Assembly of the Top Cradle of Concrete and Poly Shielding

These pictures show the assembly of a top cradle which contains and supports the upper blocks of concrete and poly shielding. The main design challenge here is to prevent the downstream end of this cradle from exerting significant weight on the downstream end of the wedges in the upper half of the HF assembly. This is a concern because any force acting on the downstream end of the wedges could put strain in the PMT box assembly or fiber connections of the upper wedges, and this is to be avoided.

Remember, only the upstream two cradle plates carry the weight of all of the absorber down to the floor. The downstream cradle plate serves only to support the downstream concrete and poly blocks. The wedges are not connected to the downstream cradle plate, even if it looks like they come close.

It is obvious from the pictures that a temporary support is needed to keep the cradle in the orientation shown or it would fall over and contact the floor on both lower corners of the vertical plates. What is less obvious is that the torsional rigidity of the frame shown in the first two pictures is not great. If the vertical plates were tied to the floor and the mid-plane temporary support removed, the weight of the concrete would twist and bend the frame. The downstream concrete blocks are longer than the upstream ones, so the center of mass of the top cradle assembly is downstream of the middle top cradle plate. I have made no calculations, but my physical intuition tells me that if one measured the gap between the top cradle plates and the floor after the structure is allowed to sag, the downstream cradle plate would be closest to the floor. This means that the top cradle wants to rock and deflect torsionally to put weight on the downstream end of the wedges below this cradle.

To prevent this from happening, the top cradle has outer cover plates that serve two essential purposes. First, they act as a shear panel and bending flange that dramatically stiffens the frame keeping the concrete from deflecting down to the wedges. Second, they overlap the bottom cradle allowing the cover plates to be bolted to the bottom cradle and helping the bottom cradle to carry the twisting moment. Finally, there is a shim plate (skinny blue plate half visible in the first two pictures,) between the upper cradle and the top wedge that only contacts the wedge directly over the absorber. Weight transmitted through this contact goes into the absorber and down to the lower cradle, not through the PMT box connection area.

You are welcome to download any of the images. If they are used for other than private viewing, credit to Bartoszek Engineering would be appreciated.

Iso view of upper steel cradle from "outside", 96K

Iso view of upper cradle looking from mid-plane side, 109K

Assembly of the first row of concrete blocks, 102K

These concrete blocks are the same overall shape as the last row on the lower cradle. Here again, I recommend the cast-in pipe method of connecting the blocks to the vertical plates.

Assembly of the top row of concrete blocks, 112K

Assembly of the first row of poly plates, 121K

Same assembly scheme here as on the lower half of the HF.

Assembly of the second row of poly plates, 127K

I have not researched the available sizes of borated polyethylene plates, but this (or any) block could be composed of smaller shapes bolted to the concrete.

Assembly of the third row of poly plates, 86K

Assembly of the top row of poly plates, 83K

Assembly of the steel top cover plates, 94K

A single row of fasteners connecting these plates to each of the vertical plates should be sufficient for the necessary shear flow. Connecting plates at the corners may also be necessary for shear flow. Analysis will determine this.

Outer view of top cradle finished, 137K

The top cradle is ready for assembly over the lower half of the HF.

Forward to final assembly

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