Optimum Semirigid Connections in Hybrid Frames for Effective Seismic Performance

The beneficial effect of using hybrid frames is realized in terms of the reduction of some desired engineering demand parameters (EDPs). However, this is achieved at the cost of increasing the values of some other EDPs as compared to the rigid frame. A good balance between the two can be achieved by selecting the optimum number of semirigid (SR) connections. In the present study, two schemes of the selection of the optimum number of SR connections are presented to obtain the desired benefit of the hybrid frame. One scheme provides the optimum number of SR connections which provides the desired reductions in the base shear (BS) and total number of plastic hinges formed ($T{H}_{\max }$) with the marginal increase in the maximum inter-story drift ratio (${\mathrm{IDR}}_{\max }$). The other scheme provides the number of SR connections to be used for achieving the limiting drift allowed in the hybrid frame and accordingly, obtains the percentage reductions of the BS and $T{H}_{\max }$. Both schemes are developed using a graphical technique. Three illustrative examples are considered to demonstrate the efficacy of the two schemes using the nonlinear time history analysis under three types of earthquakes (i.e., near and far-field) at three peak ground accelaration (PGA) levels. The results of the study show that in both schemes of providing the optimum number of SR connections, significant reductions in the BS and $T{H}_{\max }$ can be achieved as compared to the fully rigid frame. The corresponding ${\mathrm{IDR}}_{\max }$ in the hybrid frames remains less than equal to the limiting value of the ${\mathrm{IDR}}_{\max }$ prescribed in the literature.