IMPACT OF STRUCTURAL BEHAVIOUR ON CRACK ASSESSMENT DES BULL 1 & JOHN HARE 2 1 University of Canterbury & Holmes Consulting Group LP 2 Holmes Consulting Group LP ABSTRACT Assessment of damage to concrete structures became a major challenge for engineers after the earthquakes of the Canterbury series. The fundamental question: "is the building safe enough to re-occupy?" had to be addressed. Evaluation of the state of the buildings and the elements/members therein, tested the engineering understanding of expected performance of reinforced concrete elements. From observations and material testing, it was found that behaviours such as the distribution of flexure-shear cracking, and the extent and magnitude of accumulative strain in longitudinal bars of walls, beams and columns, did not match what has been seen in laboratory studies. Engineers need to determine if the damage, the "cracking" of the concrete, was significant in terms of: why has that cracking occurred; does that part of the member need to be repaired; should it be repaired; how to repair that part of the member, and how much more can that member take? This paper focuses on expected performance of concrete structures; what was observed and what has been found out about the actual performance of concrete, reinforcement and design details during these earthquakes and what are the implications for remaining capacity of these structures to deal with ongoing aftershocks or a large "design basis event" sometime in the future. These observations from the design fraternity have led to recommendations for possible changes to current design philosophies and to Standards such as NZS 3101: Concrete Structures. INTRODUCTION The significance of a crack for the performance of the building must be determined for the following reasons: • To know why the crack has occurred: Was the source of the crack from shrinkage, thermal shock, internal redistribution of loads due to creep or seismic overload? Determining what is the source of the cracking, or the contributing sources, will direct the designer to answer the flowing issues. • To know if the crack needs to be repaired Can the crack still sustain shear by aggregate interlock? Has the some of the plastic capacity of the bar, crossing a crack, been expended? If so, what is extent and magnitude of accumulated strain in longitudinal bars of walls, beams, and columns? Similar issues may arise regarding transverse reinforcement.
IMPACT OF STRUCTURAL BEHAVIOUR ON CRACK ASSESSMENT
May 19, 2023
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