• Structural Engineering and Mechanics
• /
• v.28 no.5
• /
• pp.515-524
• /
• 2008

In this paper the effect of prestressing force on the first flexural natural frequency of beams is studied. Finite element technique is used to model the beam-tendon system, and the prestressing force is applied in the form of initial tension in the tendon. It is shown that the effect of prestressing force on the first natural frequency depends on bonded and unbonded nature of the tendon, and also on the eccentricity of tendon. For the beams with bonded tendon, the prestressing force does not have any appreciable effect on the first flexural natural frequency. However, for the beams with unbonded tendon, the first natural frequency significantly changes with the prestressing force and eccentricity of the tendon. If the eccentricity of tendon is small, then the first natural frequency decreases with the prestressing force and if the eccentricity is large, then the first flexural natural frequency increases with the prestressing force. Results of the present study clearly indicate that the first natural frequency can not be used as an easy indicator for detecting the loss of prestressing force, as has been attempted in some of the past studies.

• Structural Engineering and Mechanics
• /
• v.34 no.2
• /
• pp.247-275
• /
• 2010

In this study, experimental, numerical, and analytical approaches were carried out to evaluate the behavior and prestressing effect of prestressed composite beam by external tendon and cover plate. Behavior of prestressed composite beam, load-carrying capacity, effects of prestressing, and ultimate strength were estimated. The contribution of the section increase of the prestressing method using tendon was less than the prestressing method using cover plate. In accordance with numerical and analytical approaches, the ultimate strength of the prestressed composite beam is shown to be the same value because strength is determined according to the plastic resistance moment and the plastic neutral axis; however, both plastic resistance moment and neutral axis are not affected by prestressing force but affected by sectional stiffness of the prestressing member. Based on these approaches, we concluded that the prestressing method using tendon can be useful in applications without an increase in self-weight, and the prestressing method using high-strength cover plate can be applied to reduce the deflection of the composite beam. The prestressing method using high-strength cover plate can also be used to induce prestress of the composite beam in the case of a large deflection due to a smaller sectional stiffness of the composite beam.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1998.10b
• /
• pp.649-655
• /
• 1998

In this study, the personal-computer program was developed to predict prestressing losses containment structures of Nuclear Power Plants by concrete creep and shrinkage. This program is constituted of three parts, which are pre-processor, calculation module and post-processor. Input data for his program are : material properties of concrete, rebar, liner and duct, test results of concrete creep and shrinkage, relative humidity, dimension of containment structures, and the number of prestressing tendon related on containment structures. To obtain better results, this program was made to reflect the prestressing losses due to influence that occurred after prestressing each tendon, thus it can predict prestressing losses and allowable prestressing forces of each tendon. As a case study, this program was applied to containment structures of Youngwang 3 & 4 NPP's and analytical result was compared with test results in In-service Inspection of containment structures. From this comparison, it was proved that this program could well predict prestressing losses by concrete creep and shrinkage.

• Structural Engineering and Mechanics
• /
• v.5 no.3
• /
• pp.307-327
• /
• 1997

This paper is concerned with the time dependent service load behaviour of prestressed composite tee beams. The effects of creep and shrinkage of the concrete slab are modelled using the age adjusted effective modulus method and a relaxation approach. The tendon strain is determined considering compatibility of deformations and equilibrium of forces between the tendon and the composite tee beam. A parametric study is undertaken to study the influence of various aspects on the stress, strain and deformations of the concrete slab, steel beam and prestressing tendon. The effect of loading type and tendon relaxation has also been considered for various types of prestressing tendon materials. Recommendations are then made in relation to adequate span to depth ratios for varying levels of prestressing force.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1999.10a
• /
• pp.685-688
• /
• 1999

The analysis and design of composite girders prestressed by external tendons involve difficulties related to the position of anchorages and the construction sequences. In this paper, the efficiency of the external tendon profiles and the position of anchorages in examined for the internal and external prestressing of statically indeterminate structures. It is shown that strengthening of a prestressed girder can be accomplished using a variety of methods; bonded external prestressing, tendon replacement and unbonded external prestressing.

• Proceedings of the Korea Concrete Institute Conference
• /
• 1995.10a
• /
• pp.361-365
• /
• 1995

P.C box bridges is divided into internal prestressing and extermal prestressing based on arrangement of tendon. In this research the method of establishment of dviation block in advance and analysis of block and the control relationship of tension of external tendon and displacement should be examined by practical example of high speed rail way in aspects of maintenance and repairment.

• Journal of the Korea Concrete Institute
• /
• v.19 no.6
• /
• pp.735-744
• /
• 2007

This study deals with literature review, developing a predicting equation for the ultimate stress of prestressing (PS) CFRP, and experimental test with the parameters affecting the ultimate stress of prestressing CFRF in prestressed concrete beams strengthened by external prestressing. The ACI (American Concrete Institute) predicting equation for the ultimate stress of unbonded prestressing CFRP is analyzed to develop a new integrated predicting equation. The proposed predicting equation takes rationally the effect of internal PS steel into consideration as a function of prestressing tendon depth to neutral depth ratio. In the experimental study, prestressed concrete beams strengthened using external prestressing CFRP are tested with the test parameters having a large effect on the ultimate stress of prestressing CFRP. The test parameters includes infernal prestressing steel and external prestressing CFRP tendon 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 CFRP.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2000.04a
• /
• pp.645-650
• /
• 2000

In the prestressed concrete structures, the effective prestressing force of tendon is basically most important item for structural safety and serviceability. The frictional loss is one of the major items for determinating the effective prestressing force and depend on the construction accuracy of the structures. In this thesis, it will be analyzed and found through measured hydraulic jack pressure, tendon elongation and prestressing control system that the tendancy of apparent curvature friction coefficient, the ratio of jacking force and required prestressing force, the ratio of initial jacking force and required prestressing force and compatibility of specified friction loss coefficient. The specified control limit for curvature friction coefficient of prestressing control system is about 0.25 and wobble friction coefficient 0.005. Thus, the control limit should be modified according to changed vale of friction coefficient.

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

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