Dynamic behaviour of reinforced concrete frames designed with direct displacement-based design

Student: Didier Pettinga
Supervisor: Prof. M.J.N. Priestley

 

Abstract

Using the proposed methods the six frames are redesigned and analysed at ratios of 0.5x, 1.0x and 2.0x the design earthquake intensity. In all cases the inelastic dynamic behaviour is significantly improved from that previously observed with the assumed 2% drift limit well reflected over the height of the frames at the design level intensity. The suggested design displacement profiles are found to represent the inelastic response adequately for all cases.Using the revised designs the dynamic amplification of column shear forces and bending moments due to higher modes is investigated. The time-history results show that while amplification is present over the height of all the frames, the development of inelasticity in the beams throughout the buildings substantially reduces the higher mode influences compared to the behaviour seen for structural walls. To account for the observed column shear force behaviour, the Modified Modal Superposition (MMS) found to work well for structural walls using DDBD is modified to include the effects of the ductility development and account for intensity changes. For the column moment amplification a simple intensity dependentequation is developed to satisfy the time-history demands. Both approaches are tested and found to give satisfactory results at a range of intensities.

An initial assessment of the range of applicability for the proposed methods is carried out using minor changes to the frame geometries for the 12, 16 and 20 storey buildings. The changes implied lower design ductilities and therefore were a move towards traditionally more flexible structures. The time-history results were generally well estimated by the suggested developments, hence it is probable that the methods may be applicable to a wider range of frame forms.

This work has been, or is about to be, published as a ROSE Research Report, for which reason a copy of it is not available for download, but can rather be obtained from IUSS Press.