• Journal of the Korea Concrete Institute
• /
• v.13 no.1
• /
• pp.1-8
• /
• 2001

Recently, prestressed concrete(PSC) bridge structures with many repetitive spans have been widely constructed using the segmental construction method in many countries. In these segmentally constructed PSC bridges, there exist many construction joints which is required coupling of tendons or overlapping of tendons to introduce continuous prestress through several spans of bridges. The purpose of this paper is to investigate in detail the complicated stress distributions around the tendon coupled joints in prestressed concrete girders. To this end, a comprehensive experimental program has been set up and a series of specimens have been tested to identify the effects of tendon coupling. The present study indicates that the longitudinal and transverse stress distributions of PSC girders with tendon couplers are quite different from those of PSC girders without tendon couplers. It is seen that the longitudinal compressive stresses introduced by prestressing are greatly reduced around coupled joints according to tendon coupling ratios. The large reduction of compressive stresses around the coupled joints may cause deleterious cracking problems in PSC girder bridges due to tensile stresses arising from live loads, shrinkage and temperature effects. The analysis results by finite element method correlate very well with test results observed complex strain distributions of tendon coupled members. It is expected that the results of this paper will provide a good basis for realistic design guideline around tendon coupled joints in PSC girder bridges.

• Journal of the Korea Concrete Institute
• /
• v.23 no.4
• /
• pp.421-430
• /
• 2011

As a fundamental study to introduce the reliability-based design code, a statistical study is conducted for the material strength data collected from domestic construction sites. In order to develop a rational design code based on statistics and reliability theory, it is essential to obtain the statistical properties of material strength. Material strength data for concrete, reinforcing bars, and prestressing strands which are used in domestic construction sites are collected and statistically analyzed. Then, the statistical properties are compared with those used in the process of the reliability-based calibration of internationally leading design codes. The statistical properties of the domestic data are such that the bias factor is relatively uniform between 1.13 and 1.20 and the coefficient of variation is below 0.10. Reinforcing bar data show difference among different manufacturers but there is not much difference among re-bar diameters. In the case of tendons, which are high strength materials, both of the domestic and foreign data show smaller values of the bias factor and the coefficient of variation than those of concrete and re-bar. Statistical distribution of all the material strength can be properly assumed as normal, log-normal, or Gumbel distribution after analyzing the classified data by individual construction site and manufacturer rather than the mixed data obtained from different sources in order to express the individual distribution of each structure.

• Journal of the Korea Concrete Institute
• /
• v.17 no.1 s.85
• /
• pp.85-94
• /
• 2005

Post-tensioned Precast concrete System(PPS) consists of U-shaped precast wide beams and concrete column. The continuity of beam-column joint is provided with floor concrete cast on the PC shell beam and post-tensioning. The purpose of this paper is to evaluate the response of PPS interior beam-column joint subjected to cyclic lateral loading. To this end, an experimental investigation was performed with three half-scale specimens of interior connection. The design parameters are the amount of beam reinforcement placed inside the joint core. The test results showed that cracks were distributed well without my significant degradation of strength and ductility. Also, it was found that the prestressing may affect to alter the torsional crack angle. And the specimens sufficiently resist up to limiting drift ratio of 0.035 in accordance with the provisional by ACl of acceptance criteria for concrete special moment frames.

• Journal of the Korea Concrete Institute
• /
• v.20 no.5
• /
• pp.611-618
• /
• 2008

CFRP (carbon fiber reinforced polymer) tendons can be used as an alternative to solve the corrosion problem of steel tendons. Since CFRP tendons are vulnerable to transverse pressure and stress concentration, the conventional anchorage system used for steel tendons can create an unreliable load carrying capacity and may result in a premature failure. Therefore, it is necessary to develop the anchorage system that is well suited for CFRP tendons. There are many types of anchorage systems for CFRP tendons, which can be classified into three types: wedge-type anchorage, bond-type anchorage, and compression-type anchorage. This paper deals with the compression-type anchorage system manufactured through swaging technology. Based on the previous test results performed by the authors, the dimension of anchorage sleeve, the use and non-use of the insert, and the compression pressure on the sleeve have been selected as the major parameters affecting the performance of the compression-type anchorage. Some anchorage sleeves have been tapered to reduce the stress concentration. Test results revealed that the performance of the anchorage system depends mainly on the dimension and the compression pressure. It has been verified that the tapered sleeve can effectively reduce the stress concentration.

• Journal of the Korea Concrete Institute
• /
• v.18 no.5 s.95
• /
• pp.579-588
• /
• 2006

In recent years, the availability of high-strength reinforcing and prestressing steels leads us to build economically and efficiently designed concrete structural members. One of critical problems faced to the structural engineers dealing with these types of structural member is controls of crack width that is used as a criterion for the serviceability in the limit state design. Especially, flexural cracking must be controlled to secure the structural safety and to improve the durability as well as serviceability of the load carving members. The proposed method utilizes the results of pure tension test in which tensile loads are applied both side of specimen, done by Ikki. The bond characteristics of deformed reinforcing bar under pure tension is considered by the area of concrete and rib area. The results of proposed method are compared with the test data and the results show that the proposed method can take into account the dimensions, variation of sectional properties, and direction of reinforcing and gives more accurate maximum bond stress and corresponding relative slip than the existing methods. the characteristics of bonding is considered by using dimensionless slip magnitude and effective reinforcement ratio. The validity of the proposed equation is verified by test experimental data.

• Journal of the Korea Concrete Institute
• /
• v.21 no.1
• /
• pp.105-116
• /
• 2009

Reinforced concrete (RC) structures have been most widely used because of their good economic efficiency. However, it is very weak in tensile stresses and difficult to control deflection due to the heavy self-weight of concrete. On the other hand, it is generally known that prestressed concrete structures can be the most effective to overcome the demerits of RC structures by using various tendon lay-out and its amount. In the prestressed concrete members, the inflection points of tendons should be placed effectively for the deflection control and the moment reduction. Therefore, in this study, the equations of tendon profiles are derived in terms of polynomials that satisfy essential conditions of tendon geometries such as inflection points and natural curved shapes of tendons placed in continuous members, from which vertical components of prestressing forces can be also calculated. The derived high order polynomial expression for the distributed shape of the upward and downward forces was transformed to an simplified equivalent uniform vertical force in order to improve the applicability in the calculation of member deflection. The influences of vertical forces by tendons to deflection and moment in a continuous slab were also considered depending on the distance from column face to the location of tendons. The applicability of the proposed method was examined by an example of deflection calculation for the cases of slabs with and without tendons, and the efficiency of deflection control by tendons was also quantitatively estimated.

• Journal of the Korea Concrete Institute
• /
• v.22 no.6
• /
• pp.777-786
• /
• 2010

This paper examines the flexural behavior of full-scale prestressed concrete girders that were constructed of steel fiber reinforced ultra high performance concrete (UHPC). This study is designed to provide more information about the bending characteristics of UHPC girders in order to establish a reasonable prediction model for flexural resistance and deflection for future structural design codes. Short steel fibers have been introduced into prestressed concrete T-girders in order to study their effects under flexural loads. Round straight high strength steel fibers were used at volume fraction of 2%. The girders were cast using 150~190 MPa steel fiber reinforced UHPC and were designed to assess the ability of steel fiber reinforced UHPC to carry flexural loads in prestressed girders. The experimental results show that steel fiber reinforced UHPC enhances the cracking behavior and ductility of beams. Moreover, when ultimate failure did occur, the failure of girders composed of steel fiber reinforced UHPC was observed to be precipitated by the pullout of steel fibers that were bridging tension cracks in the concrete. Flexural failure of girders occurred when the UHPC at a particular cross section began to lose tensile capacity due to steel fiber pullout. In addition, it was determined that the level of prestressing force influenced the ultimate load capacity.

• Journal of the Korea Concrete Institute
• /
• v.18 no.3 s.93
• /
• pp.303-312
• /
• 2006

The main objective of this experimental study is to examine the feasibilities of each testing method with various kinds of grip systems for the analysis of tensile strength of GFRP(glass fiber reinforced polymer) reinforcing bars. Three types of grip systems were examined such as resin-sleeved pipe-type grip proposed by CSA(Canadian Standard Association), frictional resistance type metal grip by ASTM(American Standard for Testing and Materials) and wedge-inserted cone-type grip normally used in prestressing tendons. Also, mechanical properties of GFRP rebars with different surface deformations were investigated for each different type of testing grip used in this study. All testing procedures including specimens preparation, set-up of test equipments and measuring devices were made according to the CSA S806-02 recommendations. From the test results, it was found that the highest tensile strengths of GFRP rebars were observed when tested by resin-sleeved grip system regardless of their different surface deformations. But tensile strengths of GFRP rebars by ASTM grip system are only 10% less than those by CSA grip system. On the other hand, CSA grip is not only difficult to prepare but also not disposable. Therefore, ASTM grip system is recommended as a practical alternative to estimate the tensile strength of GFRP rebars.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2010.05a
• /
• pp.39-40
• /
• 2010

The demands for longer span and reduction of story height have greatly increased as building structures become much larger and higher in recent years. Although the development of flexural members for reducing story height or making long span has been studied by many researchers and engineers, there is still a lack of efficient systems that meet these two demands simultaneously. This study aimed at developing a new composite beam system suitable for long span and reduction of story height, and proposed a prestressed composite beam with corrugated web. It has great resistance against non-symmetric construction load due to its strong out-of-plane shear strength with relatively small member height as well as good constructability and economic efficiency by removing/minimizing form work. The corrugated webs also make accordion effect introducing larger effective prestressing force to top and bottom flanges, which causes larger upward camber reducing the member deflection. Five full-scale specimens with key test parameters, which are web sectional shapes and number of drape points, were tested to understand their flexural behavior and to verify the performance of the proposed method. The experimental test results showed that the proposed prestressed composite beam had greater flexural strength and stiffness than the ordinary non-prestressed composite beam.

• Journal of the Korea Concrete Institute
• /
• v.27 no.1
• /
• pp.21-28
• /
• 2015

Recent studies on concrete floating structure development focused on connection system of concrete modules. Precast concrete modules are designed to be attached by prestressing in the water, exposing the structure to the loads from water and making the construction difficult. Therefore, a development of bond material became a key issue in successful connection of floating concrete modules. In this study, micro-silica mixed aqua epoxy (MSAE) is developed for the task. Existing primer aqua epoxy, originally used as a bond material for the retrofit of concrete structures using fiber reinforced polymers, is evaluated to find the optimum micro-silica added mix proportion. Micro-silica of 0~4 volume % was mixed in standard mixture of aqua epoxy. Then, the material property tests were performed to study the effect of micro-silica in aqua epoxy by controlling the epoxy silane proportion by 0, ${\pm}5$, ${\pm}10%$. The optimum mix design of MSAE was derived based on the test results. The MSAE was used to connect concrete module specimens with the epoxy thickness variation of 5, 10, and 20mm. Then, 3-point loading test was performed to verify the bond capacity of MSAE. The results show that MSAE improves the bond capacity of concrete module.