ENERGY DISSIPATING MODES AND DESIGN RECOMMENDATION OF H-SHAPED STEEL BAFFLES SUBJECTED TO BOULDER IMPACT

Flexible barriers are one of the most effective protective structures, which have been widely used for the mitigation of rockfalls. As the only compression members in a flexible barrier system, steel posts maintain the integrity of the interception structure to keep the function of the system. Due to the random trajectories of rockfalls, steel posts may be impacted by boulders directly. The impact scenario may result in the failure of the post and even the collapse of the system. In this paper, firstly, steel baffles were proposed to be an additional structural countermeasure to avoid the direct impact of posts. Secondly, numerical method was adopted to study the structural behaviour of steel baffles under direct boulder impact. Then, an available published experimental test of H-shaped steel beams under drop weight impact loading by others was back analyzed to calibrate the finite element model. Finally, numerical simulations were carried out to investigate the energy dissipating modes and energy dissipating efficiency of the H-shaped steel baffles. The simulation results show that there are three typical energy dissipating modes of H-shaped baffles subjected to boulder impact, namely flexural, local compression buckling and shear buckling. Local compression buckling is the most efficient energy dissipating mode. The thickness of the web of an H-shaped baffle is suggested to be 4 mm and 6 mm for the rated dissipating energy of 50 kJ and 100 kJ, respectively.

Experimental Study on the Behavior of Polyurethane Springs for Compression Members

In this study, the characteristics of the compression behavior of polyurethane springs that can be used as compression members of seismic devices, such as dampers and seismic isolators, were identified, and the effect of the design variables on the performance points of polyurethane springs was investigated. Compressive stiffness and specimen size were set as the design variables of the polyurethane spring, and the performance indicators were set as maximum force, residual strain, and energy dissipation. A total of 40 specimens with different conditions were fabricated and a cyclic loading test was performed to obtain the force-displacement curve of the polyurethane spring and to check the performance indicator. Significant strength degradation was confirmed after the first cycle by repeated loading, and it was confirmed that compressive stiffness and size demonstrated a linear proportional relationship with maximum force. In addition, the design variables did not make a significant change to the recovered strain, including residual strain, and residual strain of about 1% to 3% occurred. Energy dissipation showed a tendency to decrease by about 60% with strength degradation after the first cycle, and this also demonstrated no relationship with the design variables. Finally, the relationship between the design variables and performance indicators set in this study was reviewed and suggestions are presented for developing a simple design formula for polyurethane springs.

Analysis and Design of Cable Stayed and Suspension Bridge Subjected to Wind Loading

Bridge can be defined as a structure which is built to pass a physical obstacle such as river road or valley and this structure does not close the way underneath it. The main objective of the bridgeis to provide a passage which can surpass any obstacle. A bridge is designed according to various specific purposes depending upon the need function and various physical factors. Cable-stayed bridge is having one or more columns called towers or pylons, with the cables directly supporting the bridge deck. Cable-stayed bridge is the bridge form in which the weight of the deck is supported by a number of nearly straight diagonal cables in tension running directly to one or more vertical towers. The towers transfer the cable forces to the foundations through vertical compression. The tensile forces in the cables also put the deck into horizontal compression. A suspension bridge is able to carry vertical loads with the help of curved cables in tension. Transfer of load takes place to both the towers, which is transferred by vertical compression to the ground, and anchorages, which is able to withstand the inward and occasionally vertical pull of the cables. The suspension bridge is often looked as an upside-down arch in tension with only the towers as compression members. In this research work, analysis and design of cable stayed and suspension bridge subjected to wind loading has been carried out.