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Full contact bearing surfaces in steel column
2

Full contact bearing surfaces in steel column

Full contact bearing surfaces in steel column

(OP)
In steel structures, when do you define ‘Full contact bearing surfaces’?

Can Column to base plate joint or Column to end plate (cap) splice be defined as full ‘Full contact bearing surfaces’. Since if we define them as ‘Full contact bearing surfaces’, their tolerances are very stringent. As per EN 1090-2, squareness tolerance for 'Full contact bearing surfaces' is ‘Section Depth /1000’.
SCI P358 dictate that ‘A good quality saw in proper working order is adequate for this purpose’.
Is it possible to achieve this with the help of only band saw and no other machining? Practically we were only able to achieve up to ‘Section Depth /500’.

Do share your opinion.

GD_P

RE: Full contact bearing surfaces in steel column

i don't have an opinion concerning your question. But this topic would be incomplete without my registering a complaint against the steel erection practice of using "leveling" plates which is becoming more and more common that i've been seeing as a steel inspector. Leveling nuts all the way, everytime, grout after plumb and before the floor pour. Leveling plates lock the z-axis position down and prevent the contractor from making field adjustments for the betterment of having a plumb building to spec. the precision of setting a square foot of steel plate level will never be as accurate as setting a 25 ft column plumb, and by using leveling nuts the column can adjust if there were small errors in the welding of the column base plate (subject of the OP here). A typical steel building should have typical detail at least 2" grout space, never specify leveling plates, and always reject them as substitutions. Leveling plates should only be used for 1 thing on a typical bldg... corrective action.... when the contractor messes up with top-of-concrete and doesn't give you enough grout space to set nuts and confidently grout.

RE: Full contact bearing surfaces in steel column

GD_P,

I always thought that the end of the column would need machined to achieve a flat enough surface to consider direct bearing, however the Steel Designers Manual backs up what SCI P358 says (not surprising as both SCI publications). It says
'For nonmachined ends to the columns, axial loads are transferred through splice plates with multiple bolts. In practice, a modern cold saw can give the equivalent of a machined end to the column without the need for further machining'

RE: Full contact bearing surfaces in steel column

(OP)
Thank you darthsoilsguy2 & patswfc for your comments.

@darthsoilsguy2,
Although our scope is only limited to design only, but I always wonder how they do the adjustment with leveling plates.
Also only leveling nuts / anchors may not be always sufficient for the erection load.(may buckle due to load)

@patswfc
I think most of the fabricators use band saw for cutting the sections. Since the cold saw will not be able to cut section such as UC200 & so on.

For base plate, what if we weld the base plate all around the column & assume that the force is transmitted through the welds. Ultimately we will not need to have the perfect bearing surface, am I right?
And off course we will have to use suitable leveling methods to achieve the plumb of column.

But this will not work for the column end plate splice and there is no other option rather than providing bearing surfaces, am I right?

GD_P

RE: Full contact bearing surfaces in steel column

They don't adjust leveling plates as far as i can tell... the plate is locked into the grout. The building either absorbs the dimensional problems and we don't know what problems that causes..... or the erector leaves small positioning steel shims under the base plate that no structural engineer would ever feel comfortable seeing... I tell structural engineers all the time... that specifying/allowing leveling plates = owning floating columns somewhere in the building. truth is... those shims exist all over the world, unless the steel inspector raises concerns. there are a lot of steel inspectors who won't raise a concern out because they are only looking at bolts/welds in the framing and walk past the anchor bolts if the nut is fully fastened. i raise a stink about it and inevitably we end up settling on slamming in as many full-depth steel shims that can be worked around the anchor bolts and locking the column down.... and every time that happens... people genuinely act like this is the first time this has ever happened before or been a problem. i would be really interested in hearing how others has filled a 1/16" to 1/4" gap between a base plate and the leveling plate if they've crossed that before.

i'm sure there is more subject matter on the erection loads and stripping nuts or buckling, but i'll say that it hasn't been a problem in any building i've inspected steel on. on those buildings, steel columns have always been shipping length and grouting was always mandatory before the first elevated slab pour. OSHA does not prohibit leveling nuts, although i've heard that comment before from erectors. i've also heard erectors say that its part of their "safety policy" to not erect over leveling nuts... which i would like to discuss more openly to find some middle ground with an erector on. i'm sure we could find a reasonable solution that either involved more leveling nuts and washers... even to the point that you can barely see any thread below plate... or maybe even a centralized sacrificial steel bearing shims that gets locked in by the grouting. the whole point of having the grout space is for constructability.

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