Keynote Address Session 1 Session 2 Session 3A Session 3B Session 4A Session 4B Session 5A Session 5B Session 6 Session 7 Poster Session 

Modelling of RC Moment Resisting Frames with Precast-prestressed Flooring System

Brian Peng, Rajesh Dhakal, Richard Fenwick, Athol Carr and Des Bull

In this paper, the seismic performance of reinforced concrete moment resisting frames coupled with a floor containing precast-prestressed units is examined. Mechanisms associated with the beam strength enhancement arising from plastic hinges and floor interactions are described. A computational model is set up to predict the response of a 3D frame containing precast-prestressed floor units with cast-in-situ concrete topping. This model contains newly developed plastic hinge elements which account for flexural, shear and elongation response of plastic hinges in beams subjected to inelastic rotation and varying axial load levels. To allow for floor interaction with the beam plastic hinges, the model uses axial strut-and-tie elements to represent the linking slab between the longitudinal beams and the first precast unit. Analysis using this model shows good agreement with the experimental results indicating that the model can be used to analyse the seismic performance of RC frames containing precast-prestressed flooring systems.

Paper P29: [Read] [Presentation]

A Probabilistic Seismic Loss Assessment of Advanced Post-Tensioned Precast Bridge Systems

Dion Marriott, Stefano Pampanin, Des Bull and Alessandro Palermo

Post-tensioned precast rocking systems have emerged as the next generation seismic resisting systems; however, they are not yet widely accepted and are seldom considered in practice, particularly for bridge systems, due to a combination of lack of understanding and the fallacy that such a system may not be cost effective when compared to traditional monolithic or emulation of cast-in-place construction.

The results of a seismic loss assessment confirm that a traditional hybrid bridge system provides a significant financial benefit when compared to a monolithic precast system. Reasons for this relate to the reduced level of physical damage at each structural limit state and a greater displacement capacity for post-tensioned bridge piers. When combining viscous and hysteretic dampers within a post-tensioned bridge system (defining an advanced flag-shape system) a superior level of protection can be achieved for either far-field or near-field earthquake events. However, the initial cost of installing fluid viscous dampers (based on current market costs) can undermine the potential financial benefit of such a system.

Paper P30: [Read] [Presentation]

Seismic Response of Green Roofs

Marc Carmody, Milan Jasarevic, Piotr Omenzetter, Charles Clifton and Elizabeth Fassman

Green roofs consist of vegetation with a light-weight substrate planted over a drainage layer and waterproof membrane. The green roof retains rainwater in the plants and substrate and releases the water through evapotranspiration and some surface drainage. This research explored the green roof’s ability to resist seismic forces and the potential for the green roof to be used as an energy dissipater to reduce the response of the building to lateral dynamic loading, such as wind loading. Shake table tests showed the substrate layer was capable of resisting most seismic events and with the addition of plants it became resistant to all but the most severe earthquake events. Varying the moisture conditions showed that up until the substrate started responding to excitations as a liquid, the additional water was beneficial to the survivability of the substrate layer. The mixing and sloshing of free water within the drainage layer will provide additional damping to a structure. Laboratory-scale dynamic tests proved the concept of using free water within the drainage layer as a source of additional damping and enabled quantification of the damping effects. Numerical simulations demonstrated that significant additional damping could be achieved in full-scale buildings susceptible to excessive wind-induced vibrations.

Paper P31: [Read] [Presentation]

Experimental Validation of Selective Weakening Approach for the Seismic Retrofit of Exterior Beam-Column Joints

W.Y. Kam, Stefano Pampanin and Des Bull

The experimental validation of the concept of selective weakening (SW) for seismic retrofit of existing pre-1970s reinforced concrete frames is herein presented. The SW retrofit strategy is to modify the brittle inelastic mechanism to a more ductile mechanism by first weakening selected parts of the structure. Subsequently, the structure can be further upgraded to the desired strength/stiffness/ductility and energy dissipation capacity. Different levels of performance are achievable, from collapse prevention to damage control. For a beam-column (bc) joint, the proposed SW retrofit involves severing the bottom longitudinal reinforcement of the beam, and if required, adding external post-tensioning tendons. In this paper, the experimental implementation of the SW retrofit for poorly detailed exterior bc joint subassemblies is presented. Four 2/3 scaled exterior bc joint subassemblies are used to investigate the feasibility and effectiveness of selective weakening retrofit. Generally, the experimental results confirm previous numerical findings of the viability of SW retrofit to improve seismic performance of existing bc joints. By reducing the shear demand through beam weakening and/or increasing the joint capacity by adding horizontal axial load from external post-tensioning, the local inelastic mechanism is concentrated to a ductile flexural beam hinge, thus achieving the desirable weak-beam strong column/joint global mechanism. Complementing this paper are earlier numerical results of refined FEM 3D models of the exterior bc joint and macro-model of a multi-storey prototype structure.

Paper P32: [Read] [Presentation]

Out-of-Plane Assessment of an Unreinforced Masonry Wall: Comparison with NZSEE Recommendations

Hossein Derakhshan, Jason Ingham and Michael Griffith

Out-of-plane seismic assessment of unreinforced masonry (URM) walls is an important step in the assessment of a URM building. In this paper, a parametric study is performed on the assessment methodology proposed by the New Zealand Society for Earthquake Engineering, NZSEE, (NZSEE 2006). A single-degree-of-freedom (SDOF) model is then used in time-history analysis (THA), and an alternative assessment method is proposed based on the obtained results. The results are next compared with the NZSEE recommendations. To perform the THA, a well-known commercially available finite element (FE) program is first correlated with a special THA computer program written by researchers in Australia. The commercial program is then used to predict the behaviour of a single-storey 2-leaf URM wall subjected to several earthquake records. The selected wall, having dimensions of 4100 mm high by 220 mm thick, is one of the most common configurations of URM walls found in New Zealand. Earthquake records are selected based on New Zealand seismicity, and the analysis is repeated to account for several soil conditions.

Paper P33: [Read] [Presentation]

Keynote Address Session 1 Session 2 Session 3A Session 3B Session 4A Session 4B Session 5A Session 5B Session 6 Session 7 Poster Session