Can the working stress of a material exceed its allowable stress?
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GB150－1998, Clause 3.6.4: For the case indicated to the poster as \"Posting prohibited: account will be banned,\" when the wind load is combined with other loads mentioned in 3.5.4, the stress on the container wall shall not exceed 1.2 times the allowable stress. How to understand it?
This situation exists in many cases; a margin is always taken into account during design. For example, if the pressure that a pipe can withstand is 15 MPa, to ensure no problems occur during operation, the operating pressure is set at 10 MPa. Therefore, it’s fine if the pressure exceeds this set value. I’m just using this as an example here; I don’t know exactly what the amount of margin is. It might be different in the materials department, and it might also be different in the work environment department.
Considering the margin left in material selection, under effects such as wind load (which are not always present), the stress on the container wall is allowed to be no more than 1.2 times the allowable stress.
Under normal circumstances, the allowable stress value of a material is much lower than its yield strength, often less than half of it; of course, the specific figure also depends to some extent on temperature.
It is possible in this case. Just as in hydrostatic testing, the stress during the test may exceed the allowable stress, but as long as it is less than 0.9 times the yield strength, it’s fine. The wind load on the tower generates bending stress, which should be different from the stress produced by internal pressure.
1. Pressure is a type of long-term load; the stress it generates must not exceed the material’s allowable stress. 2. Wind loads, as well as those mentioned in “Tip to the poster: Reposting prohibited; account will be banned,” are short-term loads with a very short duration of action. Taking design tolerances into account, the stress generated by such loads can exceed the allowable stress. 3. As mentioned above, the combined stress resulting from the action of long-term and short-term loads can exceed the material’s allowable stress; the standard specifies this value as 1.2 times the allowable stress. 4. Additionally, there are concepts such as primary stress, secondary stress, and peak stress, which correspond to values of 1.0 times, 1.5 times, and 3.0 times respectively the material’s allowable stress. This is explained in detail in 4732.