Report - PEER - University of California, Berkeley

As regards the influence of different quality of masonry materials on the seismicbehavior of the tested building types, it can be seen that the models of both, terracedhouse and apartment house structural type, made of model materials simulatingcalcium silicate masonry units (models M1-1 and M2-1) exhibited substantially morebrittle behavior than the models of the same type, but made of model materialssimulating hollow clay units. However, there has been not much difference observedas regards the resistance. The confinement of structural walls with vertical R.C.confining elements in the case of the terraced house models M1-1c and M1-1d provedto be a successful measure of improving the seismic behavior of the terraced housetype of structure as regards both lateral resistance and displacement capacity.In the idealization of the experimentally obtained resistance envelopes, the storyrotation angle (relative story displacement) at the point where 20% of strengthdegradation has occurred, has been defined as the ultimate story rotation angle(displacement) which the structure can resist without risking collapse. Thisassumption has been considered in the cases where no sudden collapse of the models(such as was the case of models M1-1 and M2-1) has been observed during theshaking tests. The rotation angle (displacement) at 20 % of strength degradation hasbeen considered as ultimate in the evaluation of the idealized ultimate global ductilityfactor of the structure µ u . However, substantial damage to structural walls of themodels has occurred at that stage. Therefore and in order to fulfill also the “damagelimitation” requirement, only part of the available displacement capacity has beentaken into account in the evaluation of behavior factor q on the basis of the globalductility of the structure, limited by the displacement value where severe damage tostructural walls occurs. This value has been arbitrarily chosen to be 3-times the valueof story rotation at the damage limit Φ u = 3 Φ dam . Typical evaluation is presented inFigure 19.As has been found by this study, the ranges of values of structural behavior factorq, proposed in Eurocode 8 for different masonry construction systems, are adequate,though conservative. Since the experimental response has been evaluated, an increasein q factor values is expected as a result of overstrength of masonry structures,designed by usual design calculation methods.The study also indicated that the values of q factor depend not only on the systemof construction, but also on the properties of masonry materials and structuralconfiguration, especially structural regularity, of the building under consideration.Therefore, experimental research is needed for the assessment of a particular value fora particular structural type specified on a national basis within the recommendedrange of values in the basic document. Although such tests are helpful, the values ofbehavior factor q cannot be assessed by means of only ductility tests of structuralwalls.307