D. J. Heath

Damage Thresholds in Unreinforced Masonry

Abstract In various regions of Australia, mines and quarries employ blasting, which some home owners believe causes cracking of non-structural components such as brick veneer. The first part of this paper reports on properties affecting damage thresholds of masonry subjected to shear load at a localised unit/mortar scale using off-axis prism tests and triplet tests. The second part reports on the performance of a full-scale unreinforced masonry wall with a window penetration subjected to an increasing racking displacement. Drift and the associated strains required to initiate cracking are reported, and a correlation between drift and rate of crack propagation is proposed.

Acceleration-Displacement Response Spectrum Vibration Limits for Blast Vibrations

AbstractThis paper proposes a new method to limit vibrations from blasting to avoid damage to residential structures. The evolution of commonly adopted vibration limits and standards adopted for surface blasting operations in close proximity to residential areas is reviewed. The importance of human sensitivity to vibrations is highlighted and vibration limits preventing damage are demonstrated to be influenced by human annoyance. A robust and rational procedure is presented to replace existing vibration standards limiting vibration using the acceleration- displacement response spectrum methodology commonly adopted in earthquake engineering. The proposed approach adopts drift as a measure of damage rather than the current industry accepted measurement of ground velocity.

Dynamic performance of a brick veneer house with steel framing

Abstract Brick veneer construction is a very common form for residential structures in Australia and is growing in popularity in New Zealand. The structural frame is made from steel or timber, and non-structural brick walls are attached to the frame via brick ties. Under earthquake loading there is a complex interaction between the frame and veneer walls, particularly in the out- of-plane direction, where there is risk of brick wall collapse. While there is a standard component test method for assessing the seismic capacity of brick ties, this method has been developed around brick veneer on timber studs. In order to realistically assess the overall performance of brick veneer construction with steel framing, a full scale one-room test structure “Test House” was tested on a shaking table. The Test House incorporated veneer walls with different geometries. It was subjected to varying levels of the El-Centro earthquake ranging from moderate serviceability limit state ground motion to well beyond the design maximum considered earthquake for New Zealand. These levels of shaking were selected in order to ascertain the response for specific limit states to the New Zealand Loading Standard and to compare against minimum performance requirements. Comprehensive measurements on the frame and veneer walls were taken, including acceleration, drift and differential movements between the frame and veneer. The Test House performed very well, with no brick loss up to 2.6 times El-Centro earthquake, which is well in excess of all performance requirements. This paper presents a summary of the outcomes from the experimental test program.

Performance of high-strength concrete walls exposed to fire:

High-strength concrete is becoming very popular around the world due to its many advantages over normal-strength concrete. There are significant behavioural differences between high-strength concrete and normal-strength concrete, most notably the brittleness and sudden spalling under elevated temperatures, whereby pieces of hardened concrete explosively dislodge. Although all high-rise and even many medium-rise buildings have high-strength concrete walls, the spalling of high-strength concrete walls in fire has generally been ignored by the designers and the fire resistance of walls has been calculated using the rules specified for normal-strength concrete. Catastrophic failures could occur due to this ignorance of an important issue. Major design codes including the American and Australian Codes do not cover spalling adequately. Even the Eurocode rules are based on limited research. After a brief discussion on the present design practice, this article presents a summary of spalling research. The relevant results from a comprehensive study conducted at the University of Melbourne are briefly discussed. The authors are not aware of any other comprehensive research projects covering the fire behaviour of normal-strength concrete and high-strength concrete walls exposed not only to standard fires but also hydrocarbon fires. The results showed that spalling in high-strength concrete is more significant when subjected to hydrocarbon fire compared to normal-strength concrete. The level of compressive load on the panels was also found to have a significant effect on the fire performance of the high-strength concrete panels. The finite analysis element program, ANSYS, was used to model the concrete walls subjected to load and fire (both ISO834 Standard fire and hydrocarbon fire). The test results were used to validate the computer model.

Design of cast-in headed and hooked fasteners

Abstract Cast-in fastenings for use in concrete are widely used in Australia. While design guidelines for headed fasteners are currently in place in Europe and the US, guidance on the design of hold-down bolts and hooked bolts (J- and L- bolts) is currently only available in the US. These types of fastenings to concrete are frequently used in safety-critical applications whereby failure may have serious consequences including risk to human life and significant economic consequences. In Australia, there are currently no design guidelines for these types of fastenings. Poor design procedures and lack of understanding of performance limitation of these fastenings have resulted in failures of base structures around the country. This paper presents design guidelines for cast-in fastenings to concrete including headed fasteners and hooked bolts that have been endorsed by the Australian Engineered Fasteners and Anchors Council (AEFAC). These design guidelines provide design engineers with greater confidence that the product will perform as required throughout its service life. Included in this paper are general design considerations to deliver best practice solutions.

Blast Vibration and Environmental Loads Acting on Residential Structures: State-of-the-Art Review

AbstractThis paper provides a unique literature review of cracking defects developing in low-rise residential structures as a result of deformation caused by environmental loads and low-level blast...

Shaking table study of a brick veneer house subjected to blast vibrations

This article reports on a unique shaking table test examining the performance of a single-room house to simulated blast vibrations. The unreinforced masonry veneer specimen that is constructed to represent typical Australian residential construction is subjected to a total of 564 blast vibrations increasing in peak component velocity from 1 to 383 mm/s. Damage thresholds in the masonry veneer are examined along with the damage–drift relationship with reference to standardised damage categories provided in Australian Standard 2870. Importantly, drifts recorded in the veneer at recommended vibration limits are found to be well below the lowest drifts needed to cause damage. The lowest threshold of damage in the masonry veneer occurred at a drift equal to 0.10% (1/960) at a peak component velocity of 148 mm/s, nearly 30 times the recommended environmental limit, demonstrating that current environmental limits are conservative with respect to damage potential for residential structures in good condition.