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Because of the potential for concrete crushing, the negative moment transfer mechanism of the transverse connections above the pier support is still a point of concern. The objective of this study was to evaluate the behavior of a transverse closure pour connection used for the constructed Little Silver Creek Bridge in Iowa and to validate its adequacy for modular bridge application. To evaluate the need for the complicated compression block, two transverse connection specimens with and without the compression block were designed, fabricated, instrumented, and tested under a negative bending moment. Finite element models were established to further understand the specimens’ performance, and hand calculations were performed to estimate their moment capacity. No significant difference was found between the crack patterns of the two specimens, and the diaphragm concrete tended to crush in the bottom regardless of the configuration. The established finite element models were sufficient at representing the structural behavior of the two transverse connection specimens. The connection with a compression block had higher yield and ultimate moment capacity than the connection without a compression block. To design both types of connections according to the classic theory of reinforced concrete design, an effective width equal to the width of the steel girder bottom flange and the centroid of the compression force at the bottom of the steel girder bottom flange can be assumed for the connections with and without a compression block, respectively. Hand calculations reasonably estimated the moment capacity of the two specimens, and the two connections were safe under the codified, factored loads.

Approximately 11% of bridges in the United States are categorized as structurally deficient and there is a marked need of more accurately evaluating true structural capacity. Structural Health Monitoring (SHM) systems can provide a timely indication of the need for maintenance, repair, rehabilitation and replacement of bridges and can greatly improve the apportionment and management of limited resources. This paper presents an Automated Ambient Traffic (AAT) approach for determining load rating of bridges monitored by the BECAS SHM system under ambient traffic. The AAT approach was developed through a process integration of truck detection, bridge model calibration, and bridge load rating: (1) the quasi-static bridge strain response and the characteristics of associated trucks are collected; (2) multiple trucks are randomly sampled from a historic Weigh-In-Motion (WIM) database; and (3) for each combination of strain response and truck selection, an Finite Element (FE) model is calibrated and used to calculate a load rating. Sampling strategies were discussed for appropriately quantifying the influence of uncertainties of truck characteristics on the calibration and load rating results. To demonstrate this approach, a sample three-span, five-girder, and two-lane steel girder/concrete deck (I-80) bridge was utilized. A load rating of the I-80 Bridge using the Traditional Known Truck (TKT) approach was performed to provide benchmark results. The results of the calibration and load rating using the AAT approach were derived using three different sampling strategies and compared to those using the TKT approach. The sampling strategy, selecting strain response with a spectrum of higher peak girder strains, associated trucks with a spectrum of higher gross vehicle weights, and two truck events on south and north lanes respectively for a calibration, resulted in the best calibration and load rating results. It was concluded that the AAT approach using the BECAS SHM system is a reliable method for continuously estimating the load carrying capacity of bridges.

Bridge owners and engineers focusing on bridge design, management and maintenance continue to search for more efficient ways to design, construct, and maintain their bridge inventory. Recently, a folded plate girder system has been promoted as a cost-effective alternative for the design and construction of bridge superstructures due to merits such as low cost and facilitation of accelerated bridge construction. The folded plate girder system has a structural shape strategically press-brake formed from a single sheet of plate steel and achieves composite action with a concrete deck utilizing shear studs in between. To further facilitate the development and adaptation of the system for bridge application, this paper presents a systematic performance evaluation of the folded plate girder system through experimental and numerical programs. To this end, a folded plated girder specimen was designed, fabricated, and tested to evaluate the constructability and capacity of the girder specimen. Finite Element (FE) Analysis was performed to understand the behavior of the girder specimen under different loading conditions. The predictions using traditional design calculations and FE analysis were compared with the test results. After the FE models were validated against the test data, a full bridge model was established to further investigate the behavior of the bridge under loading condition up to the ultimate load. It was found that the ultimate capacity of the bridge girders were much higher than the bridge demand and the bridge had good ductility until failure. The predictions using the design calculations based on the AASHTO LRFD Bridge Design Specifications were in reasonable agreement with the test results. The FE models showed better predictions since more sophisticated modeling techniques and material constitutive models were used. Results obtained from the sophisticated non-linear bridge model indicated that the girder distribution factors varied along with an increase of the truck loading and especially their change trend was gradually reversed after the yield of the girder steel. And according to the FE results, the distribution factor based on the AASHTO LRFD Bridge Design Specifications was sufficient for the design of the folded plate girder bridge investigated in this study.

Accelerated bridge construction techniques taking advantage of prefabricated bridge elements and high-performance materials are being used more frequently for bridge replacement projects. They result in minimal road closure times and traffic interruption and in the reconstruction of long-lasting highway bridges. Longitudinal closure pour connections are an important deck-level component for modular bridge elements that are heavily stressed by traffic loadings and environmental effects and whose durability is a concern. To address cracking and leakage issues in such connections, the strength and failure modes of the longitudinal ultrahigh-performance concrete (UHPC) closure pour connection between adjacent prefabricated deck units were evaluated. First, specimens with and without a longitudinal UHPC closure pour connection were fabricated, instrumented, and tested. Finite element (FE) models were established to improve understanding of the behavior of the specimens under the loading condition. In addition, strut-and-tie models (STMs) were developed on the basis of FE model predictions to estimate the strength of the specimens. The jointed specimens were found not to have any cracks or leakage at the early stage but had lower cracking loads than did the jointless specimens. The strength and ductility of the jointed specimens were comparable with those of the jointless specimens. On the basis of the FE models and STMs, the ultimate strength of the specimens was accurately predicted.

The transfer of prestress force from prestressing strands to the surrounding concrete is dependent on the bond between the two materials. Understanding the actual bond stress distribution along the transfer length results in optimized design of the transfer zone of prestressed concrete members. Equations of estimating the transfer length in ACI 318 code and AASHTO LRFD bridge design specifications simply take into account the effect of the strand diameter only. The objective of this study is to provide a generalized procedure for determining the bond stress–slip relationship accurately by incorporating the effects of additional parameters, such as concrete compressive strength at prestress release, center-to-center strand spacing, and concrete bottom cover. First, the bond stress distribution along the transfer length of a prestressed concrete member is formulated based on longitudinal slip–strain compatibility, force equilibrium and invariable bond stress–slip relationship along the transfer length. Second, a generalized Inverse Problem-Solving approach is introduced to determine best parameter coefficients through minimizing the discrepancy between the calculated and measured results. Two types of measurements (i.e., transfer length and end slip) reported in the literature are utilized to demonstrate the proposed approach. Predicted transfer length and end slip values using the calibrated bond stress–slip relationship show better agreement with the test data compared to those predicted by ACI 318 code and AASHTO LRFD bridge design specifications. Third, a computational procedure is developed and an example is presented to assist engineers using the developed formulae for determining the bond stress distribution along the transfer length of prestressed concrete members.

The numbers and sizes of permitted vehicles that consist of at least four wheel lines have been increasingly crossing on highways and bridges. For safety purposes, it is necessary to understand how those truck loads are distributed to the primary bridge elements. It is widely accepted that the lateral live-load distribution factor (LDF) is affected by the spacing of adjacent wheel lines of truck loads. However, current specifications for the LDF are applicable only for vehicles that have standard axle configurations, whereas oversized vehicles usually have nonstandard wheel-line spacing. Furthermore, Iowa’s 5-ft (1.5-m) spacing requirement, which specifies that dual-lane trucks with interior-pair wheel-line spacing ≥5 ft (1.5 m) are allowed to have an axle weight up to 20 kips/lane (90 KN/lane), should also be evaluated. The objective of this paper was to investigate the impact of the wheel-line spacing of four-wheel dual-lane loads on lateral live-load distribution on slab-on-girder bridges. Twen...

In this paper, finite-element analysis (FEA) of the prestressed concrete-steel composite (PCSC) girder is performed to investigate strain and stress distributions in the girder sections and determine the influence of stud distribution on stresses in the concrete bottom flange. Approaches of FEA are discussed for the material and element models of steel, concrete, and strands, and element models of the bond between the concrete and strand and the shear studs, loading and boundary conditions, and convergence issues. A PCSC girder specimen is fabricated and instrumented in the structural laboratory to validate the proposed fabrication and design procedures. FEA and service design using the age-adjusted elasticity modulus method (AEMM) are both validated using the strain profiles at different sections and values of concrete surface strains and camber/deflection. Test results indicate that the cracking moment, ultimate moment, and ultimate shear of the PCSC girder can be well predicted using the AEMM a...

A new prestressed concrete-steel composite (PCSC) girder system is developed to provide a viable alternative for steel and prestressed concrete I-girders in bridges. The PCSC girder is composed of a lightweight W-shaped steel section with shear studs on its top and bottom flanges to achieve composite action with the pretensioned concrete bottom flange and the cast-in-place concrete deck. The PCSC girder is lightweight, economical, durable, and easy to fabricate. The proposed fabrication procedure is similar to those of prestressed concrete girders and does not need specialized equipment, materials, and forms. A service design procedure is proposed using the age-adjusted elasticity modulus method to evaluate the time-dependent stresses and strains in the PCSC girder caused by creep and shrinkage effects of concrete and relaxation of strands. The strength design method is proposed for the design of PCSC girders at prestress release. A design procedure is proposed to assist engineers to accomplish economic design and production of PCSC girders, and design examples are presented to illustrate the design procedure.

Strength design method for pretensioned flexural concrete members at prestress release was developed in 2001 as a rational alternative to the working stress design method. Load and resistance factors for the developed strength design method were selected to match those used in similar applications (e.g., tied columns) without reliability-based calibration. The purpose of this paper is to present the calibration of resistance factors for the strength design of pretensioned flexural concrete members at release to achieve a target reliability index of 3.5. Resistance models were developed to capture material, fabrication, and professional uncertainty. Statistical parameters of load and resistance were obtained from the literature. Formulae for strength design at release were developed for rectangular and flanged sections in cases when top reinforcement is needed and when top reinforcement is not necessarily needed. Reliability analysis was conducted for several rectangular and inverted-T sections and resistance factors of 0.75 and 0.70 were recommended in light of the results for 5 ksi (34.5 MPa) and 8 ksi (55.2 MPa) concrete strengths, respectively. Moreover, a simplified design procedure was proposed to assist designers and producers in applying the strength design method at prestress release. Three design examples were also presented and compared against those designed using the working stress method.

Concrete-filled steel tubes have been widely used in building and bridge construction. In this paper, the flexural behaviour of concrete-filled steel tubes is investigated using finite-element analysis and theoretical sectional analysis. The numerical results from both analytical methods are validated against published experimental test results. It is shown that both methods are capable of predicting the elastic and the ultimate moment capacities of concrete-filled steel tubes. Due to its computational efficiency, theoretical sectional analysis is more suitable for the design of concrete-filled steel tubes than finite-element analysis.

Because the deterioration rate of bridge decks is higher than that of other bridge components, intermittent replacement of bridge decks stands to be a viable approach to extending bridge service life without replacing entire bridge components. A lack of understanding of the effects of concrete removal on the horizontal shear capacity of existing shear connectors led to a question being raised about the necessity of removing all of the concrete during a deck replacement. The purpose of this study is to investigate the influence of the remaining concrete around the shear connectors on the horizontal shear capacity of the shear connection. An experimental program consisting of push-out testing was implemented. Twenty-seven small-scale specimens were fabricated using three different concrete removal levels (50%, 75%, and 100% concrete removal) and three types of shear connectors (shear stud, channel, and angle plus bar). Push-out testing was conducted for all the fabricated specimens until the specime...

Nine simply supported circular steel concrete-filled tubes (CFTs), two circular steel posttensioned concrete-filled tubes (PTCFTs), and one circular steel fiber–reinforced concrete-filled tube (FRCFT) have been tested in an instrumented drop-weight impact facility. The weight and the height of the drop-weight were varied to cause failure in some test specimens. The failure modes and local damages in those specimens have been investigated extensively. Failure in the steel tubes was commonly tensile facture or rupture along the circumference. Concrete core in the impact area commonly crushed under compression and cracked under tension. The use of prestressing strands and steel fibers significantly restrained the concrete tension cracks in the PTCFT and FRCFT specimens, respectively. The experimental results are analyzed in the context of principles of energy and momentum conservation.

Concrete-filled circular steel tubes (CFT) have recently gained significant attention for their enhanced strength and ductility over the conventional steel and reinforced concrete construction. The concrete compressive strength is significantly increased by the lateral confinement provided by the steel tube and local buckling of the steel tube is restrained by the concrete infill. This paper investigates the further enhancement of these composite actions due to post-tensioning the concrete cores inside circular steel tubes. The flexural behavior of a post-tensioned CFT as well as a non-post-tensioned CFT was studied experimentally and analytically. A numerical algorithm for predicting the moment capacities of circular CFT, with or without the post-tensioning effects, has been validated against the test results by the authors as well as those published in the literature.

Infrastructures and key members are potentially exposed to accidental loads due to extreme situations such as collisions, impacts, and terrorist bombings. Consequently, the current design concept requires that the structures or key members possess adequate capacities to resist accidental loads. To understand the mechanical response of concrete-filled steel tube (CFT) beams subjected to impact loads, this paper presents numerical simulations on the CFT beam tests in an instrumented drop-weight impact facility using finite element code LS-DYNA. The adequacy of finite element modeling (FEM) has been validated against drop-hammer impact tests in the literature. Based on the dynamic increase factors (DIFs) derived from FEM, an algorithm based on theoretical sectional analysis (TSA) is introduced to evaluate the dynamic plastic moment capacity of CFT beams. A linear relationship between initial impact energies and absorbed energies by CFT beams is found using either FEM or TSA. To assist engineers in designing simply supported circular CFT beams subjected to lateral impact, an energy design procedure using TSA is proposed, along with the ranges of key parameters, and an example is presented to illustrate the design procedure.