• Journal of the Korean Recycled Construction Resources Institute
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• v.6 no.4
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• pp.336-341
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• 2018

The prestressing force introduced to the tendon in pretensioned concrete members is transferred by direct bond between tendon and concrete, which requires a proper estimation of stress transfer length. The use of pretensiond and/or precast members with UHPC (Ultra High Performance Concrete) may give many advantages in quality control. This paper presents an experiment to estimate the stress transfer length of UHPC for various compressive strength levels of UHPC, cover depths, diameters of tendons and tensioning forces. According to the result of this experiment, the stress transfer length of UHPC member is much reduced comparing that of normal strength concrete. The reduction in stress transfer length of UHPC may come from the high bond strength capacity of UHPC. The transfer lengths obtained from this experiment are compared to those in current design code and a new formula is proposed.

• Journal of Korean Society of Steel Construction
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• v.21 no.2
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• pp.135-144
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• 2009

This study aims to suggest an appropriate flexural reinforcement technique by evaluating the reinforcement capacity of specimens that underwent flexural reinforcement according to the post-tension method with the anchoring position of an unbonded tension member on the conventional SC composite beam and the applied tension level as variables. For the experiment, up to a predetermined yield load was applied to each type of specimen and then, unbounded post-tensioning was additionally conducted to examine its reinforcement capacity. The analysis of the said experiment showed that the post-reinforced SC composite beam was characterized by significantly improved yield stress and initial stiffness, compared with the pre-reinforced one and the experimental measurements/theoretical values of maximum stress ranged from 0.95 to 1.13 following reinforcement. There was little or no change depending on the maximum stress and tension in the specimen (D160, Class 240) whose neutral axis and upper part had anchoring devices mounted prior to reinforcement. Rather, the ductility decreased with the increasing tension. On the contrary, in the case of the other specimen (Class D120) whose neutral axis had anchoring devices mounted after reinforcement, both the maximum stress and ductility increased with increasing tension, which indicates that the latter tension reinforcement was reasonably appropriate and effective for the neutral axis reinforcement.

• Journal of the Korea Concrete Institute
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• v.27 no.4
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• pp.399-409
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• 2015

Recently, the use of composite construction method using precast (PC) and cast-in-place (CIP) concrete is increased in modular construction. For PC members, pre-tensioning is used to improve efficiency of the structural performance. However, current design codes do not clearly define shear strength of prestressed PC-CIP composite members. In this study, 22 specimens were tested to evaluate shear strength of prestressed composite members with vertical shear reinforcement. The test variables were the area ratio of high-strength (60 MPa) to low-strength concrete (24 MPa), prestressing force of strands, shear span-to-depth ratio(a/d), and vertical shear reinforcement ratio. The test results showed the prestressing force did not completely restrain diagonal cracking of non-prestressed concrete in the web. Thus, the effect of prestress force was not insignificant in the effect for monolithic beams. The vertical shear strength and horizontal shear strength of the composite beams were compared with the strength predictions of KCI design method.