Adjacent Girders Research Articles

Operation of a high-gradient superconducting radio-frequency cavity with a non-evaporable getter pump

The use of non-evaporable getter (NEG) pumps in particle accelerators has increased significantly over the past few years because of their large pumping speed, particularly for hydrogen, compared to the size of the pump. A concern about using such pumps in superconducting radio-frequency (SRF) accelerators is the possibility of shedding particulates which could then migrate into the SRF cavities and produce field emission, therefore degrading the cavity performance. One option to mitigate such issue is to use sintered getter materials which intrinsically offer superior mechanical and particle retention properties. In this article we present the results from cryogenic RF tests of a high-gradient SRF cavity after being evacuated several times with an NEG pump equipped with sintered getter disks and placed in close proximity to the cavity. The results showed that the cavity performance was not affected by the pump up to the quench gradient of 34MV/m. As a result of this study, two such NEG pumps have been installed next to a cryomodule in the CEBAF accelerator to maintain ultra-high vacuum in the SRF cryomodule and two adjacent warm girder sections.

Contribution of Transverse Tie Bars to Load Transfer in Adjacent Prestressed Box-Girder Bridges with Partial Depth Shear Key

AbstractAdjacent box-girder bridges have become a popular choice as they can be constructed quickly, easily, and economically. In spite of their good performance during many years of service, one major problem has been recurrent longitudinal cracking of the grout material in the shear key. A combination of shear keys and transverse posttensioning (TPT) ties in such kind of bridges is typically used to connect the bridge girders together so that they would behave as a single integrated unit. However, information regarding the contribution of the TPT tie bars on load transfer between adjacent box girders is limited. In this study, a single-span precast prestressed concrete adjacent box-girder bridge was instrumented and monitored to study the effect of TPT tie bars on load transfer mechanism and overall bridge behavior under static and dynamic truck loads. Two sets of instruments were installed in the girders and tie bars during and after the construction of the bridge. A good correlation was achieved betwe...

Laboratory Evaluation of Ultrahigh-Performance Concrete Shear Key for Prestressed Adjacent Precast Concrete Box Girder Bridges

AbstractPrecast adjacent box girder bridges have become a preferred solution in several states due to their simple structure, economy, and ease of construction. However, longitudinal cracks often appear along the shear keys between adjacent box girders. With its superior strength and durability, ultrahigh-performance concrete (UHPC) has been used as an alternative grout material to reduce shear key cracking and enhance load transfer. The objective of the present research was to evaluate the performance of UHPC in shear keys using direct shear, direct tension, and flexural tests. Also, this study determined the effectiveness and functionality of shear reinforcement bars by applying direct shear load on specimens with shear reinforcement. In the direct shear test, a steel frame was placed around the specimens to allow the shear key to experience pure shear force. The direct shear test established the cracking threshold and ultimate shear strength of each shear key with and without shear reinforcement bars. ...

Drag Coefficients for Construction-Stage Stability Analysis of Bridge Girders under Wind Loading

AbstractLateral wind loads often control the stability of bridge girders during construction stages in which the deck is not yet structurally effective. In this study, the key objectives were to experimentally quantify aerodynamic wind-load coefficients (drag, lift, and torque) for common bridge girder shapes and to quantify shielding effects arising from aerodynamic interference between adjacent girders. Wind tunnel tests were performed on reduced-scale models of built-up steel plate girders and prestressed concrete Florida I-beams (FIBs). Aerodynamic properties were measured for individual girder cross-sectional shapes and for systems of multiple adjacent girders (tested both with and without bridge deck formwork in place). Results from the wind tunnel tests, which revealed negative drag coefficients at selected downstream girder positions, were synthesized into simplified wind-loading cases suitable for use in bridge design. Wind-load cases were separately developed for assessing overall multigirder sy...

Investigation of Seismic Response on Girder Bridges: The Effect of Displacement Restriction and Wing Wall Types

In the seismic design specified by Japanese Specifications of Highway Bridges (JSHB), a large gap size between two adjacent girders or the girder and abutment has recommended to be constructed in the concrete girder bridge with multi-spans in order to prevent the collision, when it is subjected to Level 2 ground motion. However, the adoption of large gap into PC bridge will increase the construction and seismic reinforcement costs since relatively large expansion joints have to be used. Also, it causes the girders falling in the presumption of strong earthquake. It has been suggested that allowing the girder collision at the abutment by restricting the girder bridges displacement, the size of expansion joints can be reduced. These conditions are able to reduce the seismic design and seismic reinforcement cost.Although many studies on the effect of the collision have been published, the effect of displacement restriction of girders is still remains to be elucidated. This present study aims to investigate the seismic response of concrete girder bridges taking into account the effect of displacement restriction of girders allowing the girder collision at the abutment and the wing wall. Two span concrete girder bridge was examined in theoretically by 3D FEM model of ABAQUS with four different approaches at the wing wall abutment model. The dead load and soil pressure were calculated based on JSHB loading conditions and gap between superstructure and parapet wall was chosen to be 10cm and 20cm. Level 2 earthquake ground accelerations were applied horizontally at the bottom of pier. The numerical results showed that the parameters such as shear stress, response stress, displacement, and cracking were affected by displacement restriction and different wing wall model. Installing of the wing wall in abutment generally increased the response stress in parapet wall and shear stress around vertical wall of abutment. In contrast, it significantly reduced the horizontal displacement of abutment.

Stiffness Behavior of Cross Frames in Steel Bridge Systems

AbstractCross frames are critical structural elements in both straight and horizontally curved steel bridges. In order to properly size the brace for the strength and stiffness demands of the superstructure, an accurate model of the elements comprising the cross frame is required. Conventional details most commonly used for cross frames consist of single-angle members connected to form a truss system linking adjacent girders together. Most analyses of the bridges treat the cross frames as truss elements that primarily resist applied forces through the axial stiffness of the members. This paper documents the results of a research study that included full-scale laboratory tests to measure the stiffness and strength of cross frames utilizing both conventional and new details. The tests showed that analytical solutions, as well as computer models, that are routinely used to model the cross frames in analysis software can overestimate the in-plane stiffness of the brace by more than 100%. The primary reason fo...

Joint Detailing Between Double Tee Bridge Girders for Improved Serviceability and Strength

Precast, prestressed double tee bridge girders are widely used for accelerated bridge construction on local roads in South Dakota. A common issue among double tee bridges in South Dakota is the rapid deterioration of longitudinal joints (shear keyways) between adjacent girders. Deteriorated joints allow moisture and deicing chemicals to reach the deck reinforcement, which leads to premature corrosion of reinforcing steel and spalling of concrete. The structural performance of conventional and proposed longitudinal joints between precast double tee bridge girders was examined experimentally under cyclic and monotonic loading. The proposed continuous joint with overlapping steel mesh reinforcement in a grouted shear keyway exhibited serviceability and strength performance characteristics substantially improved over those of the conventional grouted joint with discrete welded connections.

Intermediate Diaphragm and Temporary Bracing Practice for Precast Concrete Girder Bridges

AbstractIntermediate diaphragms are used in precast concrete girder bridges for three primary reasons: (1) to prevent torsional girder rotations during girder erection and deck placement operations, (2) to increase vertical load distribution between girders, and (3) to transfer and spread horizontal impact loads from an overheight vehicle to adjacent girders. Significant variation currently exists in intermediate diaphragm specifications between states. The importance of bracing girders after erection and during construction is widely accepted as essential. Although it is clear that intermediate diaphragms have some effect on bridge performance, the benefit is considered by some to be negligible. Increasing numbers of states have adopted permanent steel or temporary intermediate diaphragm alternatives in place of traditional cast-in-place concrete. Wide variations are found between states regarding the configuration, spacing, and transverse alignment of diaphragms. This article presents a detailed survey ...

EXPERIMENTAL EVALUATION OF PIPE-SHAPE SHEAR CONNECTORS FOR MULTI-BEAM BOX GIRDER BRIDGES

This study mainly focused on the experimental evaluation of pipe-shape shear connectors for multi-beam box girder bridges. The multi-beam box girder bridges are a structure to the integration with the box girders placed adjacent to each other. They are generally connected by shear keys and loop joints to resist the shear force at their interfaces, and lateral tendons for applying the compression force. However, if the integration effect decreases with time, the relative deflection between adjacent girders occurs and it causes the reflective cracks on the deck along the interfaces. Furthermore, the efficiency of constructing multi-beam box girder bridges decreases when loop joints are used because it is complicated to form the required connections using couplers. Therefore, this study evaluated behavior of pipe-shape shear connectors which are superior in workability and ductility than loop joints by push-out tests and pull-out tests.

Development and study of deck joints in prefabricated concrete bulb-tee bridge girders: Conceptual design

Speed of construction, particularly for bridge replacement and repair projects, has become a critical issue to minimize disruption of traffic and commerce. A promising system for rapid construction is a precast bridge system using decked bulb tee prestressed concrete girders. This type of bridge includes manufacturing the bridge deck precast and pretensioned with the girder in the precast plant under controlled environment. Then, the precast girders are transported to the construction site, and placed over the abutments and piers beside each other with flanges of adjacent girders field connected. Load transfer between adjacent girders is provided by longitudinal joints parallel to traffic direction. This paper presents a new bridge deck slab flange-to-flange connection system for precast Deck Bulb Tee (DBT) girders. The objectives of this study were to develop moment-transferred and intermittent-bolted connections for DBT bridge girders in view of the ultimate strength of the connection system. Two types of moment-transferring connection and two types of intermittent-bolted connection were developed. The paper presents design procedure of the developed joints based on available design equations in North American design codes for bridges and structures as well as related design equations available in the literature. The developed joint was considered successful if the theoretical resistance satisfied the requirements specified in North American Bridge Codes. Comparison between the theoretical findings and the available experimental failure loaded of actual-size bridge deck specimens simulating the developed connection justified the proposed theoretical design procedure.

Distortion-Induced Fatigue Crack Growth

Out-of-plane distortion of transverse cross-bracing systems in bridge superstructures has been known to cause localized fatigue cracking. The cracking is a result of the differential displacement of adjacent bridge girders, which causes high stress concentrations in unstiffened web-gap regions at the interface of girder and stiffener connection plates. Fatigue cracking within the web gap can occur because of cyclical loading scenarios. Rehabilitation efforts have shown to be unpredictable in preventing crack propagation once through-thickness crack profiles have developed. Therefore, understanding the mechanisms causing fatigue crack propagation in such detail is essential in developing effective repair methods. In this study, numerical analyses of typical web-gap connections are conducted using the extended FEM to characterize crack directionality and growth rate. Simulations varying the web-gap length, stress range, loading ratio, and initial crack length were used to determine the primary variables effecting crack growth in the web-gap region. Increasing the web-gap length was noted to stabilize crack propagation rates, resulting in stable growth, which can be correlated to the Paris Law. Elongation of horizontal initial crack lengths resulted in reorientation of crack growth. In stiffer web gaps, a combined high stress ratio and long initial crack length resulted in crack profiles propagating into the flange-web interface with eventual crack arrestment. The study suggests that horizontal extension of initial cracks has the potential to cause the crack to arrest, after stable propagation, without adversely compromising local structural integrity of bridge superstructures.

Double deck bridge behavior and failure mechanism under seismic motions using nonlinear analyzes

This paper investigates the behavior and the failure mechanism of a double deck bridge constructed in China through nonlinear time history analysis. A parametric study was conducted to evaluate the influence of different structural characteristics on the behavior of the double deck bridge under transverse seismic motions, and to detect the effect of bidirectional loading on the seismic response of this type of bridge. The results showed that some characteristics, such as the variable lateral stiffness, the foundation modelling, and the longitudinal reinforcement ratio of the upper and lower columns of the bridge pier bents have a major impact on the double deck bridge response and its failure mechanism under transverse seismic motions. It was found that the soft story failure mechanism is not unique to the double deck bridge and its occurrence is related to some conditions and structural characteristics of the bridge structure. The analysis also showed that the seismic vulnerability of the double deck bridge under bi-directional loading was severely increased compared to the bridge response under unidirectional transverse loading, and out-of-phase movements were triggered between adjacent girders.

Dynamic and Mitigation Analysis of Seismic Pounding Effect on Multi-Span Highway Bridges Subjected to Spatial Earthquakes

The main girder and the piers of bridges are generally linked with sliding bearings. Under seismic excitation, pounding effects between the main girder and the abutment, the adjacent girder and the blocking device caused by excessive relative displacements between piers, abutments and the girder are highly probable. The effects can not only damage the structure but also lead to collapsing. Based on a continuous viaduct, the paper studied the disciplines of the pounding response under uniform seismic excitation and the spatial seismic excitation, then put forward that the composite metal damper may reduce the effect of pounding. The research shows that under same seismic intensity, the results, including pounding force, the shear force of the fixed bearings and the plastic hinge on the piers, are amplified under multi-point excitation than under uniform excitation. And composite metal dampers can reduce the seismic responds under frequent earthquakes and prevent or largely reduce the pounding effect under severe earthquakes. Therefore the effect of pounding on the dynamic performance can be lessened. The seismic reduction is widely and well-adapted under both uniform excitation and multi-point excitation.

Capacity Evaluation of a Prestressed Concrete Adjacent Box Girder with Longitudinal Cracks in the Web

In 2008, 77 prestressed concrete adjacent box girder (PCABG) bridges were selected and inspected to determine their typical defects and document their performance. Longitudinal cracking in the web of many beams was documented as the main defect. To evaluate the influence of longitudinal cracking on capacity of the PCABG, two adjacent box girders were compared that were made with the same procedure. One box girder (beam No. 1) had no defects, whereas the other (beam No. 2) had longitudinal cracks in the web. The results show that the longitudinal cracks in the web of beam No. 2 changed the trend of the expansion of the cracks by connecting the vertical cracks close to the longitudinal ones and shortening the range of the vertical cracks covered and the length of the plastic hinges. Furthermore, the longitudinal cracks made the curvature of beam No. 1 less than that of beam No. 2 and made the compression strain of each side different. However, the existence of longitudinal cracks had little effect on the cracking moment and the ultimate flexural bearing capacity. The residual prestressing forces indicated that an approximately 23% prestressed force was lost for both beams.

Self-Stressed Steel Fiber Reinforced Concrete as Negative Moment Connection for Strengthening of Multi-Span Simply-Supported Girder Bridges

A self-stressed steel fiber reinforced concrete (SS-SFRC) moment connection is proposed to strengthen multi-span simply-supported T-section reinforced concrete (RC) girders. In the proposed moment connection technique, old concrete needs to be removed from adjacent girder ends and negative moment reinforcement is placed into cast-in-place SS-SFRC to develop continuity over the interior support. Two series of tests consisting of 15 girder specimens were conducted to investigate the reliability of the proposed SS-SFRC moment connection. An analytical model is presented to predict the load-carrying capacity of the resulting continuous composite girders. Test results show that SS-SFRC is excellent in preventing concrete cracking at the interior support. Both the load-carrying capacity and the serviceability of the strengthened girders are significantly improved. The analytical model is demonstrated to predict the load-carrying capacity of the resulting continuous composited girders with an acceptable degree of accuracy.

Finite Element Analysis of Distortion-Induced Web Gap Stresses in Multi-I Girder Steel Bridges

Unstiffened girder web gaps at the ends of transverse stiffeners that also serve as diaphragm connection plates are subjected to high local stresses during cyclic out-of- plane distortion. The out-of-plane distortion is mainly caused by the differential deflection between adjacent girders. The purpose of the paper is to investigate the effects of bridge parameters including span length, girder spacing, slab thickness, and girder stiffness on the differential deflection and distortion-induced web gap stresses. Dual-level finite element analyses that consist of both global model and sub-model were performed. The global model was used to investigate the critical truck position and maximum differential deflection between adjacent girders, while the sub-model was used for the critical web gap vertical stress. A base case bridge was a simply supported composite superstructure with three steel I-girders that support two traffic lanes, which is typical for steel bridges over intersections in Bangkok, Thailand. A parametric study was conducted by varying one bridge parameter at a time. The analysis results show that the maximum differential deflections and web gap stresses caused by one-truck loading are higher than those caused by two-truck loading (one truck on each lane). Under one-truck loading, the maximum web gap stress occurs at the interior girder. In addition, both the differential deflections and web gap stresses are primarily dependent on the bridge span length.

Demonstration of Fiber Optic Instrumentation System for Prestressed Concrete Bridge Elements

Structural health monitoring (SHM) is a relatively recent approach to managing and extending the useful life of bridge infrastructure elements. To be useful, SHM techniques must be robust, rapidly deployable, and yield information useful to those rating the structures. Fiber optic–based sensors have been used in this regard but on a relatively limited basis in North America. Fiber optic sensors have many advantages over more conventional structural monitoring sensors, and their utility has been well established. While verification of SHM-generated data with other instrumentation schemes is important, validation using simple analytic tools is critical because such tools are the basis for most bridge rating and management systems. In this paper, load testing of a decommissioned prestressed adjacent box girder is presented. The objective of the test was to demonstrate a proof of concept for a fiber optic–based instrumentation system for bridge monitoring. Fiber optic–generated measures of girder performance are compared with other experimental test data and a relatively simple but robust analytic model of the girder. The tested fiber optic system demonstrated excellent performance, and data recovered correlated well with a well-established analytical modeling technique, thereby demonstrating the immediate utility of the fiber optic system.

Simplified transverse post-tensioning construction and maintenance of adjacent box girders

Precast, prestressed concrete adjacent box girders are regularly considered for shortto medium-span bridges on secondary roads. This corresponds to spans from 20 ft to 127 ft (6.1 m to 38.7 m), though typically no more than 40 ft (12.2 m). Many of these projects have limited funding or require rapid construction. Sec- ondary roads are also subject to a certain amount of public criticism, particularly with regard to cost and aesthetic appeal. Research has shown that an appeal- ing structure can be defined as having continuously flat soffits and high span-to-depth ratios—characteristics of an adjacent box system. Proper design and detail- ing of the transverse connection between girders is essential to minimizing both initial cost and long-term maintenance. Typical connections include diaphragms and cast-in-place concrete toppings, which directly increase both cost and time of construction. Inadequate post-tensioning is the primary cause of reflective cracking leading to ingress of chlorides and the con- sequent reinforcement deterioration, excessive girder deflection, and possible unexpected failures. This paper presents the results of testing on a post- tensioned transverse system that eliminates the need for diaphragms and a concrete overlay. Post-tensioning was determined based on previous research on a simi- lar system that was not post-tensioned. Results indicate that the system does not exhibit strain change or crack- ing under fatigue loading and would be an excellent candidate for practical applications.

Experimental investigation of spatially varying effect of ground motions on bridge pounding

SUMMARYPounding between adjacent bridge structures with insufficient separation distance has been identified as one of the primary causes of damage in many major earthquakes. It takes place because the closing relative movement is larger than the structural gap provided between the structures. This relative structural response is controlled not only by the dynamic properties of the participating structures but also by the characteristics of the ground excitations. The consequence of the spatial variation of ground motions has been studied by researchers; however, most of these studies were performed numerically. The objective of the present research is to experimentally evaluate the influence of spatial variation of ground motions on the pounding behaviour of three adjacent bridge segments. The investigation is performed using three shake tables. The input spatially varying ground excitations are simulated based on the New Zealand design spectra for soft soil, shallow soil and strong rock using an empirical coherency loss function. Results confirm that the spatially nonniform ground motions increase the relative displacement of adjacent bridge girders and pounding forces. Copyright © 2012 John Wiley & Sons, Ltd.

Analysis of Seismic Responses During Near-Source Ground Motions

Seismic responses can strongly determine damages of bridge structures, e.g. due to pounding and unseating of girders as observed in many major earthquakes in the past. In the investigations often uniform ground excitation and pounding at only one location are considered. Studies on the influence of non-uniform ground excitation on bridge responses are still very limited, and they are restricted to flat ground-surface condition. Influence of multi-sided pounding is also not much investigated. If the impediment effect of abutments is considered at all. The study reveals that commonly assumed girder stiffness for the end restraint overestimates the actual effective end-restraint stiffness. Non-linear elastomeric bearings can significantly reduce the adjacent girder relative displacements. A consideration of non-uniform excitation is essential for a realistic estimation of bridge response and damage potential.