• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.258-261
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• 2006

This study investigates the flexural behavior and strengthening performance of RC beams with unbonded prestressing CFRP laminates through static bending tests. The aluminum anchorage system has been developed in tins study and successfully applied to the test specimens. The prestressing level of CFRP laminatehas was 0 %, 20 %, 30% and 50 % of its tensile strength. Experimental results revealed that RC beams with unbonded prestressing CFRP laminates showed increased crack load and yield load according to the level of prestress. It has also been observed that the length of the CFRP laminates does not have significant effect on the maximum load.

• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.828-833
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• 2003

In this paper, a study on fracture characteristics of chemically prestressed mortar with addition of expansive additives was carried out. Uni-axial tension tests with reinforced mortar specimen restrained by embedded reinforcing bar and three point bending tests with notched steel fiber reinforced beams were carried out to verify the characteristics of the cracking behavior, the tension stiffening effect due to bond between rebar and mortar, and fracture characteristic. Tension stiffening curve for the chemically prestressed mortar was obtained from uni-axial tension test. And increased fracture energy due to the chemical prestress was also obtained from bending test and tension softening curve for chemically prestressed mortar was also obtained.

• Journal of the Korea Concrete Institute
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• v.11 no.4
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• pp.73-81
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• 1999

The present study is to examine the ACI code equations for computing the unbonded tendon stress at flexural failure of prestressed beams. The equations examined for their validity are Eq. 18-4 and Eq. 18-5 of the ACI 318-95. Since the possibility of overestimation was expected with the equations, a numerical study, first, was carried out with influential variables included. From this study, it was found that amount of reinforcements, effective prestress, location of tendons, and loading type may affect the overestimation of the unbonded tendon stress. Then, an experimental study was carried out with those variables. A total of 8 specimens was tested to prove the theoretical findings as well as the effect of those variables. As a result. it was proven that the ACI Code equations can overestimate significantly the unbonded tendon stress for certain cases.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2010.04a
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• pp.641-644
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• 2010

프리스트레싱 시스템이 도입된 구조물의 사용수명이 오래됨에 따라, 이들 구조물의 잔존수명 평가와 보수 및 보강 등의 유지관리 차원에서 프리스트레싱 시스템의 현재 긴장력에 대한 평가는 매우 중요한 현안이 되어왔다. 따라서, 본 논문에서는 프리스트레싱 시스템의 현재 긴장력을 평가하기 위한 첫 단계로서 프리스트레싱 시스템의 긴장력이 구조계의 강성에 미치는 영향을 평가하였다. 이를 위하여 부착식 텐던 형식의 프리스트레싱 시스템이 도입된 시험체를 대상으로 SIMO sine sweep test를 수행하고 긴장력과 시험체의 유효 강성에 대한 상관성을 규명하였다. 그 결과, 프리스트레싱 시스템의 긴장력은 시험체의 유효강성을 증가시키며, 저차 고유진동수가 긴장력과 높은 상관성을 지니는 것으로 나타났다.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.157-160
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• 2006

Carbon fiber reinforced polymer (CFRP) laminates can be used more efficiently in strengthening applications by applying prestress to the CFRP laminates. A key problem for prestressing with CFRP laminates is anchoring the laminates. These may include fracture to the CFRP laminates due to excessive gripping force or slippage of the CFRP laminates out of the anchorage zone caused by low friction between the anchor device and the lamiantes. The main objective of this study is the development of an applicative wedge-type anchorage system for prestressed CFRP laminates through experimental study. The experimental parameters were the type of anchorage and the effect of elastic modulus of tab. The test results showed that the developed anchor assures 100% CFRP laminate strength.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.305-308
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• 2006

In this paper, the seismic performance of SRC piers for near fault motions was evaluated by shaking table tests on small scale models. Dead load of the superstructures was simulated by axial prestress at the center of the column section. A mass frame linked with steel bars was fabricated to include the effect of superstructure mass. Friction of the mass frame when it moves was minimized by special details and it was proved before tests. Five pier models with 400mm diameter were tested by increasing the acceleration of the near fault motion. Test results were discussed and compared with previous quasi-static tests.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.11a
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• pp.85-88
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• 2006

This paper deals with shaking table tests on RC piers to evaluate the seismic performance under near fault motion. Small scale models were fabricated and axial force was applied by introducing prestress at the centroid of the column section. Mass effect of the superstructures was simulated by mass frame which was linked with a pier model by steel bars because of the limited payload of shaking table. Friction of the mass frame when it moves was minimized by special details and it was proved before tests. Scale factor of the RC piers was 4.25. Main parameters of the test were details of reinforcements. After verifying the results of shaking table tests, seismic performance was evaluated by increasing the acceleration of the near fault motion.

• Wind and Structures
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• v.36 no.3
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• pp.149-160
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• 2023

Lightness and flexibility of membrane roofs make them very sensitive to any external load. One of the most important parameters that controls their behavior, especially under wind load is the sag/span ratio of edge cables. Based on the value of the pretension force in the edge cables and the horizontal projection of the actual area covered by the membrane, an optimized design range of cable sag/span ratios has been determined through carrying on several membrane form-finding analyses. Fully coupled fluid structure dynamic analyses of these membrane roofs are performed under wind load with several conditions using the CFD method. Through investigating the numerical results of these analyses, the behavior of membrane roofs with cables sag/span ratios selected from the previously determined optimized design range has been evaluated.

• Structural Engineering and Mechanics
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• v.55 no.3
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• pp.511-523
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• 2015

Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy-bonded carbon fiber-reinforced polymer (CFRP) sheets to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of seven composite girders made of I20A steel sections and 80mm-thick by 900mm-wide concrete slabs were prepared and tested. CFRP sheets and prestressed CFRP sheets were used to repair the specimens. The specimens lost the cross-sectional area of their tension flanges with 30%, 50% and 100%. The results showed that CFRP sheets had no significant effect on the yield loads of strengthened composite girders, but had significant effect on the ultimate loads. The yield loads, elastic stiffness, and ultimate bearing capacities of strengthened composite girders had been changed as a result of prestressed CFRP sheets, the utilization ratio of CFRP sheets could be effectively improved by applying prestress to CFRP sheets. Both the yield loads and ultimate bearing capacities had been changed as a result of steel beam's flange damage level and CFRP sheets could cover the girders' shortage of bearing capacity with 30% and 50% flange damage, respectively.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.3 s.55
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• pp.23-31
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• 2007

Fast bridge construction has been increasingly needed according to the changed construction environment. This paper deals with quasi-static tests on precast piers for bridge substructures. One of the most crucial aspect of the design of precast prestressed concrete bridge piers is the seismic performance. Seven precast pier elements were fabricated. The amount of prestressing bars, the prestressing force, and the location and number of the joint between segments were the main test parameters. Test results showed that the introduced axial prestress made the restoration of the deformation under small lateral displacement and minor damage. However, there was no effect of the prestress when the plastic hinge region was damaged severely due to large lateral displacement. Judging from the observed damage, the design of the joints in precast piers should be done for the first joint between the foundation and the pier segment. The amount of the necessary prestressing steel may be designed to satisfy the P-M diagram according to the service loads, not by having the same steel ratio as normal RC bridge piers. In order to satisfy the current required displacement ductility, it is necessary to have the same amount of the transverse reinforcements as RC piers. As the steel ratio increases, the energy absorption capacity increases. The number of joints showed a little influence on the energy absorption capacity.