3 resultados para sums of squares
em Iowa Publications Online (IPO) - State Library, State of Iowa (Iowa), United States
Resumo:
The United States has invested large sums of resources in multiple conservation programs for agriculture over the past century. In this paper we focus on the impacts of program interactions. Specifically, using an integrated economic and bio-physical modeling framework, we consider the impacts of the presence of working land programs on a land retirement for an important agricultural region—the Upper Mississippi River Basin (UMRB). Compared to a land retirement only program, we find that the presence of a working land program for conservation tillage results in significantly lower predicted signups for land retirement at a given rental rate. We also find that the presence of both a large working land and land retirement program can result in more environmental benefits and income transfers than a land retirement only program can achieve.
Resumo:
An 11.6 km research project was constructed in 1994 on a portion of Iowa Highway 21 in Iowa County, from U.S. 6 to Iowa Highway 212. This research is intended to evaluate the effect of four primary variables on long term performances of the PCC concrete overlay, commonly called whitetopping. The variables are thickness (50 mm, 100 mm, 150 mm, and 200 mm), joint spacing (0.6 m squares, 1.2 m squares, 1.8 m squares, and 4.6 m spacing), fiber use (concrete with and without polypropolene fibers) and surface preparation (patch only, scarifying the surface, and cold-in-place recycling). After two years, only two sections exhibit a small amount of debonding and distress cracking. Both sections are 50 mm thick. Within each of these two sections, only 2% of the area is affected. Two other 50 mm thick sections have a small number of cracks but no debonding has been found. No adverse effects of these cracks are evident. Three asphalt overlay sections were also constructed. In each asphalt section, transverse cracks have recently been found. At two years of age, the research sections are performing very well. An insignificant number of cracks and no distressed areas have been found in any research sections thicker than 50 mm.
Resumo:
In 1957, the Iowa State Highway Commission, with financial assistance from the aluminum industry, constructed a 220-ft (67-m) long, four-span continuous, aluminum girder bridge to carry traffic on Clive Road (86th Street) over Interstate 80 near Des Moines, Iowa. The bridge had four, welded I-shape girders that were fabricated in pairs with welded diaphragms between an exterior and an interior girder. The interior diaphragms between the girder pairs were bolted to girder brackets. A composite, reinforced concrete deck served as the roadway surface. The bridge, which had performed successfully for about 35 years of service, was removed in the fall of 1993 to make way for an interchange at the same location. Prior to the bridge demolition, load tests were conducted to monitor girder and diaphragm bending strains and deflections in the northern end span. Fatigue testing of the aluminum girders that were removed from the end spans were conducted by applying constant-amplitude, cyclic loads. These tests established the fatigue strength of an existing, welded, flange-splice detail and added, welded, flange-cover plates and horizontal web plate attachment details. This part, Part 2, of the final report focuses on the fatigue tests of the aluminum girder sections that were removed from the bridge and on the analysis of the experimental data to establish the fatigue strength of full-size specimens. Seventeen fatigue fractures that were classified as Category E weld details developed in the seven girder test specimens. Linear regression analyses of the fatigue test results established both nominal and experimental stress-range versus load cycle relationships (SN curves) for the fatigue strength of fillet-welded connections. The nominal strength SN curve obtained by this research essentially matched the SN curve for Category E aluminum weldments given in the AASHTO LRFD specifications. All of the Category E fatigue fractures that developed in the girder test specimens satisfied the allowable SN relationship specified by the fatigue provisions of the Aluminum Association. The lower-bound strength line that was set at two standard deviations below the least squares regression line through the fatigue fracture data points related well with the Aluminum Association SN curve. The results from the experimental tests of this research have provided additional information regarding behavioral characteristics of full-size, aluminum members and have confirmed that aluminum has the strength properties needed for highway bridge girders.