Friday Facts, October 1, 2010, Vol. 73

Bureau of Nutrition and Health Promotion part of the Iowa Department of Public Health produces of weekly newsletter about the Iowa WIC Program for the State of Iowa citizen.

The Flexural Fatigue Strength of Prestressed Steel I-Beams, HR-73, 1962

The purpose of this investigation was to study the flexural fatigue strength of two prestressed steel I-beams which had previously been fabricated in connection with a jointly sponsored project under the auspices of the Iowa State Highway Commission. The beams were prestressed by deflecting them under the action of a concentrated load at the center of a simple span, then welding unstressed high strength steel plates to the top and bottom flanges to retain a predetermined amount of prestress. The beams were rolled sections of A36 steel and the plates were USS "T-1" steel. Each of the two test specimens were subjected to an identical repeated loading until a fatigue failure occurred. The loading was designed to produce stresses equivalent to those which would have occurred in a simulated bridge and amounted to 84 percent of a standard H-15 live load including impact. One of the beams sustained 2,469,100 repetitions of load to failure and the other sustained 2,756,100 cycles. Following the fatigue tests, an experimental study was made to determine the state of stress that had been retained in the prestressed steel beams. This information, upon which the calculated stresses of the test could be superimposed, provided a method of correlating the fatigue strength of the beams with the fatigue information available on the two steels involved.

Wapello County, Township 73 North Range 13 West

Des Moines River Plat Maps.

Wapello County, Township 73 North Range 14 West

Des Moines River Plat Maps.

Wapello County, Township 73 North Range 15 West

Des Moines River Plat Maps.

Monroe County, Township 73 North Range 16 West

Des Moines River Plat Maps.

Monroe County, Township 73 North Range 17 West

Des Moines River Plat Maps.

Methods to Increase Durability of Reactive ("D" Cracking) Coarse Aggregate in Portland Cement Concrete, MLR-73-01, 1973

The coarse aggregates used for Portland Cement concrete in southwest Iowa have exhibited a poor serviceability. This early failure is attributed to a characteristic commonly referred as "D" cracking. "D" line cracking is a discolored area of concrete caused by many fine, parallel hairline cracks. "D" line cracking is primarily caused by the movement of water in and through coarse aggregate with a unique pore structure. The presence of the water in the aggregates at the time of freezing causes the "D" cracking to occur and early failure. By making the pore structure less permeable to moisture, it is thought the durability factor of the concrete should increase. By drying the aggregate before mixing and then mixing with the cement, the particles of cement should enter the outer pore structure, and upon hydration make the pore structure less permeable to moisture.

The Annals of Iowa, Winter 2014, Vol. 73, no. 1

A quarterly journal of Iowa authors and their works produced by State Historical Society of Iowa.

The Annals of Iowa, Summer 2014, Vol. 73, no. 3

A quarterly journal of Iowa authors and their works produced by State Historical Society of Iowa.

The Annals of Iowa, Spring 2014, Vol. 73, no. 2

A quarterly journal of Iowa authors and their works produced by State Historical Society of Iowa.

The Annals of Iowa, Fall 2014, Vol. 73, no. 4

A quarterly journal of Iowa authors and their works produced by State Historical Society of Iowa.