Column always in Tensions
Column always in Tensions
(OP)
The building I am workign on has a significant portion of the building cantilevered out. We have created 3 large trusses that carry this cantilever slab, that look like giant P's. Since the cantilevered portion of the floor is longer than the backspan, we have significant uplift on the first column of each of the trusses. There is ALWAYS a tension on these columns. Are there any special code provisions to consider with a column that is always in tension?






RE: Column always in Tensions
RE: Column always in Tensions
Only one of these trusses has an X down to the base of the building, the lateral system is completely seperate from the trusses, though analysis shows their stiffness does attract some lateral load - the lateral system has been designed as if these trusses do not exist.
RE: Column always in Tensions
But I would suggest the following: With a tension element (be it a column or a hanger) you have a very non-redundant condition. If the column fails - boom!
Thus, as a prudent engineer I'd consider an additional level of safety factor, perhaps 1.5 to 2 in addition to your code required levels of safety.
RE: Column always in Tensions
Mike McCann
MMC Engineering
RE: Column always in Tensions
RE: Column always in Tensions
BA
RE: Column always in Tensions
There may be details which are non-critical no-brainers under compression (such as base plate and anchor bolt details) which are of critical importance under tensile loading. A detailer may or may not know the difference.
Another example is the column splice. Column splices may usually be detailed for bearing but under tension there is no bearing!
RE: Column always in Tensions
When you get done, add some extra tension rods to the design above the number required by the calculations. It is cheap insurance. Say they are for future maintenance or something.
RE: Column always in Tensions
RE: Column always in Tensions
Are these steel or concrete columns?
Also can you clarify what the foundation are going to look like.
Thanks
RE: Column always in Tensions
The last thing you want is for some J-bolt to straighten out on you and pull out of the hole.
RE: Column always in Tensions
The columns are steel, and are MORE than appropriately sized for the tensions forced, stressed to about 10% or less, but sized so high to help control deflections.
Though not req'd by the code we are using, we have done a collapse analysis of removing one of 9 different columns, 3 of which are the tensions columns, and no strength failures occur, and no drastic deflections occur. The building uses 2 "distribution trusses" in the direction transverse to the 3 main load carrying trusses, which will send load back and forth to the other trusses if one is damaged or has a lesser stiffness.
I think as most of you stated, the detailing of connections will be most critical in this project.