Riadh Al-Mahaidi

• Phd
• Professor (Full) at Swinburne University of Technology

In this investigation, the bond performance between CFRP and concrete in Near Surface Mounted (NSM) strengthening system using cementitious-based adhesive (CBA) was evaluated at different exposure temperatures. Two types of CBA were used (CBA-A and CBA-B) with and without magnetic water (MCBA-A and MCBA-B). Magnetic device with magnetic strength of...

Shear failure in reinforced concrete (RC) structures causes a sudden and brittle failure. Occasionally, strengthening of structural concrete elements is considered to avoid shear failure. In a few previous researches, shape memory alloy (SMA) material was introduced as a strengthening material for civil engineering applications. In this study, the...

Retrofitting of concrete structures has recently become a major issue worldwide due to design errors, earthquake damages and the deterioration by the exposure to the harsh environmental conditions, in addition to increase of loads carrying capacity of the structures. CFRP composites have been used efficiently to strengthening of concrete structures...

The study reported here aims to investigate the application of shape memory alloys (SMAs) in the form of strips for strengthening cracked reinforced concrete (RC) beams. The study proposes an innovative technique for prestressing RC beams by utilizing the shape recovery property of the alloy. Nine full-scale RC beams with a length of 3.75 m and a c...

Carbon fiber reinforced polymer (CFRP) composites can be considered as one of the main methods used in strengthening reinforced concrete (RC) members subjected to flexural actions. Using CRP composites in strengthened flat and curved RC members has shown many advantages compared to other method of strengthening. However, the efficiency of this meth...

The study aims to explore the application of concrete-filled steel tube (CFST) columns as a more resilient and sustainable alternative to vulnerable reinforced concrete (RC) columns in rigid-frame bridges prone to significant damage during strong earthquakes with large vertical ground motion intensities. A series of multi-axis hybrid simulations on...

Shear failure is a sudden and brittle failure, which causes human and economic losses. Hence, enhancement of shear capacity is critical for shear-deficient members of existing structures. In this study, the effectiveness of using Shape Memory Alloy ‘SMA’ strips on the shear capacity of reinforced concrete (RC) beams was investigated in a series of...

This paper presents a two-dimensional finite element (FE) modeling is utilized to simulate experimental testing of reinforced concrete (RC) beams externally strengthened with carbon fiber reinforced laminate (CFRP). Four models of concavely curved and flat soffit RC beams were developed. These beams were simulated to be simply supported and loaded...

Carbon fibre reinforced polymer (CFRP) composites can be used to strengthen reinforced concrete (RC) members subjected to flexural, shear or axial actions. One of the main disadvantages of using this type of strengthening is the premature debonding of the FRP plate from the surface of the concrete at strain levels lower than the rupture strain of t...

The behaviour of reinforced concrete (RC) member can be evaluated by employing a reasonably accurate constitutive relationship and element type in the finite element (FE) framework. Important components like columns, beams and shear wall in an RC structure can be analysed in the FE framework by using a plane-stress element. In general, RC members a...

This paper presents the experimental results from nine full-scale concrete-filled double-skin tubular (CFDST) beam-columns. The test specimens exploited two fabrication strategies, featuring either hollow steel inner skins with corrugated geometry or ultrahigh-strength steel corner tubes to enhance the seismic performance of noncompact CFDST beam-c...

Many of the existing tension stress-strain relations for concrete used in smeared shear models consider the contribution of concrete in tension even after steel yielding. Although the contribution of concrete in tension is less significant than its contribution in compression, the use of these existing models often leads to overestimating the shear...

One of the predominant failure modes of reinforced concrete (RC) members strengthened in flexure using fiber reinforced polymers (FRP) is intermediate crack induced (IC) debonding. This failure mode is usually brittle, premature and constitutes a significant underutilisation of the FRP material. To address this type of failure, design guidelines en...

The aim of this research is to investigate the efficiency of modified cementitious bonding material to sustain the loads on retrofitted concrete beams under high temperature exposure. The evaluation was based on the performance of CFRP reinforcement to sustain a considerable load over time and to maintain the corresponding service load at high temp...

Near-surface-mounted (NSM) carbon fiber-reinforced polymers (CFRPs) have emerged as a promising strengthening technique to improve the flexural performance of reinforced-concrete (RC) structures. Although these systems have been investigated extensively for flat soffit RC beams, their performance when applied to concavely curved soffit members requ...

In case of reinforced concrete (RC) beams strengthened by means of externally bonded FRP composites to enhance its flexural capacity, several premature failure modes can be detected, namely concrete cover separation (CCS), intermediate-span crack-induced (IC) de-bonding, or end-interfacial (EI) de-bonding. The mechanism of concrete cover separation...

In recent decades, several studies have considered the use of plastic waste as a partial substitute for aggregate in green concrete. Such concrete has been limited to non-structural applications due to its low strength. This raises whether such concrete can be enhanced for use in some structural applications. This paper reports an attempt to develo...

Punching shear strengthening of existing reinforced concrete (RC) flat slabs can be required due to increased loads or design/construction defect. One of the more effective punching shear strengthening solutions, which has shown promising results is the use of post-installed L-shaped carbon fibre-reinforced polymer (L-CFRP) laminates bonded into pr...

This study is a part of a full experimental program intended to contribute to the understanding of the structural behavior of masonry arches before and after being strengthened with FRP composite materials. The work involved constructing two sets of masonry arch models and loading them to failure by applying single-point loads at the quarter span....

Previous investigations have attributed some reinforced concrete (RC) bridge piers suffered significant damages during large earthquakes due to vertical ground motion effects. This has motivated this study to investigate the use of concrete-filled steel tube (CFST) columns as a more resilient and sustainable alternative to resist combined horizonta...

Reinforced concrete (RC) slabs strengthened with carbon fibre reinforced polymer (CFRP) and subjected to flexural actions may experience many types of failure, including FRP debonding, FRP rupture and concrete crushing. Of these different types of failure modes, FRP debonding stands out as the most predominant type of failure because of its depende...

Externally-bonded (EB) fibre reinforced polymer (FRP) retrofitting system has emerged as a promising strengthening technique to improve flexural performance of concrete structures. This paper presents the results of an experimental program studying the behaviour of concavely-curved soffit reinforced concrete (RC) strengthened in flexure with EB car...

Fatigue failure of concrete bridges strengthened using fiber reinforced polymers (FRPs) can occur by fatigue damage of the FRP fibres, steel reinforcement, epoxy resin or the layer of concrete to which the FRP is bonded. Although FRPs have become predominant in strengthening of concrete bridges, the long-term fatigue performance of these materials...

This paper reports a comprehensive study on the behavior of concavely curved soffit reinforced concrete (RC) beams strengthened in flexure with carbon fiber-reinforced polymer (CFRP) composites under static loading. The main objective of this paper is to explore the effect of surface concavity on the bond performance of externally bonded wet layup...

The shear strength of existing Reinforced concrete (RC) members can be improved by bonding Carbon fibre reinforced polymers (CFRPs) as Near-surface mounted (NSM) or Externally bonded reinforcement (EBR). CFRPs are typically bonded to RC members using epoxy resins which have low glass transition temperatures resulting in poor fire performance. In an...

Although fiber reinforced polymers (FRPs) have become the most widely used material to strengthened existing concrete structures in shear, premature debonding of externally bonded FRP remains a significant cause of material under-utilisation. In an effort to suppress debonding failure, research has shown that the use of ±45° bidirectional fabric pa...

The performance of Reinforced Concrete (RC) structures and their collapse safety experiencing moderate to high-magnitude seismic excitations might not be fully understood. Factors related to the high levels of uncertainties in ground motion content, structural modelling and design uncertainties, or to the empirical nature of design codes and standa...

In regions of low-to-moderate seismicity, the design of multi-story buildings with strong-beams weak-columns are quite common, which triggers the formation of a soft-story collapse mechanism during rare ground motions. A design approach to overcome this issue is introducing a ductile soft-story at the first level, such that the damage is controlled...

Fiber reinforced polymer (FRP) composite has been used effectively for the rehabilitation of concrete and steel structures in the last decades due to its excellent properties compared with conventional reinforcing materials such as steel. Despite the major role of epoxy resins as a bonding material between fibre and substrate, the rapid deteriorati...

The most evident properties of LWAC by which it is differentiated from normal weight concrete are its lower density and better insulating potential. The aim of this study is to examine the combined effect of lightweight coarse aggregate and steel fibers on concrete’s mechanical properties. In this study, three different types of coarse aggregate (n...

Although extensive research has been conducted into the use of fibre reinforced polymers (FRPs) in strengthening of concrete structures under static loads, their fatigue behaviour when subjected to cyclic loading still requires investigation. The issue of fatigue performance of FRP strengthening systems is mostly relevant to the strengthening of co...

Fiber-reinforced polymers (FRPs) are widely used to enhance the flexural capacity of existing concrete structures subjected to various loading actions. However, when FRPs are applied to structural elements as externally bonded flexural reinforcement, premature debonding of the FRP may occur in the form of concrete cover separation (CCS). This study...

Reinforced concrete (RC) structures are subjected to combinations of axial, shear, flexure, and torsional loading during an earthquake event. Comprehensive understanding of the behavior of shear panels is essential to predict the response of members under combined loading. This work focuses on the analytical modeling of RC shear panel elements. A b...

The experimental research focuses on the performance of concavely curved soffit reinforced girders strengthened in flexure by near-surface-mounted (NSM) carbon fiber reinforced polymer (CFRP) bars. The test program was organized in such a way to highlight the benefits of this technique for flexural strengthening of concavely curved soffit RC girder...

In recent construction practice, sandwich panels have been increasingly adopted due to the fact that they are lightweight, energy efficient, aesthetically attractive, and easy to handle and erect. This study examines the impact behaviour of lightweight reinforced concrete (RC) sandwich slabs produced from local lightweight coarse aggregate. The exp...

This paper presents a numerical methodology for analysis of the behaviour of structural concrete sections subjected to cyclic loading. Classical beam theory was utilised to calculate sectional deformations (strain and curvature) under normal force and biaxial moment, while a nonlinear sectional analysis is performed via computer software written in...

There is currently a high demand in the construction industry for high-strength and durable cement-based adhesives (CBAs) for use in a variety of applications such as ground anchors, ground improvement, concrete repair or as a substitute for epoxy resins to bond carbon fiber reinforced polymers (CFRPs) to concrete structures where increased fire pe...

This paper investigates the performance of curved soffit reinforced concrete beams strengthened in flexure with carbon fiber reinforced polymers (CFRPs) under static loading. The effect of concavity on the effectiveness of flexural strengthening is explored using both pultruded CFRP laminates and wet layup CFRP sheets in terms of the degree of flex...

Pre-stressed unbonded retrofit (PUR) CFRP strengthening of steel structures is becoming a common method of strengthening metallic structures. This paper presents a comprehensive study on the use of the PUR CFRP-strengthening method for strengthening a steel bridge in Melbourne, Australia. Finite element analysis is performed in this study to model...

This paper presents a new numerical methodology for the analysis of the sectional behaviour of structural concrete members with arbitrary cross-sectional configurations under repeated loading. The proposed methodology is accompanied by computer software written in the Python language to perform the sectional analysis at different loading stages fro...

Numerous studies have been conducted on flexural strengthening using epoxy adhesive for both externally-bonded and Near-Surface Mounted carbon fibre reinforced polymer (NSM CFRP) composites. Substitution of epoxy with cementitious bonding material for flexural retrofitting of concrete structures has great potential to overcome the drawbacks and dis...

During earthquakes, reinforced concrete (RC) structures are typically subjected to high shear loading. The reliable estimate of the behaviour of RC members under shear loads depends on the analytical model used. This work focuses on the analytical modelling of RC shear panel elements, which is essential for the full understanding of member-level sh...

This paper investigated the performance of reinforced concrete beams strengthened with near-surface mounted (NSM) carbon fiber reinforced polymer (CFRP) smooth and rough strips using cement based adhesive and insulated with plasterboards for protection the beams subjected to high temperature. An experimental work was carried out on ten large scale...

Reinforced concrete (RC) slabs can be strengthened using fiber reinforced polymers (FRPs) to enhance their flexural and shear resistance. However, premature debonding of the FRP material limits the level of strengthening achievable and represents an under-utilization of the FRP material. As a result, a variety of anchorage systems have been explore...

This paper presents the application of multi-axis hybrid simulation for evaluating the seismic response of a rigid-frame bridge structure constructed with concrete-filled steel tube (CFST) columns subjected to combined horizontal and vertical ground motions. These types of bridges are believed to have superior seismic performance and better ability...

The current paper investigates the role of initial imperfections at web-flange junction on the lateral torsional buckling behavior of pultruded fiber reinforced polymeric beams. This study is based on experimental and numerical results, which are developed in two main steps: perfect beams and beams with initial imperfections at the web-flange junct...

Reinforced concrete (RC) slabs can be strengthened using fiber reinforced polymers (FRPs) to enhance their flexural and shear resistance. However, premature debonding of the FRP material limits the level of strengthening achievable and represents an under-utilization of the FRP material. As a result, a variety of anchorage systems have been explore...

Strengthening concrete bridges using fiber-reinforced polymers (FRPs) in flexure, shear, and torsion is limited by the occurrence of premature FRP debonding which often controls the degree of strengthening possible using this approach. To address this issue, anchorage systems have been developed in recent years to mitigate FRP debonding failure mod...

This paper reports test results and describes a numerical investigation of the effectiveness of using carbon fibre reinforced polymer (CFRP) fabrics for strengthening concrete cylinders that have been undamaged and damaged due to heating under preload. The purpose of this research was to investigate whether there is any difference in the performanc...

Hybrid simulation is a form of advanced testing that combines both numerical and experimental techniques to achieve an economical seismic response assessment of structures. The technique utilises the best feature of computer simulations and combines these with experimental testing. This makes hybrid simulation a powerful platform for experimentally...

Over the last few decades, fiber reinforced polymer (FRP) has been increasingly used in strengthening different structural concrete members. The main objective of this research is to study the influence of curvature on the performance of curved soffit reinforced concrete (RC) bridge girders that have been strengthened with carbon fiber reinforced p...

In recent decades, structural adhesives have become widely used in the field of construction for the purpose of retrofitting existing structures using composite materials such as fibre reinforced polymers (FRP). The available standards for strengthening structures utilise the adhesive properties as listed in manufacturer’s technical sheets. However...

Strengthening with carbon fiber-reinforced polymers (CFRP) has become one of the most significant methods of enhancing the flexural strength of reinforced concrete members. Extensive research has shown that externally-bonded CFRP sheets tend to debond from the soffit of the concrete members at much lower strains, compared with CFRP rupture strain....

Carbon-based nanomaterials are commonly used to produce nanocomposites with polymeric matrices due to their unique properties. Vapour-grown carbon nanofibres (VGCF) are employed in this work to modify highly cross-linked epoxy-based resin (DGOA) used as a bonding agent in CFRP/concrete system. The influence of such modification on adhesive properti...

Punching shear failure is a typical failure mode for flat reinforced concrete (RC) slabs and develops in a brittle manner and with little warning. To avoid this type of failure, the punching shear capacity of slabs needs to be carefully considered in the design process and adequate punching shear reinforcement provided. Many existing slabs are requ...

In this study, two-dimensional nonlinear finite element (FE) analysis was carried out to model simply-supported curved-soffit reinforced concrete (RC) beams strengthened with CFRP sheets. Five models of simply-supported RC (curved and flat) soffit beams were loaded monotonically with one incremental concentrated load up to failure. The beams were s...

Carbon fibre reinforced polymer (CFRP) has become one of the most significant methods of strengthening which can be used for enhancing the capacity of structural elements. However, extensive research has shown that the effectiveness of such strengthening systems is highly dependent on the bond properties between the CFRP composite and the concrete....

A widely-used method for flexural strengthening of reinforced concrete (RC) structures is the use of fiber-reinforced polymer (FRP) materials as externally-bonded reinforcement. FRP materials have several advantages over traditional materials in terms of their tensile strength, low cost, durability and ease of application. However, a commonly-docum...

Recently composite materials have been increasingly used in different structural engineering applications. The research reported here focuses on the performance of concavely-curved soffit reinforced concrete beams strengthened by carbon fiber reinforced polymer (CFRP). CFRP composites used to strengthen reinforced concrete members with curved soffi...

The use of fibre reinforced polymer (FRP) in civil construction applications with near-surface mounted (NSM) method has gained considerable popularity worldwide and can produce confident strengthening and repairing systems for existing concrete structures. The response of concrete structural members rehabilitated using FRP with externally-bonded (E...

While sustainability addresses the economic, social and environmental impacts distributed over the life cycle of a structure; commonly, ordinary events such as construction, normal operation and ageing are considered and the resilience of the structure to extreme events (natural disasters and man-made hazards) is often ignored. This study aims to i...

Concrete-filled steel tube (CFT) columns have been widely used in low and high seismic regions. These elements combine the high strength and ductility of steel with the ability of concrete to efficiently carry compressive loads. Numerous experimental studies have been performed to examine the behavior of CFT columns under pure axial or combined axi...

The use of the near-surface mounted (NSM) fibre reinforced polymer (FRP) strengthening method in civil construction applications has gained considerable popularity worldwide, and can produce confident strengthening and repairing systems for existing concrete structures. The response of concrete structures rehabilitated using the externally bonded (...

This study gives an overview on carbon fibre-reinforced polymer (CFRP) strengthening and wireless sensor network (WSN) monitoring of a 121-year-old metallic roadway bridge in Melbourne, Australia. A flat prestressed unbonded retrofit (FPUR) system was developed to apply prestressed CFRP plates to the steel cross-girders of Diamond-Creek Bridge. The...

This paper summarizes the strengthening of a historically significant 122-year-old roadway metallic bridge using nonprestressed bonded carbon fiber reinforced polymer (CFRP) plates. Prior to the bridge strengthening, sets of laboratory tests were conducted to characterize the mechanical properties, glass transition temperature, and CFRP-to-steel bo...

In this study, a novel unbonded mechanical clamping system was developed for the strengthening of tensile metallic members using prestressed carbon fiber reinforced polymer (CFRP) plates. The system clamps a pair of prestressed CFRP reinforcement to a metallic substrate and provides an almost uniform contact pressure over the CFRP plate along the a...

Carbon fiber reinforced polymers (CFRPs) have gained popularity and become recognized as a prominent material for engineering applications in the last few decades owing to their high strength-to- weight ratio, resilience and corrosion resistance. The key concern is the bond between the CFRP and steel elements. The type of CFRP utilized in strengthe...

Cement-based adhesive (CBA) is used as a bonding agent in Carbon Fibre Reinforced Polymer (CFRP) applications as an alternative to epoxy-based adhesive due to the drawbacks of the epoxy system under severe service conditions which negatively affect the bond between the CFRP and strengthened elements. This paper reports the results of, an investigat...

Concrete structures strengthened with fibre reinforced polymer (FRP) composites in both flexure shear can be enhanced by introducing anchorage systems to suppress or delay the occurrence of premature FRP debonding. Research has demonstrated that by ultilising FRP anchors, it is possible to increase FRP utilisation levels prior to failure resulting...

Exposure of RC beams to fire may lead to a decrease in their load capacity and stiffness of the beams, both during heating and after the beam has cooled following the fire. The degree of damage is related to the fire's intensity in terms of temperature and duration. This investigation is concerned with the effectiveness and suitability of the CFRP...

Numerous steel structures that were built following the industrial revolution, including bridges, off-shore platforms, and many buildings, are carrying excess loads of varying types over those they were originally designed for. Furthermore, the magnitude, pattern, and type of loadings have changed over the years. As a result, these structures need...

While prestressed CFRP patches are considered as attractive alternatives to traditional welding or bolting methods for enhancing the fatigue life of cracked steel structures, they commonly require hydraulic actuators and pumps, and complex setups and installations for prestressing, limiting the applicability of this method. The primary objective of...

Embedded through- section (ETS) strengthening is a promising technique which involves embedding fiber-reinforced polymer (FRP) reinforcement vertically into holes drill through a concrete member to be strengthened. To understand how the ETS reinforcement interacts with concrete, further experimental and analytical work on the bond of the reinforcem...

Carbon fibre reinforced polymer (CFRP) has become popular and used in various engineering applications. Strengthening of hollow steel sections using CFRP has proven improved structural characteristics under static loading conditions. However, there are very few studies available related to the axial dynamic impact behaviour of CFRP strengthened ste...

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...

The effectiveness of using FRP materials to strengthen existing concrete structures is hampered by the weak bond properties between the FRP and the concrete. Further, very few studies are available on the fatigue performance of FRP-strengthened reinforced concrete beams in bridges. Investigation of the fatigue performance of FRP bonded to concrete...

Current permanent ground anchor standards require the use of double protection systems encapsulating the steel strands, to ensure a serviceable design life. In recent years, where steel reinforcement use was restricted due to aggressive ground conditions, carbon fibre reinforced polymer (CFRP) reinforcement was successfully used as a durable constr...

This paper presents an application of prestressed carbon fiber-reinforced polymer (CFRP) plates for the strengthening of metallic girders of a roadway bridge in Melbourne, Australia. The study also describes the application of a wireless sensor network (WSN) system for long-term structural monitoring of the retrofitted bridge girders. A flat prestr...

This paper presents the results of a component-based model developed for an innovative type of connection, recently proposed by the authors, for beam-to-hybrid fabricated column (HFC) connections. The active constitutive components of the connection are identified and their relevant resistance and flexural stiffness are presented. The moment-rotati...

This research shows the results of an experimental and numerical study on the behaviour of RC beams damaged by heating and then strengthened using NSM CFRP laminate and cement-based adhesive. Two beams were left as reference beams and the other beams were heated under the ISO-834 standard fire curve. The experimental variables consisted of unheated...

In this study, a novel retrofitting system is developed to strengthen existing metallic I-girders using prestressed unbonded carbon fiber reinforced polymer (CFRP) plates. The system relies on a pair of mechanical clamps. Each clamp holds two CFRP plates (each having cross-sectional dimensions of 50 × 1.4 mm) and anchors their prestressing forces t...