Mitigation of higher mode effects in self-centring walls by using multiple rocking sections

Student: Lydell Wiebe
Supervisors: Prof. Constantin Christopoulos

ABSTRACT

Self-centring walls have been proposed as a means of providing life safety during rare strong earthquakes and also avoiding damage during more frequent moderate earthquakes. By allowing the wall to rock at its base, the peak structural forces are limited without structural damage.

Post-tensioning and energy dissipation are used to ensure stability and to limit displacements.Structural forces increase even when the base moment is limited because of the effects of higher modes. This dissertation proposes that these effects may be substantially reduced by providing multiple rocking sections over the height of a rocking wall system. This is confirmed by a study of the response of 24 walls to a suite of 40 earthquakes. The walls range in height from four to twenty storeys and implement a variety of joint configurations. The peak bending moments above the base are shown to be significantly reduced by providing multiple rocking joints, while the peak displacements do not generally increase in magnitude, nor are they more variable with the addition of further joints. While the rotation experienced at any rocking joint is usually reduced, the maximum centreline elongation increases. The increase in floor  accelerations and storey shears that occurs with the addition of rocking joints is shown to be due to modelling issues that are not representative of the true structural response. It is also found that the peak bending moments and storey shears in a conventional wall can also be reduced, without increasing the displacement or acceleration response, by designing multiple plastic hinge regions.

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