Crane Runway Beam Design

5-07-10 AISC 89 Crane beam design now includes a check for Web sidesway bucklin...

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PROGRAM ENHANCEMENT

DATE: May 30, 2007

[ REVISED REVISED:: April 14, 2009, see Sections D ane E] [REVISED REVISED:: February 8, 2012, Flange width used to evaluate sidesway buckling is the tension flange] [REVISED REVISED:: April 30, 2012, see Section F]

NUMBER: 5-07-10 PROGRAM: CRANEDES, CRANE, MCRANE MANUAL: Design ENHANCEMENT: AISC 89 Crane beam design now includes a check for Web sidesway buckling due to crane truck wheel loads. TO ACTIVATE: Currently active REFERENCE DWGS: None DESCRIPTION: AISC 89 code section K1.5 provides criteria on Sidesway Web Buckling. Buckling. This check is for concentrated loads that are applied to the compression flange where the flange is not restrained against rotation. A. AISC AISC 89 89 CRIT CRITER ERIA IA The criteria is: For (h / t w) / (l / bf ) <= 1.7 Allowable Wheel Load, R = 6800 * t w³ * [0.4 [0.4 * (h (h / tw / (l / b f ))³] / h

(K1-5)

For (h / t w) / (l / bf ) > 1.7: sidesway web buckling is not a concern. where: l bf

tw h

= largest largest laterally laterally unbraced unbraced length length along either flange at the point point of load, load, runway beam length, in. (mm) = compression flange width, in. (mm) beam with cap channel, use channel depth beam without cap channel, use top flange width = web thickness, in. (mm) = web web dep depth, th, in in. (mm (mm))

B. DESI DESIGN GN REPO REPORT RT:: A new section in the crane beam design reports web sidesway buckling. Web sidesway buckling information appears after the shear calculations. There are 3 groups of information depth/thickness to span/flange width ratio, wheel load, unity check (UC). A description along with a sample report is shown shown below. Depth/thickness to span/flange width ratio: The depth/thickness to span/flange width ratio is a calculated ratio as (h / t w / (l / bf )) which is compared to the limit. The limit is 1.70. Wheel load: The crane bridge truck wheel load is calculated and reported. When the depth/thickness to span/flange span/flange width ratio is less than 1.70, then allowable (Limit) wheel load is calculated and compared to the actual wheel load. When the depth/thickness to span/flange span/flange width ratio is greater than 1.70, then web sidesway sidesway buckling "Does not apply" is reported as the Wheel load limit. Unity check, UC: Actual wheel load / Allowable wheel load limit

ms-its:C:\MBS\HLPWIN1\PE07MBS.chm::/may_07_10.htm

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SHEAR & SIDESWAY BUCKLING: -----------------------------Shear(k ,ksi )----- --------Sidesway_Buckling--------Design Calc Allow [(h/tw)/(L/bf)] Wheel_Load(k ) Shear Stress Stress UC Calc Limit Calc Limit UC ------ -------- -------- -------- ---------------- -----81.42 8.13 19.76 0.41 2.27 1.70 49.50 Does not apply

C. EXAMPLES EXAMPLES:: Check Check Web Web Side Sideswa sway y Buck Bucklin ling g The following two examples illustrate two different crane runway beams and the web sidesway buckling calculation. The first beam has a cap channel and the second beam example does not have a cap channel. These two illustrations show the how the compression flange width contributes to the web sidesway buckling calculation. When the allowable wheel load is required and calculated, then then the actual wheel load is compared to the allowable wheel load. C.1 WEB SIDESW SIDESWAY AY BUCKLI BUCKLING NG DOES DOES NOT APPLY APPLY Consider a W24x68 with a C15x33.9 as a cap channel. Calculate (h / tw) / (l / bf ) = (22.56 / 0.415) / (360 / 15) = 2.265 h = web depth = 22.56" tw = 0.415" l = unbraced length of top flange = 30 * 12 = 360" bf = compression flange width (channel) = 15" For (h / t w) / (l / bf ) > 1.7, sidesway buckling does not apply. See program output below.

============================================================================== Crane Beam Design

1/ 3/08

2:33pm

============================================================================== CRANE BEAM ID: 1 ----------------BEAM SELECTED ------------Wide Flange Beam: W24x68 Top Channel : C15x33.9 SHEAR & SIDESWAY BUCKLING: --------------------------------S -Shea hear( r(k k ,ksi ,ksi )--)-----Design Calc Allow Shear Stress Stress UC ------ ------ ------ ---81.42 8.13 19.76 0.41

--------------Sid Sides esway way_B _Buc uckli klingng------------[(h/tw)/(L/bf)] Wheel_Load(k ) Calc Limit Calc Limit UC ----- ------------- ---2.27 1.70 49.50 Does not apply

C.2 WEB SIDESWA SIDESWAY Y BUCKLIN BUCKLING G Consider a W24x68 without a cap channel. In this example, the beam and channel was specified. Calculate (h / tw) / (l / bf ) = (22.56 / 0.415) / (360 / 8.97) = 1.354 h = web depth = 22.56" tw = 0.415" l = unbraced length of top flange = 30 * 12 = 360" bf = compression flange width (beam) = 8.97"


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For (h / t w) / (l / bf ) <= 1.7, Allowable Wheel Load, R = 6800 * t w³ * [0.4 [0.4 * (h / t w / (l / bf ))³] / h R = 6800 * 0.415³ * [0.4 * 1.354³] / 22.56 = 21.41 kips < 49.50 kips

Resize member

See program output below.

============================================================================= Crane Beam Design

1/ 3/08

2:33pm

============================================================================= CRANE BEAM ID: 1 ----------------BEAM SELECTED ------------Wide Flange Beam: W24x68 Top Channel : -------SHEAR & SIDESWAY BUCKLING: --------------------------------S -Shea hear( r(k k ,ksi ,ksi )--)-----Design Calc Allow Shear Stress Stress UC ------ ------ ------ ---81.42 8.27 19.76 0.42

--------------Sid Sides esway way_B _Buc uckli klingng------------[(h/tw)/(L/bf)] Wheel_Load(k ) Calc Limit Calc Limit UC ----- ------------- ---1.35 1.70 49.50 21.41 2.31*

Conclusion: If the crane wheel load is greater than 21.41 kips, beam is inadequate. -----------REVISION DATED April 14, 2009---------D. AISC 89 89 CRITERI CRITERIA, A, MODIFIE MODIFIED D AND EXPAND EXPANDED ED 1. The criteria criteria is the the same as listed listed above above except except for two two changes. changes. a) b is ten tensi sion on flan flange ge widt width, h, b) wheel load limit is a modified LRFD equation For (dc / tw) / (L / bf ) <= 1.7 Allowable Wheel Load = R n / Ω = 24000 * t w3 / (h) * [0.4 * (d c * bf / (L * t w))3] / Ω For (dc / tw) / (L / bf ) > 1.7: sidesway web buckling is not a concern. where: L = largest laterally unbraced length along either flange at the point of load, runway beam length, (in, mm) bf = tension flange width, (in, mm) tw = web thickness, (in, mm) h = web depth, (in, mm) dc = clear web depth = total depth - 2 * k k = distance from outside of flange to inside of radius between flange and web. This k is not available in the data base, use k = (t f + tw) * 1.3. Safety Factor, Ω = 1.50 2. Basis Basis for for using using the the LRFD load load limit limit equat equation ion AISC Design Manual 7 illustrates the design of crane beams. In section 18.1.3 a check is made on sidesway web buckling and this statement is made: "Although it is generally not recommended that ASD and LRFD design criteria be


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mixed, since sidesway web buckling is an independent failure mode, it seems reasonable that crane runways designed using ASD procedures can be checked using LRFD equations for sidesway web buckling." The LRFD criteria from Design Manual 7 is stated below. "Using Equation K1-7 from the AISC LRFD Steel Specification, Rn = 12000 t w3 / (h) [0.4 ((d c / t w ) / (l / b f ))3 ] However, according to the Specification, "if the concentrated load is located at a point where the web flexural stress due to factored load is below yielding, 24,000 may be used in lieu of 12,000" in this equation." The factored load web stress will be below yielding since the load factor is 1.5 and the allowable stress is a maximum of 0.66 * F y. Note 0.66 * F y * 1.5 = 0.99 F y. Hence the flexural stress is below F y. The limit state wheel load limit is: R n = 24000 * t w3 / (h) * [0.4 * (d c * bf / (l * t w))3] The allowable wheel load limit, ASD, is R n / Ω, Ω = 1.50 E. WEB SIDESWA SIDESWAY Y BUCKL BUCKLING ING DOES DOES NOT APPL APPLY Y Consider a W33x118 without a cap channel. Calculate (dc / tw) / (l / bf ) = (31.38 / 0.550) / (360 / 11.48) = 1.82 h = web depth = 31.38" tw = 0.550" tf = 0.74" k = 1.3 * (0.550 ( 0.550 + 0.740) = 1.577" dc = 31.38 + 2 * 0.740 - 2 * 1.577 = 29.706" l = unbraced length of top flange = 30 * 12 = 360" bf = compression flange width, (beam) = 11.48" (dc / tw) / (l / b f ) = (29.706 / 0.55) / (360 / 11.48) = 1.722 For (dc / tw) / (l / bf ) = 1.72 > 1.7, sidesway buckling does not apply. See program output below.


4/14/09

2:33pm

============================================================================== CRANE BEAM ID: 1 ----------------BEAM SELECTED ------------Wide Flange Beam: W33x118 Top Channel : None SHEAR & SIDESWAY BUCKLING: --------------------------------Sidesway_Buckling--------[(h/tw)/(L/bf)] Wheel_Load(k ) Calc Limit Calc Limit UC ----- ------------- ---1.72 1.70 25.85 Does not apply

E.1 E.1 WEB WEB SIDESW SIDESWAY AY BUC BUCKLI KLING NG


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Consider a W24x68 without a cap channel. In this example, the beam and channel was specified. Calculate (dc / tw) / (l / bf) = (22.56 / 0.415) / (360 / 8.97) = 1.354 h = web depth = 22.56" tw = 0.415" l = unbraced length of top flange = 30 * 12 = 360" bf = tension flange width = 8.97" k = (0.415 + 0.585) * 1.3 = 1.30" dc = 22.56 + 2 * 0.585 - 2 * 1.30 = 21.13 (dc / tw) / (l / b f ) = (21.13 / 0.415) / (360 / 8.97) = 1.269 For (dc / tw) / (l / bf ) = 1.269 <=1.7, Limit state wheel load, R n = 24000 * t w3 / (h) * [0.4 * (d c * bf / (l * tw))3] R n = 24000 * 0.4153 / (22.56) * [0.4 * (21.13 * 8.97 / (360 * 0.415)) 3] = 62.08 k Allowable wheel load, ASD, R n / Ω = 62.08 / 1.50 = 41.39 k > 25.85 kips Member is okay. See program output below.


4/14/09

2:33pm

============================================================================== CRANE BEAM ID: 1 ----------------BEAM SELECTED ------------Wide Flange Beam: W24x68 Top Channel : -------SHEAR & SIDESWAY BUCKLING: --------------------------------Sidesway_Buckling--------[(h/tw)/(L/bf)] Wheel_Load(k ) Calc Limit Calc Limit UC ----- ------------- ---1.27 1.70 25.85 41.40 0.62

Conclusion: If the crane wheel load is greater than 41.40 kips, beam is inadequate. -----------REVISION DATED April 30, 2012---------F. AISC AISC 89 89 CRI CRITER TERIA, IA, OPTIO OPTION N The AISC 05 criterion on sidesway buckling is more more up to date than the AISC 89 criteria. For those engineers that want to use the AISC89 code for structural design and also want the latest AISC 05 for sidesway buckling there is an option to use the AISC 05 sidesway buckling criteria with the AISC 89 structural code. If so, then set this parameter. DS_BUILD(SW86) - Crane runway beam sidesway buckling formula used with the AISC 89 structural code. 0.0 0.0 - Use Use AISC AISC 89 89 1.0 - Use AISC AISC 05 05 (see (see PE 7-06-3 7-06-3))


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The AISC 05 equation includes the added term of t f / h and a different constant. F.1 EXAMPLE Use the same section found in Section E.1 above as a W24x68 without a cap channel when M u < My. h = web depth = 22.56" tw = 0.415" l = unbraced length of top flange = 30 * 12 = 360" bf = compression flange width (beam) = 8.97" tf = compression flange thickness (beam) = 0.585" k = (0.415 + 0.585) * 1.3 = 1.30" dc = 22.56 + 2 * 0.585 - 2 * 1.30 = 21.13 Calculate (dc / tw) / (l / bf ) = (21.13 / 0.415) / (360 / 8.97) = 1.269 For (dc / tw) / (l / bf ) = 1.269 <= 1.7, Using AISC 89, DS_BUILD(sw86 DS_BUILD( sw86)) = 0.0 3

3

R n = 24000 * t w / (h) * [0.4 * (d c * bf / (l * t w)) ] 3

3

R n = 24000 * 0.415 / (22.56) * [0.4 * (1.269) ] = 62.08 k Allowable wheel load, ASD, R n / Ω = 62.08 / 1.50 = 41.43 k > 25.85 kips. Member is okay. Using AISC 05, DS_BUILD(sw86 DS_BUILD( sw86)) = 1.0 h = dc = 21.13 3

2

3

R n = 960000 * t w * tf / (h) * [0.4 * (h* b f / (l * t w)) ] 3

2

3

R n = 960000 * 0.415 * 0.585 / (21.13) * [0.4 * (1.269) ] = 73.48 k Wheel load Limit, ASD, R n / Ω = 73.48 / 1.76 = 41.75 k > 25.85 kips. Member is okay. Though in this example the two codes result in nearly the same capacity, other sections may provide a greater disparity due to the flange thickness being used used in the AISC 05 equation. Using the welded plate section below will illustrate how the AISC 89 formula may not be conservative. h = web depth = 17.43" tw = 0.196" l = unbraced length of top flange = 24.61 * 12 = 295.27" bf = compression flange width (beam) = 4.92" tf = compression flange thickness (beam) = 0.236" Calculate (dc / tw) / (l / bf ) = (17.43 / 0.196) / (295.27 / 4.92) = 1.482 For (dc / tw) / (l / bf ) = 1.482 <= 1.7 Using AISC 89, DS_BUILD(sw86 DS_BUILD( sw86)) = 0.0 R n = 24000 * t w3 / (h) * [0.4 * (d c * bf / (l * t w))3] 3

3

R n = 24000 * 0.196 / (17.43) * [0.4 * (1.482) ] = 13.49 k Wheel load Limit, ASD, R n / Ω = 13.49 / 1.50= 8.99 kip Using AISC 05, DS_BUILD(sw86 DS_BUILD( sw86)) = 1.0 h = dc = 17.43 3

2

3

R n = 960000 * t w * tf / (h) * [0.4 * (d c * bf / (l * t w)) ]


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R n = 960000 * 0.196 3 * 0.236 / (17.43) 2 * [0.4 * (1.482) 3] = 7.31k Wheel load Limit, ASD, R n / Ω = 7.31 7.31 / 1.76 = 4.22 kips Conclusion: The AISC 05 equation is generally more conservative than AISC 89 due to including the flange thickness in the sidesway formula.


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Crane Runway Beam Design

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