• Journal of Korean Society of Steel Construction
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• v.14 no.1
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• pp.79-85
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• 2002

Recently, prestressed H-Beam bridges with external unbonded Tendons are increasingly built. The mechanical behavior of prestressed steel H-beams is different from that of normal bonded PSC beams in a point of the slip of tendons at deviators and the change of tendon eccentricity that occurs, when service load are applied in external unbonded steel H-beams. The concept of prestressing steel structures has been widely considered, in spite of long and successful history of prestressing concrete members. In the study, The flexural test on prestressed steel H-beams has been performed in the various aspects of prestressed H-beam including the tendon type and profile. The load was plotted against the deflection and the strain respectively in the steel beam and prestressing bars. The value expected with the equation of internal force equilibrium and compatibility between the deflection of the bars and the H-beam was found to correlate well with the measured data.

• Journal of Korean Society of Steel Construction
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• v.18 no.2
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• pp.239-250
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• 2006

In this study, the experimental bending behaviors of an H-secti on-steel-beam-attached high-strength steel plate or steel beam were analyzed. Its structural performance was verified by comparing the results of the experiment and the analysis that were conducted. In fabricating an unprestressed composite beam using two members that have different strengths, the generated slip on the joint in proport problem because of the redistribution of force caused by the lose state of the joint. Therefore, when fabricating composite beams, it is important to load them with prestressed forces. Based on the results of the experiment that was conducted, the prestressed composite-steel-beam-attached steel plate or beam has a higher bending resistance and load-carrying capacit

• International Journal of Concrete Structures and Materials
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• v.11 no.1
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• pp.1-16
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• 2017

The compression or tension-controlled failure mode of concrete beams prestressed with unbonded FRP tendons is governed by the relative amount of prestressing tendon to the balanced one. Explicit assessment to determine the balanced reinforcement ratio of a beam with unbonded tendons (${\rho}^U_{pfb}$) is difficult because it requires a priori knowledge of the deformed beam geometry in order to evaluate the unbonded tendon strain. In this study, a theoretical evaluation of ${\rho}^U_{pfb}$ is presented based on a concept of three equivalent rectangular curvature blocks for simply supported concrete beams internally prestressed with unbonded carbon-fiber-reinforced polymer (CFRP) tendons. The equivalent curvature blocks were iteratively refined to closely simulate beam rotations at the supports, mid-span beam deflection, and member-dependent strain of the unbonded tendon at the ultimate state. The model was verified by comparing its predictions with the test results. Parametric studies were performed to examine the effects of various parameters on ${\rho}^U_{pfb}$.

• Journal of Korean Society of Steel Construction
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• v.20 no.2
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• pp.247-258
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• 2008

In this study, static loading tests were performed on H-beam specimens to assess the static behavior of H-beam prestressed with multi-stepwise thermal prestressing method (TPSM). The amount of induced thermal prestress and connection type were differentiated among the 400-mm-high and 6,000-mm-long H-beam specimens to evaluate their effect on the behavior of the beams. From the experimental results, it between the H-beam and the cover-plate increased in yielding load by 13~18%, whereas stiffness increased by 27~34%. In case of specimens with both bolting and welding connection, yie lding load increased by 18~29% and stiffness increased by 43~51%. Multi-stepwise initial stress distribution was also observed from the prestressed specimens, verifying the effectiveness of the multi-stepwise TPSM. By application of the multi-stepwise TPSM, a significant increase in yielding load and stiffness can be achieved, hence increasing sectional and prestressing efficiencies.

• Structural Engineering and Mechanics
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• v.68 no.4
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• pp.475-483
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• 2018

Square tubular columns are commonly used in moment resisting frames, while through-diaphragm connection is the most typical configuration detail to connect the H-shaped beam to the column. However, brittle fracture normally occurs at the complete joint penetration weld between the beam flange and the through-diaphragm due to the stress concentration caused by the geometrical discontinuity. Accordingly, three improved types of through-diaphragm are presented in this paper to provide smooth force flow path comparing to that of conventional connections. Tensile tests were conducted on four specimens and the results were analyzed in terms of failure modes, load-displacement response, yield and ultimate capacity, and initial stiffness. Furthermore, strain distributions on the through-diaphragm, the beam flange plate, and the column face were comprehensively evaluated and discussed. It was found that all the proposed three types of improved through-diaphragm connections were able to reduce the stress concentration in the welds between the beam flange and the through-diaphragm. Furthermore, the stress distribution in connection with longer tapered through-diaphragm was more uniform.

• Computational Structural Engineering
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• v.24 no.2
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• pp.15-22
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• 2011

• Computers and Concrete
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• v.20 no.5
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• pp.617-625
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• 2017

Prestress force identification (PFI) is crucial to maintain the safety of prestressed concrete bridges. A synergic identification method has been proposed recently by the authors that can determine the prestress force (PF) and the excitation force simultaneously in prestressed concrete beams with good accuracy. In this paper, the ability of this method in the application with prestressed concrete box-girder bridges is demonstrated. A reasonable assumption is made to capture the similarity of the dynamic behavior of the prestressed concrete box-girder bridge and a beam under a certain loading scenario, and the feasibility of this method for application in a prestressed box-girder bridge is affirmed. A comprehensive laboratory test program is conducted, and the effects of PF, excitation, measuring time and uncertainties are studied. Results show that the proposed method can predict the PF and the excitation force in a prestressed concrete box-girder accurately and has a great robustness against uncertainties.

• International journal of steel structures
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• v.18 no.4
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• pp.1336-1349
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• 2018

Generally, a precast prestressed concrete (PSC) beam is used as girders for short-to-medium span (less than 30 m) bridges due to the advantages of simple design and construction, reduction of construction budget, maintenance convenience. In order to increase the span length beyond 50 m of precast PSC girder, PSC hollow box girder with unbonded prestressed H-type steel beam placed at the compressive region is proposed. The unbonded compressive prestressing in the H-type steel beams in the girder is made to recover plastic deflection of PSC girder when the pre-stressing is released. Also, the H-steel beams allow minimization of depth-to-length ratio of the girder by reducing the compressive region of the cross-section, thereby reducing the weight of the girder. A quasi-static 3-point bending test with 4 different loading steps is performed to verify safety and plastic deflection recovery of the girder. The experimental results showed that the maximum applied load exceeded the maximum design load and most of the plastic deflection was recovered when the compressive prestressing of H-type steel beams is released. Also using prestressed H-type steel as compression reinforcements in the upper part of cross section, repair and restoration difficulty and cost of PSC girders should be significantly reduced. The study result and analysis are discussed in detail in the paper.

• Journal of the Korea institute for structural maintenance and inspection
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• v.9 no.2
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• pp.225-235
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• 2005

The stability of innovative prestressed wale system applied in urban excavation was investigated. The IPS is a wale system prestressed by tension of steel wires. The IPS consists of steel wires, H-beam support and wale. The IPS provides a high flexural stiffness to resist the bending moment caused by earth pressures. And the IPS transmits earth pressures due to excavation to corner struts. The IPS provides a larger spacing of support, economical benefit, construction easiness, good performance and safety control. This paper explains basic concept and mechanism of the IPS and presents the measured performances of the IPS applied in urban excavation. In order to investigate applicability and stability of the IPS in urban excavation, observations and measurements in site were performed. The IPS applied in urban excavation was performed successfully. The results of the field instrumentation were presented. The measured performances of the IPS were investigated. And behavior of the wall and corner struts was investigated.

• Journal of the Korean Geotechnical Society
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• v.20 no.2
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• pp.107-113
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• 2004

A new innovative prestressed support (IPS) earth retention system has been developed and introduced. The IPS is a wale system prestressed by steel wires. The IPS consists of wale, wires, and H-beam support. The IPS provides a high flexural stiffness to resist the bending by earth pressures. The IPS earth retention system provides a larger spacing of support, economical benefit, construction easiness, good performance, and safety control. This paper explains basic principles and mechanism of new IPS system and presents a design method of IPS earth retention system. In order to investigate applicability and safety of new IPS system, field tests were performed in a trench excavation. The new IPS system applied in a trench excavation was performed successfully. The measured performances of IPS system were presented and discussed.