: By essentially placing a jack on only one side of the strongback
: going from one end to the other, I'm surprised you don't get
: lateral bending the more you jam the single side wedge - same
: for downward bending of the single top wedge( but to a lesser
: degree because of the much greater depth). Possibly the effect
: would be more noticable with a more flexible (say plywood)
: strongback.

I agree that there is the potential for bending the strongback with the spacers and wedges, but I have not experienced any. I think there are several reasons:

A: the aluminum is stiff. Like you say, a plywood boxbeam may be more limber and more prone to bending.

B: The wedges don't put that much force on the strongback. Just enought to snug up the forms.

C: The spacers are cut at right angles. Assuming the spacers don't compress too much their natural inclination is to keep everything straight.

D: The wedges are only in one location, in the middle, so what differential pressure there is, is somewhat localized in one spot.

However, you will notice that some of the spacers are saddle or up-side-down "U" shaped. Originally I have only used "L" shaped spacers, but this time I made some additional "U" shaped spacers to minimize any potential for bending the strongback.

But again, the forms and spacers don't need to be compressed, they only need to be held in place. If you pound in the wedges enough that you bend the strongback, just loosen them up until it straightens out.