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Abstract: It is widely known that added mass has a significant influence on the natural frequency of membrane structures. Previously, the total added mass of a one-dimensional membrane has been investigated with theoretical analysis. However, no test result has been applied to verify results of the theoretical analysis. Furthermore, the distribution of the added mass is still unclear. In this study, first, thin-airfoil theory was applied to analyze the distribution of the added mass. The distribution of the added mass was found to be basically uniform for the first vibration mode of a one-dimensional membrane. Then, it was assumed that the added mass of one vibration region is independent of the added mass of another vibration region for higher vibration modes, where the vibration regions are the parts of the membrane separated by the nodal points (nodal lines for two-dimensional membranes) of the vibration mode. Based on the above analysis, a simplified added-mass model was proposed; i.e., for every vibration mode, the added mass of each vibration region is equivalent to the uniformly distributed air with a height of α m l, where α m is the added mass coefficient and l is the diameter of the inscribed circle of the corresponding vibration region. To ascertain the added-mass coefficient and verify the simplified added-mass model, a vacuum chamber was designed to test the vibration of a circular flat membrane in still air with varying air pressures. The results showed that the simplified added-mass model was accurate when the added-mass coefficient was taken as 0.65. The efficiency of the proposed simplified added-mass model was further verified by an existing test of a three-sided membrane. [Copyright &y& Elsevier]

Cable net structures are characterized by significant geometrical nonlinear properties. The linear modal superposition method (LMSM), which ignores the effect of nonlinearity, is believed not suitable for the seismic response analysis of this kind of structures. To conquer the drawback of LMSM, a non-iterative linearization method (NILM) is proposed in this paper. An energy parameter named the “stiffness parameter” is utilized in generating the nonlinear equivalent single degree of freedom (ESDF) systems for the dominant vibration modes of cable nets. The nonlinear stiffness of an ESDF system is simulated by a quadratic function about the equivalent displacement. Based on a stochastic linearization process, the relationship between the equivalent linear stiffness and the displacement response of a modal ESDF system is established. Then the structural responses are computed according to the design response spectra through a non-iterative procedure. Finally, the effectiveness of the proposed NILM is illustrated by a numerical example that carried out on a trapezoid-shaped cable net supported curtain wall structure. It is demonstrated that the proposed NILM, which takes the stiffness hardening effect into consideration, could not only yield better results than the LMSM does, but also exhibit satisfying timesaving property over the nonlinear RHA. [ABSTRACT FROM AUTHOR]

Abstract: The use of cold-formed thin-walled steel structures has increased in recent years, and some built-up section members are motivated and also widely used for their excellent structural behaviors. In this paper, a series of axially-compressed tests on built-up box section members composed of two C-section by self-drilling screws at flanges are conducted. The differences of global, local and distortional buckling behaviors between members with built-up and single sections are investigated at first. Then the effects of installation error and fastener spacing on ultimate load-carrying capacity of built-up members are analyzed. A strength estimation method for built-up members under axial compression is proposed based on the experimental investigation in this paper, as well as some existing experiments, and corresponding numerical analysis studies. Finally, the predicted capacity obtained by using the proposed strength estimation method is compared with experimental results and the nominal axial strength determined according to the AISI provisions, by which the suitability and accuracy of the proposed strength estimation method have been established. [Copyright &y& Elsevier]