Cracks in Foundation
Cracks in Foundation
(OP)
I have a foundation with an Octagonal pedestal, the diameter of the pedestal is about 3meters and rises above the ground level by about 1.5 meter.
the pedestal carries a process vessel which sits on a steel ring.
during commissioning and the vessel was filled we have noticed cracks at each corner of the octagon. the cracks are about 2 - 3 mm wide and they are moving on down the vertical face.
contractor is proposing to inject the crack with some repair material.
my question is; dosen't a crack mean that the section has failed and the design was not adequeate? is repairing by injection structurally sound? do the have to make some sort of calculations?
the pedestal carries a process vessel which sits on a steel ring.
during commissioning and the vessel was filled we have noticed cracks at each corner of the octagon. the cracks are about 2 - 3 mm wide and they are moving on down the vertical face.
contractor is proposing to inject the crack with some repair material.
my question is; dosen't a crack mean that the section has failed and the design was not adequeate? is repairing by injection structurally sound? do the have to make some sort of calculations?






RE: Cracks in Foundation
Hello.
ing. FERRARI Alberto - www.ferrarialberto.it
RE: Cracks in Foundation
If this is the case, injecting the cracks with epoxy will not solve your problem.
You need to engage a structural engineer to help you solve it. The foundation may have to be redesigned and replaced.
Mike McCann
MMC Engineering
http://mmcengineering.tripod.com
RE: Cracks in Foundation
A 2 to 3 mm is a lot to attribute to temperature shrinkage in a pedestal. A 2 to 3 mm wide crack is not something to ignore. Find out what is causing it (or what was responsible for causing it) before you decide what to do with it. Perhaps the vessel was "bumped" on the corner before swinging over the center of the pedestal during erection. Now, having no load there, all you might need is some minor cosmetic work; my point being, so far you have 0 actual information on which to base ANY decision you make, and the cracks are "moving". In any case you can't do anything else until you have made those cracks stop moving.
Don't inject grout to treat the symptoms unless you at least know what caused the disease. Only medical doctors can get away with that.
What would you be doing, if you knew that you could not fail?
RE: Cracks in Foundation
RE: Cracks in Foundation
RE: Cracks in Foundation
thanks again
RE: Cracks in Foundation
Photos and rebar scheme needed.
If injection is needed, don't use epoxy grout, just epoxy. Cracks too tight for grout.
RE: Cracks in Foundation
I would be concerned because a shear model for concrete allows for aggregate interlock at the smaller crack widths, but I think with 2-3mm you are relying on shear friction of the reinforcement and not any concrete shear/tension capacity.
To me, it almost appeared as though a cone pull-out failure crack pattern was occurring at the corners. I would investigate whether the pedestal has reinforcement at 200mm each way and also investigate temperature. The thermal expansion between concrete and steel is roughly the same but steel absorbs it faster particularly if it has a dark paint.
I had a external FC clad steel frame which was poorly insulated and had dark colours on the external wall and first thing in the morning you could really feel the heat radiating through to the internal plasterboard when you touched it. It kept cracking the plasterboard along the panel joint.
RE: Cracks in Foundation
ing. FERRARI Alberto - www.ferrarialberto.it
RE: Cracks in Foundation
is this a tall vessel and embedment of anchor is just 12d?
unless we have this info, we wont know if this is underdesigned.
RE: Cracks in Foundation
Sorry could not get a photo permit from the site manager, but here are some more details;
The foundation is octagonal
the size is 5m by 5m
the height is 1.75 m , 1m below ground and 0.75 above ground
reinforcement; 25mm mesh four layers - top, - bottom - upper intermediate,- lower intermediate
vertical bars , 25 mm every 25o mm
the vessel is 6 m heigh
the anchor is 300mm from edge
concrete is grade 50
I have requested the contractor to investigate the depth and extent of the cracks
RE: Cracks in Foundation
ing. FERRARI Alberto - www.ferrarialberto.it