• Earthquakes and Structures
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• v.3 no.2
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• pp.141-168
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• 2012

The Retrofit Yield Spectrum (RYS) is a new spectrum-based device that relates seismic demand of a retrofitted structure with the fundamental design parameters of the retrofit. This is obtained from superposition of Yield Point Spectra with design charts that summarize in pertinent spectrum-compatible coordinates the attributes of a number of alternative retrofit scenarios. Therefore, once the requirements for upgrading a given structure have been determined, the RYS enable direct insight of the sensitivity of the seismic response of the upgraded structure to the preliminary design decisions made while establishing the retrofit plan. By virtue of their spectrum-based origin, RYS are derived with reference to a single mode of structural vibration; a primary objective is to control the contribution of this mode in the retrofit design so as to produce a desirable distribution of damage at the ultimate limit state by removing soft storey formations and engaging the maximum number of structural members in deformation, in response to the input motion. Calculations are performed with reference to the yield-point, where secant stiffness is proportional to the flexural strength of reinforced concrete members. Derivation and use of the Retrofit Yield Spectra (RYS) refers to the seismic demand expressed either in terms of spectral acceleration, spectral displacement or interstory drift, at yield of the first storey. A reinforced concrete building that has been tested in full scale to a sequence of simulated earthquake excitations is used in the paper as a demonstration case study to examine the effectiveness of the proposed methodology.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1999.10a
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• pp.225-232
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• 1999

For the study of the seismic-response control, it is necessary to use an experimental system with an earthquake simulator and control devices employing a hydraulic actuator system. However, such system is too expensive to prepare at the university laboratory. In this research, an economical experimental system is developed which has a small-sized earthquake simulator and an AMD using AC servo motors. An accurate mathematical model of the three-degree-of-freedom tests structure with an AMD is developed from the measurement of the input/output relationships of the structure. This paper demonstrates experimentally the efficacy of the frequency domain optimal control algorithm H$_2$in reducing the response of seismically excited building to verify the performance of the experimental system.

• Earthquakes and Structures
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• v.27 no.4
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• pp.317-329
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• 2024

Recent earthquakes have demonstrated that even when the beams and columns in a reinforced concrete frame remain intact, the integrity of the whole structure is undermined if the joint where these members connect fails. A good seismic performance of reinforced concrete frames depends on their ability to absorb seismic energy through inelastic deformations and to avoid a sudden development of collapse mechanism in event of a strong earthquake shaking. The primary objective of this investigation is to move the plastic hinge away from the beam-column joint region and hence reducing the damage to the joint region. In this research, the seismic performance of exterior beam-column joints with four types of confinement in joint region and inclined bars from column to beam is investigated experimentally. Control specimens without inclined bars and four types of confinement Square Hoop, Square Spiral, Circular Hoop and Circular Spiral were tested along with inclined bars were tested. Seismic performance was determined via load-deflection response, ductility, stiffness, energy dissipation, strain of beam reinforcement and crack pattern. Out of the four specimens with inclined bars, seismic performance of joint with Square Spiral confinement gave the best performance in terms of all parameters.

• Journal of Korean Association for Spatial Structures
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• v.18 no.1
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• pp.18-21
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• 2018

• Coupled systems mechanics
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• v.7 no.3
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• pp.269-280
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• 2018

Post-earthquake damages investigation in past and recent earthquakes has illustrated that the ground motion spatial variation plays an important role in the structural response of long span bridges. For the structural control of seismic-induced vibrations of cable-stayed bridges, it is extremely important to include the effects of the ground motion spatial variation in the analysis for design of an effective control system. The feasibility and efficiency of different vibration control strategies for the cable-stayed bridge under multiple support excitations have been examined to enhance a structure's ability to withstand earthquake excitations. Comparison of the response due to non-uniform input ground motion with that due to uniform input demonstrates the importance of accounting for spatial variability of excitations. The performance of the optimized designed control systems for uniform input excitations gets worse dramatically over almost all of the evaluation criteria under multiple-support excitations.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.21 no.2
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• pp.127-133
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• 2008

The purpose of this study is to investigate the seismic performance of both exterior precast concrete cladding panels and their connections on steel frame, when these cladding systems are considered as the structural components. The degrees of their participation of lateral stiffness to the main building are evaluated in terms of different heights of the cladding panels. Considering the cladding system as an integrated building provides additional lateral stiffness, as well as a mechanism for energy dissipation and this system can be used as one of an advanced passive seismic control system. Hysteresis behaviors of connectors are modeled and integrated into a nonlinear finite element analysis program, ABAQUS. The results show that connections play the most important role in structural cladding system and they improve seismic performance of overall building response.

• Journal of Korean Association for Spatial Structures
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• v.22 no.2
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• pp.39-46
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• 2022

Recently, machine learning is widely used to solve optimization problems in various engineering fields. In this study, machine learning is applied to development of a control algorithm for a smart control device for reduction of seismic responses. For this purpose, Deep Q-network (DQN) out of reinforcement learning algorithms was employed to develop control algorithm. A single degree of freedom (SDOF) structure with a smart tuned mass damper (TMD) was used as an example structure. A smart TMD system was composed of MR (magnetorheological) damper instead of passive damper. Reward design of reinforcement learning mainly affects the control performance of the smart TMD. Various hyper-parameters were investigated to optimize the control performance of DQN-based control algorithm. Usually, decrease of the time step for numerical simulation is desirable to increase the accuracy of simulation results. However, the numerical simulation results presented that decrease of the time step for reward calculation might decrease the control performance of DQN-based control algorithm. Therefore, a proper time step for reward calculation should be selected in a DQN training process.

• Smart Structures and Systems
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• v.2 no.4
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• pp.339-355
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• 2006

A procedure to retrofit existing essential facilities subjected to seismic excitation is proposed. The main features of this procedure are to reduce maximum acceleration and associated forces in buildings subjected to seismic excitation by reducing their strength (weakening). The weakening retrofit, which is an opposite strategy to strengthening, is particularly suitable for buildings having overstressed components and foundation supports or having weak brittle components. However, by weakening the structure large deformations are expected. Supplementaldamping devices however can control the deformations within desirable limits. The structure retrofitted with this strategy will have, therefore, a reduction in the acceleration response and a reduction in the deformations, depending on the amount of additional damping introduced in the structure. An illustration of the above strategy is presented here through an evaluation of the inelastic response of the structure through a nonlinear dynamic analysis. The results are compared with different retrofit techniques. A parametric analysis has also been carried out to evaluate the effectiveness of the retrofitting method using different combination of the performance thresholds in accelerations and displacements through fragility analysis.

• Earthquakes and Structures
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• v.20 no.3
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• pp.353-364
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• 2021

Natural hazards like earthquakes, high winds, and tsunami are a threat all the time for multi-story structures. The environmental forces cannot be clogged but the structures can be prevented from these natural hazards by using protective systems. The structural control can be achieved by using protective systems like the passive, active, semi-active, and hybrid protective systems; but the semi-active protective system has gained importance because of its adaptability to the active systems and reliability of the passive systems. Therefore, a semi-active protective system for the earthquake forces has been adopted in this work. Magneto-Rheological (MR) damper is used in the structure as a semi-active protective system; which is connected to the current driver and proposed controller. The Proportional Integral Derivative (PID) controller and reliable PID controller are two proposed controllers, which will actuate the MR damper and the desired force is generated to mitigate the vibration of the structural response subjected to the earthquake. PID controller and reliable PID controller are designed and tuned using Ziegler-Nichols tuning technique along with the MR damper simulated in Simulink toolbox and MATLAB to obtain the reduced vibration in a three-story benchmark structure. The earthquake is considered to be uncertain; where the proposed control algorithm works well during the presence of earthquake; this paper considers robustness to provide satisfactory resilience against this uncertainty. In this work, two different earthquakes are considered like El-Centro and Northridge earthquakes for simulation with different controllers. In this paper performances of the structure with and without two controllers are compared and results are discussed.

• Earthquakes and Structures
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• v.15 no.2
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• pp.133-144
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• 2018

To study the effectiveness of sliding isolation in a CRLSS (concrete rectangular liquid-storage structure) and develop a reasonable limiting-device method, dynamic responses of non-isolation, sliding isolation with spring limiting-devices and sliding isolation with steel bar limiting-devices are comparatively studied by shaking table test. The seismic response reduction advantage of sliding isolation for concrete liquid-storage structures is discussed, and the effect of the limiting-device type on system dynamic responses is analyzed. The results show that the dynamic responses of sliding isolation CRLSS with steel bar-limiting devices are significantly smaller than that of sliding isolation CRLSS with spring-limiting devices. The structure acceleration and liquid sloshing wave height are greatly influenced by spring-limiting devices. The acceleration of the structure in this case is close to or greater than that of a non-isolated structure. Liquid sloshing shows stronger nonlinear characteristics. On the other hand, sliding isolation with steel bar-limiting devices has a good control effect on the structural dynamic response and the liquid sloshing height simultaneously. Thus, a limiting device is an important factor affecting the seismic response reduction effect of sliding isolation. To take full advantage of sliding isolation in a concrete liquid-storage structure, a reasonable design of the limiting device is particularly important.