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Strain-hardening fiber-reinforced concrete (SH-FRC), such as ultrahigh-performance concrete (UHPC), offers sustained tensile capacities up to high values of postcracking strains and, consequently, delivers shear resistance through different mechanisms than conventional concrete. Existing shear design methods for conventional concrete beams include empirical approximations of the tensile resistance offered by the cracked concrete that do not apply to SH-FRC materials. This article presents a design formulation that predicts the shear capacity of SH-FRC beams in support of ongoing efforts to develop UHPC structural design guidance in the United States. The proposed model leverages foundational concepts from engineering mechanics, similar to the modified compression-field theory (MCFT) for conventional reinforced and prestressed concrete, while integrating relationships that address behaviors specific to SH-FRC. The model predicts shear stress versus shear strain behavior of a cracked SH-FRC membrane element, which is then used to model the web of a beam. Verified against experimental shear test results of I-shaped prestressed and non-prestressed beams with different material properties, beam geometries, axial strains, and transverse reinforcement ratios, the proposed shear design model is demonstrated to conservatively predict the shear capacity of SH-FRC beams. As such, this work constitutes a fundamental step in developing mechanics-based SH-FRC shear design guidance. [ABSTRACT FROM AUTHOR]

In this study, the flexural behavior tests of steel fiber reinforced concrete beams with BFRP bars under static load are carried out by means of statics experiment and theoretical analysis. A total of seven beams were designed for this experiment, and the effects of two factors on the mid-span deflection of the beams were investigated with the steel fiber incorporation rate (0%, 0.5%, 1%, 1%/0.5%, 1.5%) and the height of steel fibers in the concrete layer in the compression zone (180 mm, 210 mm, 300 mm) as the main variables. In this study, based on the existing research results and combined with the actual test results, the formulae for calculating the cracking section moment of inertia applicable to BFRP reinforced steel fiber (full section/pressure zone reinforced) concrete beams are derived. At the same time, the results obtained from the formula and the results of the ACI code in the United States are compared with the data of the results obtained from this test, and the calculated results of this formula are in good agreement with the actual values. [ABSTRACT FROM AUTHOR]

Stainless steel strands are a new technology and option available for the bridge industry. They have high corrosion resistance, which will result in more durable and low-maintenance concrete bridges. However, stainless steel strands have lower ductility and different stress–strain behavior than carbon steel strands, affecting the design criteria for prestressed concrete girders. Stainless steel strands have already been deployed in substructure components (piles) in many projects around the United States. However, due to their low ductility and lack of full-scale research studies and structural design approaches, they have not yet been deployed in flexural members. This study investigates the flexural behavior of stainless steel strand prestressed concrete girders. Five full-scale 12.8-m (42-ft)-long AASHTO Type II girders prestressed with 15.2-mm (0.6-in.)-diameter duplex high-strength stainless steel (HSSS) strands were designed, fabricated, and tested in flexure. The prestressing reinforcement ratio was varied in this experimental program. The transfer length and prestress losses of 15.2-mm (0.6-in.)-diameter HSSS strands were measured. The flexural behavior of the girders was assessed by the evaluation of cracking load, ultimate load-carrying capacity, load-deflection response, and failure mode. As designed, all girders failed due to rupture of the HSSS strands. Experimental results showed that, although the HSSS strand has low ductility and it may control the capacity of the girders, adequate warning (noticeable deflection and many cracks before failure) can be achieved in HSSS strand prestressed concrete girders. The predicted analytical and numerical moment strengths of the five girders were in close agreement with those measured experimentally. Although the analytical model gave better predictions, the numerical approach is easier to use for design. A flexural design approach for HSSS strand prestressed concrete I-girders is proposed where rupture of strands is an acceptable failure mode. The findings from this experimental program will be useful for the development of new design specifications for concrete girders prestressed with stainless steel strands. [ABSTRACT FROM AUTHOR]

Many bridge owners have developed new precast, prestressed concrete bridge girder sections that are optimized for high-performance concrete and pretensioning strands with diameters greater than 0.5 in. (12.7 mm). Girder sections have been developed for increased span capacities, while others fill a need in shorter span ranges. Accurate geometric properties are essential for design. Common properties, including cross-sectional area, location of centroid, and major axis moment of inertia, are generally easy to compute and are readily available in standard design references. Computation of the torsion constant is a different matter. This paper presents the methods and results of a study to determine the torsion constant for many of the modern precast, prestressed concrete bridge girders used in the United States and compares the results with values from the approximate methods of the AASHTO LRFD specifications. [ABSTRACT FROM AUTHOR]

• A splitting resistance equation was proposed for highly prestressed UHPC girders. Ultra-high performance concrete (UHPC) has gained popularity gradually because of its superior mechanical properties, including high compressive and tensile strengths, and exceptional durability. Many researchers have explored the possibility of using long, precast prestressed UHPC girders in buildings and bridges. To do so, the girders generally require a large number of prestressing strands, which causes concern about potential cracking in the end zones at prestress release. Currently, there are no specifications or codes on end zone designs for precast prestressed UHPC girders in the United States. Thus, this paper presents an analytical study that explores highly prestressed UHPC girders' end zone behavior. Finite element analyses were conducted to analyze the end zones of a series of UHPC girders, including one 889-mm-deep and two 813-mm-deep I-girders, and the analysis results were validated with test data. Additional finite element models were developed for other girders with heights of 1,829 mm and 2,743 mm using various reinforcement details. Bursting stress variations in the reinforcement and UHPC were reported based upon the analytical and test results. An equation for splitting resistance attributable to the reinforcement and UHPC was proposed for highly prestressed girders. [ABSTRACT FROM AUTHOR]

Abstract: The high shear capacity of ultra-high performance concrete (UHPC) AASHTO Type II girders tested at the Federal Highway Administration labs resulted in interest by state highway agencies in applying UHPC in bridge construction. UHPC superior shear capacity results from the random steel fibers incorporated in the mix. However, steel fibers significantly increase the mix material cost (fibers cost $400 per cubic yard). This paper presents a study to compare the structural efficiency and economical feasibility of replacing random steel fibers with grade 80 welded wire reinforcement meshes. Two AASHTO Type II girders were fabricated using non-proprietary UHPC mixes developed at the University of Nebraska – Lincoln and reinforced with WWR in replacement of steel fibers. The test results showed that WWR resulting shear capacity exceeds random steel fibers. The WWR cost effectiveness and ease in construction could accelerate the application of non-proprietary UHPC and WWR in bridge construction. [Copyright &y& Elsevier]

Bridge structures nationwide across the United States are aging and in need of repair or, in some cases, full replacement. Repair decisions are common among bridge owners because of the economic feasibility when compared to the higher cost of full replacement of damaged or deteriorated bridge components such as girders. Using a proper repair approach, as a long-term or just a short-term solution, can lead to benefits that could not be achieved otherwise such as considerable savings in both time and cost. Additionally, an appropriate repair approach can help avoid adverse environmental impacts, interruptions to service, overburdening of nearby infrastructure, and local opposition to construction. The main objective of this paper is to provide a synthesis of the repair methods and materials for reinforced concrete bridge girders proposed in research studies, i.e., state-of-the-art as well as state-of-the-practice established methods. Different steps in the general repair procedure are explained first. Next, a detailed description of three common bridge girder deficiencies, i.e., shear, flexural, and fire damage, is provided. For each damage type, the main causes and common solutions found in the literature are presented. The authors then provide specific recommendations to each repair procedure. This is intended to enable researchers, engineers, and decision makers to compare the available repair methods more conveniently to find the optimal repair approach for specific projects based on economic and environmental requirements as well as structural and construction conditions. [ABSTRACT FROM AUTHOR]

Many bridges along the Gulf Coast of the United States were damaged by hurricanes, especially in the 2004 and 2005 hurricane seasons. Many more bridges are susceptible to similar damage. This research examines the structural performance of three commonly used connection details for AASHTO Type III prestressed concrete girders: headed studs, through bolts, and clip bolts. Full-scale specimens were fabricated and tested under static and dynamic cyclic load histories using expected maximum loads from previously conducted hydraulic tests of a scale model of a highway bridge spanning a coastal embayment. The load effects considered included (1) vertical uplift force, (2) lateral force, (3) combined lateral and vertical forces, and (4) dynamically applied wave force time histories. Connection performance was evaluated by comparing initial concrete cracking, strand slip, and ultimate capacity. The experimental results showed that the insert clip-bolt connections had the lowest capacity and produced significant ancillary damage to the surrounding concrete while the headed-stud connections exhibited the highest load capacity and negligible ancillary concrete damage. None of the anchorages considered would be capable of resisting newly specified vertical wave forces for large hurricane wave heights when significant air is entrapped such as those observed in Hurricane Katrina. [ABSTRACT FROM AUTHOR]

The shear contribution of transverse steel in reinforced concrete beams is generally assumed as independent of the concrete strength by most of the building codes. The shear strength of RC beams with web reinforcement is worked out by adding the individual contributions of concrete and stirrups. In this research 70 beams of medium strength concrete in the range of 52-54 MPa, compressive strength were tested in two sets of 35 beams each. In one set of 35 beams no web reinforcement was used, whereas in second set of 35 beams web reinforcement was used to check the contribution of stirrups. The values have also been compared with the provisions of ACI, Eurocode and Japanese Code building codes. The results of two sets of beams, when compared mutually and provisions of the building codes, showed that the shear strength of beams has been increased with the addition of stirrups for all the beams, but the increase is non uniform and irregular. The comparison of observed values with the provisions of selected codes has shown that EC-02 is relatively less conservative for low values of longitudinal steel, whereas ACI-318 overestimates the shear strength of RC beams at higher values of longitudinal steel. The Japanese code of JSCE has given relatively good results for the beams studied. [ABSTRACT FROM AUTHOR]