DIC-based failure analysis of high-strength continuous steel shear dowels for composite UHPFRC steel construction

Abstract

Continuous composite dowel strips in reinforced concrete composite members allow effective force transmission of shear forces between steel web and concrete. The use of high-performance materials imposes new demands on the performance of such fasteners in terms of their load-bearing capacity and deformation capability. In order to study the behavior of puzzle and clothoid-shaped composite dowels made from S460ML high-strength steel in combination with Ultra High Performance Fiber Reinforced Concrete (UHPFRC), an experimental campaign was conducted. For this purpose, a simplified push-out test setup was developed and a number of 25 specimens were tested. The degree of the conventional reinforcement, the volume percentage of fiber reinforcement, the concrete cover and the shape and thickness of the composite dowels were varied. The test specimens were monitored with a high-resolution Digital Image Correlation (DIC) system in addition to conventional measuring techniques such as LVDTs and strain gauges. These optical measurements and their visualization gave new insights into the three dominant failure modes – i.e. concrete pry-out, vertical splitting, and steel shear-bending – and allowed to identify combined failure modes in detail. With an appropriate configuration, a semi-ductile behavior of shear dowels with high-performance steel and UHPFRC was generally reached. The additional use of adequate reinforcing bars, such as stirrups and transversal bars, was crucial to finally achieve full ductility. Based on the test results, recommendations were provided for the design of thin UHPFRC plates in combination with puzzle- and clothoid-shaped composite dowels. Depending on the configuration, yielding due to steel shear-bending occurred between 60 and 90% of the average maximum load, thus demonstrating full utilization of the composite dowels. The experimental study provided valuable insights into the load-bearing behavior of composite dowels in combination with thin UHPFRC panels and complements the state-of-the-art for the use of this connection technique.