Report - PEER - University of California, Berkeley

Table 3. Comparison of calculated maximum transient inter-story drifts withacceptable limitsEarthquake level EQ-I EQ-II EQ-III EQ-IVAcceptable limit (%) 0.5 1.5 2.5 3.8HFB1 (DBD) (%) 0.75 1.29 2.16 2.85HFB2 (FBD) (%) 0.56 0.99 1.73 3.006. CONCLUSIONSSeismic performances of two hybrid frame buildings representing a 5-story prototypebuilding were analytically studied in this paper. The first building was based on adirect-displacement based design while the second building was established from aforce-based design method. Consequently, the design base shear of the first buildingwas 40% lower than that of the second building and thus the strength and stiffness ofthe two buildings were significantly different.Following validation of the analytical modeling procedure, both buildings weresubjected to short segments of earthquake input motions which were compatible withresponse spectra corresponding to four levels of earthquake intensities. Using theanalysis results, the following conclusions have been drawn:1. The force-based design described in design codes for monolithic concrete specialmoment frames and the direct-displacement design described in Reference(Priestley 2002) are acceptable procedures for the design of the prototype fivestoryprecast hybrid frame building. Because of significantly lower design baseshear, the DBD solution is expected to be more economical.2. The response of both buildings satisfied the transient and residual average interstorydrift limits imposed for different performance limit states. Consequently,both the FBD and DBD methods are expected to provide low-rise precastbuildings with acceptable performances under the four levels of input motions.3. The combination of hysteretic energy dissipation and re-centering capabilities ofthe hybrid connections produced negligible residual drifts for all earthquakelevels. Hence, by controlling the inelastic strain in the post-tensioning steel andintroducing a procedure to replace the mild steel reinforcement when required,hybrid frame buildings may be designed to achieve a higher level of seismicperformance than that considered in this study.4. Although lower drifts were generally obtained for the stiffer building that wasdesigned using a higher base shear, this trend did not hold for the input motioncorresponding to EQ-IV, which represented an event at 150% of a design levelearthquake.The response of the buildings are further examined in an ongoing study at IowaState University by subjecting them to different input motions and characterizing their455