Research

Concrete Structural Engineering

Shear Behavior of Spliced Post-Tensioned Girders with Ungrouted Tendons

This experimental study was developed to evaluate the performance of spliced, post-tensioned girders with grouted and ungrouted tendons. The spliced girder elements are subjected to significant shear forces. The current shear design provisions in the AASHTO LRFD, include shear strength reduction factors to account for the presence of the duct in the web and its condition (i.e., grouted or ungrouted). These factors are applied to the shear resistance provided by the concrete component, as well as to the shear resistance provided by the shear reinforcement. The reduction factors in AASHTO LRFD were developed from a limited database that did not include ungrouted post-tensioning systems, resulting in incomplete code specifications. This lack of knowledge served as motivation for this study presented herein. The test serve as validation studies for updated shear strength reduction factors proposed for implementation in AASHTO LRFD.

Concrete Material Characteristic

Maximum Heat of Mass Concrete

Concrete hardens through a chemical reaction that produces heat and expansion, followed by contraction as the concrete cools. Concrete near the edge of a pour cools faster and shrinks earlier than concrete further from the edge. Most concrete pours are not thick enough for this effect to cause problems, but in large pours – called mass concrete pours – such as foundations or bridge columns – the difference in rates of contraction can cause cracking. Also, the heat itself can damage the concrete if internal temperatures exceed certain levels. The amount of heat that develops in setting concrete and the rate at which it can dissipate depend on the ingredients used in the concrete and the shape of the structure. Data regarding the development and dissipation of heat in mass concrete pours are needed to calibrate software that engineers use to design concrete structures in order to better understand when heat is a critical issue.

Development of Mix Designs for RAP Concrete

The main objective was to develop mix designs for concrete incorporating minimally processed reclaimed asphalt pavement (RAP) materials to be used in the Florida Concrete Test Road. The resurfacing of asphalt roadways involves the removal, or milling, of the top pavement layer before retopping with fresh material. The milling process produces mountains of asphalt chips, and transportation agencies across the United States have worked to find appropriate uses for this material, referred to as recycled asphalt pavement, or RAP. One important use of RAP is as a replacement for part of the aggregate required to make concrete. In the right amounts, RAP improves the performance of concrete, but because the ingredients of concrete interact in complex ways, research is required to determine the correct proportions of the ingredients.

Improved Analysis Tool for Concrete Pavement

Improved 3-D finite element (FE) models were developed for analysis of (1) precast prestressed concrete pavement (PPCP) with consideration of the effects of longitudinal and transverse prestress forces, (2) JPCP, which models dowel bars with actual bar dimensions and properties, and (3) continuously reinforced concrete pavement (CRCP), which analyzes the horizontal cracking potential under environmental and traffic loading conditions. Verification of the FE models was accomplished through comparison with measured falling weight deflectometer (FWD) deflection basins and strain data from test slabs. Parametric analyses on the effects of various design parameters on the potential performance of the concrete pavements were also conducted. On top of that, the analysis methodology was recommended using a series of the guage array.