• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.528-531
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• 2004

Nowadays, many of PSC bridges has constructed because high performance and long span bridge is required. Therefore, it is required that the evaluation of PSC bridges which retain various structure performance. In this study, nonlinear FEM analysis was performed with two parameter, concrete compressive strength and effective prestress force which is dominant factor for evaluating structural behavior of PSC bridge. Concrete compressive strength was adapted between 30Mpa and 100Mpa and effective prestress force was used the value which is considered effective rate for time-dependant effect. In the result of this study, it was showed that concrete compressive strength and effective prestress force is important factor for evaluating structural behavior of PSC bridge.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.1326-1331
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• 2006

The precast concrete deck is one of suitable solutions for replacement and new construction in urban area. However, the precast concrete deck could be a weak point of the steel plate girder bridges structurally due to the connections between precast panels in the longitudinal direction. Thereafter, it is necessary for improvement of durability and load carrying capacity to introduce the prestress force in the longitudinal direction Some cracks of connections at the precast concrete deck may be occurred due to live loads, the difference of temperature and long-term effects. The shrinkage and creep of concrete may significantly affect long-term behaviors which occur tensile stresses at the precast concrete deck of steel plate girder bridges. In this study, the time-dependant analysis program has been developed to determine the initial prestress force in the longitudinal direction considering loss of stress at the precast concrete deck. Also it has been estimated the initial prestress force by construction stages and shapes of girder.

• Journal of the Korea institute for structural maintenance and inspection
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• v.13 no.4 s.56
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• pp.137-147
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• 2009

In this study, several flexural vibration characteristics of prestressed concrete girders due to changes in prestress forces are experimentally analyzed. In order to achieve the objective, the following approaches are implemented. First, several methods to extract vibration response features from output-only signal are selected. Next, a large-scaled prestressed concrete girder model is constructed to analyze relation between the prestress forces and the vibration features in the prestressed concrete girder. Then acceleration responses are measured from the girder for several prestress force scenarios. Finally, vibration characteristics of the prestressed concrete girder due to change in prestress force are experimentally analyzed. The values of features extracted by the selected methods are reduced due to prestress-loss. Especially, the value of features are linearly reduced in the early prestress-loss.

• Structural Engineering and Mechanics
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• v.17 no.3_4
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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.

• Smart Structures and Systems
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• v.17 no.6
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• pp.917-933
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• 2016

In a prestressed concrete bridge, the magnitude of the prestress force (PF) decreases with time. This unexpected loss can cause failure of a bridge which makes prestress force identification (PFI) critical to evaluate bridge safety. However, it has been difficult to identify the PF non-destructively. Although some research has shown the feasibility of vibration based methods in PFI, the requirement of having a determinate exciting force in these methods hinders applications onto in-service bridges. Ideally, it will be efficient if the normal traffic could be treated as an excitation, but the load caused by vehicles is difficult to measure. Hence it prompts the need to investigate whether PF and moving load could be identified together. This paper presents a synergic identification method to determine PF and moving load applied on a simply supported prestressed concrete beam via the dynamic responses caused by this unknown moving load. This method consists of three parts: (i) the PF is transformed into an external pseudo-load localized in each beam element via virtual distortion method (VDM); (ii) then these pseudo-loads are identified simultaneously with the moving load via Duhamel Integral; (iii) the time consuming problem during the inversion of Duhamel Integral is overcome by the load-shape function (LSF). The method is examined against different cases of PFs, vehicle speeds and noise levels by means of simulations. Results show that this method attains a good degree of accuracy and efficiency, as well as robustness to noise.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.2A
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• pp.103-111
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• 2010

A feasibility study for nondestructively estimating prestress force of a grouted tendon using axial vibrations has been investigated. Total eight prestressed concrete beams with different stress levels have been specially designed and constructed for this investigation. The various axial vibration tests have been conducted in order to extract the dynamic characteristics of the prestressed concrete beams. It turns out that the axial frequency, elastic wave velocity and elastic modulus are nonlinearly increased as the prestress force level increases. It seems that the axial vibration characteristics of the existing grouted tendons are a feasible indicator for the identification of their tensile force.

• Journal of the Korea institute for structural maintenance and inspection
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• v.7 no.1
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• pp.227-238
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• 2003

Due to deterioration of bridge, usually be using the external prestressing method among repair reinforcement method. But, there is much to be desired about a detailed account, almost it has analysed by cambers of girders, deflections of middle span and upper, bottom stresses of girders. Also, it is not examined closely that effect of internal prestress by external prestressing. The purpose of this study is confirmed the effect of internal tendons by external prestressing, estimation of additional external prestressing force and look for exact external prestressing force.

• Structural Engineering and Mechanics
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• v.77 no.1
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• pp.1-17
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• 2021

The influence of prestress force on the fundamental frequency and static deflection shape of uncracked Prestressed Concrete (PC) beams with a parabolic bonded tendon was examined in this paper. Due to the conflicts among existing theories, the analytical solutions for properly considering the dynamic and static behavior of these members is not straightforward. A series of experiments were conducted for a total period of approximately 2.5 months on a PC beam made with high strength concrete, subsequently and closely to the 28 days of age of concrete. Specifically, the simply supported PC member was short term subjected to free transverse vibration and three-point bending tests during its early-age. Subsequently, the experimental data were compared with a model that describes the dynamic behavior of PC girders as a combination of two substructures interconnected, i.e., a compressed Euler-Bernoulli beam and a tensioned parabolic cable. It was established that the fundamental frequency of uncracked PC beams with a parabolic bonded tendon is sensitive to the variation of the initial elastic modulus of concrete in the early-age curing. Furthermore, the small variation in experimental frequency with time makes doubtful its use in inverse problem identifications. Conversely, the relationship between prestress force and static deflection shape is well described by the magnification factor formula of the "compression-softening" theory by assuming the variation of the chord elastic modulus of concrete with time.

• Journal of the Korean Society for Precision Engineering
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• v.19 no.3
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• pp.46-51
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• 2002

Recently, High capacity alternator are used fur some special equipments in industry. But, several serious problem are occured, especially, broken coil of rotor, caused by crash with stator on rotating the rotor. Although added coil cover thor protect coil of rotor, coil cover is broken. In this study purpose 2 step for corrected that problems. First, three dimensional finite element method far investigate what is most important point. For that purpose, performed stress analysis of coil and coil cover that modeling and finite analysis by ANSYS software. Second, Apply prestress when winding the coil on stator to modify direction of net force. Vector analysis is used for determine corrected prestress. Result of the analysis and prestress are reviewed.

• Journal of the Korean GEO-environmental Society
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• v.16 no.10
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• pp.15-22
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• 2015

In this study, to evaluate the long-term behavior characteristics and the loss of prestress force, the long-term measurement of the tensile anchors in the actual construction was performed and the results were analyzed comparing with the existing estimation. As the reinforcement member used for the purpose of slope stability or uplift-resisting of the permanent structure, etc, the permanent anchor should maintain the functions during the performance period of the structure differently from the temporary anchor. However, as the time passes by, since the relaxation and the creep of the anchor occur constantly, the management for the loss of tensile force is essential to perform the functions stably. So far, the loss of the tensile force has been estimated according to the reduction of the prestress using elasticity theory and using the relaxation value according to the type of tension member and the test using the long-term measurement is limited. Therefore, in this study, the site condition and the ground were investigated for the tensile anchor in the actual construction and the long-term measurement results more than 500 days was analyzed by installing the loadcell, inclinometer and the groundwater level gauge. In addition, the long-term behavior characteristics were evaluated by comparing the disposition of the measured earth retaining wall and the tension force loss of the anchor with the existing interpretation results. In the evaluation results, the most of the tension force loss occurs within 90 days and the loss was measured less than the estimated values.