Journal of Bridge Engineering

Because of budget constraints, many state and county highway agencies are often forced to develop innovative and economical replacement strategies for deteriorated bridges. One such option is to use a retired railroad flatcar (RRFC) for a bridge superstructure. Many states have found RRFCs to be successful and economical alternatives to more traditional structural systems. Although the performance of RRFCs has been satisfactory, there is little to no guidance in the AASHTO specifications for load rating these structures. Such inexperience has led some to take overly conservative approaches when rating these bridges. This paper, the first of two companion papers, presents the use of field instrumentation and controlled load testing on seven RRFC bridges located in Indiana. Stress data were used to gain an understanding of the in situ response of these structures, including global bending, secondary bending, and lateral load distribution. Proposed load rating guidelines presented in the second companion paper were developed using data from these load tests as well as other data found in the literature.

Many state and county highway agencies are often forced to develop innovative and economical replacement strategies for deteriorated bridges. One such option is to use a retired railroad flatcar (RRFC) for a bridge superstructure. Many states have found RRFCs to be successful and economical alternatives to more traditional structural systems. Although the performance of RRFCs has been satisfactory, there is little to no guidance in the AASHTO specifications for load rating these structures. This inexperience has led some to take overly conservative approaches when rating these bridges for strength and fatigue. This paper, the second of two companion papers, presents the development of proposed load rating guidelines for RRFC bridges. The guidelines were developed based on previous research found in the literature and through the use of controlled load testing of RRFC bridges as presented in the first companion paper.

The models for prediction of creep in codes and design guides are mainly based on tests in which the load is sustained for a number of years, rarely exceeding 10; however, most models predict that creep reaches its extreme after approximately 30 years. An exception is the frequently accepted Model B3; it predicts indefinite increase of creep with the logarithm of the number of days of sustained loading. Analysis of deflection using Model B3 of a large number of bridges agrees with measured deflection in terms of magnitude and continued increasing tendency. Modern design requires satisfactory serviceability sustainable for a long life span. The absolute value of camber or deflection must not be excessive. This paper shows that by adopting Model B3, combined with appropriate prestressing, it is possible to satisfy this requirement for 125 years.

The majority of continuous girder bridges in regions of moderate seismicity were designed before the introduction of modern seismic codes that prescribe seismic design verification for such structures. The objective of this study is to investigate the seismic performance of typical Hungarian continuous girder bridges through a parametric study. A design space is described by a set of eight parameters. More than 10,000 bridge archetypes are designed without any seismic verification to mimic the design of conventional bridges. The seismic performance of each archetype is then evaluated with modal response spectrum analysis of a detailed finite-element model. The results highlight the vulnerability of piers and bearings and imply that the superstructures are not expected to fail under moderate ground motion intensities. Long bridges with short piers and large spans show the worst performance, especially if the number of fixed bearings in the longitudinal direction is small. This indicates the large influence of the longitudinal ground motion component on the overall response. Based on the fair performance of the investigated structures, detailed inspection and strengthening of similar bridges in moderately seismic areas is recommended.

Several modal identification techniques have been developed in the past few decades, and their use is rapidly expanding due to new focus on the instrumentation of major structures. This paper focuses on the expansion of the eigenvalue realization algorithm (ERA)–observer Kalman filter identification (OKID) to identify modal parameters of output-only systems (OO) by splitting the state-space model into deterministic and stochastic subsystems (ERA-OKID-OO). The performance is then compared with other output-only identification methods in terms of the level of accuracy and efficiency. A newly developed software package [Structural Modal Identification Toolsuite (SMIT)] is used to provide a uniform and convenient way of utilizing several system identification (SID) methods, including variations of ERA, auto-regressive with exogenous terms (ARX) models, system realization using information matrix (SRIM), and numerical algorithms for subspace state space system identification (N4SID). The main purpose of SMIT is to provide a convenient platform for an expanding list of SID methods to estimate the modal parameters based on measured data and produce reports and compare them. With a brief explanation of the theoretical background of implemented algorithms, the paper continues with the preprocessing procedure to define the geometric information, sensor data, and setup for the applied method. It then explains the postprocessing procedure to construct stabilization diagrams, obtain modal parameters from the overparameterized estimation, and visualize and save the results. The applications for a numerically simulated simply supported beam as well as sensor data from the Lehigh River Bridge (LRB) on Highway 33 and Golden Gate Bridge (GGB) are used to demonstrate the validity of SMIT and investigate the performance of ERA-OKID-OO.

High-strength steel reinforcement provides various benefits to the concrete construction industry, including a more efficient use of high-performance concrete, reduction of reinforcing bar congestion, and materials savings. Prior to the 2013 interim revisions of the AASHTO LRFD Bridge Design Specifications, the value of reinforcing steel yield strength used in design was limited to being no greater than 517 MPa (exceptions were permitted with owner approval for cases with a yield strength of less than 414 MPa). In 2007, National Cooperative Highway Research Program Project 12-77 was initiated to evaluate the AASHTO specifications with respect to the use of high-strength reinforcing steel and other grades of reinforcing steel having no discernible yield plateau. Among the objectives of this project was the investigation of ductility and crack control of flexural members using high-strength reinforcement. This research led to a number of recommendations that were subsequently incorporated into the 2013 interim revisions of the specifications. The flexural behavior and design of members reinforced with high-strength steel are presented. This paper also provides the background information for the AASHTO specification revisions related to strength reduction factors for flexure. The research demonstrates that the strain limits for high-strength reinforcement must be changed to achieve the curvature ductility comparable to that implicit with the current use of Grade 414 reinforcing steel. Moreover, the service load stresses in steel should be limited to 60% of the yield strength.

Preventive maintenance on aged steel railway structures is all important due to their long service time after completion. This paper introduced a strengthening method for old steel railway bridges by using rubber-latex mortar, glass fiber reinforced polymer (GFRP) plates, lightweight rapid hardening concrete, and reinforcing bars. Both laboratory tests and field tests were performed to confirm the effects of the present strengthening method. In total, two old railway bridges were employed in this study. One of them has been in service for around 100 years. The static loading test was performed in the laboratory. Experimental results, including load-deflection response, strain distribution on the structural steel, GFRP plates as well as concrete, were given and compared between the original steel railway bridge and the strengthened bridge. Theoretical results were also provided to make a comparison with the experimental results. Both the experimental and theoretical results indicated that the present renovation method could greatly enhance the rigidity and reduce the stress levels of old steel members, resulting in the extension of the residual service life of the old steel railway bridge. In addition, field tests were performed on the other old railway bridge, which has been used for 86 years, and stress variation on the railway bridge under the running train was measured and the effects of the present strengthening method in the real service condition were also confirmed.

Full-scale data on the natural frequencies and the damping ratios of 114 highway bridges in China, and the dynamic characteristics monitoring data of four bridges under ambient excitation, have been collected and analyzed. The data indicate that the natural frequencies of the long-span bridges have power function relationships with the lengths of the main spans, whereas the damping ratios of the bridges scatter with the influence of the width of section, the piers, the material, the test environment, and the bridge type. Values of the damping ratios of different bridge types in China are proposed based on the collected data. With the increase in service ages, the natural frequencies of the bridges change little, whereas the damping ratios of the bridges decrease and tend toward stable after certain years. The forms of damage, the locations of damage, and the strengthening methods have a great influence on the changing of damping ratios.

This paper describes an experiment on the in-plane mechanical behaviors of the steel truss web–RC composite arch subjected to the unsymmetrical concentrated loads applied simultaneously at the $2\text{/}3$ and $5\text{/}6$ span points of the arch. The experimental results show that loads were transmitted as shear forces through the steel truss webs. The maximum measured strain in two steel tubes near the cross section at the $5\text{/}6$ span point was less than the yield strain, and punching shear failure was observed at the loading sections. Using the experimental model, the authors developed and performed a finite-element simulation. They found that double N-shaped webs might be the most conducive to the stiffness and bearing capacity of the composite arches and require comparatively less steel. The critical wall thickness of the web tubes at which punching shear failure occurred was 3.5 mm for this arch model. Given the same wall thickness, the ultimate bearing capacity of the composite arch decreased as the incline angle of the web members increased. In the composite arch, there is no substantial difference in terms of bearing capacity between the steel truss webs and the corrugated steel webs, but both types of webs are better than the flat steel webs in relation to bearing capacity and steel consumption.

This paper numerically investigates the three-dimensional seismic response of six reinforced concrete bridges hypothetically located in Oakland, California, 3 km from the Hayward fault. Three of the bridges are 17 m tall and three are 8 m tall. Three types of column-foundation designs are studied: (1) columns that form flexural plastic hinges, which are conventionally designed according to CALTRANS seismic design criteria; (2) columns on rocking pile foundations that are designed to remain elastic; and (3) columns designed to remain elastic that are supported on rocking shallow foundations. The bridges with rocking foundations use lead rubber bearings at the abutments to enhance strength, stiffness, and hysteretic energy dissipation. Using two components of horizontal excitation, three-dimensional nonlinear response history analyses are performed for two seismic hazard levels with return periods of 975 and 2,475 years, respectively. At both levels of shaking, the conventionally designed bridges experience substantial inelastic deformations and damage in the columns, whereas the bridges with rocking foundations result in negligible structural damage and a nominally elastic response and small residual deformations.

A small degree of uncertainty has been observed in determining the significance of thermal loads when designing the superstructure of a horizontally curved steel bridge. This investigation focuses research on a three-span curved bridge with fixed piers and integral abutments. Combining horizontal curvature with increased levels of fixity (e.g., integral abutments and fixed piers) presents a growing concern with regard to the influence of changing temperatures. The purpose of this work was to analytically investigate bridge superstructure behavior under design thermal loading conditions. In doing so, a bridge previously subjected to an empirical field study was modeled using a commercial finite-element analysis software package. The results indicated that thermal stresses in the lower flange of the girder were greatest at the fixed pier locations. These stresses were mostly the result of lateral flange bending caused by the pier restraining lateral movement of the girder. While these stresses were small for this particular bridge, adding only up to 20,684 kPa (3.0 ksi), bridges incorporating integral abutments and fixed piers with increased curvature and skew may require special attention in future practice.

Uncoated weathering steel (UWS) bridges have been in use in the United States for nearly 50 years, now enabling the long-term performance of these structures to be assessed. This was accomplished by surveying the varied experiences of 52 U.S. transportation agencies, along with data analysis on all UWS bridges known within these and other agencies, which total nearly 10,000 structures. Climate and age were key considerations in this data analysis. Contrary to previous, more limited research, this analysis showed that there is not a strong trend in UWS bridge performance as a function of climate. A similar climate analysis for non-UWS bridges also showed a counterintuitive relationship between some climate types and these bridges. This suggests that design and maintenance practices may be more influential to UWS performance than climate, and further research to cultivate current best practices in this regard is recommended. Comparison between the UWS and non-UWS data sets also reveals that UWS bridges generally perform well in relation to non-UWS bridges.

Long-term monitoring of two precast deck panels constructed with glass fiber–reinforced polymer (GFRP) bars and six girders of a single-span bridge is reported. Each instrumented panel is 12.5 m long, 2.1 m wide, and 235 mm thick; all panels in the bridge are reinforced with GFRP bars. Static truck-load test results are discussed and observations are made regarding the overall response of the bridge. The deflections of the girders to known static loads and AASHTO distribution factors are evaluated. Data from loads applied to the bridge were collected remotely for approximately 3 years and analyzed. Collected data also include concrete strains in the deck panels and relative displacements of the panels with respect to the girders. The response of the girders and bridge deck is evaluated by comparing test results to design requirements as well as to finite-element analyses. It is shown that, after 3 years in service, the performance of the bridge including the precast concrete deck is well within design requirements.

In response to the bridge damages observed in past earthquakes and the absence of practical analysis methods, a simplified analysis procedure named the fault rupture-response spectrum analysis (FR-RSA) method was developed in this research as an alternative to the onerous nonlinear response history analysis (RHA) method for bridges crossing strike-slip earthquake fault rupture zones. For validation of the FR-RSA method, this research investigated seismic responses of two representative curved bridges in California, including one three-span bridge and one four-span bridge. The selected bridges were analyzed using both the FR-RSA method and the nonlinear RHA method. Ground motion, earthquake fault rupture location, and fault orientation were varied in the analyses to expand the validation work under a broad range of the parameters. Result comparisons show that the FR-RSA method provides estimates of peak bridge displacement response that are close enough to the exact nonlinear RHA results in all considered cases; therefore, it is recommended for future practical application.