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Composite beams comprising of concrete slabs and steel beams joined by conventional headed stud shear connectors are commonly used in modern steel-framed building construction. However, because the headed stud shear connectors are welded onto the top flange of the steel beam and cast into the in situ concrete slab, deconstruction of the composite beam and the reuse of its components at the end of structural life in defence to demolition is virtually impossible, which is at odds with the increasing demands placed on improving the sustainability of building infrastructure. As an alternative, an innovative sustainable composite beam and slab system is proposed, in which precast geopolymer concrete panels are attached to the steel beams using high-strength friction-grip bolts instead of cast in situ floors with pre-welded headed stud connectors. The advantages of a low-carbon design, both by the use of geopolymer concrete elements and system deconstructability, can be achieved in this proposed system. In this paper, a three-dimensional finite element model is developed to investigate the structural behaviour of the proposed sustainable composite beam and slab system. Material non-linearities and the interaction of the structural components are included in the model. The accuracy and reliability of the finite element formulation developed are validated by comparisons with experimental results. Extensive parametric studies are conducted to elucidate the effects of the change in the concrete panel configuration, the number and diameter of the bolts, the type and strength of the concrete and the grade of the steel beam on the behaviour of the system. The use of modified rigid plastic analysis is assessed, and a modification is suggested to predict the flexural strengths of the composite beams and slab system. [ABSTRACT FROM AUTHOR]

Abstract: This paper investigates the time-dependent creep and shrinkage behaviour of horizontally curved steel–concrete composite beams, including the partial interaction existing between the concrete deck and the steel girder. The flexibility of the shear connection in the radial direction, as well as in the tangential direction at the steel and concrete interface, are taken into account in the proposed formulation. The creep and shrinkage effects of the concrete deck including concrete aging effects are considered by using the analytic Age-adjusted Effective Modulus Method (AEMM). This method is efficient in converting the creep analysis into pseudo-elastic analysis. The accuracy and efficiency of the proposed approach is validated by comparing its results with available experimental results reported in the literature and those based on a more sophisticated but computationally less efficient ABAQUS shell finite element model. The effects of initial curvature and partial interaction on the time-dependent behaviour of curved composite beams under serviceability conditions are also elucidated and the slip effect due to warping is examined. [Copyright &y& Elsevier]

This paper presents a three-dimensional finite element modelling of an innovative flush end plate semi-rigid beam-to-column composite joint comprising deconstructable post-installed friction-grip bolted shear connectors. The moment versus rotation relationship for these prototype joints subjected to a hogging bending moment with the influence of partial shear connection is investigated using ABAQUS software. This relationship is an indicator of the ductility of a composite joint and is a necessity for a semi-rigid frame analysis. A detailed finite element model of the connection region including the precast concrete slab, steel beam, flush end-plate, bolted shear connectors and the steel column is developed in the paper. Material and geometrical non-linearities as well as the non-linearity of the interfaces are incorporated in the model. The accuracy and reliability of the numerical formulation are verified against experimental data reported elsewhere. In addition, a composite joint with partial shear connection is constructed and tested in this study, and the numerical predictions are compared with the test results. An extensive parametric study is then conducted, using several parameters that include the degree of shear connection, reinforcement ratio, thickness of the precast concrete slab, spacing of bolted shear connectors, size of the bolts in the connection zone, thickness of the flush end plate, steel grade for the beam, column and end plate and the column flange thickness. Finally, moment versus rotation models for deconstructable flush end plate beam-to-column composite joint are proposed, and it is demonstrated that the design models developed can also be used for composite joints with high strength steel components. [ABSTRACT FROM AUTHOR]

• LC sheet is characterised by a rounded stress–strain response with two "knee" regions. • A simplified full-range engineering stress–strain model for LC sheets is proposed. • An average weight method is used to determine post-necking true stress–strain curves. • Recommended values of weight factor and toughness coefficient for LC sheets are obtained. Laser cladding (LC) is being used increasingly in civil engineering owing to its high efficiency and minimal distortion since requiring little heat input; especially for repairing or strengthening damaged metal structures. LC stainless steel sheets are characterised by a rounded stress–strain response, with two "knee" regions and no sharply defined yield point. Such behaviour cannot be accurately represented by using previous stress–strain models. Moreover, determining the true stress–strain curve and toughness coefficient for the fracture model is essential to carry out a non-linear finite element analysis for solving elastoplastic problems. In the present study, one simplified full-range engineering stress–strain model for LC 316L stainless steel sheets is proposed based on the three-stage Hradil model and is validated against the experimental results of thirty tensile coupon tests. The proposed model redefines the second and third stages of the stress–strain curve following the experimental observations. All parameters in this simplified model can be derived directly from only four basic material property parameters: the initial elastic modulus, 0.2 % proof stress, ultimate stress and the strain corresponding to the ultimate stress. For defining the fracture model of LC stainless steel sheets, an average weight method is employed to determine the post-necking true stress–strain curves. The recommended values of the weight factor and toughness coefficient for the LC sheets are also obtained based on the available tensile coupon test results. The comparisons between the experimental force–displacement curves of the tensile coupons and the finite element analysis results using the proposed stress–strain relationship and fracture model for the LC sheets shows both results to be in good agreement. Therefore, the stress–strain relationship and fracture model proposed in this paper is suitable for use in the analytical and numerical modelling of structures having LC 316L stainless steel sheets. [ABSTRACT FROM AUTHOR]

• Residual stress in steel column repaired by LC is measured using blind-hole method. • RS values in both the LC sheet and substrate are less than their respective yield strength values. • RS in LC sheet is much greater than that in substrate located far away from LC sheet. • A simplified RS model was developed by introducing the linear-exponential two-stage cooling curve. • RS results predicted by simplified RS model are in good agreement with experimental results. This paper presents a study that investigates the magnitude and distribution of residual stress (RS) in laser cladding (LC) repaired circular steel tubular columns. The study involves experimental tests and numerical simulation. The familiar blind-hole method is employed in the experimental investigation for two RS measurement tests, while the finite element method is used for numerical thermal-mechanical analysis to obtain the temperature field and RS field. The results indicate the presence of residual tensile stress in the LC sheet and its surrounding area. The RS in the LC sheet area and in the vicinity of the LC sheet-substrate boundary is much greater than that in the substrate area located far away from the LC sheet. Additionally, the RS in the LC sheet along the scanning direction is larger than that perpendicular to the scanning direction. Nevertheless, the RS values in both the LC sheet and substrate are less than their respective yield strength values. The temperature-time cooling curves obtained from the finite element analysis, which simulate the laser cladding process for repairing the circular steel tubular column, are used to develop a theoretical model for predicting the RS in the LC sheet. A simplified RS model is proposed based on the thermal-mechanical theory, utilising the linear-exponential two-stage cooling curve. Comparisons between the experimental results and the theoretical results that are predicted using the proposed simplified RS model show both results to be in good agreement. Therefore, the simplified RS model proposed in this paper is suitable for efficiently and accurately predicting the RS in LC sheet for circular steel tubular columns repaired by LC. [ABSTRACT FROM AUTHOR]

• Locally corroded steel structures were repaired by laser cladding (LC) additive manufacturing technology. • The stiffness, strength, and geometric dimensions of repaired member are almost the same as those of original intact member. • LC repair technique significantly reduces strain concentration due to local corrosion. • Using LC repair technique can prevent local buckling due to local corrosion. • A FE model is developed to accurately describe axial behaviour of repaired member. Surface damage, such as corrosion, fatigue, and impact, poses a serious threat to the service life and safety of steel structures. To address this issue, this study employed the laser cladding (LC) additive manufacturing technology as a novel repair method for damaged steel structures. The aim was to achieve a "restored repair" that restores the stiffness, strength, and geometric dimensions of the repaired member to those of the original intact member. To evaluate the effectiveness of the LC repair method, axial compression tests were conducted on six circular steel tube columns, including one intact specimen, one corroded specimen and four repaired specimens. The study focused on the steel tubes with mid-height surface corrosion and also investigated the influence of corrosion angle, corrosion depth, and repair material on the mechanical behaviour of the repaired members. The experimental results showed that the stiffness and strength of the repaired compression members were restored and even slightly enhanced compared with those of the corroded member. The strain analysis indicated that the LC repair technique could significantly reduce stress/strain concentration caused by local corrosion. Furthermore, finite element models for simulating the axial compressive behaviour of repaired circular steel tube columns were developed and validated by comparing the experimental and numerical results. The findings of the paper confirm that the proposed LC strengthening method provides an additional solution for effectively repairing damaged steel structures. [ABSTRACT FROM AUTHOR]

It is an effective solution to strengthen structural column by using steel jacket and infill concrete for reinforced concrete (RC) structure retrofitting. In this research, the recycled aggregate concrete (RAC) is adopted as an infill concrete instead of using the normal concrete, in order to reduce the carbon footprint of construction. Fifteen columns including twelve steel-jacket strengthened columns, one unstrengthened column and two concrete filled steel tube (CFST) columns are tested to investigate the axial compressive behaviour of steel-jacket retrofitted RC columns with RAC. The variables among the tested specimens include the recycled coarse aggregate replacement ratio, RAC strength, steel tube thickness and preload of original column. Experimental results illustrate that using steel jacketing approach for retrofitting could significantly improve the strength, stiffness and ductility of the columns. The axial compressive strength of the steel-jacket retrofitted column with RAC is slightly lower than the one with normal infill concrete, but the influence of recycled coarse aggregate replacement ratios is negligible. The peak strengths of steel-jacket retrofitted columns can be significantly enhanced by increasing the thickness of steel tube. The performances of the steel-jacket retrofitted columns are similar to that of the CFST columns. The effect of the preload of original column on the ultimate strength of steel-jacket retrofitted column is limited. A finite element (FE) model is also developed by using ABAQUS software to simulate the performance of steel-jacket retrofitted columns. The accuracy of the model is validated through comparing with the experimental results. By using the developed FE model, the mechanical behaviour of the column is further discussed in details and extended parametric studies are undertaken to elucidate the effects of various influencing factors on the behaviour of the column and its components. The design methods for predicting the axial compressive strength of the retrofitted column with RAC are suggested. [ABSTRACT FROM AUTHOR]

This paper investigates the seismic behaviour of a new type of through-beam connection between a square concrete-filled steel tubular (CFST) column and a reinforced concrete (RC) beam. In this new connection system, the steel stub is completely interrupted in the connection zone, with longitudinal steel bars of the frame beam being continuous through this zone. The connection incorporates a strengthening joint system with a steel cage consisting of multi-layer steel meshes and radial pattern stirrups to compensate the possible decrease of strength of connection due to the interruption of the steel tube. The connection is rigid with the integrity and continuity of the columns and beams. Cyclic loading tests on five beam-column specimens are conducted to evaluate this new connection. The hysteretic response, the skeletal and load–deflection curves, the strain, ductility, strength and the stiffness degradation and energy dissipation are obtained. Experimental results demonstrate the favourable seismic performance of the connection including their superior ductility and energy dissipation capacity. A sophisticated solid finite element model is developed and verified by comparing with the experimental results, and being applied for further parametric studies. A simple fibre finite model using OpenSEES is also proposed and the efficiency and accuracy of the model are illustrated. [ABSTRACT FROM AUTHOR]