Engineering Computations, γβ(β), β015, 4β4-451 SEISMIC DAMAGE EVALUATION OF REINFORCED CONCRETE SLIT WALLS SERGIU A. BAETU, ALEX H. BARBAT, IOAN P. CIONGRADI 1. Introduction Reinforced concrete walls are structural elements used in multi-story buildings in earthquake prone countries like Romania, Turkey, Chile, Mexico, China, Japan, USA, Peru etc., because they have a high capacity of resisting lateral loads. Nevertheless, it is important to maintain the seismic vulnerability of buildings made with such walls within reasonable limits (Barbat el al, β006, Barbat et al. β010), providing them sufficient ductility to avoid their brittle failure under the action of strong seismic loads. When a structure is subjected to strong earthquakes, it is necessary to assure, for economical design reasons, inelastic deformations without the failure of the building; this is because the design of buildings based on performance criteria takes into account the dissipation of seismic energy accumulated in the structure. The fact is that, in a tall structural wall, plastic hinges appear only at the base of the wall and the rest of the wall remains undamaged. There is an alternative solution which overcomes this drawback, consisting of creating a slit zone with short connections introduced into the wall structure. The slits are complete breaks in concrete and reinforcements in order to change the solid structural reinforced concrete wall to a series of flexural wall-columns. In this way, the deflection capacity of the wall is larger, adequate to be used in high-rise buildings. This solution assures small lateral deflections of the buildings during minor earthquakes and a large, beyond the elastic limit, storey displacement during major earthquakes. The solution proposed in this paper –structural reinforced concrete slit walls– changes the behaviour of a the solid wall and provides to the structure more ductility, energy dissipation and adequate crack patterns (see Figure 1). In Romania, many multi-storey buildings with structural walls have suffered serious damages during high intensity earthquakes. For instance in Bucharest, during the 1977 Vrancea (Romania) earthquake, these buildings showed a high seismic vulnerability: one building with cast-in situ reinforced concrete structural walls totally collapsed, seven other buildings suffered partial collapse, 19 were significantly damaged and 7β were moderately damaged. Some of the reasons of the collapses were the inadequate wall density, the inadequate amount and detailing of the wall reinforcement and the lack of confinement in the boundary elements (Bostenaru and Sandu, β00β). In Romania, these types of structural walls are not currently used as a solution for dissipating the energy induced by earthquakes in high-rises buildings but we consider that they could be successfully used in the future. The main reason of this statement is the presence of soft soils that represent a major problem in many areas of Romania, together with the deep-focus earthquakes, leading to soil periods higher than 1s. In the case of soft soil and stiff building, the soil will absorb the seismic energy through deformations that can cause the overturning of the building (Marin and Roman, β010). The implementation of slit walls in high-rise buildings produces a sudden decrease of the stiffness at a high seismic threat and the natural period of the building increases avoiding, in this way, resonance. The sudden decrease of the stiffness is due to the degradation of the short connections of the slit walls. With this solution, the seismic demands can be significantly reduced and an economical design can be reached. The first precast slit panel was patented by Professor K. Muto, in Japan, in 197γ (Fig. 1a) (Muto et al., 197γ). This is the first energy dissipation system used in Japan. This solution consisted of precast RC vertical strips introduced in the steel frames. Other solutions of slit walls have been proposed by Chinese, Korean, Iranian and Russian researchers. The Korean researchers proposed a slit panel used for reinforced concrete framed buildings in which strips are anchored into the beams (Fig. 1b) (Liou and Sheu, 1998). These types of panels were experimentally tested at four types of lateral loads: monotonic loading, repeated loading, reverse cyclic loading and random cyclic loading. From the experimental tests, it was found that the failure mechanism is changed through this solution from shear to flexural.