• Structural Engineering and Mechanics
• /
• v.34 no.2
• /
• pp.189-211
• /
• 2010

The behaviour of a reinforced concrete tension member is governed by the contribution of concrete between cracks, tension stiffening effect. Under highly repeated loading, this contribution is progressively reduced and the member response approximates that given by the fully cracked member. When focusing on the unloaded state, experiments show deformations larger than those of the naked reinforcement. This has been referred to as negative tension stiffening and is due to the fact that concrete carries compressive stresses along the crack spacing, even thought the tie is subjected to an external tensile force. In this paper a cycle-dependent approach is presented to reproduce the behaviour of the axially loaded tension member, paying attention to the negative tension stiffening contribution. The interaction of cyclic bond degradation and time-dependent effects of concrete is investigated. Finally, some practical diagrams are given to account for the negative tension stiffening effect in reinforced concrete elements.

• Journal of the Korean Society for Railway
• /
• v.9 no.2 s.33
• /
• pp.160-168
• /
• 2006

The major objective of this study is to investigate the effects and application of external post-tensioning method far steel plate girder bridge. It analyzed the mechanical behaviors of steel plate girder bridge with applying external post-tensioning on the finite element analysis, field test and laboratory test fur the lateral dynamic characteristics. As a result, the reinforcement of steel plate girder bridge the external post-tensioning method are obviously effective for the lateral dynamic response which is non-reinforced. The analytical and experimental study are carried out to investigate the post-tension force decrease lateral acceleration and deflection on steel plate girder bridge for serviceability. And the external post-tensioning method reduce dynamic maximum displacement(about $10{\sim}24%$), the increase of dynamic safety is predicted by adopting external post-tensioning method. From the dynamic test results of the servicing steel plate girder bridge, it is investigated that the change degree of natural frequency is very low with applying the external post-tensioning method The servicing steel plate girder bridge with external post-tensioning has need of the reasonable reinforcement measures which could be reducing the effect of lateral dynamic behavior that degradation phenomenon of structure by an unusual response characteristic and a drop durability.

• Journal of the Korean Society of Safety
• /
• v.14 no.1
• /
• pp.129-140
• /
• 1999

This study presents test results of RC beams strengthened by steel plates, carbon fiber sheets(CFS) and aramid fiber sheets(AFS) for increasing flexural and shear resistance. The test was performed with different parameters including the type of strengthening materials, flexural-strengthening methods and shear-strengthening methods. In case of flexural test, RC beams are initially loaded to 70% of the ultimate flexural capacity and in case of shear test loaded to 60 or 80 percent of the ultimate shear capacity and subsequently reinforced with steel plates, CFS and AFS. Experimental data on strength, steel strain, deflection, and mode of failure of the reinforced beams were obtained, and comparisons between the different shear reinforced schemes and the non-strengthened control beams were made. The test results showed that damaged RC beams strengthened by steel plates, CFS and AFS have more improved the flexural and shear capacity. For the beams with external reinforcement by steel plates, aramid fiber sheets and carbon fiber sheets increases in ultimate strength of 4 to 21, 17 to 43 and 26 to 36 percent were respectively achieved. Initial load had small effect on strength after reinforcement, but an important influence on deflection. One sheet reinforced was stronger than two sheets reinforced but less deflected than two sheets reinforced.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2002.05a
• /
• pp.399-404
• /
• 2002

This paper presents the results cf research on improved flexural performance cf reinforced concrete beams strengthened with bonded carbon fiber reinforced polymer plate. Recently, strengthening technique with CFRP plate were almost carried out by external bonding. But current external bonding technique cf CFRP plates may result in debonding CFRP plate. Therefore, this study proposes a strengthening method that prevents or delays debonding between CFRP plates and concrete and at the same time improves the strength. For this test, there were only 14 test beams manufactured and failure load, deflection, strains and modes cf failure have been examined Test variables included the type cf strengthening, steel ratio and strengthening length, and the effects according to each test variables were analyzed. The experimental results show that the strength and stiffness cf the beam significantly increased between 34.55 and 116.51% and the increase cf the more lead-carrying capacity than the control beams.

• Journal of the Korea Concrete Institute
• /
• v.15 no.4
• /
• pp.585-593
• /
• 2003

This study deals with literature review, developing a predicting equation for the ultimate stress of prestressing steel, and experimental test with the parameters affecting the ultimate stress of prestressing steel in reinforced concrete beams strengthened by external prestressing. The ACI predicting equation for the ultimate stress of unbonded prestressing steel is analyzed to develop a new integrated predicting equation. The proposed predicting equation takes rationally the effect of internal reinforcing bars into consideration as a function of prestressing steel depth to neutral depth ratio. In the experimental study, steel reinforced concrete beams strengthened using external prestressing steel are tested with the test parameters having a large effect on the ultimate stress of prestressing steel. The test parameters includes reinforcing bar and external prestressing steel reinforcement ratios, and span to depth ratio. The test results are analyzed to confirm the rationality and applicability of the proposed equation for predicting the ultimate stress of external prestressing steel.

• Steel and Composite Structures
• /
• v.19 no.2
• /
• pp.417-439
• /
• 2015

Many methods are developed for strengthening of reinforced concrete structural members against the effects of shear. One of the commonly used methods in recent years is turned out to be bonding of fiber reinforced polymers (FRP). Impact loading is one of the important external effects on the reinforced concrete structural members during service period among the others. The determination of magnitude, the excitation time, deformations and stress due to impact loadings are complicated and rarely known. In recent year impact behavior of reinforced concrete members have been researched with experimental studies by using drop-weight method and numerical simulations are done by using finite element method. However the studies on the strengthening of structural members against impact loading are very seldom in the literature. For this reason, in this study impact behavior of shear deficient reinforced concrete beams that are strengthened with carbon fiber reinforced polymers (CFRP) strips are investigated experimentally. Compressive strength of concrete, CFRP strips spacing and impact velocities are taken as the variables in this experimental study. The acceleration due to impact loading is measured from the specimens, while velocities and displacements are calculated from these measured accelerations. RC beams are modeled with ANSYS software. Experimental result and simulations result are compared. Experimental result showed that impact behaviors of shear deficient RC beams are positively affected from the strengthening with CFRP strip. The decrease in the spacing of CFRP strips reduced the acceleration, velocity and displacement values measured from the test specimens.

• Journal of the Architectural Institute of Korea Structure & Construction
• /
• v.35 no.11
• /
• pp.137-146
• /
• 2019

Recently, the Near-Surface-Mounting method using Fiber reinforced polymer (FRP) has been developed and applied to the reinforcement of many concrete structural members. However, as a part of the fire resistance design, there is a lack of research related to fire insulation for the areas reinforced with FRP. In case of NSM reinforcement, there is a difference in the transferred temperature from the external surface to the groove corresponding to the location of the groove where the FRP is embedded, and the effect of this should be reflected in the fireproof insulation design. Therefore, in this study, after forming grooves for surface embedding in concrete blocks, fireproof insulation reinforcement was performed using Calcium Silicate (CS) fireproof board and an experiment to evaluate the temperature transfer was performed. By observing the temperature at these groove positions, the reduction of temperature transfer according to fireproof insulation detail was studied. As a result, when the NSM-FRP is properly fire-insulated using the CS-based fireproof board, the epoxy inside the groove does not reach its glass transition temperature until the external temperature reaches $800^{\circ}C$.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1994.10a
• /
• pp.267-272
• /
• 1994

This work presents a method of optimum design for reinforced concrete building frames with rectangular cross sections. The optimization techniques used is based on the principle of divided parameters. The design variable parameters are divided into two groups, external and internal, and the optimization is also divided into external and internal procedure. This principle overcomes difficulties arising from the presence of two materials in one element, the property peculiar to reinforced concrete. Several search algorithms are tested to verify their accuracy for the external optimization. Among them pattern search algorithms has been found consistent. This work proposes a new method, modified pattern search, and a number of sample problems prove its accuracy and usefulness. Exhaustive search for all local minima in the design spaces for two sample problems has been carried out to understand the nature of the problem. The number of local minima identified is quite more than expected and it has become understood that the researcher's task in this field is to find a better local minimum if not global. The designs produced by the method preposed have been found better than those from other method, and they are in full accord with ACI Building Code Requirments(ACI 318-89).

• Magazine of the Korea Concrete Institute
• /
• v.9 no.1
• /
• pp.133-141
• /
• 1997

This work presents a method of optimum design for reinforced concrete building frames with rectangular cross sections. To overcome difficulties arising from the presence of two materials in one element(concrete and steel) , the principle of divided parameters is adopted. The design variable parameters are divided into two groups - external and internal. The optimization is also divided into external and internal procedure. Several scarxh algorithms are tested to verify their accuracy for the external optimization. This work proposes a new search method, a modified pattern search, and sample problems prove its accuracy and uscf'ulness. The design obtained by this method is an optimum and in full accord with ACI Building Code Ftequirements(ACI'318-89).

• Journal of the Korea Concrete Institute
• /
• v.11 no.6
• /
• pp.129-135
• /
• 1999

Reinforced concrete structures are constructed under the basic assumption of perfect bonding between steel and concrete. The corrosion of steel in the reinforced concrete beams results in the excessive cracks and gradual deterioration of concrete. This paper are concerned about the slip characteristics of reinforced concrete between steel and concrete. The accelerated test by external power supply was conducted with the three corrosion rates in the laboratory. As a result, it was obtained as follows: (1) the yield strength of steel was reduced according to corrosion states. (2) the equivalent steel area should be considered for detailed analysis. (3) According to the use of corroded steel or not, slip amounts between concrete and steel in test beams increased as the corrosion rate increased. These results can be explained from the bond loss between concrete and steel in test beams.