Report - PEER - University of California, Berkeley

To examine how accurately numerical simulation is able to trace the experimentalcyclic behavior, the analysis program adopted for the pushover analyses was usedagain. This analysis this time was different from the previous analysis in thefollowing aspects. Yield strength values obtained from the associated coupon testswere used instead of the nominal strength values, resulting in a 31% increase forbeams, a 32-35% increase for columns, and a 5-8% increase for column bases. Strainhardening after yielding was included, with the modulus of strain hardening (relativeto the elastic stiffness) determined by trial and errors. Increase of moment capacityby composite action was adjusted based on the experimental results. A slip modelwas incorporated to represent the hysteretic behavior of the column bases that involvesignificant pinching.Figure 8(b) shows comparison between the experimental and numerical resultsfor the cycles of 1/25 amplitude. In the development of the analytical curves, 5, 5,and 13% of strain hardening were adopted for the columns, column bases, and beamsand panel-zones, respectively. The positive moment capacity was increased by 20%to allow for composite action. The thin and bold lines are the experimental andanalytical curves. Correlation between the experimental curves and analytical curvesobtained for the frame model is excellent, with the difference in the maximumstrength not greater than 2.6% (positive) and 4.7% (negative), and the difference inthe dissipated energy (areas of enclosed loops) not greater than 4.0%. Pinchingbehavior notable particularly in the first story is also reproduced very reasonably.Analysis parameters (degree of strain hardening and increase in the positivebending moment) were chosen in reference to the experimental results; hence theanalyses are typical post-analyses and are not fair in terms of “prediction.” Thewriters’ contention is that the analyses commonly used in daily design and analysispractices are reasonable enough to duplicate the inelastic behavior up to the driftangle of 1/25, which is significantly larger than the range of deformations consideredin contemporary seismic design, if strain hardening and composite action are estimateproperly. How to estimate reasonable strain hardening and composite action is asubject of further exploration.6. CONCLUSIONSThis paper introduced the outline and some results of the cyclic loading tests appliedto a full-scale, three-story, two-bay by one-bay steel moment frame. Notableobservations obtained in this paper are summarized below.(1) Balanced deformations between the beams, panel-zones, and column bases(primarily due to yielding of the anchor bolts) were observed. Pinching behaviorwas notable for cyclic loading with larger amplitudes (up to 1/25 in the overalldrift angle) primarily because of cyclic yielding and resulting slip-type hysteresisexperienced at the column bases.(2) The effect of ALC panels (used for exterior finishes) on the structural behaviorwas nearly null up to the story drift angle of 1/25 rad, indicating that the278