Experimental and numerical study on the lateral torsional buckling of full-scale steel-timber composite beams

The lateral torsional buckling (LTB) of steel-timber composite (STC) beam with partial interaction was investigated in this paper. The composite beam is constructed by connecting the timber to both flanges of the H-shaped steel with bolts or screws. Twelve push-out specimens were designed to evaluate the shear performance of bolt or screw connectors. It was shown that the slip stiffness and the shear bearing capacity of the connectors increased with the thickness of timber increasing. Then, eight full-scale composite beams with lengths of 6000 mm were studied through bending tests and compared to a bare steel beam. The experimental behaviors of the specimens were identified, including the failure mode, load-deflection relationship and load-strain response. The LTB phenomenon and composite action were discussed by analyzing the strain distribution, stiffness and strength. The results demonstrated that the STC beams fastened with bolts or screws displayed partial composite action. Although the stiffness of the composite beam showed little augmentation, the maximum strength of the composite beam substantially increased by suppressing the LTB phenomenon. A finite element analysis was conducted to reveal the failure mechanism of the specimens with different geometric and physical parameters, including the number of timber layers, the interface shear stiffness and the initial imperfection. It was found that increasing the number of timber layers in the upper flange suppressed the lateral torsional buckling, and the interface shear stiffness was the key factor to control the stiffness and failure modes of STC beams.

REVIEW OF VARIOUS SHEAR CONNECTORS IN COMPOSITE STRUCTURES

Shear connectors are devices that provide shear connection at the interface of steel girders and reinforced concrete slabs in composite structures to accomplish composite action in a flexure. The seismic response of composite structures can be controlled using properly designed shear connectors. This state-of-the-art review article presents considerable information about the distinct types of shear connectors employed in composite structures. Various types of shear connectors, their uniqueness and characteristics, testing methods and findings obtained during the last decade are reviewed. The literature, efficacy, and applicability of the different categories of shear connectors, for example, headed studs, perfobond ribs, fibre reinforced polymer perfobonds, channels, pipes, Hilti X-HVB, composite dowels, demountable bolted shear connectors, and shear connectors in composite column are thoroughly studied. The conclusions made provide a response to the flow of the use of shear connectors for their behaviours, strength, and stiffness to achieve composite action.

Finite Model Analysis and Practical Design Equations of Circular Concrete-Filled Steel Tube Columns Subjected to Compression-Torsion Load

The objective of this study is to investigate the mechanical properties and the composite action of circular concrete-filled steel tube (CFST) columns subjected to compression-torsion load using finite element model analysis. Load–strain (T–γ) curves, normal stress, shear stress, and the composite action between the steel tubes and the interior concrete were analyzed based on the verified 3D finite element models. The results indicate that with the increase of axial force, the maximum shear stress at the core concrete increased significantly, and the maximum shear stress of the steel tubes gradually decreased. Meanwhile, the torsional bearing capacity of the column increased at first and then decreased. The torque share in the columns changed from the tube-sharing domain to the concrete-sharing domain, while the axial force of the steel tube remained unchanged. Practical design equations for the torsional capacity of axially loaded circular CFST columns were proposed based on the parametric analysis. The accuracy and validity of the proposed equations were verified against the collected experimental results.

Structural performance of sandwich wall made of concrete cast in between GFRP facings

The structural performance of concrete walls reinforced with pultruded glass fibre-reinforced polymer (GFRP) ribbed plates on either side has been experimentally investigated. The GFRP plates were used as a stay-in-place (SIP) structural formwork replacing internal steel reinforcement. The pultruded flat plates incorporated 51 mm deep T-shape ribs on one side, spaced at 100 mm, which provided interlocking with concrete. Six 3000 × 616 mm panels, either 150 or 200 mm thick, were tested in bending ( M), under axial compression ( N) and under combined loads to establish the completed ( M- N) failure envelope of the wall. The effect of surface treatment of the GFRP forms was also investigated. It resulted in full composite action with no concrete slip, reaching 30% higher flexural strength than untreated panels. The effect of reinforcement ratio was studied by varying wall thickness. In all panel tests, diagonal concrete shear cracking occurred and propagated into a horizontal delamination above the GFRP ribs. Slenderness effect and secondary moments were accounted for in developing the ( M- N) interaction curve. Initially, M increased by 25% as N increased from zero to 17% of pure axial strength. Then, M reduced linearly to zero at pure N as concrete crushing occurred when the GFRP compression plate separated from the ribs and buckled outwards at midspan. A simplified design approach is also presented.

Strength Capacity and Failure Mode of Shear Connectors Suitable for Composite Cold Formed Steel Beams: Numerical Study

In this paper, the findings of numerical modeling of the composite action between normal concrete and Cold-Formed Steel (CFS) beams are presented. To obtain comprehensive structural behavior, the numerical model was designed using 3-D brick components. The simulation results were correlated to the experimental results of eight push tests, using three types of innovative shear connectors in addition to standard headed stud shear connectors, with two different thicknesses of a CFS channel beam. The proposed numerical model was found to be capable of simulating the failure mode of the push test as well as the behavior of shear connectors in order to provide composite action between the cold-formed steel beam and concrete using the concrete damaged plasticity model.

Experimental study on the flexural behavior of structural insulated sandwich timber panels

A series of flexural test and creep tests were conducted on 53 OSB structural insulated sandwich timber panels to predict their behavior when subjected to gravity loading when used in residential and low rise nonresidential buildings. The experiments were designed and performed to test full-scale panels for roof and floor residential construction. The structural adequacy of the developed sandwich panel system is investigated with respect to the effectiveness of the foam core in providing composite action required to meet both strength and serviceability limit-state design reruirements per Canadian Standards for timber design. Strength requirements included flexure and shear, while serviceability check included limiting deflection under operating conditions as well as creep performance under sustained loading. Results from experimental testing were used to draw conclusions with respect the structural qualifications for these SIPs to be "as good as" the structural capacity of conventional wood-frame buildings

Experimental study on the flexural behavior of structural insulated sandwich timber panels

A series of flexural test and creep tests were conducted on 53 OSB structural insulated sandwich timber panels to predict their behavior when subjected to gravity loading when used in residential and low rise nonresidential buildings. The experiments were designed and performed to test full-scale panels for roof and floor residential construction. The structural adequacy of the developed sandwich panel system is investigated with respect to the effectiveness of the foam core in providing composite action required to meet both strength and serviceability limit-state design reruirements per Canadian Standards for timber design. Strength requirements included flexure and shear, while serviceability check included limiting deflection under operating conditions as well as creep performance under sustained loading. Results from experimental testing were used to draw conclusions with respect the structural qualifications for these SIPs to be "as good as" the structural capacity of conventional wood-frame buildings