Refined nonlinear flexibility-based model for fire performance assessment of RC and composite members

Chapter 1 - Introduction

This paper investigates the inelastic behaviour of composite steel concrete beams, with particular emphasis on cyclic deterioration effects. A detailed continuum model is firstly developed to represent the hysteretic response of composite steel beam and concrete slab assemblages, validated against available experimental cyclic results on both steel and composite members. The proposed model is then adopted to perform detailed parametric assessments which are used to gain insights into the key response characteristics related to the inelastic cyclic performance of composite steel/concrete members, including their stiffness, capacity, and ductility. A synthetically generated numerical database is subsequently used to develop relationships governing the plastic rotation and cyclic degradation of dissipative composite beams as a function of the main geometric and material properties, with focus on members designed to European codified procedures. The deterioration effects are shown to be dependent on a number of key factors including, most significantly, the composite beam depth and the steel cross-section slenderness. In addition to the asymmetry in behaviour under sagging and hogging moments, it is shown that composite members typically exhibit 20% more degradation under cyclic loading compared to their bare steel counterparts. Importantly, the proposed cyclic degradation expressions for composite beams also enable the calibration of widely used uniaxial deterioration models which are suitable for implementation in computationally efficient nonlinear inelastic frame analysis for structural systems. These expressions also provide fundamental information required for idealised pushover representations for practical seismic assessment and design purposes.

The easy-to-use point-load on elastic foundation (PoEF) test with biaxial bending stress state, similar to a conventional ball-on-ring test, is studied for determining the thin silicon die strength, which may feature geometric and contact nonlinearities. The feasibility of this test method with a linear theory is evaluated by a nonlinear finite element method (NFEM) with taking into account geometric and contact nonlinearities. The results show that the geometric nonlinearity would cause significant errors of strength calculation of using the linear theory for thin dies in this test. The NFEM results, more accurate than theoretical formulation, are proposed for calculating the strength of thin dies. As a result, the geometric nonlinearity has to be taken into account for this PoEF test, when the thin silicon dies are tested for bending strength data.

Effect and behaviours of composite steel concrete members – review

Behavior of Hollow Composite Steel-concrete Members under Long-term Axial Compression

Background/Objectives: The proper analysis of beam is important for understanding the actual behavior and economical use of sections. The prime objective of this research paper is the comparative study of linear and geometric nonlinear load-deflection behavior of beams under vertical load. Methods/Statistical Analysis: In geometrically linear analysis, the equations of equilibrium are formulated before the deformation state and are not updated with the deformation, while in geometrical nonlinear analysis updated stiffness matrix is used at each load increment. In this study a three noded steel beam is formulated for linear and nonlinear analysis. The incremental central point load is applied to the beam. Linear and geometrically nonlinear deflection is computed for the beams. Three beams of the same length were taken for analysis, but having different thickness&support conditions. The linear and geometrical nonlinear load-deflection behavior is studied using STAAD PRO. The linear deflection is also computed by developing a finite element based code using MATLAB. Findings: The results obtained after the analysis of beams deformations are quite interesting. The percentage variation of linear and geometrical nonlinear deflection is very high for beam with lesser thickness. It was found that the support conditions also affect variation of deflection for the linear and nonlinear cases. The variation between linear and geometrical nonlinear deflection of beam is negligible when the ends are fixed. But for the same beam with simply supported end conditions the defections were found having variation up to 37 percentages. Geometrical nonlinearity is more when the load is very high and section is thin. At the initial stages of loading behavior of beam is linear only and it behaves nonlinear when we go for higher loads. Application/Improvements: Linear analysis is only an approximation, so for understanding the actual behavior of the structure and for the economical/optimized usage of sections it is suggested to go for nonlinear analysis.

Elastic local buckling of steel plates in composite steel-concrete members

This study evaluates the performance of the design equations given in the Australian/New Zealand bridge and steel structures design standards AS 5100.6, AS 4100 and NZS 3404.1 based on reliability analysis. For this evaluation, the following two methods were utilised: (i) a capacity factor calibration method to meet the target reliability level when there are a limited number of steel yield strength tests; and (ii) an inverse reliability analysis method to calculate the required minimum number of steel yield strength tests to achieve the target reliability level when using capacity factors provided in the design standards. The methods were applied to steel and composite members including I-beams, hollow section columns, CFST columns, and composite beams. To ensure the adoptability of imported steel for these members, structural steel that conforms to European, Korean, Japanese, American, Chinese and Australasian manufacturing standards were considered in the analyses. The results showed that, for an infinite range of manufacturing data, the capacity factors were insensitive to the different manufacturing tolerances. Furthermore, when a limited number of mechanical tests were available, a much larger number of results were needed to achieve the target capacity factor for composite members in comparison with non-composite members. Finally, when considering hollow sections used as columns, the current design equations were unable to deliver the target reliability levels for any of the manufacturing standards used internationally.

The ball-on-ring (BoR) test, one of the most popular biaxial bending tests, is thoroughly investigated in this study for determining the bending strength of thin silicon dies. The application of this test method with a linear theory to the thin dies is also reevaluated using a nonlinear finite element method (NFEM) by taking into account the geometric nonlinearities, including large-deflection (global) and contact (local) nonlinearities. Mechanics of the BoR test is also discussed in terms of geometric linearity and nonlinearity. It is found that the bending strength calculated by the existing linear theory for the BoR test is still valid for the nonthin die specimens, but not for thin ones. The reason is that the thin-die specimens in the test suffer a contact-nonlinearity effect, due to a maximum applied stress moving away from the loading pin center during the loading process. The global geometric nonlinear (large-deflection) behavior occurring in the three-point bending test is not observed in the test. For applications, the fitting equations of the maximum stress in terms of applied load are proposed based on the NFEM results. Those fitting equations only depend on the specimen thickness, the head radius of the loading pin, and the elastic modulus of the specimen, but not on the specimen radius, a supporting ring radius and the head radius of the ring. The 110 μm and 160 μm-thick silicon dies in the BoR test are also demonstrated with the related fitting equations.

Development and implementation of a geometrically nonlinear beam theory model for SMA composite beams with asymmetric behavior

Modelling of continuous steel–concrete composite beams: computational aspects

Behavior of concrete-filled square steel tubular stub columns stiffened with encased I-section CFRP profile under biaxial bending

This paper develops a numerical formulation for the nonlinear time-dependent analysis of steel-concrete composite members that are curved arbitrarily in space, which includes the effects of concrete shrinkage, creep, and geometric nonlinearity. This formulation is applicable to the analysis of composite arches and composite beams curved in plan, representing the limiting cases of members that are vertically and horizontally curved. The flexibility of the shear connection at the interface surface between the steel girder and the concrete deck is taken into consideration in the formulation. For an accurate serviceability limit state analysis of composite curved members, it is essential to include the shrinkage and creep response of the concrete component in the analysis. To also include the effects of geometric nonlinearity, a step-by-step incremental iterative solution procedure is adopted. Comparisons of the numerical solutions with those based on much less efficient and tractable viscoelastic ABAQUS shell element models, and with available experimental results, verify the accuracy of the computational formulation that is developed. Examples are chosen to illustrate the effects of partial interaction and initial curvature on the time-dependent behavior of spatially curved composite beams.

The corrugated webbed prestressed (CWPS) composite member was developed to improve the efficiency of the prestress introduced into the steel beam, and experimental studies were performed to examine its structural behavior. Additionally, a unified analysis model that can estimate the nonlinear flexural behavior of the composite member and the accordion effect of the corrugated webbed steel beams at the prestressing stage was proposed. As a consecutive experimental series, in this study, the discontinuous-webbed prestressed (DWPS) composite member was developed, and this innovative composite member can reduce the amount of steel materials used, compared with the former CWPS composite member. Flexural tests were carried out to investigate their structural performances, and their behaviors were analyzed in detail by a nonlinear finite element analysis.

Thermal-induced restraint forces in reinforced concrete columns subjected to eccentric loads