Nigel Priestley, Damian Grant and Carlos Blandon
There has been considerable discussion recently in New Zealand about the relative merits of displacement-based, and displacement-focused force-based seismic design. This paper puts the case for direct displacement-based seismic design. It is shown that the emphasis on secant stiffness to maximum displacement, rather than initial stiffness (as in force-based seismic design) is important for rational force-distribution to different seismic-resisting structural elements, and in most cases obviates the need for iteration in the design process, which is inherent in displacement-focused force-based seismic design. It is shown that the influence of hysteretic characteristics has been underestimated in recent force-based studies. These assertions are supported by results of recent analytical studies, which have included refinement of ductility/equivalent-viscous damping relationships, and an examination of the important (and largely ignored) role of “elastic” damping in inelastic time-history analyses.
Paper P33: [Read]
Procedures for designing structures to resist earthquakes have evolved from those used to design for other environment loadings. The force-based procedure commonly used for seismic design requires the designer to apply a set of forces to the structure, detail it to have adequate strength and check that the structure and its components have adequate deformation capacity. A more rational design procedure is proposed in this paper that focuses on the deformations that result form ground movement beneath the structure. The deformation capacity of the structure and its components are checked first. Once the deformations are acceptable, the equivalent-static design forces are applied to the structure and the components are detailed to have adequate strength.
Paper P34: [Read]
Resetable devices with customised performance for semi-active seismic hazard mitigation of structures
Geoff Chase, Kerry Mulligan, Alexander Gue, John Mander, Thierry Alnot, Geoffrey Rodgers, Bruce Deam, Lance Cleeve and Doug Heaton
A one fifth scale semi-active, resetable device is designed and tested. A novel design that utilises each chamber independently allows more flexible control laws than previous resetable devices. Manipulation of the force-displacement hysteresis curve via innovative control laws allows the hysteresis loop to be pre-determined with one such manipulation resulting in removal of energy without increasing the base shear demand. The device characteristics with air as the working fluid, are determined and an analytical model developed. The design stiffness is 250 kN.m-1 with the prototype having a stiffness between 185 kN.m-1 and 236 kN.m-1. The peak force is in excess of 20 kN at a displacement of 33 mm. The impact of the actuator in a structure is studied using an iterative hybrid approach, a virtual structure, and an experimentally proved device model.
Paper P35: [Read]
Alessandro Palermo and Stefano Pampanin
Following the research developments in the seismic design of precast frame and shear wall systems based on innovative jointed ductile connections, similar innovative alternative solutions can be proposed for concrete piers for an improved seismic performance when compared with traditional monolithic solutions. In particular, the possible extension to bridge piers and system of the concept of a peculiar jointed ductile connection, the hybrid system, where self-centring properties (unbonded post-tensioned cables) are adequately combined with additional energy dissipation (longitudinal mild steel bars or energy dissipation devices), is herein considered and investigated. After brief introduction on the development of the hybrid systems, a description of the peculiarities of their cyclic behaviour is carried out, considering the most significant parameters governing the response. A critical comparison of the seismic response, in the transverse direction, of hybrid and monolithic connections at both local (single bridge piers) and global level (bridge systems) is carried out through inelastic dynamic time history analyses using lumped plasticity models.
Paper P36: [Read]
Brabhaharan Brabhaharan and Greg Saul
Road networks are key lifelines for the community, and improving their performance is critical to the availability of road access after earthquakes. The performance of the Wellington Road network in moderate to large earthquakes as well as storms and the consequential risks were identified through a systematic study with the aid of a geographical information system. The performance assessment and mitigation of two retaining walls along Ngaio Gorge Road is presented. A performance based approach was used to decide on the mitigation solutions and an appropriate level of risk mitigation. This enabled the selection of strengthening solutions that meet the performance requirements for the Ngaio Gorge Road, but also at optimum cost. One breastwork retaining wall was strengthened using soldier piles, and tied back using rock anchors. The other breastwork wall site was improved using soil nailing of the retaining wall backfill and the slope below. The soil nail design solution allows for significant deformation of the road during a large earthquake, but would maintain access along this section of the road. An economic analysis was used to justify the strengthening work for funding.
Paper P37: [Read]