Formwork Design Tables for Temporary Structures by Professor Kamran M. Nemati, Study notes of Introduction to Business Management

Download Formwork Design Tables for Temporary Structures by Professor Kamran M. Nemati and more Study notes Introduction to Business Management in PDF only on Docsity! Formwork Design Tables Professor Kamran M. Nemati Winter Quarter 2007 1 Temporary StructuresCM 420 420 0 Temporary StructuresCM 420 Formwork Design Tables Temporary Structures Temporary Structures CM 420 1 Temporary StructuresCM 420 Based on the principles outlined so far, safe spans for many timber and plywood formwork components have been calculated and arranged in tables for use by formwork designer. The tables cover single span beams, two-span beams, and beams continuous over three or more spans carrying a uniform distributed load. The tables can be used to develop a preliminary design for cases where rigorous structural analysis is required for formwork design. Formwork Design Tables 2 Temporary StructuresCM 420 Four sets of allowable (adjusted) stresses are included in the tables. Adjusted stresses for long term and short term loading stresses for formwork made of No. 2 grade Southern Pine and Douglas Fir- Larch. Adjusted stresses for both short term and long term loading of No. 2 Spruce-Pine-Fir and No. 2 Hem-Fir. Table 7-1 shows the expressions which are used to calculate the safe support spacings (spans). Formwork Design Tables Formwork Design Tables Professor Kamran M. Nemati Winter Quarter 2007 2 Temporary StructuresCM 420 420 3 Temporary StructuresCM 420 Table 7-1: Expressions Used in Calculating the Safe Support Spacings of Chapter 7 Design Tables Formwork Design Tables 4 Temporary StructuresCM 420 The tables are in four groups: Table 7-2 through 7-4 for plywood sheathing Tables 7-5 through 7-7 for joists, studs, stringers or any other beam components of the formwork where framing members are used singly Tables 7-8 through 7-10 for wales or other formwork components where the members are used double Table 7-11 and 7-12 for shore loading and bearing checks Formwork Design Tables 5 Temporary StructuresCM 420 Nominal lumber sizes are shown in the tables. All calculations are based on lumber finished on all four surfaces (S4S). Actual thicknesses are shown for plywood. In each table, it is shown whether the safe span is controlled by bending, deflection of shear. Formwork Design Tables Formwork Design Tables Professor Kamran M. Nemati Winter Quarter 2007 5 Temporary StructuresCM 420 420 12 Temporary StructuresCM 420 Formwork Design Tables- EXAMPLE Flat Slab DL + LL = 200 psf 4 ft. 4 ft. 4 ft. 13 Temporary StructuresCM 420 From Table 4-2, the base stress values are: Fb = 875 psi Fv = 95 psi E = 1,600,000 psi As explained above, Tables 7-5.1, 7-6.1, and 7-7.1 are developed with adjusted stresses that can be applied for No. 2 Douglas Fir- Larch or Southern Pine, under long term loads, with conditions as stated. Formwork Design Tables- EXAMPLE Flat Slab 14 Temporary StructuresCM 420 STRINGERS With shores placed 4 ft on centers both ways, the stringers will be 4 ft apart and have a span of 4 ft between supports. They will be designed as continuous beams with an equivalent uniform load equal to the distance between stringers times the uniform load on the formwork (psf): 4 ft x 200 psf = 800 lb/lf Use Table 7-5.1, since the stringers will be continuous over three or more spans. Enter the table at the left on the 800 lb/lf load line. Formwork Design Tables- EXAMPLE Flat Slab Formwork Design Tables Professor Kamran M. Nemati Winter Quarter 2007 6 Temporary StructuresCM 420 420 15 Temporary StructuresCM 420 STRINGERS (Cont’d) Note which members can be used for stringers having a 48-in. span. Among the smaller members that are suitable are: 2x10 ⇒ Allowable span 55” 3x8 ⇒ Allowable span 59” 4x6 ⇒ Allowable span 55” The 2x10 provides the necessary span with the least lumber. (But check with local suppliers for availability) Formwork Design Tables- EXAMPLE Flat Slab 16 Temporary StructuresCM 420 SHEATHING Shore spacing places the stringers 4 ft apart, and this 4 ft then is the span of the joists. How joists are spaced depends on requirements of the sheathing. Assume 3/4-in. Plywood Class I or equal quality plywood is used with its face running in the direction of the span. Since sheathing is continuous over several spans, refer to Table 7-2. The right side of the table, with F’V = 1545 psi, applies since this is a multiple-use form. Formwork Design Tables- EXAMPLE Flat Slab 17 Temporary StructuresCM 420 SHEATHING (Cont’d) From the column for 3/4-in. thickness with face grain parallel to the span, for load of 200 psf, read the allowable span of 19 in. In order to use 4x8 sheets of plywood efficiently, a span of 96 ÷ 5 or 19.2 in. probably will be used, dividing each 8-ft. piece of plywood into five equal spans, while permitting edge support for the plywood panels. Formwork Design Tables- EXAMPLE Flat Slab Formwork Design Tables Professor Kamran M. Nemati Winter Quarter 2007 7 Temporary StructuresCM 420 420 18 Temporary StructuresCM 420 JOISTS This 19.2 in. becomes the required joist spacing, and joist span has already been fixed at 4-ft. What is the required joist size? Joist loading = Joist spacing (ft.) x Load on forms (19.2 ÷ 12) x 200 =320 lb/lf Again using Table 7-5.1 since joists are continuous over several spans, note that a 2x6 loaded at 300 lb/lf has an allowable span of 59 in. and at 400 lb/lf has an allowable span of 51 in. Formwork Design Tables- EXAMPLE Flat Slab 19 Temporary StructuresCM 420 JOISTS (Cont’d) By inspection, the 2x6 appears to be the lightest joist that would be satisfactory on a 48-in. span. But also consider the 4x4 which has an allowable span of 53 in. at 400 lb/lf. The 4x4 is often selected for this type of form, because its shape provides inherent lateral stability. Bearing A check of bearing stresses where joists rest on stringers and where stringers rest on shores would be advisable. Formwork Design Tables- EXAMPLE Flat Slab 20 Temporary StructuresCM 420 Use the tables to determine spacing of wall form members, assuming continuous reuse of the forms and No. 2 grade Douglas Fir-Larch or equal lumber, with sheathing of plywood. Design a 10-ft high wall form for a maximum lateral pressure of 600 psf, assuming no reduction of pressure near the top of the form. Formwork Design Tables- EXAMPLE Wall Forms