The Development of High-Performance Post-Tensioned Rocking Systems for the Seismic Design of Structures
Thesis DisciplineCivil Engineering
Degree GrantorUniversity of Canterbury
Degree NameDoctor of Philosophy
It is not economical, nor practical, to design structures to remain elastic following a major earthquake event. Therefore, traditional seismic design methodologies require structures to respond inelastically by detailing members to accommodate significant plasticity (“plastic hinge zones”). It can be appreciated that, while life-safety of the occupants is ensured, structures conforming to this traditional design philosophy will be subjected to excessive physical damage following an earthquake. Thus, the direct costs associated with repair and the indirect costs associated with business interruption are expected to be great. Adding to this, structures located within a near-field region, close to a surface rupture, can be subjected to large velocity pulses due to a ground motion characteristic known as forward directivity in which a majority of the earthquake’s energy arrives within a very short period of time. Conventionally constructed systems are, in general, unable to efficiently deal with this ground motion. In the last two decades, advanced solutions have been developed to mitigate structural damage utilising unbonded post-tensioning within jointed, ductile connections, typically combined with hysteretic damping. While there is a growing interest amongst the engineering fraternity towards more advanced systems, their implementation into mainstream practice is slow due to the lack of understanding of unfamiliar technology and the perceived large construction cost. However, even considering such emerging construction technology, these systems are still susceptible to excessive displacement and acceleration demands following a major velocity-pulse earthquake event. In this research, the behaviour of advanced post-tensioned, dissipating lateral-resisting systems is experimentally and analytically investigated. The information learned is used to develop a robust post-tensioned system for the seismic protection of structures located in zones of high seismicity within near-field or far-field regions. A series of uniaxial and biaxial cyclic tests are performed on 1/3 scale, post-tensioned rocking bridge piers, followed by high-speed cyclic and dynamic testing of five 1/3 scale, post-tensioned rocking walls with viscous and hysteretic dampers. The experimental testing is carried out to develop and test feasible connection typologies for post-tensioned rocking systems and to improve the understanding of their behaviour under cyclic and dynamic loading. Insights gained from the experimental testing are use to extensively refine existing analytical modelling techniques. In particular, an existing section analysis for post-tensioned rocking connections is extended to assess the response of post-tensioned viscous systems and post-tensioned connections under biaxial loading. The accuracy of existing macro-models is further improved and a damping model is included to account for contact damping during dynamic loading. A Direct-Displacement Based Design (DDBD) framework is developed for post-tensioned viscous-hysteretic systems located in near-field and far-field seismic regions. The single-degree-of-freedom (SDOF) procedure is generic and has applications in new design and retrofit, while the multi-degree-of-freedom (MDOF) procedure is developed specifically for continuous bridge systems. Detailed design guidelines and flow-charts are illustrated to encourage the knowledge transfer from this report and to promote the use of emerging technology. Combining the information gathered from experimental testing, modelling and design, a probabilistic seismic hazard analysis is performed on three post-tensioned viscous-hysteretic bridge systems. In all cases, the post-tensioned bridge systems are shown to be more feasible than a traditional monolithic ductile bridge. Furthermore, while a post-tensioned hysteretic bridge is shown to be the most economic solution, the viscous-hysteretic system becomes more advantageous as the cost of fluid-viscous-dampers reduces.