• Computers and Concrete
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• v.19 no.1
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• pp.1-6
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• 2017

Prestressed concrete I-girders are subject to different load types at their construction stages. At the time of strand release, i.e., detensioning, prestressed concrete girders are under the effect of dead and prestressing loads. At this stage, the camber, total net upward deflection, of prestressed girder is summation of the upward deflection due to the prestressing force and the downward deflection due to dead loads. For the calculation of the upward deflection, it is generally considered that prestressed concrete I-girder behaves linear-elastic. However, the field measurements on total net upward deflection of prestressed I-girder after detensioning show contradictory results. In this paper, camber calculations with the linear-elastic beam and elastic-stability theories are presented. One of a typical precast I-girder with 120 cm height and 31.5 m effective span length is selected as a case study. 3D finite element model (FEM) of the girder is developed by SAP2000 software, and the deflections of girder are obtained from linear and nonlinear-static analyses. Only geometric nonlinearity is taken into account. The material test and field measurement of this study are performed at prestressing girder plant. The results of the linear-elastic beam and elastic-stability theories are compared with FEM results and field measurements. It is seen that the camber predicted by elastic-stability theory gives acceptable results than the linear-elastic beam theory while strand releasing.

• Proceedings of the Korea Concrete Institute Conference
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• 2001.11a
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• pp.841-846
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• 2001

The applicability of the concept of IPC(Incrementally Prestressed Concrete) girder which effectively reduces the depth of the conventional prestressed girders by introducing prestress in two different stages is theoretically reviewed in this research. Expressions on top and bottom stresses resulting from different loading stages are presented. Beneficial effects of IPC girder compared with those traditional prestressed girders are evaluated by investigating the girder depth for the same span or girder span for the same girder depth. Parking structures and ware house structures which need relatively longer span and are subject to large live loads are considered in comparison. It was found that the single or double tee slab designed by IPC concept could be built upto 50% longer in its span and upto 45% less in its depth compared to those of traditionally prestressed single or double tee slabs. In addition, the amount of prestressing tendons could be reduced.

• Journal of the Korea Concrete Institute
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• v.11 no.5
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• pp.33-40
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• 1999

An improved finite element modeling technique is proposed for the assessment of load carrying capacity of partially prestressed concrete girder bridges. Based on the finite element method of analysis, shell and frame elements are used to model the slab and girders of the superstructure, respectively. In the modeling of superstructure, the emphasis is placed on the use of rigid link between the middle surface of slab an mid-plane of girder. This paper also includes the comparision of three different equations that are used in the calculation of effective moment of inertia for the partially prestressed concrete girders. Numerical analysis is performed for the unstrengthened and strengthened bridges. The obtained results are compared with those of load test for a prototype bridge. A good agreement is achieved between the numerical solutions by using the proposed method load test results.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.1-2
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• 2010

In this study, flexural test was conducted to pretensioned prestressed girders applied with 80MPa concrete to evaluate the applicability of high strength concrete.

• Proceedings of the Korea Concrete Institute Conference
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• 1989.10a
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• pp.73-76
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• 1989

A numerical procedure is developed to analyze the time-dependent behavior of prestressed concrete bridges constructed by the segmental cantilever method. The developed computer program accounts for the time-dependent properties of prestressed concrete materials due to the varing modulus of elasticity, creep and shrinkage of concrete and the stress relaxation of prestressing steel. It also accounts for the stiffness increase due to the presence of the steel reinforcements and the effects of the shear deformation of the prestressed concrete bridge girders. The program is applied to a multi-span continuous segmental prestressed concrete bridge to demonstrate its capabilities.

• Advances in Computational Design
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• v.2 no.2
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• pp.147-168
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• 2017

Over the past couple decades, externally bonded fiber reinforced polymer (FRP) composites have emerged as a repair and strengthening material for many concrete infrastructure applications. This paper presents an analytical investigation of the use of carbon FRP (CFRP) for a specific problem that occurs in concrete bridge girders wherein the girder ends are damaged by excessive exposure to deicing salts and numerous freezing/thawing cycles. A 3D finite element (FE) model of a full scale prestressed concrete (PC) I-girder is used to investigate the effect of damage to the cover concrete and stirrups in the end region of the girder. Parametric studies are performed using externally bonded CFRP shear laminates to determine the most effective repair schemes for the damaged end region under a short shear span-to-depth ratio. Experimental results on shear pull off tests of CFRP laminates that have undergone accelerated aging are used to calibrate a bond stress-slip model for the interface between the FRP and concrete substrate and approximate the reduced bond stress-slip properties associated with exposure to the environment that causes this type of end region damage. The results of these analyses indicate that this particular application of this material can be effective in recovering the original strength of PC bridge girders with damaged end regions, even after environmental aging.

• International Journal of Concrete Structures and Materials
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• v.7 no.1
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• pp.71-78
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• 2013

Prestressed concrete (PC) is the predominant material in highway bridge construction. The use of high-strength concrete has gained wide acceptance in the PC industry. The main target in the highway industry is to increase the durability and the life-span of bridges. Cracking of elements is one aspect which affects durability. Recently, nine 7.62 meter long PC I-beams made with different concrete strength were designed according to a simple, semi-empirical equation developed at the University of Houston (UH) (Laskar et al., ACI Journal 107(3): 330-339, 2010). The UH Method is a function of shear span-to-depth ratio (a/d), concrete strength $\sqrt{f^{\prime}_c}$, web area $b_wd$, and amount of transverse steel. Based on testing these girders, the shear cracking strength of girders with different concrete strength and different shear span-to-depth ratio was investigated and compared to the available approaches in current codes such as ACI 318-11 (2011) and AASHTO LRFD Specifications (2010).

• Journal of Korean Society of Steel Construction
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• v.25 no.4
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• pp.369-377
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• 2013

The age-adjusted effective modulus method has been known to provide more precise assessment than the traditional Yassumi method for long-term behavior estimation of prestressed composite girders. The age-adjusted effective modulus method, however, involves complicated calculation, thereby making the Yassumi method more prevalent in actual design. This study presents rational approaches to revise creep coefficients for the Yassumi method by using parametric study results obtained from the age-adjusted effective modulus method.

• International Journal of Concrete Structures and Materials
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• v.4 no.2
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• pp.77-87
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• 2010

Prestressed concrete (PSC) I-type girders have been used for span length around up to 40 m in domestic region. PSC girders are very cost effective girder type and extending their lengths more than 50 m will bring large benefit in cost. A new design method was proposed by combining two notable design concept in order to extend the applicable span length in this study. First of all, several numbers of openings was introduced in the girder web, and half of the anchorage devices were moved into the openings. In this way, large compressive stress developed at end zone was reduced, and the portion of design load coming from self-weight was reduced as well. Secondly, prestressing force was introduced in the girder not once at the initial stage, but through multiple loading stages. A full scale girder with the length of 50 m with the girder depth of 2 m was fabricated, and a flexural test was conducted in order to verify the performance of newly developed girder. Test results showed that the new holed web design concept can provide a way to design girders longer than 50 meters with the girder height of 2 m.

• Proceedings of the Korea Concrete Institute Conference
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• 2010.05a
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• pp.13-14
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• 2010

The main purpose of this study is to investigate the static behavior of spliced prestressed concrete girder with bending moment connector and lateral prestressing. Same geometry and materials are used to fabricate these spliced and monolithic girders. A monolithic and spliced specimens materials and dimensions are same. The specimens are comprised of one spliced girder without lateral bending concrete as a control specimen and three spliced girders with lateral bending connectors. Deflections at the middle of girders have been measured for evaluation. Also, strains of the concrete at the middle of span and connection points have been measured.