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Structural engineers have assessed the possibility of replacing part of natural aggregates with rubber particles in concrete in recent years to obtain sustainable structural members. It has been confirmed that the use of rubber particles can enhance ductility and energy absorption capacity of concrete. By contrast, the compressive capacity of rubberized concrete (RuC) is usually lower than the normal concrete (NC). Confining RuC with steel tubes can be considered as an appropriate solution for reaching to a ductile member with adequate strength. This paper, therefore, investigates the behavior of rubberized concrete-filled double skin steel tubular (RuCFDST) short columns by performing a series of nonlinear finite element (FE) analyses. The developed FE models were verified against the experimental test results by comparing the axial load–displacement curves, ultimate axial strength, and failure mechanism of specimens. The validated FE model was used to investigate the effects of geometric and material properties on the behavior of RuCFDST columns with 5%, 15%, and 30% rubber contents, and to compare the performance of RuCFDST and concrete-filled double skin steel tubular (CFDST) columns. The results showed that using RuC for filling square CFDST columns could significantly enhance the ductility. By contrast, CFDSTs presented greater axial strengths than RuCFDSTs. Reduced confining stresses between the outer tube and the concrete core were displayed when RuC was applied compared to CFDST.

Structural strengthening comprises modification of the structural elements to enhance their load bearing capability, stiffness, toughness, and ductility. The present study is an experimental investigation on the performance of reinforced concrete (RC) beam specimens strengthened by the side near surface mounted (SNSM) technique with reinforcement strengthening of glass fiber reinforced polymer (GFRP) bars in flexure. Sustainable palm oil fuel ash (POFA) mortar (PM) and normal mortar were used as bonding mediators between the concrete substrate and GFRP bars as a replacement for epoxy adhesive. A total of eight specimens, in which one was a control, one was strengthened by GFRP bars and full epoxy adhesive in grooves, and six specimens were strengthened by GFRP bars and partial replacement of epoxy adhesive by PM and NM, respectively. The specimens were tested in the static condition under four-point bending. During the test, the loads, deflection, and strains of the specimens were stored in a data logger and the failure modes of the specimens were observed. Critical discussions were made based on the flexural capacities, load-deflection, ductility, energy absorption, the influence of epoxy replacement and the type of mortars in the strengthened specimens as compared to the control specimen. ACI 440.2R-08 and ACI 318-11 were applied to predict the ultimate load-carrying capacity and deflection characteristic graphs of the tested specimens. The predicted results of the specimens were in close agreement with the experimental results. The test results also exhibited that the epoxy substituted by sustainable PM had superior flexural performance to the NM strengthened SNSM-GFRP bar specimens, particularly when considering the economic and eco-friendly viewpoint.

In this study, grouted couplers were used to connect steel bars as an alternative approach to the conventional steel bar lapping method. The aim is to avoid bar congestion problems and to reduce the required quantity of steel bars in order to achieve the development length in practice. Two categories of couplers, i.e., short-threaded grout coupler and long grout coupler, in nine groups as well as one group of deformed bars, were tested under uniaxial tension. In total, 30 samples (including three repeated samples in each group) were tested. The examined parameters were types of couplers, embedded bar length, and bar eccentricity. For the short-threaded grout couplers, the embedded bar length, which is equivalent to 8 times bar diameter with bar eccentricity equal to zero, exhibited the best performance in terms of strength, ductility, energy absorption, and failure mode, which is suitable to be used in the high seismic zone. Additionally, the short-threaded grout couplers with the embedded bar length equal to 7 times bar diameter and the long grout couplers that required embedded bar length that is equal to 8 times bar diameter, are suitable to be used in the low-to-medium seismic zone. Besides, the embedded bar length that is smaller than or equal to the 6 times bar diameter was not sufficient to be utilised in the short-threaded grout couplers and long grout couplers to resist the seismic load due to inadequate bar embedded length. Also, the predicted model is sufficient to estimate the ultimate tensile strength of the grouted couplers.

To enhance the behavior of steel plate shear walls, stiffeners are attached on the infill plate. The various researches on the stiffened Steel Plate Shear Walls (SPSWs) with Low Yield Point (LYP) infill steel plate have approved excellent capacity of this system. In those studies, the researcher focused on the specific type on stiffeners and in some cases, different results was reported. To cover different aspects, to provide comprehensive necessary data for structure designers and, to study the post-buckling and performance factors, this research is conducted. Using the validated Finite Element (FE) models with experimental test results, an analytical study of a single story SPSWs conducted to determine the influence of the selected parameters on the strength, stiffness, energy absorption and seismic performance factors. The variant parameters include the stiffeners pattern, stiffeners thickness, one-side or double-sides stiffeners and the slenderness of the stiffened infill plates. The results showed that cross-stiffened pattern is preferable in the one-side stiffening method while, diagonal pattern in double-side shape. Finally, the value of seismic performance factors is proposed for stiffened SPSWs.

In recent decades, the application of carbon fibre-reinforced polymer (CFRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads, or repair due to fatigue cracking. The premature failure due to end-debonding is a key limitation to achieve high fatigue performance of strengthened steel beams with externally bonded CFRP plates. The objective of this study is to explore the reinforcing techniques using the CFRP in-plane end cutting shapes and the triangular spew fillet of adhesive at the tips of the plate to care for fatigue damaged of wide-flange steel I-beams due to end-debonding. Four in-plane CFRP end cutting shapes were chosen, namely: rectangular, semi-elliptical, semi-circular and trapezoidal. The application of the trapezoidal end shape was found to be the best configuration for delaying the end-debonding failure mode and high fatigue life compared to the other CFRP in-plane end cutting shapes. Applying the triangular spew fillets of adhesive significantly increased the end-debonding and steel beam fracture initiation life of the strengthened beams.

Oil-palm-boiler clinker (OPBC) is an agricultural waste from the palm oil industry and is considered a serious threat to the environment. Moreover, the high consumption of concrete as a construction material results in a continuous demand for natural aggregates, thereby negatively affecting the environment. Thus, channeling OPBC waste materials into the concrete industry aids in promoting the use of a sustainable and lightweight member. This research presents a novel sustainable composite beam that uses an OPBC as a replacement of the natural coarse aggregate. Flexural behaviour of steel tubes infilled with conventional and OPBC concretes were investigated. The results showed that the ductility, flexural stiffness and structural efficiency were higher in the OPBC concrete filled steel tube (CFST) than conventional CFST by 15%, 12% and 20%, respectively. Furthermore, in comparison to conventional CFST, the 10% less self-weight in OPBC CFST will significantly reduce the construction cost of the material. Conclusively, the utilisation of OPBC as infill material for CFSTs will solve disposal problem, preserve natural resources, reduce environmental pollution and will make the structural system sustainable.

Side Near Surface Mounted (SNSM) strengthening technique is among the latest technique introduced recently. In this paper, SNSM carbon fiber reinforced polymer (CFRP) strips strengthening technique is proposed for enhancing the flexural performance of reinforced concrete (RC) beams. A total of seven RC beam specimens were tested: one un-strengthened control specimen, and six specimens strengthened by SNSM-CFRP strips. All beam specimens were tested under four-point bending. Analytical prediction methods were used to verify the experimental results. The load, mid-span, deflection, and strains data were recorded until failure of the specimens. The ductility, stiffness, and energy absorption capacity of the strengthened specimens by CFRP strips were enhanced due to SNSM technique. The results also showed that the SNSM-CFRP strips strengthening technique significantly enhanced the first cracking, yield, and ultimate load capacities up to 153%, 108%, and 147% respectively, compared with that of the control beam. Further, the comparison between the experimental and predicted values shows good agreement.

The utilisation of beam to concrete-filled tubular (CFT) column bolted construction remains limited due to the severe slippage of bolts, column surface deformation and low moment-resisting capacity. This study proposes a novel blind bolt, known as the TubeBolt, for beam to CFT column connections. Ten pull-out test specimens were evaluated under tensile monotonic loading. Bolt type, bolt diameter, end anchor member, hollow tube wall thickness and bolt hole diameter were varied for the test. The failure modes, anchorage performance, load-carrying capacity, strength, slippage and elongation of the bolts were analysed. The behaviour of the TubeBolt specimens was compared with that of the Extended Hollo-bolt specimens under the same condition. Experimental results indicated that the novel TubeBolt in concrete-filled tubes exhibited excellent anchorage performance, higher strength and less slip and elongation until the failure state was reached.

In this study, experiments were conducted on five specimens of stiffened and unstiffened steel plate shear walls under cyclic loading. First, the specimens and frame design, material properties, and test setup were described. The behaviors of the unstiffened aluminum and steel infill plates were compared with three configurations of stiffened steel plate, i.e., cross-stiffened, circular-stiffened, and diagonally stiffened. The cross-sectional areas of the stiffeners were the same for all stiffened specimens. The results showed that the aluminum infill plate exhibited less ductility. By contrast, the unstiffened steel plate was very ductile, exhibiting a stable hysteresis curve and no tearing. The energy-absorption capacity of the steel plate shear walls increased for all stiffening configurations. Among all configurations, the cross-shaped stiffeners showed considerable increase in shear stiffness, ductility, and energy-dissipation capacity. The plate frame interaction method could predict the ultimate shear strengths of the unstiffened and cross-stiffened panels with good precision. The circular-stiffened steel shear wall seems to behave more desirably in high-amplitude displacements.

In general, precast concrete structure has insufficient ductility to resist seismic load. Detailed understanding on the behaviour of precast concrete connections are limited and current researches are focused addressing this. In this study, two precast and two monolithic concrete joints for exterior beam-to-column connection were tested under cyclic loading. The installation of precast specimens was prepared using dry type method while the monolithic joints were casted in-situ. The evaluation of seismic performance of the joints was conducted by applying hysteretic reverse cyclic loading until failure. Information regarding the strength, ductility and stiffness properties of the connection were recorded and analysed. Based on the test results and damage condition, the initial design of the joint was improved. Consequently, a new joint was constructed and tested, which exhibited a better performance. Precast concrete connections showed stable load–displacement cycles and dissipated a higher energy. The structural drift obtained was up to 9.0%. Pinching and deterioration were attained at a drift ratio of 4.5%. Also, there was improvement in the tested precast joints based on deflection, plastic hinges, crack pattern and shear deformation. Thus, the precast joints had a satisfactory resistance to seismic loads.

In this research, numerical investigations were carried out to study the behaviour of concrete filled steel tubes having square or rectangular cross-sections. Separate models were used for both normal strength concrete and high strength concrete. More than 50 experimental results were used to verify the FE model and it was found that the FE model accurately predicts the load-deflection curve and ultimate moment capacity of the Concrete filled steel tube (CFST) beams. Thereafter, a parametric study was carried out to evaluate the effect of depth-to-thickness ratio (20−200), compressive strength of infilled concrete (2–100 MPa), shear span-to-depth ratio (1–8), depth-to-width ratio (0.6–2), and yield strength of steel tube (380–490 MPa) on the flexural behaviour of square and rectangular CFST members. It was found that the depth-to-thickness ratio, yield strength of steel and height-to-width ratio has significant effect on the ultimate capacity of CFST beams. The effect of shear span-to-depth ratio and strength of infilled concrete was found to be marginal. Finally, the results of parametric study and experimental data available in literature were used to check the accuracy of the existing design methods presented in EC4 (2004), CIDECT, AISC (2010) and GB50936 (2014). From comparison, it was found that GB50936 (2014) was more accurate but unsafe for low strength infilled concrete. For all cases, EC 4 (2004) was found to be safe and hence is recommended.

Huge amount of virgin materials is being used in the production of concrete and the negative impact caused by exploitation of natural resources to our eco-system is beyond recovery. In order to produce a cleaner and greener concrete, waste palm oil clinker (POC) powder, a by-product from palm oil industry was used as filler and amorphous material in the development of sustainable and environmental friendly lightweight concrete. The utilization of POC powder as cement replacement in concrete will certainly have positive impact on the environment due to potential reduction in greenhouse gas emission. Further, whole replacement of virgin crushed granite coarse aggregate with coarser POC as coarse aggregate would enable conservation of natural resources. The properties including workability, density, compressive strength in different moisture contents, splitting tensile and flexural strengths, stress-strain curve, modulus of elasticity, ultrasonic pulse velocity (UPV) water absorption and sorptivity of the sustainable lightweight concrete were obtained and analysed. It has been found that the addition of 15% waste POC powder produced the optimum mixture as the strength enhancement of compressive and flexural strengths of 30% and 15%, respectively, was found. In addition, the filler effect of waste POC powder could be seen as it decreased the water absorption and sorptivity. Moreover, the use of two palm oil industrial waste materials up to a volume of 56% in concrete as replacement to cement and coarse aggregate will not only reduce cost but it will spur research and commercial interests as environmental friendly high strength lightweight concrete could be produced using these wastes.

Reinforced concrete (RC) structures necessitate strengthening for various reasons. These include ageing, deterioration of materials due to environmental effects, trivial initial design and construction, deficiency of maintenance, the advancement of design loads, and functional changes. RC structures strengthening with the carbon fiber reinforced polymer (CFRP) has been used extensively during the last few decades due to their advantages over steel reinforcement. This paper introduces an experimental approach for flexural strengthening of RC beams with Externally-Side Bonded Reinforcement (E-SBR) using CFRP fabrics. The experimental program comprises eight full-scale RC beams tested under a four-point flexural test up to failure. The parameters investigated include the main tensile steel reinforcing ratio and the width of CFRP fabrics. The experimental outcomes show that an increase in the tensile reinforcement ratio and width of the CFRP laminates enhanced the first cracking and ultimate load-bearing capacities of the strengthened beams up to 141 and 174%, respectively, compared to the control beam. The strengthened RC beams exhibited superior energy absorption capacity, stiffness, and ductile response. The comparison of the experimental and predicted values shows that these two are in good agreement.

This paper proposes a new moment-resisting connection known as a through rib stiffener beam connection, which is directly passed through a pre-slotted circular column with concrete infill. Four half-scale cruciform specimens with orthogonal beams were tested under cyclic loading. The failure modes, hysteretic performance, rotation capacity, strength and stiffness degradation, ductility, and energy dissipation of the connections were analysed. The effect of different parameters, such as through rib stiffener and beam section size, on the connection performance was investigated. The experimental results indicated that the new through rib stiffener beam connected with circular columns exhibited a large hysteretic enclosed area, good ductility, and excellent energy dissipation. The results proved that the proposed connection satisfies the seismic provisions and ductility design requirements for it to be utilized as moment-resisting frames in a seismically active area.

In recent years, vehicle demographics have changed to include a relatively large proportion of light trucks, such as pickups, vans and sport-utility vehicles. It is found that several types of guardrail systems, including the G4(2W) guardrail system, are unable to redirect the pickup trucks to roadway safely. Therefore, in this study, several options are considered; they include improving the splice connections and adjusting the guardrail height and the post spacing to improve the performance of this system. The G4(2W) guardrail system is modelled in LS-DYNA and validated with a previous full-scale crash test conducted by the Texas A&M Transportation Institute. A parametric study based on the results of the LS-DYNA crash simulation according to Length of Need test 3-11 and 3-10 is conducted to investigate key factors of guardrail systems, including the splice configuration, the post spacing and the guardrail height. The purpose of this study is to find a model that satisfies the requirements of Test Level 3 outlined in Manual for Assessing Safety Hardware (MASH)'s criteria.

Beam-to-column connections (BCCs) in steel pallet racks (SPRs) govern the stability of the structure in the down-aisle direction and possess a complex behavior as compared with the customary steel connections used in building structures because of the absence of bolts and welds. This behavior becomes increasingly complicated in case of hazardous conditions, such as fire, and needs careful design considerations. Warehouse fires are associated with higher average property losses per fire than most other occupancies. The existing literature completely lacks the studies focusing on the behavior of SPR BCCs under fire. This paper predicts the experimental and numerical behavior of SPR BCCs subjected to elevated temperatures. Eight sets of connection specimens, with three specimens in each set, were selected based on the variation in column thickness, beam depth, and the number of tabs in the beam end connector. A total of twenty-four tests were performed at three different temperature ranges (450 °C, 550 °C, and 700 °C) using the double cantilever test method. The major failure modes and the moment-rotation (M-θ) behavior of the SPR BCCs at elevated temperatures were evaluated and compared with the results of ambient temperature testing of SPR BCCs available in the literature. The findings indicated a noticeable degradation in the strength and stiffness of the connection due to thermal action. A non-linear three-dimensional (3D) Finite element (FE) model was developed to simulate the experimental investigations. The FE model exhibited a close agreement with the experimental results.

Structural performance of steel-concrete composite structures relies deeply on the characteristics of the shear connectors. Recently, great attention has been focused on the implementation of C-shaped connectors due to numerous advantages when used in composite beams. However, very little information is available in regard to the response of such connectors when embedded in the high strength concrete (HSC). To address this research gap, sixteen experiments on push-out specimens were conducted to compare the performance of channel and angle shear connectors embedded in HSC. The shear resistance and ductility of the connectors were primarily investigated by applying static and cyclic loadings. Results were also compared with the cases when using normal reinforced concrete. Furthermore, the evaluation of the available equations suggested by the American and Canadian codes for estimating these connectors' capacities when using HSC was carried out. In general, channel connectors exhibited 6.8-30.1% more shear strength than those of angle under monotonic loading, and up to 18.5% more when subjected to cyclic loading. Angle connectors were also less ductile than channel connectors and did not satisfy the ductility criteria specified in the codes' requirements. Connector fracture mode of failure was recorded for both connector types.

Steel pallet racks (SPRs) are used in the industrial buildings, warehouses and superstores for storing a multitude of different kinds of goods. Because of changing needs over the years, it is often desirable that such installations be readily demountable and capable of reassembly. Therefore, the beam-to-column connections (BCCs) used in SPRs are boltless in nature. SPR BCCs govern the stability of the frame in the down-aisle direction. The design of SPR BCCs is one of the problems for designers that cannot be handled routinely within the existing design specifications available for bolted and welded connections. Moreover, the studies on the considerations necessary for the design and performance of SPR BCCs solely are rarely available. It is therefore, essential to bring to light the factors that play significant role to improve the design and performance of SPR BCCs. A critical review of the research performed over the last few decades into the global stability of SPR structures in the down-aisle direction only is presented in this paper. The information about the design methodologies and testing procedures defined in the literature and design codes as well as the factors governing the performance of boltless connections are identified. The major failure modes are highlighted. The characteristics of the main elements constituting SPRs are also succinctly discussed. Based on the findings, the limitations of current study are highlighted and future research areas are identified.

The agricultural industry is a source of many types of solid waste. For instance, oil palm shell (OPS), is a waste from the palm oil industry and is produced in enormous quantities in tropical countries. This waste material is considered to be a major problem in terms of pollution, while, on the other hand, normal concrete needs a large amount of the raw materials as coarse and fine aggregate. Due to the limitations of raw materials, the use of normal aggregate can have a negative effect on the environment. In addition, the high self-weight of raw aggregate in normal concrete is considered to be another disadvantage of this type of concrete for the construction of structural members. This paper presents a novel sustainable composite column by using of lightweight OPS concrete instead of conventional aggregate concrete. Composite columns in the form of concrete filled steel tubes (CFTs) are acknowledged to be a highly efficient group of columns with wide usage in different types of structure. In this study, the axial compressive behaviour of CFT columns constructed with conventional normal weight and OPS lightweight concretes was investigated. In the new composite column, 22% of the total volume of the composite was replaced with waste OPS aggregate. The test results showed that the CFT column containing OPS lightweight concrete had the same ultimate axial load capacity as the CFT column with conventional concrete. This new green composite column is about 15% lighter than a normal CFT column, with significantly higher specific energy absorption, structural efficiency and flexibility.

This paper investigated the platform motion and tether tension of tension leg platform subjected to eight sea states ranging from extreme to moderate states. The mass, stiffness and damping force matrices were formulated for the platform and the tethers were considered as non-linear springs. The surface elevation and wave kinematics were calculated by small wave amplitude theory. On the other hand, the force vector was calculated by integrating over the entire length of the hull members using Morison equation. The various degree of non-linearity considered include the drag force, the variable added mass, large displacement as well as variations in tether tension. A finite element numerical research program was developed for solution of the nonlinear problem. The statistical response parameters for the degrees of freedom show that as we move towards the less severe sea states, all the responses were decreasing. Response comparison of one tether missing and an intact tendon of tension leg platform show an increase in surge and tether tension but heave response decreased due to reduction in stiffness against vertical movement. Dynamic analysis of the platform under the combined action of wave, current and wind is recommended so as to know true platform behaviours.

Tubular column members have been widely adopted in current construction due to its numerous advantages. However, the closed-section profile characteristics of tubular columns severely limit the connection possibilities. Welding type is acceptable but discouraged because of on-site issues. Blind-bolted connection is preferable because of its simplicity, economic benefit, and easy assembly. This paper presents a state-of-the-art review on bolted connections to tubular columns for bare steel tubes, including square and circular sections. Available studies on bolted connections at ambient and elevated temperatures are reviewed, but emphasis is given on the latter. Various methods of determining the connection performance through experimental, analytical, component based, and finite element approaches are examined. Future research areas are also identified.

Nonlinear finite element models of through beam connection to concrete filled circular steel tube (CFCST) column with three types of connection failures (column, beam and joint shear failures) under monotonic loading were proposed by ABAQUS programme. The connection detail composed of a steel I-beam which is completely passed through the circular steel tube column and welded to it by fillet or full penetration weld and the tube is then filled with concrete. The connection parameters investigated included different ratios of column-to-beam flexural strength, fillet or full penetration weld to connect the beam to the tube, using rebar inside of the column and effect of beam web and concrete core inside the joint. Buckling analysis, concrete damage, weld fractured and tube tearing were defined in the model. Good agreement was achieved between the model and existing test results in terms of the beam tip force-storey drift relationship, joint distortion and joint shear strain. As a result, the models could correctly predict the linear, nonlinear and post-failure behaviours of the connection. In addition, other parameters of the connection were investigated for the specimens. Finally, the effect of column axial load level for the connection behaviour in the three types of failures was investigated as a parametric study.

Concrete-filled steel tubes (CFTs) exhibit superior performance under static and dynamic loads, due to composite action. Factors, such as the thickness of the steel tube and the concrete core condition, have a significant effect on the structural behaviour of CFT columns, particularly in the post-yield behaviour. Studies show that if the concrete core is reinforced with steel bars, the new composite member has better characteristics compared to CFT columns. In this study, the axial compressive behaviour of reinforced concrete-filled steel tube (RCFT) columns using spirally reinforced concrete (SRCFT) was investigated and compared with CFTs. The main variation was the pitch spacing of the spiral shear reinforcement. Fifteen specimens, including three CFTs and twelve SRCFTs, were tested in five groups. The test results indicated that a SRCFT column has much better post-yield behaviour than a CFT column. A reduction in the pitch spacing rate further improves the post-yield behaviour of the SRCFTs. A comparison of the measured strength of the specimens with corresponding values predicted by two international codes (ACI 318-11 and EC4-1994) shows a good prediction of EC4 and a conservative estimation of ACI.

Beam-to-column connections (BCCs) used in steel pallet racks (SPRs) play a significant role to maintain the stability of rack structures in the down-aisle direction. The variety in the geometry of commercially available beam end connectors hampers the development of a generalized analytic design approach for SPR BCCs. The experimental prediction of flexibility in SPR BCCs is prohibitively expensive and difficult for all types of commercially available beam end connectors. A suitable solution to derive a particular uniform M-θ relationship for each connection type in terms of geometric parameters may be achieved through finite element (FE) modeling. This study first presents a comprehensive description of the experimental investigations that were performed and used as the calibration bases for the numerical study that constituted its main contribution. A three dimensioned (3D) non-linear finite element (FE) model was developed and calibrated against the experimental results. The FE model took into account material nonlinearities, geometrical properties and large displacements. Comparisons between numerical and experimental data for observed failure modes and M-θ relationship showed close agreement. The validated FE model was further extended to perform parametric analysis to identify the effects of various parameters which may affect the overall performance of the connection.

Concrete-filled steel tubular (CFST) columns have been used in the construction of modern structures such as high-rise buildings and bridges as well as infrastructures as they provide better structural performance than conventional reinforced concrete or steel members. Different shapes of CFST columns may be needed to satisfy the architectural and aesthetic criteria. In the study, three dimensional FE simulations of circular, square, hexagonal, and octagonal CFST stub columns under axial compression were developed and verified through the experimental test data from the perspectives of full load-displacement histories, ultimate axial strengths, and failure modes. The verified FE models were used to investigate and compare the structural performance of CFST columns with different cross-section shapes by evaluating the overall load-deformation curves, interaction stress-deformation responses, and composite actions of the column. The extent of the ultimate-axial-strength enhancement due to enhanced steel yield strength and concrete compressive strength was evaluated through the parametric studies. At last, the accuracy of available design models in predicting the ultimate axial strengths of CFST columns were investigated. Research results showed that the behaviors of hexagonal and octagonal CFST columns were generally similar to that of the square CFST column as their overall structural performance was relatively improved.

In this paper, the effectiveness of cement mortar as bonding materials in the strengthening of reinforcements and concrete surface for flexural improvement of reinforced concrete (RC) beams were investigated. Recently, side near surface mounted (SNSM) and existing near surface mounted (NSM) techniques with glass fiber reinforced polymer (GFRP) bars are adopted as the strengthening methods for RC beams in which varieties of epoxy adhesive were replaced with cement mortar. In this study, one control and seven strengthened beams were tested under four-point loading in a static condition. The load-carrying capacities, failure modes, deflection, strains characteristic, parametric study and energy absorption capacities are addressed through laboratory experiments. The results revealed that the flexural performance was successfully achieved by using cement mortar as a replacement for adhesive. The SNSM strengthening technique exhibited better structural performance compared with the existing NSM technique in all aspects.

This paper studies the characteristics of square concrete-filled double-skin steel tubular (CFDST) short columns with inner circular steel tube by performing a series of nonlinear finite element (FE) analysis. The precise definitions of the behavior of the material are the initial requirement of numerical modeling. The existing models for predicting the behavior of the concrete core confined by the circular tube are not suitable since the mechanism of the concrete confinement in square composite columns is different from that of the circular ones. Also, ignoring the confinement effects on improving the concrete strength may lead to conservative results. In this paper, the confinement effects provided by the steel tubes on the concrete core in square CFDST columns are taken into account in the concrete constitutive model. The verified FE model is utilized to investigate the effects of important parameters on the ultimate axial strength, energy absorption capacity, ductility, and interaction performance of CFDST columns. A new design equation is suggested based on stress distribution over the concrete cross-section. It is shown that material properties and dimensions of composite columns can highly affect their performance. Also, the thickness of the inner tube must be controlled to prevent its premature failure. Validation of the design equation shows that it leads to the satisfactory predictions of the ultimate strengths of square CFDST short columns under axial loading.

Structural connection systems are a major challenge for precast construction systems. A dowel system requires designers to have sound knowledge of the fundamental requirements for seismic loads. In addition, it is important to consider unforeseen impact loads to prevent buildings from collapsing in the event of an earthquake. At present, the available building codes does not offer a complete design and analysis requirements for beam-to-column connection systems. Thus, this article provides researchers with a comprehensive review of the literature of the dowel precast beam-column connections. The key areas covered in this review are as follows: (1) studies on the behaviour of precast dowel beam-column connection systems in earthquake-prone areas; (2) studies on the design and development of precast dowel connection elements; (3) an evaluation of the effect parameters in precast connection systems and (4) a determination of the appropriate precast beam-to-column connections for seismic loads. The strength, ductility, energy dissipation, rotation and plastic hinges of joints in critical regions were considered in order to evaluate the performance of the dowel connection system.

The existing literature concerning the axial performance of concrete-filled double-skin steel tubular (CFDST) columns has been reviewed in this paper. The models in the literature for predicting the behavior of steel materials and confined concrete are summarized, and their effects of the results of finite element analysis are discussed. The applicability and accuracy of four design guidelines to predict the ultimate axial strength of CFDST columns have been assessed through this review by using an expanded database of published compression tests. Code limits in cross-sectional slenderness and material strength are reviewed. The impacts of different structural parameters on the axial behavior are reviewed and discussed. The discussion results indicate that material properties and dimensions have significant effects on the axial performance of CFDST columns. The European and Australian codes give the most reliable predictions, while American design codes give conservative predictions. Finally, recommendations for future studies are provided.

The behavior of shear connectors plays a significant role in maintaining the required strength of a composite beam in normal and hazardous conditions. Various types of shear connectors are available and being utilized in the construction industry according to their use. Channel connectors are a suitable replacement for conventional shear connectors. These connectors have been tested under different types of loading at ambient temperature; however, the behavior of these connectors at elevated temperatures has not been studied. This investigation proposes a numerical analysis approach to estimate the behavior of channel connectors under fire and compare it with the numerical analysis performed in headed stud and Perfobond shear connectors subjected to fire. This paper first reviews the mechanism of various types of shear connectors and then proposes a non-linear thermomechanical finite element (FE) model of channel shear connectors embedded in high-strength concrete (HSC) subjected to fire. Initially, an accurate nonlinear FE model of the specimens tested at ambient temperature was developed to investigate the strength of the channel-Type connectors embedded in an HSC slab. The outcomes were verified with the experimental study performed on the testing of channel connectors at ambient temperature by Shariati et al. (2012). The FE model at ambient temperature was extended to identify the behavior of channel connectors subjected to fire. A comparative study is performed to evaluate the performance of channel connectors against headed stud and Perfobond shear connectors. The channel connectors were found to be a more economical and easy-To-Apply alternative to conventional shear connectors.

Shear connectors are key components to ensure the efficient composite action and satisfactory transfer of shear forces at the steel'concrete interface in composite beams. Under hazardous circumstances, such as fire in a building, the performance of a composite beam significantly relies on the performance of shear connectors. Studies on the behavior of shear connectors subjected to elevated temperatures performed in the last decade are reviewed in this paper. The experimental testing of push-out specimens, the design approaches provided by researchers and different codes, the major failure modes, and the finite element modeling of shear connectors are highlighted. The critical research review showed that the strength of a shear connector decreases proportionally with the increase in temperature. Compared with the volume of work published on shear connectors at ambient temperatures, a few studies on the behavior of shear connectors under fire have been conducted. Several areas where additional research is needed are also identified in this paper.

In this paper a new shear connector called V-shaped angle shear connector for steel–concrete composite system is proposed. This shear connector was proven to improve some mechanical properties of shear connectors, including high shear transfer, uplift resistance, sufficient ductility, and strength degradation resistance under cyclic loading, as well as to being cost effective compared with similar shear connectors, such as C-shaped channel and angle shear connectors. A total of 14 push-out tests were performed on composite beams with these connectors under monotonic and low cyclic loading. The failure mode, shear resistance, and ductility of the push-out specimens were investigated. The study also comprises of finite element and parametric analysis using an effective numerical model of the experimental push-out tests using the program ABAQUS. The finite element models were validated against the test results presented in experimental tests. Results showed that V-shaped angle shear connector has excellent behavior in terms of both shear strength and ductility. In addition, high resistance under cyclic loading was exhibited since the shear resistance of this connector was almost similar in both monotonic and cyclic loadings. Finite element results show good agreement with experimental results. The results discussed on the ductility and strength of this connector with different size and slope of inclination. In addition, the channel and angle shear connectors were compared with V-shaped angle shear connectors. V-shaped angle shear connectors behave much better than other similar connectors, such as normal angle shear connectors, and are superior to channel shear connectors in most specimens.

In this study, a finite element model of a top-seat angle connection at elevated temperature is developed to study the effect of axial restraints on the connection behavior. Models are first validated with existing fire test results of top-seat angle connection. Non-linear behavior of the materials was modeled with the definition of elastic-plastic multi-linear properties and frictional contact between surfaces is included to simulate actual conditions. Validation of the model behavior shows that the model is in good agreement with existing experimental results and therefore the model is used for further study on the effect of axial restraints towards connection behavior. Both isothermal and anisothermal conditions were analyzed considering the effect of axial restraints. Results from the model shows that an increase in axial restraints has increased connection capacity while the stiffness remains similar for low axial levels. On the other hand, the shrinkage of the beam, may lead to tensional axial loads, causing axial pulling on the connection, resulting in higher deformation and different deformation patterns of the component angle sections. Effect on the design guidelines for connection design with axial restraints provided by Eurocode 3:2005 (Part 1-8) is also discussed at the end.

The aim of this study was to develop intumescent flame-retardant coatings that incorporate chicken eggshell (CES) waste as a novel eco-friendly bio-filler. Three flame-retardant additives, namely, ammonium polyphosphate phase II, pentaerythritol and melamine were mixed with flame-retardant fillers and acrylic binder to synthesize the intumescent coatings. The fire performance of the coatings was evaluated in accordance with ‘BS 476: Part 6-Fire Propagation’ and ‘BS 476: Part 7-Surface Spread of Flame’ test standards. It was found that 4 out of 5 of the coated specimens (B, C, D and E) neither showed surface spread of flame nor any afterglow combustion upon fire exposure. The addition of 5.0 wt% and 2.5 wt% eggshell bio-filler into formulations B and E, respectively, improved fire protection due to char formation, with better morphology, height and structure of the protecting shield. The filler compositions of samples D (3.4 wt% TiO2/3.3 wt% Al(OH)3/3.3 wt% Mg(OH)2) and E (2.5 wt% TiO2/2.5 wt% Al(OH)3/2.5 wt% Mg(OH)2/2.5 wt% CES) applied at a thickness of 1.5 ± 0.2 mm achieved the lowest fire propagation index with a value of 4.5 and 5.0, respectively (BS 476 Part 6, Class 0 materials) which indicates excellent fire-stopping properties. The results showed that the coatings were effective in fire protection, with good qualities of water resistance, thermal stability, and adhesion strength. Significantly, coating E (with CES) has proved to be efficient in the protection of plywood against fire.

a b s t r a c t A combination of acrylic binder and flame-retardant ingredients was used to synthesize the solvent-borne intumescent coatings designed for steel substrates. The influences of individual and various combinations of flame-retardant fillers on the fire protection and mechanical properties of the coatings were character- ized by using Bunsen burner, thermogravimetric analysis, limiting oxygen index, field emission scanning electron microscopy, freeze-thaw cycles, static immersion and pull-off type equipment. It was found that the combination of aluminium hydroxide (Al(OH)3) and titanium dioxide (TiO2) has significantly improved the fire protection, thermal stability and water resistance of the coating. This formulation had an LOI value of 34, which indicated good flammability resistance of the coating. The adhesion strength tests showed that the coating added with magnesium hydroxide (Mg(OH)2) exhibited maximum bonding strength to the metal surface due to its effective interface adhesion. Hence, the findings from this study revealed that the selection of appropriate combinations of flame-retardant fillers strongly influenced the physical and chemical properties of the coatings.

Reinforced concrete (RC) structures require strengthening for numerous factors, such as increased load, modification of the structural systems, structural upgrade or errors in the design and construction stages. The side near-surface mounted (SNSM) strengthening technique with glass fiber-reinforced polymer (GFRP) bars is a relatively new emerging technique for enhancing the flexural capacities of existing RC elements. Nine RC rectangular beams were flexurally strengthened with this technique and tested under four-point bending loads until failure. The main goal of this study is to optimize the structural capacity of the RC beams by varying the amount of strengthening reinforcement and bond length. The experimental test results showed that strengthening with SNSM GFRP bars significantly enhanced the flexural responses of the specimens compared with the control specimen. The first cracking and ultimate loads, energy absorption capacities, ductility and stiffness were remarkably enhanced by the SNSM technique. It was also confirmed that the bond length of the strengthened reinforcement greatly influences the energy absorption capacities, ductility and stiffness. The effect of the bond length on these properties is more significant compared to the amount of strengthening reinforcement.

The type of frame system, materials, and power consumption used for the construction of new buildings cause environmental issues because of the production of carbon dioxide (CO2) emissions. Therefore, a new type of sustainable precast concrete structural system called SMART frame has been introduced to reduce the CO2 emissions during the construction of buildings. To determine the effectiveness of the CO2 emission reduction based on the new SMART frame, a similar frame configuration based on reinforced concrete (RC) was used. The SMART and RC building frames consisted of 12 storeys with similar floor areas and were designed under similar conditions. The CO2 emissions based on the material resources and construction methods used for the two building models were analysed. Additionally, the power consumption associated with the use of electricity and fuels for the devices and equipment was considered in the analysis of the total CO2 emissions. The total CO2 emissions of the SMART and RC frame buildings in kilograms (kg) per square meter (m2) are 455.94 and 516.12 kg CO2/m2, respectively. Thus, the total amount of CO2 emission reduction achieved in this study is 60.18 kg CO2/m2. In terms of the individual effects of materials and power consumption, the SMART building has a larger contribution, accounting for a 12.42% and 8.12% decrease in the CO2 emissions, respectively, compared with the RC building. Overall, based on the materials and power consumption used during the construction stage of the SMART frame building, the total CO2 emissions decreased by 11.66% compared with the RC building. Therefore, the SMART frame can be adopted as a sustainable frame alternative to the RC frame system.

This research strives to develop a high-temperature resistant lightweight aggregate (LWA) mortar skin layer for use in sandwich concrete composite. The first phase of the research was focused on the development of the LWA mortar while the subsequent phase of work dealt with assessing the performance of the resulting sandwich concrete composite. In phase 1 of the investigation, it was found that mortar incorporating calcium aluminate cement (CAC) as binder and lightweight expanded clay aggregate (LECA) as fine aggregate had the best resistance towards high temperature of 1000 °C. The developed mortar along with basalt fibre mesh were used to form textile reinforced concrete (TRC) as skin layer which could still exhibit residual strength upon heated to high temperature. Furthermore, sandwich composite beam made of the TRC skin and aerated concrete as core had better flexural strength/weight ratio compared to that using conventional EPS foam as the core material. There was also no significant damage found on the sandwich concrete composite upon exposure to direct flame. The findings suggest that the development of the sandwich concrete composite is promising and further works can be explored to improve the performance.

Precast construction of structural buildings requires connection techniques that can shorten the process using only simple on-site activities while still guaranteeing adequate strength, energy dissipation, stiffness, and ductility. The construction methods should decrease the use of formwork and temporary bracing to save time and costs. In this study, innovative hybrid connections using steel tubes, steel plates, and steel couplers to join beams and columns were proposed and tested under reversed cyclic loading. Five half-scale samples of the hybrid precast joints, including the monolithic and precast joints, were examined to evaluate the seismic performance of the connections. The hybrid connections showed better performance in terms of load, displacement, drift ratio, ductility, strength, stiffness, and energy dissipation compared to a monolithic connection. The drift ratio, moment capacity, strength, and total cumulative energy dissipation of the hybrid connections were higher by 12.5–50.0%, 34.68–59.57%, 35.0–60.0%, and 50.99–331.32%, respectively, when compared with a monolithic connection. The failure modes of the hybrid connections were governed by yielding steel reinforcement, yielding steel plate, and flexural failure, with less extensive damage compared to the monolithic joint. The hybrid connections were effective in shifting the plastic hinges to outside the connection zone. Therefore, the hybrid connections can be used in high seismic zones because the superior performance results meet the requirements of the seismic codes.

This paper presents an investigation on solvent-borne intumescent flame-retardant coatings that can provide good bonding strength, water resistance and fire protection to the steel substrate. The fire protection performance and characterisations of the coatings were investigated by using the Bunsen burner test, thermogravimetry analysis, field emission scanning electron microscope, static immersion test and Instron Micro Tester. It was found that the fire protection and foam structure of the coating significantly improved by adding the combination of Mg(OH)2 and TiO2 flame-retardant fillers to the flame-retardant additives and acrylic binder. The formation of uniform foam structure and reaction of the coating which decompose into voluminous and multicellular char layers with thermal insulation properties contribute an important fire protection to the steel substrate from reaching its critical temperature. However, the combination of [Al(OH)3 and Mg(OH)2] flame-retardant fillers to the flame-retardant additives and epoxy binder led to maximum adhesion strength. The improvement in the bonding properties of the coating to the metal surface was attributed to the effective [Mg(OH)2 and TiO2] fillers/epoxy binder interface adhesion. Hence, the findings of this study reveal that the selection of appropriate combination of binders and flame-retardant fillers strongly influenced the fire protection, water resistance and mechanical properties of intumescent coatings.

To inspect the fatigue energy dissipation of angle shear connectors under fully reversed cyclic fatigue loading while embedded in a high strength concrete (HSC) slab, a series of experimental push-out tests was conducted. The experimental tests comprised eight push-out test specimens with different geometries of angle connector. The failure of the angle connector under monotonic and low cyclic fatigue loading was tested and the observations were discussed. The results show that the ductility performance for angle shear connectors embedded in HSC was inadequate. However, reasonable strength resistance under monotonic loading and a small amount of fatigue energy dissipation under cyclic fatigue loading for connector was detected. All push-out test specimens experienced connector fracture failure with very low energy dissipation when subjected to fatigue loading. Details of the failure analysis and fatigue energy dissipation of the angles in HSC are fully described in the results.

The strengthening reinforcement is glued to the soffit of the reinforced concrete (RC) beams in the mainstream externally bonded reinforcement (EBR) technique for flexural strengthening. However, the soffit of RC beams could be inaccessible for strengthening due to limited or no space at the soffit because of walls or doors, or the spalling of concrete. To overcome such difficulties, this paper investigates the feasibility of the flexural strengthening of lightweight non-pre-cracked and pre-cracked reinforced concrete (RC) beams using the side externally bonded reinforcement (S-EBR) technique with carbon fiber reinforced polymer (CFRP) fabric. A total of eight full-sized RC specimens were fabricated, strengthened, and tested under four-point loading until failure. The test variables were the internal reinforcement ratio, percentage of pre-cracking loads, and the effect of cracking loads on the flexural performance. The loads, deflection, and ultimate failure of the specimens were recorded and the types of modes of failure were also observed. The S-EBR strengthening technique with CFRP fabric significantly enhanced the flexural capacity of non-pre-cracked and pre-cracked lightweight RC beams compared to the control specimen. An analytical model in accordance with ACI 440.2R-08 was developed to verify the experimental results. The flexural capacity predicted by the model was in reasonable agreement with the experimental results.

An experimental study was performed to investigate the behaviour of angle shear connectors embedded in high strength concrete (HSC) slab. Eight push-out specimens were tested covering various geometries of angle shear connector. On top of the experimental study, the accuracy of the available equations to estimate the load capacities of angle connectors is also evaluated for the angles embedded in HSC. The results show inadequate ductility behaviour for the angle shear connectors embedded in HSC. Nonetheless, the angle connectors exhibited good behaviour in the case of strength degradation under cyclic loading. All specimens experienced the angle fracture type of failure and showed a very low strength degradation (0.1%–1.4%) when they were subjected to low cyclic fatigue loading. This study also concludes that the current available equations estimated the shear capacity of angle connectors embedded in HSC either are conservative or overestimate the ultimate capacity.

In recent decades, the application of fibre-reinforced polymer (FRP) composites for strengthening structural elements has become an efficient option to meet the increased cyclic loads or repair due to corrosion or fatigue cracking. Hence, the objective of this study is to explore the existing FRP reinforcing techniques to care for fatigue damaged structural steel elements. This study covers the surface treatment techniques, adhesive curing, and support conditions under cyclic loading including fatigue performance, crack propagation, and failure modes with finite element (FE) simulation of the steel bridge girders and structural elements. FRP strengthening composites delay initial cracking, reduce the crack growth rate, extend the fatigue life, and decrease the stiffness decay with residual deflection. Prestressed carbon fibre-reinforced polymer (CFRP) is the best strengthening option. End anchorage prevents debonding of the CRRP strips at the beam ends by reducing the local interfacial shear and peel stresses. Hybrid-joint, nanoadhesive, and carbon-flex can also be attractive for strengthening systems.

Cool roof systems play a significant role in enhancing the comfort level of occupants by reducing the attic temperature of the building. Heat transmission through the roof can be reduced by applying thermal insulation coating (TIC) on the roof and/or installing insulation under the roof of the attic. This paper focuses on a TIC integrated with a series of aluminium tubes that are installed on the underside of the metal roof. In this study, the recycled aluminium cans were arranged into tubes that act as a moving-air-cavity (MAC). The TIC was formulated using titanium dioxide pigment with chicken eggshell (CES) waste as bio-filler bound together by a polyurethane resin binder. The thermal conductivity of the thermal insulation paint was measured using KD2 Pro Thermal Properties Analyzer. Four types of cool roof systems were designed and the performances were evaluated. The experimental works were carried out indoors by using halogen light bulbs followed by comparison of the roof and attic temperatures. The temperature of the surrounding air during testing was approximately 27.5 C. The cool roof that incorporated both TIC and MAC with opened attic inlet showed a significant improvement with a reduction of up to 13 C (from 42.4 C to 29.6 C) in the attic temperature compared to the conventional roof system. The significant difference in the results is due to the low thermal conductivity of the thermal insulation paint (0.107 W/mK) as well as the usage of aluminium tubes in the roof cavity that was able to transfer heat efficiently.

a b s t r a c t The objective of this study was to evaluate the effect of chicken eggshell (ES) as a bio-filler on the adhe- sion strength and thermal stability of acrylic coatings. The influence of different particle sizes of ES on the performance of acrylic coatings was compared with commercial calcium carbonate filler by using thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and pull-off type equipment. The surface morphologies of the coatings were characterized through field emission scanning electron microscopy (FESEM). The resistance of the coating was also investigated using water immersion and freeze-thaw tests. Morphological studies revealed that the ES filler was well-distributed in the poly- mer matrix. Furthermore, it was observed that the adhesion strength, thermal properties, water and freeze-thaw resistance of the coating improved with decrease in particle size of ES filler. Overall, the best results were obtained from using ES bio-filler with the smallest particle, although the particle size was bigger than that of commercial calcium carbonate. The improvement in the properties of the coating was attributed to the even distribution of ES particles and better ES/matrix interface.