14 research outputs found
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Multi-angle and non-uniform ground motions on cable-stayed bridges
The definition of the spatial variability of the ground motion (SVGM) is a complex and multi-parametric problem. Its effect on the seismic response of cable-stayed bridges is important, yet not entirely understood to date. This work examines the effect of the SVGM on the seismic response of cable-stayed bridges by means of the time delay of the ground motion at different supports and of the loss of coherency of the seismic waves. The focus herein is the effect of the SVGM on cable-stayed bridges with various configurations in terms of their length and of design parameters such a s t he pylon shape and the pylonâcable system configuration, combined with the influence of the incidence angle of the earthquakes. The aim of this paper is to provide general conclusions that are applicable to a wide range of cable-stayed bridges, instead of attempting to interpret the effect SVGM on a case-by-case basis, and to contribute to the ongoing effort to interpret and predict the effect of the SVGM. It has been found that the effect of the SVGM on the seismic response of cable-stayed bridges varies depending on the pylon shape, height and section dimensions, on the cable-system configuration and on the response quantity of interest. Furthermore, the earthquake incidence angle defines whether t he S VGM is important t o t he seismic response of the cable-stayed bridges. It is also observed that the SVGM excites vibration modes of the bridges that do not contribute to their seismic response when identical support motion is considered
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Dynamics and seismic performance of asymmetric rocking bridges
The governing equations of motion for bridges with rocking piers of unequal height and unequal span lengths are derived accounting for the effect of end joint gaps and the abutment-backfill system. The attenuation of the rocking motion stems from the impacts at the rocking interfaces, described through the coefficient of restitution, and also from the impacts (pounding) of the superstructure on the abutment backwalls. This is the first study that combines both energy dissipation sources in the analytical derivation of the equations of motion. The results of response-history analysis of bridges with different levels of asymmetry in their pier height show that the performance of both the symmetric and asymmetric configurations is very similar with regard to longitudinal displacements. Although the studied bridges safely resisted ground motions with an intensity about twice that of the design earthquake, regardless of the degree of asymmetry, it was found that the higher the difference in the pier height, the larger is the rotation of the superstructure due to the differential uplift of the piers, a point that has to be addressed in seismic design for rocking response
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A Method for Along-wind Vibration Control of Chimneys by Tuning Liners
Reinforced concrete chimneys with steel liners are widely used in waste gas discharge of industrial facilities, and guaranteeing their safety performance in harsh environments is important for industries and society. This paper proposes a novel method for the reduction of along-wind vibration in chimneys with liners by tuning the movement of the suspended liners to the response of the outer cylinder, and the conventional rigid supporting platform is replaced by a combination of radial horizontal tuning systems and vertical suspension systems. This âtuned linersâ method is applied to a simplified beam-like model that is able to capture the liners/chimney interaction and is validated against a more detailed finite-element shell model. A design method is proposed to obtain parameters of the tuning system that lead to significant reduction of along-wind vibrations whilst satisfying the relative response requirement. A comprehensive study of the structural vibration under stochastic wind actions is performed to demonstrate the effectiveness of the proposed system. The characteristics of the relative vibration of the outer cylinder and the liners are studied. Comparison with conventional TMD solution is conducted to further explore the advantage of the tuned-liners system under stochastic wind actions. The results indicate that the top displacement and acceleration of the outer cylinder is effectively reduced by 62% and 70% with the tuned liners, respectively. A similar performance using a conventional TMD would require an auxiliary vibrating mass that is approximately 300 tons, which is avoided with the proposed tuned liners. Results show that the proposed technique could be effective in the wind-induced control of chimneys in multiple directions, even with some unintentional eccentricities
The impact of surgical delay on resectability of colorectal cancer: An international prospective cohort study
The SARS-CoV-2 pandemic has provided a unique opportunity to explore the impact of surgical delays on cancer resectability. This study aimed to compare resectability for colorectal cancer patients undergoing delayed versus non-delayed surgery