Fibermesh / Metal building
Fibermesh / Metal building
(OP)
I am reviewing a job engineeered by another structural engineering company.
The engineer specified fibermesh as reinforcement for a slab on grade for a premanufactured metal building. He also specified "hairpins" at the columns.
The building was built in October 07 and there are significant cracks around the column footings. I'm wondering if the fibermesh wasn't sufficient to disperse the tensile load (horizontal column load) throughout the slab.
I'm wondering if anyone has any experience with using fibermesh reinforcing with a metal building.
The engineer specified fibermesh as reinforcement for a slab on grade for a premanufactured metal building. He also specified "hairpins" at the columns.
The building was built in October 07 and there are significant cracks around the column footings. I'm wondering if the fibermesh wasn't sufficient to disperse the tensile load (horizontal column load) throughout the slab.
I'm wondering if anyone has any experience with using fibermesh reinforcing with a metal building.






RE: Fibermesh / Metal building
Another thought - were expansion/contraaction joints specified and used in the concrete slab?
Mike McCann
McCann Engineering
RE: Fibermesh / Metal building
What are the shapes of the cracks? What is the calculated thrust?
Has the building seen its full roof live load? (If it is a snow load area, it might have).
RE: Fibermesh / Metal building
I believe they are caused by tensile spreading due to the horizontal force or kick of the frame. If the cracks were due to differential sttelement, I believe they would be circular rather than semicircular.
Have you ever used Fibermesh in a slab that supports a metal building with a "kick"?
Saw cuts were placed in the slab.
RE: Fibermesh / Metal building
Maximum thrust is D-5.5K , COL-2.7K, L-11.05K.
It has not seen maximum live load.
RE: Fibermesh / Metal building
RE: Fibermesh / Metal building
RE: Fibermesh / Metal building
These measures might include addining additional in-slab hairpins, longer and sawcut/epoxied in place, or addditional footings next to the existing footings to take the lateral thrust to the soil matrix. Might even install a rebar tenstion-tie link across the width of the building at each mainframe, epoxy grouted in as with the exgtra hairpins. Could be a costly solution.
Mike McCann
McCann Engineering
RE: Fibermesh / Metal building
Mike McCann
McCann Engineering
RE: Fibermesh / Metal building
RE: Fibermesh / Metal building
RE: Fibermesh / Metal building
Dik
RE: Fibermesh / Metal building
The slab is only reinforced with polypropylene fibers
The column footings are placed monolithically with the slab and are 8'-0" x 8'-0".
Are you saying that even if the slab is plain concrete, if the hairpins have adequate embedment, there will be no tensile cracks?
RE: Fibermesh / Metal building
If the cracks are right at the location of the footing perimeter, then the cracks may be due to stress concentraction at deep footing and the thin slab interface. The spread and depth can be minimized if adequate reinforcement is provided.
RE: Fibermesh / Metal building
Do I understand you to say that there are two #5 hairpins at each mainframe and not just one? If so, that is good. If not...
I did a calc on the 19 Kip load and based on my standard 2:1 flare of the hairpin legs for one hairpin, one #5 hairpin is insufficient and two are needed. I come up with an As required of .53 Sq. In.
If two were provided, did they have the same, or different flares to the legs? They should have been different to spread the tensile load out better to the slab, and of different leg lengths too.
Can you describe the geometry of the hairpin(s) to us more precisely please?
Mike McCann
McCann Engineering
RE: Fibermesh / Metal building
Honestly, my first thought would be a problem with concrete curing and not so much the kickout forces. I mean, how does the 19kip into the slab...with the anchor rods sitting in oversized holes? Baseplate friction? Did the building see enough load to cause a problem?
RE: Fibermesh / Metal building