Fancy Shoring

by Don Friedman on March 1, 2016

One of the more popular posts in our blog over the last few years is The Short Run, where I wrote about temporary shoring. So I thought I’d show a very different example to give an idea of the breadth of the shoring field. It’s a project I’ve shown before (four years ago!), but I didn’t describe the bracing in detail at that time.

This project was the complete reconstruction of the interior of a double-width house in Manhattan.  We ordinarily try to phase demolition and construction so that shoring is not required. In the case, the new interior structure was too complex for that scheme to work, so the interior was completely demolished. On the other hand, simply removing the old interior would have left the remaining walls and neighboring buildings vulnerable, so shoring was installed to keep the shell stable until the new structure was available as permanent bracing.

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The picture above is a view looking toward the street facade. All of the steel visible is temporary bracing; the beams directly overhead are near the basement floor level – we’re standing on the cellar floor.

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Angling the camera up, you start to get a sense of the complexity of the shoring. This is a big open volume of space, and it was effectively in this state for about a year. The “beams” are actually compression struts (horizontally-oriented columns) and are far too small to carry floor load, but that’s not a problem since there are no floors. The truss-like cross-bracing in the horizontal plane of steel at each level is there to take lateral forces distributed along the side walls and concentrate them in the struts, and then to take the forces in the struts and redistribute them on the far wall.

Something that’s not obvious in these pictures is that the various horizontal planes of bracing are not at the floor levels. They are about two feet above the permanent floor levels, so that the new permanent framing can be installed without touching the bracing. Similarly, the bracing was installed before the old floors were cut out. The building was never in an unbraced condition.

Hey, what’s that white plastic pipe doing there?

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It’s a temporary roof drain from the temporary roof. The permanent design was still in the works when all of this was built, so the top plane of bracing was built above the old roof level (soon to be the new top floor of the building, once the extension was constructed) with heavier beams that could carry snow or rain.

I could keep going, but I think the idea is clear: install enough bracing to create a big empty box for us to build the new structure inside.

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