The operation that makes our foremen most nervous is removing reshores. We go along with them in the idea that it is better to leave reshores in place a little longer than to take a chance on a collapse. But we don't think we're using our forms and shores efficiently, and we can't find any tables that make it clear how soon it is safe to remove reshores under all conditions. Can you provide any guidance ?
There is no really firm answer because of the many uncertainties regarding concrete strength development as well as load distribution and reshore capacity. One contracting firm decided to check the loads for itself by inserting small load test cells under the primary form shores of the floor to be cast. By monitoring the loads they were able to observe how rapidly the load was being transferred to the concrete. They also measured loads under the reshores. When loads on the bottom set of reshores were low enough the reshores were removed. Their system is described in "Stop Guessing at Reshore Loads—Measure Them," published in
July 1975, page 277.