• Smart Structures and Systems
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• v.8 no.4
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• pp.399-412
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• 2011

This study compares the performance of two smart isolation systems that utilize superelastic shape memory alloys (SMAs) for seismic protection of bridges using energy balance concepts. The first isolation system is a SMA/rubber-based isolation system (SRB-IS) and consists of a laminated rubber bearing that decouples the superstructure from the bridge piers and a SMA device that provides additional energy dissipation and re-centering capacity. The second isolation system, named as superelastic-friction base isolator (S-FBI), combines the superelastic SMAs with a flat steel-Teflon bearing rather than a laminated rubber bearing. Seismic energy equations of a bridge structure with SMA-based isolation systems are established by absolute and relative energy balance formulations. Nonlinear time history analyses are performed in order to assess the effectiveness of the isolation systems and to compare their performance. The program RSPMatch 2005 is employed to generate spectrum compatible ground motions that are used in time history analyses of the isolated bridge. Results indicate that SRB-IS produces higher seismic input energy, recoverable energy and base shears as compared to the S-FBI system. Also, it is shown that combining superelastic SMAs with a sliding bearing rather than rubber bearing significantly reduce the amount of the required SMA material.

• International Journal of Railway
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• v.5 no.1
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• pp.10-21
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• 2012

Open steel plate girder (OPSG) bridges are the most prevalent railroad bridge type in Korea, constituting about 40% of all railroad bridges. Solid steel bearings, known as line type bearings, are placed in most OSPG railway bridges. However, the line type rigid bearings generate several problems with the bridge's dynamic behavior and maintenance in service. To compare and investigate the dynamic behaviors of line type, spherical and disk bearings, the vertical displacements of each bearing, including fixed and expansion type, under running vehicles are measured and analyzed. The displacements of disk and spherical bearings are measured after replacing the line type bearings with spherical and disk bearings. This study also analyzed dynamic behaviors of bridges. Furthermore, the deformation of the PTFE (Polytetrafluoroethylene) plate that is placed inside of expansion type spherical and disk bearings is measured and its effect on the dynamic behavior of the bridges is discussed. The up-lift phenomenon at the bearings installed for the steel bridges is estimated. The vertical displacements at mid-span of the bridges are compared according to the bearing types. Finally, the 1st mode natural frequencies are estimated, and the relationship to the vertical displacement is discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.10a
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• pp.591-604
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• 2008

In this study, two design examples of drilled shafts on soft ground in Ho-Chi-Minh City, Vietnam are introduced. One is for a 27-story apartment and the other is for a Arch bridge over Saigon river. Unlikely the normal cases in Korea, all of the bored pile foundations are supposed to be placed on soil layers. Therefore, skin friction between pile and ground is the most crucial design parameter. Three methods using SPT N value of sandy soil -Korean Road Bridge Code(1996), Reese and Wright (1977), and O'Neill and Reese (1988)- were adopted to obtain an ultimate axial bearing capacity. In order to verify the calculated bearing capacity, 3 sets of static load test and a Osterberg Cell test were performed at an apartment site and a bridge site respectively. LRFD (Load Resistance Factored Design) method was compared with ASD (Allowable Stress Design) method. On application of ASD method, safety factor for skin friction was adopted as 2 or 3 while safety factor for end bearing was 3. The design bearing capacities from ASD method matched well with those from LRFD method when safety factor for skin friction was adopted as 2.

• Journal of the Earthquake Engineering Society of Korea
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• v.6 no.5
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• pp.19-27
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• 2002

Dynamic responses of a multi-span simply supported bridge are investigated to examine the effect of bearing damage under seismic excitations. The damaged bearings are modeled as sliding elements with friction between the superstructure and the top of the pier. Various values of the friction coefficients are examined to figure out the effect of damaged bearings with various levels of peak ground accelerations. It is found that the global seismic behaviors are significantly influenced by the occurrence of bearing damage. It should be noticed that the most possible location of unseating failure of superstructures differs from that in the bridge model without considering the bearing damage. It can be concluded that the bearing damage may play the major role in the unseating failure of a bridge system, so that the damage of bearings should be included to achieve more rational seismic safety evaluation.

• Journal of The Korean Society For Urban Railway
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• v.6 no.4
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• pp.383-392
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• 2018

This study investigated the change of additional axial stress of rail and reaction force at bridge bearings due to the track-bridge interaction when laying CWR on non-ballasted railway bridges including truss bridges with relatively long span. According to the results of the present study, additional axial stresses of rail and reaction forces at bridge bearings showed a large increase when CWR is installed on the non-ballasted railway bridge. The additional axial stress of rail can be acceptable if sufficient lateral resistance can be obtained. However, if the reaction force increases, there is a risk of damage of the bearing or pier, and therefore, it is necessary to take measures to mitigate the reaction force. It is found that additional axial stress of rail decreases when considering the frictional resistance of the bridge movable support, but its effect on the bearing reaction force is very small. On the other hand, when the longitudinal track restraint decreases, both additional axial stress of rail and bearing reaction force are reduced to a large extent. Also, when the ZLR fastening devices are applied to the region where the additional axial stress of rail is highest, bearing reaction force as well as additional axial stress of rail greatly decreased. Therefore, the application of ZLR fastening devices with the reduction of the longitudinal track restraints is very effective for installing CWR on non-ballasted railway bridges.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.311-319
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• 2001

Recently, the number of seismically isolated bridges increased suddenly since the occurrence of strong earthquakes. However, because isolator lies between pier and girder, the response of the superstructure of seismically isolated bridge may be magnified and induce risk of unseating girder Consequently, the response of girder constitutes a crucial factor in designing bridge. In the case of frictional bearing, the inherent nonlinearity makes the use of former linear response spectrum unable to estimate the maximum response of the bearing, and nonlinear tlme history analysis shall be applied. In this paper, nonlinear response spectrum considering frictional element is established, and simple analysis method using such nonlinear spectrum is proposed to estimate the maximum response of the superstructure.

• Proceedings of the KSR Conference
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• 2009.05a
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• pp.599-605
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• 2009

The aim of the present study is the characteristics of bridge rubber pads and suggested how to determine the stiffness the pads. A disk bearing is operated as an elastic bearing in the vertical direction and is composed of a Polyether Urethane (polyurethane) disk for elastic support and Polytetrafluoroethylene (PTFE) to accommodate movement. Static tests are conducted in a laboratory to determine the static behavior of a Polyurethane disk. Finite Element (FE) analysis is also performed to verify the static performance. For dynamic behavior, four disk bearings having the identical Polyurethane disk used in the static tests are installed in a full size railway bridge and tested under a running locomotive. From the tests results, the static and dynamic stiffness of disk bearings are estimated and compared with each other. In the procedure to estimate the stiffness of a pad, the dead load(pre-load) of a bridge and live load of a vehicle are considered.

• Proceedings of the Korean Geotechical Society Conference
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• 1999.03a
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• pp.241-248
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• 1999

The existing bridge with deck joint has many problems during construction and maintenance. To overcome these difficulties, an integral bridge, which is defined as the practice of constructing bridges without deck joints, is proposed in this study. A test bridge with 3 spans of PC beam was selected to verify the function of the bridge and is under construction. Characteristics of integral bridge are followings: $\circled1$ Flexible H-piles under the abutment are installed to accommodate thermal movements of the superstructures of bridge. $\circled2$ PC beam of the superstructure and the abutment are integrated. $\circled3$ The existing approach and relief slabs are applied to minimize the stress transfer occurred from the bridge deck to the pavement. $\circled4$ A cyclic control joint is installed between approach and relief slabs to absorb the thermal movement. $\circled5$ It is used a dual direction bearing which is cheaper than single direction bearing and has a good workability as well. It is also installed a shear block on the top of pier coping to protect the lateral movement caused by temperature change and earthquake.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.320-328
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• 2001

Base Isolation system is an effective design strategy that provides a practical substitute for the seismic design of bridge. In this study, the dynamic tests were performed on two kinds of aseismic bridge bearings : Hydampot (hysteretic damping bearing) and Dynapot . Then, the dynamic analysis was carried out far a bridge using the experimental results to estimate the seismic performance of the bearings. Analysis was performed for four types oi earthquake loadings. The results of the dynamic test and theoretical analysis indicate that the performance of both bridge bearings is appropriate fur the earthquake loading.

• Proceedings of the KSR Conference
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• 2005.05a
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• pp.115-122
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• 2005

This study analyzed the characteristics of four kinds of bridge rubber pads and suggested how to determine the stiffness the pads. The stiffness of rubber pads can be estimated by a direct static test. In the procedure to estimate the stiffness of a pad, the dead load(preload) of a bridge and live load of a vehicle are considered. The polyurethane rubber pads have larger hardness than natural and chloroprene rubber pads and thus carry larger load bearing capacity. In addition, they showed higher stiffness with the same shape factor than the others and thus are more avaliable as for bridge bearings. Although natural and chloroprene rubber pads are elongated to large deformation in horizontal direction due to vertical loads, polyurethane rubber pads almost do not generate horizontal deformation due to vertical loads regardless to the thickness and hardness of the pads. Therefore, they do not need reinforced plate to restrict horizontal deformation.