Step 6. Calculate the UL stringer.
Step 7. Determine the maximum shoring spacing.
(a) Spacing based on stringer strength. Refer to table 3-2.
(b) Spacing based on the shoring strength and end bearing of the stringer, based on the allowable load in tables 3-5 and 3-6.
Allowable load based onshore strength. (See table 3-5.)
Allowable load based on end bearing stresses. (See table 3-6.) Since we do not know what species of wood we are using, you must assume the most critical and lowest compression perpendicular to the grain equals 250, and the allowable load for a 4 by 4 (S4S) equals 3,100 pounds.
Select the most critical load.
Determine shore spacing based on allowable load.
Select the most critical shore spacing. The spacing determined in step (7(a)) is less than the spacing determined in step (7(b)); therefore, the shore spacing to be used is 35 inches.
Step 8. Shore deflection check.
Therefore, lateral and cross bracing are not required.
Step 9. Summary.
Sheathing: 3/4-inch plywood
Joists: 4" x 4" (S4S) lumber spaced@ 22 inch OC
Stringers: 4" x 4" (S4S) lumber spaced @ 55 inch OC
Shores: 4 x 4 (S4S) lumber spaced@ 35 inch OC
Bracing: Not Required
Beam forms, like slab forms, carry a vertical load, and they are also subjected to the lateral pressure of freshly placed concrete just as wall forms are. Beams can be formed independently to span walls and columns or monolithically (one continuous pour) as part of a floor slab system. When formed as part of a slab system, a part of the load from the slab forms may be carried by the beam form to the supporting shores and must be accounted for in the formwork design.
Figure 3-5 shows atypical interior beam form with slab forming supported on the beam sides. This drawing indicates that 3/4-inch plywood serves as the beam sides and that the beam bottom is a solid piece of 2-inch dimension lumber supported on the bottom by 4- by 4-inch T-head shores.
Close examination of figure 3-5 shows that when a beam is to be formed as part of a slab system, some of the design procedures have been completed. For example, the lateral pressure against the beam sides is compensated for by the slab joists which butts against the beam sides and rests on the attached ledger. All that remains to complete the design of a beam form is to determine the design load for which the form must be designed. Knowing the design load, the maximum allowable bottom sheathing span (shore spacing) for the materials available can be determined. Next the total load per shore can be determined and the designContinue Reading