global or local beam deflection
global or local beam deflection
(OP)
if i have steel structure modeled using computer..
if i check beam deflection.. which one it the proper one,
local beam deflection check or global beam deflection check..
if i check beam deflection.. which one it the proper one,
local beam deflection check or global beam deflection check..






RE: global or local beam deflection
Mike McCann
MMC Engineering
RE: global or local beam deflection
RE: global or local beam deflection
RE: global or local beam deflection
The supported beam is the "local" deflection and the system of the cantilever ane the supported beam is the "global" condition.
Mike McCann
MMC Engineering
RE: global or local beam deflection
i can get both deflections from my software.. just dont know which one i should use for deflection check..
RE: global or local beam deflection
For a floor system, however, it would require a very unique condition to warrant using the global displacements.
RE: global or local beam deflection
However, for the total system design, you should know how the total system is deflecting as it could affect head height restrictions and gravity draining systems such as plumbing that are attached to it.
Mike McCann
MMC Engineering
RE: global or local beam deflection
RE: global or local beam deflection
Mike McCann
MMC Engineering
RE: global or local beam deflection
RE: global or local beam deflection
The local beam/slab deflection needs to be checked for events local to that member eg, if a wall is loading directly onto a specific beam, then the deflection of that beam, over the length of the wall only needs to be checked.
But the overall deflection of a panel of a floor system also needs to be checked. It is not sufficient, if you are designing a one way beam and slab floor, to simply check the deflection of the beam in isolation and the slab in isolation, the overall deflection of the combination is also important and must be checked. This applies to all structural types. The next Australian code is specifically requiring this as many designers have ignored it in the past.
RE: global or local beam deflection
I asked the same question last month with regard to checking the overall deflection of a steel panel taking a diagonal span, similar to flat slab reinforced concrete design. The consensus from that thread was NO, a steel member is a one dimensional element so, the local deflection of the beam must first be satisfied and then, the deflection criteria of the girder must also be satisfied for relative deflections i.e. local deflections.
An exception to this would be designing a transfer structure, where the displacement of supported elements will be directly effected by the displacement of the transfer element.
Now if we consider reinforced concrete design, then YES, you do consider the additiona of slab deflections on top of the beam/column strip deflections with reference to a diagonal span, as per rapt's comments.
However in writing this, there has been a move from the senior engineers in my office to consider panel deflections on a diagonal span for steel design. Mainly because of the simplicity in which a three-dimensional frame analysis can be conducted by modern packages.
Rapt,
I agree with you, the summation of deflections in both directions in two-way systems is generally ignored by many engineers (particulary in my office). I have also discover most engineers are switching off the patterned live load as well, must to my disliking as per our previous discussion.
RE: global or local beam deflection
For example, if you have 40'x40' bays, and limit LL deflection to L/360 for beams and girders, you global deflection at mid point of the bay will exceed 2.5 inches! THat is way too much in my opinion. If you check L/360 across the diagonal, your limit would be 1.9", and you would have exceeded that limit for a hard ceiling. Also, vibration could be more of a problem here too.
RE: global or local beam deflection
RE whole panel deflection, it is needed where the effect of the global rather then local deflection can be experienced, eg if the slope of the floor is a problem (the case with brittle partitions or floor finishes or for people traffic) then the panel deflection must be investigated as well as the local deflection. This applies to all buildings, steel, concrete, timber.
RE pattern load deflections, the code says you have to check for pattern load under certain circimstances and that includes deflection as well as strength.
The next AS3600 specifically says pattern live load has to be checked for deflection in all cases, no .75 factor for ll/dl ratio for this.