AbstractsPhysics

Last fall as school opened, Mr. Sigmund Eiken and the author, were presented with the opportunity of measuring the stresses in a highway bridge, about to be erected, near Ames Iowa. This structure is located just east of Ames, on Thirteenth Street extended, and spans the Skunk River at this point. [...] As previously stated this bridge is located near Ames Iowa, and is a 120-foot span, 20-foot roadway, through riveted steel highway bridge, with an 8-inch concrete floor on steel stringers. A view of the bridge is shown in Fig. 1 and elevation of the truss in Fig. 2. The bridge was designed under the Iowa State Highway Commission Specifications of 1919 and is a T-type, through riveted Pratt truss. In planning the work it was thot that it would be possible to make a complete study of the action of the bridge during erection. This would have resulted in the measurement of the erection stresses, the stresses due to the weight of the steel and the stresses due to the weight of the concrete floor. Conditions and lack of time caused the scope of the work to be reduced to the measurements of the floor load stresses. These stress measurements were taken on all of the members at the two upper and two lower panel points at the east end of the north truss of the bridge. From these readings we obtained the primary and secondary stresses in the structure, and a comparison of the observed and computed value will be made. In this connection a study of the distribution of stress in the upper chords and end post was also deemed advisable. A complete study of the observed and computed stresses in the transverse bents was also made. In addition the action of the portal members was studied for floor load stresses and stresses due to a horizontal load, applied to represent the action of the wind. In the following work a plus sign will be used to designate tensile stresses while a minus sign will be used to designate compressive stresses.