• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3A
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• pp.235-241
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• 2009

PSC girder bridge is known to be more economical than other types of bridges and has been usually applied to a span range of 25 m to 35 m according to the standard shapes for highway bridges in Korea. The spans of the recently developed new types of PSC girders are also limited to 50 m at most. In this study, therefore, feasibility of the long-span PSC girder that reaches more than 50 m is investigated by applying several strategies from the perspectives of materials, design and construction. A systematic procedure is proposed that can be used to assess the effect of each strategy on the span. The proposed scheme adopts a graphical approach that represents a relationship between the number of prestressing tendons and the span, and is derived on a basis of safety assessment equations of the girder in each stage of fabrication and in service. In the companion paper, the amount of span extension is quantitatively evaluated by applying the proposed scheme into a sample PSC girder bridge.

• Wind and Structures
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• v.9 no.4
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• pp.271-296
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• 2006

The frequency of a traditional tuned liquid column damper (TLCD) depends solely on the length of liquid column, which imposes certain restrictions on its application to long span cable-stayed bridges during construction. The configuration of a cable-stayed bridge varies from different construction stages and so do its natural frequencies. It is thus difficult to apply TLCD with a fixed configuration to the bridge during construction or it is not economical to design a series of TLCD with different liquid lengths to suit for various construction stages. Semi-active tuned liquid column damper (SATLCD) with adaptive frequency tuning capacity is studied in this paper for buffeting response control of a long span cable-stayed bridge during construction. The frequency of SATLCD can be adjusted by active control of air pressures inside the air chamber at the two ends of the container. The performance of SATLCD for suppressing combined lateral and torsional vibration of a real long span cable-stayed bridge during construction stage is numerically investigated using a finite element-based approach. The finite element model of SATLCD is also developed and incorporated into the finite element model of the bridge for predicting buffeting response of the coupled SATLCD-bridge system in the time domain. The investigations show that with a fixed container configuration, the SATLCD with adaptive frequency tuning can effectively reduce buffeting response of the bridge during various construction stages.

• Wind and Structures
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• v.10 no.4
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• pp.301-314
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• 2007

The lever-type active multiple tuned mass dampers (LT-AMTMD), consisting of several lever-type active tuned mass dampers (LT-ATMD), is proposed in this paper to attenuate the vibrations of long-span bridges under the excitation directly acting on the structure, rather than through the base. With resorting to the derived analytical-expressions for the dynamic magnification factors of the LT-AMTMD structure system, the performance assessment then is conducted on the LT-AMTMD with the identical stiffness and damping coefficient but unequal mass. Numerical results indicate that the LT-AMTMD with the actuator set at the mass block can provide better effectiveness in reducing the vibrations of long-span bridges compared to the LT-AMTMD with the actuator set at other locations. An appealing feature of the LT-AMTMD with the actuator set at the mass block is that the static stretching of the spring may be freely adjusted in accordance with the practical requirements through changing the location of the support within the viable range while maintaining the same performance (including the same stroke displacement). Likewise, it is shown that the LT-AMTMD with the actuator set at the mass block can further ameliorate the performance of the lever-type multiple tuned mass dampers (LT-MTMD) and has higher effectiveness than a single lever-type active tuned mass damper (LT-ATMD). Therefore, the LT-AMTMD with the actuator set at the mass block may be a better means of suppressing the vibrations of long-span bridges with the consequence of not requiring the large static stretching of the spring and possessing a desirable robustness.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.248-259
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• 2010

In the case of relatively good ground and construction condition in the deep excavation for the construction of subway, railway, building etc., flexible earth retaining systems are often used in an economical point of view. It is generally known that the mechanism of behavior in the flexible earth retaining system is relatively more complicated than the rigid earth retaining system. Moreover in the case of long span strut supporting system the analysis of strut axial force change becomes more difficult when the differences of ground condition and excavation work progress on both sides of excavation section are added. When deeper excavation than the specification or installation delay of supporting system is done or change of ground condition is faced due to the construction conditions during construction process, lots of axial force can be induced in some struts and that can threaten the safety of construction. This paper introduces one example of long span deep excavation where struts and rock bolts were used as a supporting system with flexible wall structure. The characteristics of ground deformation and strut axial force change, the measured data obtained during construction process, were analysed, the effects of relatively deeper excavation than the specification on one excavation side and rapid drawdown of ground water level on the other excavation side were deeply investigated from the viewpoint of mutual influences between ground deformations of both excavation sides and strut axial force changes. The effort of this article aims to improve and develop the technique of design and construction in the coming projects having similar ground condition and supporting method.

• Proceeding of KASS Symposium
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• 2008.05a
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• pp.66-69
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• 2008

This study presents deflection analysis of long span structures for pedestrian bridge on crossroads. For long span structures, the size of structural members should be determined considering the esthetic view and vehicle below the structures. As a result, the slenderness ratio of members is increased and the structure may be suffered from significant deflection. The under-tensioned system on lower part of the structure, is applied in order to reduce the deflection and the size of members. In this regard, the under-tensioned system enables the load of upper parts to carη to the end of beam by means of tensional force in cable. In addition, effectiveness of under-tensioned system can be different depending on the size of cable, the number and spacing of posts. This study is performed with conforming the effect by analytical various parameters (size of cable, number and spacing of post). Dead and live loads is supposed to apply in the slab, and the analytical result by MIDAS program are presented addressing the effect of the under-tensioned system.

• Structural Engineering and Mechanics
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• v.74 no.5
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• pp.635-655
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• 2020

The sag effect of long stay cables is one of the key factors restricting further increase in the span of cable-stayed bridges. Based on the formerly proposed concept of long stay cables lifted by an auxiliary suspension cable in cross-strait cable-stayed bridges, corresponding static approximate calculations and analytical theory based on catenary and parabolic cable configurations are established. Taking a main span 1400 m cable-stayed bridge as the research object, three typical lifting conditions and the whole process of auxiliary cable lifting are analyzed and discussed. The results show that the sag effect is effectively reduced. The support efficiency is only improved when the cables are lifted above the original cable chord. Reduction of the horizontal component force of the cable is limited. The equivalent elastic modulus and the vertical support stiffness of the lifted cables are significantly increased with increased horizontal projection length and not sensitive to the change of the lifting point position. The scheme of lifting the cable to the chord midpoint is more economical because of the less steel required for the auxiliary suspension cable, but its effect on improving the vertical support efficiency is limited. The support efficiency is better when the cable is lifted to the cable end tangential to the original cable chord, but the lifting force and the cross-sectional area of the auxiliary suspension cable are doubled. The approximate calculation results of the lifted cables are very close to the numerical analysis results, which verifies the applicability of the approximation method proposed in this study. The results of parabolic approximation calculations are approximately equal to that of catenary cable geometry. As the parabolic approximation analysis theory of lifted cables is more convenient in mathematical processing, it is feasible to use parabolic approximation analysis theory as the analytical method for the conceptual design of lifted cables of super-long span cable-stayed bridges.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.308-319
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• 2009

In the case of relatively good ground and construction condition in the deep excavation for the construction of subway, railway, building etc., flexible earth retaining systems are often used in an economical point of view. It is generally known that the mechanism of behavior in the flexible earth retaining system is relatively more complicated than the rigid earth retaining system. Moreover in the case of long span strut supporting system the analysis of strut axial force change becomes more difficult when the differences of ground condition and excavation work progress on both sides of excavation section are added. When deeper excavation than the specification or installation delay of supporting system is done or change of ground condition is faced due to the construction conditions during construction process, lots of axial force can be induced in some struts and that can threaten the safety of construction. This paper introduces two examples of long span deep excavation where struts and rock bolts were used as a supporting system with flexible wall structure. And the sections of two examples are 50 meters apart in one construction site, they have almost similar design and construction conditions. The characteristics of ground deformation and strut axial force change were analysed, the similarity and difference between measurement results of tow examples were compared and investigated. The effort of this article aims to improve and develop the technique of design and construction in the coming projects having similar ground condition and supporting method.

• Journal of the Korean Society of Marine Environment & Safety
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• v.18 no.1
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• pp.49-54
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• 2012

The purpose of this study is to define emergency response procedures by BDMS [Building Disaster Management System] when earthquake occurs on long-span bridge structures. The study is about developing a computer-based algorithm for various earthquake intensities that works with the System. Presently, long-span bridge disaster prevention relies on closed-system centered on human intervention alone. However, this study combines IT technology and internet-based open system creating a more practical system. Additionally, assigned duties and tasks are clearly defined to all personnel involved in various disaster situations using the Active Action Diagram(AAD) techniques. Also, the design of 3-dimensional view assists to determine the appropriate initial response in times of earthquake and other disasters. The combination of the existing manual emergency response procedures and the scenario-based (IT) response system being developed will create an efficiency and fast response actions in times of emergencies.

• Journal of the Korea institute for structural maintenance and inspection
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• v.14 no.2
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• pp.113-120
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• 2010

Recently, various evaluations concerning structural stability under construction step and completely constructed step have been executed during a Long-span Arch Bridge designing procedure. However, the breakage of cable-hangers of arched bridge in unexpected accident or periodic cable-replacement has not been considered. Therefore, the purpose of this study is that analyzing structural safety of arched bridge when the cable-hangers being fractured by that reasons. Dynamic analysis are performed by idealizing impact load to three types of impact functions as fracturing the cables. Consequently, when the hangers are fractured, the maximum tensile force by dynamic analysis is larger than those by static analysis. Therefore, the dynamic analysis is demanded to accurately obtain the responses for the structural stability with a realistic impact loading model in the breakage and replacement of cable hangers of long-span arched bride. Moreover, the analysis method and results in this study can be used to basic criteria in design.

• Wind and Structures
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• v.17 no.3
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• pp.317-343
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• 2013

When evaluating flutter instability, it is often assumed that incident wind is normal to the longitudinal axis of a bridge and the flutter critical wind speed estimated from this direction is most unfavorable. However, the results obtained in this study via oblique sectional model tests of four typical types of bridge decks show that the lowest flutter critical wind speeds often occur in the yaw wind cases. The four types of bridge decks tested include a flat single-box deck, a flat ${\Pi}$-shaped thin-wall deck, a flat twin side-girder deck, and a truss-stiffened deck with and without a narrow central gap. The yaw wind effect could reduce the critical wind speed by about 6%, 2%, 8%, 7%, respectively, for the above four types of decks within a wind inclination angle range between $-3^{\circ}$ and $3^{\circ}$, and the yaw wind angles corresponding to the minimal critical wind speeds are between $4^{\circ}$ and $15^{\circ}$. It was also found that the flutter critical wind speed varies in an undulate manner with the increase of yaw angle, and the variation pattern is largely dependent on both deck shape and wind inclination angle. Therefore, the cosine rule based on the mean wind decomposition is generally inapplicable to the estimation of flutter critical wind speed of long-span bridges under skew winds. The unfavorable effect of yaw wind on the flutter instability of long-span bridges should be taken into consideration seriously in the future practice, especially for supper-long span bridges in strong wind regions.