• International Journal of Railway
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• v.3 no.3
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• pp.83-89
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• 2010

This paper attempts to extract the fundamental dynamic properties, i.e. natural frequencies, damping ratios of the 48 m-long, $20^{\circ}$ skewed real bridge with PSC girders wrapped by a steel plate. The forced vibration test is achieved by mounting 12 Hz-capacity of artificial oscillator on the top of bridge deck. The acceleration histories at the 9 different locations of deck surface are recorded using accelerometors. From this full-scaled vibration test, the two possible resonance frequencies are detected at 2.38 Hz and 9.86 Hz of the skewed bridge deck by sweeping a beating frequency up to 12 Hz. The absolute acceleration/energy exhibits much higher in case of higher-order twist mode, 9.86 Hz due to the skewness of bridge deck which leads asymmetric situation of vibration. This implies the test bridge is under swinging vertically in fundamental flexure mode while the bridge is also flickered up and down laterally at 9.86 Hz. This is probably by asymmetric geometry of skewed deck. A detailed 3D beam-shell bridge models using finite elements are performed under a series of train loads for modal dynamic analyses. Thereby, the effect of skewness is examined to clarify the lateral flickering caused by asymmetrical geometry of bridge deck.

• Steel and Composite Structures
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• v.32 no.3
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• pp.325-336
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• 2019

Concrete placement and temporary formwork of bridge deck overhangs result in unbalanced eccentric loads that cause exterior girders to rotate during construction. These construction loads affect the global and local stability of the girders and produce permanent girder rotation after construction. In addition to construction loads, the skew angle of the bridge also contributes to girder rotation. To prevent rotation (in both skewed and non-skewed bridges), a number of techniques have been suggested to temporarily brace the girders using transverse tie bars connecting the top flanges and embedded in the deck, temporary horizontal and diagonal steel pipes placed between the webs of the exterior and first interior girders, and permanent cross frames. This study includes a rigorous three-dimensional finite element analysis to evaluate the effectiveness of several bracing systems for non-skewed and several skewed bridges. In this paper, skew angles of $0^{\circ}$, $20^{\circ}$, $30^{\circ}$, and $45^{\circ}$ were considered for single- and three-span bridges. The results showed that permanent cross frames worked well for all bridges, whereas temporary measures have limited application depending on the skew angle of the bridge.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.647-657
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• 2017

To achieve this goal, two four-span concrete box-girder bridges with typical configurations of California highway bridges are selected as representative bridges: an integral abutment bridge and a seat-type abutment bridge. A detailed numerical model of the representative bridges is created in OpenSees to perform dynamic analyses. To examine the effect of earthquake incidence angle on the fragility of skewed bridges, the representative bridge models are modified with different skew angles. Dynamic analyses for all bridge models are performed for all earthquake incidence angles examined. Simulated results are used to develop demand models and component and system fragility curves for the skewed bridges. The fragility characteristics are compared with regard to earthquake incidence angle. The results suggest that the earthquake incidence angle more significantly affects the seismic demand and fragilities of the integral abutment bridge than the skewed abutment bridge. Finally, a recommendation to account for the randomness due to the ground motion directionality in the fragility assessment is made in the absence of the predetermined earthquake incidence angle.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.389-396
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• 1998

One solution to prevent deterioration due to expansion joint and to extend lifetime of short span bridges, is jointless integral abutment bridge. To understand behavior of pile foundation of skewed plate girder bridge with integral abutment, finite element analysis was performed for the model of different skew angle from 90。 to 50。. Comparison of stresses at pile and abutment was made for each case. It is found that effect of temperature change is major factor to influence the behavior of skewed integral abutment bridge.

• Earthquakes and Structures
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• v.14 no.5
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• pp.467-476
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• 2018

The seismic vulnerability of skewed bridges had been observed in many past earthquakes. Researchers have found that the in-plane rotation of the girders was one of the main reasons for the vulnerability of these types of bridges. To date, not many experimental works have been done on this topic, especially those including pounding between adjacent structures. In this study, shake table tests were performed on a bridge-abutment system consisting of a straight, $30^{\circ}$, and $45^{\circ}$ bridge with and without considering pounding. Skewed bridges with the same fundamental frequency and those having the same girder mass as the straight bridge were studied. Under the loadings considered, skewed bridges with the same frequency as the straight tend to have smaller responses than those with the same mass. The average maximum bending moment developed in the piers of the $30^{\circ}$ bridge with the same mass as that of the straight when pounding was not considered was 1.6 times larger than when the frequencies were the same. It was also found that the NZTA recommendations for the seat lengths of skewed bridges could severely underestimate the relative displacements of these types of bridges in the transverse direction, especially when pounding occurs. In the worst case, the average transverse displacement of the $45^{\circ}$ bridge was about 2.6 times the longitudinal displacement of the straight, which was greatly over the limit suggested by the NZTA of 1.25 times.

• Earthquakes and Structures
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• v.10 no.4
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• pp.789-810
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• 2016

Reinforced concrete (RC) bridges with both skew and curvature are pretty common in areas with complex terrains. Existing studies have shown skewed and/or curved bridges exhibit more complicated seismic performance than straight bridges, and yet related seismic risk studies are still rare. These bridges deserve more studies in low-to-moderate seismic regions than those in seismic-prone areas. This is because for bridges with irregular and complex geometric designs, comprehensive seismic analysis is not always required and little knowledge about actual seismic risks for these bridges in low-to-moderate regions is available. To provide more insightful understanding of the seismic risks and the impact from the geometric configurations, analytical fragility studies are carried out on four typical bridge designs with different geometric configurations (i.e., straight, curved, skewed, skewed and curved) in the mountain west region of the United States. The results show the curved and skewed geometries can considerably affect the bridge seismic fragility in a complex manner, underscoring the importance of conducting detailed seismic risk assessment of skewed and curved bridges in low-to-moderate seismic regions.

• Earthquakes and Structures
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• v.9 no.6
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• pp.1153-1179
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• 2015

This paper focuses on presenting modeling considerations and insight into the performance of typical straight, curved, and skewed box-girder bridges in California which form the bulk of the bridge inventory in the state. Three case study bridges are chosen: Meloland Road Overpass, Northwest Connector of Interstate 10/215 Interchange, and Painter Street Overpass, having straight, curved, and skewed superstructures, respectively. The efficacy of nonlinear dynamic analysis is established by comparing the response from analytical models to the recorded strong motion data. Finally insights are provided on the component behavioral characteristics and shift in vulnerability for each of the bridge types considered.

• Computers and Concrete
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• v.20 no.4
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• pp.419-427
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• 2017

A methodology, based on fragility functions, is proposed to evaluate the seismic performance of seismic isolated $45^{\circ}$ skewed concrete bridge: 1) twelve types of seismic isolation devices are considered based on two different design parameters 2) fragility functions of a three-span bridge with and without seismic isolation devices are analytically evaluated based on 3D nonlinear incremental dynamic analyses which seismic input consists of 20 selected ground motions. The optimum combinations of isolation device design parameters are identified comparing, for different limit states, the performance of 1) the Seismic Isolated Bridges (SIB) and 2) Not Seismic Isolated Bridge (NSIB) designed according to the AASHTO standards.

• Earthquakes and Structures
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• v.20 no.4
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• pp.389-403
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• 2021

Skewed bridges, being irregular structures with complicated dynamic behavior, are more susceptible to earthquake damage. Reliable seismic-resistant design of skewed bridges can be achieved by accurate determination of nonlinear seismic demands. However, the effect of geometric characteristics on the response modification factor (R-factor) is not accounted for in bridge design practices. This study attempts to investigate the effects of changes in the number of spans, skew angle and bearing stiffness on R-factor values and to assess the seismic fragility of skewed bridges. Results indicated that changes in the skew angle had no significant effect on R-factor values which were in consonance with code-prescribed R values. Also, unlike the increase in the number of spans that resulted in a decrease in the R-factor, the increase in bearing stiffness led to higher R-factor values. Findings of the fragility analysis implied that although the increase in the number of spans, as well as the increase in the skew angle, led to a higher failure probability, greater values of bearing stiffness reduced the collapse probability. For practicing design engineers, it is recommended that maximum demands on substructure elements to be calculated when the excitation angle is applied along the principal axes of skewed bridges.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 1998.10a
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• pp.113-119
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• 1998

This study is focused on evaluation of the structural behavior of skewed bridge during earthquake. The variation of natural frequencies and the lateral forces at pier shoes by the skewness and the rotational effect about vertical axis of skewed bridge due to seismic activity are analytically evaluated and identified through case studies. For this purpose, the composite steel girder highway bridges are selected as case study models. The seismic analyses by response spectrum method and time history method are performed for the selected models. It has been recognized that the frequency of longitudinal model increased as the skew angle decreased, while the lateral mode frequency showed the opposite trends. When the skew angle decreased, longitudina seismic forces of the bridge at the pier were increased but decreased in transverse direction. And it also has been found that the skewed bridges of the case study models showed the rotational behavior about vertical axis due to motion of San Fernando earthquake at Pacoima Dam.