Fiber-reinforced polymer (FRP) composite materials been widely used in civil engineering new construction and repair of structures due to their superior properties. FRP provides options and benefits not available using traditional materials. The promise of FRP materials lies in their high-strength, lightweight, noncorrosive, nonconducting, and nonmagnetic properties. ACI Committee 440 has published reports, guides, and specifications on the use of FRP materials for may reinforcement applications based on available test data, technical reports, and field applications. The aim of these document is to help practitioners implement FRP technology while providing testimony that design and construction with FRP materials systems is rapidly moving from emerging to mainstream technology.

This volume represents the thirteen in the symposium series and could not have been put together without the help, dedication, cooperation, and assistance of many volunteers and ACI staff members. First, we would like to thank the authors for meeting our various deadlines for submission, providing an opportunity for FRPRCS-13 to showcase the most current work possible at the symposium. Second, the International Scientific Steering Committee, consisting of many distinguished international researchers, including chairs of past FRPRCS symposia, many distinguished reviewers and members of the ACI Committee 440 who volunteered their time and carefully evaluated and thoroughly reviewed the technical papers, and whose input and advice have been a contributing factor to the success of this volume.

This paper investigates experimentally the effect of sand coating bond enhancer on the flexural behavior of circular concrete-filled FRP tube (CFFT) by testing two full-scale CFFT cantilevers under lateral cyclic load. The full-bond between concrete and any kind of reinforcement is one of the main factors affecting on its flexural behavior. Limited research has investigated the bond effect on CFFT flexural behavior. The bond between the concrete core and the interior surface of the FRP tube is the main parameter of this study. Embedded-concrete strain gauges were used to measure the strain values inside the concrete core, then compared with the strain values measured from the electric strain gauges installed on the tube outer surface. The observed experimental results illustrate that the sand coating increases the flexural strength and stiffness of circular CFFT members. No slippage was observed on the sand-coated specimen; while 6 mm (0.24 in) slippage was measured on the specimen without sand coating. The internal and external strain curves are identical for the sand-coated specimen; while these curves are incompatible for the specimen without sand coating. The experimental results demonstrate the significance of investigating the bond effect and the sand coating contribution to improve the bond between the concrete core and the FRP tube, and assure a good composite action under flexural loads.

Structural retrofitting of flat slabs is often required mainly due to corrosion of reinforcement, change of use and design errors. Punching shear failure is a common type of failure in flat slabs in the area of connection with the column, which could lead to progressive collapse. The slab-column connection is critical as it exposes to bending moments and significant shear stresses in RC flat slabs. Utilization of FRP attachment as strengthening method for concrete structures is becoming the most popular approach for improving their characteristics. CFRP laminates are already well established structural strengthening material and the further optimisation of their application in case of punching shear strengthening will allow for developing of effective solution for this problem. The research comprises testing of seven small scale reinforced concrete slabs (550x550x75 mm) (21.7x21.7x3 inch) with a column stud (80x80x75 mm) (3.1x3.1x3 inch) at the centre to simulate the slab-column connection. One control sample and six CFRP strengthened samples were prepared and tested against punching shear failure. The primary variable of the experiment was the positioning, layout and configuration of the CFRP laminates. The total width and thickness of the CFRP laminates were kept constant and the objective was to determine the most efficient layout. It was found out that using CFRP laminates as externally bonded reinforcement significantly enhances the punching shear capacity and results in improved stiffness of the slabs. The result shows a significant increase in ultimate load and stiffness.

Standard constitutive modeling of fiber-reinforced polymer composite laminates is typically based on uniaxial properties. The nonlinear in-plane shear behavior, of angle-ply laminates, is recognized long ago. This paper presents a model using test data generated from (±55o)ns symmetric angle-ply coupons to determine material response using an inverse mechanics approach. Nonlinear classical lamination theory is used to assemble the ply constitutive properties for global axial tensile response in terms of the secant shear modulus G12s values. The main objective of this study is to obtain the nonlinear in-plane shear stress-strain curves along the principal fiber-matrix direction. The resulting full-range material model is used to predict the response of (±55o)4s angle-ply FRP tubes used for stay in place form members manufactured by the filament winding process. The resulting analysis procedure accurately predicts the ultimate moment of the concrete filled tube and traces the deformation response reasonably well. In addition, the load-deflection analysis of the entire tube is performed and found to match well the experimental curve up to the limits of nonlinear material analysis when the large deformation of the tube is ignored.

In recent research, the use of the near-surface mounted (NSM) technique has been proven to increase the torsional strength of reinforced concrete (RC) members. In this paper, an investigation into the torsional deformation characteristics of the ten RC beams strengthened using the NSM technique is reported and evaluated using photogrammetry. The experimental results of two control beams and eight beams strengthened using CFRP laminate embedded into pre-cut grooves using epoxy and mortar are evaluated. The Digital Image Correlation Photogrammetry (DIC) is used to determine the three-dimensional displacement of targets placed on the north and south faces of the beams at selected load levels up to failure. The main aim of this study was to measure the propagation of torsional crack width with increasing torque for each beam. The torsional deformations of the beams are evaluated and verified with the photogrammetry measurements and the differences in the width of the large torsional cracks across the tested beams are highlighted and compared. The width of the torsional cracks for the strengthened beams was smaller than that that of the control beams at the same load level. Similar deformation mechanisms were observed for the strengthened and control beams.