Yaohua Deng

Flexural Behavior of Concrete-Filled Circular Steel Tubes under High-Strain Rate Impact Loading

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.

Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. II: Finite-Element Analysis and Experimental Investigation

AbstractIn 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...

Impact of Concrete Deck Removal on Horizontal Shear Capacity of Shear Connections

Due to the higher deterioration rate of bridge decks compared to 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 question was raised regarding the necessity of removing all of the concrete during a deck replacement due to a lack of understanding of the effects of the extent and quality of concrete removal on the horizontal shear capacity. 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 (i.e., 50%, 75% and 100% concrete removal) and three types of shear connectors (i.e., shear stud, channel and angle-plus-bar). Push-out testing was conducted for all the fabricated specimens until the specimens failed. During testing, the ultimate horizontal shear load of each shear connection and the slip between the concrete deck and the steel girder were recorded. The failure modes of all specimens were also documented. Simplified analysis and finite element (FE) analysis were conducted to assist understanding and interpreting the test results. It was found that the horizontal shear strengths of the shear stud shear connection and the channel shear connection were not sensitive to the quantity of concrete removed.

Efficient Prestressed Concrete-Steel Composite Girder for Medium-Span Bridges. I: System Description and Design

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.

Lateral Live-Load Distribution of Dual-Lane Vehicles with Nonstandard Axle Configurations

AbstractThe 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...

Performance Evaluation of Transverse High-Performance Concrete Closure Pour Connection for Use in Modular Bridge Construction

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.

Performance Evaluation of Longitudinal Ultrahigh-Performance Concrete Closure Pour Connection for Use in Modular Bridge Construction: Pairwise Comparison of Capacity and Ductility at Failure Limit State

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.

Calibration of Strength Design of Pretensioned Flexural Concrete Members at Release

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.