Equipping Schools of I.R. Iran (DRES), because of its affordability and ease of application. The performance of the detailing used by DRES is verified by conducting multiple shake able tests in previous researches [3-4]. In general, the failure modes observed in URM buildings can be categorized in [1] (1) in-plane diagonal and horizontal cracks of load-bearing and non-bearing walls, (2) out-of-plane overturning of non-bearing walls, (3) rocking of the piers between or adjacent to windows and openings, (4) toe crushing and crack propagation at the corner of the walls and openings, and (5) sliding of the floor slabs on the walls at the region of slab-to-wall connections. If applied correctly, each retrofitting method is aimed to diminish one or several of the failures and improve the integrity and flexibility of the structure. On the other hand, a method such as shotcrete loses effectiveness in the case of: (1) using poor-quality materials, (2) insufficient splice length for steel bars, (3) immature reinforced wall-to-wall and slab-to-wall connections, and (4) discontinuity of the reinforcement layer at the opening regions. So, it is very important to consider most-probable failure scenarios, use a feasible retrofitting method and carry out the constructions in accordance with standard instructions.

کلیدواژه ها:

Shake table test ، URM buildings ، Seismic retrofit ، Shotcrete ، Damaged buildings rehabilitation