J.Y. Richard Liew

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.

Spread-of-plasticity analysis of three-dimensional steel frames

Abstract A second-order spread-of-plasticity analysis program has been developed for analysing three-dimensional (3-D) steel frames. Material nonlinearity is modelled through the von Mises yield criterion in conjunction with the associated flow rule and the assumption of isotropic hardening. Gradual yielding is modelled through numerical integration of the material points on the cross-sections, which are located at the selected integration points along the member length. A mixed element formulation is proposed for analysing large-scale framework analysis. Established benchmark results are used to verify the proposed spread-of-plasticity analysis. The inelastic behaviour of a 3-D steel frame is investigated, and the computing efficiency and accuracy of using the mixed-element approach for advanced analysis of large-scale framework is illustrated.

Advanced analysis for the assessment of steel frames in fire

Abstract This paper describes the methodology of an advanced analysis technique for studying the large-displacement inelastic behaviour of building frames subjected to localised fire. The main feature of the proposed analysis is its use of one element per member to model each structural component and thereby obtain a realistic representation of material and geometrical nonlinear behaviour of the overall framework. Both ISO fire and natural fires can be simulated by the analysis model. The transient heat transfer is calculated by using a refined finite element mesh, whereas the structural responses are calculated with a nonlinear finite element technique based on an elasto-plastic beam–column formulation. Numerical studies are carried out on portal frames and multi-storey frames exposed to natural fires. The computed results are compared and contrasted with those from the conventional approach based on ISO standard fire, so that the advantage of using advanced analysis for direct assessment of the performance of steel structures in fire can be highlighted. Effects of fire load and ventilation resulting in localised fires in building frames are studied. The design implication of fire spreading in the storey of a building in which cooling and heating are taking place simultaneously is discussed.

Nonlinear analysis of steel-concrete composite beams curved in plan

Abstract This paper deals with the behavior of structural steel–concrete composite beams curved in plan. The finite element package ABAQUS has been used to study the nonlinear behavior and ultimate load-carrying capacity of such beams. A three-dimensional finite element model has been adopted. Shell elements have been used to simulate the behavior of concrete slab and steel girder, and rigid beam elements to simulate the behavior of shear studs. The proposed finite element model has been validated by comparing the computed values with available experimental results. An acceptable correlation has been observed between the computed and experimental results obtained for beams of realistic proportion.

Limit states design of semi-rigid frames using advanced analysis: Part 1: Connection modeling and classification

Abstract This paper presents a method for modeling connection moment-rotation curves which are essential for proportioning two-dimensional semi-rigid steel frame structures analyzed based on a second-order inelastic analysis. Procedures for calculating the key parameters used to describe the moment-rotation curves of various types of angle connections are presented. Design aids are generated in which salient size parameters that affect the moment-rotation behavior of the connection can be identified. Two schemes by which connections can be classified in terms of strength, stiffness and rotation capacity are presented, and their design implications are discussed. Analysis and design methodologies are provided in Part 2, a companion paper in which the ultimate strength and serviceability limit state behavior of a semi-rigid frame example are studied using an advanced analysis. The aim of these two-part papers is to advance the use of second-order plastic hinge based analysis for proportioning two-dimensional semi-rigid frames without the need of separate specification equation checks.

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.

Novel Steel-Concrete-Steel Sandwich Composite Plates Subject to Impact and Blast Load

This paper investigates the structural performance of steel-concrete-steel (SCS) sandwich composite system subject to impact and blast load. Novel J-hook shear connector was invented to prevent the separation of face plates from the concrete core. SCS sandwich specimens subject to 100 kg TNT blast a 5 m standoff distance were tested. The test results are reported and the factors affecting the blast resistance of SCS sandwich structures are discussed. Finite element analysis was carried out and the numerical results are verified against the blast test results. Parametric study of sandwich core strength and plate thickness is presented. Due to the superior impact performance of the proposed SCS sandwich structures, an ice caisson protective offshore structure is proposed based on the curved sandwich panel. The ultimate strength behavior of curved SCS sandwich panels is tested. The effect of arch effect is studied both experimentally and numerically.

Ultra-High Strength Concrete Filled Composite Columns for Multi-Storey Building Construction

A test programme was carried out to investigate the performance of 27 axially loaded column specimens, including 18 steel tubes infilled with ultra-high strength concrete (UHSC) of compressive strength close to 200 MPa, 4 steel tubes infilled with normal strength concrete (NSC) and 5 hollow steel tubes. Steel fibres were added into the UHSC to study their effect in enhancing the ductility and strength. Concrete filled double-tube columns were also investigated for potential application in multi-storey and high-rise constructions. Test results showed that UHSC filled tubular columns achieved ultra-high load-carrying capacities, but they could become brittle after the maximum load was attained. In addition, the ductility and strength of composite columns infilled with UHSC was improved by applying load only on the concrete core, adding steel fibres into the concrete core or increasing the steel contribution ratio. Comparison of test results with Eurocode 4s predictions indicates that the Eurocode 4 method could be safely extended to predict the compressive resistance of UHSC filled composite stub columns. On average, Eurocode 4 approach underestimated the resistance by 14.6% if the confinement effect was not considered and by 3.5% if the confinement effect was considered for all the specimens involving UHSC. However, to ensure sufficient ductility, it is recommended that a minimum steel contribution ratio of 0.30 or 1% steel fibres should be used. Furthermore, strength enhancement due to confinement effect should be ignored in estimating the ultimate strength of concrete filled composite columns with Class 3 steel sections.

Assessment of current methods for the design of composite columns in buildings

Abstract This paper presents the design assessment of encased I-sections and concrete filled composite columns based on the approaches given in Eurocode 4: Part 1.1, BS 5400: Part 5 and AISC LRFD. This includes studies on the design parameters, comparison of the nominal strength predicted by the three codes and comparison of the predicted strengths with the available test results. In some cases, results obtained from the above three codes may vary considerably. This is because of the different design considerations adopted in these codes. However, the design methods are found to be mostly conservative when compared with the test results. Eurocode 4: Part 1.1 has major factors in its favour in terms of its comprehensiveness and wide scope of application.

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.