• Computers and Concrete
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• 제22권2호
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• pp.133-142
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• 2018

The deterioration of existing bridges has become a major problem around the world. In the paper, a new model and an associated stress checking method are proposed for concrete box girders strengthened by external prestressing. The new model called the spatial grid model can analyze all the spatial behaviors clearly by transforming the box girder into discrete orthogonal grids which are equivalent to plate elements. Then the three-layer stresses are employed as the stress checking indices to evaluate the stress state of the plate elements. The initial stress check before strengthening reveals the cracked and potential cracking areas for existing bridges, making the strengthening design more targeted and scientific; the subsequent stress check after strengthening evaluates the strengthening effect and ensures safety. A deficient bridge is selected as the practical example, verifying the accuracy and applicability of the proposed model and stress checking method. The results show that principal stresses in the middle layer of plate elements reflect the main effects of external prestressing and thus are the key stress checking indices for strengthening. Moreover, principal stresses check should be conducted in all parts of the strengthened structure not only in the webs. As for the local effects of external prestressing especially in the areas near anchorage and deviator, normal stresses check in the outer and inner layers dominates and local strengthening measures should be taken if necessary.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 춘계학술발표회 논문집(I)
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• pp.266-269
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• 2006

External pre-stressing strengthening method is the most popular way to strengthen concrete structures because of its efficiency and economic advantage. The laboratory test was performed to reinforce the slave bridge with the external tendon strengthening by longitudinally and transversally, which is concerned with formal feature of slave bridge, generally. Based on this test, anchoring device to strengthen the external tendon strengthening method was established and its strengthening effects were verified by evaluating the load bearing capacity.

• Structural Engineering and Mechanics
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• 제15권4호
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• pp.437-449
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• 2003

The aim of this study is to develop an analytical model of a beam with open cracks and external strengthening which is able to predict its modal scheme components (natural frequencies and mode shapes). The model is valid as far as the excitation level is low enough not to activate non linear effects. The application field of the model are either the prediction of the efficiency of the reinforcement or the non destructive assessment of the structural properties. The degrees of freedom associated to the fault lips must be taken into account in order to introduce the effect of the external strengthening. In a first step, an analytical formulation of a beam with thin notches is proposed according to the references. The model is then extended to incorporate the strengthening consisting in a longitudinal stiffness applied in the vicinity of the cracks. In a second step, the analytical results are compared with these obtained from a finite element simulation.

• 한국구조물진단유지관리공학회 논문집
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• 제9권3호
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• pp.178-186
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• 2005

본 연구에서는 장기공용 중 외부강선보강공법에 의하여 보강된 PSC Beam교량에 대한 강선 파단 시험을 통하여 보강효과를 분석하였다. 외부강선 보강효과를 분석하기 위하여 기 보강된 강선을 인위적으로 절단하면서, 교량의 처짐과 변형률을 측정하였다. 또한 강선절단 전과 후에 재하시험을 실시하여 교량의 거동변화를 평가하였다. 실험결과에 의하면 외부강선 절단 전과 후의 재하시험을 통하여 보강효과가 교량의 거동특성을 크게 변화시키지는 않지만, 보강시의 긴장력에 의하여 고유진동수는 증가하였다. 외부강선 절단시의 처짐과 응력 계측결과로부터 보강효과가 충분히 유지되고 있다는 것을 확인할 수 있었으며, 구조해석 결과와도 잘 일치하였다. 따라서 외부강선을 이용하여 노후교량을 보강할 경우 정밀구조해석을 통하여 그 효과를 예측할 수 있을 것으로 판단된다.

• Advances in concrete construction
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• 제8권2호
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• pp.101-117
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• 2019

Structural strengthening of reinforced concrete (RC) beams is becoming essential to meet the up-gradation of existing structures due to the infrastructure development. Strengthening is also essential for damaged structural element due to the adverse environmental condition and other distressing factors. This article reviews the state of the field on repair, retrofitting and rehabilitation techniques for the strengthening of RC beams. Strengthening of RC beams using various promising techniques such as externally bonded steel plates, concrete jacketing, fibre reinforced laminates or sheets, external prestressing/external bar reinforcement technique and ultra-high performance concrete overlay have been extensively investigated for the past four decades. The primary objective of this article is to discuss investigations on various strengthening techniques over the years. Various parameters that have been discussed include the flexural capacity, shear strength, failure modes of various strengthening techniques and advances in techniques over the years. Firstly, background information on strengthening, including repair, retrofitting, and rehabilitation of RC beams is provided. Secondly, the existing strengthening techniques for reinforced concrete beams are discussed. Finally, the relative comparisons and limitations in the existing techniques are presented.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 가을 학술발표회 논문집
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• pp.475-480
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• 2002

This study is to develop a strengthening method for slab bridges with external prestressing. There are so many different strengthening methods for damaged slab bridges, external prestressing method is the most effective, economical and durable strengthening method among them. But, its problem lies in anchoring devices, so recently, an effective anchoring method was developed and showed its improvements. In this study, a more improved method is suggested. Longitudinal tendons placed on both side of slab strengthens the whole bridge, and lateral tendons placed under the slab strengthens the middle of slab, and conveys the load at middle slab to both sides. Structural analysis for the tensile force for strengthening were analysed. Generally, 200-280tons for longitudinal tendon and 130-190 tons for lateral tendons are good enough to strengthen the damaged slab. This method has no upward roof work, so it is very convenient for installing. And no spaces under the slab are need, so it is good for shallow slabs which has less space under the slab.

• Steel and Composite Structures
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• 제3권1호
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• pp.33-46
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• 2003

This study focuses on the influence of a composite external strengthening on the natural frequencies of a steel beam with open cracks. In a first step, the leading parameters associated with the effect of the composite strengthening are experimentally identified. An analytical model is developed in order to quantify the importance of the force transfer within the resin interface. In a second step, the analytical model of a cracked beam with composite external strengthening is compared to experiments.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2006년도 추계 학술발표회 논문집
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• pp.117-120
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• 2006

This study is for the strengthening method of continuous bridge through external tendon strengthening that is the most general and effective among concrete bridge's strengthening method. Recently, it is numerous that slab's parts between spans have continuity for improving trafficable ability. However, in this case, slab would have a crack; bridge's durability would be damaged, and also it is too difficult to manage and maintain bridge due to the tensile strength of negative moment. Therefore, the purpose of this study is to demonstrate load-carrying through experiments and develop new external pre-stressing strengthening method for reinforcing continuous bridge.

• 한국구조물진단유지관리공학회 논문집
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• 제7권1호
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• pp.157-163
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• 2003

Recently, the number of Prestressed Concrete(PSC) bridges needed repair and retrofit because of the increase of heavy traffic loads and aging of concrete materials. But there are a few related researches about strengthening PSC bridges. In this study, the practicability of strengthening methods for PSC beam were studied by the static experimental method. PSC beams in length of 6m were made with concrete slabs. Glass fiber sheeting and external post-tensioning methods were used for strengthening PSC beams. Some beams were strengthened after cracks to investigate the applicability for cracked bridges. As a result, there strengthening methods were efficient at increasing the cracking loads and the failure load, to decrease deflection and prevent cracks. In the case of using glass fiber retrofit methods, it should be careful in the anchorage problems for preventing the bonding failure.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2002년도 봄 학술발표회 논문집
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• pp.411-416
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• 2002

With a rapid industrialization, repair and strengthening methods for a damaged bridges are raised a head in face of safety and reduction of physical distribution costs of bridges. Above all, external prestressing method has the high adaptability for concrete structures and the reliable effect of strengthening. Innovative ideas for bridges strengthening were considered along with established methods. That methods are identified, described. However there is not a systematic and categorized manual for external prestressing method. This study will provide a systematic and reliable manual with investigating the arrangement shape of cable and characteristics of brackets. And the key result of this study is an extensive compilation, which can be used by practicing engineers, of the most effective techniques for strengthening existing bridges.