Pertinent issues on the strength design of steel structures to AS4100-1998

Mark A. Bradford 국제구조공학회 2005 Steel and Composite Structures, An International J Vol.5 No.2

This paper describes of an overview to the strength rules in the Australian AS4100 Steel Structures Code that was first issued in Limit States Format in 1990. It focuses on pertinent and characteristic issues, such as the means of analysis for second order effects in frames, and highlights how the tiered approach may lead to efficient design using advanced analysis techniques. It also considers design against buckling in some detail, and shows how advanced solutions may be readily incorporated into the design rules. Implicit in the formulations are the necessity for ductility of the steel, and the scope of the code is limited to steels that display this necessary ductility characteristic.

Inelastic lateral-distortional buckling of continuously restrained rolled I-beams

Mark A. Bradford,Dong-Sik Lee 국제구조공학회 2002 Steel and Composite Structures, An International J Vol.2 No.4

An energy method of analysis is presented which can be used to study the inelastic lateral-distortional buckling of hot-rolled I-sections continuously restrained at the level of the tension flange. The numerical modelling leads to the incremental and iterative solution of a fourth-order eigenproblem, with vey rapid solutions being obtainable, so as to enable a study of the factors that influence the strength of continuously restained I-beams to be made. Although hot-rolled I-scetions generally have stocky webs and are not susceptible to reductions in their overall buckling loads as a result of cross-sectional distortion, the effect of elastic restraints, particulartly against twist rotation, can lead to buckling modes in which the effect of distortion is quite severe. While the phenomenon has been studied previously for elastic lateral-distortional buckling, it is extended in this paper to include the constitutive relationship characteristics of mild steel, and incorporates both the so-called 'polynomial' and 'simplified' models of residual stresses. The method is validated against inelastic lateral-torsional buckling solutions reported in previous studies, and is applied to illustrate some inelastic buckling problems. It is noted that over a certain range of memeber slenderness the provisions of the Australian AS4100 steel standard are unconservative.

Retrofitting by adhesive bonding steel plates to the sides of R.C. beams. Part 1: Debonding of plates due to flexure

Oehlers, Deric. J.,Nguyen, Ninh T.,Bradford, Mark A. Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.9 No.5

A convenient method for enhancing the strength and stiffness of existing reinforced concrete beams is to bond adhesively steel plates to their tension faces. However, there is a limit to the applicability of tension face plating as the tension face plates are prone to premature debonding and, furthermore, the addition of the plate reduces the ductility of the beam. An alternative approach to tension face plating is to bond adhesively steel plates to the sides of reinforced concrete beams, as side plates are less prone to debonding and can allow the beam to remain ductile. Debonding at the ends of the side plates due to flexural forces, that is flexural peeling, is studied in this paper. A fundamental mathematical model for flexural peeling is developed, which is calibrated experimentally to produce design rules for preventing premature debonding of the plate-ends due to flexural forces. In the companion paper, the effect of shear forces on flexural peeling is quantified to produce design rules that are applied to the strengthening and stiffening of continuous reinforced concrete beams.

Nonlinear P-Δ analysis of steel frames with semi-rigid connections

Hamid R. Valipour,Mark A. Bradford 국제구조공학회 2013 Steel and Composite Structures, An International J Vol.14 No.1

This paper presents the formulation for a novel force-based 1-D compound-element that captures both material and second order P-Δ nonlinearities in steel frames. At the nodal points, the element is attached to nonlinear rotational and a translational springs which represent the flexural and axial stiffness of the connections respectively. By decomposing the total strain in the material as well as the generalised displacements of the flexible connections to their elastic and inelastic components, a secant solution strategy based on a direct iterative scheme is introduced and the corresponding solution strategy is outlined. The strain and slope of the deformed element are assumed to be small; however the equilibrium equations are satisfied for the deformed element taking account of P-Δ effects. The formulation accuracy and efficiency is verified by some numerical examples on the nonlinear static, cyclic and dynamic analysis of steel frames.

Static behaviour of multi-row stud shear connectors in high- strength concrete

Qing-Tian Su,Guotao Yang,Mark A. Bradford 국제구조공학회 2014 Steel and Composite Structures, An International J Vol.17 No.6

In regions of high shear forces in composite bridges, headed stud shear connectors need to be arranged with a small spacing in order to satisfy the design requirement of resisting the high interface shear force present at this location. Despite this, studies related to groups of headed studs are somewhat rare. This paper presents an investigation of the static behaviour of grouped stud shear connectors in high-strength concrete. Descriptions are given of five push-out test specimens with different arrangements of the studs that were fabricated and tested, and the failure modes, load-slip response, ultimate load capacities and related slip values that were obtained are reported. It is found that the load-slip equation given by some researchers based on a single stud shear connector in normal strength concrete do not apply to grouped stud shear connectors in high-strength concrete, and an algebraic load-slip expression is proposed based on the test results. Comparisons between the test results and the formulae provided by some national codes show that the equations for the ultimate capacity provided in these codes are conservative when used for connectors in high-strength concrete. A reduction coefficient is proposed to take into account the effect of the studs being in a group.

Experimental and numerical investigations on remaining strengths of damaged parabolic steel tubular arches

Yonghui Huang,Airong Liu,Yong-Lin Pi,Mark A. Bradford,Jiyang Fu 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.1

This paper presents experimental and numerical studies on effects of local damages on the in-plane elastic-plastic buckling and strength of a fixed parabolic steel tubular arch under a vertical load distributed uniformly over its span, which have not been reported in the literature hitherto. The in-plane structural behaviour and strength of ten specimens with different local damages are investigated experimentally. A finite element (FE) model for damaged steel tubular arches is established and is validated by the test results. The FE model is then used to conduct parametric studies on effects of the damage location, depth and length on the strength of steel arches. The experimental results and FE parametric studies show that effects of damages at the arch end on the strength of the arch are more significant than those of damages at other locations of the arch, and that effects of the damage depth on the strength of arches are most significant among those of the damage length. It is also found that the failure modes of a damaged steel tubular arch are much related to its initial geometric imperfections. The experimental results and extensive FE results show that when the effective cross-section considering local damages is used in calculating the modified slenderness of arches, the column bucking curve b in GB50017 or Eurocode3 can be used for assessing the remaining in-plane strength of locally damaged parabolic steel tubular arches under uniform compression. Furthermore, a useful interaction equation for assessing the remaining in-plane strength of damaged steel tubular arches that are subjected to the combined bending and axial compression is also proposed based on the validated FE models. It is shown that the proposed interaction equation can provide lower bound assessments for the remaining strength of damaged arches under in-plane general loading.

Long-term structural analysis and stability assessment of three-pinned CFST arches accounting for geometric nonlinearity

Kai Luo,Yong-Lin Pi,Wei Gao,Mark A.Bradford 국제구조공학회 2016 Steel and Composite Structures, An International J Vol.20 No.2

Due to creep and shrinkage of the concrete core, concrete-filled steel tubular (CFST) arches continue to deform in the long-term under sustained loads. This paper presents analytical investigations of the effects of geometric nonlinearity on the long-term in-plane structural performance and stability of three-pinned CFST circular arches under a sustained uniform radial load. Non-linear long-term analysis is conducted and compared with its linear counterpart. It is found that the linear analysis predicts long-term increases of deformations of the CFST arches, but does not predict any long-term changes of the internal actions. However, non-linear analysis predicts not only more significant long-term increases of deformations, but also significant long-term increases of internal actions under the same sustained load. As a result, a three-pinned CFST arch satisfying the serviceability limit state predicted by the linear analysis may violate the serviceability requirement when its geometric nonlinearity is considered. It is also shown that the geometric nonlinearity greatly reduces the long-term in-plane stability of three-pinned CFST arches under the sustained load. A three-pinned CFST arch satisfying the stability limit state predicted by linear analysis in the long-term may lose its stability because of its geometric nonlinearity. Hence, non-linear analysis is needed for correctly predicting the long-term structural behaviour and stability of three-pinned CFST arches under the sustained load. The non-linear long-term behaviour and stability of three-pinned CFST arches are compared with those of twopinned counterparts. The linear and non-linear analyses for the long-term behaviour and stability are validated by the finite element method.

Retrofitting by adhesive bonding steel plates to the sides of R.C. beams. Part 2: Debonding of plates due to shear and design rules

Oehlers, Deric. J.,Nguyen, Ninh T.,Bradford, Mark A. Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.9 No.5

A major cause of premature debonding of tension face plates is shear peeling (Jones et al. 1988, Swamy et al. 1989, Ziraba et al. 1994, Zhang et al. 1995), that is debonding at the plate ends that is associated with the formation of shear diagonal cracks that are caused by the action of vertical shear forces. It is shown in this paper how side plated beams are less prone to shear peeling than tension face plated beams, as the side plate automatically increases the resistance of the reinforced concrete beam to shear peeling. Tests are used to determine the increase in the shear peeling resistance that the side plates provide, and also the effect of vertical shear forces on the pure flexural peeling strength that was determined in the companion paper. Design rules are then developed to prevent premature debonding of the plate ends due to peeling and they are applied to the strengthening and stiffening of continuous reinforced concrete beams. It is shown how these design rules for side plated beams can be adapted to allow for propped and unpropped construction and the time effects of creep and shrinkage, and how side plates can be used in conjunction with tension face plates.

Treatment of locking behaviour for displacement-based finite element analysis of composite beams

R. Emre Erkmen,Mark A. Bradford,Keith Crews 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.1

In the displacement based finite element analysis of composite beams that consist of two Euler-Bernoulli beams juxtaposed with a deformable shear connection, the coupling of the displacement fieldsmay cause oscillations in the interlayer slip field and reduction in optimal convergence rate, known as sliplocking. In this study, the B-bar procedure is proposed to alleviate the locking effects. It is also shown that by changing the primary dependent variables in the mathematical model, to be able to interpolate the interlayer slip field directly, oscillations in the slip field can be completely eliminated. Examples are presented to illustrate the performance and the numerical characteristics of the proposed methods.

Treatment of locking behaviour for displacement-based finite element analysis of composite beams

Erkmen, R. Emre,Bradford, Mark A.,Crews, Keith Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.51 No.1

In the displacement based finite element analysis of composite beams that consist of two Euler-Bernoulli beams juxtaposed with a deformable shear connection, the coupling of the displacement fields may cause oscillations in the interlayer slip field and reduction in optimal convergence rate, known as slip-locking. In this study, the B-bar procedure is proposed to alleviate the locking effects. It is also shown that by changing the primary dependent variables in the mathematical model, to be able to interpolate the interlayer slip field directly, oscillations in the slip field can be completely eliminated. Examples are presented to illustrate the performance and the numerical characteristics of the proposed methods.