From what I've read, ASD basically deals with making sure the stress in a structure does not exceed a certain limit, the yield stress of the material. It ensures that structures remain in their elastic region while subject to designed structural loads. Limit state design on the other hand defines a set of ultimate limit states against which the structure has to be checked. But don't these two design philosophies in the end boil down to the same thing, making sure the structure steel structure for example does not reach a stress too high?
For example, we might check a steel beam against loads by calculating the expected characteristic loads such as wind and dead load, combine these according to different defined ultimate states and then check that the stress resulting from these does not exceed the yield stress of the beam. But isn't this in the end what allowable stress design does? What is the practical difference between the two? For example, in Eurocode 3, part , 6. In this Youtube video, the differences are given:.
Here the difference is given to be that in ASD, we use service loads which are the expected loads without any safety factors applied. Aren't these what are known as characteristic loads in limit state design? In contrast, it is stated that limit state design uses factored loads.
So why is it that in ASD we use loads without any factors? Aren't safety factors there to take uncertainties in things like material properties and modeling theories into account? Why don't they exist in ASD? Sign up to join this community. The best answers are voted up and rise to the top.
Stack Overflow for Teams — Collaborate and share knowledge with a private group. Create a free Team What is Teams? Learn more. What really is the difference between allowable stress design and ultimate limit state design?
In the above equation, is the allowable stress , is the yield stress , and is the factor of safety or safety factor. This factor is generally defined by the building codes based on particular condition under consideration. Since tension members do not generally buckle, they can resist larger loads larger due to small value.
And while you may not be an engineer, allowable stress meaning and applications are important for EHS professionals to translate safe building principles to safe worker practices. Allowable stress, or allowable strength, is the maximum stress that can be safely applied to a structure. This is usually defined in building codes and the strength of the metal in question. In the allowable stress design method , the designer must size the anchorage in such a way that the service load does not exceed the allowable load.
The designer has to read the allowable load from the applicable table and adjust for all applicable design parameters for the anchor. Calculating allowable stress is a relatively straightforward process. Allowable stress is determined by a factor of safety and the yield strength of the object, i. As such, calculating allowable stress begins with finding the yield strength of the materials in question.
From there, select a factor of safety. These are usually set by the industry in question since different industries need materials to perform in different ways. If there is no industry standard set, a good overall safety factor is 4. After that, simply divide the yield strength by the factor of safety to calculate the allowable stress.
In safety, allowable stress is a critical factor in maintaining a sound, stable structure. The applications in safety are obvious. Take construction, for example, where workers routinely deal with heavy loads. A structure is no longer safe if workers overload it, which means you need to understand how allowable stress works and how it translates into safe work practices.
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