Questions regarding the allowable bearing stress in B31.3
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I am looking at the Chinese version of the B31.3-2006 standard published by Sinopec Press. Paragraph 302.3.1(b) states as follows: (b) Shear and Bearing: The allowable shear stress is 0.8 times the allowable tensile stress listed in Tables A-1 and A-2, while the allowable bearing stress is 1.60 times that value. The original text in the English version of B31.1-2006 reads: (b) Shear and Bearing. Allowable stresses in shear shall be 0.80 times the basic allowable stress in tension tabulated in Table A-1 or A-2. Allowable stress in bearing shall be 1.60 times that value. I have only heard of tensile stress, compressive stress, shear stress, torsional stress, and bending stress; what exactly does the term \"bearing stress\" refer to here? Thank you!
Do you mean the ability to withstand pressure?:o
I don’t think so, because the specifications go on to mention compressive stress: (c) Compressive stress: The allowable stress shall not be greater than the basic allowable tensile stress listed in Table A of Appendix A, and the stability of the structure must also be taken into account. (c) Compression. The allowable stresses under compression shall not be greater than the basic allowable stresses in tension as listed in Appendix A. Structural stability must also be taken into consideration.
I find the word “bearing” a bit awkward when translating it; from the materials I’ve seen, it refers to what we commonly call “compressive stress,” which is briefly explained in mechanics of materials, and it can also be seen from the calculation formulas. I seem to have seen a specific English explanation there, but I can’t remember it.
This is the first time I’ve heard of such stress; it’s really unusual. I’m waiting for experts to give me some guidance!
I think it’s still \"shear stress\" – a lateral compression – and there is a difference between bearing and compression.
In GB 50316－2000: the allowable shear stress is 0.8 times the allowable stress specified in Appendix A of this code； The allowable stress on the support surface is 1.6 times the allowable stress ； The allowable compressive stress is the allowable stress specified in Table A of Appendix A to this code. In my opinion, the allowable stress in a bearing refers to the allowable stress of the supporting surface in this case. Multiplying the allowable stress by 1.6 gives the yield strength of the material; thus, the safety factor when bearing loads is 1. The load-bearing capacity mentioned here refers to the ability to withstand gravity.
There is still a fundamental difference between the two: a bearing generally refers to a situation where, under external forces, a large pressure is transmitted between the connecting element and the component being connected, due to the small contact area; this can result in local plastic deformation of the contact surface. This type of stress generally exists at the contact surface and over a small area; accordingly, the allowable stress value is set relatively high. Compression generally spans the entire stress-bearing cross-section, has a wide distribution area, and possesses significant destructive force; it is determined using allowable stress. This post was last edited by power on 2009-3-16 16:34.]
The bearing stress is generally required to be less than the yield strength in theory, but according to other equipment standards, its allowable stress is set at 1.2 times the allowable stress or 0.9 times the yield strength.
Bearing stress is not just something that \"should be taken into account when designing mechanical fastenings\"; it also needs to be considered, for example, when calculating lifting lugs.