• Smart Structures and Systems
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• 제9권6호
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• pp.489-504
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• 2012

For the safety of prestressed structures such as cable-stayed bridges and prestressed concrete bridges, it is very important to ensure the prestress force of cable or tendon. The loss of prestress force could significantly reduce load carrying capacity of the structure and even result in structural collapse. The objective of this study is to present a smart PZT-interface for wireless impedance-based prestress-loss monitoring in tendon-anchorage connection. Firstly, a smart PZT-interface is newly designed for sensitively monitoring of electro-mechanical impedance changes in tendon-anchorage subsystem. To analyze the effect of prestress force, an analytical model of tendon-anchorage is described regarding to the relationship between prestress force and structural parameters of the anchorage contact region. Based on the analytical model, an impedance-based method for monitoring of prestress-loss is conducted using the impedance-sensitive PZT-interface. Secondly, wireless impedance sensor node working on Imote2 platforms, which is interacted with the smart PZT-interface, is outlined. Finally, experiment on a lab-scale tendon-anchorage of a prestressed concrete girder is conducted to evaluate the performance of the smart PZT-interface along with the wireless impedance sensor node on prestress-loss detection. Frequency shift and cross correlation deviation of impedance signature are utilized to estimate impedance variation due to prestress-loss.

• Smart Structures and Systems
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• 제17권6호
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• pp.881-901
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• 2016

In this study, a method to compensate the effect of temperature variation on impedance responses which are used for prestress-loss monitoring in prestressed concrete (PSC) girders is presented. Firstly, an impedance-based technique using a mountable lead-zirconate-titanate (PZT) interface is presented for prestress-loss monitoring in the local tendon-anchorage member. Secondly, a cross-correlation-based algorithm to compensate the effect of temperature variation in the impedance signatures is outlined. Thirdly, lab-scale experiments are performed on a PSC girder instrumented with a mountable PZT interface at the tendon-anchorage. A series of temperature variation and prestress-loss events are simulated for the lab-scale PSC girder. Finally, the feasibility of the proposed method is experimentally verified for prestress-loss monitoring in the PSC girder under temperature-varying conditions and prestress-loss events.

• Structural Engineering and Mechanics
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• 제17권3_4호
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• pp.467-482
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• 2004

One of the uncertain damage parameters to jeopardize the safety of existing PSC bridges is the loss of the prestress force. A substantial prestress-loss can lead to severe problems in the serviceability and safety of the PSC bridges. In this paper, a nondestructive method to detect prestress-loss in beam-type PSC bridges using a few natural frequencies is presented. An analytical model is formulated to estimate changes in natural frequencies of the PSC bridges under various prestress forces. Also, an inverse-solution algorithm is proposed to detect the prestress-loss by measuring the changes in natural frequencies. The feasibility of the proposed approach is evaluated using PSC beams for which a few natural frequencies were experimentally measured for a set of prestress-loss cases. Numerical models of two-span continuous PSC beams are also examined to verify that the proposed algorithm works on more complicated cases.

• 비파괴검사학회지
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• 제31권6호
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• pp.616-625
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• 2011

Ensuring the designed prestress force is very important for the safety of prestressed concrete bridge. The loss of prestress force in tendon could significantly reduce load carrying capacity of the structure. In this study, an automated prestress-loss monitoring system for prestressed concrete girder using PZT-interface and wireless impedance sensor node is presented. The following approaches are carried out to achieve the objective. Firstly, wireless impedance sensor nodes are designed for automated impedance-based monitoring technique. The sensor node is mounted on the high-performance Imote2 sensor platform to fulfill high operating speed, low power requirement and large storage memory. Secondly, a smart PZT-interface designed for monitoring prestress force is described. A linear regression model is established to predict prestress-loss. Finally, a system of the PZT-interface interacted with the wireless sensor node is evaluated from a lab-scale tendon-anchorage connection of a prestressed concrete girder.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2000년도 봄 학술발표회 논문집
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• pp.417-422
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• 2000

In prestressed concrete structures, determining serviceability and safety it is important to exactly calculate effective prestress force acting on structures. for the determination of effective prestress force, friction loss of the prestressing tendon should be decided exactly, but it is very difficult to measure the exact prestress force on the site and there is no actual field data. Therefore the friction loss coefficient recommended by the specification is not verified. in this paper, the friction loss standard PSC-Beam will be investigated, and is will be found what kind of relationship between the specification and the site. The results from this study can be summarized as follows. For jacking at both ends, actual intial prestress force in the center section of PCS-Beam was about 1.61% larger than theoretical initial prestress force and for hacking at one end, actual initial prestress force was approximate 4.9% lower than theoretical initial prestress force. Thus, for the exact calculation of friction loss, friction coefficient should be modified according to jacking methods.

• Smart Structures and Systems
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• 제5권1호
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• pp.81-94
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• 2009

A vibration-impedance-based monitoring method is proposed to predict the loss of prestress forces in prestressed concrete (PSC) girder bridges. Firstly, a global damage alarming algorithm using the change in frequency responses is formulated to detect the occurrence of damage in PSC girders. Secondly, a local damage detection algorithm using the change in electro-mechanical impedance features is selected to identify the prestress-loss in tendon and anchoring members. Thirdly, a prestress-loss prediction algorithm using the change in natural frequencies is selected to estimate the extent of prestress-loss in PSC girders. Finally, the feasibility of the proposed method is experimentally evaluated on a scaled PSC girder model for which acceleration responses and electro-mechanical impedances were measured for several damage scenarios of prestress-loss.

• 한국전산구조공학회논문집
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• 제21권1호
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• pp.83-90
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• 2008

본 논문에서는 프리스트레스 콘크리트(PSC) 거더교의 긴장력 손실을 예측하기 위한 진동기반 모니터링 체계를 제안하였다. 제안한 체계는 긴장력 손실 경보 단계와 긴장력 손실 정도를 평가하는 단계로 구성하였다. 먼저, 긴장력 손실 경보를 위해 두 위치에서 취득된 주파수 응답의 변화를 사용하여 긴장력 손실의 발생을 모니터링하는 새로운 전역적 손상경보기법을 제안하였다. 제안된 기법은 응답신호의 파워스펙트럼만을 이용하기 때문에 별도의 모드해석과정 없이 실시간으로 손상경보가 가능하다. 다음으로, 긴장력 손실 정도를 평가하기 위하여 고유진동수의 변화로부터 긴장력의 상대적인 손실 정도를 평가할 수 있는 긴장력 손실 예측 기법을 선정하였다. 제안된 체계의 유용성을 축소 모형 PSC 거더에 대한 실험을 통해 평가하였다.

• 한국구조물진단유지관리공학회 논문집
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• 제5권2호
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• pp.111-120
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• 2001

This paper aims at estimating instantaneous prestress losses by measuring the actual prestress forces in prestressed concrete (PSC) box girder bridges. Measurement were taken to study initial prestress losses such as friction losses and slip losses. A new strain gauge system was developed to measure strains in internal tendons. The system was installed on a total of 20 tendons in a PSC box girder bridges. The variation of prestress forces were monitored during prestressing tendon and after prestress transfer. The prestress losses are also calculated including friction losses and slip losses. The measured data were compared with the theoretical values. The result shows that the measured prestress forces agree well with the theoretical values. It is shown that prestress force of each strand in the same tendon is a bit different. This study also shows that prestress losses of continuity tendons during prestress transfer are significantly different each other, which results from the variety of buttress location and tendon profile. The present study provides realistic information on the estimation of actual prestress forces and losses in PSC box girder bridges.

• 한국해양공학회지
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• 제24권1호
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• pp.123-132
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• 2010

This paper presents a prestress-loss monitoring technique for prestressed concrete (PSC) girder structures that uses a vibration-based system identification method. First, the theoretical backgrounds of the prestress-loss monitoring technique and the system identification technique are presented. Second, vibration tests are performed on a lab-scaled PSC girder for which the modal parameter was measured for several prestress-force cases. A numerical modal analysis is performed by using an initial finite element (FE) model from the geometric, material, and boundary conditions of the lab-scaled PSC girder. Third, a vibration-based system identification is performed to update the FE model by identifying structural parameters since the natural frequency of the FE model became identical to the experimental results. Finally, the feasibility of the prestress-loss monitoring technique is evaluated for the PSC girder model by using the experimentally measured natural frequency and numerically identified natural frequency for several prestress-force cases.

• Smart Structures and Systems
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• 제15권4호
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• pp.1159-1175
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• 2015

In this study, the effect of temperature variation on the wireless impedance monitoring is analyzed for the tendon-anchorage connection of the prestressed concrete girder. Firstly, three impedance features, which are peak frequency, root mean square deviation (RMSD) index, and correlation coefficient (CC) index, are selected to estimate the effects of temperature variation and prestress-loss on impedance signatures. Secondly, wireless impedance tests are performed on the tendon-anchorage connection for which a series of temperature variation and prestress-loss events are simulated. Thirdly, the effect of temperature variation on impedance signatures measured from the tendon-anchorage connection is estimated by the three impedance features. Finally, the effect of prestress-loss on impedance signatures is also estimated by the three impedance features. The relative effects of temperature variation and prestress-loss are comparatively examined.