supporting access hatch on concrete slab

[PDaddy]

We are rehabilitating an existing underground transformer vault in a sidewalk. Part of the top slab of the vault is a removable 8" (or 9") thick 1-way concrete slab (7.5ft span) with a 4ftx4ft aluminum double-leaf access hatch (Bilco). The 5.5" deep support shelf of the hatch needs to be supported by either the remaining thickness (2.5" to 3.5") of concrete or by using a steel frame (under the hatch) that is then tied to the concrete slab. (The remaining thickness of the concrete under the hatch shelf does not seem to have enough shear/bending strength to support occasional H20 loading.) Could you give me advice on the best practices to get this structurally supported? Thanks.

 

[ishvaaag]

if the thing is so bad you can add an inverted L shape surrounding the hole to which you will be able to tie the frame of the acces hatch. So you regain the whol depth of the slab. Attach the unequal sides L as well to the concrete.

I use to pass every day over some big transformer requiring huge cranes to be removed and they sere doing so frequently by whatever the reasons. It seems they remove the whole top slab and reseal or something so. This can give them support enough.

Do not like aluminum/steel touching; I read of one aluminum engineer that the designers of WTC shouldn't be permitted to practice just on that; the article sustained the Al/Fe joints were in bad state out of corrossion.

 

[msquared48]

When they want to drive over the vault lid that was obviously not designed for a truck loading, just have the driver enter the vault with a number of precut wet 6X6's to install as tempory supports around the edge of the opening before driving over the lid.

Before he proceeds into the vault, also show him an insurance policy you took out making you the beneficiary should anything happen to him.

Trust me, he will find another route. Problem solved.

Mike McCann
MMC Engineering