Single Angle Bending Allowable BTH-1
Single Angle Bending Allowable BTH-1
(OP)
I'm reviewing a design to the rules of ASME BTH-1-2014. There is a deadweight which is supported by two single angles (3x2x1/4 with some areas machined away). They are unconnected and support half the deadweight each. These angles are unbraced over 48 inches. I believe the angle cross sections meet the rules for non-compact for "legs of single angle struts..." in Table 3-2.2-1. I have no control over the design at this point (it already exists).
In section 3-2.3 for flexural members, the most appropriate sections is 3-2.3.2 I believe since this isn't explicitly major or minor axis bending because it's an angle, and this is a non-compact section since there is no compact section listed for angles in Table 3-2.2-1. However in reading through the allowable bending stress formulas in 3-2.3.2, there is nothing that appears to me to apply to single angles. 3-9, 3-14, 3-16 and 3-17 seem to apply to I-beams, box beams, and channels. The closest approximation is 3-18, but this is for Tees and double-angle members. This is the equation I would tentatively try to use, even though the words don't explicitly call out single angles. Is there something I'm missing? Anywhere else in BTH-1 that I would turn to for an allowable bending stress for a single angle in bending?
In section 3-2.3 for flexural members, the most appropriate sections is 3-2.3.2 I believe since this isn't explicitly major or minor axis bending because it's an angle, and this is a non-compact section since there is no compact section listed for angles in Table 3-2.2-1. However in reading through the allowable bending stress formulas in 3-2.3.2, there is nothing that appears to me to apply to single angles. 3-9, 3-14, 3-16 and 3-17 seem to apply to I-beams, box beams, and channels. The closest approximation is 3-18, but this is for Tees and double-angle members. This is the equation I would tentatively try to use, even though the words don't explicitly call out single angles. Is there something I'm missing? Anywhere else in BTH-1 that I would turn to for an allowable bending stress for a single angle in bending?






RE: Single Angle Bending Allowable BTH-1
"Some areas cut away" ????? Those area removed specifically MUST be detailed, because those areas are the stress risers!
RE: Single Angle Bending Allowable BTH-1
The two angles are noted as part 9. You can see the 3" leg of the angle is machined down to 1.25" to support the drum at the centre. Not sure if this affects which allowable to use (obviously it affects the beam's local properties such as r, I, etc).
RE: Single Angle Bending Allowable BTH-1
Angles in general are a mess, and it can be worth a few extra ounces to simplify the design by using flat bars or other symmetrical shapes.
RE: Single Angle Bending Allowable BTH-1
RE: Single Angle Bending Allowable BTH-1
Assume only a 1-1/4 x 3 x 1/4 angle iron, or a 1-1/4 x 2-1/4x1/4 angle iron all the way across. If you really don't like that assumption, use a single rib 1/4 x 1-1/4 high. But your structure is weak in the bending resistance of the angle iron's vertical web.
RE: Single Angle Bending Allowable BTH-1
racookpe1978, you are correct it wasn't labeled. I just took a screenshot of the sketch from the existing report. The vertical leg was the 3" leg and the remaining whole horizontal leg is the 2" leg. I agree that the basic assumption should be that this is a 1-1/4 x 2-1/4 x 1/4 angle iron all the way across to determine the bending stress at the critical centre. My issue was that I wasn't sure what allowable to compare that to. Pretty sure in this case the design is inadequate and that we'll have to ship it back and modify, but I wanted to be able to say with confidence what the exceedance of failure over the code specified limit was.