Shear live load analysis of NEXT beam bridges for accelerated bridge construction

Using precast concrete elements in bridge structures has emerged as an economic and durable solution to enhance the sustainability of bridges. The northeast extreme tee (NEXT) beams were recently developed for accelerated bridge construction by the Precast/Prestressed Concrete Institute (PCI). To date, several studies on the live load distribution factor (LLDF) for moment in NEXT F beam bridges have been reported. However, the LLDFs for shear in NEXT F beam bridges are still unclear. In this paper, the lateral distributions of live load shear in NEXT F beam bridges were examined through a comprehensive parametric study. The parameters covered in this study included bridge section, span length, beam section, number of beams, and number of lanes loaded. A validated finite element (FE) modeling technique was employed to analyze the shear behavior of NEXT F beam bridges under the AASHTO HL-93 loading and to determine the LLDFs for shear in NEXT beam bridges. A method for computing the FE-LLDF for shear was proposed for NEXT beam bridges. Results from this study showed that the FE-LLDFs have a similar trend as the AASHTO LFRD-LLDFs. However, it was observed that some LRFD-LLDFs are lower than the FE-LLDFs by up to 14.1%, which implied using the LRFD-LLDFs for shear could result in an unsafe shear design for NEXT beam bridges. It is recommended that a factor of 1.2 be applied to the LRFD-LLDF for shear in NEXT F beam bridges for structural safety and design simplicity.

Estimation of Live Load Distribution Factor for a PSC I Girder Bridge in an Ambient Vibration Test

Maintenance of bridges in use is essential and measuring the live load distribution factor (LLDF) of a bridge to examine bridge integrity and safety is important. A vehicle loading test has been used to measure the LLDF of a bridge. To carry this out on a bridge in use, traffic control is required because loading must be performed at designated positions using vehicles whose details are known. This makes it difficult to measure LLDF. This study proposed a method of estimating the LLDF of a bridge using the vertical displacement response caused by traveling vehicles under ambient vibration conditions in the absence of vehicle control. Since the displacement response measured from a bridge included both static and dynamic components, the static component required for the estimation of LLDF was extracted using empirical mode decomposition (EMD). The vehicle loading and ambient vibration tests were conducted to verify the validity of the proposed method. It was confirmed that the proposed method can effectively estimate the LLDF of a bridge if the vehicle type and driving lane on the bridge are identified in the ambient vibration test.

Structural Design Issues For Integral Abutment Bridges

In recent years, integral abutment bridges have been increasingly used in Canada due to their low maintenance costs. Whereas a rational guideline to determine the maximum length and skew angle limits for integral bridges due to temperature variations do not exist in bridge codes. As such, structural behavior of integral bridges subjected to temperature variation was investigated through a numerical modeling. First, detailed 3D finite-element models were developed. The accuracy of finite-element models was validated against data collected from filed testing available in the literature on integral bridges subjected to the seasonal temperature variations and truck loading. Then, a parametric study was carried out to study the effects of key parameters on the performance of integral bridges when subjected to temperature variations. The numerical results indicated that number of design lanes, bridge length, abutment height, abutment-pile connection, pile size and skew angle had a significant impact on the behavior of integral bridges. Based on the data generated from the parametric study, new limits for the maximum length and skew angle of integral bridges based on displacement-ductility limit state of piles were established. Literature review revealed that live load distribution among girders in integral bridges due to truck loading conditions is as yet unavailable. This study is extended to develop new equations to estimate girder live load distribution factors for integral bridges. First, 2D and 3D finite-element models (FEMs) of integral bridges were developed. Then, a parametric study was performed to study the effects of parameters such as abutment height, abutment thickness, wingwall length, wingwall orientation, number of design lanes, span length, girder spacing and number of intermediate diaphragms. The results indicated that the live load distribution factors obtained from the FEMs were lower than those obtained from current CHBDC equations. Consequently, sets of empirical expressions were developed in the form of reduction factors that can be applied to CHBDC live load distribution factors to accurately calculate the girder distribution factors. Also, other set of equations for the live load distribution factors were developed in a similar form as that specified in CHBDC for possible inclusion in the bridge code.

Structural Design Issues For Integral Abutment Bridges

In recent years, integral abutment bridges have been increasingly used in Canada due to their low maintenance costs. Whereas a rational guideline to determine the maximum length and skew angle limits for integral bridges due to temperature variations do not exist in bridge codes. As such, structural behavior of integral bridges subjected to temperature variation was investigated through a numerical modeling. First, detailed 3D finite-element models were developed. The accuracy of finite-element models was validated against data collected from filed testing available in the literature on integral bridges subjected to the seasonal temperature variations and truck loading. Then, a parametric study was carried out to study the effects of key parameters on the performance of integral bridges when subjected to temperature variations. The numerical results indicated that number of design lanes, bridge length, abutment height, abutment-pile connection, pile size and skew angle had a significant impact on the behavior of integral bridges. Based on the data generated from the parametric study, new limits for the maximum length and skew angle of integral bridges based on displacement-ductility limit state of piles were established. Literature review revealed that live load distribution among girders in integral bridges due to truck loading conditions is as yet unavailable. This study is extended to develop new equations to estimate girder live load distribution factors for integral bridges. First, 2D and 3D finite-element models (FEMs) of integral bridges were developed. Then, a parametric study was performed to study the effects of parameters such as abutment height, abutment thickness, wingwall length, wingwall orientation, number of design lanes, span length, girder spacing and number of intermediate diaphragms. The results indicated that the live load distribution factors obtained from the FEMs were lower than those obtained from current CHBDC equations. Consequently, sets of empirical expressions were developed in the form of reduction factors that can be applied to CHBDC live load distribution factors to accurately calculate the girder distribution factors. Also, other set of equations for the live load distribution factors were developed in a similar form as that specified in CHBDC for possible inclusion in the bridge code.

Field Determined Live Load Distribution Factors for Modular Press-Brake-Formed Tub Girders

This paper is focused on the field performance of a modular press-brake-formed tub girder (PBFTG) system in short span bridge applications. The scope of this project to conduct a live load field test on West Virginia State Project no. S322-37-3.29 00, a bridge utilizing PBFTGs located near Ranger, West Virginia. The modular PBFTG is a shallow trapezoidal box girder cold-formed using press-brakes from standard mill plate widths and thicknesses. A technical working group within the Steel Market Development Institute’s Short Span Steel Bridge Alliance, led by the current authors, was charged with the development of this concept. Research of PBFTGs has included analyzing the flexural bending capacity using experimental testing and analytical methods. This paper presents the experimental testing procedures and performance of a composite PBFTG bridge.