Reinforce existing steel beam for deflection
Reinforce existing steel beam for deflection
(OP)
I have a 3 span continuous steel beam, uniform load on top flange. Contractor wants to remvoe the two interior beams. Beam has adequate strength without the two interior columns, but fails the deflection criteria. Does anyone know of any references or articles that discusses how to calculate the amount of reinforcing needed to reduce the beam deflection.
Does the reinforcing have to be the full length of the member?
I think I can do a 3 member model with the middle member being the reinforced part. And by changing the middle member properties and moving the two interior nodes out, I can determine the reinforcing required and how long it needs to be. Does anyone know of a better mouse trap?
Does the reinforcing have to be the full length of the member?
I think I can do a 3 member model with the middle member being the reinforced part. And by changing the middle member properties and moving the two interior nodes out, I can determine the reinforcing required and how long it needs to be. Does anyone know of a better mouse trap?






RE: Reinforce existing steel beam for deflection
My experience is the amount of reinforcing needed will be more than you expect. For example, don't start with a cover plate on the bottom flange--start with a WT welded to the bottom flange!
DaveAtkins
RE: Reinforce existing steel beam for deflection
RE: Reinforce existing steel beam for deflection
You need to drastically increase the beam inertia, and whatever you do, this will require you to make the beam deeper. This thing is going to get real heavy, real quick, if you can't increase the depth.
Don't forget to check (and most likely reinforce) the beam's end connections, and maybe the remaining supporting columns.
With all due respect, this is much more than a "moving the nodes" exercise. Your reinforcement needs to extend past the nodes in your analysis, in order to develop the strength of the reinforcement. You should discuss this with a more experienced engineer.
tg
RE: Reinforce existing steel beam for deflection
Would you shore the entire basement framing at the beam with makeshift walls while you remove the post(s) and reinforce the beam?
It just seems like much more of a task than simply reinforcing the beam.
RE: Reinforce existing steel beam for deflection
Alternatively moment connect to the columns and beef these up as necessary.
RE: Reinforce existing steel beam for deflection
There is hardly any load on this beam...beam end reactions after the interior columns are removed is only 5 kips. The problem is that the beam is a W8x35 and is 29 feet long. It is supported at the ends by steel columns..not by walls.
I know how to reinforce steel for strength, never had to do it for just deflection.
RE: Reinforce existing steel beam for deflection
1. Weld two 8" deep plates to the flanges, one each side of the beam to create a box section, thickness dependent on inertia requirements, and,or
2. Add more beams parallel to the existing beam to reduce the tributary width, and, or
3. Add another one or two beams transverse to the existing beam with moment connections at the splice points to serve as supports where the columns used to be. This would be two way beam action, with equal deflections at the points of moment connection for load analysis.
Mike McCann
McCann Engineering
RE: Reinforce existing steel beam for deflection
RE: Reinforce existing steel beam for deflection
Will that help with deflection? My hunch is that the steel modulus of elasticity is a lot higher than the CFRP modulus of elasticity, and so the CFRP would not help much with stiffness.
DaveAtkins
RE: Reinforce existing steel beam for deflection
If this doesnt quite work then combine it with stiffening the beam.
RE: Reinforce existing steel beam for deflection
There are many ways to stiffen the beam. You need to consider all the factors that should be weighed when choosing what you want to do. These can include efficiency, cost, accessibility, availibility of the steel shape and so on. It takes a little grunt work to investigate several options but that's our job. you may try altering the connections also, as suggested above, but again there may be other factors that rule this option out.
I would reinforce the whole length unless you check the deflection as a non-prismatic beam with varying moment of inertia.
RE: Reinforce existing steel beam for deflection
You have indicated that you do not want to add depth, or much depth, to the bottom of the beam due to clearance reasons. Is there a way to add anything to the top of the beam to increase its depth? Or this is occupied space as well?
I have come to this, or similiar problems, many times over the years. I agree with DaveAtkins, the amount of reinforcing required will be a more than you would expect, particularly if you cannot add to the beam depth significantly.
I also ususally resort to a trial and error process. Fortunatley, many software packages have simple routines to calculate built up section properties. They take a lot of the grunt math work out of the process.
RE: Reinforce existing steel beam for deflection
RE: Reinforce existing steel beam for deflection
Contractor came back and said can move the interior columns instead of removing them completely. Now the options are remove the columns and add 1" plate to the bottom of a 30' long beam. Or relocate the interior columns and not have to reinforce the beam. But two new footings will have to be installed through an existing sleeper floor joist and slab on ground.
Which is cheaper? I guess that is for the contractor to decide.
RE: Reinforce existing steel beam for deflection
RE: Reinforce existing steel beam for deflection
Especially if this is where they keep their treadmill!
RE: Reinforce existing steel beam for deflection
Mike McCann
McCann Engineering
RE: Reinforce existing steel beam for deflection