PUBLISHED WORKS

January 24, 2015
4th International Conference on Bridges (4IBC), Iran

SEISMIC BEHAVIOR AND VIBRATION CONTROL OF LALI CABLE-STAYED BRIDGE USING TMD

With the length of 460 m, Lali Cable-Stayed Bridge is located in Khouzestan, Iran, crossing Karoun River. Because of the great importance of this bridge and the earthquake-prone area in which it is located, its seismic behavior is by far an essential issue which should be investigated precisely. Vibration control of such important structures is considered as a beneficial and economical method in order to reduce hazard probability. An effective passive control system for vibration mitigation of cable-stayed bridges is to utilize tuned mass dampers (TMDs). Relatively complex behavior of cable-stayed bridges leads us to a great demand for using a strong finite element software to achieve thorough and effective simulations and analyses. The simulation should include the real behavior of different types of elements, especially the RC and pre-stressed cable elements as well as the possibility to provide TMD system with variable characteristics to optimize the control system.
The present study deals with simulation, seismic response, and vibration control of Lali Bridge. A comprehensive 3-D model is created using OpenSees software. Pre-stressed cable elements are modeled using a special kind of material intended to represent the most possibly real behavior of cable elements. Seismic response of the bridge is investigated using adequate excitation records. Some TMD systems are utilized in order to mitigate the vibration of the bridge subjected to different excitation records. In each case, the characteristics of TMD system are modified in order to achieve optimized condition. Finally, the effects of mass, stiffness, damping ratio, and number of TMDs installed on the bridge, on the efficiency of control systems are discussed.

July 29, 2015
International Conference on Civil Engineering, Architecture, and urban infrastructure, Iran

VIBRATION CONTROL OF AN INCLINED SAGGED CABLE USING TWO DIFFERENT PASSIVE SYSTEMS, A COMPARATIVE STUDY

Cables are widely used in different structures such as cable stayed bridges, suspension bridges, and other cable structures. The dynamic behavior of an inclined sagged cable as an individual structural element, is highly complicated due to its high tension and geometrical nonlinearity. Moreover, the high flexibility and low inherent structural damping of stay cables, intensify their vulnerability to seismic support excitations as well as rain-wind induced vibrations. For vibration mitigation of cables, two different major systems are commonly used: first, transversely attached mechanical dampers, with one end connected to the cable and the other end to the ground; and second, tuned mass dampers (TMDs) which can be installed along the cable without position limitations. In this study the structural behavior of a three dimensional (3-D) nonlinear inclined stay cable with sag is simulated in OpenSees software with finite element method. The two aforementioned major kinds of control systems are applied to the cable. The control systems are subjected to different support excitations, and their efficiency is calculated based on three performance criteria. Then, the efficiency of each control system is examined and compared with others’. The results show that the both kinds of control systems are capable of making remarkable reductions in seismic response of the inclined sagged cable. The normed value of cable displacement can be suppressed by up to 79 and 74 percent using TMD systems and fixed transversely attached dampers, respectively. However, the latter system exhibits a relatively lower efficiency. In other words, in order to achieve an equal efficiency, an excessively much higher damping coefficient is needed in fixed transversely attached dampers compared to TMD systems.

July 29, 2015
International Conference on Civil Engineering, Architecture, and urban infrastructure, Iran

APPLICATION OF TMD SYSTEMS IN VIBRATION CONTROL OF STAY CABLES SUBJECTED TO SEISMIC LOADING

Stay cables are crucial elements that greatly influence the structural behavior of cable stayed bridges. Cable elements are susceptible to external excitations due to their high flexibility and low inherent damping. Though traditional mechanical dampers, with one end connected to the cable and the other end to the deck, are useful for vibration reduction, their installation position restrictions make their efficiency low. Tuned mass dampers (TMDs) which can be placed anywhere along cables, are more effective for cable vibration mitigation. In this study a two dimensional stay cable with sag coupled with the TMD is simulated in OpenSees software. Nine control systems with differences in number of TMDs, mass ratio, and TMD location are utilized. The control systems are subjected to different external seismic excitations and their efficiency is evaluated by comparing the system's responses with those of the uncontrolled system based on three different criteria. The results show that the implementation of the control systems can effectively reduce the seismic response of stay cables by reducing the maximum displacement of the cable by up to 76 percent. The optimum frequency of TMD systems is close to the fundamental natural frequency of cable. Increasing the mass ratio of TMD leads to an increase in effectiveness of control system, but the economic and practical limitations usually prevent us from using mass ratios more than 5 percent. The optimal location for installing the TMD is at the midpoint of the cable in which the maximum displacement is more likely to happen. Utilizing additional masses in quarter points does not bring out a remarkable promotion in the efficiency of control system.

May 08, 2018
11th International Congress on Civil Engineering, Iran

VIBRATION CONTROL OF NONLINEAR STAY  CABLES USING SEMI-ACTIVE RESETTABLE SMART DAMPERS

Resettable smart dampers, also known as pneumatic springs, are deemed as promising semi-active control devices for application to civil engineering structures. They are low-cost, highly-reliable, and effective energy dissipators. Stay cables are inclined structural elements with sag which are vulnerable to seismic excitations due to their high tension, geometrical nonlinearity, high flexibility, and low inherent damping. In present study, the main goal is to investigate the application of resettable devices for vibration mitigation of inclined sagged stay cables subjected to earthquake loading. A 120 m long stay cable of Lali Bridge is considered and its structural behavior is simulated using a three dimensional (3-D) nonlinear model in OpenSees. Three different control systems are utilized to suppress the cable vibrations. The first control system is a conventional Tuned Mass Damper (TMD) including a lumped mass connected to the cable using a viscous damper in parallel with a spring. In the second control system, the lumped mass is connected to the cable using a single resettable spring. Finally, the third system utilizes a viscous damper in parallel with a resettable spring. The control systems are subjected to different support excitations, and their efficiency is calculated based on four performance criteria. The performance of the systems is evaluated and compared to each other. The results show that the proposed control systems are capable of remarkably reducing the dynamic response of the cable with respect to the uncontrolled system. Despite of its simple configuration, the performance of the single resettable spring is comparable to the conventional TMD. Moreover, including pneumatic spring instead of conventional spring element increases the efficiency of control system.

December 17, 2018
KSCE Journal of Civil Engineering, Springer

INNOVATIVE MOBILE TMD SYSTEM FOR SEMI-ACTIVE VIBRATION CONTROL OF INCLINED SAGGED CABLES

In this study an innovative mobile Tuned Mass Damper (TMD) system is proposed which enables the TMD device to move along the cable and optimize its position. A three  dimensional model of an inclined cable with sag is created using OpenSees. A mobile TMD device incorporating a semi-active Magnetorheological (MR) damper is implemented. Nine different control strategies, including six fuzzy strategies as well as a continuous sky-hook, an on-off sky-hook, and a passive-on strategy, are employed for the purpose of vibration mitigation. A locating algorithm is also devised so as to optimize the TMD position. A specific load pattern containing a chirp signal is utilized with the purpose of performing the nonlinear time history analyses. The results investigate the efficiency of different control systems in a comparative manner. The effect of locating algorithm is also examined. The results claim that although the suggested control systems can effectively reduce the displacements of the cable, they are relatively incompetent to make a remarkable reduction in maximum and normed values of the cable tension. The output data certify the significant contribution of LA for promoting the performance of control systems. This algorithm especially influences the reduction of normed values of displacement. In general, the fuzzy control algorithms show a much higher performance compared with the passive-on and sky-hook counterparts.

2019
Journal of Vibration and Control, SAGE

INNOVATIVE ADAPTIVE VISCOUS DAMPER TO
IMPROVE SEISMIC CONTROL OF STRUCTURES

In this paper, a new adaptive viscous damper (AVD) is proposed and required equations are developed to describe its
mechanical behavior. As opposed to conventional adaptive devices, the proposed damper is capable of adapting its own mechanical properties without any need for other devices such as sensors, processing unit, actuators, energy supplies, and wired or wireless connections. Eliminating such equipment not only reduces costs, but also removes related time lag and improves the efficiency of the control system. The proposed AVD includes a cylinder filled with viscous fluid and a piston with a nozzle at its head. The passing area of the nozzle is variable and as a result, the device can cover a range of damping coefficients. For non-extreme excitations, the damping coefficient is relatively small and consequently the damping force is reduced. Conversely, when extreme movements occur, the nozzle contracts a bit and generates relatively large control forces in order to protect the main structure efficiently. The mechanical model of the AVD is created in OpenSees and the damper is implemented in a two-story building example subjected to different earthquake records. The results show that compared to a typical viscous device, the proposed AVD can reduce the mean values of displacement, acceleration, and base shear by up to 52.5, 62.9, and 44.4% and increase the energy dissipation by up to 94.3% for extreme cases. Moreover, for non-extreme cases, the AVD shows a more flexible behavior and reduces the unfavorable damping forces.