In recent years, considerable attention has been paid to the research of dynamic response of long-span bridges with particular emphasis on seismic behavior. Cable-stayed and suspension bridges are the most popular types. Since long-span bridges have multi-supports and extreme lengths, due to the spatial variation effects, the ground motions at different supports might be non-uniform. A state-of-the-art update review of the response of long-span bridges subjected to non-uniform excitation is presented. The review mainly focuses on the theoretical aspects of non-uniform excitation, numerical studies, and experimental studies to verify some of the theoretical findings. In this paper, a review of the use of shake-table in experimental studies of long-span bridges is also presented. The non-uniform cases considered include a time delay with the same support excitations, multiple support excitations, and the combination of the first and the later. The results are discussed and summarized in comparison to the cases of uniform support excitation.
Pitting corrosion often leads to the creation of small holes in steel tubular member of platform structures when a protective coating is damaged. A single pit on slender compression element can cause a significant reduction in the buckling capacity of the member. Euler formula is no longer applicable for determining the critical buckling load when cutout presence on the member. This research was conducted to numerically study the effect of a circular hole on the buckling capacity of slender steel tubular member. A variation on hole positions was at 0.125 L, 0.25 L, 0.375 L, and 0.5 L, where L is the length of the member. The hole was taken to be 0.5 pipe diameter. Two nonlinear geometric 3D Finite Element models were developed to analyzed the member critical buckling load: (a) buckling analysis, where the problem was formulated as eigenvalue problem based on the nonlinear incremental equilibrium equations, and (b) nonlinear analysis, where the nonlinear equilibrium equations were developed and solved by several schemes to get the load – deflection curve. For the both models, the tubular member was discretized into: (a) shell elements, and (b) solid elements. The numerical results were verified by experimental investigation. The results showed that: (a) the presence of cutout reduced the buckling load significantly, (b) the reduction ranging from 3% to 10% depending on the hole positions, (c) the maximum reduction occurs when the hole position was in the middle of the member length, (d) compared to experimental results, the critical buckling load obtained from buckling analysis deviated 1~4% while those of nonlinear analysis deviated 1~5%, (e) the buckling mode corresponded with member bent away to opposite side of the cutout position.
Fly ash based geopolymer normally gets the optimum strength by heat curing. This is considered as a hindrance to in-situ applications. Therefore, development of fly ash based geopolymer that suitable for ambient curing will widen the application to the concrete structure. This paper reports the results of an experimental study on setting time and development of compressive strength of class C fly ash based geopolymer paste produced in ambient curing condition. The main synthesis parameters such as water to the geopolymer solid ratio, alkali to cementitious ratio and molarity of NaOH were varied to understand their individual effect on setting time and the mechanical properties of the resulting geopolymer. The results suggested that generally the setting time increased with the NaOH molarity and the compressive strength of 59 MPa was obtained for geopolymer mixture cured at ambient temperature for 28 days with alkali to a cementitious ratio of 0.35 and 10 M NaOH. The results will be useful for developing the knowledge of the use of high calcium fly ash in producing geopolymer. This would be beneficial to the understanding the future applications of this material as new binding material.
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