Length (ft) At 1 = At 1 (floors) : DL = 61 psf LL = 80 psf

Transcription

1 SUBJECT: EDGE SHEET 80 of 131 Design Columns for the lightest W10's and W12's section. Columns are to be sized for two options: Option I Continuous, Option II with Splices. Then prices are to be compared to select most economical option. Both explicit calculations or Column Design Tables may be used. COLUMN B-4 LOAD TAKEOFF Roof = 3 rd Floor = 2 nd Floor = Dead load (psf) KLL= 4 Live load (psf) Fy (ksi)= Bold Numbers are 80 Roof Live Loads Tributary Areas (At): Width (ft) Length (ft) At 1 = At 1 30 At 1 (floors) : DL = 61 psf LL = 80 psf 18 Note: Live load reduction can be applied in accordance with ASCE 7-02 section (see ASCE 7-02 Eq. 4-1) L = L o *( /AI^0.5) ASCE 7-02 Eq. 4-1 Use the larger of: L = reduced design live load value in psf L > 0.5*Lo (columns supporting one floor) L o = unreduced live load in psf L > 0.4*Lo (columns supporting two or more floors) A I = influence area A I = Tributary area *KLL if AI > 400 ft^2 live load reduction is allowed AI (1) = 2160 >400 ft^2 L (2nd floor) = L (3rd floor) = 46 psf > 32 psf, thus use = psf > 40 psf, thus use = 46 Note: Roof Live loads are NOT allowed to be Reduced

2 SUBJECT: EDGE SHEET 81 of 131 METHOD 1 - EXPLICIT CALCULATIONS METHOD 2 - USE TABLES CONTINUOUS - L =13 FEET Notation: φpn - design compressive strength, kips Fcr - critical design force λc - width-thickness ratio Ag - gross area of member, in 2 Fy - specified yield strength, ksi E - modulus of elasticity, ksi K - effective length factor l - Laterally unbraced length of member, in r - governing radius of gyration about the axis of buckling, in Begin Load Takeoff from roof and proceed downward: From Ground floor to 2nd floor: dead loads (psf) live loads (psf) Roof rd Floor nd Floor P u = [1.2*dead load + 1.6*live load] P u = [1.2*dead load + 1.6* roof live load] Pu (Roof) = Pu (3rd Floor) = Pu (2nd Floor) = 68 psf * A1 = 37 kips 147 psf * A1 = 79 kips 147 psf * A1 = 79 kips sum = 195 kips PU = 195 kips Note: Use column B2 for ALL Interior Columns.

3 SUBJECT: EDGE SHEET 82 of 131 From Ground floor to 2nd floor: Note: For small axial loads the smallest section from the column design Tables (Table 4-2 LRFD) may not be the lightest. If this is the case, do explicit calculations and then try a section from the Table 1-25 LRFD. Use W8x24 as the smallest size (do not use W10 s or W12 s with a nominal weight less than 24 lb/ft). If the column tables are used you only need to write down the section selected and its capacity. φpn = 0.85 * Ag * Fcr Fcr = (.658 λc^2 ) * Fy when λc < 1.5 Fcr = (0.877 / λc 2 ) * Fy when λc > 1.5 λc = (K * L/π r) * (Fy / E) 0.5 (Equation E2-1 LRFD p ) (Equation E2-2 LRFD p ) (Equation E2-3 LRFD p ) (Equation E2-4 LRFD p ) Fy = 50 ksi K = 1 L = ft Pu = 195 kips E = ksi Assume KL/r = 60 to start λc = Fcr = 38.4 ksi Ag = 5.97 in 2 LRFD p.4-25 Check W 12: Select W12x40 KL/rx = 30.4 Ag = 11.7 in 2 KL/ry = 80.4 ry = 1.94 in λc = 1.07 rx/ry = 2.64 in Fcr = 31.0 rx = 5.13 in φpn = LRFD p.4-26 Check W 10: Select W10x33 KL/rx = 37.2 Ag = 9.71 in 2 KL/ry = 80.4 ry = 1.94 in λc = 1.06 rx/ry = 2.16 in Fcr = 31.2 rx = 4.19 in φpn = 257.5

4 SUBJECT: EDGE SHEET 83 of 131 METHOD 1 - EXPLICIT CALCULATIONS METHOD 2 - USE TABLES CONTINUOUS - L =13 FEET Notation: φpn - design compressive strength, kips Fcr - critical design force λc - width-thickness ratio Ag - gross area of member, in 2 Fy - specified yield strength, ksi E - modulus of elasticity, ksi K - effective length factor l - Laterally unbraced length of member, in r - governing radius of gyration about the axis of buckling, in From Ground 2nd floor to 3rd floor: dead loads (psf) live loads (psf) Roof rd Floor nd Floor - - P u = [1.2*dead load + 1.6*live load] P u = [1.2*dead load + 1.6* roof live load] Pu (Roof) = Pu (3rd Floor) = 68 psf * A1 = 37 kips 147 psf * A1 = 79 kips sum = 116 kips PU = 116 kips

5 SUBJECT: EDGE SHEET 84 of 131 From Ground 2nd floor to 3rd floor: Note: For small axial loads the smallest section from the column design Tables (Table 4-2 LRFD) may not be the lightest. If this is the case, do explicit calculations and then try a section from the Table 1-25 LRFD. Use W8x24 as the smallest size (do not use W10 s or W12 s with a nominal weight less than 24 lb/ft). If the column tables are used you only need to write down the section selected and its capacity. φpn = 0.85 * Ag * Fcr Fcr = (.658 λc^2 ) * Fy when λc < 1.5 Fcr = (0.877 / λc 2 ) * Fy when λc > 1.5 λc = (K * L/π r) * (Fy / E) 0.5 (Equation E2-1 LRFD p ) (Equation E2-2 LRFD p ) (Equation E2-3 LRFD p ) (Equation E2-4 LRFD p ) Fy = 50 ksi K = 1 Pu = 116 kips L = ft E = ksi Assume KL/r = 60 to start λc = Fcr = 38.4 ksi Ag = 2.42 in 2 LRFD p.4-25 Check W 12: Select W8x24 KL/rx = 45.6 Ag = 7.08 in 2 KL/ry = 96.9 ry = 1.61 in λc = 1.28 rx/ry = 2.12 in Fcr = 25.2 rx = 3.42 in φpn = LRFD p.4-26 Check W 10: Select W8x24 KL/rx = 45.6 Ag = 7.08 in 2 KL/ry = 96.9 ry = 1.61 in λc = 1.28 rx/ry = 2.12 in Fcr = 25.2 rx = 3.42 in φpn = 151.5

6 SUBJECT: EDGE SHEET 85 of 131 METHOD 1 - EXPLICIT CALCULATIONS METHOD 2 - USE TABLES CONTINUOUS - L =13 FEET Notation: φpn - design compressive strength, kips Fcr - critical design force λc - width-thickness ratio Ag - gross area of member, in 2 Fy - specified yield strength, ksi E - modulus of elasticity, ksi K - effective length factor l - Laterally unbraced length of member, in r - governing radius of gyration about the axis of buckling, in From 3rd floor to roof level: dead loads (psf) live loads (psf) Roof rd Floor nd Floor - - P u = [1.2*dead load + 1.6*live load] P u = [1.2*dead load + 1.6* roof live load] Pu (Roof) = 68 psf * A1 = 37 kips sum = 37 kips PU = 37 kips

7 SUBJECT: EDGE SHEET 86 of 131 From 3rd floor to roof level: Note: For small axial loads the smallest section from the column design Tables (Table 4-2 LRFD) may not be the lightest. If this is the case, do explicit calculations and then try a section from the Table 1-25 LRFD. Use W8x24 as the smallest size (do not use W10 s or W12 s with a nominal weight less than 24 lb/ft). If the column tables are used you only need to write down the section selected and its capacity. φpn = 0.85 * Ag * Fcr Fcr = (.658 λc^2 ) * Fy when λc < 1.5 Fcr = (0.877 / λc 2 ) * Fy when λc > 1.5 λc = (K * L/π r) * (Fy / E) 0.5 (Equation E2-1 LRFD p ) (Equation E2-2 LRFD p ) (Equation E2-3 LRFD p ) (Equation E2-4 LRFD p ) Fy = 50 ksi K = 1 Pu = 37 kips L = ft E = ksi Assume KL/r = 60 to start λc = Fcr = 38.4 ksi Ag = 1.12 in 2 LRFD p.4-25 Check W 12: Select W8x24 KL/rx = 45.6 Ag = 7.08 in 2 KL/ry = 96.9 ry = 1.61 in λc = 1.28 rx/ry = 2.12 in Fcr = 25.2 rx = 3.42 in φpn = LRFD p.4-26 Check W 10: Select W8x24 KL/rx = 45.6 Ag = 7.08 in 2 KL/ry = 96.9 ry = 1.61 in λc = 1.28 rx/ry = 2.12 in Fcr = 25.2 rx = 3.42 in φpn = Lab Note: When beams and girders are framed to columns with simple shear connections, the columns are usually designed as concentrically loaded members.

8 SUBJECT: EDGE SHEET 87 of 131 SPLICED vs CONTINOUS W10's Continous: Member Length (ft) Weight (tons) Cost W10x $1,030 Wt. / ft (lb)= 33 Total cost = $1,030 Steel Prices per ton = $1,600 Wt of additional splice (lb) b = 500 All columns spliced: Member Length (ft) Weight (tons) Cost W10x $343 Wt. / ft (lb)= 33 W8x $250 Wt. / ft (lb)= 24 W8x $250 Wt. / ft (lb)= 24 1 splice = 0.25 Total cost = $400 $1,242 TOTAL COST = $1,242 Answer: Continuous columns are more economical b -- indicates general value according to Modern Steel Construction. April 2000.

9 SUBJECT: EDGE SHEET 88 of 131 SPLICED vs CONTINOUS W12's Continous: Member Length (ft) Weight (tons) Cost W12x $1,248 Wt. / ft (lb)= 40 Total cost = $1,248 Steel Prices per ton = $1,600 Wt of additional splice (lb) b = 500 All columns spliced: Member Length (ft) Weight (tons) Cost W12x $416 Wt. / ft (lb)= 40 W8x $250 Wt. / ft (lb)= 24 W8x $250 Wt. / ft (lb)= 24 1 splice = 0.25 Total cost = $400 $1,315 TOTAL COST = $1,248 Answer: Continuous columns are more economical b - indicates general value according to Modern Steel Construction, April 2000