New trends in the architectural design of footbridges feature an unprecedented slenderness, especially when these are located in the urban environment. For this reason, static analyses and a design towards the ultimate limit state have proven inadequate in many circumstances, and the main objective in the structural design is becoming that of assessing the serviceability limit state through dynamic analyses. On the other hand, the key issue of dynamic analyses is the availability of reliable models for the structure and for loads, and in the particular case of pedestrian action the lack of commonly accepted models for walking, running and jumping has become the weak link in the whole structural design process. In a first stage of the present work, vibration measurements were taken on a recently built cable-stayed footbridge, whose second vibration mode was excited by runners. As a second step, a dynamic loading model for the vertical component of the running-induced force was developed, which was used for the finite element analyses of the footbridge. Finally, tuned mass dampers (TMDs) represent a quite mature technology for reducing the resonant response of flexible structures, but their effectiveness is heavily dependent on the tuning ratio. In the case of footbridges, pedestrians can act as a significant part of the vibrating mass; thus, varying the vibration frequency, which makes it difficult to properly tune the damper frequency. Semi-active TMDs can be looked at as passive devices able to adjust their dynamic parameters according to a given control logic. A physical description of a control algorithm is given in the paper, and its performance is discussed.
The possibility of reducing structural response under strong external excitations such as earthquakes and wind storms via control systems is attracting the interest of a large number of researchers. In the field of civil structures, control systems based on semi-active devices seem to be close to feasible implementation. Semi-active devices are typically passive elements capable of self-adjusting their own mechanical properties according to the instantaneous response of the hosting structure and, therefore, they can be considered as smart devices. Even though dampers based on magnetorheological fluids are considered very effective in practical implementations, the literature examining their properties from the structural control point of view is still quite limited. This paper aims to show the potential of such devices and to describe their properties from this special perspective. These properties include manufacturing issues, powering, range of variability of the mechanical parameters, their dependence on the feed current and overall response time.
This paper presents the results of an extensive experimental campaign of bond tests aimed to assess and compare the influence of several environmental conditioning factors (humidity and temperature) on the bond behavior of two different types of composites systems glued to concrete elements: a fiber-reinforced polymer (FRP) system made of a carbon sheet applied with epoxy resin and a polybenzoxozole (PBO) grid applied with a cement-based mortar, i.e., a fiber-reinforced cementitious matrix (FRCM) system. Several environmental conditions have been considered (partial immersion in water at 23, 30, and 40°C for short and long periods with and without further drying processes, exposure in air at 30 and 40°C) before testing the specimens according to two well-known setups for bond tests: a single push-pull shear test and a beam test. The experimental results were mainly analyzed in terms of failure modes and loads, showing a clearly negative effect of the conditioning factors for the specimens with the carbon fibre reinforced polymer (CFRP) sheet as the conditioning time increases because of the plasticization phenomena of the epoxy adhesive. Conversely, for the specimens with the PBO grid, the failure loads were slightly lower or even greater than the ones relieved for the reference specimens as the exposure periods increase, whereas in the case of short exposure, the bond strength reduced and the scattering of the experimental resulted increased
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.