I've got a parking garage repair project going and have a condition that I'd like to get some opinions on.
The garage floor is a two-way reinforced concrete flat slab (10" thick slab with drop panels at the columns). The columns are steel W14's that are connected to the floors with steel channel shearheads that extend about 3 feet either side of the column (4 directions in plan).
The slab was originally covered with a waterproof membrane and a 3" concrete topping slab. The floor below was a storage area and the garage floor was leaking from snow-melt.
Our project called for the topping slab to be removed, the membrane scraped off, a new topping slab to be placed integrally bonded with the structural slab, and a traffic bearing waterproofing membrane added to the top where the building owner could properly maintain it without tearing out concrete every time there was a leak.
My issue is that after removing the membrane, the structural slab shows numerous cracks extending radially out from the columns, like spider legs in all directions. However, the cracks are primarily running down the length of the column lines, perhaps 4 or 5 parallel cracks spaced out within 3 feet of the column centerlines.
The cracks are very obvious as the scraping equipment has rounded off all the edges, making them look worse than they really are. I think most are hairlline tension cracks but some do show some openness.
Also, the main concern is that there are some cracks that circle the columns, approximately at the point where the shearhead channels would end...about 3' out from the column.
The concrete, as viewed from below, looks beautiful, no cracks near the columns (compression zone) or in midspan regions.
Would there be a shear problem here? I initially don't think so as the tension area around each column is assumed cracked in flexure (basic reinforced concrete design assumption) and the shear capacity at a column should be based on the fact that some tension cracking will occur.
Any thoughts on this?
The garage floor is a two-way reinforced concrete flat slab (10" thick slab with drop panels at the columns). The columns are steel W14's that are connected to the floors with steel channel shearheads that extend about 3 feet either side of the column (4 directions in plan).
The slab was originally covered with a waterproof membrane and a 3" concrete topping slab. The floor below was a storage area and the garage floor was leaking from snow-melt.
Our project called for the topping slab to be removed, the membrane scraped off, a new topping slab to be placed integrally bonded with the structural slab, and a traffic bearing waterproofing membrane added to the top where the building owner could properly maintain it without tearing out concrete every time there was a leak.
My issue is that after removing the membrane, the structural slab shows numerous cracks extending radially out from the columns, like spider legs in all directions. However, the cracks are primarily running down the length of the column lines, perhaps 4 or 5 parallel cracks spaced out within 3 feet of the column centerlines.
The cracks are very obvious as the scraping equipment has rounded off all the edges, making them look worse than they really are. I think most are hairlline tension cracks but some do show some openness.
Also, the main concern is that there are some cracks that circle the columns, approximately at the point where the shearhead channels would end...about 3' out from the column.
The concrete, as viewed from below, looks beautiful, no cracks near the columns (compression zone) or in midspan regions.
Would there be a shear problem here? I initially don't think so as the tension area around each column is assumed cracked in flexure (basic reinforced concrete design assumption) and the shear capacity at a column should be based on the fact that some tension cracking will occur.
Any thoughts on this?
