Stiffness and strength of metal bridge deck forms

Light gauge metal sheeting is often utilized in the building and bridge industries for concrete formwork. Although the in-plane stiffness and strength of the metal forms are commonly relied upon for stability bracing in buildings, the forms are generally not considered for bracing in steel bridge construction. The primary difference between the forming systems in the two industries is the method of connection between the forms and girders. In bridge construction, an eccentric support angle is incorporated into the connection details to achieve a uniform slab thickness along the girder length. While the eccentric connection is a benefit for slab construction, the flexible connection limits the amount of bracing provided by the forms. This paper presents results from the first phase of a research study investigating the bracing behavior of metal bridge deck forms. Shear diaphragm tests were conducted to determine the shear stiffness and strength of bridge deck forms, and modified connection details were developed that substantially improve the bracing behavior of the forms. The measured stiffness and strength of diaphragms with the modified connection often met or exceeded the values of diaphragms with conventional noneccentric connections. The experimental results for the diaphragms with the modified connection details dramatically improve the potential for bracing of steel bridge girders by metal deck forms

Partial Depth Precast Concrete Deck Panels on Curved Bridges: Finite Element Analytical Model of PCPs

Report on partial depth precast concrete deck panels on curved bridges

Evaluation of Seamless Bridges

0-7011The research study included experimental testing and numerical modeling to obtain and develop much needed experimental data and analytical tools to study the performance of seamless systems, identify design issues, and propose design guidelines for the U.S. practice

Improved Tub Girder Details: Final Report

0-6862Steel trapezoidal box girders, generally referred to as tub girders, have been widely used on a number of bridges throughout the State of Texas. The smooth profile of the girder systems provides an aesthetically appealing bridge that also possesses several structural advantages compared to other girder types. Due to the significant torsional stiffness of the closed box section, the girders are a popular choice in horizontally curved systems where the bridge geometry leads to large torsional moments. The girders have also been used on a number of straight girder systems throughout the state leading to improved bridge aesthetics. While tub girders have primarily been used on bridges with longer spans where concrete girders are not viable, an application of relatively shallow steel tub girders was recently used in the TxDOT Waco District on a bridge with span lengths normally reserved for concrete girder systems. The resulting bridge provided an aesthetically appealing structure that satisfied a demanding vertical clearance requirement and was cost-comparable with precast concrete girders. This shallow tub girder application demonstrates that steel trapezoidal box girders offer a viable alternative that should be considered for a wider variety of bridge applications. However, to augment the viability of tub girders, improved details need to be considered to further enhance their economic and structural advantages. Modifications in the girder geometry can provide more efficient systems. The objective of this research is to develop improved details for tub girders as well as design methodologies for the girders and bracing components

Fatigue Resistance and Reliability of High Mast Illumination Poles (HMIPs) with Pre-Existing Cracks: Final Report

0-6829High mast illumination poles (HMIPs) are used throughout Texas and the U.S. to provide lighting along highways and at interchanges. Texas currently has about 5000 HMIPs, varying in height from 100 to 175 ft. Failures of HMIPs have been reported in several states, attributed to failures at the shaft-to-base plate connection. No collapses of HMIPs have been reported in Texas. However, recent studies have shown that many galvanized HMIPs in Texas have pre-existing cracks at their shaft-to-base plate connection, most likely caused by the galvanization process before the poles were placed in service. Previous research has also shown that pre-existing cracks may significantly reduce the fatigue life of galvanized HMIPs. The Texas Department of Transportation (TxDOT) has identified three major issues/concerns with respect to HMIPs with pre-existing cracks: the lack of reliable experimental data about the fatigue life of pre-cracked HMIP base-connection details; the significant uncertainty regarding the natural wind response of HMIPs to the various major wind environments in Texas (much of this uncertainty is related to the lack of measured data from comprehensive field studies); and, due to this lack of data, the \u2018safe/serviceable\u2019 life of in-service TxDOT HMIPs with pre-existing cracks cannot be reliably predicted. The main goal of this research project was to generate data and information to support a probabilistic-based assessment of the remaining life of HMIPs with pre-existing cracks. The research included extensive laboratory fatigue testing of HMIPs with pre-existing cracks, field monitoring of in-service HMIPs at five locations across Texas, and the development of a reliability based framework to assess the safety of in-service HMIPs with pre-existing cracks. The results of this study show a wide range in the predicted lives of HMIPs with pre-existing cracks at different locations throughout the state. Based on a probability of failure of 5 percent, the predicted fatigue life at a number of locations analyzed throughout the state showed predicted lives varying from approximately 30 years to over 300 years. The variation in predicted lives is mainly affected by differing wind characteristics at each location

Applications of Partial Depth Precast Concrete Deck Panels on Horizontally Curved Steel and Concrete Bridges

0-6816Horizontally curved bridges are commonly used for direct connectors at highway intersections as well as other applications. The majority of curved bridges utilize continuous steel curved I-girder or tub girder systems. In recent years, isolated applications of spliced prestressed concrete U-beams have been successfully used for curved bridge applications in Colorado and are currently being considered for use in Texas bridges. One of the most critical construction stages from a stability perspective is placement of the wet concrete deck at which point the girders must support the full construction load of the system until the deck stiffens and acts compositely. Bridges with a curved geometry experience significant torsional forces and require a substantial amount of bracing to control deformation during construction. Bracing in the form of cross frames for steel I-girder systems, top lateral trusses for steel tub girder systems, and lid slabs for concrete U-beams are provided to improve the girder behavior. While partial depth precast concrete panels (PCPs) are commonly used as stay-in-place formwork for straight bridges, the panels are not currently permitted on horizontally curved girder systems in Texas. TxDOT would like to extend the use of PCPs to bridges with curved girders. This report focuses on the stability of PCPs that rest on polystyrene bedding strips. The project studied the behavior for PCPs with and without a positive connection to steel girders and also considered the behavior of the current TxDOT reinforcing details for PCPs with concrete U-beam systems. The experimental portion of this study consists of large-scale PCP shear tests and large-scale combined bending and torsion tests on both a twin steel I-girder system and on a single steel tub girder. The PCP shear tests were used to develop a simple and effective connection between the PCPs and the girder, as well as to empirically determine the in-plane stiffness and strength of the PCP/connection system. The large-scale girder tests were used to investigate the performance of PCPs and their connection to a system that simulates the load experienced in a realistic construction situation. Also, parametric finite element modeling of the PCPs and the curved girder systems were performed and validated with the results from the experimental tests. The finite element models were used to develop an understanding of the fundamental behavior of the steel girder systems in combination with the PCP systems. In addition to focusing on connection methods to the PCPs, guidelines were also developed for cases where the panels can be used on horizontally curved girder systems without a positive connection to the girders

Buckling behavior of steel bridge I-girders braced by permanent metal deck forms

Permanent metal deck forms (PMDFs) are often used in the bridge industry to support wet concrete and other loads during construction. Although metal formwork in the building industry is routinely relied on for stability bracing, the forms are not permitted for bracing in the bridge industry, despite the large in-plane stiffness. The forms in bridge applications are typically supported on cold-formed angles, which allow the contractor to adjust the form elevation to account for changes in flange thickness and differential camber between adjacent girders. Although the support angles are beneficial toward the constructability of the bridge, they lead to eccentric connections that substantially reduce the in-plane stiffness of the PMDF systems, which is one of the reasons the forms are not relied on for bracing in bridge applications. This paper documents the results of an investigation focused on improving the bracing potential of bridge deck forms. Modifications to the connection details were developed to improve the stiffness and strength of the forming system. Research included buckling tests on a 15-m (50-ft) long, twin-girder system with PMDFs for bracing. In addition, twin-girder tests were also used to validate computer models of the bracing systems that were used for parametric finite-element analytical studies. The buckling test results demonstrated that modified connection details make PMDF systems a viable bracing alternative in steel bridges, which can significantly reduce the number of cross-frames or diaphragms required for stability bracing of steel bridge I-girders during construction.TxDO

Lateral stiffness of steel bridge I-girders braced by metal deck forms

The lateral-torsional buckling capacity of steel bridge girders is often increased by incorporating bracing along the girder length. Permanent metal deck forms (PMDF) that are used to support the wet concrete deck during bridge construction are a likely source of stability bracing; however, their bracing performance is greatly limited by flexibility in the connections currently used with the formwork. This paper outlines results from a research study that assessed and improved the bracing potential of metal deck forms used in bridge applications. The research study included shear tests of PMDF panels, and also lateral displacement and buckling tests of twin girder systems braced with PMDF. This paper will provide key results from the shear panel tests and then focus on the lateral displacement tests. Parametric investigations of PMDF bracing behavior were conducted using finite-element analyses and the results from the lateral displacement tests served a critical role in calibrating the finite element models. This paper documents key results from lateral load tests of 17 girder-PMDF systems using a variety of bracing details and PMDF thickness values. © 2009 ASC