Modern Engineering Design: Analytical and Numerical Modelling of Semi-rigid Connection

The concept of semi-rigid connection and steel-concrete composite action has been extensively researched in the past. However, they are not widely used in practice due to the lack of detailed information, not only about the advantages of the semi-rigid design philosophy, but also about the potential risks if its effect is not accounted for. The above considerations were the motivations in taking up this research. Firstly, a numerical study to investigate the effect of connection stiffness on the natural frequency of semi-rigid frame was carried out using ABAQUS software. The results of this numerical study confirmed the necessity of incorporating this effect to get safe and economical design. Consequently, an analytical procedure for a beam with semi-rigid connections under gravity load was developed which overcomes the limitations of previously published procedures. The frequency of a steel beam was also calculated using effective length concept. Furthermore, two new analytical "hand'' calculation methods to estimate the first three frequencies of a semi-rigid frame were developed. Both methods were developed by modifying or improving for existing methods in the literature for rigid-jointed plane steel frame to incorporate the effect of connection stiffness. Fist method is suitable only for a semi-rigid plane steel frame which has uniform properties along its height so as it can be modelled as equivalent flexural-shear cantilever beam. The proposed second method is suitable for non-uniform plane steel frame. Both the above methods can be extended to composite structure using the equivalent stiffness concept of composite beam. Moreover, examples of steel frame were used to demonstrate the application of the proposed analytical methods. It was shown that the proposed methods not only can predict the difference in frequency of rigid and semi-rigid frames, but they are also simple enough to be used in day-to-day design practices. Secondly, as the stiffness of connection is essential in the calculation of natural frequency of a semi-rigid frame, a new simple mechanical component-based model was developed to determine the initial rotational stiffness of commonly used flush end-plate steel or composite connection incorporating the partial interaction effect. The traditional axial spring of shear connectors was replaced by rotational spring to make the model suitable to extending further than the linear region. A chart was developed to estimate the appropriate values of the secant stiffness and strength of a shear stud, since the empirical equations that researchers have used in the past can lead to unrealistic results in some cases. Thirdly, a simplified model, which combined three components of a composite connection in one "lump'' component (RCCS), was developed. It can be used in the finite element modelling of a composite connection to overcome the convergence problems associated with cracking of concrete and also it will reduce the computational time significantly with adequate accuracy. A new procedure to determine the number of "active'' studs was developed. The relationship between the number of "active'' shear studs and the maximum number of shear studs required for a full shear connection was derived. Finally, the relationship between connection ductility and frame ductility was investigated. It was found that the moment resistance and ductility of connection affect significantly the whole behaviour of a frame. Consequently, a simple flowchart to predict the failure mode of a flush end-plate composite connection was developed. A procedure to estimate the moment resistance of a flush end-plate composite connection by modifying the existing procedures in the literature to incorporate the partial shear connection effect was proposed. Also, the proposed mechanical model was further extended using the appropriate post-linear values of its components in order to calculate the rotational ductility of a connection. All the suggested procedures have been validated with the numerical results using ABAQUS, the results from other existing models and experimental tests in the literature where available.