2010 NZSEE
Conference
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2010 NZSEE Conference |
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Contents |
Keynote Address Tribute to Tom Paulay Session 3 Session 4A Session 4B Session 5A Session 5B Session 6 Session 7A Session 7B Session 8A Session 8B Poster Session Seismic Performance of Prestressed Timber Beam-Column Sub-AssembliesAsif Iqbal, Stefano Pampanin and Andy Buchanan Prestressed timber systems made of laminated veneer lumber (LVL) members held together by unbonded post-tensioning have recently been introduced in multi-storey timber buildings. The system can be supplemented with mild steel energy dissipation elements. The whole arrangement, with enhanced recentering and energy dissipation characteristics, has shown excellent seismic performance. This paper summarizes the results of an experimental investigation into the seismic response of full-scale LVL beam-column joints, performed as part of a larger research programme at the University of Canterbury. The subassembly was tested for practicality of the arrangements as well as for examination of behaviour of the whole system. The joint was designed as part of a building frame for a six-storey building located in a high-seismic zone. The timber beams and column, and the recentering/dissipating elements, were optimized to produce the intended behaviour in a real structure. Commercially available prestressing arrangements were used. The externally attached mild steel energy dissipaters were designed to be installed and replaced easily. Both exterior and interior joints were tested. Different arrangements of the members, with and without steel armouring plates were investigated. Effectiveness of the energy dissipation elements was also verified. A novel approach to overcome the inherent weakness in the timber joint was tried with steel reinforcement in the form of long screws embedded inside the joint region. The results of these full-scale tests helped to develop further understanding, and to solve practical issues with connection details for implementation in large multi-storey timber buildings. Paper P27: [Read] Global Response of a Two Storey Pres-Lam Timber BuildingMichael Newcombe, Stefano Pampanin and Andy Buchanan Judged 'Best Research Paper' for 2010 Recent structural timber innovations at the University of Canterbury have let to the construction and experimental testing of a large scale, 2 storey, post-tensioned timber frame and wall building. The building was subjected to uni-directional and bidirectional quasi-static cyclic seismic testing, up to a maximum drift of 3.0%. The influence of concrete diaphragms and additional mild steel reinforcement for frames and walls are examined. For these tests, the structure responded essentially elastically. The addition of a thin concrete diaphragm had limited effect on the hysteretic response of the frames and walls, providing a 15% and 25% increase in strength respectively at design displacements (2% drift). Compressive deformation of beam-column connections resulted in minimal beam elongation, avoiding damage to the concrete slab. Additional mild steel reinforcement across the beam-column connections had little effect on the lateral resistance of the frames at 2% drift but was more effective at 3% drift. Simultaneous bidirectional loading induced a minor increase in the in-plane resistance of the frame and wall systems. Paper P28: [Read] A Summary of Test Results for Selective Weakening and Post-tensioning for Retrofit of Non-Ductile R.C. Exterior Beam-Column JointsW.Y. Kam, S. Pampanin and D.K. Bull This paper summarises the experimental results of a counter-intuitive seismic retrofit strategy – Selective Weakening, targeted at improving the seismic performance of poorly detailed (pre-1970) exterior beam-column joints, a critical weakness of non-ductile reinforced concrete frames. The retrofit interventions investigated comprised of: a) selectively weakening the beams (reducing joint shear demand) and/or b) adding external post-tensioning to the beam-column joints (adding horizontal confinement and axial force to the joint) with the aim to change the local inelastic mechanism of the external joints. This would result in improved global displacement, ductility and energy dissipation capacities without significant increase in demand of foundation strength, typical of strengthening retrofit. Extending from previously presented preliminary experimental results, a comprehensive test matrix and its results are presented herein. Nine 2/3-scaled exterior beam-column joints subassemblies – as-built and retrofitted were constructed and tested to investigate the feasibility and effectiveness of the proposed retrofit strategy. Parameters considered in the tests were the levels of external post-tensioning forces, locations of beam weakening, the presence of column lap-splice and the presence of cast-in-situ slab and transverse beams. Experimental results have indicated that joint shear and column lap-splice failures can be prevented or mitigated using a Selective Weakening retrofit approach, leading to the targeted seismic performance. This research is part of the six-year NZ FRST national project on “Seismic retrofit solutions for NZ multi-storey buildings”. Paper P29: [Read] The Seismic Performance of a Non-Tearing Floor Precast Concrete Structural SystemBen Leslie, Des Bull and Stefano Pampanin Judged 'Best Student Research Paper' for 2010 The interaction between reinforced concrete moment frames and precast flooring systems during an earthquake is a well established topic of concern for structural engineers. Beam elongation and displacement incompatibility between the frame and floor cause high levels of damage in the diaphragm and beams, and can ultimately lead to collapse of the composite floor (precast units and cast-in-place topping) if particular detailing to mitigate these effects is not applied. Recently focus of research has shifted from detailing for significant localised damage to beams and adjacent floors to that of minimising damage to the structural system of beam and floor by creating a “Non-Tearing [of the floor]” beam-to-column connection. This is where the relative rotation of the beam to the column, under lateral displacement of the building, does not result in large plasticity of the beam and avoids the detrimental damage (tearing) of the floor-to-column junction. This paper contributes to an on-going research programme of a precast non-tearing floor and frame system for seismic regions (supported by FRST). The experimental and analytical results of the recently completed 2/3 scale frame test, incorporating three beam-to-column connection details are presented and design issues and recommendations particular to these options are discussed. Paper P30: [Read] Keynote Address Tribute to Tom Paulay Session 3 Session 4A Session 4B Session 5A Session 5B Session 6 Session 7A Session 7B Session 8A Session 8B Poster Session |