Comparative study of failure mechanisms in steel and concrete members strengthened with CFRP composites

Over the last decade advanced composite materials, like carbon fibre reinforced polymer (CFRP), have increasingly been used in civil engineering infrastructure. The benefits of advanced composites are rapidly becoming evident. This paper focuses on the comparative performance of steel and concrete members retrofitted by carbon fibre reinforced polymers. The objective of this work is a systematic assessment and evaluation of the performance of CFRP for both the concrete and steel members available in the technical literature. Existing empirical and analytical models were studied. Comparison is made with respect to failure mode, bond characteristics, fatigue behaviour, durability, corrosion, load carrying capacity and force transfer. It is concluded that empirical expressions for the concrete-CFRP composite are not readily suited for direct use in the steel-CFRP composite. This paper identifies some of the major issues that need further investigation

Introducing Australia’s first hybrid testing facility for performance-based assessment of structures

Hybrid simulation is a cost-effective cyber-physical testing technique, in which computational models and physical components are integrated at run-time. This method can be viewed as conventional finite element analysis, where physical models of some portions of the structure are embedded in the numerical model. In such a way, the errors related to the simplification of the theoretical modeling of complex nonlinear structures or subassemblies can be effectively mitigated as they are tested physically in the lab. This paper introduces Australia’s first hybrid testing facility, referred to as the Multi-Axis Substructure Testing (MAST) system, which is capable of simulating the complex three-dimensional time-varying boundary effects on large-scale structural components. The MAST system is unique in Australasia and is capable to serve the research community and practice, nationally and internationally. An application of the MAST system to investigate the performance of a CFRP-repaired limited-ductile RC column under sequential ground motions from linear-elastic response range through collapse is also presented

Flexural Behavior of RC Beams Strengthened by NSM-CFRP Laminates or Bars

The strengthening and enhancing the structures represents an important aspect in the construction industry due to the growing need to increase the tolerability of origin to a specific level and within the required rehabilitation and maintenance work. This paper assessed the performance and effectiveness of the Near Surface Mounted (NSM) strengthening technique for the reinforced concrete beams. Three (140x260x2700 mm) reinforced concrete beams were strengthened in flexure with NSM strengthening systems using Carbon Fiber Reinforced Polymer (CFRP) strips, bars, and cement-based adhesive as a binding materials. The flexural behaviour of the beams was evaluated by testing the specimens under three-point loading to failure. The structural performance, deflection, ductility, stiffness, and modes of failure of the tested beams are presented and discussed in this paper. The test results indicate that using NSM-CFRP strips and bars is practical and significantly improves the stiffness and increases the flexural capacity of reinforced concrete beams. The strength increments were 48, 42, and 15 percent recorded with CFRP bars, rough strips, and smooth strips respectively. The deflection of the strengthened beams was reduced by about 66, 48, and 58 percent for CFRP smooth strips, rough strips, and CFRP bars respectively, compared with the control beam due to the increased stiffness of the strengthened beams

Preface: fibre reinforcement in concrete structures

Preface to a special issue of the Australian Journal of Structural Engineering, which contains seven papers on the use of FRP composites in concrete and masonry structures

Strength assessment strategies and rehabilitation of bridges using advanced composite materials

Abstract not availabl

Use of FRP retrofitting systems and nanotechnology in civil infrastructure

Due to the significant level of investment that developed and developing countries have placed in their public and private infrastructure, and the aging of this infrastructure, rehabilitation and strengthening of existing concrete and steel structures have become a research focus. Traditionally, the repair and strengthening of concrete and steel structures have been via heavy steel plates mechanically connected to the structure. However, these repair techniques are usually cumbersome, requiring closing the facility for prolonged periods of time with a subsequent loss of production time, which can be costly. In the last 15 years, or so, with the advent of fibre reinforced plastics (FRPs), new strengthening approaches have come to the fore using external bonding technologies. This approach has shown significant advantages compared to traditional methods, mainly due to the outstanding mechanical properties of the composite materials, their light weight and the simple application to structural members. The use of lightweight fibre reinforced plastics and, in particular, CFRP as an alternative to steel plates have been investigated for repair and strengthening applications. Carbon fibre reinforced plastic repair techniques consist of gluing thin strips of CFRP plates or fabric to concrete members to add strength in flexure and/or shear. The lightweight nature of CFRP means easier and speedier repairs are possible with the advantage that the plant can remain in operation during the repair. This paper provides an overview of critical issues that relate to rehabilitation of civil infrastructure using fibre reinforced polymers. It also provides recent research findings on the use of nano materials to improve the bond performance and durability of the adhesives used in bonding CFRP to steel and concrete structures

Experimental and finite element analysis of a double strap joint between steel plates and normal modulus CFRP

Strengthening of steel structures using externally-bonded carbon fibre reinforced polymers ‘CFRP’ is a rapidly developing technique. This paper describes the behaviour of axially loaded flat steel plates strengthened using carbon fibre reinforced polymer sheets. Two steel plates were joined together with adhesive and followed by the application of carbon fibre sheet double strap joint with different bond lengths. The behaviour of the specimens was further investigated by using nonlinear finite element analysis to predict the failure modes and load capacity. In this study, bond failure is the dominant failure mode for normal modulus (240 GPa) CFRP bonding which closely matched the results of finite elements. The predicted ultimate loads from the FE analysis are found to be in good agreement with experimental values

Investigation into CFRP plate end anchorage utilising uni-directional fabric wrap

Carbon fibre reinforced polymers (CFRP) has become a very popular method of improving the capacity of structural elements. Failure of CFRP strengthening systems when applied to concrete structures is usually typified by de-lamination of the CFRP from the concrete substrate. Research has shown that anchoring the ends of the CFRP plates or sheets can result in a significantly higher load/stress being reached before de-bonding occurs and that when sufficiently anchored, the CFRP material strain at failure can approach its ultimate strain at rupture. The following is continuation of experimental studies into CFRP anchorage systems used to retrofit concrete structures. It follows from previous investigations conducted by the authors into the bond behaviour of a new anchorage system utilising a mechanically strengthened substrate. The paper presents two alternative anchorages; both utilising uni-directional fabric wrap oriented horizontally across and parallel to the direction of the laminate. Both forms of anchorage are found to be effective in increasing the CFRP to concrete bond strength by distributing contact stresses over a greater area of concrete

Effect of prestressed CFRP patches on crack growth of centre-notched steel plates

Carbon fibre reinforced polymers (CFRPs) are now accepted in the retrofit and repair industry as extremely efficient and capable of compensating for the loss of structural integrity, resistance and serviceability. Nevertheless, the application of these materials can be improved in various ways to meet structural requirements. One of the methods of improving the usage of CFRP sheets and laminates and benefiting from their full capacity is prestressing. The fatigue performance of steel plates retrofitted with CFRP patches was investigated in this research. The test samples included three main types: reference centre-notched steel plates (unrepaired), repaired centre-notched steel plates using CFRP patches and repaired centre-notched steel plates using prestressed CFRP patches. In the specimens in which prestressed CFRP patches were used, the patches consisted of 1 or 2 layers of CFRP sheets and were prestressed up to 25% or 50% of their ultimate capacity. All specimens were then tested under uniaxial tensile fatigue. In order to measure the crack propagation rate, the beach marking method was used. Two different double-block fatigue loads were studied: one causing a stress range of 135 MPa and the other with a stress range of 150 MPa relative to the gross section of the steel plate

Looking from the outside in (Research at Swinburne)

Swinburne's Prof John Wilson discusses the new glass-walled, street-level Strong Structures Lab, which provides a revolutionary space for researchers to test the strength of building materials