Grade beam design
Grade beam design
(OP)
I'm having a problem on a certain project site because it is swampy
do you have any good reference for Grade beam or tie beam design?
thank you
do you have any good reference for Grade beam or tie beam design?
thank you
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds






RE: Grade beam design
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Grade beam design
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds
RE: Grade beam design
RE: Grade beam design
How are you using shallow spread footings for those (swampy) soil conditions?
RE: Grade beam design
from what I understand, grade beam can be design just like the ordinary beam.... But I still want to find a reference so that I can justify this
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds
RE: Grade beam design
Grade beams are used between piles to support structure above.
Strip footings are used to support walls bearing on soil, unless that wall is also being supported on pile, then the wall sits on a grade beam.
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Grade beam design
Reinforce the same in all spans, unless there is significant span or load difference. I usually design with the same reinforcing top and bottom. As usual, choose the (largest, fewest) bars for maximum permitted spacing. (Like 4#6 T&B).
Usually, you end up with minimum shear stirrups (uniform spacing @ d/2) since your section will probably be large enough that Vc is sufficient. Use 2-piece closed stirrups, rather than 1-piece which are difficult to place.
RE: Grade beam design
As noted by others, it's no different than any other concrete beam.
RE: Grade beam design
Over expansive soils I have used grade beams without piles. In this case the difference between the grade beam and the regular spread footing is that you have top and bottom steel and stirrups if required. That way if you have a soft spot somewhere along your foundation it will bridge over it.
John Southard, M.S., P.E.
http://www.pdhlibrary.com
RE: Grade beam design
RE: Grade beam design
RE: Grade beam design
RE: Grade beam design
the concrete cover changes on the grade beam because it is exposed to earth
and yes we are actually asked for the soil report, that is why we are in need using grade beam for this project
Poems are made by fools like me, but only God can make a tree. engineers creates wonderful buildings, but only God can creates wonderful minds
RE: Grade beam design
RE: Grade beam design
As the spans are often short then the end sections where shear does not need to be designed for become significant.
If they are very short compared to depth then you may find that you need to analyse it by strut and tie method.
The width is often dictated by the size of the piles/piers/caissons under.
RE: Grade beam design
A grade beam is used to span between deep foundation elements (piers, piles); it is only cast against soil where the soils are not expansive. Grade beams act to carry loads to the deep foundations and are not designed to bear on the soil, even where cast against soil. With expansive soils, a void must be maintained below the grade beam to prevent the expanding soil from lifting the grade beam and compromising the deep foundation (and the structure.)
Strip footings are used to bear loads directly on soil at or near grade, with each increment of footing transmitting the load applied to it to the soil in the same increment. A strip footing may also have a sort of grade beam on top of it acting as a stiff element to distribute loads relatively equally along the footing.
RE: Grade beam design
1. It will be more expensive to bore piles than to provide a deeper grade beam so it may be worthwhile to use 24" piles opposed to 18" and have the grade beam span further.
2. If the soil is reactive, consider the construction sequencing. What I have done in the past is use collapsible cardboard void formers under the slab as sacrificial formwork. For a 28"x12" grade beam, the first 20" of the grade beam is placed first with all shear ties crossing the horizontal construction joint. Between the grade beams is then backfilled with a free draining material before the 7" slab is pour on cardboard void formers with the 20"x12" grade beam supporting the slab pour.
If you don't get the construction sequencing correct and the cardboard void formers take on moisture too early than the pour could fail epically.
It is would be advisable to include test certificates from the cardboard void former manufacturer and an installation procedure. Also specify the horizontal cold joint to be rough (but not too rough).
RE: Grade beam design
I don't think the grade beam mentioned by jen is supporting a structural slab, although maybe it should be if the site is swampy.
I typically use 24" deep grade beams with thickness equal to the wall thickness but not less than 8". Under the grade beam, a compressible void former or "cushion" is placed to prevent heaving of the beam. Piles are used to carry the grade beam reactions.
Design of grade beams is no different than design of any concrete beam except that top and bottom reinforcement is normally continuous with laps of bottom steel at piles and top steel at midspan.
BA