Tracing Initiation and Propagation of Cracks in Composite Slabs

This paper presents test results obtained from studies aimed at determining whether the impact-echo method, a nondestructive test technique based on the use of transient stress waves, can be used to trace the initiation and propagation of cracks in composite slabs subjected to static loads. The number of shear studs in the specimens was designed to satisfy the requirement of the American Institute of Steel Construction Allowable Stress Design (ASD) specifications for full-composite and 80 partial-composite structures. To trace the initiation and propagation of cracks in the specimens, impact-echo tests were carried out at steps with different load levels. Throughout the test, the strains of shear studs were also measured to verify the results obtained from the impact-echo tests. It is shown that changes in the impact-echo responses are the key to detecting the formation of a crack in the composite slabs. The location of the crack can be determined by the impact-echo method. Results also show that the strains of shear studs start to have sharp increases after the applied load corresponding to the presence of cracks. Besides the conventional measurement devices, this study successfully introduces a newly developed nondestructive technique used for detecting cracks in concrete specimens to add valuable information to experimental results for better interpretation of structural failure mechanism.