N.E. Shanmugam

State of the art report on steel–concrete composite columns

Abstract Steel–concrete composite columns are used extensively in modern buildings. Extensive research on composite columns in which structural steel section are encased in concrete have been carried out. In-filled composite columns, however have received limited attention compared to encased columns. In this paper, a review of the research carried out on composite columns is given with emphasis on experimental and analytical work. Experimental data has been collected and compiled in a comprehensive format listing parameters involved in the study. The review also includes research work that has been carried out to date accounting for the effects of local buckling, bond strength, seismic loading, confinement of concrete and secondary stresses on the behaviour of steel–concrete composite columns.

Improved nonlinear plastic hinge analysis of space frame structures

Abstract This paper is concerned with second-order plastic hinge analysis of three-dimensional frame structures. The beam–column formulation is based on the use of stability interpolation functions for the transverse displacements, and considers the elastic coupling effects between axial, flexural and torsional displacements. The developed computer program can be used to predict accurately the elastic flexural buckling load of columns and frames by modelling each physical member as one element. It can also be used to predict the elastic buckling loads associated with axial-torsional and lateral-torsional instabilities, which are essential for predicting the nonlinear behaviour of space frame structures. The member bowing effect and initial out-of-straightness are also considered so that the nonlinear spatial behaviour of structures can be captured with fewer elements per member. Material nonlinearity is modelled by using the concentrated plastic hinge approach. Plastic hinge between the member ends is allowed to occur. Numerical examples including both geometric and material nonlinearities are used to demonstrate the robustness, accuracy and efficiency of the proposed analytical method and computer program.

Design formula for axially compressed perforated plates

This paper is concerned with post-buckling behaviour and the ultimate load capacity of perforated plates with different boundary conditions and subjected to uniaxial or biaxial compression. Plates were analysed using the finite element method (FEM), and extensive studies were carried out covering parameters such as plate slenderness, opening size, boundary conditions and the nature of loading. A design formula to determine the ultimate load carrying capacity was established based on a best-fit regression analysis using the results from the finite element analyses. The accuracy of the proposed formula was established by comparison with experimental values of ultimate capacity and similar finite element values. Ultimate load values are also presented in the form of charts for various values of plate slenderness and opening size.

Finite element modelling of plate girders with web openings

Abstract This paper is concerned with a finite element model to predict the behaviour and ultimate load of plate girders with web openings. The finite element package ABAQUS is used to model the plate girders with web openings. Accuracy of the model is assessed by applying it to plate girders tested earlier by other researchers. Comparison of analytical results with the available experimental results for yielding patterns, ultimate load values and load–deflection relationships show good agreement between the finite element and experimental results thus validating the accuracy of the proposed model. The proposed finite element method was extended to carry out a parametric study. The study covered parameters such as web slenderness and flange stiffness.

An analytical model for thin-walled steel box columns with concrete in-fill

Concrete-filled steel box columns are widely used as a major structural element in tall buildings as they provide efficient structural performance in resisting axial compression. Local buckling of steel plates is a common failure criteria when plate slenderness ratio is large in box sections. A method using an effective width principle is proposed in this paper to predict the behaviour and load carrying capacity of thin-walled steel tubes with concrete in-fill. The present investigation addresses columns pinned at their ends and subjected to biaxial loading. Columns tested by other researchers have been analysed using the proposed method and the predicted results are compared with the corresponding test results. The proposed model is also verified against Eurocode 4. The comparison shows that the method could predict the ultimate load with sufficient accuracy.

Steel–concrete composite plate girders subject to combined shear and bending

Abstract Details of an experimental investigation on steel–concrete composite plate girders subject to the combined action of shear and bending are presented in this paper. Six composite plate girders have been tested to failure in order to study their ultimate load behaviour. Two different web-depth to thickness (d/t) ratios and two different moment/shear ratios have been considered. Attention is focused on the variation in tension field action in web panels due to composite action between the steel girder and concrete slab. Extensive strain measurements have been made on the web panels in order to obtain a detailed picture of tension field action. The ultimate load carrying capacity and the tension field width of composite plate girders are found to increase significantly compared to the bare steel girders.

Experimental study on steel-concrete composite beams curved in plan

Abstract This paper is concerned with experimental study on the ultimate load behaviour of steel-concrete composite beams curved in plan. Five beams of realistic dimensions built from rolled steel beam and concrete slab were tested to failure. Extensive measurements of strain in both concrete and steel, and of displacements were made in order to obtain a complete picture of elastic and ultimate load behaviour. Each of the beams was simply supported at the ends and was subjected to a concentrated load applied at mid-span. All the beams tested were analyzed by using the finite element method and the results were compared with those obtained experimentally. The test results indicate that the load-carrying capacity decreases with the increase in the “span/radius of curvature” ratio. The experimental results for deformations, for stress distributions and for ultimate strengths were found to be in good agreement with the corresponding values predicted by finite element analysis.

Testing of steel-concrete composite connections and appraisal of results

Abstract This paper presents results obtained from tests carried on six full-scale composite beam-to-column joints. The steelwork connection consists of a flush end plate welded to the beam end and bolted to the column flange. The steel beam section and concrete slab remained identical for all six specimens. Three types of column are used: bare steel, partially encased and fully encased columns. Other variables include the area of reinforcement in the slab and the presence of stiffeners in the column web. Moment–rotation curves obtained from the tests are compared with those predicted by an analytical model. Plastic analysis of cross section is used to develop the analytical model for the prediction of moment capacity. A simple spring model for the slab combined with that of the steel joint model, as proposed in Revised Annex J of EC3, is used to assess the stiffness of the composite joints. Generally, the proposed model can predict the moment capacity of composite joints with good accuracy. However, the model tends to over predict the rotational stiffness.

Advanced analysis and design of spatial structures

Abstract Modern limit-state design codes are based on limits of structural resistance. To determine the ‘true’ ultimate load-carrying capacity of spatial structures, an advanced analysis method which considers the interaction of actual behaviour of individual members with that of the structure is required. In the present work, a large-displacement inelastic analysis technique has been adopted to compute the maximum strength of spatial structures considering both member and structure instability. The actual behaviour of individual members in a spatial structure is depicted in the form of an inelastic strut model considering member initial imperfections as ‘enlarged’ out-of-straightness. The maximum strength of the strut is computed based on a member with ‘equivalent out-of-straightness’ so as to achieve the specifications strength for an axially loaded column. The results obtained by the strut model are shown to agree well with those determined using plastic-zone analysis. The nonlinear equilibrium equations resulting from geometrical and material nonlinearities are solved using an incremental-iterative numerical scheme based on generalised displacement control method. The effectiveness of the proposed advanced analysis over the conventional analysis/design approach is demonstrated by application to several space truss problems. The design implications associated with the use of the advanced analysis are discussed.

Testing of semi-rigid unbraced frames for calibration of second-order inelastic analysis

Abstract This paper examines the behaviour of semi-rigid unbraced frames through a series of tests on a variety of rectangular frames as well as their joints so that the analysis and design methodology can be developed and verified against the test results. The frame and joint tests employed similar beam and column sizes and had the same connection details. The two types of connections studied were top-seat-double-web angle and extended end-plate. Column-base connections were also included in the studies. Load-displacement plots are presented for all the test frames subjected to gravity loads applied to the beam and columns, and a horizontal load applied at the beam level. The principal objective of the joint tests is to provide a comprehensive set of moment-rotation data, in terms of stiffness and moment capacity, so that a comparative assessment of the frame performance due to the different connection types could be undertaken. Detailed descriptions of test arrangement, load sequences, test methods and data acquisition techniques are given. The general observed behaviour is discussed. Results from the frame tests are compared with the corresponding theoretical results obtained from a second-order inelastic analysis.