Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Concept Development

This paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck that is cast and prestressed with the girder provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is a perceived problem with durability of longitudinal joints used to connect adjacent girders. This paper presents the results of a study to assess potential alternate joint details based on constructability, followed by testing of selected details. Seven reinforced concrete beam specimens connected with either lapped headed reinforcement or lapped welded wire reinforcement were tested along with a specimen reinforced by continuous bars for comparison. Test results were evaluated based on flexural capacity, curvature at failure, cracking, deflection, and steel strain. Based on the survey and the experimental program, a headed bar detail with a 152 mm (6 in.) lap length was recommended for replacing the current welded steel connector detail.     

Improved Longitudinal Joint Details in Decked Bulb Tees for Accelerated Bridge Construction: Fatigue Evaluation

This companion paper focuses on an investigation of improved continuous longitudinal joint details for decked precast prestressed concrete girder bridge systems. Precast concrete girders with an integral deck, which are cast and prestressed with the girder, provide benefits of rapid construction along with improved structural performance and durability. Despite these advantages, the use of this type of construction has been limited to isolated regions of the United States. One of the issues limiting more widespread use is the perceived problem with durability of longitudinal joints used to connect adjacent girders. Four full-scale slabs connected by No. 16 (#5) headed reinforcement detail using a 152 mm (6 in.) lap length were fabricated and tested. An analytical parametric study was conducted to provide a database of maximum forces in the longitudinal joint. These maximum forces are then used to determine the loading demand necessary in the slab testing due to the service live load. Static and fatigue tests under four-point pure-flexural loading, as well as three-point flexural-shear loading, were conducted. Test results were evaluated based on flexural capacity, curvature behavior, cracking, deflection, and steel strain. Based on these test results, the improved longitudinal joint detail is a viable connection system that transfers the forces between the adjacent decked bulb tee girders.     

Effect of Intermediate Diaphragms on Decked Bulb-Tee Bridge System for Accelerated Construction

One of the promising systems for accelerated bridge construction is the use of the decked precast prestressed concrete girders or decked bulb-tee girders for the bridge superstructure. Using the calibrated three-dimensional finite-element models through field tests, a parametric study was conducted to determine the effect of intermediate diaphragms on the deflections and flexural strains of girders at the midspan as well as the live load forces in the longitudinal joint. The following diaphragm details were considered: different diaphragm types (steel and concrete), different diaphragm numbers between two adjacent girders, and different cross-sectional areas for steel diaphragms. Five bridge models with different diaphragm details were developed, and the short span length effect on the bridge behavior was also studied. It was found that as long as one intermediate diaphragm was provided between two adjacent girders at midspan, changing the diaphragm details did not affect the girder deflection, the girder strain, and the live load forces in the longitudinal joint significantly. The effect of diaphragms on the midspan deflection was more prominent in the short span bridge; however, the reduction in the maximum bending moment by the diaphragms was more significant in the long span bridge than in the short span bridge. Specific design recommendation is provided in this paper.     

Live Load Distributions on an Impact-Damaged Prestressed Concrete Girder Bridge Repaired Using Prestressed CFRP Sheets

This paper describes detailed flexural behavior, including live load distributions, of a four-span prestressed concrete girder bridge supported by 14?m long C-shape girders (4 @ 14.05 = 56.2?m). The bridge has been damaged by frequent impact from heavy trucks, and repaired using prestressed carbon fiber-reinforced polymer sheets. A calibrated finite element analysis is conducted to investigate the flexural behavior (i.e., stress redistribution, deflection, live load distribution, and applied load effects) of the bridge in three different phases (i.e., undamaged, damaged, and repaired states) under various loading configurations. Strain localizations are noted at the damaged and repaired locations. Assessment of existing bridge codes such as the Association of State Highway and Transportation Officials Load Resistance Factor Design and Canadian Highway Bridge Design Code is conducted. The bridge codes predict well the nominal live load effect on the exterior girder, but underestimate the effect on the interior girders. A refined analysis may be recommended for this type of bridge.     

Collapse during Construction of a Precast Girder Bridge

This paper describes the collapse during construction of a precast concrete girder bridge crossing Highway 15, north of Montréal. The bearing conditions for the girders at the time of collapse are discussed. The tie rods that were used to restrain the movement of the girder top flanges were tested to determine their effective stiffness and strength. Rotational and sliding tests were also performed on the pot bearing units. These experimental results were used in an analytical study to confirm the sequence of collapse of the girders. Bracing requirements during construction for precast girder bridges supported on pot bearings are discussed.     

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.     

Nonlinear Flexural Behavior of Prestressed Concrete Girder Bridges

This paper presents a procedure to improve the accuracy of the classical grillage method for the nonlinear analysis of concrete girder bridges. The procedure uses equivalent element plastic hinge lengths that account for the actual mesh size instead of using a mesh-independent global plastic hinge length. A thorough review of the results of tests conducted on two 1∕3-model prestressed concrete girders and a 1∕3-model prestressed concrete girder bridge is undertaken in order to model the nonlinear properties of prestressed concrete girder bridges. The purpose of this review is to study the extent of plastification and plastic hinge length development as well as the evaluation of the validity of the grillage method for the nonlinear analysis of girder bridges. An Lp transfer model is used to calculate the plastic hinge length for every beam element of the grillage based on the results from the experiments and other empirical models. The Lp transfer model allows the use of empirical data obtained from tests on individual girders to model the response of a variety of bridge configurations subjected to different loading conditions. The equivalent grillage element plastic hinge length Lgp is calculated as a function of the grillage mesh size. A number of examples are presented to demonstrate the validity of the proposed method by comparing the analytical results of grillage analysis using the Lp transfer model with those of laboratory and in situ tests on full-scale and model-scale prestressed concrete bridges. The proposed approach has a high potential for use in engineering practice because of the simple input requirement and improved accuracy.     

Live Load Distribution Formulas for Single-Span Prestressed Concrete Integral Abutment Bridge Girders

In this study, live load distribution formulas for the girders of single-span integral abutment bridges (IABs) are developed. For this purpose, two and three dimensional finite-element models (FEMs) of several IABs are built and analyzed. In the analyses, the effects of various superstructure properties such as span length, number of design lanes, prestressed concrete girder size, and spacing as well as slab thickness are considered. The results from the analyses of two and three dimensional FEMs are then used to calculate the live load distribution factors (LLDFs) for the girders of IABs as a function of the above mentioned parameters. The LLDFs for the girders are also calculated using the AASHTO formulas developed for simply supported bridges (SSBs). The comparison of the analyses results revealed that LLDFs for girder moments and exterior girder shear of IABs are generally smaller than those calculated for SSBs using AASHTO formulas especially for short spans. However, AASHTO LLDFs for interior girder shear are found to be in good agreement with those obtained for IABs. Consequently, direct live load distribution formulas and correction factors to the current AASHTO live load distribution equations are developed to estimate the girder live load moments and exterior girder live load shear for IABs with prestressed concrete girders. It is observed that the developed formulas yield a reasonably good estimate of live load effects in prestressed concrete IAB girders.     

Evaluation of Prestressed Concrete Girders Strengthened with Carbon Fiber Reinforced Polymer Sheets

This paper details the use of carbon fiber reinforced polymer (CFRP) sheets to repair and strengthen prestressed concrete bridge girders in flexure and shear. Three specimens that were removed from an overloaded bridge (Bridge No. 56) in Graham County, Kansas were tested. Two of the specimens were repaired and strengthened, and all three were tested to failure to determine flexural capacity. Test results showed that two layers of longitudinal CFRP sheets increased the flexural capacity of the strengthened specimens by 20% compared to an unstrengthened control specimen. Shear capacity was also evaluated on both ends of each specimen. Two different cases were evaluated in shear. One case allowed shear cracks to propagate inside the transfer length of the prestressing strand, allowing a bond failure to occur. The second case forced the shear cracks to remain outside of the transfer length, thereby preventing a bond failure. The test results show that transverse CFRP sheets increased the shear capacity of the specimens tested by as much as 28%, but did not prevent bond failures.     

Demonstration of Use of High-Performance Lightweight Concrete in Bridge Superstructure in Virginia

The general objective of this research was the construction and evaluation of a bridge using high-performance lightweight concrete (HPLWC). The resulting bridge over the Chickahominy River near Richmond, Va., consists of 15 prestressed American Association of State Highway and Transportation Officials (AASHTO) Type IV girders made of HPLWC with a density of 1,920?kg/m3 and a minimum required 28-day compressive strength of 55?MPa. The bridge also has a lightweight concrete (LWC) deck with a density of 1,850?kg/m3 and a minimum required 28-day compressive strength of 30?MPa. This research study is chiefly concerned with investigating the effects of using lightweight concrete in prestressed girders on transfer length, development length, flexural strength, girder live-load distribution factor, and dynamic load allowance. Transfer length was determined to be 432?mm, or 33?db, for several girders at the time of prestress transfer. The development length was determined to be between 1,830 and 2,440?mm, while the flexural strength ranged from 11 to 30% higher than the AASHTO flexural capacity. The measured distribution factors and dynamic load allowance were smaller than the AASHTO standard and LRFD values.