Damage of adjacent bridge structures due to relative responses, such as pounding and unseating, have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces. However,... more
Damage of adjacent bridge structures due to relative responses, such as pounding and unseating, have been observed in many earthquakes. The isolators in bridge structures are effective in mitigating the induced seismic forces. However, the deck displacement becomes excessively large when subjected to ground motion with unexpected characteristics. This increases the possibility of pounding; and contributes to the unseating of bridge decks and subsequent collapse. An analytical model of expansion joints, that takes account of the interaction between adjacent bridge segments and the effect of impact and restrainers, is developed and nonlinear time history analyses are performed on a typical isolated multi-span bridge using three standard ground motions. The numerical simulation results show that pounding between adjacent bridge segments could amplify the relative displacement, resulting in the requirement of using an unseating prevention system. Restrainers are substantially effective in reducing the relative opening displacements and impact forces due to pounding at the expansion joints. However, the impact and the stretch of cable restrainers at expansion joints results in a large lateral force transfer from one deck to the other, which, consequently, significantly changes the global response of the participating structural systems. Therefore, it is effective to provide a shock absorber for the mitigation of impact effects between bridge segments or at the restrainers’ ends. The sudden changes of stiffness during poundings can be smoothed by using a natural rubber shock absorber, which prevents, to some extent, the acceleration peaks due to impact. The reaction forces at the pier bases and the pounding forces exerted on the superstructure can be satisfactorily reduced.
Starting from the investigation of the simple case of a cantilevered road deck, this paper attempts to demonstrate that deeper investigations of a structural safety problem may lead to significant modifications of the goals of the... more
Starting from the investigation of the simple case of a cantilevered road deck, this paper attempts to demonstrate that deeper investigations of a structural safety problem may lead to significant modifications of the goals of the investigation.The assignment by the owner authority consisted of assessing the bending moments due to traffic loads, above all from axle loads, at the clamping of a cantilevered slab and to propose appropriate measures if needed. The slab carries the road deck, being the hard shoulder of the Swiss North–South motorway close to the Italian border.In a first step, the regular axle loads of the new Swiss action code are applied to calculate the inner forces by simple hand calculations. It is found that the shear resistance is noticeably more critical than the bending resistance, considering both the new Swiss structural concrete code as well as, for reasons of comparison, Eurocode 2.In a second step, the reduction of the axle loads is investigated considering actualised load models developed for the assessment of existing road bridges. It is found that applying these models achieves structural safety in large parts of the structure, but that other parts still exhibit insufficient structural safety.In the third part, the possible range of strengthening measures is investigated. It is pointed out that every strengthening method should be carefully checked for its application conditions and the corresponding consequences. Qualitative criteria are adequate to judge a specific strengthening method in a certain situation. The last part of the paper discusses the effectively executed measures.Conclusions on the application of the findings from the paper to other assessment situations are drawn.
The goal of this research program was to investigate new and modified crystal-growth techniques that would lead to high-optical-quality BaTiO3 with increased photorefractive speed and sensitivity. The research program consisted of (1)... more
The goal of this research program was to investigate new and modified crystal-growth techniques that would lead to high-optical-quality BaTiO3 with increased photorefractive speed and sensitivity. The research program consisted of (1) feed material purification, (2) crystal growth by the top-seeded-solution technique as well as by a barium borate flux technique, (3) new furnace design studies and (4) photorefractive characterization experiments. Iron and nickel- doped BaTiO3 crystals were grown under the program. BaTiO3 is a promising photorefractive material due to its large electrooptic coefficient and excellent self-pumped phase conjugation. Our furnaces were limited by certain design and operating characteristics, and crystals grown in these furnaces were easily contaminated by the furnace itself. Two new furnaces, cylindrical and octagonal furnaces, were developed with commercially available parts that are cleaner, more mechanically reproducible , more uniform in temperature an...
Bridges are traditionally built with expansion joints at the ends to allow for longitudinal displacements of the superstructure due to temperature variations. Thus, most conventional bridges possess expansion joints and bearings, which... more
Bridges are traditionally built with expansion joints at the ends to allow for longitudinal displacements of the superstructure due to temperature variations. Thus, most conventional bridges possess expansion joints and bearings, which are expensive in their materials and installation. Elimination of expansion joints in bridges may reduce the construction costs, overcome many of the maintenance problems, and increase the stability and durability of the bridges. These economic and functional advantages are generally recognized by bridge Engineers leading to the concept of integral construction or integral bridge. The lack of expansion joints in integral bridges results in reduced repair and maintenance costs throughout the service life of the bridge. It improves seismic resistance and extends long-term serviceability. The need to design bridges to withstand flood and debris loads has long been recognised however bridges are still failing to live their entire design life when subjected to extreme flooding events. This project presents a structural evaluation of bridges when subjected to the flood loadings that took place in Kerala , 2018. For this study, an existing conventional bridge is selected and flood analysis is carried out using SAP 2000. For the same site conditions, an integral bridge with equivalent cross section is analyzed, and results are compared.
