Does a handrail provide additional support against defelction?

[randymel]

I am designing a catwalk for a customer but there is too much deflection in the beam supporting the walking surface (beam a). The client argues that the handrail provides two additional support points against deflection, but I disgree. Does it help? If so, how do I calculate the amount that it helps? Thanks. (see attachment)

 

[jike]

The answer: it may or may not!

A 3 dimensional analysis would have to be done to know for sure.

It depends upon how the handrail interacts with the beam, the various stiffnesses of the componets, connection details, slip between pieces, stress levels, etc.

If the client knows better, why isn't he designing it?

 

[w16x26]

Unless you can prove that the beam/ handrail works as a Vierendeel truss, I would not consider it. I have never tried to make this work since the increased cost of the oversized handrail and proper detailing of the handrail/beam connection would offset the cost of just using a larger size beam.

 

[miecz]

I've never seen a handrail counted on for this purpose in design. It's not thought of as a structural item, so, it could be replaced in the future (say it gets damaged) by a rail with less strength or stiffness.

 

[randymel]

Assume there is no slip and that the handrail is the same type of beam as beam a. The left side of the handrail is affixed to the wall, as is the left side of beam a. the right side of both the handrail and beam a are attached via another similar beam to the back wall (I forgot to draw in the top of the handrail's attachment on the right side). They purposely specified a beam to be used for the handrail in hopes of countering deflection in beam a. All of these beams are sqaure metal tubing, so it could conceiveably be used as a handrail. Does this information help?

 

[JStephen]

I would not assume that the handrail contributed to the beam for strength.

Is there actually a limitation on beam deflection in this case? It might make more sense to consider for checking deflection.

 

[hokie66]

It could work, but if the top beam is working to carry the load, I would stop calling it a handrail. The main problem with this scheme is bracing the top beam laterally. Closed sections are good for this, but you still have to make sure it won't buckle.

 

[Lion06]

I say baloney. There is no way that the handrail is working to help with deflection (not in any significant and quantifiable way). I am assuming the handrail and posts are of sections significantly less flexurally stiff than the actual beam? That aside, the "vierendeel truss" has no bracing at the far end.

 

[jike]

Generally, I agree. I would not count on the handrail providing additional stiffness but you are trying to keep the client happy in this case by considering it. If you run a quick analysis to prove it doesn't work, you will have the ammunication you need to shoot the idea down. If the posts are stiff enough, it could work similar to a pony truss (thru truss) but the engineering of such a system requires more than any potential savings. You cannot bolt the handrail down with oversized or slotted holes without slip critical bolts (not practical)!

Try to discourage the client from his request.

 

[randymel]

Yeah, all of the members shown in my drawing are of the same material. The client specifically asked for it that way hoping the handrail (actually made of the beam material) would be able to counter deflection. I don't think it would help, either. Here's what my structural engineering friend said, any comments?

Unless the handrail can act like a truss you can not count on it for gravity loads (deflection). The beams that connect at the handrail going back to the wall could provide a lateral brace thus reducing the unbraced length of the beam which could allow for a smaller beam to be used to resist gravity loads. Although by doing this you would increase the deflection. You were correct in only using the end supports for the deflection calculations.

 

[Tomfh]

I agree with hokie66. It can work. It would significantly reduce deflection because at the very least you are doubling up your floor beam. That's before you consider anything like vierendeel action etc.

As mentioned, bracing the handrail is an issue.

If the client wants it, why not give it to him?

 

[IFRs]

I think there are two issues here. (1) can the two parallel beams be considered together as a system and (2) since the top beam is also a handrail should it be discounted. I think that in reality the handrail will add to the stiffness of the system but it should not be counted because it is a handrail and as such must be designed to resist sidewards loading which would limit it's design usefulness as a top chord of a system in which it will experience compression. Also, the client may want it but your PE license requires you to look out for the public safety in addition to your other responsibilities. If the client insists, I would bow out gracefully and respectfully suggest that the client go elsewhere for their engineering in this case.

 

[Tomfh]

Here is a similar situation with full vierendeel action.

 

[kslee1000]

If both the handrail and floor beam are the same type of material, both are connected at its ends, and the two elements are connected by vertical posts , then yes, the handrail would help, because now you are loading on two beams, each will take its share and deform together. Though this system may not be very efficient compared to others ,such as a truss.

I don't think the deflection can be calculated directly. You have to determine the rigidity of the individual beam in the system, and distribute the loads accordingly. The amount of the deflection shoild be identical for both beams.

 

[slickdeals]

Between the time you spend discussing this and getting back to the client after reanalysis and recalculation, I think the heavier beam already paid for itself.

It looks like a case of a tail wagging a dog. I know these are difficult economic times and money is important, but ........

My 2 cents, I suppose.

 

[ali07]

If beam A is supporting glass rail, make sure your deflection are within acceptable limit.
Is this a existing structure, then what is problem strengthening beam A.

 

[mdavis1]

i'd just go with a bigger beam. no sense on count on the handrail to act against deflection when there's no good way to analyze exactly how much less the deflection will be.

 

[Lion06]

You said the beams/handrails/posts are all the same material. Are they all the same section? What sections are you using for each?