• Journal of the Korea institute for structural maintenance and inspection
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• v.25 no.4
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• pp.75-82
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• 2021

The objective of this study is to examine the loss of prestressing stress in the developed prestressing reinforcing units using steel bar and pipe (SP). The main parameters were the reinforcing bar type, the magnitude of prestressed force, and prestressing method. The test results showed that the loss of prestressing stress for SP was highest in the initial prestressing step, which was higher for the compression introduction typed specimens than tension introduction typed specimens. The loss of prestressing stress of SP made with P800 was 1.6% for the compression introduction typed specimen with 0.8f_y, which was lowest than the other specimens. Meanwhile, the relaxation of SP with the respect to the time ranged between 0.4 and 1.9%, irrespective of SP material type, the magnitude of prestressed force, and prestressing method. These values were less than 2.5%, which is the maximum value for the relaxation of prestressed reinforcing steel bars in design codes. Consequently, considering the loss of stress developed in the initial prestressing step, the developed SP material type, prestressing introduction method, and magnitude are recommended to be P800, compression introduction type, and 0.8f_y.

• Computers and Concrete
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• v.5 no.2
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• pp.135-154
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• 2008

This paper presents a nonlinear finite element analysis procedure for the seismic performance assessment of reinforced concrete bridge piers with unbonded reinforcing or prestressing bars. A computer program named RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology) is used to analyze reinforced concrete structures; this program was also used in our study. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used account for material nonlinearity of reinforced concrete. The smeared crack approach was incorporated. To represent the interaction between unbonded reinforcing or prestressing bar and concrete, an unbonded reinforcing or prestressing bar element based on the finite element method was developed in this study. The proposed numerical method for the seismic performance assessment of reinforced concrete bridge piers with unbonded reinforcing or prestressing bars is verified by comparison of its results with reliable experimental results.

• Computers and Concrete
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• v.9 no.1
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• pp.63-79
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• 2012

The purpose of this study is to evaluate the behavior and strength of prestressed concrete deep beams using nonlinear analysis. By using a sophisticated nonlinear finite element analysis program, the accuracy and objectivity of the assessment process can be enhanced. A computer program, the RCAHEST (Reinforced Concrete Analysis in Higher Evaluation System Technology), was used for the analysis of reinforced concrete structures. Tensile, compressive and shear models of cracked concrete and models of reinforcing and prestressing steel were used to account for the material nonlinearity of prestressed concrete. The smeared crack approach was incorporated. A bonded or unbonded prestressing bar element is used based on the finite element method, which can represent the interaction between the prestressing bars and concrete of a prestressed concrete member. The proposed numerical method for the evaluation of behavior and strength of prestressed concrete deep beams is verified by comparing its results with reliable experimental results.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.5
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• pp.101-108
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• 2008

The primary objective of this research is a study on the pullout bond characteristics of untensioned prestressing strand in concrete. The bond characteristics of untensioned prestressing strand in concrete differs from that of deformed reinforcing bar. In order to use and design untensioned prestressing strand as deformed reinforcing bar, a study for bond characteristics of the untensioned prestressing strand was progressed. Major test variables are embedment length ($10d_b{\sim}60d_b$), concrete cover (45mm, 70mm, 100m) and diameter of strands. (12.7mm : SWPC7, 9.3mm : SWPC7A) As a results, these showed that average bond stress was decreased as a growing the embedment length, and then showed that the bond performance of untensioned prestressing strand was improved if embedment length was above 60$60d_b$.

• Journal of Korean Association for Spatial Structures
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• v.11 no.1
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• pp.77-85
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• 2011

In this study, micro genetic algorithm is used to find an optimum cross section of grid structures with pretension. Design optimization of trusses consists of arriving at optimum sizes of cross-section and prestressing force parameters, when weight of the truss is minimum, satisfying a set of specified constraints. The present approach is verified by ten-bar truss example showing good agreements with previous results. Features of the proposed method, which help in modeling and application to optimal design of pretensioned truss structures, are demonstrated by solving a problem of seventy two bar truss structures. The minimum weight design of seventy two bar truss is performed for various magnitudes of pretension and optimal prestressing forces are also found for various configurations of pretensioned truss structures.

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

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.477-480
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• 2004

This paper present test result to develop wedge-type anchor system for external prestressing method with CFRP. The test results indicated that the lower a slope angle and elastic of wedge are, the higher ultimate strengths are for plate types. Bar types showed premature failure because of local high stress in FRP of anchor system. Therefore, to improve the strength for bar types needs further work of strengthening sleeves, slope angles of wedge and materials.

• Steel and Composite Structures
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• v.19 no.1
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• pp.43-58
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• 2015

There are many studies on the optimization of steel trusses in literature; and, a large number of them include a shape optimization. However, only a few of these studies are focused on the prestressed steel trusses. Therefore, this paper aims to determine the amounts of the material and cost savings in steel plane trusses in the case of prestressing. A parallel-chord simply supported steel truss is handled as an example to evaluate the used approach. It is considered that prestressing tendon is settled under the bottom bar, between two end supports, using deviators. Cross-sections of the truss members and height of the truss are taken as the design variables. The prestress losses are calculated in two steps as instantaneous losses and time-dependent losses. Tension increment in prestressing tendon due to the external loads is also considered. A computer program based on genetic algorithm is developed to solve the optimization problem. The handled truss is optimized for different span lengths and different tendon eccentricities using the coded program. The effects of span length and eccentricity of tendon on prestressed truss optimization are investigated. The results of different solutions are compared with each other and those of the non-prestressed solution. It is concluded that the amounts of the material and the cost of a steel plane truss can be reduced up to 19.9% and 14.6%, respectively, by applying prestressing.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.05a
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• pp.172-175
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• 2004

This study is to investigate the tensile properties of glass fiber reinforced polymer(GFRP) reinforcing bars with various kinds of anchor systems experimentally. Three types of anchor systems were examined: resin sleeve anchor adopted by CSA Standard, metal overlay anchor by ASTM Standards and wedge anchor normally used in prestressing tendons. Also, three different types of GFRP bars with different surface deformations were tested in this study. All test procedures including specimens preparation, test apparatus and measuring devices were made according to the recommendations of CSA Standard S806-02. From the test results, it was found that the highest tensile strength of GFRP bar was developed by resin sleeve anchor, and tensile strength of GFRP bar with CSA anchor system is $10\%$ higher than that with ASTM anchor system in the case of sand-coated GFRP bar.

• Structural Engineering and Mechanics
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• v.83 no.6
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• pp.799-810
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• 2022

This study investigated the effect of the strengthening efficiency of unbonded steel-bar truss system on the out-of-plane behavior of perforated masonry walls. Four full-scale unreinforced masonry (URM) walls with two different planes were prepared using the unbonded steel-bar truss system and a URM walls without strengthening. All masonry walls were tested under constant axial and cyclic lateral loads. The obtained test results indicated that the pinching effect in the out-plane behavior of masonry walls tends to decrease in the in- and out-of-plane strengthened URM walls using the unbonded steel-bar truss system with the higher prestressing force ratio (R_p) of vertical reinforcing bars in the unbonded steel-bar truss system, regardless of the perforated type of the masonry wall. Consequently, the highest maximum shear resistance and cumulative dissipated energy at peak load in the post-peak behavior were observed in the in- and out-plane strengthened URM walls with the highest R_p values, which are 2.7 and 6.0 times higher than those of URM. In particular, the strengthening efficiency of the unbonded steel-bar truss system was primarily attributed to the vertical prestressed steel-bars rather than the diagonal steel-bars, which indicates that the strains in the vertical prestressed steel-bars at the peak load were approximately 1.6 times higher than those in the diagonal steel-bars.