• Smart Structures and Systems
• /
• 제23권3호
• /
• pp.307-318
• /
• 2019

The frequently excessive vibrations presented in civil structures during seismic events or service conditions may result in users' discomfort, or worst, in structures failure, producing economic and even human casualties. This work contributes in proposing the synthesis of a nonlinear optimal control strategy for semiactive structural control, with the main characteristic that the synthesis considers both the structure model and the semiactive actuator nonlinear dynamics, which produces a nonlinear system that requires a nonlinear controller design. The aim is to reduce the unwanted vibrations in the response of civil structures, by means of intelligent fluid semiactive actuator such as the Magnetorheological Damper (MRD), which is a device with a low level of power consumption. The civil structures for which the proposed control methodology can be applied are those admitting a state-dependent coefficient factorized representation model, such as buildings, bridges, among others. A scaled model of a three storey building is analyzed as a case study, whose dynamical response involves displacement, velocity and acceleration of each one of the storeys, subjected to the North-South component of the September 19th., 2017, Puebla-Morelos (7.1M), Mexico earthquake. The investigation rests on comparing the structural response over time for two different conditions: with no control device installed and with one MRD installed between the first floor and the ground, where a nonlinear optimal signal for the MRD input voltage is determined. Simulation results are presented to show the effectiveness of the proposed controller for reducing the building's dynamical response.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 춘계 학술발표회 논문집
• /
• pp.435-442
• /
• 2002

본 연구에서는 사장교의 제어기법 개발을 위한 구조물로 제공되는 벤치마크(benchmark) 사장교에 대해 복합제어 기법을 적용하였다. 이 벤치마크 문제에서는 2003년 완공 예정으로 미국 Missouri 주에 건설 중인 Cape Girardeau 교를 대상 구조물로 고려하였다. Cape Girardeau 교는 New Madrid 지진구역에 위치하고, Mississippi 강을 횡단하는 주요 교량이라는 점 때문에 설계단계에서부터 내진 문제에 대하여 자세하게 고려되었다. 상세 설계도면을 기반으로 하여 교량의 전체적인 거동 특성을 정확하게 나타낼 수 있는 3차원 모델이 만들어졌고, 사장교의 제어 성능에 관련된 평가 기준이 수립되었다. 본 연구에서 사용한 복합제어 기법이란 지진하중으로 인해 구조물에 발생되는 하중을 줄이기 위한 수동제어 기법과 상판변위와 같은 구조물의 응답을 추가적으로 제어하기 위한 능동제어 기법이 결합된 제어방법이다. 수동제어 장치로는 현재 일반적으로 많이 사용되고 있는 납고무받침(lead rubber bearing)을 사용하였다. 능동제어 방법에는 $H_2$/LQG 제어 알고리듬(algorithm)을 사용하였다. 수치해석 결과 제안방법의 성능은 수동제어 방법에 비해 매우 효과적이며, 능동제어 방법에 비해서는 좀더 좋은 제어성능을 나타내었다. 또한, 복합제어 방법은 수동제어 부분 때문에 능동제어 방법에 비해 좀더 신뢰할 수 있는 제어 방법이다. 따라서 제안된 제어방법은 지진하중을 받는 사장교의 제어를 위해 효과적으로 사용될 수 있다.

• Structural Monitoring and Maintenance
• /
• 제3권1호
• /
• pp.51-69
• /
• 2016

Monitoring the performance and estimating the remaining useful life of aging civil infrastructure in the United States has been identified as a major objective in the civil engineering community. Structural health monitoring has emerged as a central tool to fulfill this objective. This paper presents a review of the major structural monitoring programs that have been recently implemented in the United States, focusing on the integrity and performance assessment of large-scale structural systems. Applications where response data from a monitoring program have been used to detect and correct structural deficiencies are highlighted. These applications include (but are not limited to): i) Post-earthquake damage assessment of buildings and bridges; ii) Monitoring of cables vibration in cable-stayed bridges; iii) Evaluation of the effectiveness of technologies for retrofit and seismic protection, such as base isolation systems; and iv) Structural damage assessment of bridges after impact loads resulting from ship collisions. These and many other applications show that a structural health monitoring program is a powerful tool for structural damage and condition assessment, that can be used as part of a comprehensive decision-making process about possible actions that can be undertaken in a large-scale civil infrastructure system after potentially damaging events.

• Smart Structures and Systems
• /
• 제4권2호
• /
• pp.183-194
• /
• 2008

An important historical monument of Cyprus is an aqueduct that was built in 1747 to provide water to the city of Larnaca and to its port. Because of its importance to the cultural heritage of Cyprus, the aqueduct has been selected as one of the case-study monuments in the project Wide-Range Non-Intrusive devices toward Conservation of Historical Monuments in the Mediterranean Area (WIND-CHIME). Detailed drawings of the aqueduct obtained from the Department of Antiquities of Cyprus have been used for the development of a computational model. The model was fine-tuned through the measurement of the dynamic characteristics of the aqueduct using forced and ambient vibrations. It should be noted that measurement of the dynamic characteristics of the structure were performed twice in a period of three years (June of 2004 and May of 2007). Significant differences were noted and they are attributed to soil structure interaction effects due to seasonal variations of the water-level in a nearby salt-lake. The system identification results for both cases are presented here. This monument was used to test the effectiveness of shape memory alloy (SMA) pre-stressed devices, which were developed during the course of the project, in protecting it without spoiling its monumental value.

• Steel and Composite Structures
• /
• 제26권5호
• /
• pp.573-582
• /
• 2018

This study develops and numerically verifies an innovative seismically resilient bracing system. The proposed self-centering tension-only brace (SC-TOB) is composed of a tensioning system to provide a self-centering response, a frictional device for energy dissipation, and a high-strength steel cable as a bracing element. It is considered to be an improvement over the traditional self-centering braces in terms of lightness, high bearing capacity, load relief, and double-elongation capacity. In this paper, the mechanics of the system are first described. Governing equations deduced from the developed analytical model to predict the behavior of the system are then provided. The results from a finite element validation confirm that the SC-TOB performs as analytically predicted. Key parameters including the activation displacement and load, the self-centering parameter, and equivalent viscous damping are investigated, and their influences on the system behavior are discussed. Finally, a design procedure considering controlled softening behavior is developed and illustrated through a design example.

• Smart Structures and Systems
• /
• 제5권3호
• /
• pp.209-221
• /
• 2009

A control algorithm for seismic protection of building structures based on the theory of variable structural control or sliding mode control is presented. The paper focus in the design of sliding surface. A method for determining the sliding surface by pole assignment algorithm where the poles of the system in the sliding surface are obtained on-line, based on the frequency content of the incoming earthquake signal applied to the structure, is proposed. The proposed algorithm consists of the following steps: (i) On-line FFT process is applied to the incoming part of the signal and its frequency content is recognized. (ii) A transformation of the frequency content to the complex plane is performed and the desired location of poles of the controlled structure on the sliding surface is estimated. (iii) Based on the estimated poles the sliding surface is obtained. (iv) Then, the control force which will drive the response trajectory into the estimated sliding surface and force it to stay there all the subsequent time is obtained using Lyapunov stability theory. The above steps are repeated continuously for the entire duration of the incoming earthquake. The potential applications and the effectiveness of the improved control algorithm are demonstrated by numerical examples. The simulation results indicate that the response of a structure is reduced significantly compared to the response of the uncontrolled structure, while the required control demand is achievable.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2002년도 가을 학술발표회 논문집
• /
• pp.338-345
• /
• 2002

This paper presents a hybrid control strategy for seismic protection of a benchmark cable-stayed bridge, which is provided as a testbed structure for the development of strategies for the control of cable-stayed bridges. In this study, a hybrid control system is composed of a passive control system to reduce the earthquake-induced forces in the structure and an active control system to further reduce the bridge responses, especially deck displacements. Lead rubber bearings and ideal hydraulic actuators are used fur the passive and active control systems. Bouc-Wen model is used to simulate the nonlinear behavior of lead rubber bearings and an H₂/LQG control algorithm is adopted as an active control algorithm. Numerical simulation results show that the performance of the proposed hybrid control strategy is superior to that of the passive control strategy and slightly better than that of the active control strategy. The proposed control method is also more reliable than the fully active control method due to the passive control part. Therefore, the proposed hybrid control strategy can effectively be used to seismically excited cable-stayed bridges.

• Steel and Composite Structures
• /
• 제2권1호
• /
• pp.1-20
• /
• 2002

Fiber-Reinforced Plastics (FRP) have received significant attention for use in civil infrastructure due to their unique properties, such as the high strength-to-weight ratio and stiffness-to-weight ratio, corrosion and fatigue resistance, and tailorability. It is well known that FRP wraps increase the load-carrying capacity and the ductility of reinforced concrete columns. A number of researchers have explored their use for seismic components. The application of concern in the present research is on the use of FRP for corrosion protection of reinforced concrete columns, which is very important in cold-weather and coastal regions. More specifically, this work is intended to give practicing engineers with a more practical procedure for estimating the strength of a deficient column rehabilitated using FRP wrapped columns than those currently available. To achieve this goal, a stress-strain model for FRP wrapped concrete is proposed, which is subsequently used in the development of the moment-curvature relations for FRP wrapped reinforced concrete column sections. A comparison of the proposed stress-strain model to the test results shows good agreement. It has also been found that based on the moment-curvature relations, the balanced moment is no longer a critical moment in the interaction diagram. Besides, the enhancement in the loading capacity in terms of the interaction diagram due to the confinement provided by FRP wraps is also confirmed in this work.

• Earthquakes and Structures
• /
• 제10권1호
• /
• pp.239-260
• /
• 2016

Tuned mass dampers (TMDs) have been frequently proposed to mitigate the detrimental effects of dynamic loadings in structural systems. The effectiveness of this protection strategy has been demonstrated for wind-induced vibrations and, to some extent, for seismic loadings. Within this framework, recent numerical studies have shown that beneficial effects can be achieved by placing a linear TMD on the roof of linear elastic structural systems subjected to pulse-like ground motions. Motivated by these positive outcomes, closed-form design formulations have been also proposed to optimize the device's parameters. For structural systems that undergo a near-fault pulse-like ground motion, however, it is unlikely that their dynamic response be linear elastic. Hence, it is very important to understand whether such strategy is effective for inelastic structural systems. In order to provide new useful insights about this issue, the paper presents statistical results obtained from a numerical study conducted for three shear-type hysteretic (softening-type) systems having 4, 8 and 16 stories equipped with a linear elastic TMD. The effectiveness of two design procedures is discussed by examining the performances of the protected systems subjected to 124 natural pulse-like earthquakes.

• Smart Structures and Systems
• /
• 제24권3호
• /
• pp.391-401
• /
• 2019

Control of vibrations against extraordinary excitations such as wind and earthquake is very important to the protection of life and financial concerns. One of the methods of structural control is to use Tuned Liquid Damper (TLD), however due to the nature of TLD only one sloshing frequency can be created when the water is sloshing. Among various ideas proposed to compensate this problem, by changing the angle of some rotatable baffles embedded inside a TLD, a frequency range is created such that these baffles are tuned manually at different frequencies. In this study, the effect of cross sectional shape of container with rotating baffles on seismic behavior of TLD is experimentally studied. For this purpose, rectangular and cylindrical containers are designed and used to suppress the vibrations of a Single Degree-Of-Freedom (SDOF) structure under harmonic and earthquake excitations considering three baffle angles. The results show that the rectangular-shaped damper reduces the structural response in all load cases more than the damper with a cylindrical shape, such that maximum differences of two dampers to reduce the structural displacement and structural acceleration are 5.5% and 3% respectively, when compared to the cases where no baffles are employed.