Reza is an Associate Professor at Chalmers University of Technology, Department of Architecture and Civil Engineering. His field of research covers infrastructural application of fiber reinforced polymer materials.
Strengthening, repair and retrofit of existing bridges using adhesively bonded fibre reinforced p... more Strengthening, repair and retrofit of existing bridges using adhesively bonded fibre reinforced polymers (FRP) composites have attracted a great deal of attention over the past four decades. Despite numerous studies that have been conducted to evaluate the short-term behaviour of FRPs bonded to steel members, the subject of durability is by far less researched. To date, concerns about the long-term performance presents a major obstacle to the widespread application of FRPs in steel bridges. The aim of this work is to identify the most damaging environmental factors and to experimentally investigate the effects of them on mechanical behaviour of Carbon-FRP/steel joints. In this regards, after a review of the literature, both bulk material and bonded specimens were exposed to a number of aging scenarios and tested. The results indicate the deleterious effects of de-icing salts on joint strength by degrading the interlaminar shear strength of FRPs.
Proceedings of the Institution of Civil Engineers, Dec 1, 2015
In the past two decades, fibre-reinforced polymer (FRP) bridge decks have attracted a great deal ... more In the past two decades, fibre-reinforced polymer (FRP) bridge decks have attracted a great deal of attention for applications in the refurbishment of existing bridges and for the construction of new bridges. FRP decks are lighter, more corrosion resistant and easier to install than conventional concrete decks. A considerable amount of research effort has been devoted to FRP decks and numerous bridges have been rehabilitated or constructed using these decks. This paper presents a review of the structural and field performance of FRP decks. The latest research and current practices have been synthesised, and several experts and practitioners have been consulted. Aspects related to the structural behaviour of steel bridges with FRP decks, including fatigue performance, composite action between the deck and underlying girders, the performance of various connections as well as observed failure modes are reviewed and summarised. This paper concludes by identifying areas for further research.
Using bonded fiber reinforced polymer (FRP) laminates for strengthening and repair of structural ... more Using bonded fiber reinforced polymer (FRP) laminates for strengthening and repair of structural members has been proven to be an effective and economic method. High strength and stiffness, light weight and good fatigue and durability properties of FRP composites together with advantages offered by adhesive bonding have made FRP bonding a suitable alternative for traditional strengthening and repair techniques. It has also been recognized that pre-stressing the FRP laminates prior to bonding would bring additional advantages such as reduced crack widths, postponing the yielding in tensile reinforcement, increasing the load bearing capacity and saving reinforcement material. Using pre-stressed laminates, however, is associated with very high interfacial stresses in the bond line at the laminate ends, which necessitates the use of mechanical anchors. This paper presents a new method and a device for applying pre-stressed FRP laminates to flexural structural members without the need for mechanical anchorage of the laminates.
This chapter explains some behavioural aspects of adhesive joints used to bond fibre-reinforced p... more This chapter explains some behavioural aspects of adhesive joints used to bond fibre-reinforced polymer (FRP) composites to steel substrates using the finite element method. The chapter aims to give the reader an overview of conventional stress/strain analysis techniques including analytical and numerical analyses as well as the applications, advantages and drawbacks of each technique.
Abstract This paper presents an innovative method of prestressing carbon fibre reinforced polymer... more Abstract This paper presents an innovative method of prestressing carbon fibre reinforced polymer (CFRP) plates used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. The proposed method aims to achieve self-anchorage of the prestressed CFRP plate and thus eliminate the need for conventional mechanical anchorage at its ends. Experimental tests of RC beams in four-point bending were conducted to investigate the strengthening efficiency of the self-anchored prestressed CFRP plate. The experimental results showed that using the self-anchored prestressed CFRP significantly improved the flexural performance of the strengthened beam in terms of bending stiffness, crack widths, and load-carrying capacity. The utilisation ratio of the prestressed CFRP plate reached 81% at its debonding. Numerical analyses using nonlinear finite element (FE) method were conducted to model the tested specimens. Based on the reliable simulation of flexural cracks and crack-induced CFRP debonding, parametric studies were conducted using FE analyses, in order to investigate the effect of prestressing levels and the CFRP plate’s stiffness on the flexural behaviour. Recommendations were then made for selecting a proper prestressing level and the mechanical properties of CFRP plates.
Concerns regarding the durability of adhesively-bonded fibre-reinforced-polymer (FRP)/steel joint... more Concerns regarding the durability of adhesively-bonded fibre-reinforced-polymer (FRP)/steel joints in bridges have been a major obstacle to their growing application. On the one hand, the available long-term data of FRPs used in bridges is rare and, on the other hand, the existing assessment approaches have mainly been developed to address the needs of industries, such as the aviation sector, with distinct differences. This paper uses both experimental and numerical approaches to investigate the effects of moisture, as one of the most influential factors, on the long-term performance of FRP/steel joints used in bridges. Gravimetric measurements are used to characterise the 3D moisture-diffusion properties for different FRPs and an adhesive material in various ageing conditions. Fast curing of the adhesive was found to have no significant effect on the diffusion properties of fully cured epoxy specimens. Salt water was found to degrade the mechanical properties of adhesive to a lesser degree than distilled water. The tested double-lap-shear joints of FRP/steel showed ca. 5% strength gain after eight months and ca. 9% reduction in the failure load after 12 months of ageing. While the elastic modulus of adhesive was found to decrease significantly with increasing moisture content, the stiffness reduction was found to be trivial in the joint-level. The results of coupled diffusion-mechanical finite element analyses indicate the importance of adherend permeability on moisture ingression into the joints. Moreover, the presence of small amounts of moisture at the steel/adhesive interface for less than a critical period is found to increase the joint strength. However, prolonged exposure to the same moisture content degrades the strength of the joint, and is, thus, time dependent.
As the use of fibre reinforced polymer materials in bridge construction is becoming more popular,... more As the use of fibre reinforced polymer materials in bridge construction is becoming more popular, appropriate joining techniques, particularly for field joints, are necessary. Bolted joints are a common method for joining fibre reinforced polymer structures. The main advantage of bolted joints is their detachability, but they have a number of shortcomings. On the one hand, hole clearances, which are needed to facilitate on-site assembly, reduce the stiffness and joint efficiency. On the other hand, it is not possible to rely on the beneficial effects of bolt pre-defined tension loads, i.e. load transfer in friction, due to the considerable losses of bolt tension caused by the creep deformation in the composite material. To tackle these problems, a solution utilising metallic inserts in the hole is proposed in this paper. A series of experimental tests have been conducted to investigate the effect of inserts on the bolt-tension relaxation, the stiffness and the load-bearing behaviour of joints. Finite element analyses were also employed. The study demonstrates several benefits of the inserts: the bolt tension relaxation is minimised, the load transfer by friction may be feasible to be utilised in the bridge service state and the joint efficiency is increased in terms of stiffness and strength.
Strengthening, repair and retrofit of existing bridges using adhesively bonded fibre reinforced p... more Strengthening, repair and retrofit of existing bridges using adhesively bonded fibre reinforced polymers (FRP) composites have attracted a great deal of attention over the past four decades. Despite numerous studies that have been conducted to evaluate the short-term behaviour of FRPs bonded to steel members, the subject of durability is by far less researched. To date, concerns about the long-term performance presents a major obstacle to the widespread application of FRPs in steel bridges. The aim of this work is to identify the most damaging environmental factors and to experimentally investigate the effects of them on mechanical behaviour of Carbon-FRP/steel joints. In this regards, after a review of the literature, both bulk material and bonded specimens were exposed to a number of aging scenarios and tested. The results indicate the deleterious effects of de-icing salts on joint strength by degrading the interlaminar shear strength of FRPs.
Proceedings of the Institution of Civil Engineers, Dec 1, 2015
In the past two decades, fibre-reinforced polymer (FRP) bridge decks have attracted a great deal ... more In the past two decades, fibre-reinforced polymer (FRP) bridge decks have attracted a great deal of attention for applications in the refurbishment of existing bridges and for the construction of new bridges. FRP decks are lighter, more corrosion resistant and easier to install than conventional concrete decks. A considerable amount of research effort has been devoted to FRP decks and numerous bridges have been rehabilitated or constructed using these decks. This paper presents a review of the structural and field performance of FRP decks. The latest research and current practices have been synthesised, and several experts and practitioners have been consulted. Aspects related to the structural behaviour of steel bridges with FRP decks, including fatigue performance, composite action between the deck and underlying girders, the performance of various connections as well as observed failure modes are reviewed and summarised. This paper concludes by identifying areas for further research.
Using bonded fiber reinforced polymer (FRP) laminates for strengthening and repair of structural ... more Using bonded fiber reinforced polymer (FRP) laminates for strengthening and repair of structural members has been proven to be an effective and economic method. High strength and stiffness, light weight and good fatigue and durability properties of FRP composites together with advantages offered by adhesive bonding have made FRP bonding a suitable alternative for traditional strengthening and repair techniques. It has also been recognized that pre-stressing the FRP laminates prior to bonding would bring additional advantages such as reduced crack widths, postponing the yielding in tensile reinforcement, increasing the load bearing capacity and saving reinforcement material. Using pre-stressed laminates, however, is associated with very high interfacial stresses in the bond line at the laminate ends, which necessitates the use of mechanical anchors. This paper presents a new method and a device for applying pre-stressed FRP laminates to flexural structural members without the need for mechanical anchorage of the laminates.
This chapter explains some behavioural aspects of adhesive joints used to bond fibre-reinforced p... more This chapter explains some behavioural aspects of adhesive joints used to bond fibre-reinforced polymer (FRP) composites to steel substrates using the finite element method. The chapter aims to give the reader an overview of conventional stress/strain analysis techniques including analytical and numerical analyses as well as the applications, advantages and drawbacks of each technique.
Abstract This paper presents an innovative method of prestressing carbon fibre reinforced polymer... more Abstract This paper presents an innovative method of prestressing carbon fibre reinforced polymer (CFRP) plates used as externally bonded reinforcement for flexural strengthening of reinforced concrete (RC) beams. The proposed method aims to achieve self-anchorage of the prestressed CFRP plate and thus eliminate the need for conventional mechanical anchorage at its ends. Experimental tests of RC beams in four-point bending were conducted to investigate the strengthening efficiency of the self-anchored prestressed CFRP plate. The experimental results showed that using the self-anchored prestressed CFRP significantly improved the flexural performance of the strengthened beam in terms of bending stiffness, crack widths, and load-carrying capacity. The utilisation ratio of the prestressed CFRP plate reached 81% at its debonding. Numerical analyses using nonlinear finite element (FE) method were conducted to model the tested specimens. Based on the reliable simulation of flexural cracks and crack-induced CFRP debonding, parametric studies were conducted using FE analyses, in order to investigate the effect of prestressing levels and the CFRP plate’s stiffness on the flexural behaviour. Recommendations were then made for selecting a proper prestressing level and the mechanical properties of CFRP plates.
Concerns regarding the durability of adhesively-bonded fibre-reinforced-polymer (FRP)/steel joint... more Concerns regarding the durability of adhesively-bonded fibre-reinforced-polymer (FRP)/steel joints in bridges have been a major obstacle to their growing application. On the one hand, the available long-term data of FRPs used in bridges is rare and, on the other hand, the existing assessment approaches have mainly been developed to address the needs of industries, such as the aviation sector, with distinct differences. This paper uses both experimental and numerical approaches to investigate the effects of moisture, as one of the most influential factors, on the long-term performance of FRP/steel joints used in bridges. Gravimetric measurements are used to characterise the 3D moisture-diffusion properties for different FRPs and an adhesive material in various ageing conditions. Fast curing of the adhesive was found to have no significant effect on the diffusion properties of fully cured epoxy specimens. Salt water was found to degrade the mechanical properties of adhesive to a lesser degree than distilled water. The tested double-lap-shear joints of FRP/steel showed ca. 5% strength gain after eight months and ca. 9% reduction in the failure load after 12 months of ageing. While the elastic modulus of adhesive was found to decrease significantly with increasing moisture content, the stiffness reduction was found to be trivial in the joint-level. The results of coupled diffusion-mechanical finite element analyses indicate the importance of adherend permeability on moisture ingression into the joints. Moreover, the presence of small amounts of moisture at the steel/adhesive interface for less than a critical period is found to increase the joint strength. However, prolonged exposure to the same moisture content degrades the strength of the joint, and is, thus, time dependent.
As the use of fibre reinforced polymer materials in bridge construction is becoming more popular,... more As the use of fibre reinforced polymer materials in bridge construction is becoming more popular, appropriate joining techniques, particularly for field joints, are necessary. Bolted joints are a common method for joining fibre reinforced polymer structures. The main advantage of bolted joints is their detachability, but they have a number of shortcomings. On the one hand, hole clearances, which are needed to facilitate on-site assembly, reduce the stiffness and joint efficiency. On the other hand, it is not possible to rely on the beneficial effects of bolt pre-defined tension loads, i.e. load transfer in friction, due to the considerable losses of bolt tension caused by the creep deformation in the composite material. To tackle these problems, a solution utilising metallic inserts in the hole is proposed in this paper. A series of experimental tests have been conducted to investigate the effect of inserts on the bolt-tension relaxation, the stiffness and the load-bearing behaviour of joints. Finite element analyses were also employed. The study demonstrates several benefits of the inserts: the bolt tension relaxation is minimised, the load transfer by friction may be feasible to be utilised in the bridge service state and the joint efficiency is increased in terms of stiffness and strength.
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Papers by Reza Haghani