Stephen J. Lawrence

Reliability-Based Calibration of the Capacity Reduction Factor for Design of Masonry in Compression to AS3700

Abstract The paper examines the reliability of masonry walls designed for compression in accordance with AS3700. The results of a large number of tests on full-scale masonry walls in compression have been used to obtain probabilistic models of behaviour. Structural reliability was then estimated for vertical loading of unreinforced masonry walls loaded concentrically, considering variations of unit compressive strength, mortar type, tributary area and live-to-dead load ratios. A reliability-based calibration of the Australian masonry design code AS3700 was then conducted using a target reliability index specified in AS5104. Recommendations are made for changes to ϕ used for compression design in AS3700 that, if adopted, would lead to an increase of 66% in the design compressive strength of walls.

Spatial Correlation of Material Properties and Structural Strength of Masonry in Horizontal Bending

AbstractSpatial variability of material properties might significantly affect the structural performance and reliability of unreinforced masonry (URM) walls. The paper develops a computational method to predict the strength for URM walls subject to one-way horizontal bending considering unit-to-unit spatial variability of the material properties of mortar joints and bricks. In this context, the term unit is being used to describe the location in the wall associated with a single brick and the adjacent mortar joints. In this way, the material properties are assumed to be uniform along the length, height, and thickness of individual bricks but may vary from brick to brick within the wall. Tensile strength, shear bond strength, and associated fracture energies of the mortar joints and tensile strength and fracture energy of the bricks are the main parameters considered herein. The authors examine how correlation and spatial variability in unit strengths (mortar joints and bricks) affect the variability of ul...

Moment Capacities of Unreinforced Masonry Sections in Bending

Abstract Current unreinforced masonry design relies on limited models of flexural behaviour in the orthogonal and inclined directions, which are partly empirical and do not fully account for the beneficial effects of compressive stress. This paper presents the results of a theoretical and experimental investigation to develop improved expressions for the horizontal and diagonal bending moment capacities contributing to the ultimate wall strength. The new expressions were verified against experimental data and were shown to give accurate predictions of the bending strength for 63 full-scale wall panels, including walls with openings, using the virtual work method of AS 3700.

Earthquake Design of Unreinforced Masonry Residential Buildings Up to 15 Metres in Height

Abstract The paper summarises the results of a displacement-based assessment (DBA) of the seismic capacity of typical load-bearing unreinforced masonry buildings between two and five storeys in height across a range of site sub-soil classes (B to D) and earthquake hazard factors (0.05 to 0.12), covering all of the capital cities and major regional centres in Australia. The study found that the DBA for out-of-plane bending of walls in the top storey of buildings identified far fewer cases of failure than did a traditional strength-based assessment. A similar trend was observed for the DBA for in-plane shear of walls at the ground storey of buildings. The DBA implied, for all practical purposes, that typical walls will have the in-plane shear displacement capacity to withstand the earthquake induced loads and displacements for any site soil conditions, and earthquake hazard factor up to 0.12. This contrasts with the corresponding strength-based calculations, which identified significant numbers of cases where failure would occur.

Earthquake Performance of Unreinforced Masonry Residential Buildings Designed to Australian Standards

Abstract This paper examines the earthquake resistance of unreinforced masonry residential structures up to 15 m in height, with a view to identifying the critical actions under a range of conditions. The study considers the wall forces and associated actions due to earthquake loads corresponding to the proposed revision of the Australian Standard for earthquake actions, AS 1170.4. The seismic demands under various conditions are compared with the corresponding seismic capacities given by the Australian Standard for masonry structures, AS 3700. A parametric study was used to examine the effects of a wide range of parameters, including number of storeys, wall geometries, support conditions and openings. The results of the parametric study indicate, for a typical office building and a typical home unit building, the range of conditions leading to earthquake failure using the current design criteria of AS 3700.