Structural behaviour of elliptical hollow sections

Imperial Users onl

Influence of boundary conditions and geometric imperfections on lateral–torsional buckling resistance of a pultruded FRP I-beam by FEA

Presented are results from geometric non-linear finite element analyses to examine the lateral torsional buckling (LTB) resistance of a Pultruded fibre reinforced polymer (FRP) I-beam when initial geometric imperfections associated with the LTB mode shape are introduced. A data reduction method is proposed to define the limiting buckling load and the method is used to present strength results for a range of beam slendernesses and geometric imperfections. Prior to reporting on these non-linear analyses, Eigenvalue FE analyses are used to establish the influence on resistance of changing load height or displacement boundary conditions. By comparing predictions for the beam with either FRP or steel elastic constants it is found that the former has a relatively larger effect on buckling strength with changes in load height and end warping fixity. The developed finite element modelling methodology will enable parametric studies to be performed for the development of closed form formulae that will be reliable for the design of FRP beams against LTB failure

Comparison investigation on the load capacity of octagonal, circular and square concrete filled steel tubes

[EN] This paper presents a comparative investigation on the load capacity of octagonal concrete filled steel tubes (CFST) with that of the commonly used circular and square CFST. Existing experimental data of octagonal CFST were collected and based on the cross-sectional properties of the existing octagonal specimens, the corresponding circular and square cross-section were generated under three different control parameters: total cross-sectional area of column, confinement ratio and axial stiffness. Those circular and square cross-sections were used in the numerical analysis of CFST to obtain the load capacity for the comparative investigation. Validated finite element models were built for the modeling of the circular and square CFST. The outcome of comparison shows that the confinement ratio is the crucial parameter to the difference of axial behaviour between octagonal and circular CFST. Under the same confinement ratio, octagonal CFST has a very close axial bearing performance to that in circular CFST and are much better than the square CFST.Zhu, J.; Chan, T. (2018). Comparison investigation on the load capacity of octagonal, circular and square concrete filled steel tubes. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 331-336. https://doi.org/10.4995/ASCCS2018.2018.7071OCS33133

Lateral-torsional buckling design for pultruded FRP beams

This paper presents an investigation into the development of a design procedure for Pultruded Fibre Reinforced Polymers (PFRP) beams failing by the elastic buckling mode of Lateral-Torsional Buckling (LTB). The design procedure is based on the European design approach for uniform members in bending of structural steel. In particular, the calibration method adopts the general case ‘resistance’ formula in Eurocode 3 (EN 1993-1-1:2005), and follows a standard design from testing procedure given in Eurocode 0 (EN 1990:2002) when calibrating the ‘design model’ to determine the partial factor γM for a member instability check. The test population for calibration has 114 LTB buckling resistances using four PFRP section sizes of I and channel shapes. The non-dimensional slenderness parameter is defined using the local flange buckling strength instead of the yield strength. An imperfection factor of 0.34 and partial factor of 1.3 are shown to be appropriate for calculation of the LTB moment of resistance

Reliable in-plane shear modulus for pultruded FRP shapes

Presented is a simple test method to determine the in-plane shear properties of pultruded materials where the mat reinforcement is of random oriented continuous fibres. Existing standard test methods have a number of weaknesses and a number of them can be overcome by using the 10 degree off-axis tensile test method, proposed in 1976 by Chamis and Sinclair. Straightsided specimens have unidirectional fibre reinforcement oriented at 10o to the direction of tensile load. Tension generates a biaxial in-plane stress state that, by employing stress and strain transformations, enables the shear modulus to be determined. The mean shear moduli for the web material in four shapes, from 20 coupon tests in batches of five, are found to be consistent and from 4.2 - 4.8 GPa. Given that the 10 degree off-axis coupon is easy to be prepared, with Text - 2/35 no technical difficulties this non-standard method can be recommended to characterize the in-plane shearing of pultruded materials having continuous filament (or strand) mat reinforcement

Simplified modelling of circular CFST members with a Concentrated Plasticity approach

[EN] The research reported herein aims to propose an accurate and efficient simplified numerical modelling approach for circular Concrete-Filled Steel Tubes (CFST) under flexural loading. Experimental tests were carried out to characterize the monotonic and cyclic behaviour of CFST members under bending. To assess the seismic performance of a composite structure with CFST members, both Distributed Plasticity (DP) and Concentrated Plasticity (CP) models were considered as potential simplified models for CFST members. The DP model was developed on the basis of a fibre discretization of the composite cross-section and displacement-based beam-column finite element. It was concluded that one could not accurately capture the development of local buckling of the steel tube and the development of multi-axial stress state effects (e.g. concrete confinement). Thus the DP model was found to be unsuitable for modelling of CFST members under cyclic flexural loading. Regarding the CP modelling, the modified Ibarra-Medina-Krawinkler deterioration model (with peak-oriented hysteretic response) was selected to define the behaviour of the plasticity spring associated with the plastic hinging region of the member. In order to accurately simulate the cyclic behaviour of the CFST section within the response of the spring, the deterioration model was calibrated, within a parameter-optimization framework, on the basis of 3D comprehensive numerical models in ABAQUS. The CP model was found to capture well the deterioration in both strength and stiffness of the hysteretic loops of the CFST members, which may be mostly associated with the development of local buckling phenomena. Furthermore, the elastic stiffness, the ultimate strength and the pinching effects of the hysteretic loops were also well simulated. Thus, the proposed CP model, coupled with the advanced calibration framework, was concluded to have a high level of accuracy in terms of simulating the cyclic flexural response of CFST members.Jiang, Y.; Silva, A.; Macedo, L.; Castro, J.; Monteiro, R.; Chan, T. (2018). Simplified modelling of circular CFST members with a Concentrated Plasticity approach. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 693-700. https://doi.org/10.4995/ASCCS2018.2018.7162OCS69370