		2006 NZSEE Conference
	Abstracts

Keynote Address Learning from Hawke's Bay 1931 Earthquake Performance Assessment and Retrofit Decision Making for Risk Mitigation Behaviour of Walls and Piers Understanding Reinforced Concrete Behaviour Modelling Earthquake Performance Earthquake Performance Poster Papers Design and Development

The Influence of Diaphragms on Strength of Beams

Richard Fenwick, Des Bull, Cameron MacPherson and Renee Lindsay

In the seismic design of ductile multi-storey moment resisting frames the majority of potential plastic regions are located in the beams. Capacity design requires the maximum likely flexural strength of these zones to be determined. The remainder of the structure is then proportioned to resist the maximum actions that these regions can apply without exceeding their nominal strengths. This process is intended to ensure that inelastic deformation is confined to the potential plastic regions, which have been detailed to sustain the required deformation. Recent research at the Universities of Auckland and Canterbury on the performance of perimeter reinforced concrete frames has shown that interaction of typical floors with the beams can lead to a substantial increase in the flexural over-strength of potential plastic regions. This increase is considerably greater than that predicted by the current Structural Concrete Standard (NZS 1995). An under-estimate of beam over-strengths may have serious consequences in that non-ductile failure mechanisms, such as a column sway mechanism, may form leading to premature collapse of the building in a major earthquake. This paper describes basic theory related to determination of over-strength actions together with some test results obtained from a recent large scale test.

Paper P21: [Read]

A Concept for Consideration of Slab Effects on Building Seismic Performance

Gregory MacRae and Umarani Gunasekaran

Slabs exist in the majority of buildings worldwide but they are seldom modelled explicitly in analysis for design. In traditional steel moment frame systems, where the slab is not separated from the column flanges the beam overstrength is increased, whereas separating the slab from the column flanges minimizes the beam overstrength. In gap opening systems made of materials such as steel, traditional reinforced concrete, or precast concrete, the column demands are increased due to beam / slab overstrength and beam elongation, and the slab is also damaged during the deformations. This paper describes the development of a simple model for explicit evaluation of the slab effect on moment-resisting (MR) structural systems which considers the slab contribution to the beam overstrength at different storey drifts and the slab opening displacements which can be related to damage. The model captures important aspects of the behaviour of a reinforced concrete joint with a floor slab, well.

Paper P22: [Read]

Three-dimensional Modelling of Poorly Detailed RC Frame Joints

Rolf Eligehausen, Josko Ožbolt, Giovacchino Genesio, Matt Hoehler and Stefano Pampanin

This paper presents preliminary work on three-dimensional numerical modelling of seismic strengthening measures for poorly detailed reinforced concrete frames, primarily designed for gravity loads, as was typical in seismic-prone countries before the introduction of more advanced seismic codes in the early 1970s. These buildings are at risk due to inadequate structural detailing, deficiencies in reinforcement anchorage and the absence of measures to prevent brittle failure modes. Representative beam-column joints tested experimentally at the University of Pavia are analyzed using a continuum finite element program specially developed for detailed modelling of fracture in quasi-brittle materials. The microplane material model with relaxed kinematic constraint is used for the concrete. In the first stage of this work, which is presented in this paper, the proper modelling of the behaviour of smooth reinforcement with hooked ends, as well as the accurate representation of brittle shear failure modes in joints, are of particular interest. In the second stage of the project, strengthening measures that incorporate post-installed anchors for connection to the existing structure will be assessed.

Paper P23: [Read]

Uni and Bi-directional Quasi Static Tests on Alternative Hybrid Precast Beam Column Joint Subassemblies

Alejandizo Amaris, Stefano Pampanin and Allesandro Palermo

Recent developments on high performance seismic resisting precast concrete frame systems, based on the use of unbonded post-tensioned tendons with self-centring capabilities in combination with additional sources of energy dissipation, are herein presented. Alternative arrangements for jointed ductile connections to accommodate different structural or architectural needs have been implemented and validated through quasi-static cyclic tests on a series of 2/3 scaled beam-column subassemblies under uni- or bi-directional loading regime. The satisfactory results confirmed the unique flexibility and potentiality of the proposed solutions for the development of the next generation of seismic resisting buildings.

Paper P24: [Read]

Accounting for the Effects on Residual Deformations Due to Torsional Response

Didier Pettinga, Nigel Priestley, Stefano Pampanin and Constantin Christopoulos

Recent developments in performance-based seismic design and assessment approaches have emphasised the importance of properly assessing and limiting the residual (permanent) deformations typically sustained by a structure after a seismic event, even when designed according to current code provisions.

In this contribution, the performance-based design framework for residual deformations, previously developed by the authors for 2-D regular structures, is further extended to the behaviour of 3-D irregular (asymmetric in-plan) buildings. The seismic response of a set single storey systems, comprising of seismic resisting frames, and made of alternative materials (concrete or steel), is investigated under uni-directional earthquake loading excitations. Different layouts in plan, leading to either torsionally unrestrained or restrained systems, are considered.

Sensitivity analyses are carried out in order to identify the influence of varying levels of torsional restraint on the residual deformations/displacements in the response of a 3-D irregular building, the irregularity being given by an imposed mass eccentricity.

Paper P25: [Read]