Algor Helps Civil Engineer Design Time- and Money-Saving Arch Structures

Algor is best known as a powerful, state-of-the-art mechanical engineering software package. But, if you give Bob Sogge, P.E., Ph.D., a few minutes of your time, he'll tell you that Algor is the powerful civil engineering program of his choice.

Mr. Sogge of Watson Engineering, in Tucson, Arizona, uses Algor daily to perform soil-structure interaction analyses that enable him to design arched, reinforced concrete culverts. Arch culverts are aesthetically pleasing, but more importantly, they cost less time and money to build than the standard box culverts.

Mr. Sogge of Watson Engineering uses Algor to study the interaction between the reinforced concrete arch culvert, shown here, and the soil which surrounds it.

Modeling Soil-Structure Interaction

Mr. Sogge typically begins by modeling the arched culvert and the soil that surrounds it. Because the soil supports the reinforced concrete arch, both are crucial to the analysis. Typically, Mr. Sogge uses 2-D models. However, 3-D models are used when more conclusive results regarding load distribution are needed.

Although Watson Engineering typically designs culverts in standard widths ranging from 6 to 28 feet, different heights, soil conditions and vehicle loads vary, necessitating analysis in many cases.

The material property, El, of the arch structure's reinforced concrete depends on the axial load and the cracked section properties. The soil properties are dependent on the density of the ground at the site and backfill materials. Field testing can determine the value of the in-situ density. A linear stress analysis is then conducted.

Studying Results with Superview

"Algor enables me to easily input the necessary data, and Superview beautifully displays the displacements and stresses," said Mr. Sogge.

"By looking at the output in Superview and seeing where stresses are highest, I can easily decide what my next design step should be," Mr. Sogge continues.

	By studying stress contours like the one shown here, Mr. Sogge is able to determine how well the soil supports the arch culvert. The picture below illustrates the two materials used in the model, with concrete represented in blue and soil represented in brown.

Building a Better Culvert

The arch culverts designed by Watson Engineering have the advantages of being less costly and time consuming to build and more aesthetic than the typical box type culvert. In addition, the use of soil beneath the road decreases roadway icing. The arch culvert is quickly constructed using steel forms and shotcrete sprayed on concrete. Spraying concrete onto the single-sided forms uses less form material than pouring techniques.