• Wind and Structures
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• v.30 no.1
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• pp.55-67
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• 2020

Wind tunnel test is one of the most important means to study the flutter performance of bridges, but there are blockage effects in flutter test due to the size limitation of the wind tunnel. On the other hand, the size of computational domain can be defined by users in the numerical simulation. This paper presents a study on blockage effects of a simplified box girder by computation fluid dynamics (CFD) simulation, the blockage effects on the aerodynamic characteristics and flutter performance of a long-span suspension bridge are studied. The results show that the aerodynamic coefficients and the absolute value of mean pressure coefficient increase with the increase of the blockage ratio. And the aerodynamic coefficients can be corrected by the mean wind speed in the plane of leading edge of model. At each angle of attack, the critical flutter wind speed decreases as the blockage ratio increases, but the difference is that bending-torsion coupled flutter and torsional flutter occur at lower and larger angles of attack respectively. Finally, the correction formula of critical wind speed at 0° angle of attack is given, which can provide reference for wind resistance design of streamlined box girders in practical engineering.

• Structural Engineering and Mechanics
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• v.75 no.5
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• pp.595-605
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• 2020

In this study, the flexural behaviors of full-scale prestressed concrete box girders are experimentally investigated. Four girders were fabricated using two types of concrete (compressive strengths: 50 MPa and 70 MPa) and tested under four-point bending until failure. The measured parameters included the deflection, the stress and strain in concrete and steel bars, and cracks in concrete. The measurement results were used to analyze the failure mode, load-bearing capacity, and deformability of each girder. A finite element model is established to simulate the flexural behaviors of the girders. The results show that the use of high-performance concrete and reasonable combination of prestressed tendons could improve the mechanical performance of the box girders, in terms of the crack resistance, load-carrying capacity, stress distribution, and ductility.

• Smart Structures and Systems
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• v.1 no.4
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• pp.355-368
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• 2005

Large and complex structures are being built now-a-days and, they are required to be functional even under extreme loading and environmental conditions. In order to meet the safety and maintenance demands, there is a need to build sensors integrated structural system, which can sense and provide necessary information about the structural response to complex loading and environment. Sophisticated tools have been developed for the design and construction of civil engineering structures. However, very little has been accomplished in the area of monitoring and rehabilitation. The employment of appropriate sensor is therefore crucial, and efforts must be directed towards non-destructive testing techniques that remain functional throughout the life of the structure. Fiber optic sensors are emerging as a superior non-destructive tool for evaluating the health of civil engineering structures. Flexibility, small in size and corrosion resistance of optical fibers allow them to be directly embedded in concrete structures. The inherent advantages of fiber optic sensors over conventional sensors include high resolution, ability to work in difficult environment, immunity from electromagnetic interference, large band width of signal, low noise and high sensitivity. This paper brings out the potential and current status of technology of fiber optic sensors for civil engineering applications. The importance of employing fiber optic sensors for health monitoring of civil engineering structures has been highlighted. Details of laboratory studies carried out on fiber optic strain sensors to assess their suitability for civil engineering applications are also covered.

• Special Issue of the Society of Naval Architects of Korea
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• 2005.06a
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• pp.90-96
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• 2005

This paper presents the results of the reliability analysis of PAU (Preliminary Assembly Unit) seat of the floating Production Storage and Off1-loading Unit (FPSO) The main aim of the analysis was to demonstrate that a sufficient safety of structural members is guaranteed against PAU loads, internal and external pressure, and hull girder moments. Topside loads for PAU design are based on owner's request. According to the seat type, topside loads are classified into maximum values of same seat type for design efficiency. Totally, 26 loading cases for each model are used for this analysis with the combination of the reactions of PAU loafing and the hull girder bending moments according to LR offshore (2). The analysis results are evaluated according to the acceptance criteria for yielding given in LR offshore and guidance note (3) and The panel buckling resistance is verified by LR offshore and SDA (4). For 900,000 bbls FPSO, the PAU support foundation analysis using 3-D F.E. model is carried out to verify the structural adequacy of PAU foundation and structure members in way of PAU. The modified structures in way of PAU support are safe against considered load cases and all stresses in way of PAU support are within design criteria.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.525-530
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• 2007

Although just developed in recent years, curved box girder has widely used in modern highway system due to their load resistance capacity as well as aesthetic considerations. According to recent literature reviews on curved box girder designs, distortional load was not considered as much as it deserves to be. In practice, the effect of distributional force is very small in straight bridge systems but yet unknown how it is in curved bridge systems. For the reason, this paper will show up an extensive parametric study on distortional behavior of curved box girder with trapezoidal section. Based on Dabrowski formulas, using finite element method, various bridges were investigated. In this study, following parameters will be included: span length, curvature radius, section height, section width, and internal section angle (web slope). From the obtained results, some initial geometric parameters are proposed for curved box girder bridges.

• Journal of the Korea institute for structural maintenance and inspection
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• v.6 no.2
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• pp.225-231
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• 2002

Severe cracks on Reinforced Concrete (RC) structures caused by structural displacement can be often one of the main reasons for the degradation of tensile and flexural rigidities of RC structures and for the deterioration of durability and serviceability of RC structures through accelerated steel corrosion. These combined factors adversely affect the performance of RC concrete, leading to shortened life time of RC structures. In consideration of these problems, we conducted 3 point bending experiments by employing three different types of concrete specimens: fiber-net reinforced concrete (FNRC), polypropylene-fiber reinforced concrete (PFRC), and plain concrete (PC). FNRC is well known for its strong corrosion resistance, light self-weight, and excellent tensile strength, while PFRC is known to be effective in crack control. FNRC was found to have the best first and final crack resistances followed by PFRC and PC, as evidenced by the highest initial crack load and the smallest final crack width, respectively. The FNRC specimens with various tensile strength of fiber net exhibited greater ultimate strengths than those for PFRC and PC. Furthermore, the crack widths of FNRC specimens were smaller than those calculated by the crack-width estimation equation of the KCI and ACI code. Therefore, we conclude that fiber net reinforcement is effective not only on crack control, but also on loading share.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.122-129
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• 1988

Recently with the rapid development in marine and shipbuliding industries such as marine structures, ship and chemical plants, there occurs much interest in the study of corrosion fatigue characteristics which was closed up an important role in mechanical design. In this study, the 5086 Al-alloy was tested by use of rotary bending fatigue tester. The retardation effect of overload on the corrosion fatigue crack propagation in sea environment was quantitatively studied. 1) Retardation effect of corrosion fatigue crack propagation is most eminent when overload ratio is 1.52, overload magnitude corresponds to about 77% and 55% of yield strength and tensile strength respectively. 2) After overload ratio 1.52 was used, retardation of corrosion fatigue crack growth rate is largely retarded and quasi-threshold stress intensity factor range($\Delta\textrm{K}_{th}$) appears. 3) According to m of experimental constant, retardation effect of corrosion fatigue crack propagation corresponds to about 25% of constant stress amplitude when overload ratio is 1.52. 4) When overload ratio 1.52 was used, retardation parameter (RP) decreases to about 0.43 and corrosion sensitivity (S)decreses to about 2.1.

• Structural Engineering and Mechanics
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• v.53 no.1
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• pp.173-188
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• 2015

Several structural calamities in the second half of the 20th century have shown that adequate collapse-resistance cannot be achieved by designing the individual elements of a structure without taking their interconnectivity into consideration. It has long been acknowledged that membrane behaviour of reinforced concrete structures can significantly increase the robustness of a structure and delay a complete collapse. An experimental large-scale test was conducted on a horizontally restrained, continuous reinforced concrete slab exposed to an artificial failure of the central support and subsequent loading until collapse of the specimen. Within this investigation the development of catenary action associated with the formation of large displacements was observed to increase the ultimate load capacity of the specimen significantly. The development of displacements, strains and horizontal forces within this investigation confirmed a load transfer process from an elastic bending mechanism to a tension controlled catenary mechanism. In this contribution a special focus is directed towards strain and crack development at critical sections. The results of this contribution are of particular importance when validating numerical models related to the development of catenary action in concrete slabs.

• Steel and Composite Structures
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• v.20 no.1
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• pp.57-70
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• 2016

The predominant type of buckling that I-steel concrete composite beams experience in the negative moment area is distortional buckling. The key factors that affect distortional buckling are the torsional and lateral restraints by the bottom flange. This study thoroughly investigates the equivalent lateral and torsional restraint stiffnesses of the bottom flange of an I-steel concrete composite beam under negative moments. The results show a coupling effect between the applied forces and the lateral and torsional restraint stiffnesses of the bottom flange. A formula is proposed to calculate the critical buckling stress of the I-steel concrete composite beams under negative moments by considering the lateral and torsional restraint stiffnesses of the bottom flange. The proposed method is shown to better predict the critical bending moment of the I-steel composite beams. This article introduces an improved method to calculate the elastic foundation beams, which takes into account the lateral and torsional restraint stiffnesses of the bottom flange and considers the coupling effect between them. The results show a close match in results from the calculation method proposed in this paper and the ANSYS finite element method, which validates the proposed calculation method. The proposed calculation method provides a theoretical basis for further research on distortional buckling and the ultimate resistance of I-steel concrete composite beams under a variable axial force.

• Steel and Composite Structures
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• v.17 no.6
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• pp.907-927
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• 2014

Ultra-lightweight cement composite (ULCC) with a compressive strength of 60 MPa and density of $1450kg/m^3$ has been developed and used in the steel-concrete-steel (SCS) sandwich structures. ULCC was adopted as the core material in the SCS sandwich composite beams to reduce the overall structural weight. Headed shear studs working in pairs with overlapped lengths were used to achieve composite action between the core material and steel face plates. Nine quasi-static tests on this type of SCS sandwich composite beams were carried out to evaluate their ultimate strength performances. Different parameters influencing the ultimate strength of the SCS sandwich composite beams were studied and discussed. Design equations were developed to predict the ultimate resistance of the cross section due to pure bending, pure shear and combined action between shear and moment. Effective stiffness of the sandwich composite beam section is also derived to predict the elastic deflection under service load. Finally, the design equations were validated by the test results.