As performance-based seismic design approaches become more commonplace and as more emphasis is placed on damage control, research has increasingly focused on developing high-performance lateral force resisting systems (LFRS), such as self-centering systems. The concept of rocking self-centering walls is not new, but the concept has not previously gained traction in practice. The project objective was to assess whether a self-centering concrete wall system, with or without supplemental energy dissipation, is viable as a high-performance, low-cost lateral load resisting system in low- to mid-rise reinforced concrete and composite buildings.
Unbonded post-tensioned (UPT) precast concrete walls are part of the family of self-centering systems. The traditional plastic hinge mechanism of conventional LFRS, which is associated with structural damage and the potential for large post-earthquake deformations, is replaced in UPT walls by a rocking mechanism at the wall-foundation interface. The rocking mechanism allows the UPT wall to undergo large nonlinear displacements with minimal structural damage and no residual deformations.
A case study was undertaken to investigate whether UPT walls are an economically viable alternative to conventional systems. To this end, three alternative design approaches for a three-storey building (steel moment-resisting frames, SMF; reinforced concrete walls, RC; and the self-centring unbonded post-tensioned walls, UPT) were compared in terms of initial construction cost, seismic performance, and economic losses from damage to structural and nonstructural components under different ground shaking intensities.
The UPT wall is found to be a reliable and cost-effective option for the lateral-force resisting system of the 3-storey case study building.
Detailing is simplified relative to conventional systems, as no special reinforcing detailing is required except for the need to adequately confine the wall ends at the base.
Provided that floor accelerations are taken into account during the design process to protect the acceleration-sensitive nonstructural components, UPT buildings could lead to a nearly damage-free building that is operational after a maximum-considered earthquake (MCE) event.
As more emphasis is being placed on the structural damage caused by earthquakes and associated economic impact (including downtime and repair costs), high-performance seismic structural systems have become a primary research focus.
Next generation seismic design methodologies encourage high-performance structural systems that limit or eliminate permanent deformations. Such systems have high energy-dissipation capacity and are able to contain and limit damage. As development of these structural systems gains momentum, the results of this study will be relevant as such systems are introduced and codified.
This research has focused on the application of a self-centering wall concept to buildings with reinforced concrete or structural steel gravity-framing. The concept has the potential to provide a low-cost, repairable, earthquake-load-resisting system that could limit the transient and residual drift of the structure in an earthquake event.
The self-centering unbonded post-tensioned (UPT) precast wall system offers a high-performance, low-cost, easily constructable system for use in new and existing mid-rise buildings located in seismically-vulnerable regions:
- for new buildings: the system is repairable, it limits downtime, it limits non-structural and structural damage; and it is relatively low cost.
- for retrofit of existing buildings: the system needs relatively little floor area, and it could limit the extent of a seismic retrofit by reducing the displacement demand on existing structural and non-structural members.