• Proceedings of the Korea Concrete Institute Conference
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• 2006.05a
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• pp.238-241
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• 2006

The needs for strengthening and rehabilitation of the concrete bridges are a growing concern in many countries and has been emphasized in various researches and papers. Traditional external post-tensioning method using either steel bars or tendons is commonly used as a strengthening method. However, the method has some disadvantages such as stress concentration at the anchorages. Multi-stepwise thermal prestressing method is a newly proposed method for strengthening and rehabilitation of concrete girder bridges. Founded on a simple concept of thermal expansion and contraction of steel, the method is a hybrid method of external post-tensioning and steel plate bonding, combining the merits of two methods. In this paper, basic concepts on strengthening and rehabilitation of concrete girder are presented and an illustrative experiment is introduced.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2001.04a
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• pp.223-232
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• 2001

This paper describes Genetic Algorithm-Based Relay Search Method, RS-GA, which is developed in this study to search the multiple design variables in the design space. The RS-GA based on Simple-GA consists of some functions to search many variables from some wide variable space. It repeats a Simple-GA, that is the convergence process of the Simple-GA, which makes many time reiteration itself. From the results of the numerical studies, it was actually found that RS-GA can search all peak-variable from the 2D functions including 5 peaks. Finally, RS-GA applied for design-strengthening problems in composite plate girder bridges using the external prestressing technique is also verified.

• Proceedings of the Korea Concrete Institute Conference
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• 1998.10b
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• pp.815-820
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• 1998

Many composite girder bridges have been constructed for about thirty five years. Nowadays they are aged or deteriorated because of th increase in traffic and vehicle loads. In this study, the effect of strengthening with glass fiber sheet is investigated to estimate the possibility for appling for damaged prestressed concrete bridges. One normal and eight cracked specimens which had been preloaded were tested. The cracked specimens were strengthened with either external prestressing or bonding glass fiber sheet, or using both methods. The results showed that the maximum loads are almost same for both methods. So it seems that the strengthening with glass fiber sheet can be used for strengthening damaged prestressed concrete girders. It is important that proper devices should be selected to prevent glass fiber sheet from premature bonding failure below its maximum load, which is similar to end anchorage problem in external prestressing method. It is proved that the devices proposed in this paper have sufficient anchoring capability to increase load carrying capacity.

• 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.

• Coupled systems mechanics
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• v.4 no.2
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• pp.191-209
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• 2015

Hybrid girders can be constructed in different geometrical forms and from different materials. Selection of beam's effective constellation represents a complex process considering the variations of geometrical parameters, changes of built in material characteristics and their mutual relations, which has important effect on the behavior of the girder. This paper presents the theoretical and experimental research on behavior of the timber-steel hybrid girders' different geometrical constellation with external prestressing and in different conditions of timber moisture. These researches are based on linear elastic analysis, and further refine by using the plasticity and damage models.

• Journal of the Korea institute for structural maintenance and inspection
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• v.12 no.1
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• pp.91-100
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• 2008

Multi-stepwise Thermal Prestressing Method(TPSM) is a newly proposed prestressing method, which is combined the external prestressing method and the external bonding method. Multi-stepwise thermal prestressing force is induced by cooling process of cover-plate in the multi-stepwise temperature distribution after the cover-plate being bolted to the girder. In this study, the heating capacity test of the developed heating system for applying the multi-stepwise TPSM effectively and multi-stepwise TPSM inducing test of H-beam is performed. Also, a field test of the rhamen type temporary bridge is carried out to evaluate the effect and application of the multi-stepwise TPSM. Truck load was loaded and compared with the structure analysis results.

• Magazine of the Korea Concrete Institute
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• v.16 no.1 s.78
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• pp.65-72
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• 2004

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.3
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• pp.178-186
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• 2005

In this study, the PSC girder bridge retrofitted with external tendons is tested to verify the strengthening effects. We measure the variations of the displacement and strain at mid-span of each beam as external tendons are removed in sequence. The structural behavior of the bridge are examined using controlled truck load tests for the systems before and after all external tendons were removed. From the test results, the characteristics of structural behavior of the bridge do not change significantly, but the natural frequency is decreased after the external tendons are removed. The strengthening effects of bridges can be exactly estimated by analytical methods some extent. As a result of this study, when a PSC girder bridge is deteriorated, the bridge can be retrofitted effectively by External Prestressing Strengthening Method, and the strengthening effects can be predicted through accurate structural analysis.

• 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.

• Structural Engineering and Mechanics
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• v.48 no.5
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• pp.615-642
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• 2013

In this paper a study on prestressed concrete slab bridges is presented. A design philosophy based on the concept of load balancing through prestressing is proposed in order to minimize the effects of delayed deformations due to creep. Aspects related to the stress redistribution inside these bridges for time-dependent phenomena are analyzed and discussed, by applying the principles of aging linear visco-elasticity. Prestressing is seen as an equivalent external load which counterbalances the permanent loads applied to the bridge, nullifying the elastic deflections due to sustained loads, and thus avoiding the related delayed deformations. An optimization of the structural behavior through the use of one-way prestressing is achieved. The determination of a convenient variable depth of slab bridges and the correspondent layout of tendons is considered as a useful means for applying the load balancing concept in actual cases of structures like long cantilevers or bridge decks. A case-study related to the slab bridges built 30 years ago at Jeddah in Saudi Arabia is presented and discussed, in order to show the effectiveness of the proposed approach to the conceptual design of prestressed concrete bridges.