Laboratory Study of Structural Behavior of Alternative Dowel Bars, April 2006

Load transfer across transverse joints has always been a factor contributing to the useful life of concrete pavements. For many years, round steel dowels have been the conventional load transfer mechanism. Many problems have been associated with the round steel dowels. The most detrimental effect of the steel dowel is corrosion. Repeated loading over time also damages joints. When a dowel is repeatedly loaded over a long period of time, the high bearing stresses found at the top and bottom edge of a bar erode the surrounding concrete. This oblonging creates multiple problems in the joint. Over the past decade, Iowa State University has performed extensive research on new dowel shapes and materials to mitigate the effects of oblonging and corrosion. This report evaluates the bearing stress performance of six different dowel bar types subjected to two different shear load laboratory test methods. The first load test is the AASHTO T253 method. The second procedure is an experimental cantilevered dowel test. The major objective was to investigate and improve the current AASHTO T253 test method for determining the modulus of dowel support, k0. The modified AASHTO test procedure was examined alongside an experimental cantilever dowel test. The modified AASHTO specimens were also subjected to a small-scale fatigue test in order to simulate long-term dowel behavior with respect to concrete joint damage. Loss on ignition tests were also performed on the GFRP dowel specimens to determine the resin content percentage. The study concluded that all of the tested dowel bar shapes and materials were adequate with respect to performance under shear loading. The modified AASHTO method yielded more desirable results than the ones obtained from the cantilever test. The investigators determined that the experimental cantilever test was not a satisfactory test method to replace or verify the AASHTO T253 method.

Examining Driver Behavior in Response to Work Zone Interventions: A Driving Simulator Study, 2010

Construction zones pose a significant threat to both workers and drivers causing numerous injuries and deaths each year. Innovations in work zone safety could reduce these numbers. However, implementing work zone interventions before they are validated can undermine rather than enhance safety. The objective of this research is to demonstrate how driving simulators can be used to evaluate the effect of various work zone interventions on driver performance.

Drivers' Behavior at Railroad Grade Crossings: Before and After Safety Campaign, HR-335, 1992

In April 1991 the Iowa Department of Transportation, the CNW Transportation Company, the SOO Line, and local agencies and business in the Mason City/Clear Lake area initiated an Operation Lifesaver program to attempt to increase public awareness of safety issues and safe behavior at railroad-highway grade crossings. This document reports an initial study of data on traffic characteristics at a selected set of grade crossings in Cerro Gordo County taken before and after the safety program. Twenty-two crossings were studied. The 13 crossings at which collisions were reported for the five years prior to the study were included in the sample of sites. Two field observations were made at each study crossing before the Operation Lifesaver campaign was in full swing, and two observations were made after the conclusion of the main effort of the campaign. The summary of each data set is contained in a companion volume. The research shows that Operation Lifesaver altered drivers' behavior in the following ways: (1) reduced approach speeds and crossing speeds at crossings with low speed limits, (2) reduced the percent of drivers approaching the crossing at speeds in excess of the posted speed limit, and (3) increased alertness of drivers to railroad crossing hazards as evidenced by more drivers looking for a clear track. Thus, Operation Lifesaver enhanced safety in street and highway traffic operations in the vicinity of railroad-highway grade crossings.

Behavior of Asphalts in the Production of Asphaltic Concrete, HR-107, 1965

Project 540-S of the Iowa Engineering Experiment Station (Project HR-107, Iowa Highway Research Board) was started in June, 1964. During the year ten 2-gallon samples of asphalt cement and ten 100-lb samples of asphaltic concrete were studied by the personnel of the Bituminous Research Laboratory, Iowa State University. The samples were from tanks and mixers of asphalt plants at various Iowa State Highway Commission paving jobs. The laboratory's research was in two phases: 1. To ascertain if properties of asphalt cement changed during mixing operations. 2. To determine whether one or more of the several tests of asphalt cements were enough to indicate behavior of the heated asphalt cements. If the reliability of one or more tests could be proved, the behavior of asphalts would be more simply and rapidly predicted.

Nonlinear Pile Behavior in Integral Abutment Bridges, HR-227, Part 1, 1982

The highway departments of all fifty states were contacted to find the extent of application of integral abutment bridges, to survey the different guidelines used for analysis and design of integral abutment bridges, and to assess the performance of such bridges through the years. The variation in design assumptions and length limitations among the various states in their approach to the use of integral abutments is discussed. The problems associated with lateral displacements at the abutment, and the solutions developed by the different states for most of the ill effects of abutment movements are summarized in the report. An algorithm based on a state-of-the-art nonlinear finite element procedure was developed and used to study piling stresses and pile-soil interaction in integral abutment bridges. The finite element idealization consists of beam-column elements with geometric and material nonlinearities for the pile and nonlinear springs for the soil. An idealized soil model (modified Ramberg-Osgood model) was introduced in this investigation to obtain the tangent stiffness of the nonlinear spring elements. Several numerical examples are presented in order to establish the reliability of the finite element model and the computer software developed. Three problems with analytical solutions were first solved and compared with theoretical solutions. A 40 ft H pile (HP 10 X 42) in six typical Iowa soils was then analyzed by first applying a horizontal displacement (to simulate bridge motion) and no rotation at the top and then applying a vertical load V incrementally until failure occurred. Based on the numerical results, the failure mechanisms were generalized to be of two types: (a) lateral type failure and (b) vertical type failure. It appears that most piles in Iowa soils (sand, soft clay and stiff clay) failed when the applied vertical load reached the ultimate soil frictional resistance (vertical type failure). In very stiff clays, however, the lateral type failure occurs before vertical type failure because the soil is sufficiently stiff to force a plastic hinge to form in the pile as the specified lateral displacement is applied. Preliminary results from this investigation showed that the vertical load-carrying capacity of H piles is not significantly affected by lateral displacements of 2 inches in soft clay, stiff clay, loose sand, medium sand and dense sand. However, in very stiff clay (average blow count of 50 from standard penetration tests), it was found that the vertical load carrying capacity of the H pile is reduced by about 50 percent for 2 inches of lateral displacement and by about 20 percent for lateral displacement of 1 inch. On the basis of the preliminary results of this investigation, the 265-feet length limitation in Iowa for integral abutment concrete bridges appears to be very conservative.