Journal of Bridge Engineering

The AASHTO LRFD Bridge Design Specifications, in versions up to and including the 2003 interim, limit the shear resistance of hybrid steel I-girders to the shear buckling or shear yield load and prevent consideration of the additional capacity due to tension field action, which homogeneous girders are allowed to include. This limitation severely affected the economy of girders utilizing high-performance steel, whose optimum configuration is often hybrid. Therefore, an experimental investigation was initiated by the National Bridge Research Organization at the University of Nebraska-Lincoln to address the limitation on the consideration of tension field action in hybrid girders. This paper presents the findings of that research. Eight simply supported steel I-girders were designed, constructed, and loaded to failure to investigate their failure mechanisms and shear capacities. All girders tested were capable of supporting loads greater than those predicted, considering full contribution from tension field action. Further, despite the coincidence of high levels of both shear and moment, relative to their respective capacities, the specimens were all capable of supporting loads greater than those predicted if shear and moment interaction were ignored. Due in part to the results of the research being presented, modifications appeared in the 2004 version of the AASHTO LRFD bridge design specifications such that the shear strength provisions apply equally to both hybrid and homogeneous girders.

The basic mechanisms and procedures of finite-element (FE) modeling and calibration are briefly presented in the context of bridge condition assessment. Different physical parameters of FE models are adjusted to simulate experimental measurements. To quantify the calibration process, static-response-based objective functions are carefully developed based on two powerful condition indices: bridge girder condition indicators and unit influence lines. Critical issues related to the indices are discussed in detail. Using an existing calibration strategy, a nominal FE bridge model is optimized by minimizing this global static-response-based objective function. The value of the objective function is reduced from 12.98 to 4.45%, which indicates convergence of the calibration process. It is shown that the automated calibration becomes practical due to the formulation of the static-response-based objective function.

The basic mechanism and procedures of finite-element (FE) bridge modeling and calibration are briefly presented. Different physical parameters of FE models are adjusted during the calibration process. Dynamic-response-based objective functions are carefully developed based on two powerful indices: the modal assurance criterion and frequency correlation trend line. The nominal bridge models are calibrated by minimizing the quantified difference between analytical results and experimental measurements. Using an existing calibration strategy, a nominal FE bridge model is optimized by minimizing this global dynamic-response-based objective function. The value of the objective function is reduced from 10.70 to 4.61%. The minimization of the objective function indicates the convergence of calibration and it is shown that the automated calibration becomes practical due to the formulation of the dynamic-response-based objective function.

Behavior of reinforced cement concrete (RCC) T-beam bridges with cross diaphragms is studied for a realistic range of values of three parameters, such as span, type of loading (specified by Indian Roads Congress), and type of bridge deck layout. The method used for this study is based on the grillage idealization of RCC T-beam bridge superstructures. Material nonlinearity is considered through elastoplastic idealization of moment curvature and torque-twist relationships of the cross section. Geometrical nonlinearity has been neglected. The important conclusions which have emerged from this study are as follows: The behavior of RCC T-beam bridge superstructures can be broadly classified into two categories depending on the type and location of formation of the first plastic hinge. Category I is identified with the formation of first plastic hinge, which is a torsional hinge in the mid outer cross girders. Category II is identified with the formation of the first plastic hinge, which is a flexural hinge in the exterior longitudinal girder under the maximum loading. Bridge superstructures falling under Category I are associated with a greater degree of redistribution and more ductility as compared to those under Category II.

This paper reports on a new bridge deck slab flange-to-flange connection system for precast deck bulb tee (DBT) girders. In prefabricated bridge system made of DBT girders, the concrete deck slab is cast with the prestressed girder in a controlled environment at the fabrication facility and then shipped to the bridge site. This system requires that the individual prefabricated girders be connected through their flanges to make it continuous for live load distribution. The objectives of this study are to develop an intermittent bolted connection for DBT bridge girders and to provide experimental data on the ultimate strength of the connection system. This includes identifying the crack formation and propagation, failure mode, and ultimate load carrying capacity. In this study, three different types of intermittent bolted connection were developed. Four actual-size bridge panels were fabricated and then tested to collapse. The effects of the size and the level of the fixity of the connecting steel plates, as well as the location of the wheel load were examined. The developed joint was considered successful if the experimental wheel load satisfied the requirements specified in North American bridge codes. It was concluded that location of the wheel load at the deck slab joint affected the ultimate load carrying capacity of the connections developed. Failure of the joint was observed to be due to either excessive deformation and yielding of the connecting steel plates or debonding of the embedded studs in concrete.

In this paper, flexural behavior of horizontally curved prestressed (posttensioned) box bridges is studied by using three-dimensional and refined finite-element modeling and analysis. Bridge length, section geometry, and material properties are the same in all the models, while angle of curvature varies from 0 to $90°$ . The results of analysis show that in curved bridges, stress distribution is significantly different in comparison to straight bridges. Also, the level of stresses at some locations of section width is considerably high. It is proposed to vary the distribution of the prestressing tendons across section width in order to optimize the bridge capacity. Results show that by proper redistribution of prestressing in section width, significant reduction in resultant stress is possible.

Experimental tests were conducted on six 1/3-scale specimens to define the vulnerabilities of existing outrigger bents under in-plane and out-of-plane seismic loading and to develop retrofit measures that address the identified vulnerabilities. The specimens represented knee joints in the SR 99 Spokane Street overcrossing in western Washington State but included deficiencies present in a number of older bridges. The as-built specimens failed at low ductility levels due to shear distress, low torsional strength of the outrigger beam, and reinforcement bond failures within the joint. Threshold principal tension stress values describing the expected condition of the joints were established and compared to values obtained by other researchers. Circular steel jackets were used to retrofit the as-built specimens. The retrofitted specimens developed plastic hinging in the column, with enhanced strength, energy, and ductility capacities. Design and detailing guidelines for retrofitting outrigger bents were proposed.

This paper investigates a seismic retrofit technique that allows bridge steel truss piers to uplift and rock on their foundation. Displacement-based passive energy dissipation devices (buckling-restrained braces, or BRBs) are implemented at the uplifting location to control the rocking response while providing additional energy dissipation. The hysteretic behavior of the controlled rocking system is developed for a static cyclic load applied to the top of a bridge pier, representing the dominant mode of vibration. Some existing methods of analysis are considered in predicting the response of the controlled rocking system in terms of maximum displacements. A capacity-based design procedure is established for sizing the BRBs and a design example provided to illustrate the key steps. Methods to predict design response values (displacements, velocity, forces) are discussed, and a parametric study, based on nonlinear time history analysis, is performed to verify the effectiveness of these methods. The parameters in the study include the pier aspect ratio $(h∕d)$ , the local strength ratio $\left({\eta }_L\right)$ and an effective period of vibration $\left(T_{\mathrm{eff}}\right)$ . Results of the study are presented as normalized by the design response values and are shown, in almost all cases, to be conservative.

Seismic evaluations of typical concrete girder bridges are conducted for both a multispan simply supported and a multispan continuous girder bridge common to the Central and Southeastern United States. These evaluations are performed for an approximate hazard level of 2% in $50\text{years}$ by performing nonlinear time history analyses on three-dimensional analytical models. The results show significant vulnerabilities in the reinforced concrete columns, the abutments, and also in unseating of the girders. In general, the longitudinal loading of the bridges results in larger demands than the transverse loading. However, the simply supported bridge sustains bearing deformations in the transverse direction which are on the same order as their longitudinal response. These results suggest that both longitudinal and transverse loading are significant and should be considered when performing seismic hazard analyses of these bridges.

Large numbers of conventionally reinforced concrete (CRC) bridges in the national bridge inventory built during the 1950s are lightly reinforced for shear. Inspections revealed many of these bridges exhibit diagonal cracks resulting in load postings, monitoring, emergency shoring, repairs, and unscheduled bridge replacements. A research program was conducted to investigate the behavior and capacity of CRC bridge girders with vintage details. Laboratory tests of large-size girders representative of 1950s design and construction practice were carried out. Various steel reinforcement configurations were tested. Loading conditions were varied to reproduce girder behavior at different positions in a bridge and various loading protocols were considered. Test results provide a comprehensive data set for comparison of analysis methods and repair strategies; and indicated that anchorage of flexural steel was key to developing higher ultimate capacity, initial crack damage may not necessarily contribute to the final failure mode, and crack width alone may not indicate the level of damage to the beam.

The Val-Alain Bridge, located in the Municipality of Val-Alain on Highway 20 East, crosses over Henri River in Québec, Canada. The bridge is a slab-on-girder type with a skew angle of 20° over a single span of $49.89\mathrm{m}$ and a total width of $12.57\mathrm{m}$ . The bridge has four simply supported steel girders spaced at $\mathrm{3,145}\mathrm{mm}$ . The deck slab is a $225\text{-}\mathrm{mm}$ -thick concrete slab, with semi-integral abutments, continuous over the steel girders with an overhang of $\mathrm{1,570}\mathrm{mm}$ on each side. The concrete deck slab and the bridge barriers were reinforced with glass fiber reinforced polymer (GFRP) reinforcing bars utilizing high-performance concrete. The Val-Alain Bridge is the Canada’s first concrete bridge deck totally reinforced with GFRP reinforcing bars. Using such nonmetallic reinforcement in combination with high-performance concrete leads to an expected service life of more than $75\text{years}$ . The bridge is well instrumented with electrical resistance strain gauges and fiber-optic sensors at critical locations to record internal strain data. Also, the bridge was tested for service performance using calibrated truckloads. Design concepts, construction details, and results of the first series of live load field tests are presented.

Currently, estimations of the crack width in the deck slab of bridges given by codes of practice are based on either theoretical or empirical approaches considering mainly the monotonic loading behavior. However, cracking in reinforced tensile members is highly influenced by the loading history (including both the loading and unloading processes) because of the irreversible nonlinear behavior of bond and of tensile response of concrete, resulting into residual cracks of non-negligible width. This paper investigates the influence of this phenomenon and presents a physical model describing it. An analytical model is developed and its results are compared to various tests with good agreement. Finally, a simple design formula is derived and recommendations for its application to practical cases are proposed.

A crack condition evaluation method is proposed that identifies the damaged state of deteriorated reinforced concrete (RC) girders on bridges directly on-site. This nondestructive testing approach is based on stress wave propagation theory and can identify the profile of flexural crack tips inside RC girders. A damage index is further determined by comparing the measured crack tip and the theoretical neutral axis of a girder. This index can be utilized to analyze the current loading capacity of deteriorated RC girders according to the AASHTO-LRFR Manual (AASHTO 2003), Manual for Condition Evaluation and Load and Resistance Factor Rating of Highway Bridge, Washington, D.C. Experimental results demonstrate that the position of crack tip can be accurately located.

The Tanaro Bridge, an 18-span $225\text{-}\mathrm{m}$ long bridge on the Tanaro River in northwestern Italy, presented the following elements of interest: (1) the barrel divided into adjacent arches; and (2) transverse tie bars and internal spandrels connecting the three parts of the barrels. Its demolition, in 2003, gave the opportunity of performing dynamic tests on a couple of spans at two stages of demolition: (1) fill removed; and (2) fill and internal spandrels removed. Without the uncertain contribution of the fill, some features of the mechanical response of masonry bridges are discussed and the efficiency of tie bars and internal spandrels is addressed. The data provided can be useful for safety assessment procedures.