Reinforcing Steel Concrete Cover - Equipment Bases

[supplm]

I am a PE (mechanical) working on a construction project. Our contractor is in the process of building reinforced concrete equipment bases for tanks, pumps, etc. The reinforcing steel and form work have been completed but concrete has not been placed. The design calls for the top mat of steel in the equipment bases to have 1-1/2" of concrete cover however, as constructed, the contractor has installed the steel to have 3" of concrete cover. I am not a structural engineer but I would like to be armed with a technical understanding of what could happen if the amount of concrete cover over the top mat of steel is not corrected. What are the technical problems that could result from leaving this matter uncorrected?

[JAlberts]

First, let state that I am not a structural engineer; but, based upon my time as a mechanical engineer overseeing construction projects I would suggest the following with the hope that more qualified forum members will lend more expertise to my comments.

The design thickness of an equipment pad is generally based upon providing adequate equipment loading support with a minimum amount of concrete volume and cost. So my first question is "who is paying the cost of the added concrete volume?".

Assuming the contractor is working under a fixed price bid and must absorb the added concrete cost, the good news is that the thickness is being added above the rebar level which effectively increases the vertical offset between the pad's horizontal center plane and the rebar layer plane and this increases the rebar structure's effectiveness in preventing tensile bending in the pad.

At the same time, the overall area of an equipment pad, in addition to being dependent upon the size of the structure, is also designed based upon the bearing strength and stability of the underlying soil; but, assuming that the equipment load being supported by the pad is significantly greater than the weight of the pad itself, the added pad weight may not be a issue.

Good Luck, in 14 years of onsite construction monitoring I fought many battles with contractors over variances from design specifications.

[Cake of Doom]

A deeper cover can be a good thing, especially if the pads are to open to the elements. What measurement did they set any bottom and face cover out for? Not seeing any geotech reports, its hard to comment on the ground conditions but usually they are dug deep enough that there is enough allowable pressure in the bag that the self-weight of the pad can be lost. If it was worrying me, I'd look into getting an 'as built' assessment done or at least talk to the original designer to find out how much tolerance we have each way.