Mohammad J. Alshannag’s research while affiliated with King Saud University and other places

Residual drifts are an important measure of post-earthquake functionality in bridges and buildings, and can determine whether the structure remains fit for its intended purpose or not. This study aims at investigating numerically, through finite element (FE) analysis in ABAQUS, the cyclic response of exterior steel I beam-hollow column connection using welded shape memory alloys (SMA) bolts and seat angles. This is followed by validating the numerical model using an accredited experimental data available in the literature through different techniques, (1) SMA bolts, (2) SMA angles, (3) SMA bolts and angles. The parameters investigated included: SMA type, SMA angle thickness, SMA bolt diameter, SMA angle stiffener and SMA angle direction. The cyclic performance of the steel connection was enhanced further by varying the bolt diameter, plate thickness, angle type and direction. The results revealed that the connections equipped with a combination of SMA plates and SMA angles reduced the residual drift by up to 94%, and doubled the self-centering capability compared to conventional steel connections. Moreover, the parametric analysis showed that Fe-based SMA members could be a good alternative to NiTi based SMA members for improving the self-centering capability and reducing the residual drifts of conventional steel connections.

Upgraded design standards coupled with the damage caused by natural disasters have led to the development of smart materials with the potential to modernize current construction practices. This investigation proposes a nonlinear finite element (FE) model for evaluating the performance of beam-column joints (RC-BCJ) reinforced with shape memory alloys (SMA) and steel rebars. The model was validated based on accredited experimental data, followed by parametric analysis in ABAQUS to optimize the use of SMA bars for enhancing the seismic resistance of RC-BCJ without compromising their energy dissipation capacity. Parameters investigated include the (a) SMA-steel reinforcement ratio, (b) lengths of SMA bars, (c) elastic modulus of SMA, (d) compressive strength of concrete, and (e) axial load applied on the column. The finite element simulation results indicated that the model was capable of predicting the optimum length of SMA bars sufficient for relocating the plastic hinge away from the face of the column along the beam. Further, simulation results proved that the use of SMA bars in conjunction with steel reinforcement could be considered as an effective tool for enhancing the seismic performance of RC-BCJ joints. Among the parameters investigated, high-strength concrete was the most effective in improving joint resistance.

Recent advances in materials science have led to the development of smart materials that can continuously adapt to different loading conditions and changing environment to meet the growing demand for smart structural systems. The unique characteristics of superelastic NiTi shape memory alloys (SMAs) have attracted the attention of structural engineers worldwide. SMAs are metallic materials that can retrieve their original shape upon exposure to various temperatures or loading/unloading conditions with minimal residual deformation. SMAs have found increasing applications in the building industry because of their high strength, high actuation and damping capacities, good durability, and superior fatigue resistance. Despite the research conducted on the structural applications of SMAs during the previous decades, the existing literature lacks reviews on their recent uses in building industry such as prestressing concrete beams, seismic strengthening of footing–column connections, and fiber-reinforced concrete. Furthermore, scarce research exists on their performance under corrosive environments, elevated temperatures, and intensive fires. Moreover, the high manufacturing cost of SMA and the lack of knowledge transfer from research to practice are the main obstacles behind their limited use in concrete structures. This paper sheds light on the latest progress made in the applications of SMA in reinforced concrete structures during the last two decades. In addition, the paper concludes with the recommendations and future opportunities associated with expanding the use of SMA in civil infrastructures.

This paper reports on the flexural response of lightweight high strength concrete beams, (LWHSC) reinforced with different combinations of discrete, discontinuous and randomly distributed steel, crimped polypropylene and recycled plastic fibers. All the LWHSC beams tested failed in a typical flexural failure mode, in which flexural vertical cracks appeared within the constant moment zone. Analysis of the test results indicated that the fiber reinforced LWHSC beams exhibited significant increase in load carrying capacity, flexural toughness and ductility indices compared to control LWHSC beams without fibers. Among all the beams tested, the ones reinforced with 0.5% of 60 mm long steel fibers and 0.25% of crimped polypropylene fibers exhibited the largest increase, about 18% in load carrying capacity and flexural toughness compared to control beam specimens without fibers. While, the beams reinforced with 0.5% (50/50 blend) of short steel fibers (30 mm and 60 mm long), and 0.25% of recycled plastic fibers outperformed the flexural toughness of similar beams containing equal content of steel fibers and 0.25% of crimped polypropylene fibers by about 6%. Furthermore, test results indicated that an eco-friendly locally produced recycled plastic fibers could be successfully used for enhancing the flexural performance of LWC beams without compromising their load carrying capacity. Moreover, finite element software ABAQUS was used for predicting numerically the flexural response and crack progression of the beams investigated. The numerical predictions compare fairly well with the experimental test results

Laboratory tests were performed for evaluating the flexural performance of Portland cement mortars reinforced with recycled fibers. The objective was to find the best blend of unsorted recycled post-consumer tire steel fibers (RTSF), and recycled plastic fibers (RPF) for enhancing the flexural behavior and ductility of cement-based composites. Ten mortar mixes containing various blends of RTSF and RPF were cast and tested under a displacement-controlled four-point bending ASTM test. Test results indicate that the mortar mixes reinforced with recycled fibers satisfied the ASTM flow requirements and achieved a flexural response and toughness comparable to the response of similar mixes, containing manufactured steel fibers (MSF) only, at the same fiber dosage. Among the recycled fiber blends investigated, the mix containing 0.5% RTSF and 0.5% RPF (on volume basis) exhibited relatively superior flexural characteristics compared to the mixes reinforced with the same dosage of MSF only. Moreover, the positive synergetic effect of fiber blends on the post-cracking strength and flexural toughness was pronounced at 0.5% RTSF and 0.5% RPF (on volume basis). Hence, as an echo-friendly material, recycled fiber blends of RTSF and RPF could be recommended for enhancing the flexural performance of cement-based composites at a lesser cost.

This paper assesses the condition of a 45 years old precast reinforced concrete multistorey building and proposes innovative repair techniques for extending its service life. The residential building investigated consists of six floors, and each floor consists of 4 apartments with a total floor area of 900 m ² . Initially, visual inspection was conducted to identify the extent of deterioration in all parts of the building, followed by field non-destructive and destructive tests to determine the root causes of the damage. Moreover, analytical tools such as ETABS and SAFE design softwares were used by applying the same loading assumptions and material properties given by the designer, to check the compliance of the building with the safety requirements specified in ACI 318-14/SBC 304-18 building codes. The field and laboratory checks confirmed the occurrence of considerable degree of deterioration in some elements of the building due to reinforcement corrosion, alkali silica reaction (ASR), salt–scaling and leaching. The analytical checks revealed excessive deflections, due to a design error. Several advanced repair techniques including carbon fiber reinforced polymer sheets (CFRP), and steel jackets were implemented to restore the structural load carrying capacity of the columns and beams that suffered extensive deterioration. The excessive deflections were reduced below the code limit by supporting the deflected slabs using wide flanged I-section steel beams. Moreover, the Repair strategy proposed included, removal of the deteriorated concrete, coating the exposed steel bars with a protective anti-corrosive coating, and cathodic protection of the steel bars followed by injecting high strength cementitious grout.

This paper evaluates experimentally the feasibility of utilizing local natural lightweight aggregates (LWA) for designing reinforced concrete (RC) beams. The aggregates investigated were of scoria origin, with an absorption capacity of 10%, and dry densities ranging between 860 and 1120 kg/m³. A series of full-scale 16 simply supported RC beams of rectangular cross section were designed using two concrete strengths, normal and high, and two tension steel ratios of the balanced reinforcement ratio, following ACI code requirements. For the lightweight concrete (LWC) mixes designed, the replacement level of normal weight aggregates (NWA) with coarse LWA was 100%, whereas the replacement level for fine LWA was 62.5%. Data presented include load-deflection, and moment-curvature graphs, cracking behavior, mode of failure and ductility indexes. Test results indicated that the flexural response of LWC beams was similar to that of normal weight concrete (NWC) beams. All the LWC beams tested failed in ductile flexural mode, exhibited relatively larger mid span deflections, higher curvatures, and wider cracks, compared to NWC beams of equal concrete strength and steel ratio. The most influential parameter on the ductility indexes of LWC beams was the steel ratio. Moreover, the scoria LWA investigated can be used successfully in structural design.

An experimental investigation was conducted to determine the effect of internal curing of natural lightweight aggregates (LWAs) on the shrinkage, mechanical properties, and durability of high-performance concrete (HPC). Conventional aggregates were partially substituted with prewetted coarse and fine LWA at dosages of 5, 10, and 20% by volume. The early age autogenous shrinkage and drying shrinkage of the HPC mixtures were monitored for up to 180 days. The investigated properties of the HPC mixtures included compressive strength, modulus of elasticity, and splitting tensile strength at 28 days, as well as rapid chloride permeability and water absorption. The results revealed that, at a replacement level of 20% for both coarse and fine aggregates, the reduction in autogenous shrinkage of the HPC mixtures was approximately 118% at 28 days and 65% at 18 days. Furthermore, the test results indicated that the autogenous shrinkage measured between 15 h and 7 days after casting was reduced by approximately 75%. Fine LWAs were more effective in reducing autogenous shrinkage than coarse LWAs. This was attributed to the small particles, which allowed a good distribution of the water-filled internal curing within the cement matrix. It was also found that using up to 20% LWA could modify the 28-day autogenous shrinkage of HPC by reducing the cube compressive strength up to 70 MPa as compared to 86 MPa for the control mixture. In addition, the obtained strength values of the concrete mixes were found to be within the acceptable range specified by the ACI standard to be categorized as HPC. The findings of the study revealed that the utilization of LWA is feasible as an internal curing method for decreasing the volume changes, particularly at the early ages, and for avoiding the formation of cracks in HPC.

The deterioration of lightweight concrete (LWC) members due to intensive fires, necessitate the development of strengthening techniques for extending their service life. Fourty reinforced concrete (RC) beams were cast, heated at 600 °C for 3 hrs., strengthened using polymeric sheets (FRP), for regaining their flexural capacity. The flexural behavior of the beams investigated including the ultimate load, stiffness, deflection, and cracking pattern were described. The heated LWC reinforced beams regained a large portion of their load capacity, and exhibited typical flexural cracks in the pure bending zone, and flexure-shear cracks in the shear span, after strengthening. Among the strengthening schemes proposed, using a single layer and U shaped jacket of FRP sheets at the bottom, and sides of the beams, was effective for regaining their full flexural capacity. The experimental results indicated that FRP laminates can be considered as a promising material for maintenance and rehabilitation of heat damaged LWC members.