Journal of Bridge Engineering

This paper characterizes the experimental approach used for the evaluation of traffic-induced dynamic effects in Salgueiro Maia cable-stayed bridge. It presents the most significant results obtained both in terms of the static load tests developed at the commissioning phase, and of the dynamic tests under controlled heavy traffic. These tests were specifically conducted for the evaluation of dynamic amplification factors considering the passage of heavy trucks isolated or in groups, along several lanes and at different speeds. Furthermore, the experimental characterization of the random characteristics of the pavement roughness, using an appropriate spatial laser scanning measurement system, is referred.

This paper describes the development of a numerical model to simulate the dynamic response of the bridge–vehicle system of Salgueiro Maia cable-stayed bridge, using the results from an extensive experimental investigation to calibrate this model. Further, a set of stochastic Monte Carlo simulations of the bridge–vehicle dynamic response is also presented, with the purpose of evaluating dynamic amplification factors, taking into account the randomness of different factors associated to characteristics of the pavement, of the vehicles and of the traffic flow.

This paper deals with the applicability of multiple tuned mass dampers (MTMDs) to suppress train-induced vibration on bridges. A railway bridge is modeled as an Euler-Bernoulli beam and a train is simulated as a series of moving forces, moving masses, or moving suspension masses. According to the train load frequency analysis, resonant effects will occur as the modal frequencies of a bridge are close to the multiple of the impact frequency of the train load to the bridge. An MTMD system is then designed to alter the bridge dynamic characteristics to avoid excessive vibrations. Numerical results from simply supported bridges of the Taiwan High-Speed Railway (THSR) under real trains show that the proposed MTMD is more effective and reliable than a single TMD in reducing dynamic responses during resonant speeds, as the train axle arrangement is regular. It is also found that the inner space of a bridge box-girder of the THSR is wide and deep enough for installation and movement of MTMDs.

The Lavic Road Bridge in San Bernardino County, California, was severely damaged during the October 16, 1999, Hector Mine Earthquake (7.1 Mw). The earthquake epicenter was approximately 16 km (10 mi) south-southwest of the structure’s location on Interstate 40. Prior to the earthquake, periodic modal field tests were being conducted on the structure to evaluate the impact of on-going reactive-aggregate induced structural deterioration. A scheduled field test was performed on the structure two weeks prior to the event. A second, unscheduled field test was performed three days after the event in order to capture any changes in the structure’s modal properties that might have resulted from damage incurred as a result of the earthquake. This paper provides a visible description of the damage sustained by the structure, documents the field test procedures used to determine modal properties (preevent and postevent modal frequencies, damping, and mode shapes), and discusses the changes observed in the preevent and postevent modal properties. The extracted modal results indicated that lower-mode natural frequencies decreased 18% relative to preevent values, that the frequency order of modes did not change, and that the modal damping levels increased by 25% relative to preevent levels.

In this paper, the efficiency of seismic isolation for seismic retrofitting of bridges with light superstructures and heavy substructures in the state of Illinois is studied. For this purpose, a representative bridge was selected by Illinois Department of Transportation. A detailed structural model of the bridge capable of simulating the nonlinear behavior of its components and soil–bridge interaction effects was first constructed. Iterative multimode response spectrum analysis (IMMRSA) of the bridge were conducted to assess its seismic vulnerability. The results from IMMRSA were also verified with nonlinear time history analyses. It was found that the bearings and substructures of the bridge need to be retrofitted. A conventional retrofitting technique was then adopted for the bridge and the cost of retrofit was estimated. Next, the existing bearings were replaced with seismic isolation bearings (SIB) and the seismic analysis was repeated. It was found that SIB effectively mitigated the seismic forces and eliminated the need for retrofitting of the substructures. The cost of retrofitting using SIB was then calculated and found to be only 30% of the conventional retrofitting cost.

Elastomeric expansion bearings are often restrained laterally by retainers on each side. The retainers are in the form of a concrete shear block, rolled steel angles, or welded plates. To allow for longitudinal temperature movements, the retainers are placed with a slight clearance (gap) from the elastomer. The gap introduces nonlinearity in the seismic analysis of the bridge and, therefore, is often ignored by designers for the sake of simplicity. This paper compares the seismic response of straight and skewed slab-girder single-span bridges under the conditions of zero gap and standard gap for the retainers. Nonlinear time-history analysis is employed to measure the seismic demand on retainers, elastomers, and pinned bearings in each case. The stiffness of end-diaphragms and elastomeric bearings is included in the analysis. It is shown that these relationships are nonlinear in nature and depend on the frequency content of the input motion. It is also proved that ignoring the nonlinearity in the seismic bridge model can lead to erroneous results that are unsafe to use.

In 1995, the Federal Highway Administration (FHWA) required that all bridges, regardless of the design method used for the original design, be based on the load factor design (LFD) method. In order to comply with the FHWA requirements, state departments of transportation have converted to the LFD method for all new bridge ratings. Further, all existing bridges previously rated using the working stress design (WSD) method must be converted to the LFD method. Consequently, thousands of bridges must be rerated using the LFD method. Steel bridges rated by the WSD method have critical data missing to make the proper conversion to the LFD method. This paper presents a methodology and an intelligent decision support system to help bridge engineers convert a WSD-based bridge rating to the LFD-based rating with little human effort using the artificial intelligence approach of case-base reasoning. The proposed methodology can help bridge engineers create the missing LFD-based data efficiently and quickly with a minimum amount of work. This research demonstrates how bridge engineers can use a novel computing paradigm and modern computer tool to convert an antiquated database to current design.

Condition assessment is a term that is used to describe the process of characterizing the physical condition of constructed systems. This paper summarizes a condition assessment (CA) procedure based on a complete system of field-testing, finite element (FE) modeling, and load rating. Experimental techniques, including both modal testing and truckload testing, are used to collect measurements of the constructed systems. The basic mechanism and procedure of the FE modeling and calibration are presented. Different physical parameters of FE models are adjusted during the calibration process using both static and dynamic responses as criteria to achieve convergence between experimental measurements and analytical results using carefully developed objective functions. Finally, a bridge load rating is completed on the basis of the calibrated model. These developments are described and illustrated using a representative bridge as an example.

Due to aggressive environmental stressors and increasing traffic loads, highway bridges are undergoing significant deterioration in both condition and safety. Timely and adequate maintenance interventions are therefore crucial to ensure the functionality of existing bridges in a network. Under budget constraints, it is important to prioritize maintenance needs to bridges that are most significant to the functionality of the entire network. In this paper, the network-level bridge maintenance planning problem is posed as a combinatorial optimization and is automated by a genetic algorithm (GA) to select and allocate maintenance interventions of different types among networked bridges as well as over a specified time horizon. Two conflicting objective functions are considered simultaneously: (1) The overall performance of a bridge network expressed by the time-dependent reliability of connectivity between the origin and the destination locations and (2) the present value of total maintenance cost over the specified time horizon. A variety of maintenance types, which differ in unit costs as well as in effects on bridge performance in terms of improvement in structural reliability levels, are used in the optimization. An event tree analysis is carried out to obtain a closed-form expression for the network connectivity reliability. As an illustration example, the GA-based procedure is applied to deteriorating deck slabs of an existing 13-bridge network located in Colorado. It is shown that the proposed maintenance planning procedure has the capability of both prioritizing scarce maintenance needs to deteriorating bridges that are most crucial to the network performance and cost-effectively distributing maintenance interventions over the time horizon.

Soil embankment settlement causes concrete approach slabs of bridges to lose their contact and support from the soil. When soil settlement occurs, the slab will bend in a concave manner that causes a sudden change in slope grade near its ends. Meanwhile, loads on the slab will also redistribute to the ends of the slab, which may result in faulting across the roadway at the ends of the approach slab. Eventually, the rideability of the bridge approach slab will deteriorate. The current American Association of State Highway Transportation Officials code specifications do not provide clear guidelines to design approach slabs considering the embankment settlements. State Departments of Transportation are spending millions of dollars each year to deal with problems near the ends of approach slabs. To investigate the effect of embankment settlements on the performance of the approach slab, a three-dimensional finite element analysis was conducted in the present study, considering the interaction between the approach slab and the embankment soil, and consequently the separation of the slab and soil. The predicted internal moments of the approach slab provide design engineers with a scientific basis to properly design the approach slab considering different levels of embankment settlements. A proper design of the approach slab will help mitigate the rideability problems of the slab.

The moment–inelastic rotation behavior of hybrid steel girder bridges is experimentally investigated. Six welded girders having compact flanges and webs are statically loaded under three-point bending condition in order to simulate the interior pier section of a two-span continuous girder. Six girders, three with hybrid sections and three with homogeneous sections, are designed with three types of web slenderness ratios, resulting in three pairs of hybrid and homogeneous girders. The inelastic rotation capacities obtained from the experimental tests are then compared between hybrid and homogeneous girders. In addition, the results are compared with the prediction moment–inelastic rotation curve proposed in 1998 by White and Barth. It is concluded that, under the condition in this study, hybrid girders have more deformation capacity than homogeneous girders, and that the prediction curve is more conservative for a specimen with higher web slenderness ratio.