Semi-continuous Composite Beams Research Articles

Numerical analysis of composite steel and concrete beams subjected to fire under different support conditions

abstract: To evaluate the behavior of semi-continuous composite beams in fire, six finite elements numerical models with several steel profiles and slab dimensions were developed in ABAQUS software. The models took into account several behaviors usually suppressed in simplified analyzes such as: geometric and materials non-linearity properties and thermal expansion effects, including indirect stresses. Three support conditions were analyzed: simply supported (axial released), axial restrained and semi-continuous, totaling 18 analyzes. The different support conditions results were compared to each other and to the fire resistance time designed by simplified methods, which followed design code recommendations.

Elastic Critical Moment of Lateral-Distortional Buckling of Steel-Concrete Composite Beams under Uniform Hogging Moment

Great attention has been given in the last few years to steel–concrete composite beams due to the gains in strength that can be obtained with the small cost of installing a shear connection between the steel profile and the concrete slab. In continuous and semicontinuous composite beams close to the internal supports, hogging bending moments are developed and the compressed bottom flange may buckle laterally in an unstable way known as the lateral-distortional buckling, characterized by a horizontal displacement and twist of the bottom flange with an out-of-plane distortion of the web. In the literature, several formulations were proposed to determine the critical moment for this type of buckling. Among them, some of the most relevant are presented by [K. Roik, G. Hanswille and J. Kina, Solution for the lateral torsional buckling problem of composite beams (in German), Stahlbau 59 (1990)] and [G. Hanswille, J. Lindner and D. Munich, Lateral torsional buckling of composite beams (in German), Stahlbau 67 (1998)]. In the present work, a new procedure is developed to determine the elastic critical moment of lateral–distortional buckling of composite beams under uniform hogging moment. To assess and calibrate this procedure, 7[Formula: see text]772 numerical models were analyzed by the finite element code ANSYS and the results were compared with the ones obtained from the new proposed formulas. The procedure presented excellent agreement with the numerical results, with an average deviation of 2.33% from the computational simulations. The formulations of [K. Roik, G. Hanswille and J. Kina, Solution for the lateral torsional buckling problem of composite beams (in German), Stahlbau 59 (1990)] and [G. Hanswille, J. Lindner and D. Munich, Lateral torsional buckling of composite beams (in German), Stahlbau 67 (1998)] did not lead to such satisfactory results, presenting an average deviation of 12.41% and 16.51%, respectively.

Lateral distortional buckling of cellular composite-beams

Abstract In the region of negative bending moments of continuous and semi-continuous steel and concrete composite beams, the inferior portion of the steel section is subjected to compression while the top flange is restricted by the slab, which may cause a global instability limit state know as lateral distortional buckling (LDB) characterized by a lateral displacement and rotation of the bottom flange with a distortion of the section’s web when it doesn’t have enough flexural rigidity. The ABNT NBR 8800:2008 provides an approximate procedure for the verification of this limit state, in which the resistant moment to LDB is obtained from the elastic critical moment in the negative moment region. One of the essential parameters for the evaluation of the critical moment is the composite beam’s rotational rigidity. This procedure is restricted only to to steel and concrete composite beams with sections that have plane webs. In this paper, an equation for the calculation of the rotational rigidity of cellular sections was developed in order to determine the LDB elastic critical moment. The formulation was verified by numerical analyses performed in ANSYS and its efficiency was confirmed. Finally, the procedure described in ABNT NBR 8800:2008 for the calculation of the critical LDB moment was expanded to composite beams with cellular sections in a numerical example with the appropriate modifications in geometric properties and rotational rigidity.

Numerical studies on composite connections under fire

A three-dimensional finite-element thermal model is proposed to predict the temperature histories of various components of composite connections under fire. The model was carefully calibrated against a series of standard fire tests. Temperature histories both within connections and in composite sections are compared and calibrated. A two-dimensional finite-element mechanical model is adopted and calibrated to predict the structural response of composite connections at elevated temperatures. Both of the models are efficient tools for integrated analysis and design of composite end-plate connections; they are also readily extended to study the structural behavior, under various fire scenarios, of semi-continuous composite beams and floors with different connections to columns with enhanced fire-resistant performance, considering both membrane and catenary floor actions.

A Study On Semi-Continuous Composite Beams With Realistic Modelling of End-Plate Connections

A comprehensive parametric study is presented in this paper, which examines numerically the structural behaviour of semi-continuous composite beams with end-plate connections of different material properties and geometrical configurations adopting a two-dimensional finite element model. Both ductile and non-ductile shear connectors are covered to investigate the effect of flexibility of the shear connectors on the overall structural behaviour of semi-continuous composite beams. Moreover, the effect of the uniform elongation strain limits of tensile reinforcement is also studied. Various structural performances, including load-deformation characteristics, concrete cracking and moment redistributions, are covered and studied in depth.

A study on semi-continuous composite beams with realistic modelling of end-plate connections

A comprehensive parametric study is presented in this paper, which examines numerically the structural behaviour of semi-continuous composite beams with end-plate connections of different material properties and geometrical configurations adopting a two-dimensional finite element model. Both ductile and non-ductile shear connectors are covered to investigate the effect of flexibility of the shear connectors on the overall structural behaviour of semi-continuous composite beams. Moreover, the effect of the uniform elongation strain limits of tensile reinforcement is also studied. Various structural performances, including load-deformation characteristics, concrete cracking and moment redistributions, are covered and studied in depth.

Studies on Semi-Continuous Composite Beams with Non-Uniform Fire Protection

An innovative type of non-uniform arrangements of fire protection materials is proposed for efficient fire protection to semi-continuous composite beams. The fire protection is arranged according to applied bending moments and shear forces. Heavy fire protection is applied in high bending and shear regions, while relative thin or even no fire protection is applied in low bending regions. Different failure modes are identified from the results of finite element analyses under different combinations of temperature profiles in both heavily and less fire-protected regions. A simple design approach is then proposed to predict load carrying capacities of semi-continuous composite beams for each of the identified failure modes. A parametric study is conducted thereafter to optimise the arrangements of fire protection materials.

Effects of partial shear connection on the behavior of semi-continuous composite beams

In this paper, the effects of partial shear connection on the behavior of semi-continuous composite beams were studied numerically using two-dimensional finite element model with plane stress elements. The finite element model takes into account the nonlinearity of the different materials involved. For the shear connectors, a non-linear (shear-slip) relation, drawn from the push-out tests, was used. The accuracy of the proposed finite element model was verified against test results available in the literature. A simplified method to predict load capacity and deflection of the semi-continuous composite beams was also proposed. Based on the results obtained from the finite element analysis, the concept of partial shear connection in the hogging moment regions can be accepted provided that the shear connectors are sufficiently ductile.

Two-dimensional FE model for evaluation of composite beams, I: Formulation and validation

This paper develops a two-dimensional finite element model for composite beams, based on the use of the commercial package ANSYS. Different degrees of continuity can be taken into account, permitting the investigation of systems ranging from simply-supported to fully-continuous. Beams with either full or partial shear connection can be considered, as well as different slab typologies. The model represents the behaviour of all components of the composite arrangement, based on the best available current understanding, including the reinforcing bars (considering the tension-stiffening effect), the load–slip characteristic of the shear connectors, and the key components of the beam to column connection. In addition, material nonlinearity for all components is taken into account. The model has been fully verified by extensive comparisons against experimental and numerical results and it has been demonstrated that it is suitable for comprehensive parametric studies of the behaviour of composite beams. A sensitivity study focusing on both the required and the available rotation capacities and their importance for moment redistribution in semi-continuous composite beams is presented in the companion paper.

Two-dimensional FE model for evaluation of composite beams, II: Parametric study

In the present paper, the 2D finite element (FE) model presented and validated in the companion paper “Two-dimensional FE model for evaluation of composite beams, I: Formulation and Validation” is used to undertake a parametric study focused on both the required and available rotations and the moment redistribution capacity of semi-continuous composite beams. The investigation has shown that some tendencies already established in the literature regarding beams with full shear connection are not applicable to cases with partial shear connection.

A Simplified Design Method for Semi-Continuous Composite Beams

A Simplified Design Method for Semi-Continuous Composite Beams

Analysis of Semi-Continuous Composite Beams with Partial Shear Connection Using 2-D Finite Element Approach

Analysis of Semi-Continuous Composite Beams with Partial Shear Connection Using 2-D Finite Element Approach

Bending and rotational behaviour of semi-continuous composite beams

Stresses and deflections were measured in various semi-continuous composite beams. The bending and rotational capacities of the composite connections were measured in terms of beam curvatures and deflections by using two full-scale semi-rigid composite frames with monotonic loadings. The effect of semi-rigid connections on the performance of composite beams with various loadings was compared with predictions and codes. The tests show that the semi-continuous composite beams are more economic and effective than the simple or continuous composite beams. The semi-rigid connections affect the bending capacities and beam deflections, so the connection behavior should be considered in the design of composite beams. Yielding analysis of the steel beam bottom flange has some influence on the deflection calculation of composite beams.

Modelling of unpropped semi-continuous composite beams

For ease of construction steel–concrete composite beams are usually unpropped during construction, with the steel section alone supporting the weight of the concrete slab during casting. The subsequent applied loading is resisted by the composite action of the steel and concrete. This mode of construction results in significant stresses built into the steel section. A numerical method is presented for modelling the load–deformation behaviour of composite beams unpropped during construction and incorporating composite connections at the supports. The method accounts for the effect of dead load stresses built into unpropped beams. A 3D moment–curvature–dead load stress relationship is defined, utilising the non-linear stress–strain properties of the steel and concrete. This relationship is used subsequently for calculating the distribution of curvature along the length of a beam. The curvature may be double integrated, using the support displacements as boundary conditions, to determine the deflected shape. The accuracy of the technique has been assessed experimentally using a 24 m long test frame incorporating unpropped composite beams and composite connections. The model predictions of end rotations and displacements are shown to be in good agreement with observed values. Standardised composite connection details are currently only available for use with propped composite beams. This work has been carried out to assess the conditions in which these details can be safely used with beams, which are unpropped during construction. The work is of particular interest to those attempting to model accurately the load–deformation response of unpropped composite beams.

Practical design guidlines for semi-continuous composite braced frames

This paper presents a simplified approach for the design of semi-continuous composite beams in braced frames, where specific attention is given to the effect of joint rotational stiffness. A simple composite beam model is proposed incorporating the effects of semi-rigid end connections and the nonprismatic properties of a `cracked` steel-concrete beam. This beam model is extended to a sub-frame in which the restraining effects from the adjoining members are considered. Parametric studies are performed on several sub-frame models and the results are used to show that it is possible to correlate the amount of moment redistribution of semi-continuous beam within the sub-frame using an equivalent stiffness of the connection. Deflection equations are derived for semi-continuous composite beams subjected to various loading and parametric studies on beam vibrations are conducted. The proposed method may be applied using a simple computer or spreadsheet program.

Practical design guidlines for semi-continuous composite braced frames

This paper presents a simplified approach for the design of semi-continuous composite beams in braced frames, where specific attention is given to the effect of joint rotational stiffness. A simple composite beam model is proposed incorporating the effects of semi-rigid end connections and the nonprismatic properties of a 'cracked' steel-concrete beam. This beam model is extended to a sub-frame in which the restraining effects from the adjoining members are considered. Parametric studies are performed on several sub-frame models and the results are used to show that it is possible to correlate the amount of moment redistribution of semi-continuous beam within the sub-frame using an equivalent stiffness of the connection. Deflection equations are derived for semi-continuous composite beams subjected to various loading and parametric studies on beam vibrations are conducted. The proposed method may be applied using a simple computer or spreadsheet program.

Required rotation of composite connections

According to the method developed previously for calculating the required rotation for composite connections, typical cases are studied and the required connection rotations are evaluated. Maximum span:depth ratios are presented so that the required connection rotations are smaller than 20, 25 or 30 mRad respectively. Conclusions are made on the effects of different load cases, steel grades and end conditions on the required rotation for plastic design of semi-continuous composite beams.