18. Design of a Plan Irregular RC Frame Building by Direct Displacement-Based Design Method

In this chapter, an application of the direct displacement-based design (DDBD) to multistorey irregular in-plan RC frame buildings is made. A case study is carried out in order to extend and validate the methodology to this type of structures. The design of a torsionally flexible system is carried out according to DDBD, and its seismic performance is compared, through nonlinear dynamic analyses, to the performance of the same building designed according to elastic modal response spectrum analysis. Lumped plasticity models are implemented for nonlinear dynamic analyses, which are carried out according to EC8 provisions: seven real earthquakes, selected in order to fit on average the elastic design spectrum, are used as input. The two different design methods provide very different reinforcement ratios: the DDBD allows a reinforcement saving of about 70% for beams and 50% for columns. In spite of this, the verification at the ultimate limit state, performed by nonlinear dynamic analyses according to EC8, is satisfied. Furthermore, nonlinear analyses show a better response of the structure designed by DDBD: the torsional twist is reduced and the damage is better distributed.