Report - PEER - University of California, Berkeley

uildings, up to five stories high (Gobierno, 2004). For all cases, an equivalent staticlateral force analysis and/or a modal analysis are specified. Details on analysisrequirements can be found elsewhere (Alcocer et al., 2003; Gobierno, 2004).Lateral load, kNM2 (M-0-E6)M4 (M-1/4-E6)2001000,60,40,200-0,2-100-200-0,4-0,6-0,02 -0,01 0 0,01 0,02 -0,02 -0,01 0 0,01 0,02Drift angle, mm/mmDrift angle, mm/mmFigure 1. Typical hysteresis curves of confined masonry walls without and withhorizontal reinforcement.In structures analyzed with methods other than the simplified method, inelasticinterstory drifts shall be checked. These values are calculated through multiplying theelastic drift angles, obtained in the analysis from a reduced set of lateral forces, by theseismic behavior factor, Q. The seismic behavior factor Q is equal to 2 for confinedmasonry walls built with solid units or with multiperforated bricks with horizontalreinforcement and exterior tie-columns; 1 for unreinforced masonry; and 1.5 for othercases. Calculated inelastic drift angles shall not exceed allowable values, which werederived from experimental results, and are intended to be consistent with a moderatelevel of damage, generally accepted in Mexico as a desirable performance of housingunder the design earthquake. For example, for confined masonry walls built with solidunits, allowable inelastic lateral drift angle is 0,0025.Masonry standards prescribe the spacing of TCs and BBs, as well as theirreinforcement detailing (Fig. 2). The masonry contribution to shear strength iscalculated from Eq. 1, in which FR is the strength reduction factor, AT is the walltransverse area, and P is the vertical load acting on the wall. This equation is intendedto predict the shear force at first diagonal cracking, and was calibrated fromexperimental results.Shear stress, MPaVmR=FR(0.5 vm*AT+0.3 P) ≤ 1.5 FRvm*AT (1)The contribution of the horizontal reinforcement to shear strength is determinedfrom Eq. 2, in which η is an efficiency factor (see Fig. 3), p h is the percentage ofhorizontal reinforcement, and f yh the specified yield stress of the horizontalreinforcement. In this regard, “horizontal reinforcement” refers to steel wiresembedded along the joint mortar and also refers to the horizontal wires of a steelwelded wire mesh properly anchored to the masonry and covered with a cementbasedmortar.236