• Proceedings of the Korea Concrete Institute Conference
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• 2003.05a
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• pp.955-960
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• 2003

For box girders in which the longitudinal tendon is profiled in the inclined webs. longitudinal prestressing force will induce transverse effects as well as longitudinal ones. In this paper. the method estimating transverse effects induced by longitudinal prestressing is proposed. The transverse effects in the slabs of box girders due to longitudinal prestressing are investigated. Numerical analyses are carried out depending on the parameters such as web inclination and ratio of girder length to tendon eccentricity. Analysis results show that when only prestressing are considered the magnitude of stresses in the slabs of box grder is not so large. However. if the other stresses due to dead and live load et al. are superposed on these stresses. it may be that the longitudinal prestressing effects are significant.

• Journal of the Korea Concrete Institute
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• v.15 no.5
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• pp.679-688
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• 2003

For box girders in which the longitudinal tendon is profiled in the inclined webs, longitudinal prestressing force will induce transverse effects as well as longitudinal ones. In this paper, the method to estimate transverse effects induced by longitudinal prestressing is proposed. The concept of transverse equivalent loading which is calculated through longitudinal prestressing analysis is developed. The transverse stress in slabs of box girders due to longitudinal prestressing are investigated. The comparison of numerical results of the proposed method and those of folded plate method represents that the method is reasonable. Numerical analyses are carried out depending on the parameters such as web inclination and ratio of girder length to tendon eccentricity. Analysis results show that when only prestressing are considered the magnitude of transverse stress in slabs of box girder is not so large. However, if the other stresses due to dead and live load et al. are superposed on these stresses, it may be that the longitudinal prestressing effects are significant.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.77-80
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• 2004

In bridge deck systems, deflections and cracking can be controlled by longitudinal and transverse prestressing, There are some benefits, longitudinal cracking control, the thickness reduction of deck slab, the widening of deck width and the reduction of the cross section area, in transversely post-tensioned concrete box girder bridges. However, it has been not sufficient to study the structural behaviors of transversely post-tensioned concrete box girder. Therefore, It is needed to predict the structural behaviors by prestressing and static loading. In this study, the analytical and experimental load tests are carried out to study the effect of transverse prestressing on concrete box girder. For these objectives, four test specimens are fabricated with various tendon spacing and steel ratio of top slab. The analytical and experimental studies are performed to estimate effects of the prestressing and failure tests.

• Journal of the Korea Concrete Institute
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• v.27 no.2
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• pp.137-145
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• 2015

The slab-type precast modular bridge consists of the precast slab bridge modules which are connected in the transverse direction. The longitudinal joints between the precast slab bridge modules are filled with cast-in-place mortar. The construction of the slab-type precast modular bridge is completed by applying the prestressing force on the longitudinal joints. In this study, 4-points bending tests and 3-points bending tests were conducted to examine the effects of the prestressing force and the shape of joint on the flexural strength and crack serviceability of longitudinal joint. The results of 4-points bending tests showed that the flexural strength is affected by the prestressing force but not by the shape of join. From the results of 3-points bending tests by which the bending moment and the shear force are simultaneously applied on the joints of the specimens, it is observed that the shape of joint affects on the flexural strength and the crack behavior. The results of two types of bending tests confirmed that the prestressing force according to the design code is appropriate and the joint with two shear keys gives the better performances against the crack of joint.

• Proceedings of the Korea Concrete Institute Conference
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• 2002.10a
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• pp.475-480
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• 2002

This study is to develop a strengthening method for slab bridges with external prestressing. There are so many different strengthening methods for damaged slab bridges, external prestressing method is the most effective, economical and durable strengthening method among them. But, its problem lies in anchoring devices, so recently, an effective anchoring method was developed and showed its improvements. In this study, a more improved method is suggested. Longitudinal tendons placed on both side of slab strengthens the whole bridge, and lateral tendons placed under the slab strengthens the middle of slab, and conveys the load at middle slab to both sides. Structural analysis for the tensile force for strengthening were analysed. Generally, 200-280tons for longitudinal tendon and 130-190 tons for lateral tendons are good enough to strengthen the damaged slab. This method has no upward roof work, so it is very convenient for installing. And no spaces under the slab are need, so it is good for shallow slabs which has less space under the slab.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.573-578
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• 2001

In order to apply a precast deck to continuous composite bridges, several experiments and analytical studies were performed. Design criterion for crack prevention should be such that it does not permit tension at the joint to occur when the service loads are applied. Details of the shear pocket for studs and material properties of filler in the pocket and the joint are very important considerations in design and construction. Combination of longitudinal prestressing methods, internal tendon and prestressing after shear connection, should be used for prevention of cracking in continuous precast deck bridges. Design guides for the determination of prestressing force are suggested.

• Computers and Concrete
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• v.20 no.4
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• pp.469-481
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• 2017

This paper aims to analytically investigate the effect of shear stress at the concrete-steel interface on the mechanical behavior of the circular steel tube-confined concrete (STCC) stub columns with active and passive confinement subjected to axial compression. Nonlinear 3D finite element models divided into the four groups, i.e. circumferential-grooved, talc-coated, lubricated, and normal groups, with active and passive confinement were developed. An innovative method was used to simulate the actively-confined specimens, and then, the results of the finite element models were compared with those of the experiments previously conducted by the authors. It was revealed that both the predicted peak compressive strength and stress-strain curves have good agreement with the corresponding values measured for the confined columns. Then, the mechanical properties of the active and passive specimens such as the concrete-steel interaction, longitudinal and hoop stresses of the steel tube, confining pressure applied to the concrete core, and compressive stress-strain curves were analyzed. Furthermore, a parametric study was performed to explore the effects of the concrete compressive strength, steel tube diameter-to-wall thickness ratio, and prestressing level on the compressive behavior of the STCC columns. The results indicate that reducing or removing the interfacial shear stress in the active and passive specimens leads to an increase in the hoop stress and confining pressure, while the longitudinal stress along the steel tube height experiences a decrease. Moreover, prestressing via the presented method is capable of improving the compressive behavior of STCC columns.

• Journal of the Korea Concrete Institute
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• v.23 no.5
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• pp.617-626
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• 2011

Seven post-tensioned lightweight concrete (LWC) beam specimens were tested under a symmetrical two-point top loading system. The parameters investigated were the amounts of mild longitudinal reinforcement and effective prestressing. The design compressive strength and dry density of the LWC tested were 30 MPa and 1,770 $kg/m^3$, respectively. Similar to post-tensioned normal weight concrete (NWC) beams, the crack propagation and stress increase of the unbonded tendons were significantly affected by the amounts of mild longitudinal reinforcement and effective prestressing. With the increase in the amounts of mild longitudinal reinforcement and effective prestressing, the serviceability and flexural capacity of the beams were enhanced whereas the stress increase in the unbonded tendons decreased. To control the crack width in post-tensioned LWC beams, a minimum amount of mild longitudinal reinforcement specified in ACI 318-08 provision is required. The flexural behavior of post-tensioned LWC beams and stress increase of the unbonded tendons could be rationally predicted by the proposed non-linear two-dimensional analysis. On the other hand, ACI 318-08 flexure provision was too conservative about the post-tensioned LWC beams.

• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.406-409
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• 2006

Serviceability resign is required to control the cracking at the joint of precast decks having longitudinal prestress in continuous composite bridges. Especially, details of twin girder bridges are complex not only due to main reinforcements and transverse prestress for the resign of long-span concrete slabs but also due to shear pockets for obtaining the composite action. This paper suggests the design guidelines for the magnitude of the effective prestress and for the selection of filling materials and their requirements in order to use precast decks for twin-girder continuous composite bridges. The necessary initial prestress was also evaluated through the long-term behavior analysis. From the analysis, existing design examples were revised and their effectiveness was estimated. When a filling material having bonding strength higher than the requirement is used in the region of high negative moment, uniform configuration of longitudinal prestressing steels along the whole span length of continuous composite bridges can be achieved resulting in simplification of details and enhancement of the construction costs.

• Journal of the Korea Concrete Institute
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• v.23 no.1
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• pp.39-48
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• 2011

The present investigation evaluates the flexural behavior of pre-tensioned lightweight concrete beams under two-point symmetrical concentrated loads according to the variation of the partial prestressing ratio and the effective prestress of prestressing strands. The designed compressive strength of the lightweight concrete with a dry density of 1,770 $kg/m^3$ was 35 MPa. The deformed bar with a yield strength of 383 MPa and three-wire mono-strands with tensile strength of 2,040 MPa were used for longitudinal tensile reinforcement and prestressing steel reinforcement, respectively. According to the test results, the flexural capacity of pre-tensioned lightweight concrete beams increased with the increase of the partial prestressing ratio and was marginally influenced by the effective prestress of strands. With the same reinforcing index, the normalized flexural capacity of pre-tensioned lightweight concrete beams was similar to that of pre-tensioned normal-weight concrete beams tested by Harajli and Naaman and Bennett. On the other hand, the displacement ductility ratio of pre-tensioned lightweight concrete beams increased with the decrease of the partial prestressing ratio and with the increase of the effective prestress of strands. The load-displacement relationship of pre-tensioned lightweight concrete beam specimens can be suitably predicted by the developed non-linear two-dimensional analysis procedure. In addition, the flexural cracking moment and flexural capacity of pre-tensioned lightweight concrete beams can be conservatively evaluated using the elasticity theorem and the approach specified in ACI 318-08, respectively.