tie rods for rigid frames
tie rods for rigid frames
(OP)
I am designing a foundation for a 155' clear span rigid frame. I need to design a tie rod to carry the horizontal thrust at the base of the frame. What is the best way anyone has seen this done. Please be specific in your response concerning the load path from the column baseplate to the tie rod and how the tie rod is actually fastened to the concrete or coulmn. Thanks in advance.






RE: tie rods for rigid frames
RE: tie rods for rigid frames
DaveAtkins
RE: tie rods for rigid frames
I plan on writing a paper with a design example on how I design the hairpins. As a matter of fact, I have done so many; I have developed a table with various values. Some metal building suppliers used to issue similar tables in their literature. I think they are shying away or getting cheap.
Good luck
RE: tie rods for rigid frames
RE: tie rods for rigid frames
I suspect that what you are really looking for is not the tie rod design, but the design of a foundation that can resist lateral column reactions. Tie rods represent only one -- and not necessarily the best -- approach. There are other solutions (see Newman, Metal Building Systems, McGraw-Hill, 1997). Some of them, such as moment-resisting foundations in combination with slab dowels, may be better.
The main problems with tie rods are:
1. They elongate under load -- and allow the foundations to spread. This may be OK for a flexible metal building but not for one clad in brittle masonry. The best but $$ solutions are to encase them in heavy grage beams (say 16" x 16")or to post-tension them.
2. The tie rods do nothing against resisting wind loads acting inward (again, the grade beams would help here).
3. The tie-rods must be protected against corrosion, so they are ofter enclosed in grouted sheaths ($$)or, again, in concrete grade beams.
4. ACI 318 requires mechanical connections at tension-tie members...so sorry guys, lap splicing them is not allowed. For the same reason, hairpins are a no-no code-wise, despite the fact that pre-engineered manufacturers push them as a cheap solution to a complex problem.
5. Last, and most importantly, tie rods, if used, should be located well below the slab (12", say) so as not to be cut during future renovation activities. It is only a matter of time before someone will cut the slab to replace some piping or conduits. For the same reason, hairpins should be avoided in slabs on grade.
RE: tie rods for rigid frames
You wrote:
"I plan on writing a paper with a design example on how I design the hairpins. As a matter of fact, I have done so many; I have developed a table with various values. Some metal building suppliers used to issue similar tables in their literature. I think they are shying away or getting cheap."
How's that design paper coming? I've been looking for information on designing haripins, and the metal building manufacturer's no longer have design handbooks available; so...how's that design paper coming? (hint,hint)
RE: tie rods for rigid frames