|Author:||Wang, Juan Aaron|
|Title:||Advanced nonlinear finite element investigation into structural behaviour of composite beams|
|Subject:||Hong Kong Polytechnic University -- Dissertations.|
Composite construction -- Mathematical models.
Finite element method.
|Department:||Department of Civil and Structural Engineering|
|Pages:||1 v. (various pagings) : ill. ; 30 cm.|
|Abstract:||Objectives This thesis reports the findings of a four year research project using advanced nonlinear finite element modelling to investigate the structural behaviour of various types of composite beams with practical constructional features. The objectives of the research project are: ‧ To examine the structural behaviour of simply supported, continuous and semi- continuous composite beams through advanced nonlinear finite element modelling which incorporates the nonlinear deformation characteristics of shear connectors and tensile reinforcement. ‧ To provide detailed understanding on the structural behaviour of various types of composite beams based of the results of extensive parametric studies with advanced nonlinear finite element modelling. ‧ To develop integrated analysis and design models for composite beams with practical constructional features, and to provide guidance for practical design of composite beams. The major activities of the research project are summarized together with the associated findings as follows: Shear connectors A three-dimensional finite element model with solid and shell elements and with material, geometrical and boundary non-linearities is established to study the structural behaviour of shear connectors in conventional push-out tests. The proposed finite element model is used to simulate the push-out tests of 8 specimens with various material properties and geometrical configurations. Through the calibration of the numerical model with test data, the proposed model is verified to be able to predict nonlinear load-slippage curves of shear connectors accurately with little to moderate cracking in concrete at an end-slippage up to 5 mm. Nevertheless, a simplified approach with interfacial spring elements is adopted in the finite element models of composite beams and composite beam-column connections in the present project. This approach is verified to be able to model the flexibility effect of shear connectors in composite beams under limited slippage with sufficient accuracy. Simply supported composite beams A two-dimensional finite element model with material, geometrical and boundary non-linearities is established to predict the structural behaviour of simply supported composite beams, in which both steel sections and concrete flanges are modelled with two-dimensional plane stress elements while interfacial spring elements are adopted to simulate the flexibility effect of shear connectors. Through a calibration against 6 well documented tests on composite beams, it is shown that the numerical results of the composite beams compare well with the test data in terms of various load-deformation characteristics. This model is further extended to study the structural behaviour of perforated composite beams. Two perforated composite beams with full test documentation are simulated, in which one of the composite beams is with a solid slab while the other is with a composite slab. It is demonstrated that the finite element models are able to predict the ultimate loads of composite beams with rectangular web openings against 'Vierendeel' mechanism satisfactorily after careful calibration against test data. Furthermore, an extensive parametric study is also conducted to study the effect of flexible shear connectors on the overall structural performance of perforated composite beams. A close examination on the results of the finite element models reveals that pull-out forces exist in those shear connectors in the close vicinity of the web openings. Thus, it is essential to ensure structural adequacy of those shear connectors against combined shear and tension forces. Continuous composite beams Advanced finite element models with material, geometrical and boundary non-linearities are set up to study the structural behaviour of continuous composite beams. The accuracy of the proposed models is verified through a detailed calibration against a total of 10 tests on continuous composite beams with various material properties and geometrical configurations. Tests of both double-span and triple-span composite beams under point loads are covered in the calibration exercise. The results from the finite element analyses are also compared with those obtained from codified design rules. It is found that the codified design rules often under-predict the deflections of composite beams due to negligence on the flexibility of shear connectors. Hence, there are significant errors in determining the internal force distributions in continuous composite beams with structural indeterminacy. A comprehensive parametric study on 30 continuous composite beams is also conducted to examine the structural behaviour of continuous composite beams with various material properties and geometrical configurations. Composite beams with both ductile and non-ductile shear connectors are included to investigate the effects of the highly nonlinear deformation characteristics of the shear connectors on the overall structural behaviour of continuous composite beams. It is found that the non-ductile deformation characteristics of shear connectors has significant effects on the structural behaviour of continuous composite beams, which may lead to premature knock-down, especially for composite beams with deep steel sections and high strength steel. Semi-continuous composite beams Both three-dimensional and two-dimensional finite element models are established to predict the structural behaviour of composite end-plate connections. Finite element models are verified through a calibration against test results of 9 composite end-plate connections. A comprehensive parametric study is also conducted to examine the structural behaviour of composite beam-column connections as well as semi-continuous composite beams. A total of 33 composite end-plate connections and 36 semi-continuous composite beams with different material properties and geometrical configurations are studied. It is found that the non-ductile deformation characteristics of shear connectors and the rupture of tensile reinforcement have significant effects on the moment-rotation behaviour of composite beam-column connections. Moreover, significant reduction in both the hogging and the sagging moment capacities is also observed in semi-continuous composite beams with non-ductile shear connectors. This leads to overall non-ductile behaviour of semi-continuous composite beams. Furthermore, reduction in the hogging moment capacities due to the rupture of tensile reinforcement is also observed for semi-continuous composite beams with ductile shear connectors and tensile reinforcement with normal ductility. Significance of the project This project provides detailed understanding on the structural behaviour of simply supported, continuous and semi-continuous composite beams used in modern composite construction. The effects of nonlinear as well as non-ductile deformation characteristics of shear connectors and tensile reinforcement are also studied, which provides in-depth understanding of the effects of the shear connectors and the tensile reinforcement on the overall structural behaviour of composite beams. This extends the design provisions provided in codes of practice, and allows composite beams with material properties and geometrical configurations significantly different from those conventional arrangements to be designed accurately. A number of finite element models are also proposed for the integrated analysis and design of various types of composite beams with practical construction features, which are not readily covered in current codes of practice. This supplements the scope of the current codified design rules and leads to a more 'user-friendly' design of composite beams. Due to the high efficiency of the proposed finite element models, the computational efforts of those models are found to be acceptable in modern design offices. Structural engineers are strongly encouraged to employ the models in their practical work to exploit the full advantages offered by composite construction.|
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