Metal Building Footer Cracks
Metal Building Footer Cracks
(OP)
I started a new job (came from bridges and sign structures). I came into this project a bit late. This will probably be hard to understand without pictures. Contractor is building a pre-engineered metal building. He had an engineer design the footer. The engineer came up with continuous footers for the columns with a trench footer to connect each column footer. The column footers were to have #6 bars spaced @ 10" o.c. long. & transverse top and bottom. The trench was #5 bars spaced 15" o.c. on bottom. He also called for I believe #5 bar hairpins at the columns extending 20' in the slab. The column footer cages were to extend to 3" from the outer of the exterior perimeter of the trench. However, the column footer cages were installed and fell 7"-9" short of the exterior perimeter. The frame of the metal building is up but no roof or siding. We haven't poured the slab with the hairpins. We are seeing cracks in the trench footer ranging from 1/16" to up to 1/4" mostly within a foot of the columns. To me, anything over 1/8" is excessive and cannot be argued as shrinkage cracks. Also, the cracks are still growing slowly. I believe they are settlement cracks due to the footer not being continuous due to improper rebar placement and the nature of the cracks. I am worried it could be from a horizontal force since our slab is not in with hairpins. However, I was thinking this force should be small due to no roof or siding. In addition, the contractor wants to skip the hairpins. This in my opinion is a no no since there will be no alternative to resist the horizontal loads. Thoughts on settlement?






RE: Metal Building Footer Cracks
You can get cracking from settlement of the concrete around top rebar (this is actually a form of segregation of the concrete rather than true settlement), particularly if the cover is not good.
There are numerous reasons for the cracks to occur. Would need more info to help. What were the temperatures at the time of concrete placement? What were the wind conditions? What was the slump of the concrete? Was the concrete vibrated?
DO NOT ALLOW THE CONTRACTOR TO CHANGE THE STRUCTURAL DESIGN BY DELETING THE HAIRPINS. There will be lateral thrust that needs to be accommodated and it is apparent that the structural engineer chose that method to do so.
Also, please refer to the "footers" as footings or foundations. "Footer" is a contractor's misnomer.
RE: Metal Building Footer Cracks
The temperature was in the 80s and wind around 10mph. Nothing out of the normal. Concrete was tested and was fine. It was vibrated.
The cracks are mostly in the trench footing. There is no top bar. Just longitudinal and transverse bar which I refer to as a ladder. It is 3" off the bottom of the trench which is 1' wide and 1.5' deep.
I am not allowing the contractor to disregard the hairpins. The client has already agreed to disregard before I came on the job. However, things are on hold with these cracks in the footings and since the rebar was not installed according to the engineers plans we are discussing our options.
RE: Metal Building Footer Cracks
Pictures would be highly useful.
Do the cracks run perpendicular to the flexural rebar of the footing or are they randomly oriented? Do the cracks start at discontinuities (typically reentrant corners)? How thick are the footings where the cracking is occurring?
Footer is what you have at the bottom of a document.
Footing is what you place your foundation piers on.
Continuous or strip footing is what you place foundation walls on.
Maine EIT, Civil/Structural.
RE: Metal Building Footer Cracks
There is a block wall going up on the outside of the steel structure (non structural). The first two course were started 2 months after the footing was poured. The large crack (1/4" wide) has caused the mortar to separate above the crack. I assume the block was leveled with mortar on top of the footing. One side is level and the other is a hair out of level. That is the reason I was leaning towards settlement.
RE: Metal Building Footer Cracks
Also, the client (unless he is the structural engineer of record) has no authority to modify the structural requirements of the project. I will assume you are in the US....if so, to deviate from the record plans is a building code violation unless such deviation is submitted and approved by the building department. Such a submittal would have to be signed and sealed by a licensed profession engineer.
RE: Metal Building Footer Cracks
The client is exempt from being overseen by the local building department. This is why we are in this issue in the first place. The local inspector would have never allowed the rebar to be placed the way it was. However, there wasn't really any inspector on site. I agree the engineer plans should never be deviated from unless the design engineer was consulted.
This is why I am also apprehensive of posting pictures rather than sketches.
RE: Metal Building Footer Cracks
Column Footing in each corner
Column footing on exterior wall columns.
Pier Footing
Trench Footing
How all exterior and corner column footings were installed.
RE: Metal Building Footer Cracks
http://files.engineering.com/getfile.aspx?folder=a...
http://files.engineering.com/getfile.aspx?folder=8...
http://files.engineering.com/getfile.aspx?folder=9...
http://files.engineering.com/getfile.aspx?folder=f...
That didn't work the way I intended it to.
RE: Metal Building Footer Cracks
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Metal Building Footer Cracks
With a block wall going up before the slab is cast, how will you now install the hairpins? I'm not a fan of hairpins in general, but in the situation which you now have, there is no other load path for the thrust at the bottom of the column.
RE: Metal Building Footer Cracks
I would have liked to see a grade beam for the strip footings. I believe that is our crack issues near the column footings. I will post a plan view of the crack locations.
Apparently the footing was excavated before I was on the project. I'm taking others word that the cracks extend to the bottom.
There is still room to fit hairpins in with the block walls. If the blocks need to come out it isn't a big deal. They only have two courses on and they are the half blocks so about 8" in height. I think they were thinking to use those as their forms for the slab (contractor had form issues and had burp outs on the side of footing). That is another issue altogether. I'd rather see the block on top of the slab.
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
Here is the plan view of cracks.
http://files.engineering.com/getfile.aspx?folder=7...
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
1) The strip footing thing is hanging up at hard spots like the edges of the column footings.
2) The "hanging up" is resulting in negative, hogging moments in the strip footings.
3) Because your strip footings have no top reinforcement, they're developing cracks to relieve the negative moment.
It's poor design but not a terribly big deal.
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Metal Building Footer Cracks
The greatest trick that bond stress ever pulled was convincing the world it didn't exist.
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
Maine EIT, Civil/Structural.
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks
RE: Metal Building Footer Cracks