The recent collapses of two multi-story concrete apartment buildings, largely because of insufficient temporary support to carry the fresh concrete floors, points to the necessity to set up some empirical standards to guide the industry. Design of formwork, including shores or struts supporting form loads, is completely covered in the reports issued by American Concrete Institute Committee 347 and its formwork handbook, "Formwork for Concrete." Most codes and handbooks cover the necessity for reshores by a general requirement that adequate support be provided but usually it is left to the job superintendent to decide what is adequate. A great variation can be noted in the number of stories of reshoring used in similar buildings in the same construction area, and the range of time periods that it is left in place indicates that no rational approach is being used. The solution of the problem is to add up the carrying strengths of the number of floors needed to exceed the total weight of the slabs and formwork, the higher the design live load, the more load carrying capacity is available. A table found in the article gives the number of floor slabs that must be combined into a system, not counting the floor slab just concreted, each shored to a floor slab below. The number includes any levels of formwork still in place at the time of placing the top level. The table covers the range of ratios of LL to DL.
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