Seismic design considerations for tall buildings

Student: Hiep Pham Tuan
Supervisors: Dr Timothy J. Sullivan, Prof Gian Michele Calvi

ABSTRACT

The aim of this research is to study the performance of tall reinforce concrete frame-wall structures under seismic loading.

The current seismic design procedures in the code have been issued without any recommendation for tall buildings. Therefore, when structural engineers design a structure, they use the same rules for structures with very large differences in height: same response spectrum, same behaviour factors, same P-delta limits, etc. However, it is considered that tall buildings have particular characteristics that warrant special consideration.

In this research, a 45-storey reinforced concrete frame-wall case study structure is designed using the modal response spectrum analysis procedures of the Eurocode 8, then small and large displacement non-linear time-history analyses are carried out to check the realistic performance of the designed structure. Through this case study, some significant design considerations for tall frame-wall structures, such as the response spectrum used, higher mode effects, likely ductility demands on structural components, the significance of P-delta effects, and beam lengthening effects are highlighted.

It is shown that axial forces in beams tend to resist the tendency of P-delta effects to increase displacements. Furthermore, it is shown that beam-lengthening could imply that it may not be appropriate to rely on the beam axial stiffness.

The case study results also indicate that P-delta effects may not be as significant for long period structures as current code requirements suggest. To investigate this further, a suite of equivalent single-degree of freedom analyses is conducted to examine a larger range of tall building periods. The results of these SDOF studies also indicate that the P-delta limits in current codes could be relaxed.

Various issues to be explored in future work are also identified.

You may download a digital version of this MSc dissertation here.