Category: Technical Report

Title and Subtitle: 

Impact on Construction Loads on Steel Diaphragm Bridge Design

Lead PI: 

Lauren Stewart

Lead Affiliate: 

Georgia Institute of Technology

Co Pi: 

Lawrence Kahn (Georgia Institute of Technology); Yang Wang (Georgia Institute of Technology); Nadine Fahed (Georgia Institute of Technology)

Abstract: 

Bridges are critical structures, serving an important function that is vital to the safe and economical conveyance of people and goods throughout Georgia. They are designed with specifications to carry loads including their self-weight and a design vehicle load, among others, when they are in service. Satisfying all design specifications is crucial to the structure’s strength, stiffness, stability, and durability throughout its lifetime. In addition to the in-service dead and live load conditions, bridges are also designed to accommodate various loading conditions during the construction process. In some cases, these construction load and associated stability requirements are the governing load conditions for some of the bridges’ components. Georgia Department of Transportation (GDOT) has recently allowed the substitution of steel diaphragms for concrete diaphragms in its bridges. This substitution is gaining popularity among contractors for its ease of construction and subsequent reduction of cost. Currently, there is no standardized design for GDOT steel diaphragms, and contractors are allowed to produce their own designs based on loading scenarios currently specified in the 2018 GDOT Bridge and Structures Design Manual. These scenarios include full long-term wind loadings and are thought to be overly conservative because the actual loads to which the bridges are subjected during the construction process are poorly understood. This project seeks to provide the data and recommendations for a more efficient, yet safe, steel diaphragm design. Specifically, this project will (1) observe and measure GDOT construction practices through visual observations by experts and by electronic sensors, (2) quantify the effects of the construction practices in terms of loadings via observations and computational models, (3) assess the overall impact of construction load variations on bridge designs, and (4) make recommendations to GDOT for loading specifications and for a standardized steel diaphragm design.

NTL Report: 

GDOT RP 18-02

Title and Subtitle: 

Development of GDOT Ultra-High Performance Concrete for Bridge Deck Closure Pours

Lead PI: 

Lauren Stewart

Lead Affiliate: 

Georgia Institute of Technology

Co Pi: 

Lawrence Kahn (Georgia Institute of Technology); Kimberly Kurtis (Georgia Institute of Technology); Giovanni Loreto (Georgia Institute of Technology)

Abstract: 

The use of precast prestressed girders with composite precast deck panels along with the use of precast prestressed deck bulb-T girders provide for more economical bridges because of their ability to utilize accelerated bridge construction techniques. The use of concrete deck panels and deck bulb-T systems require the use of closure pours between the units. Ductal™, a proprietary ultra-high performance concrete (UHPC), has been shown to provide an outstanding link between deck segments for closure pours as narrow as 6-in, but Ductal is expensive. This research develops a concrete based on locally available materials (GDOT-UHPC), which has a direct tensile strength greater than 750 psi and ductility and toughness under tensile loads such that the concrete can develop the tensile yield stress of #5 (⅝-in. diameter) reinforcing bars within a 5-in. embedment length. Minimizing the width of the closure between deck and bulb-T units provides further economies by greatly simplifying formwork and eliminating shoring. Testing assured not only the short development length of reinforcement but also ultimate strength capacity of transverse and longitudinal closure pours. Further, best practices for formwork, closure design, UHPC mixing and placement, and quality assessment are considered.

NTL Report: 

GDOT RP 18-01