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Stress versus Strength

Long ago structural engineers use to design buildings by evaluating the stress in each and every component, bolt, beam, ect. Somewhere along the history, structural engineers found an easier way to evaluate the building structure. Hence the strength base design came about where the structural engineers evaluated the strength of each component and connection. This saved a tremendous amount of computation time (especially considering the use on computers). Instead of looking at the stress in each bolt of a connection, designers only had to look at the strength of the connection as a whole.

Why is this important?

For non-structural components and anchors, the allowable load data from anchor manufactures is depicted in stress design values or ultimate load values. This will not always be the case. Just recently, a relatively new standard ACI 318 (02) was issued resulting in anchor manufactures to distribute catalog data in terms of strength. And just last year (2003) the test labs finally were certified to test the anchors per a test standard ACI 355.2 for strength based data. So soon designers will be seeing both sets of numbers.


To design the anchorage designers must use the appropriate data for their application. Today designers use stress based design and selection of anchors. But in the future, a strength based design will be required. Stress based design will not disappear. Stress based design is applicable now and in the future for evaluating pipe supports such as an angle welded to a plate bolted to the wall. Evaluating the stress in the weld is still easier than trying to define the strength (in our opinion).

Conversion Factor and the Map

As stated above, current design uses a stress based design for evaluating anchors. But the map and maximum credible earthquake data in the codes are based on a strength based design. Calulations use a factor to convert strength based MCE values to stress based design values for selecting anchors as used in our calculation tools. So *** Subscribe Today *** and gain access to the tools you need for selecting anchors in some of the most typical installations.