Finite Element Modelling of Anchorage to Concrete Systems at Different Strain Rates

Abstract

Demand for flexibility in design and faster construction times has resulted in the increasing use of fasteners in a variety of concrete structures. These structures are exposed to static and dynamic loading conditions. Furthermore, these structures can be exposed to high strain rate loading such as encountered in impact and blast loads. Thus, anchorage systems used to fasten elements to concrete structures are also exposed to the high strain rates of loading which can be tensile and shear loads. If not adequately designed and constructed, anchorages can fail in a catastrophic manner and pose significant threat to building safety and the life of building occupants. Behaviour of anchors embedded into concrete and subjected to static load has been widely investigated experimentally. However, despite the fact that many structures that contain anchorage systems are exposed to dynamic loads, the research in this vital area is limited. Currently, no guidance is available in design codes for the anchorage response under high strain rate loading. The American Concrete Institute and Concrete Capacity Design methods are recommended for anchorage system subjected to static and low cycle dynamic loading only. Hence, there is a need to develop a design method to predict the anchorage response and capacity under impact and blast loading. The project presented in this thesis aims to investigate the tensile and shear behaviour of cast-in-place, adhesive and undercut anchors subjected to different strain rates using LS-DYNA software. Numerical models of the anchorage systems with different design parameters were developed and mesh sensitivity analyses were carried out to determine mesh sizes that best simulated the experimental results obtained from the literature. The ultimate static capacity results were verified with the design methods. Effect of strain rate, embedment depth, and anchor diameter on the tensile and shear failure loads was investigated. Failure modes for the anchorage systems were also examined at different strain rates. Concrete cone breakout diameter and failure cone angles were investigated. A relation between the ultimate loads and the strain rates was investigated and dynamic increase factors (DIF) for design were determined. Regression analysis was performed to predict a relation that accurately represents the finite element results.Results of the tensile and shear loading of the anchorage to concrete systems show that anchorage to concrete system capacity increases with an increase in the strain rates. The failure mode of the anchorage systems is influenced by the strain rate. Maximum DIFs of 1.74, 1.13and 1.58were obtained for the cast-in-place, adhesive and undercut anchors under tensile load respectivelywhere concrete cone breakout failure mode was observed. Maximum DIFs of 1.17, 1.13 and 1.44 respectively were obtained for the cast-in-place, adhesive and undercut anchors exhibited steel failure mode. The maximum DIFs were 1.15, 1.18 and 1.45respectively for the anchors subjected to shear loadwhere steel failure was observed.