Skewed Bridges Research Articles

Analysis and Design of Straight and Skewed Slab Bridges

Results of an investigation aimed at determining bending moments and shear forces, required to design skewed concrete slab bridges using the equivalent-beam method are presented in this paper. Straight and skewed slab bridges were modeled using grillage and finite-element models to characterize their behavior under uniform and moving loads with the objective of determining the most appropriate modeling approach for design. A parametric study was carried out on 390 simply supported slabs with geometries covering one to four lane bridges of 3- to 20-m spans and with skew angles ranging from 0 to 60°. The analyses showed that nonorthogonal grillages satisfactorily predict the amplitude and the transverse distribution of longitudinal bending moments and shear forces, and can be used for the analysis of skewed slab bridges. Results of the parametric study indicated that shear forces and secondary bending moments increase with increasing skew angle while longitudinal bending moments diminish. Equations are prop...

Load rating of concrete-deck-on-steel-stringer bridges using field-calibrated 2D-grid models

This paper presents and discusses issues related to structural identification, calibrated model-based load rating, and sensitivity of rating to the analytical model, along with experimental studies conducted on an existing concrete-deck-on-steel-stringer bridge. The proposed model-updating procedure uses collected dynamic data (mode shapes, modal frequencies, and order of modes) as well as static deformed shape information. Two-dimensional (2D) grid models were developed to successfully simulate the transverse load transfer mechanisms between girders, torsional flexibility, and effects of skewed bridge architecture. The rating results obtained from the 2D-grid models were close to 3D-FEM-based evaluation, while simplified 1D bar models had serious shortcomings. Grouping the parameters of the analytical model at different stages of model calibration enhanced the speed and convergence success of the objective function. Although cross-braces are considered as non-structural members, they have been found to be the most critical members of the selected bridge during rating studies. Failure of cross-braces deemed to alter the load transfer mechanism between girders and possibly resulting in the premature failures of interior girders.

Prediction of vehicle-induced local responses and application to a skewed girder bridge

This paper proposes an innovative and flexible simulation method that predicts the dynamic responses of bridges induced by passing vehicles. The decoupled equations of motion of the vehicle–bridge system are derived from Lagrange equations and include the effect of road surface roughness, while the interaction forces between the two systems are calculated step by step, using Newmark’s method. This algorithm does not require a special finite element (FE) code and can be implemented with standard FE software and general numerical software such as ABAQUS and MATLAB, respectively. In order to illustrate the practicability of the method, an extensive case study is then presented in which some aspects of the dynamic behaviour of a skewed bridge monitored under vehicle-induced loads are investigated. After adjustment of the boundary conditions and the spectral roughness coefficient, good agreement is obtained between the bridge vibrations predicted by the numerical model and the field measurements. The validated model is further used to analyse the distinctive dynamic effects caused by the skewness. For that purpose, a reference non-skewed bridge model is prepared according to the same design as the original skewed bridge. The obtuse corner of the skewed bridge located near the loading path is found to be a critical region where the slab-negative moments, the girder stress near the sole plate and the bearing force are significantly greater than those in the reference bridge.

Analytical Investigation of Potential Seismic Damage to a Skewed Bridge

Investigative reports on the 1994 Northridge earthquake in California indicated significant damage experienced by skewed highway bridges. Specifically, the damage sustained by the Pico-Lyons Bridge near Newhall, California, was noted to have been triggered by the skewed geometry of the bridge. In an effort to portray the behavior of this bridge analytically, a series of simulation studies was conducted using nonlinear finite-element analyses. The objective was to demonstrate that certain damage potentials in skewed bridges during earthquakes can be captured analytically. Dynamic time history and pushover analyses were used to capture the behavior of the superstructure of the skewed bridge using the Northridge ground motion record as the input seismic force. Results from the simulation studies showed that potential damage areas, comparable to those reported in the field investigation of the Pico-Lyons Bridge, can be portrayed through analytical modeling. The study also provided the percentage increase in critical stresses in the superstructure of skewed bridges as the angle of skew increases compared with a comparable nonskewed bridge. The study showed that cases in which the angle of skew is approximately 40°, the percentage increase in stress due to the skewness effect at the end girders can be as high as 50–60%.

Influence of skew angle on live load moments in steel girder bridges

This paper presents the results of a parametric study evaluating the effect of skew angle on the wheel load distribution in steel girder highway bridges. The finite element method was used to investigate the effect of various parameters such as the span length, girder spacing, and skew angle, on simply supported, one-span, two-lane, three-lane and four-lane steel girder bridges. A total of 270 bridge cases were analyzed and subjected to AASHTO HS20 design trucks positioned on each bridge to produce maximum bending in the interior steel girders. A combination of five typical span lengths, three girder spacing, and six skew angles were used in evaluating bending moments in skewed steel girder bridges. The finite element results were used to calculate the maximum bending moment in steel girders due to the various skew angles and compared to the reference straight bridges, and then compared to the reduction factors used in AASHTO LRFD Bridge Design Specifications. The finite element results showed the reduction in bending moment for all skewed bridges up to 30 degrees can be neglected and such bridges can be designed as straight bridges. These results are consistent with the AASHTO Standard Specifications and the LRFD procedure by not specifying any reduction factor for bridges with skew angles up to 30 degrees. For highly skewed bridges and span length less than 80 ft (24 m), the finite element results showed a reduction in moment ranging between 10% and 20% for skew angles up to 40 degrees, and between 20% and 35% for skew angle up to 50 degrees. For practical application, a conservative reduction in girder bending moment of 15% is suggested for skew angles between 30 and 40 degrees and another conservative reduction in girder bending moment of 25% for bridges with skew angles between 40 and 50 degrees. Furthermore, the AASHTO LRFD reduction factors, ranging between 15% and 5%, were more conservative when compared with the finite element results for short-span bridges with high skew angles.

Web plumb influence on skewed I-girder, steel bridges during construction

At different stages during the construction of steel, I-girder bridges having severely skewed abutments and differential deflections between adjacent and interconnected girders cause rotations and deflections out of plane. These deformations are more pronounced during deck placement when appreciable additional dead load is added to the bridge and the girders are non-composite. As a result, girder webs can end up out of plumb at the completion of construction, especially at the supports. Although it is commonly desired by bridge designers and contractors to alleviate this out of plumbness via different erection and detailing strategies, out of plumbness effects on skewed bridge response at the completion of construction are not completely understood. The present research employs finite element analysis to study effects that different detailing methods have on girder stresses, vertical and lateral deformations, and cross-frame forces for single-span bridges with varying skew angles.

Operational modal analysis of a multi-span skew bridge using real-time wireless sensor networks

A large-scale field deployment of high-density, real-time wireless sensors networks for the acquisition of local acceleration measurements across a medium length, multi-span highway bridge is presented. The advantages, performance characteristics, and limitations of employing this emerging technology in favor of the traditional cable-based acquisition systems are discussed in the context of the in-service instrumentation and ambient vibration testing of a multi-span bridge. Of particular highlight in this study is the deployment of a large number of stationary rather than reference-based accelerometers to uniquely permit simultaneous acquisition of vibration measurements across the structure and thereby ensure consistent temperature, ambient vibration, and traffic loading. The deployment consisted of 30 dual-axis accelerometers installed across the girders of the bridge and interfaced with 30 wireless acquisition and transceiver nodes operating in two star topology networks. Real-time wireless acquisition at a per channel sampling rate of 128 samples per second was maintained across both networks for the specified test durations of 3 min with insignificant data loss. Output-only system identification of the structure from the experimental data is presented to provide estimates of natural frequencies, damping ratios, and operational mode shapes for 19 modes. The analysis of the structure under test provides a unique case study documenting the measured response of a multiple-span skewed bridge supported by elastomeric bearings. The feasibility of embedded wireless instrumentation for structural health monitoring of large civil constructions is concluded while highlighting relevant technological shortcomings and areas of further development required. In particular, previously undocumented obstacles relating to radio transmission of the sensor data using low-power 2.4 GHz wireless instrumentation, such as the effect of solid piers within the line-of-sight and the reflection of the radio waves on the surface of the water, are discussed.

Simplified Seismic Response Assessment Method and Parametric Study of Multi-Girder Skew Bridges

A simplified grillage bridge model suitable for parametric study of skew bridge is presented, and the formulae for computing the seismic response of skew bridges are developed. Considering the existence of crossbeams and elastic bearings, the effects of stiffness eccentricity ratios, frequency ratios, the number of beams and skew angles are assessed using response spectrum analysis. The results show that the natural frequencies and mode shapes depend mainly on the stiffness eccentricity ratio and frequency ratios. The study also demonstrates that the seismic response of skew bridge is influenced quite noticeably by stiffness eccentricity ratio and frequency ratio. The maximum seismic response of skew bridge can be reduced by increasing stiffness eccentricity ratio and frequency ratio. Based on this study, a theory to evaluate the dynamic behavior and seismic response of skew bridges is presented and it can be conveniently applied in bridge seismic design.

SEISMIC TORSION RESPONSE OF SKEWED BRIDGE PIERS

Skewed bridge piers are suspected to be susceptible to seismic torsion during an earthquake because the inplane rotation of skewed bridge deck, due to the collision with the abutments or the adjacent spans, possibly causes the torsional rotations in the piers. An analytical study is carried out in order to investigate the seismic torsion response of skewed bridge piers. A 4 span continuous skewed bridge is analyzed by using the finite element method. Various conditions; skewed angle, pounding gap and the locking of steel bearing after failure, are taken into consideration. The analytical results indicate that the locking of bearing movement can cause sharp peak seismic torsion in skewed bridge pier.

Cyclic Testing of Large-Scale Rectangular Bridge Columns under Bidirectional Earthquake Components

Bidirectional cyclic testing was performed on four half-scale reinforced-concrete rectangular bridge column specimens to examine the need to account for bidirectional seismic loading in design for earthquakes expected in eastern and western regions of North America. The prototype structures are common two-span, skewed bridge structures designed according to the seismic provisions of Canadian Standards Association (CSA)-S6-06. The column specimens are 1.2×0.6 m in cross section and 3.0 m tall and assumed to carry a gravity load of 6% Agfc′. Two specimens were designed for Montreal, Quebec, Canada (east site), using 0 and 30% combination rules, resulting in longitudinal steel ratios of 0.41 and 0.57%. Two specimens represented the column part of bridges located in Vancouver, British Columbia, Canada (west site), with longitudinal steel ratios of 0.97 and 1.72% resulting from the application of 0 and 40% combination rules. Site-specific cyclic displacement test protocols were developed from time-history ana...

An approximate method for dynamic analysis of skewed highway bridges with continuous rigid deck

In this paper using a 3DOFs analytical model an approximate hand-method is presented for dynamic analysis of skewed highway bridges with continuous rigid deck. In modeling the structure it is assumed that the deck of the bridge is rigid in-plane. As a result of this assumption the deck moves only on a horizontal plane and the vertical movements are restrained. The translational and rotational stiffness of the substructure and the shear stiffness of the elastomeric bearings on the two abutments are modeled with linear springs. To calculate the natural circular frequencies and internal forces of skewed highway bridges, simplified formulae are presented. The capability and accuracy of the proposed method for seismic analysis are compared with the results of finite element modeling of a practical example. It is generally possible that the deck rigidity assumption underestimates the seismic responses of bridge, but the results show that it sufficiently estimates the natural frequencies and internal forces with a reliable margin of error which is favorable and acceptable for designers in the preliminary stages of design. The approximate method is capable of dynamic analysis of skewed highway bridges with continuous rigid deck in the preliminary stages of the design process. In addition, the preliminary values of this method can help to identify the unknown errors occurring during finite element modeling of the structural model.

Skewed Slab-on-Girder Steel Bridge Superstructures with Bidirectional-Ductile End Diaphragms

Specially designed ductile end diaphragms of steel bridge superstructures have previously proved, both theoretically and experimentally, to dissipate seismic input energy, protecting other substructure and superstructure members. Although ductile diaphragms have been introduced in the latest AASHTO guide specifications as a structural system that can be used to resist transverse earthquake effects, no guidance is provided on how to implement these ductile diaphragms in skewed bridges. To address this need and to resolve some shortcomings of the known end diaphragm systems (EDSs), two bidirectional end diaphragm configurations, namely, EDS-1 and EDS-2, with buckling restrained braces (BRBs) are proposed and numerically investigated. Bidirectional end diaphragm is a new concept, and can be implemented both in straight and skewed steel bridge superstructures to resist bidirectional earthquake effects. To assess the relative effectiveness of the proposed systems and to investigate how various parameters relate to seismic response, closed-form solutions are developed using nondimensional bridge geometric ratios. Numerical results indicate that skewness more severely affects end diaphragm behavior when φ≥30°. Also, comparisons reveal that although both end diaphragm systems can be used with confidence as ductile seismic fuses, each of the two systems considered have advantages that may favor its implementation, depending on project-specific constraints.

Behavior of Reinforced Concrete Bridge Decks on Skewed Steel Superstructure under Truck Wheel Loads

This paper focuses on the behavior of skewed concrete bridge decks on steel superstructure subjected to truck wheel loads. It was initiated to meet the need for investigating the role of truck loads in observed skewed deck cracking, which may interest bridge owners and engineers. Finite-element analysis was performed for typical skewed concrete decks, verified using in situ deck strain measurement during load testing of a bridge skewed at 49.1°. The analysis results show that service truck loads induce low strains/stresses in the decks, unlikely to initiate concrete cracking alone. Nevertheless, repeated truck wheel load application may cause cracks to become wider, longer, and more visible. The local effect of wheel load significantly contributes to the total strain/stress response, and the global effect may be negligible or significant, depending on the location. The current design approach estimates the local effect but ignores the global effect. It therefore does not model the situation satisfactorily. In addition, total strain/stress effects due to truck load increase slightly because of skew angle.

Full-Scale Test of Continuity Diaphragms in Skewed Concrete Bridge Girders

Continuity diaphragms used in prestressed girder bridges on skewed bents have caused difficulties in detailing and construction. The results of the field verification for the effectiveness of continuity diaphragms for skewed, continuous, and prestressed concrete girder bridges are presented. The current design concept and bridge parameters that were considered include skew angle and the ratio of beam spacing to span (aspect ratio). A prestressed concrete bridge with continuity diaphragms and a skewed angle of 48° was selected for full-scale test by a team of engineers from Louisiana Department of Transportation and Development and the Federal Highway Administration. The live load tests performed with a comprehensive instrumentation plan provided a fundamental understanding of the load transfer mechanism through these diaphragms. The findings indicated that the effects of the continuity diaphragms were negligible and they can be eliminated. The superstructure of the bridge could be designed with link slab....

Nonlinear Soil–Abutment–Foundation–Structure Interaction Analysis of Skewed Bridges Subjected to Near-Field Ground Motions

This paper investigates the behavior of skewed highway bridges subjected to earthquake loading with strong velocity pulses. The behavior of bridges with skewed abutments in the longitudinal direction is strongly coupled by transverse loading. The interaction between skewed bridge abutment foundations and backfill has a strong impact on dynamic bridge response. While bridge structures may remain in the linear range during seismic loading, local nonlinear behavior at the abutment–embankment interface can cause significant nonlinear bridge structure response. Skewed bridge models are presented incorporating soil–abutment–structure interaction using nonlinear abutment springs. As a case study, a global three-dimensional nonlinear finite element model of the skewed and seismically instrumented Painter Street overpass in Rio Dell, California, with monolithic abutments was developed. The model used nonlinear foundation–soil interaction based on approach soil properties from geotechnical tests. A soil continuum finite element analysis was performed using constitutive hardening soil material to evaluate abutment backfill passive resistance considering backwall skew. The bridge response resulting from seismic ground motion records was compared with structure response data. The computer models represented fairly well the overall seismic response of the skewed bridge. Bent pile foundations had much less impact on overall bridge response than the abutments. Near-fault ground motions with high-velocity pulses generated asymmetrical impulsive loading and large displacements in transverse directions leading to significant rotation and residual deck displacement. These permanent structure displacements can control the design of the abutment seat width and shear keys and could exceed column displacement capacity and impose additional moment at the column not considered in current design.

Full-Scale Destructive Bridge Test Allows Prediction of Ultimate Capacity

Contemporary bridge design is generally based on designing individual members for the maximum force effect that each member may experience. This approach ignores the system-level interactions of these individual members, which may greatly increase the ultimate strength of the complete structure. In an attempt to understand better the load redistribution mechanisms that lead to this increase in ultimate strength, the destructive testing of a skewed steel I-girder bridge was planned and executed. However, because of the enormous system-level reserve capacity of the structure, the structure generally responded elastically, despite being loaded with the equivalent of 17 HS-20 design vehicles. Thus, a validated finite element analysis (FEA) approach was used to predict the ultimate capacity of this structure and to analyze the force redistribution as the bridge's elastic limit was exceeded. The FEA results predicted that the equivalent of 41 HS-20 vehicles was needed to plastify fully the four girders of the subject bridge and show the significant amount of yielding that occurs in the cross-frames when the ultimate capacity of the girders is achieved.

Improved Seismic Response of Multisimple-Span Skewed Bridges Retrofitted with Link Slabs

Results of a recent bridge inventory evaluation indicated that about 50% of Turkish highway bridges have more than 30° of skew angle and can be classified as irregular bridges. During the recent major earthquake in Turkey, multisimple-span bridges with continuous decks and link slabs performed well even though these bridges were in the vicinity of the fault line. This study aims to evaluate the improvements in seismic response of skew bridges in terms of forces and displacements when link slabs are added as a retrofit tool. A series of elastic dynamic analyses and nonlinear time history analyses were conducted to investigate the seismic response of various standard highway bridges with different span lengths and skew angles. A new reinforcement design for edge zones of link slabs is proposed for bridges located in high seismic zones. In practice, link slabs can be implemented easily during a regular redecking of a bridge.

Destructive Testing and Finite Element Analysis to Determine Ultimate Capacity of Skewed Steel I-Girder Bridges

Current bridge design and rating techniques are based at the component level and thus cannot account for the increase in ultimate capacity that bridges experience because of system-level interactions. Compared with that of a normal bridge, the ultimate capacity of a bridge increases to an even greater extent as bridge supports are skewed because of changes in load paths. Although advances in computer technology have made it possible to conduct accurate system-level analyses, which would allow for more efficient bridge design and rating, the knowledge base surrounding system-level bridge behavior is still too small to make it a highly accurate or intuitive tool. To advance system-level design and rating, two studies were undertaken. First, to evaluate the ultimate capacity of a skewed simple-span steel bridge, a ⅕-scale, slab-on-steel girder bridge was tested to ultimate capacity and then modeled by using finite element analysis. This test provided both insight into the system behavior and validation of an ABAQUS Explicit analysis algorithm and associated modeling techniques. Second, to investigate the effects of skew on the ultimate capacity of simple-span bridges, a parametric study was conducted with finite element analysis. A four-girder, simple-span bridge was modeled with skews varying from 0 to 75 degrees. The results showed that the ultimate capacity of the bridge increased with skew; these results were compared with simple analytical equations to provide insight into the fundamental behavior and load distribution characteristics of skewed bridges.

Seismic response of skewed RC box-girder bridges

It is critical to ensure the functionality of highway bridges after earthquakes to provide access to important facilities. Since the 1971 San Fernando earthquake, there has been a better understanding of the seismic performance of bridges. Nonetheless, there are no detailed guidelines addressing the performance of skewed highway bridges. Several parameters affect the response of skewed highway bridges under both service and seismic loads which makes their behavior complex. Therefore, there is a need for more research to study the effect of skew angle and other related factors on the performance of highway bridges. This paper examines the seismic performance of a three-span continuous concrete box girder bridge with skew angles from 0 to 60 degrees, analytically. Finite element (FE) and simplified beam-stick (BS) models of the bridge were developed using SAP2000. Different types of analysis were considered on both models such as: nonlinear static pushover, and linear and nonlinear time history analyses. A comparison was conducted between FE and BS, different skew angles, abutment support conditions, and time history and pushover analysis. It is shown that the BS model has the capability to capture the coupling due to skew and the significant modes for moderate skew angles. Boundary conditions and pushover load profile are determined to have a major effect on pushover analysis. Pushover analysis may be used to predict the maximum deformation and hinge formation adequately.

Effect of Nonlinear Seismic Torsion on the Performance of Skewed Bridge Piers

This article presents an analytical investigation on the effect of seismic torsion on the performance of a skewed bridge. A nonlinear torsional hysteretic model developed by the authors is applied to idealize the torsional behavior of bridge piers. Deterioration of the torsional strength of piers due to combined flexure is considered and deterioration of flexural strength due to torsion is not taken into account. The effects of pounding between deck and abutments, cable restrainers, and damage of bearing supports are also included in analysis. It is found that the eccentric impact force due to lock of bearing movement results in extensive torsion in piers.