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Reinforcing an Existing Joist on One Side

Reinforcing an Existing Joist on One Side

Reinforcing an Existing Joist on One Side

(OP)
I have gone through the analysis and design of an existing joist to be reinforced using SJI's technical note 12. Unfortunately the contractor does not have access to the outside of the joist. They are requesting that the reinforcing be done on one side only. Both the top and bottom chords and the majority of the webs. I can't find any information on this subject related to potential issues this solution may present. Has anyone done this before? Thanks!

RE: Reinforcing an Existing Joist on One Side

I'm okay with it. It will create some eccentricity in the shear centre but it will be small compared to the proportions of the joist. Channels have the same sort of issue and we use them for beams. It might be prudent to brace the bottom chord intermittently as it Twill tend to bend away from the accessible side.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Reinforcing an Existing Joist on One Side

Wondering if your chords consist of double members such as a double angle, or if they are a single member, such as a hat shaped bent plate, or T section.

RE: Reinforcing an Existing Joist on One Side

Looks like it's just you and me now Triangled. I'm curious about your comment. Are you concerned about the eccentricities involved in having to deliver horizontal shear from the webs to an asymmetrical, two piece chord section? Or about the amount of lateral bending induced in the chords? If so, me too. Black belt level joist reinforcing concerns as it were.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Reinforcing an Existing Joist on One Side

I never like reinforcing only one side. In fact, I think every time a contractor has recommended it I've shot it down. Especially something like double angles, they're too susceptible to drastic changes in section properties.

RE: Reinforcing an Existing Joist on One Side

I don't see a problem with reinforcing one side. Since the top of the I-joist is restrained, so any eccentricity would be cancelled out.

RE: Reinforcing an Existing Joist on One Side

My concern is not so much for the eccentricity. I am thinking more about the adequacy of the weld between the web and the chord in a dual chord system..... If all of the chord reinforcements is applied to one side of a dual chord system, I am wondering if the existing weld between the web and the reinforced chord is being asked to overperform.

RE: Reinforcing an Existing Joist on One Side

@Triangled: that's exactly what I was trying to get at with this statement:

Quote (KootK)

Are you concerned about the eccentricities involved in having to deliver horizontal shear from the webs to an asymmetrical, two piece chord section?

The horizontal shear transfer is eccentric, more being required on one side than the other. Thanks for clarifying your earlier comments.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Reinforcing an Existing Joist on One Side

@KootK: And thank you too for clarification!
As I recall, the SJI procedure posited by the OP offers several alternatives, one of which leads to a reinforcement scheme intended to not overstress the existing welds. If that is the alternative the OP selected, and if the chords are a double member system, then I am concerned that some reanalysis may be warranted in the review of the contractor's request.

RE: Reinforcing an Existing Joist on One Side

Agreed. To be honest, I can think of at least half a dozen consequences of the one-sided reinforcing that would be beastly to evaluate and would stand a pretty good chance of sinking the solution. Rather that write a thesis, as I'm prone to doing, I decided to just leave that to the good judgement of the OP.

The greatest trick that bond stress ever pulled was convincing the world it didn't exist.

RE: Reinforcing an Existing Joist on One Side

I think that it would be cheaper to replace the joist or install a sister joist next to it if the physical layout allows it.

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