Journal of Bridge Engineering

This paper studies the dynamic seismic behavior of a typical highway bridge in New York State. The topological layout and structural details of this multispan simply supported steel-girder bridge are identified as the most typical of the New York State Department of Transportation bridge inventory database. Three-dimensional finite-element models of the bridge are established considering the nonlinear behavior of critical bridge components. An in-depth parametric study is carried out to evaluate the sensitivity of the bridge’s seismic response to variations in its structural parameters. The parametric analysis determined that uncertainties associated with the steel reinforcement’s yield strength, the superstructure’s weight, the expansion joints’ gap size, the friction coefficient of expansion bearings, and the concrete compressive strength should be considered during the fragility analysis of the bridge system. The Latin hypercube sampling (LHS) approach is used to obtain representative samples for the fragility analysis based on the mean values and probability distributions of each critical random variable. The LHS is thus used to create a set of nominally identical but statistically different bridge samples for performing the fragility analysis. The individual bridges from this statistically representative set are matched with earthquake samples of various intensities for the nonlinear seismic demand analysis. The seismic capacity of critical bridge components are estimated for each bridge sample from published experimental data. Through extensive numerical simulations, the sensitivity analysis identified the most vulnerable bridge components. Two seismic retrofit strategies for reducing the seismic risk of multispan simply supported steel bridges are studied: (i) steel bearing replacement by elastomeric bearings and (ii) deck/girder-splicing (continuity) with steel bearing replacement by elastomeric bearings. The analysis verified that retrofit option ii is the most effective. The finite-element model of the bridge samples, along with the assembled data on parameter uncertainties and member capacities, as well as a simulated set of ground motion records are suitable for use during the development of fragility curves for bridges with and without retrofit. Detailed description of the fragility analysis is presented in the companion paper.

This paper presents the seismic fragility analysis of a typical multispan simply supported steel bridge in New York State. A detailed description of the bridge model including an analysis of parameter uncertainties was provided in the companion paper. The companion paper also describes a sensitivity analysis that was performed to determine the most critical parameters that control the seismic response of the bridge. A set of statistically independent bridge samples and earthquake samples were specified for the fragility analysis. Two alternative seismic retrofit designs were also presented in the companion paper. The results of the seismic fragility analysis performed in this paper based on the data assembled in the companion paper show that typical multispan simply supported steel bridges in New York State have more than 50% probability of exhibiting slight damage when subjected to earthquakes with peak ground accelerations (PGAs) of 0.51 g. A 50% probability of incurring moderate damage is observed for earthquakes with $\text{PGA}=0.63\text{g}$ and 50% probabilities of extensive damage and collapse are obtained for earthquakes with PGAs equal to 1.02 and 1.50 g, respectively. The detailed fragility analysis of the as-built bridge shows that the fixed steel bearings in the bridge are the most vulnerable components. Hence, the two most appropriate seismic retrofit measures consist of (i) steel bearing replacement by elastomeric bearings and (ii) deck/girder-splicing (continuity) with steel bearing replacement by elastomeric bearings. The seismic fragility analysis shows that although both retrofit strategies reduce the fragility of bridge piers drastically as compared to the as-built condition, the second retrofit strategy (i.e., the combination of steel bearing replacement and superstructure continuity) is overall more effective in reducing the seismic fragility of both piers and bearings. The results of the fragility analysis developed in this paper for both as-built and retrofitted bridges would help state engineers develop effective strategies for seismic retrofit prioritization and network seismic vulnerability assessment.

This paper presents the development of numerical models that investigated the seismic response of a simple two span prototype bridge system during warm and frozen temperatures. Models from both temperature conditions were subjected to a range of seismic intensities to examine the effect of seasonal freezing on the response of the system. Stiffness characteristics were defined using cyclic models of a bridge pier that were previously developed and validated using results from an experimental program on identical full-scale column-foundation units, which were tested during the summer and winter months. Dynamic characteristics of the seismic models were defined using approaches found in the literature. Frozen conditions increased the maximum bending moment and shear force demands for all seismic intensities, with nonlinearity in the column/foundation reducing the difference between the peak responses at higher intensities. At the depth of maximum foundation shear for the frozen model, demand was three times higher than the unfrozen for the 500-year return period and twice during the 2,500-year event. This is significant as one will assume shear is not critical at this location if the effects of frozen conditions are ignored. Apart from the smallest intensity event, increased peak lateral displacements were developed by the warm model down the length of the column and foundation. However, the displacement demand to capacity ratio was higher at the column top for the frozen model, exceeding the capacity during the 2,500-year return period event.

The AASHTO LRFD Bridge Design Specifications state that the spacing between the shear connectors for steel girders should not exceed 610 mm (24 in.). This decision was made based on research conducted more than three decades ago. The goal of this research is to investigate the possibility of extending this limit to 1,220 mm (48 in.) for stud clusters used with full-depth precast concrete deck panels installed on steel girders. This paper presents the history of the 610 mm (24 in.) limit, various formulas developed to calculate fatigue and design capacity for stud clusters and concerns about extending the current LRFD limit. This paper also presents information on the first phase of the experimental investigation, which is conducted on push-off specimens to validate extending the limit to 1,220 mm (48 in.).

The purpose is to analyze the interface shear connection behavior for ultrahigh-performance fiber-reinforced concrete (UHPFRC) and normal concrete (NC) composite girders. The shape and dimension of the shear stud in the conducted tests are referenced from the traditional interface connection design and engineering experiences. The interface shear connection parameters, i.e., initial stiffness and slippage capacity of a single shear stud, are measured from three groups of lateral direct push test specimens with different numbers of studs. Based on the UHPFRC tensile failure characteristics and cracked section rotational mechanisms of the UHPFRC-NC composite structures with flexural, or flexural and shear failure, the limit state is defined as a full pullout from the bottom fiber of the UHPFRC girders. Pseudostrain hardening behavior of the UHPFRC is simplified as an equivalent rectangular stress block. From this mechanism, the interface equilibrium equations are constituted and the interface shear connection degree of the UHPFRC-NC composite girders is derived. It is recommended that the interface shear connection degree may be used as minimum design standard for UHPFRC-NC composite interface shear connection design.

The performance of a new full-depth precast overhang panel system for concrete bridge decks is investigated experimentally. In contrast to conventional cast-in-place deck overhangs, the proposed full-depth precast overhang system has the potential to speed up construction, reduce costs, and improve safety. Load-deformation behavior up to factored design load limits is first investigated. The panel is then loaded near its edge to examine the collapse capacity and the associated failure modes—particularly the influence of panel-to-panel connections that exist, transverse to the bridge deck axis. Comparative tests are also conducted with a conventional cast-in-place overhang system. When compared to the conventional cast-in-place overhang behavior, the experimental results show that the precast full-depth overhang introduces different behavior modes, largely due to the influence of the partial depth panel-to-panel connection, which reduces the capacity by some 13%.

This companion paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck, which are cast and prestressed with the girder, provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, the use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is the perceived problem with durability of longitudinal joints used to connect adjacent girders. Four full-scale slabs connected by No. 16 (#5) headed reinforcement detail using a 152 mm (6 in.) lap length were fabricated and tested. An analytical parametric study was conducted to provide a database of maximum forces in the longitudinal joint. These maximum forces are then used to determine the loading demand necessary in the slab testing due to the service live load. Static and fatigue tests under four-point pure-flexural loading, as well as three-point flexural-shear loading, were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection, and steel strain. Based on these test results, the improved longitudinal joint detail is a viable connection system that transfers the forces between the adjacent decked bulb tee girders.

Bridge piers located in navigable inland waterways are designed to resist impact forces from barges and flotillas in addition to other design considerations (e.g., scour dead, live loads, etc.). The primary design tool for estimating these forces is the AASHTO Guide Specification that provides a simple hand calculation method to determine an “equivalent impact force.” The simplicity comes at a cost of excluding the effect of the pier shape, impact duration, and interaction between barges in a flotilla. The objective of this paper is to present a hand calculation method for determining barge or flotilla impact forces on bridge piers. The primary advantage of this approach lies in its incorporation of pier geometry, interaction between barges, and impact duration. The proposed method is derived from the conduct of hundreds of finite-element dynamic simulations of jumbo hopper (JH) barges and flotillas, made up of JH barges, impacting bridge piers. Results are presented and compared with those derived from the AASHTO method and detailed finite-element modeling.

The writers are conducting a comprehensive research program, with the goal to develop modern bamboo structures for buildings and bridges. This paper reports the design, construction, and testing of modern bamboo bridges. Laminated bamboo girders or glubam were developed and verified for satisfactory mechanical performance through full-scale testing. It was demonstrated that the laminated bamboo girders have satisfactory stiffness and load carrying capacity. The use of carbon fiber-reinforced plastics can further enhance the stiffness and capacity of the bamboo girders. Based on the test results and analysis, a 10-m long single lane roadway bridge was designed and constructed, which was the first of its kind in the world. The field tests were carried out using an over loaded two-axel truck with a total weight of 8.6 t which exceeded the given design truckload of 8.0 t. The bridge performed satisfactorily with the midspan deflection corresponding to the critical service loading condition being much smaller than the code required limit. Computer simulation of the field tests shows that the trend of the measured midspan deflection can be reasonably well captured. Examples of other bridge applications are also reported in this paper.

This paper presents the performance of constructed bridges in cold regions through examining the bridges in North Dakota that is one of the coldest regions in the United States. Unique approach of a combined multiple regression and geographic information system technology is employed to evaluate the performance and to identify the critical sources affecting deterioration of the 5,289 bridges sampled from the National Bridge Inventory database inspected between 2006 and 2007. Typical parameters examined include physical, material, and environmental factors associated with the existing bridges. The importance of maintenance and repair is highlighted. Traffic volume significantly influences the level of deterioration of the bridge decks. Year built is the most significant contribution to the structural deficiency of the bridges, followed by structural characteristics and traffic volumes. The presence of water particularly influences the deterioration. Concrete bridges are more durable than steel bridges. Truss systems may not be recommended for cold regions.

A finite-element (FE) model of a structure is a highly idealized engineering model that may or may not truly reflect the physical structure. The purpose of model updating is to modify the FE model of a structure in order to obtain better agreement between the numerical and field-measured structure responses. In this paper, a new practical and user-friendly FE model updating method is presented. The new method utilizes the response surface method for the best experimental design of the parameters to be updated based on which numerical analysis can be performed in order to obtain explicit relationships between the structural responses and parameters from the simulation results. The parameters are then be updated using the genetic algorithm (GA) by minimizing an objective function. A numerical example of a simply supported beam has been used to demonstrate the concept. This method has also been applied to the model updating of an existing bridge. Results show that this method works well and achieves reasonable physical explanations for the updated parameters.

Macdonald was one of the leading bridge engineers from 1867 to 1912. His bridges crossed major rivers of the United States and Australia. He was Chief Engineer for several major bridge companies and finished his career as a member of the Board appointed to select the replacement design for the Quebec Bridge that collapsed under construction in 1907.

Evaluation and rating of steel truss bridge connections has become imperative for many transportation agencies after the recent collapse of the I-35W Bridge in Minneapolis. Detailed engineering capacity calculations of gusset plate connections are time consuming and thus expensive. Large numbers of connections are in the national inventory and must be evaluated. A screening process and a simplified rapid screening process are proposed for ranking gusset plate connections in steel truss bridges to help bridge engineers identify possible vulnerable connections and aid field inspections. The procedures consider member demands relative to the connection geometric proportions for four different parameters: fasteners, plate tension, plate compression, and overall horizontal shear. The methods are demonstrated for two bridges, including the collapsed I35W Bridge, and clearly identify connections U10 and L11 as vulnerable for three of the four parameter types (fasteners were not identified as vulnerable for these connections). The ranking approach is not proposed as a substitute for thorough, detailed, and expert assessment of the connections, but rather allows rating engineers to more quickly prioritize detailed evaluations in an ordered systematic way from the most likely vulnerable connections to the least likely vulnerable connections. This technique may be considered analogous to performing screening tests on a new patient to indicate the likely medical condition prior to conducting more sophisticated and costly investigations.

Development of diagnostic and prognostic routines for application to in-service measurements from highway bridges necessitates analysis of experimental measurements from in-service highway bridges under natural or prescribed induced damage. This is generally limited to the unique opportunity of investigating end-of-service life bridges prior to reconstruction and consequently only a limited library of such case studies exist. This paper documents a field test of an end-of-service bridge span with prescribed progressive damage to a bearing as well as several diaphragm connections. Thirty dual-axis accelerometers were distributed across the bridge span with data acquisition and transmission facilitated by a real-time lossless wireless sensor network. A highway department service truck applied traffic excitation to the structure through routine passes on a consistent lane of traffic. Output-only system identification was applied to the baseline time history response to develop a state-space model of the bridge dynamics used for forward prediction in the form of a Kalman filter. Simple statistical evaluation of the prediction error in the model demonstrates the variance can be used to localize and generally quantify the degree of damage in the structure. The case study additionally illustrates the potential importance of monitoring lateral acceleration along the girders to permit identification of damage to elements, such as the diaphragms, that contributing primarily to the lateral and torsional response of primary structural members.

The I-35W bridge over the Mississippi River in Minneapolis, Minnesota, collapsed suddenly on August 1, 2007. This note briefly summarizes an analysis based on original design drawings, an investigation of material evidence provided by the National Transportation Safety Board (NTSB), and a full-scale load rating of the bridge superstructure. The results of the investigation and conclusions of the analysis include. (i) The thickness of gusset and the thickness of the side wall of the upper chords were designed proportional to the bending moment solution of a one-dimensional influence line analysis. This fact reveals that the NTSB-disclosed undersized gusset plates are the consequence of a bias toward a “one-dimensional model” in the original design that did not give sufficient consideration to the effects of the forces from diagonal truss members. (ii) Although the bridge’s truss-cell structure was appropriately designed, the design of the node that connected the floor members to the main truss-frame was inadequate to effectively distribute live and dead loads. Consequently, the local redundancy provided by the truss-cells was significantly reduced. (iii) A three-dimensional, nonlinear, finite-element, computation-based load rating indicates that some of the gusset plates had almost reached their yield limit when the bridge experienced the design load condition. The bridge was sustained by the additional safety margin provided by the ultimate strength of the ductile steel that comprised the gusset plates.

Lightweight self-consolidating concrete (LWSCC) is advantageous in the bridge industry because members made with this material have a significantly lower self-weight, and in its fresh state, LWSCC has a low viscosity which eliminates the need for vibration during fabrication. A composite section was fabricated with a single precast bulb-tee LWSCC beam and a lightweight concrete cast-in-place deck. A simply supported test configuration was constructed with two point loads to quantify the web-shear strength of the girder. The experimental shear strength is compared to four analytical models from different AASHTO specifications. Based on the results of this limited study, the theoretical predictions for the web-shear strength of this girder were all conservative when compared to the experimentally measured failure strength. With these results in mind, further research is recommended on the use of LWSCC girders in the bridge industry to better understand the material properties, structural properties, and cost advantages.