Qingshan Yang

Wind-Induced Response and Equivalent Static Wind Loads of Long Span Roofs

Long span space roofs are characterized as multimode wind-induced response. Participation factors on the basis of the structural strain energy are defined to select dominant eigenmodes in the background response and dominant vibration modes in the resonant response. These dominant eigenmodes and dominant vibration modes are chosen as fundamental vectors to evaluate the universal equivalent static wind loads (ESWL) that would simultaneously reproduce multiple largest load effects. A least-squares approximation method is employed to calculate the combination factors of these fundamental vectors. The proposed method is then employed to study wind-induced response and universal ESWL of the Beijing National Stadium. The results show that the background response is much higher than the mean response and the resonant response; low-order eigenmodes and vibration modes have the most important contribution to the wind-induced response; the structural response at selected nodes and selected supports under the universal ESWL agrees well with actual dynamic peak response.

Dominant mode selection and modal coupling analysis for wind-induced response of long-span roofs

Mode selection and modal coupling analysis are important to estimate wind-induced structural response of long-span roof structures. This article presents a framework for predicting wind-induced structural response of long-span roof structures based on modal analysis. This framework first identifies the dominant modes according to the correlation between the mode shape and the wind load spatial distribution on the structure as well as a proposed “modal participation coefficient.” Second, the concept of modal strain energy is introduced and a modal coupling coefficient is defined, based on which the dominant coupling modes are determined. A modified square root of the sum of the squares methodology is then developed to account for the modal coupling effects of the background and the resonant response components. The total responses can be obtained by combining the contributions of the dominant coupling modes and the square root of the sum of the squares results from the dominant modes. This avoids the use of the computation expensive complete quadratic combination method. Finally, an illustrative example of wind-induced response analysis of the China National Stadium roof structure is provided to demonstrate the effectiveness of the proposed framework.

An Investigation on Aseismic Connection with Opening in Beam Web in Steel Moment Frames

Providing an opening in a beam web (OBW) is a possible approach to improving the aseismic behaviour in beam-to-column connections in steel moment frames. The finite element analysis in this paper shows that the behaviour of the OBW connection depends on a size of the opening, R, and the opening location, b. When parameters are properly selected, Vierendeel hinges form in the weakened areas resulting in a beam with high ductility. Quasi-static tests were carried out based on the finite element analysis results. The test results showed that Vierendeel hinges formed in the weakened areas and brittle weld fracture was avoided in the OBW connections. The performance indicators of the OBW connection are not reduced with a weakened section. Aseismic behaviour of the beam-to-column connections are improved with an opening in the beam web. To explain the failure mechanism of the OBW connection, the stress distribution obtained from the finite element analysis was studied. The stress distribution around the opening was found dramatically changed because of the provision of the opening. Four plastic zones formed in the web around the opening under the interaction of normal and shear stresses at the critical locations resulting in ductile Vierendeel hinges.