• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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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.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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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.

• KCI Concrete Journal
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• v.12 no.2
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• pp.45-54
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• 2000

Precast R.C. slabs are being used widely for the construction of bridge structures due to their simplicity in construction processes. However, one of the disadvantages in precast R.C. slabs is the existence of transverse joints between two precast slabs. The transverse joints are structurally fragile and the task of strengthening the joints is difficult one due to their structural discontinuity. The aim of this study was to improve the behavior of transverse joints between precast R.C. slabs by introducing prestress with external cables. Three steel-concrete composite bridge specimens, which were prestressed with the external cables anchored on steel girders, were fabricated in the laboratory. Both pretension and post-tension methods were applied to introduce prestressing on the concrete slab with a straight tendon arrangement. Static tests were conducted at service load and ultimate load test was performed to evaluate punching shear capacity of the transverse joint. In this paper, two prestressing methods were tested and their effects were evaluated with respect to the elastic behavior and ultimate loading capacity of the transverse joints.

• Journal of the Korea institute for structural maintenance and inspection
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• v.15 no.5
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• pp.136-149
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• 2011

Large portion of the domestic bridges are slab bridges reflecting the geographical characteristic of the country, where exists lots of inclines and small winding brooks. Many of the slab bridges are damaged and superannuated as they become obsolete. Deterioration is accelerated when the traffic density becomes large and heavy vehicles pass frequently. A strengthening method for deteriorated slab bridges was studied in this work. The examined net-type strengthening method uses both longitudinal and transverse prestressing for strengthening. In this way, the deflection at the center of the slab can be better controlled, and consequently, the slab is more efficiently strengthened. Three slab specimens were fabricated for the experimental test and subjected to three different loading conditions, and the load bearing capacities and deflections of slabs were examined. Flexural stiffness of slabs increased by 30.7~107.3%, and deflection of slabs decreased by 27.6~52.2% after net-type strengthening. The net-type prestressing is efficient to the strengthening for the center of a slab, and its efficiency is also valid under eccentric loadings. Since extra prestress forces can be added in the future, if necessary, the net-type strengthening system is advantagous for the maintenance and repair of slab bridges.

• Proceedings of the Korea Concrete Institute Conference
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• 1999.04a
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• pp.721-726
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• 1999

Diverse strengthening methods for reinforced concrete are applied to real structures with a variety of materials. On the other hand, only external prestressing is used for strengthening damaged prestressed concrete girders. But the end brackets for external prestressing are hard to design and to manufacture, the magnitude of prestressing is limited when applied to real structures. The current end brackets are not clearly understood in load transmitting mechanisms and they may damage the original girder by drilling during construction. And also the designed welding area of the current bracket is insufficient to support the high load. The problems of current end bracket are solved in this study. And a new and improved end bracket is proposed and tested. The tested end bracket is similar to the end bearing bracket, but many supportting plates are addded to increase its welding length of the weakest point of the bracket. The increased welding length finally increases its load carrying capacity significantly.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.11a
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• pp.363-366
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• 2003

This study is to develop a strengthening method for RC slab bridges and rigid-frame bridges with external prestressing. In this study, we design the slab specimen that have a strengthening of the DB-13 and set up the 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 and we know that displacement and strain was improved from this test. 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 inder the slab.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.549-558
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• 2000

In strengthening structure, the external post-tensioning method which secure clearness in the structure analysis process is adopted to bridges as well as architecture structure. In this study, to investigate the behavior of composite beam in the process of post-tensioning, the amount of prestress force loss, the amount of prestressed compression stress at the lower flange and the behavior of lower flange connected with anchorage are analyzed by comparing the results of finite element analysis with the measured results of installed strain gauges. After finishing the post-tensioning, the strengthening effect of external post-tensioning method is analyzed by static loading test. It is also investigated that the strengthening effect of shear section in the harped external post-tensioning specimens.

• Journal of the Korea Concrete Institute
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• v.18 no.5 s.95
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• pp.603-610
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• 2006

The external unbonded strengthening offers advantages in speed and simplicity of installation over other strengthening techniques. Unlike externally bonded steel plate or carbon fiber sheet, surface preparation of the concrete for installation of high-tension bar is not required and installation is not affected by environmental conditions. Anchoring pin or anchoring plate are installed at the end of beam to connect the high-tension bar to concrete beam. The deviator are used in order that supplementary external bars would follow the curvature of the tested beam. A set often laboratory tests on reinforced concrete beam strengthened using the technique are reported. The main test parameters are the section area of strengthening bar, the depth of deviator and the number of deviators. The paper provides a general description of structural behavior of beams strengthened using the technique. The test result of strengthened beam are compared with those from a reference specimen. It is shown that the reinforcing technique can provide greater strength enhancements to unstrengthened beam and that the provision of deviator enhances efficiency. The ultimate moment of specimen with two deviators was higher than that of specimens with one deviator. It is also shown that the external bars enhance strength of beams in shear.

• Journal of the Korea Concrete Institute
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• v.21 no.2
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• pp.139-146
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• 2009

Experimental study was performed to evaluate the long-term behavior of CFRP (carbon fiber reinforced polymer) strips under sustained loads including prestressing force in strengthening RC members with post-tensioned CFRP strips. Two types of CFRP strip such as unidirectional CFRP strip and hybrid CFRP strip which is composed of carbon fiber and steel plate were considered. Also two types of loading scheme were included in this study. Direct sustained loading test had been carried out to estimate the creep deformation and relaxation of CFRP strips including slip deformation at both mechanical anchorages for over 700 days. Also, flexural sustained loading test had been conducted to estimate the initial prestress losses on clamping the CFRP strips at jacking anchorages for over 90 days. From the sustained loading tests, it was observed that stress losses of unidirectional CFRP strips due to the creep deformation and relaxation of material itself and slip deformation at mechanical anchorage were ignorable. On the other hand, significant stress losses caused by the yielding of steel embedded in CFRP strips were found in case of hybrid CFRP strips due to the initial jacking force over steel yielding stress. Also, initial prestress losses during setting of CFRP strips on mechanical anchorage were about 10% of intial jacking force, which must be considered in the design.