Experimental testing and modeling strategies of carbon fiber-reinforced polymer blast retrofits using steel anchorage systems
Pezzola, Genevieve Louise Foster
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The ongoing presence and persistence of terrorist groups continually threaten the United States of America and its allies. This perpetual threat emphasizes the urgency to strengthen and retrofit any structural vulnerabilities, especially vulnerabilities that when exploited could lead to catastrophic damage of expensive infrastructure or loss of life. To avoid these losses, the application of fiber-reinforced polymer (FRP) laminates as a retrofit on reinforced concrete (RC) structural elements has been proven to increase the flexural strength of beams, columns, and slabs, as well as the blast resistance. FRP has been the subject of many studies due to its high strength, stiffness to weight ratio, and ease of installation. In these studies, it is often seen that the retrofit fails prematurely before rupturing in tension and reaching its full tensile strength. The premature failure most often observed is a debonding failure of the FRP from the concrete, but this failure rarely occurs in the adhesion layer. Anchorage devices can be utilized to improve the performance of the FRP retrofit. Several studies have been conducted to observe the performance of mechanical anchors, but there is limited research on mechanical anchorage systems. As a part of this research effort, two test series were conducted to investigate RC slabs retrofitted with FRP and two different mechanical anchorage systems. One mechanical anchorage system used 17 small steel plates dispersed throughout the specimen and the other mechanical anchorage system consisted of three long steel straps placed at the mid-height and quarter points of the specimen that spanned the width of the specimen. The first test series utilized live explosives and investigated both anchorage systems. The second test series was conducted with four non-explosive blast generators and investigated the steel strap anchorage system further. The research concluded that the failure modes between the two different testing methods were very similar. Finite element analyses and SDOF methods using current approaches were developed. The results of the two test series emphasized gaps in the literature about RC slabs retrofitted with FRP and mechanical anchors, which motivated the objectives of this dissertation. The first objective was to characterize the governing phenomena of the performance and failure of mechanical anchorage systems applied to FRP retrofits on RC slabs which was done by performing a spall analysis and timeline analysis of each slab tested. The second objective was to develop an analytical model that predicts RC slab behavior retrofitted with FRP and includes the presence of anchors and dynamic loading. A new analytical tool was developed that incorporates anchors and the phenomena of the failure modes observed in the test series. The third objective was to provide design recommendations for specific RC slab FRP retrofits depending on the desired level of protection. Design recommendations were developed using the new analytical tool for a variety of blast scenarios and slab dimensions. The fourth objective was to validate the non-explosive blast generator as an appropriate means to test the response of RC slabs retrofitted with FRP subjected to blast loading. The blast generator was validated through computational analysis and a thorough comparison between the loading and behavior of the slabs in each test series.