Papers by Riadh Al-Mahaidi
It has been demonstrated that the governing failure mode of concrete structures strengthened with... more It has been demonstrated that the governing failure mode of concrete structures strengthened with fiber reinforced polymer composites (FRP) is by premature debonding of the FRP material from the concrete substrate. Research has shown that one means by which the FRP-to-concrete bond performance may be improved is to provide anchorage measures that resist the interfacial shear and peeling stresses that are generated along the FRP bond line. FRP spike anchors and bidirectional fiber patch anchors are a proven means to enhance the bond performance of FRP materials when bonded to concrete. Although the above mentioned anchorage systems have shown significant promise when investigated independently, the present research aims to combine their unique properties into a hybrid anchorage system. In this study, FRP spike anchors were used to anchor bidirectional fiber patches and used to restrain FRP laminates tested in direct shear resulting in a superior anchorage strength which was demonstra...
Composite Structures, 2016
Abstract Near surface mounted (NSM) fiber reinforced polymer (FRP) bars became more effective in ... more Abstract Near surface mounted (NSM) fiber reinforced polymer (FRP) bars became more effective in strengthening reinforced concrete (RC) beams. This is because it increases the bond capacity and makes a protection against external damage. Most of previous related researches stated that the failure of the tested RC strengthened beams with NSM FRP is due to debonding or concrete cover separation. In this research the ends of the NSM glass fiber reinforced polymer (GFRP) bars were bent to delay or prevent NSM FRP debonding and concrete cover separation and thus increasing the load carrying capacity of the strengthened beams. The inclination angles of GFRP bars with bent ends were 90° and 45°. Straight GFRP bars with variable lengths were also used for comparison. The test results demonstrated that the GFRP bars with bent ends prevented the concrete cover separation and increased the load carrying capacity of the strengthened beams. The load carrying capacity of the strengthened beams by straight NSM bars and those having 45° and 90° inclined ends were 177%, 201%, and 185% of that of their control beam, respectively.
Journal of Structural Engineering, 2017
Hybrid simulation combines the flexibility and cost-effectiveness of computer simulations with th... more Hybrid simulation combines the flexibility and cost-effectiveness of computer simulations with the realism of experimental testing 7 to provide a powerful platform for large-scale experimental investigation of the seismic response of structures through collapse. This paper 8 presents applications of hybrid simulation for (1) tracing the seismic response of a limited-ductility reinforced-concrete (RC) column through 9 collapse and (2) evaluating the capability of carbon fiber reinforced polymer (CFRP) repair on rehabilitating the earthquake-damaged RC 10 column to its initial collapse resistance capacity. A state-of-the-art hybrid testing facility, referred to as the multiaxis substructure testing 11 (MAST) system, was used to simulate complex time-varying six-degrees-of-freedom (6-DOF) boundary effects on the physical specimens 12 using mixed load/deformation modes. Based on the experimental results, a comparative collapse risk assessment of the initial and repaired 13 column was conducted, which illustrates the effectiveness of using CFRP repair to restore and improve the collapse resistance of earthquake-14 damaged RC columns.
Journal of Composites for Construction
Journal of Physics: Conference Series, 2021
The most evident properties of LWAC by which it is differentiated from normal weight concrete are... more 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 (normal weight, crushed clay brick and Attapulgite) with different percentages of steel fiber (0%, 0.5%, and 1%) were used. The results show that replacing normal weight concrete with lightweight concrete leads to a decrease in unit weight, compressive strength, splitting-tensile strength and modulus of elasticity, while water absorption increases. With the increase of steel fiber ratios in the mixtures, the mechanical properties of lightweight concrete improve significantly compared with the control sample with no fiber. When 1% steel fiber is used, the splitting-tensile strength increases by about 115.6% and 55.7% and compressive strength ...
Insights and Innovations in Structural Engineering, Mechanics and Computation, 2016
Bridge Maintenance, Safety, Management, Life-Cycle Sustainability and Innovations, 2021
Tubular Structures XVI, 2017
CFRPs are widely used in the automobile industry and civil engineering applications. However, the... more CFRPs are widely used in the automobile industry and civil engineering applications. However, the structural behaviour of CFRP-wrapped steel hollow sections under axial impact loading is not yet fully understood. This paper evaluates the effect of impact mass on the axial impact behaviour of CFRP-wrapped steel hollow square sections. FE models were developed using LS-DYNA explicit finite element code and validated using existing experimental data. The axial impact behaviour of the tubes was evaluated by studying the responses to peak impact force, axial deflection and energy absorption. Appropriate results are presented and the trends discussed.
Engineering Structures, 2020
Reinforced concrete (RC) slabs can be strengthened using fiber reinforced polymers (FRPs) to enha... more 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 explored by researchers in an attempt to prevent or delay this type of failure. This paper presents a new FRP patch anchorage system which can be used to mitigate the commonly-observed failure mode of intermediate crack-induced (IC) debonding. This is the first experimental application where patch anchors are investigated in flexurally-strengthened RC slabs. Seven slabs 2700 mm × 400 mm × 150 mm in size were tested. Of these, two were unstrengthened, three were strengthened with 100 mm wide × 1.4 mm thick FRP sheet and two were strengthened in the same manner and anchored with four patch anchors. The use of patch anchors showed significant enhancement of both the strength and ductility of RC slabs compared with unanchored specimens.
Construction and Building Materials, 2018
h i g h l i g h t s Two large-scale RC slabs representing an interior slab-column connection were... more h i g h l i g h t s Two large-scale RC slabs representing an interior slab-column connection were tested. Steel bolts increased the load capacity of the slab by 15.4%. Strengthening technique change the punching shear failure to flexural failure. Numerical results showed good correlations with the experimental results.
Thin-Walled Structures, 2018
Steel hollow sections used in structures such as bridges, buildings and space structures involve ... more Steel hollow sections used in structures such as bridges, buildings and space structures involve different strengthening techniques according to their structural purpose and shape of the structural member. One such technique is external bonding of CFRP sheets to steel tubes. The performance of CFRP strengthening for steel structures has been proven under static loading while limited studies have been conducted on their behaviour under impact loading. In this study, a comprehensive numerical investigation is carried out to evaluate the response of CFRP strengthened steel tubes under dynamic axial impact loading. Impact force, axial deformation impact velocities are studied. The results of the numerical investigations are validated by experimental results. Based on the developed finite element (FE) model several output parameters are discussed. The results show that CFRP wrapping is an effective strengthening technique to increase the axial dynamic load bearing capacity by increasing the stiffness of the steel tube.
Thin-Walled Structures, 2018
Steel hollow sections used in structures such as bridges, buildings and space structures involve ... more Steel hollow sections used in structures such as bridges, buildings and space structures involve different strengthening techniques according to their structural purpose and shape of the structural member. One such technique is external bonding of CFRP sheets to steel tubes. The performance of CFRP strengthening for steel structures has been proven under static loading while limited studies have been conducted on their behaviour under impact loading. In this study, a comprehensive numerical investigation is carried out to evaluate the response of CFRP strengthened steel tubes under dynamic axial impact loading. Impact force, axial deformation impact velocities are studied. The results of the numerical investigations are validated by experimental results. Based on the developed finite element (FE) model several output parameters are discussed. The results show that CFRP wrapping is an effective strengthening technique to increase the axial dynamic load bearing capacity by increasing the stiffness of the steel tube.
Engineering Structures, 2018
This paper presents an application of prestressed carbon fiber-reinforced polymer (CFRP) plates f... more 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 prestressed unbonded retrofit (FPUR) system was developed to apply prestressed CFRP plates to the steel girders of the Diamond Creek Bridge (122 years old), which is subjected to daily passenger and heavy vehicles. The first section explains the results of sets of static and fatigue tests performed in the laboratory to examine the efficiency of the proposed FPUR system prior to its installation on the bridge. The second section presents details of different aspects of the CFRP strengthening of the bridge girders, fatigue design criteria, and layouts for short-and long-term monitoring. For the short-term measurements, the bridge was loaded with a 42.5-ton semi-trailer before and after strengthening. The CFRP plates were prestressed up to approximately 980 MPa (≈38% of the CFRP ultimate tensile strength), which resulted in about 50% reduction in the maximum tensile stress in the bridge girders. The third section discusses the development, installation, and preliminary results of the WSN system used to monitor the pre-stress level in the CFRP plates. The results of the short-and long-term measurements in this study show that the FPUR system is very effective for flexural and fatigue strengthening of bridge girders. Finally, a set of recommendations for long-term structural monitoring is provided. (I) concerns related to the long-term performance of CFRP-to-steel bonded joints under special environmental conditions (e.g.,
Composite Structures, 2019
The effectiveness of using FRP materials to strengthen existing concrete structures is hampered b... more 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 is important due to the fact that bridges are subjected to very high levels of cyclic loading throughout their lifetime. This paper focuses on a numerical and experimental investigation of the fatigue life of FRP laminates bonded to concrete. FRP-to-concrete joints were subjected to cyclic loading at various stress ratios and the number of cycles prior to failure was used to generate S-N curves which relate the stress ratio to the number of cycles. Further, numerical simulations using the finite element method were performed using a concrete material model capable of sustaining fatigue damage. The finite element results were found to be in good agreement with the experimental data and were used to provide further insights into the mechanisms of fatigue damage. Both the experimental and numerical results showed that no fatigue degradation occurred when the maximum stress ratio was less than 75% of the ultimate static capacity.
Composites Part B: Engineering, 2018
In this study, a novel retrofitting system is developed to strengthen existing metallic I-girders... more 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 to a metallic I-girder via friction. A finite element (FE) model was established to optimize the design of the required mechanical components, and a set of pull-off tests was performed to evaluate the capacity of the optimized system. The proposed flat prestressed unbonded retrofit (FPUR) system was then applied on a 6.4-m-long steel I-beam, and the excellent performance of the system, in terms of stress reduction in the beam bottom flange, was confirmed based on the results of a set of static four-point bending tests. Moreover, a fatigue fourpoint bending test was conducted on the steel I-beam, strengthened using the proposed FPUR system with a prestressing level of 53% (i.e., approximately 1120 MPa prestress in the CFRPs). Experimental results of the high-cycle fatigue test confirmed the excellent fatigue performance of the proposed FPUR system, as no prestress loss was observed after 20 million fatigue cycles. An analytical model is proposed to accurately predict the stress state in an I-girder strengthened with the proposed FPUR system, while design recommendations are provided concerning the practical use of the system. Relying on the laboratory experimental test results, the proposed FPUR system was used to strengthen the metallic cross-girders of a 121-year-old bridge in Australia.
Composite Structures, 2017
Evaluation of bond properties of degraded CFRP-strengthened double strap joints. Composite Struct... more Evaluation of bond properties of degraded CFRP-strengthened double strap joints. Composite Structures, 173, pp. 144-155.
FRP Composites in Civil Engineering - CICE 2004, 2004
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Papers by Riadh Al-Mahaidi