• Journal of the Korea Concrete Institute
• /
• v.22 no.6
• /
• pp.777-786
• /
• 2010

This paper examines the flexural behavior of full-scale prestressed concrete girders that were constructed of steel fiber reinforced ultra high performance concrete (UHPC). This study is designed to provide more information about the bending characteristics of UHPC girders in order to establish a reasonable prediction model for flexural resistance and deflection for future structural design codes. Short steel fibers have been introduced into prestressed concrete T-girders in order to study their effects under flexural loads. Round straight high strength steel fibers were used at volume fraction of 2%. The girders were cast using 150~190 MPa steel fiber reinforced UHPC and were designed to assess the ability of steel fiber reinforced UHPC to carry flexural loads in prestressed girders. The experimental results show that steel fiber reinforced UHPC enhances the cracking behavior and ductility of beams. Moreover, when ultimate failure did occur, the failure of girders composed of steel fiber reinforced UHPC was observed to be precipitated by the pullout of steel fibers that were bridging tension cracks in the concrete. Flexural failure of girders occurred when the UHPC at a particular cross section began to lose tensile capacity due to steel fiber pullout. In addition, it was determined that the level of prestressing force influenced the ultimate load capacity.

• Journal of Korean Society of Steel Construction
• /
• v.24 no.5
• /
• pp.571-582
• /
• 2012

Prestressed composite girders provide efficient composite action by applying prestress to the sub-encasing concrete. In this study, an enhanced prestressed composite girder with forms suspended from the steel girder is utilized. Long-term behavior of the prestressed composite girder is estimated using age-adjusted effective modulus method, which is verified experimentally using measurements obtained from an in-service bridge. Then, parametric study is carried out to investigate the influences caused by ambient temperature, humidity, prestressing and concrete casting date.

• Computers and Concrete
• /
• v.25 no.6
• /
• pp.497-507
• /
• 2020

This paper presents a numerical method for evaluating fire performance of prestressed concrete (PC) T shaped bridge girders under combined effect of structural loading and hydrocarbon fire exposure conditions. A numerical model, developed using the computer program ANSYS, is employed to investigate fire response of PC T shaped bridge girders by taking into consideration structural inherent parameters, namely; arrangement of prestressing strands with in the girder section, thickness of concrete cover over prestressing strands, effective degree of prestress and content of prestressing strands. Then, a sequential thermo-mechanical analysis is performed to predict cross sectional temperature followed by mechanical response of T shaped bridge girders. The validity of the numerical model is established by comparing temperatures, deflections and failure time generated from fire tests. Through numerical studies, it is shown that thickness of concrete cover and arrangement of prestressing strands in girder section have significant influence on the fire resistance of PC T shaped bridge girders. Increase in effective degree of prestress in strands with triangular shaped layout and content in prestressing strands can slow down the progression of deflections in PC T shaped bridge girder towards the final stages of fire exposure, to thereby preventing sudden collapse of the girder. Rate of deflection based failure criterion governs failure in PC T shaped bridge girders under most hydrocarbon fire exposure conditions. Structural inherent parameters incorporated into sectional configuration can significantly enhance fire resistance of PC bridge girders; thus mitigating fire induced collapse of these bridge girders.

• Advances in concrete construction
• /
• v.3 no.2
• /
• pp.113-126
• /
• 2015

Holed-Incrementally Prestressed Concrete (H-IPC) girders are designed using the following new design concepts. At first, web openings reduce the self-weight of the girder, and also diffuse prestressing tendon anchorages. The reduced end anchoring forces decrease the web thickness of the end sections. Additionally, precast technology help to improve the quality of concrete and to reduce the construction period at the site. For experimentally verification, two 50 m full-scale H-IPC girders are manufactured with different concrete strength of 55 MPa and 80 MPa. The safety, stiffness, ductility, serviceability and crack development of H-IPC girder are measured and compared with each other for different strengths. Both girders show enough strength to carry live load and good stiffness to satisfy the design criteria. The experimental result shows the advantages of using high strength concrete and adopting precast girder. The test data can be used as a criterion for safety control and maintenance of the H-IPC girder.

• Structural Engineering and Mechanics
• /
• v.55 no.3
• /
• pp.511-523
• /
• 2015

Damaged steel-concrete composite girders can be repaired and retrofitted by epoxy-bonded carbon fiber-reinforced polymer (CFRP) sheets to the critical areas of tension flanges. This paper presents the results of a study on the behavior of damaged steel-concrete composite girders repaired with CFRP sheets under static loading. A total of seven composite girders made of I20A steel sections and 80mm-thick by 900mm-wide concrete slabs were prepared and tested. CFRP sheets and prestressed CFRP sheets were used to repair the specimens. The specimens lost the cross-sectional area of their tension flanges with 30%, 50% and 100%. The results showed that CFRP sheets had no significant effect on the yield loads of strengthened composite girders, but had significant effect on the ultimate loads. The yield loads, elastic stiffness, and ultimate bearing capacities of strengthened composite girders had been changed as a result of prestressed CFRP sheets, the utilization ratio of CFRP sheets could be effectively improved by applying prestress to CFRP sheets. Both the yield loads and ultimate bearing capacities had been changed as a result of steel beam's flange damage level and CFRP sheets could cover the girders' shortage of bearing capacity with 30% and 50% flange damage, respectively.

• Journal of Korean Society of Steel Construction
• /
• v.17 no.5 s.78
• /
• pp.637-648
• /
• 2005

Innovative prestressed steel plate girders were presented in this study. Hot-rolled H beams were loaded first, then relatively high-strengthsteel plates were welded on the top and bottom flanges of preloaded H beams. Finally, high prestressed plate (HiPP) girder was manufactured by simply releasing prestresses of rolled beams. To verify prestress distributions induced in this girder, the experimental study was conducted and some guidelines to manufacture these girders effectively were addressed. In addition, methods to determine the allowable bending stress of HiPP girders and to check welding stresses were addressed for design of temporary bridges. The efficiency and effectiveness of the present girder were demonstrated through design examples of temporary bridges adapting the prestress-induced girder or the plate girder of the same section without prestresses. As a result, it has been found to be possible that the span length of HiPP girders for temporary bridges is longer than that of girders without prestresses.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.30 no.3A
• /
• pp.287-295
• /
• 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. Four (4) spliced girders and one (1) monolithic girder had been fabricated and tested to compare their static behaviors. Same geometry and materials are used to fabricate these spliced and monolithic girders. A monolithic girder and one (1) spliced girder without lateral bending connector are used as control specimens to estimate the performance of three (3) spliced girders with lateral bending connector. 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. It was found from the result that laterally strengthened spliced girders showed improved ultimate strength but less stiffness compared to the monolithic girder at the ultimate state. Laterally strengthened spliced girder also showed improved strength as well as improved stiffness compared to the spliced girder without lateral strengthening.

• Structural Engineering and Mechanics
• /
• v.62 no.6
• /
• pp.663-674
• /
• 2017

This paper presents an approach for evaluating performance of prestressed concrete (PC) bridge girders exposed to fire. A finite element based numerical model for tracing the response of fire exposed T girders is developed in ANSYS. The analysis is carried out in three stages, namely, fire temperature calculation, cross sectional temperature evaluation, and then strength, deformation and effective prestress analysis on girders exposed to elevated temperatures. The applicability of the computer program in tracing the response of PC bridge girders from the initial preloading stage to failure stage, due to combined effects of fire and structure loading, is demonstrated through a case study, and validated by test data of a scaled PC box girder under ISO834 fire condition. Results from the case study show that fire severity has a significant influence on the fire resistance of PC T girders and hydrocarbon fire is most dangerous for the girder. The prestress loss caused by elevated temperature is about 10% under hydrocarbon fire till the girder failure, which can lead to the increase in deflection of the PC girder. The rate of deflection failure criterion is suggested to determine the failure of PC T girder under fire.

• Journal of Ocean Engineering and Technology
• /
• v.24 no.3
• /
• pp.1-10
• /
• 2010

In this study, hybrid smart sensor nodes were developed for the autonomous structural health monitoring of prestressed concrete (PSC) girders. In order to achieve the objective, the following approaches were implemented. First, we show how two types of smart sensor nodes for the hybrid health monitoring were developed. One was an acceleration-based smart sensor node using an MEMS accelerometer to monitor the overall damage in concrete girders. The other was an impedance-based smart sensor node for monitoring the local damage in prestressing tendons. Second, a hybrid monitoring algorithm using these smart sensor nodes is proposed for the autonomous structural health monitoring of PSC girders. Finally, we show how the performance of the developed system was evaluated using a lab-scaled PSC girder model for which dynamic tests were performed on a series of prestress-loss cases and girder damage cases.

• Structural Engineering and Mechanics
• /
• v.17 no.6
• /
• pp.879-898
• /
• 2004

A method of making simply supported girders continuous is described for bridges with spans of 30-45 m. The splicing method takes advantage of an induced secondary moment to transform the self-weight stresses in the precast simply supported girders into values representative of a continuous girder. The secondary moment results from prestressing of continuity tendons and detensioning of temporary tendons in the girders. Preliminary sections are selected for spliced U-girder bridges with a range of span lengths. Use of the proposed technique results in girder depth reductions of 500-800 mm when compared to standard simply supported I-girder bridges. The flexural behavior of an example bridge with 40-m spans is examined to illustrate the necessary considerations for determining the optimum sequence of splicing operations.