knowing when members in bracing are in tension or compression
knowing when members in bracing are in tension or compression
(OP)
Is there a way of knowing, just by seeing the member on the brace or looking at the steel shape, if the member is in tension or compression? for example, my professor would look at a WT shape in a diagonal horizontal bracing and say: that member is in tension....HELP!






RE: knowing when members in bracing are in tension or compression
X- bracing: Each brace takes tension only
Single, diagonal brace: Takes tension or compression (depending on load direction)
Chevron brace: One brace in tension, the other brace in compression (depending on load direction)
Hope this helps.
RE: knowing when members in bracing are in tension or compression
1)Tension. You pretty much have to assume that all bracing members will take tension unless you know both the overall structure and the nature of the loading well enough to say otherwise.
2)Compression. With some sections like cables, rods, and small angles, you can pretty safely say that the designer's intent was for them not to resist appreciable compression based on the fact that their slenderness ratios would render them useless for resisting appreciable compression. There are exceptions to most rules, however, so it's best to have an understanding of your structure in which your bracing exists in addition to knowledge of the cross section.
I like to debate structural engineering theory -- a lot. If I challenge you on something, know that I'm doing so because I respect your opinion enough to either change it or adopt it.
RE: knowing when members in bracing are in tension or compression
The web members will be in tension or compression. If you were to draw a "shear diagram" for the truss, then the rule is as follows:
When there is positive shear, members with their right side up are in compression while members with their left side up are in tension.
When there is negative shear, the situation is vice versa.
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
Or at least, that's how I've always seen it done.
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
BA
RE: knowing when members in bracing are in tension or compression
The only way to "instantly" tell if a member is designed for tension only, is to follow KootK's advice. A slender member (cable, rod, small single angle) won't be able to take compression.
DaveAtkins
RE: knowing when members in bracing are in tension or compression
Wendy, another thing to consider is that, in typical buildings, braces don't have ANY forces (of any significance) unless there is an earthquake happening or strong winds blowing.
When this situation occurs, the braces will undergo stress reversals, acting in tension when forced one way and acting in compression when forced the other way.
Of course, if KL/r > 200 then the compression force will be negligible.
It's quite impressive your teacher had the composure to note the axial force of a brace during an earthquake! Joking
Lomarandil, thanks for the clarification. I should've said in sections of positive moment the top is C and bottom is T, vice versa for negative moment
RE: knowing when members in bracing are in tension or compression
RE: knowing when members in bracing are in tension or compression
Mike McCann, PE, SE (WA)
RE: knowing when members in bracing are in tension or compression