A blast retrofit technique for concrete structures using carbon fiber-reinforced polymer (CFRP) layers was investigated for use in large infrastructure systems with the overarching goal of preventing against major loss of life and considerable damage that would require extensive repair. Large-scale experiments were conducted and the retrofit behavior was investigated for application on relatively large reinforced concrete walls subjected to blast-like loadings. The experimental program utilized the University of California San Diego (UCSD) Blast Simulator. The Blast Simulator is able to induce various blast-like shock waves to the test specimen in a controlled laboratory environment. The performance of this blast retrofit was tested and then analyzed using SDOF and finite element modeling methods. A finite element model was created using LS-DYNA and utilized contact algorithms for the CFRP-concrete interface. Results and comparisons between the two analysis methods are given. Keywords: blast, CFRP, finite element, reinforced concrete, SDOF. INTRODUCTIONFiber-reinforced polymer (FRP) laminates have been shown in many studies to effectively retrofit and repair reinforced concrete structural elements [1][2][3][4][5]. The use of FRP as a retrofit is popular as it can be installed post-construction to strengthen the structure. It allows for fast installation, and has a very high stiffness and tensile strength [6,7]. Often times anchorage systems are used to mechanically restrain the FRP and to prevent delamination between the FRP and concrete, and in order to try and achieve the full tensile capacity of the FRP. Many tests have been conducted and the results are mixed and inconclusive [8][9][10].The performance of anchorage systems in retrofits is extremely important, as failure modes of the FRP are not tensile failures, but failures due to local stress concentrations by the anchors and delamination of the FRP to the concrete [1,[11][12][13][14]. These failures are much more sudden and less ductile than a tensile strength failure of the FRP, which emphasizes the need to achieve an anchoring system that allows the FRP to achieve full tensile failure.

The ongoing presence and persistence of terrorist groups is a perpetual threat that 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 blast resistance. There have been few studies, however, on the anchorage behavior in large-scale RC systems retrofitted with FRP subjected to blast. To bridge this gap, two different mechanical anchorage techniques for concrete structures using carbon fiber-reinforced polymer (CFRP) layers were subjected to explosive loading to investigate system behavior with the different mechanical anchorage retrofits: a steel strap retrofit system and smaller steel plate retrofit system. The experimental program utilized a hemisphere C4 charge and tested the retrofit with scaled distances of 1.42 m/kg 1/3 and 1.09 m/kg 1/3. The performance of the two blast retrofits were evaluated and compared in terms of the displacements of the slab systems and associated failure modes.