Seismic Design of services using Dynamic Principles

Seismic design, without bracing!

AS1170.4 provides simple, static force-based methods for determining earthquake design actions on building services.

But there’s nothing static about an earthquake. Seismic ground motions are dynamic events that shake buildings in dynamic ways, and the standard allows for the design of buildings and building services using dynamic methods.

Dynamic analysis of suspended services can demonstrate that under certain circumstances, the seismic design actions of AS1170.4 will result in a relatively small dynamic response. In other words, there are scenarios where earthquake design actions will only cause suspended services to swing by a small and tolerable amount.

The benefits of this approach were highlighted during the construction of a new chiller plantroom within the previous carpark levels of a 35yr old CBD tower. The existing overhead slabs were unable to support the gravity and seismic loads of the new pipework, and the lower slab was unable to support the static force-based seismic reactions of goal-post framing.

However, dynamic modelling of the pipework and support systems proved that acceptable seismic performance could be achieved without the installation of any seismic bracing.

The dynamic movement of the pipe network under earthquake design loads was modeled, and the resultant pipe stresses and equipment reactions were analysed. Minor changes to the pipe design improved the system flexibility and reduced stresses and reactions to acceptable limits. The structural performance of the support framing was assessed, and the resultant reactions on the building structure were reported for review and approval.

While the engineering analysis was relatively complex, it addressed the structural constraints of the building, and the end outcome cost considerably less than a typical seismic-restraint solution.

To learn how dynamic analysis can help you achieve the seismic performance requirements of your project, and reduce construction complexity and cost, contact our office and speak to one of our engineers.