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For the last 4 decades, concrete bridges have benefited from larger diameter prestressing strands, which have increased from 13 to 15 mm in diameter and are now the standard in the US. The largest commercially available strands in the US are 7-wire–18-mm-diameter strands, but they are not used as often despite researchers finding that they can provide longer spans and lighter structures. This research seeks to experimentally benchmark the bond of 28.6-mm-diameter grade 1780 prestressing strands to normal-weight concrete and mortar for the first time. The large-block pullout test (LBPT), the North American strand producer test (NASP), and concentrically reinforced prism (CRP) pullout test were conducted to quantify the pullout force of these strands when they were embedded in concrete as well as to determine an experimental reference value. The results showed that the strands exhibit adequate bonding to the concrete when implementing the LBPT, NASP, and CRP tests to evaluate them in combination with extrapolated values from the literature using a ratio of strand diameters. Furthermore, CRP tests indicated that the transfer length would likely be approximately 1,200 mm and the development length between 1,800 and 2,400 mm for 58-MPa concrete. It was also determined that due to their much larger surface area, the bond stress of these large-diameter strands was lower than that of 13-, 15-, and 18-mm-diameter strands for similar case scenarios of bond evaluation or transfer length estimation using prisms. However, there is limited information for comparison, and the testing program presented is the only one of its kind for this strand size. [ABSTRACT FROM AUTHOR]

Studies have shown that experimentally determined dynamic properties can be used to identify the characteristics of a structure. In this paper, a damage detection technique is developed and demonstrated using system identification, finite-element modeling, and a modal update process. The proposed approach, SFM, provides a rapid estimate of damage locations and magnitudes. The proposed methodology is applied to three case studies. The first is a numerical simulation using computer generated data. The second is an ASCE benchmark problem for structural health monitoring, where the results can be compared to other researchers. The third is a full-scale highway bridge that was field tested using a forced vibration shaking machine. In this case study, the bridge was shaken in several states of damage and the proposed methodology was utilized to detect and determine the location and extent of the damage. It was found that, using the collected data, the SFM approach was able to consistently predict the location of damage as well as estimate the magnitude of the damage. DOI: 10.1061/(ASCE)0887-3828(2008)22:4(238) CE Database subject headings: Monitoring; Structural reliability; Damage; Modal analysis; Field tests; Laboratory tests.

A curved, three-span continuous, steel I-girder bridge in Salt Lake City was tested in order to determine its dynamic and static load carrying properties for three boundary condition states. For each of the three boundary condition states, two dynamic forced vibration methods were applied to the bridge as well as a static live-load test. The first forced vibration method used an eccentric mass shaker. The second method involved striking the side of the bridge with an impact hammer. The live-load test was performed by slowly driving a truck at a crawl speed across the bridge. Velocity transducers, accelerometers, and strain gauges were utilized to record the response of the bridge. The analysis and compilation of recorded dynamic response of the bridge enabled the preparation of mode shapes and natural frequencies for each boundary condition. This paper discusses the resulting changes in relevant dynamic properties and compares them with the changes in the static properties that were determined from the bridge response recorded from the live-load tests. DOI: 10.1061/(ASCE)0887-3828(2007)21:3(185) CE Database subject headings: Model analysis; Beams; Bridges, steel; Dynamic tests; Field tests; Curvature.

A nondestructive strength evaluation of the I-40 Bridge over the Rio Grande River in Albuquerque, N.M. was completed for the New Mexico Department of Transportation (NMDOT). The I-40 Bridge is a precast, prestressed concrete girder bridge located within 3 mi. of the 'Big I' interchange carrying Interstates I-40 and I-25. Because of its location, the I-40 Bridge is subjected to large amounts of heavy truck traffic. The primary objective of the study reported herein was to determine a more accurate capacity rating for the I-40 Bridge and thus, reduce the number of overweight vehicle permit denials. To achieve this objective, a conventional rating analysis is first performed based on American Association of State Highway and Transportation Officials (AASHTO) guidelines. A diagnostic load test and a finite-element analysis are then completed. Details of the AASHTO rating analysis as well as the approach by which measured girder strains from the load test and finite-element results were considered in the capacity rating of the I-40 Bridge are discussed. Findings from the study confirmed that the capacity ratings of the I-40 Bridge could be safely increased by a factor of 1.7. CE Database subject headings: Bridge tests; Finite element method; Load distribution; Nondestructive tests; Permits; Strain measurement: New Mexico.

A collection of condition and appraisal ratings of bridges prior to collapse is presented and analyzed to show commonalities among collapsed bridges in New York State. General observations of bridge collapses are presented in addition to select consequences. Bridge inspection data are collected for the most recent inspection dates prior to the collapse of each collapsed bridge. Trends obtained from statistical analysis of existing data show 45 (46%) of collapsed bridges were structurally deficient prior to collapse, and a collapse rate of structurally deficient bridges is estimated to be 1=1,200 annually. Age and structural deficiency are shown to be related. Structural deficiency and collapse are shown to be related. Age of structure at the time of collapse is contingent on collapse cause. Deterioration-caused and overload-caused bridge collapses are age related, but hydraulic-caused and collision-caused bridge collapses have no age-determined relationship. Fifty-seven percent of hydraulic-caused bridge collapses had a scour vulnerability rating that indicated the foundations were stable for calculated scour and scour conditions. Collision-caused bridge collapses appear to be contingent on the vertical clearance: roughly 90% of bridges analyzed had a vertical clearance less than 4.5 m (14 ft 9 in.). Overload-caused bridge collapses have a relationship with the bridge being load restricted. The overloadcaused collapse rate for a bridge that is load restricted is estimated to be 1=3,500 annually. Life loss is associated with 5% of bridge collapses, most of which are collision-caused. The majority of bridge collapses have low consequences related to life loss, average daily traffic, and detour length. [ABSTRACT FROM AUTHOR]

This study addresses the feasibility of using a single-span bridge as a weigh-in-motion (WIM) tool to quantify the gross vehicle weights (GVWs) of trucks inexpensively with a small number of sensors and without using axle detectors. Field testing was performed on an interstate without any lane closures. Four preweighed trucks with different axle configurations traveled over a bridge at three different speeds and in two separate lanes. Measured strain data were used to implement bridge weigh-in-motion (B-WIM) algorithms and calculate the corresponding velocities and GVWs. A comparison was made between calculated and actual measured static weights, and between the calculated and specified speeds of the trucks. In addition to field testing, a finite-element (FE) model of the tested bridge was created and calibrated based on the measured strains at different locations. This calibrated FE model enabled the acquisition of the influence values for the bridge at any location (influence surface). Ten different points were selected to calculate the influence surface values, and a comparison was made between calculated strains from the influence surface and the actual response of the bridge recorded by strain gauges. The comparison showed that the updated FE model was capable of providing the influence surface values at different locations. The validated influence surfaces were then used to simulate the passing of common types of trucks with various weights and axle configurations over the bridge. The measured GVWs based on simulated strain measurements provided by the FE model and validated influence surfaces verified the applied method. [ABSTRACT FROM AUTHOR]

This paper describes the experimental testing of 48-year-old concrete bridge girders that were fabricated using lightweight concrete. After the bridge was decommissioned, three girders were transported to the Systems, Material, and Structural Health (SMASH) Laboratory at Utah State University (USU). The double-tee girders were tested to quantify the effective prestress, flexural capacity, and deck punching shear strength. The experimental results were compared with calculated values based on recommended procedures in the AASHTO LRFD bridge design specifications. The AASHTO refined method underestimated the loss of prestress of the three girders by an average of 17.6%. The calculated flexural capacities were overestimated by an average of 34.0% when compared with the measured values. This unconservative result is believed to be a result of the deck deterioration. The average calculated punching shear capacity was within 3.0% of the measured values. The experimental results were also compared with analytical values using computer software. These nonlinear finite-element analyses (FEAs) were found to replicate the behavior of the flexural and punching shear experiments in terms of both the failure mechanism and magnitude. [ABSTRACT FROM AUTHOR]

The Kettle River Bridge is an arched, steel cantilevered deck, Pratt Truss bridge. To quantify the live-load performance of the bridge superstructure and provide a baseline for future comparisons, it was instrumented with 151 strain gauges on various beam, stringer, and truss members. In addition, 8 displacement gauges were attached along the truss. All gauges were simultaneously monitored while the bridge was subjected to a nondestructive, live-load test. The recorded bridge response was analyzed to quantify in situ behavior. The measured behavior was then used to validate a finite-element model using solid and frame elements, which was subsequently used to obtain an inventory- and operating-load rating of 2.03 and 2.64, respectively. Based on the results of the test, it was concluded that the large gusset plates added partial fixity to the truss members, as evident from the significant measured in-plane bending strains. However, the beam-and-stringer deck support system showed minimal rotational restraint between consecutive panels and behaved nearly simply supported. The validated finite-element model was used to determine distribution factors. The actual bridge distribution factors were found to be conservative in comparison to those calculated according the AASHTO LRFD specifications, by 17-44%. [ABSTRACT FROM AUTHOR]

A regional bridge failure database was used to determine the bridge failure rate with associated causes. Using a sample population from one DOT over a 25-year period, the average number of bridge failures was approximately 1=4,700 annually with a 95% confidence interval from 1=6,900 to 1=2,700 annually. The number of bridge failures per year was modeled with a geometric distribution that requires a constant failure rate. Based on a validation analysis with bridge failures from six separate DOTs, other DOTs have bridge failure rates within the determined sample population 95% confidence interval. Analysis of the failed bridges by year of construction shows no apparent era of construction that is more susceptible than another to failure. Correspondingly, the determined constant failure rate ascertained in the model selection indicates that the changes in bridge design specifications and maintenance regulations do not appear to have significantly reduced bridge failure rates. Based on the data extrapolation, the estimated average annual bridge failure rate in the United States is between 87 and 222 with an expected value of 128. [ABSTRACT FROM AUTHOR]

This paper describes a case study to quantify the behavior of precast, prestressed-concrete bridge girders made with high-strength concrete. As part of the case study, four bridge girders made with 77.2-MPa (11.2-ksi) concrete were salvaged from a decommissioned bridge in Orem, Utah. Each girder was subjected to a flexural cracking test to determine a prestress loss of 22% after approximately 7 years of service life. Once the prestress losses were quantified, a flexural capacity test was performed on one girder. Shear capacity tests were performed at various distances from the support on the remaining three girders. The measured prestress losses and various capacities were compared with estimated values calculated according to procedures in current bridge specifications. The predicted flexural capacity was found to be 7.3% conservative compared with the measured capacity. The measured shear capacities were all within 12% conservative compared with the AASHTO shear procedures. In addition to the physical tests, a nonlinear finite-element analysis was conducted and was found to replicate the experimental behavior, failure mechanism, and magnitude. [ABSTRACT FROM AUTHOR]

This paper presents a comparison of two live-load tests performed on a posttensioned, box-girder bridge. The initial live-load test was performed more than 20 years before the most recent test. Strain gauges were placed at the same location for both tests. In each case, the bridge was subjected to nearly identical loads so that changes in strain could be correlated as a heavy truck drove across the instrumented bridge. A comparison of the bridge behavior based on the two load tests is presented. The changes in recorded strain were also used to validate a detailed finite-element (FE) model using primarily shell elements. From this calibrated FE model, the live-load distribution factors for moment were obtained. These factors were used to calculate both the inventory and operating rating factors of the bridge. These values were compared with those calculated in accordance to the AASHTO LRFD specifications for distribution factors. It was found that the rating factors could be increased by 26% because of the partial fixity caused by the integral abutments. [ABSTRACT FROM AUTHOR]

Accelerated bridge construction techniques have resulted in state-of-the-art options that save time and money during the construction of new or existing bridges. One such group of techniques that has generated considerable interest is the use of precast-concrete deck panels. Using precast-concrete deck panels allows for off-site curing, thus eliminating long delays from formwork construction and concrete curing time. Despite the benefits, problems can develop as a result of the inherent joints between the individual panels. These joints are locations for potential leakage, which can result in corrosion or inadequate long-term performance. Posttensioning the precast deck panels helps to eliminate leakage, but conventional longitudinal posttensioning systems require complete deck replacement in the event of a single faulty deck panel. The proposed posttensioned curved-strand connection presented in this paper allows for single-panel replacement. The capacity of the proposed curved-strand connection was investigated to compare its behavior with that of other systems currently in use. The curved-strand connection was found to be comparable to a standard posttensioning system. The ultimate capacity of the curved-strand connection in negative bending was found to be 97% of the standard posttensioning connection. [ABSTRACT FROM AUTHOR]

This paper describes an investigation to quantify the behavior of a precast deck system. As part of this investigation, a live-load test was performed on a steel I-girder bridge made with accelerated bridge construction precast deck panels. It was found that the bridge was behaving compositely in some locations and noncompositely in others. When the bridge was decommissioned, a two-girder specimen was salvaged and transported to Utah State University for shear-capacity testing. The primary shear failure mechanism was found to be buckling of the girder web. A nonlinear finite-element analysis was conducted using ANSYS that was found to replicate the experimental behavior and reproduce the failure mechanism and magnitude. It was concluded that the effect of the noncomposite behavior on the ultimate shear capacity was a reduction of approximately 8.0%. The measured ultimate capacities were compared with estimates calculated according to procedures in the AASHTO LRFD specifications. When using the specified steel strength, the code predicted shear resistance ranging from 8.0% higher to 0.7% lower. [ABSTRACT FROM AUTHOR]

Precast deck panels are increasingly being used to reduce construction times as part of a push for accelerated bridge construction by some state departments of transportation. Despite the short-term benefits, the connections between panels have a history of serviceability problems. To evaluate the service and ultimate behavior of current and newly proposed connections, 12 push-off tests were performed on precast bridge deck transverse connections for shear. These tests used an improved shear specimen geometry that allowed the connection to deform in more realistic shear. This new test setup included spaces that allowed diagonal cracks to form and reinforcement to pull out of the connection. The push-off tests established the cracking and ultimate shear strengths of each connection detail. These details included a welded connection, an unreinforced grouted connection, and a post-tensioned-type connection tested with and without an applied compression force. Results of each detail type are compared. The test results show that the post-tensioned connection outperformed the other connection details, with 2.1 times the shear capacity of a welded connection spaced at 45.7 cm (18 in.). [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of flexural live-load distribution factors for cast-in-place box-girder bridges. The response of a typical box-girder bridge was recorded during a static live-load test. This test involved driving two heavily loaded trucks across the instrumented bridge on selected load paths. The instruments used to record the response of the bridge were strain gauges, displacement transducers, and tilt sensors. The measured data were then used to calibrate a finite-element modeling scheme using solid elements. From this finite-element model, the theoretical live-load distribution factors and load ratings for the test bridge were determined and compared with the factors and ratings predicted in the AASHTO LRFD specifications. A parametric study of cast-in-place, box-girder bridges using the calibrated finite-element modeling scheme was then used to investigate how various parameters such as span length, girder spacing, parapets, skew, and deck thickness affect the flexural live-load distribution factors. Based on the results of the parametric study, a new equation, which more accurately predicts the exterior girder distribution factor, is proposed. [ABSTRACT FROM AUTHOR]

Seven prestressed concrete bridge girders that had been in service for 42 years, and represented two span lengths and reinforcement designs, were tested to determine their effective prestress force and ultimate shear capacity. A cracking moment test was used to determine the effective prestress force in the girders. The measured effective prestress force was compared with calculated values according to the AASHTO LRFD prestress loss equations to investigate their adequacy. The AASHTO refined method was shown to provide the most accurate results to within 10% of the measured values. An ultimate shear test was also performed on two of the girders. An external load was applied near the support and increased until the girder failed in shear. The various procedures in the AASHTO LRFD specifications were compared with the measured results. The AASHTO simplified procedure predicted only 51% and 39% of the average measured shear capacity for the short and long span girders, respectively. The strut-and-tie models were found to estimate the shear capacity more accurately. The AASHTO refined method was shown to provide the most accurate results. [ABSTRACT FROM AUTHOR]

Sixteen shear capacity tests were performed on eight decommissioned AASHTO prestressed concrete girders that had been in service for over 42 years. These bridge members presented a unique opportunity to investigate carbon fiber-reinforced polymer (CFRP) retrofit schemes to enhance the shear capacity of underreinforced girders that were nonrectangular. Four destructive tests were performed to quantify the in-service strength of the girders and the remaining 12 tests were performed on CFRP retrofitted girders. In all, five configurations of the CFRP reinforcement were evaluated. Two anchoring techniques were investigated that either involved epoxying a horizontal CFRP strip over the vertical strips or a new methodology of epoxying a CFRP laminate into a groove over the vertical strips that was cut at the web-to-flange interface. Two methodologies that predicted the shear contribution of the carbon fiber reinforcement were compared with the test results. A carbon fiber-reinforcing scheme of vertical strips and horizontal anchorage strip was found to be the most effective in resisting the applied shear. [ABSTRACT FROM AUTHOR]

In this paper, an experimental and analytical investigation of concrete-filled steel tubular (CFST) laced columns is presented. These columns consist of four concrete-filled steel tubes that are laced together. A total of 27 experimental tests were conducted to quantify the column failure mechanism at ultimate loads. The experiments were designed to obtain the load-deflection curves. These curves were subsequently used to quantify the structural behavior for each element of the hybrid column. Experimental results indicate that the compression force in the longitudinal members dominated the failure mechanism in the CFST columns. In-plane bending occurred when member segments reached the compression failure load. The forces in the lacing members (diagonal and horizontal bracing) were found to be small and remained in the elastic range through failure. The experimental study was used to validate an analytical parametric study. The analytical study showed that increasing slenderness ratios and eccentricities reduced the ultimate load capacity. Additionally, finite-element analyses of CFST columns based on four in situ structures were performed to determine the ultimate load-carrying capacity and were subsequently compared to several building codes. On the basis of the analytical results, a new methodology for calculating the ultimate load-carrying capacity is proposed. This purposed methodology is compared with five different building codes to quantify the increased accuracy. [ABSTRACT FROM AUTHOR]

Precast deck panels are increasingly being utilized to reduce construction times and traffic delays as many departments of transportation (DOTs) emphasize accelerated bridge construction. Despite the short-term benefits, the connections between panels have a history of service failure. This research focused on the evaluation of the service and ultimate capacities of five precast deck panel connections. Full-scale tests were developed to determine the cracking and ultimate flexural strengths of two welded connections, a conventionally posttensioned connection, and two newly proposed, posttensioned, curved bolt connections. The conventionally posttensioned specimens were shown to perform well with the highest cracking loads and 0.42 times the theoretical capacity of a continuously reinforced concrete deck panel. The proposed curved bolt connections were shown to be a promising connection detail with approximately 0.5 times the theoretical capacity of a continuously reinforced panel. Data from the welded specimens showed that some welded connection types perform significantly better than others. The experimental results also compared closely with values calculated on the basis of finite-element modeling, which can be used for future analytical studies. [ABSTRACT FROM AUTHOR]

In the field of nondestructive evaluation and damage detection, there is continued interest in the utilization of vibrational techniques. Structural damage will result in permanent changes in the distribution of structural stiffness. These changes may be detected through structural monitoring. Because of the direct relationship of stiffness, mass, and damping of a multi-degree-of-freedom system to the natural frequencies, mode shapes, and modal damping values, many studies have been directed at using these dynamic properties for the purpose of structural health monitoring. The use of vibrational monitoring is a developing field of structural analysis and is capable of assisting in both detecting and locating structural damage. Vibrational data have been shown to be most useful when used in conjunction with other monitoring systems if a remote and robust damage detection scheme is desired. This paper includes a literature review that summarizes the basic approaches to vibrational monitoring, suggested guidelines for sensor selection and monitoring, and concludes with three example case studies. [ABSTRACT FROM AUTHOR]

This paper presents an evaluation of flexural live-load distribution factors for a series of three-span prestressed concrete girder bridges. The response of one bridge, measured during a static live-load test, was used to evaluate the reliability of a finite-element model scheme. Twenty-four variations of this model were then used to evaluate the procedures for computing flexural live-load distribution factors that are embodied in three bridge design codes. The finite-element models were also used to investigate the effects that lifts, intermediate diaphragms, end diaphragms, continuity, skew angle, and load type have on distribution factors. For geometries similar to those considered in the development of the American Association of State Highway and Transportation Officials Load and Resistance Factor Design Specifications, the distribution factors computed with the finite-element models were within 6% of the code values. However, for the geometry of the bridge that was tested, the discrepancy was 28%. Lifts, end diaphragms, skew angle, and load type significantly decreased the distribution factors, while continuity and intermediate diaphragms had the least effect. If the bridge had been designed using the distribution factors calculated with the finite-element model rather than the code values, the required concrete release strength could have been reduced by 6.9 MPa (1,000 psi) or the live load could have been increased by 39%. [ABSTRACT FROM AUTHOR]

Two sections from a decommissioned bridge were salvaged and tested to quantify flexure and punching shear capacities. The salvaged bridge sections each consisted of two built-up, steel-plate girders, compositely attached to precast concrete, deck panels. The deck panels were part of an accelerated bridge construction (ABC) project and were connected to one-another using female-to-female, flexurally discontinuous, transverse joints. Experimental results were compared with theoretical-based results produced from AASHTO LRFD specifications design procedures. Measured flexural capacities exceed the AASHTO computational design capacity by 30%. The precast panels and transverse joints were also tested for punching shear capacity and found to range from 144 to 87% in comparison to the AASHTO LRFD values, depending on the proximity to the transverse joint. Nonlinear, finite-element models validated the experimental results. The analytical models had excellent agreement with experimental deflection, reaction forces, regions of yielding, and the ultimate flexural capacity. [ABSTRACT FROM AUTHOR]