Report - PEER - University of California, Berkeley

Efficiency η, %100806040203D-RWBW-BN2N3 M-072M3WBW-ENTC-M 2004Confined, solid brick, horizontal reinforcementConfined, solid brick, welded wire meshConfined, hollow brick, horizontal reinforcementLadder-shaped reinforcement (not allowed)M-147M1(Alcocer 1996b & 1999)0 0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8p hfyh , MPa0.3 MPa0.3 f m*Limits forNTC-M 2004:V ≤ p f ≤mR h yh 1.2 MPa, solid unitsFRA0.9 MPa, hollow unitsTN4M4M-211Measured stiffnesseswere obtained as theslope of the secantdrawn from the pointwith zero load of theprevious half-cycle tothe peak in the nexthalf-cycle. Initialstiffness was the slopeof the secant linedrawn at a point wherethe slope of theenvelope curvechanges significantly.Figure 3. Efficiency factor of horizontal reinforcementfor contributing to wall shear strength.The normalized stiffness degradation curves for the loading and unloadingbranches, for confined masonry walls without horizontal reinforcement, and the bestfitcurve of the data are shown in Fig. 4. According to the model proposed, loadingstiffness is constant until reaching the envelope. If higher drifts are imposed, theloading branch will follow the envelope. To compute the stiffnesses for the loadingand unloading branches for the next half-cycle, the maximum drift angle reachedmust be recorded. This implies that stiffness decay in the loops will not be calculatedif the drift ratios were smaller than a value reached before. Calibration criteria andresults can be found elsewhere (Flores and Alcocer, 1996).4. SEISMIC PERFORMANCE EVALUATION OF CONFINED MASONRYSTRUCTURES4.1 Performance Criteria for Masonry StructuresBased on experimental results and damage observations in the laboratory and in thefield, performance criteria for confined masonry structures made of solid clay unitsare suggested (Table 1). Three limit states were identified, namely, serviceability,reparability and safety.238