Performance of Bridges Isolated with Sliding-Lead Rubber Bearings Subjected to Near-Fault Earthquakes

This paper investigates the seismic performance of bridges installed with a sliding-lead rubber bearing (LRB) isolation system subjected to near-fault earthquakes. A three-span continuous bridge isolated with sliding-LRB system is used as an example. Nonlinear time history analyses are conducted to investigate the sensitivity effects of isolation period, friction coefficient and sliding displacement limit on the bridge responses. The responses of the sliding-LRB system are compared with those of the conventional LRB system. The results show that the base forces of the piers can be reduced by employing proper friction coefficients. However, the residual displacement of the sliding-LRB system may be larger compared with that of the conventional LRB system. To overcome this disadvantage, an improved solution to reduce the residual displacement is proposed with its effectiveness investigated. It was also demonstrated that the residual displacement and peak displacement can be effectively reduced by employing the shape memory alloy devices in the sliding-LRB system without significantly increasing the base forces.

Effects of temperature and lead core heating on response of seismically isolated bridges under near-fault excitations

Seismic responses of bridges isolated by lead rubber bearings under near-fault excitations are presented in this article. A bilinear force-deformation model is employed to represent the hysteretic behaviors of lead rubber bearings. The joint effects of ambient temperature, initial displacement, and lead core heating on the responses of seismically isolated bridges are investigated. Nonlinear time history analyses are conducted with the employed hysteretic models of lead rubber bearings. Comparisons of the responses with and without the joint effects are performed, in terms of maximum isolator displacements, maximum isolator forces, and base forces of the piers. Results show that ambient temperature, initial displacement, and lead core heating have significant joint effects on the responses of seismically isolated bridges. When such joint effects are ignored at low temperatures, the maximum isolator displacements could be overestimated, whereas the maximum isolator forces and the base forces could be underestimated. However, as for ambient temperatures above 20°C, the maximum isolator displacements could be underestimated, whereas the maximum isolator forces and the base forces could be overestimated with small maximum isolator displacements and underestimated with large maximum isolator displacements.

Liberating the River: Land and Politics in Tagore’s Plays

In matters of development and progress, it has always been a question of the acquisition of land. As history shows, control over land—extendable to different metaphors—and its resources has been instrumental in the development and destruction of human civilisation. Tagore’s Muktadhara dwells on the principle of identifying how the manipulation of a river-course could change the destiny of two neighbouring states and establish the rule of one man over others. So, in the character of Abhijeet, a typical Tagore-protagonist, one who breaks the dam to put an end to the authoritarian regime, a prototype of modern day environmental activists could be seen. The text goes beyond a mere pantheistic and humanist quest for the freedom of man as Tagore politicises the concept of land into a geopolitical space, and relates it to the imperialist policies and hegemonic propaganda that he experienced personally in his travels across Europe, Japan and America during this time. From Muktadhara (1922) to Raktakarabi (1924), Tagore seems to continue with this politics of land. If the former text represents the appropriation of nature for political benefit, the latter shows how industrialisation destroys the agricultural base, forces migration, and how these steps would be the only logical progress of the economy that advocates rampant capital accumulation. Interestingly, a play set in a mine uses a theme song about ‘pous’—a month of cultivation and opulence. The essays written by Tagore during this period, like his Introduction to Elmhirst’s ‘The Robbery of the Soil’, also reveal his vision of a sustained and inclusive human development.

Passive Control System for Mitigation of Longitudinal Buffeting Responses of a Six-Tower Cable-Stayed Bridge

This paper presents an investigation of mitigation of longitudinal buffeting responses of the Jiashao Bridge, the longest multispan cable-stayed bridge in the world. A time-domain procedure for analyzing buffeting responses of the bridge is implemented in ANSYS with the aeroelastic effect included. The characteristics of longitudinal buffeting responses of the six-tower cable-stayed bridge are studied in some detail, focusing on the effects of insufficient longitudinal stiffness of central towers and partially longitudinal constraints between the bridge deck and part of bridge towers. The effectiveness of viscous fluid dampers on the mitigation of longitudinal buffeting responses of the bridge is further investigated and a multiobjective optimization design method that uses a nondominating sort genetic algorithm II (NSGA-II) is used to optimize parameters of the viscous fluid dampers. The results of the parametric investigations show that, by appropriate use of viscous fluid dampers, the top displacements of central towers and base forces of bridge towers longitudinally restricted with the bridge deck can be reduced significantly, with hampering the significant gain achieved in the base forces of bridge towers longitudinally unrestricted with the bridge deck. And the optimized parameters for the viscous fluid dampers can be determined from Pareto-optimal fronts using the NSGA-II that can satisfy the desired performance requirements.

Multiobjective Optimal Control of Longitudinal Seismic Response of a Multitower Cable-Stayed Bridge

The dynamic behavior of a multitower cable-stayed bridge with the application of partially longitudinal constraint system using viscous fluid dampers under real earthquake ground motions is presented. The study is based on the dynamic finite element model of the Jiashao Bridge, a six-tower cable-stayed bridge in China. The prime aim of the study is to investigate the effectiveness of viscous fluid dampers on the longitudinal seismic responses of the bridge and put forth a multiobjective optimization design method to determine the optimized parameters of the viscous fluid dampers. The results of the investigations show that the control objective of the multitower cable-stayed bridge with the partially longitudinal constraint system is to yield maximum reductions in the base forces of bridge towers longitudinally restricted with the bridge deck, with slight increases in the base forces of bridge towers longitudinally unrestricted with the bridge deck. To this end, a multiobjective optimization design method that uses a nondominating sort genetic algorithm II (NSGA-II) is used to optimize parameters of the viscous fluid dampers. The effectiveness of the proposed optimization design method is demonstrated for the multitower cable-stayed bridge with the partially longitudinal constraint system, which reveals that a design engineer can choose a set of proper parameters of the viscous fluid dampers from Pareto optimal fronts that can satisfy the desired performance requirements.

Research on the Wind Tunnel Force Balance Tests of Long-Span Closed Coal Trestle

Structures with long span and high flexibility are very sensitive to the wind forces, so it is necessary to study on the wind effects on such structures. In this paper, based on section model wind tunnel high-frequency force balance tests, two horizontal base bending moments and shear forces of the typical supporting columns as well trestle bridge deck of the closed coal trestle under different wind directions were measured. The shape coefficients and their variations with the wind directions of the typical supporting columns as well trestle bridge deck were calculated then analyzed by the mean values of base forces. The experimental values of the shape coefficients were compared with those in the Chinese Load Code, the results shown that both were in good agreement, which verified the reliability of the test, which also illustrated that wind-resistant design of the coal trestle in accordance with the Code was reasonable. Based on analysis of the variances of base forces between overall model with and without surrounding buildings, influences of surroundings buildings were studied. Interference factors were proposed which provided the basis for the base forces checking and wind-resistant design of the long-span closed coal trestle structures.

Path-Independent Ĵ-Integral Based on Finite Deformation Theory

For a finite deformation body, there are large strains and displacements on the crack tip. So it is necessary to study-integral based on finite deformation theory. Base forces theory is a new theory for describing finite deformation. In this paper, -integral based on base forces theory are presented. This work provides a new theoretical foundation for studying dynamic crack propagation.

A 4-Mid-Node Plane Model of Base Force Element Method on Complementary Energy Principle

Using the base forces as fundamental variables to describe the stress state and the displacement gradients that are the conjugate variables of the base forces to describe the deformation state for the two-dimensional elasticity problems, a 4-mid-node plane model of base force element method (BFEM) based on complementary energy principle is proposed. In this paper, the complementary energy of an element of the BFEM is constructed by using the base forces. The equilibrium conditions are released by the Lagrange multiplier method, and a modified complementary energy principle described by the base forces is obtained. The formulation of the 4-mid-node plane element of the BFEM is derived by assuming that the stress is uniformly distributed on each edge of the plane elements. A procedure of the BFEM on complementary energy principle is developed using MATLAB language. The numerical results of examples show that this model of the BFEM has high precision and is free from mesh sensitivity. This model shows good performances.