Robin Kalfat

Anchorage Devices Used to Improve the Performance of Reinforced Concrete Beams Retrofitted with FRP Composites: State-of-the-Art Review

The anchorage of fiber-reinforced polymer (FRP) composites when applied to reinforced concrete (RC) structures as externally bonded reinforcement is an effective means to achieve higher levels of fiber utilization prior to premature debonding failure. Commonly documented anchorage methods for FRP-to-concrete applications demonstrating encouraging results include FRP U-jackets, FRP anchors (also known as spike anchors, among other names), patch anchors (utilizing unidirectional and bidirectional fabrics), nailed metal plates (also known as hybrid bonding), near-surface mounted rods, mechanical fastening, concrete embedment, and mechanical substrate strengthening. Anchorages applied to FRP systems have been verified through experimental testing and numerical modeling to increase the ductility, deformability, and strength of the member and also prevent, delay, or shift the critical mode of FRP debonding failure. Although the benefits of anchorage solutions have now been widely acknowledged by researchers, further studies are required in order to establish reliable design formulations to negate the requirement for ongoing laboratory verification by industry. The present paper is a state-of-the-art review of experimental studies conducted in the area of FRP anchorage systems applied to FRP-strengthened RC flexural members. Available experimental data are compiled and catalogued and an anchorage efficiency factor for each anchorage type under investigation is assigned in order to quantify the anchor’s efficiency. Finally, current shortcomings in knowledge are identified, in addition to areas needing further investigation.

Development and validation of multi-axis substructure testing system for full-scale experiments

Abstract Structural engineers are engaged in the development, design, construction and maintenance of new generation smart structures that are capable of withstanding multiple catastrophic events such as earthquakes, fire and tsunamis. Accordingly, the prediction of structural performance from initial linear-elastic behaviour to collapse is essential to assess the effectiveness of new design methods and the implementation of new retrofitting strategies. Although there has been much advancement in numerical methods, experimental observations remain critical for better understanding and predicting a structure’s response. The Multi-Axis Substructure Testing (MAST) system has been developed to expand the capabilities of experimental testing for three-dimensional simulation of extreme loads on critical components of large and complex structural systems. The MAST system uses eight high-capacity hydraulic actuators and a sophisticated 6-DOF mixed-mode control system that enables simultaneous application of multi-directional continuously varying states of deformation or load to structural components. An overview of the MAST facility and its components, the actuator assemblies and the details of 6-DOF control system are presented in this paper. Three experiments including quasi-static cyclic, local and distributed hybrid simulation tests were conducted on a seismically excited concrete structure to validate the performance of the MAST system in mixed-mode control by imposing simultaneously the axial load in force control and lateral deformations in displacement control.

The West Gate Bridge: Strengthening of a 20th Century Bridge for 21st Century Loading

Synopsis: Retrofitting of existing concrete structures and civil infrastructure has become necessary due to environmental degradation, changes in usage and heavier loading conditions. The use of advanced carbon fiber composite materials (CFRP) as externally bonded reinforcement has found wide application in recent years and has proven to be an effective method of improving the structural performance of existing structures. A good example of this is the West Gate Bridge in Melbourne, Australia for which the following case study is presented. Key innovations in CFRP technology developed specifically for this project have been described in the areas of design and testing of CFRP anchorage technology, involving the utilization of unidirectional and bidirectional fabrics together with mechanical substrate strengthening. These have all resulted in increases in material utilizations and enabled successful transfer of combined shear and torsional forces. Key aspects of the detailing, application, quality control and monitoring program adopted in the project are also presented along with the key aspects which resulted in the successful execution of this world class project.

Numerical and Experimental Validation of FRP Patch Anchors Used to Improve the Performance of FRP Laminates Bonded to Concrete

AbstractNumerical simulations using the nonlinear finite-element method (FEM) have been successfully used to predict the full nonlinear response of reinforced concrete (RC) members strengthened with fiber-reinforced polymers (FRPs). Calibrated numerical models have the potential to reduce the number of experimental tests through the use of parametric studies that can provide further data on the influence of key parameters. A relatively new area of research is the use of FRP anchorage systems to improve the efficiency of FRP-strengthened members by preventing the various modes of deboning failure. Although FRP anchorage systems have shown exceptional potential for widespread use, further experimental and numerical data are required before establishing theoretical models and design guidelines. The focus of the present work is to develop and validate an FE modeling approach to expand the available data on FRP-to-concrete joints anchored using unidirectional and bidirectional fiber patch anchorages. The criti...

Application of the MAST System for Collapse Experiments

This chapter presents the results of a range of experiments, including switched/mixed load/deformation mode quasi-static cyclic and hybrid simulation tests to highlight the unique and powerful capabilities of the MAST system, specifically for the assessment and mitigation of the collapse risk of structures.

Response of Earthquake-Damaged RC Columns Repaired with CFRP Composites Using Hybrid Simulation

International experience from the effects of past earthquakes on the existing reinforced-concrete (RC) structures with limited-ductility has shown that many behave poorly and some possess very low levels of safety, to the extent that they are at risk of collapse. While the seriously damaged RC frames may be demolished and reconstructed, a large number of earthquake-damaged RC frames can be repaired and operative again. The primary objective of this paper is to evaluate the capability of carbon-fibre reinforced polymer (CFRP) repair on rehabilitating the earthquake-damaged columns to their initial collapse resistance capacity. A state-of-the-art hybrid testing facility, referred to as the Multi-Axis Substructure Testing (MAST) system, was used to simulate complex time-varying six-degrees-of-freedom (6-DOF) boundary effects on the physical specimens using mixed load/deformation modes. Based on the experimental results, a comparative collapse risk assessment of the column before and after repair was conducted, which illustrates the effectiveness of using CFRP-repair to restore and improve the collapse resistance of earthquake-damaged RC structures.

Strengthening of slab–column connections against punching shear using FRP materials: state-of-the-art review

Abstract Many existing concrete slabs require strengthening in punching shear due to increased loading, change in use, design defect and structural damage. Of the different retrofitting techniques, the use of fibre reinforced polymer (FRP) reinforcements has proven to be an effective way to increase the punching shear capacity and ductility of flat slabs. There are many techniques for strengthening with FRP so in order to select and design an appropriate method, the most common documented methods should be known. A comprehensive literature review of the different FRP-strengthening methods for flat slabs against punching shear is presented in this paper. Each technique is discussed in terms of its results, advantages and disadvantages.

Experimental study on crack propagation of CFRP-strengthened RC beams subjected to torsion

ABSTRACT This paper presents an experimental study into the torsional behaviour and crack propagation of 28 reinforced concrete (RC) beams comprising of 6 unstrengthened beams and 22 beams strengthened using near surface-mounted (NSM) carbon-fibre-reinforced polymers (CFRP). The strengthened beams were designed to capture the influence of: FRP spacing, full wrapping vs U-jacketing and the use of discontinuous CFRP laminates vs continuous FRP sheets within the grooves. A photogrammetry technique was 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 aim of this study was to measure the torsional crack width propagation for each beam. The torsional deformations of the beams were evaluated and verified using photogrammetry measurements and the differences in the width of the large torsional cracks across the tested beams were examined. It was observed that the width of the torsional cracks for the strengthened beams was smaller than that of the control beams under the same load. In addition, the results also indicate that the crack widths of the beams using mortar as the FRP bonding agent showed clear differences from the beams strengthened using epoxy bonding.

State-of-the-Art System for Hybrid Simulation at Swinburne

This chapter describes the different components of the state-of-the-art system for hybrid simulation at Swinburne, including the design details of the MAST facility, the reaction systems including the strong wall/floor and the cruciform crosshead, servo-hydraulic actuators and the 6-DOF controller system, and hybrid simulation architecture.