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74-3 STRUCTURAL DESIGN3.1 MATERIAL

All conform to ASTM~A36the purpose for which the steel is to be used and for thesuitable materials may be used provided that the are proportioned to comparablefactors.

3.2 WELDINGAll welding designs and procedures shall conform to the current issue of AWS D14.1 , "Specifi-cation for Welding Industrial and Mill Cranes." Weld stresses determined by load combinationCase 1, Sections 33.2 ..5.1 and shall not exceed that shown in the applicable Section3.4.1 or Table 3.4 7-1. Allowable weld stresses for load combination Cases 2 and :3 , Sections3.3.2.5.2 and 3.3.2.5.3 are to be proportioned in accordance with Sections 3A.2 and 3A3.

3.3 STRUCTURE3.3.1 General

The crane girder shall be welded structural steel box section, wide flange beam, standard Ibeam,reinforced beam or a section fabricated from structural plates and shapes. The manufacturershall specify the type and the construction to be furnished. Camber and sweep should bemeasured by the manufacturer prior to shipment

3,3.2 LoadingsThe crane structures are subjected, in service, to repeated loading varying with time whichinduces variable stresses in members and connections through the interaction of the structuralsystem and the cross-sectional shapes. The loads acting on the structure are divided into threedifferent categories, All the loads having an influence on engineering strength analysis areregarded as principal loads, namely the dead loads, which are always present; the hoist load,acting during each cycle; and the inertia forces acting during the movements of cranes, cranecomponents, and hoist loads. Load effects, such as operating wind loads, skewing forces,snow loads, temperature effects, are classified as additional loads and are only considered forthe general strength analysis and in stability analysis. Other loads such as collision, out ofservice wind loads, and test loads applied during the load test are regarded as extraordinaryloads and except for collision and out of service wind loads are not part of the Specification.Seismic forces are not considered in this design Specif ication. However, if required, accelera-tions shalf be specified at the crane rail elevation by the owner or specifier. The allowablestress levels under this condit ion of loading shall be agreed upon with the crane manufacturer.Principal loadsDead Load (DL)

3.3.2.13,3.2.1.1

3.3.2.1.2The weight of all effective parts of the bridge structure, the machinery parts and the fixed equip-ment supported by the structure.Trolley Load (TL)The weight of the trolley and the equipment attached to the trolley.Lifted Load (ll)The fifted load consists of the working load and the weight of the lif ting devices used for handlingand holding the working load such as the load block, lif ting beam, bucket, magnet, grab and theother supplemental devices.

3.3.2.1.3

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Vertical Inertia ForcesThe vertical inertia forces include those due to the motion of the cranes or the crane cornpo-nents and those due to lifting or lowering of the hoist load. These additional loadings mayincluded in a simplified manner by the application of a separate factor for the dead load (DLF)and for the hoist load (HLF) by which tile vertical acting loads. the member forces or tile stressesdue to them must be multipl ied.

3.3.2.1.4.1 Dead Load Factor (DLF)This factor covers only the dead loads of the crane, trolley and its associated equipment andshall be taken according to:

Travel Speed (FPM)(DLF) = 1.1 ~ 1.05 + 2000 . ~ 1.2

3.3.2.1.4.2 Hoist Load Factor (HLF)This factor applies to the motion of the rated load in the vertical direction. and covers inertiaforces, the mass forces due to the sudden lifting of the hoist load and the uncertainties in allowing for other influences. The hoist load factor is 0.5 percent of the hoisting speed in feet perminute, but not less than 15 percent or more than 50 percent, except for bucket and magnetcranes for which the value shall be taken as 50 percent of the rated capacity of the bucket ormagnet hoist.

3.3.2.1.5

3.3.2.23.3.2.2.1

14

(HLF) = D .15 ~ 0.005 x Hoist Speed (FPM):5: 0.5Inertia Forces From Drives (IFD)The inertia forces occur during acceleration or deceleration of crane motions and depend on thedriving and braking torques applied by the drive units and brakes durinq each cycleThe lateral load due to acceleration or deceleration shall be a percentage of the vertical loadand shall be considered as 7.8 times the lateral acceleration or deceleration rate (FT/SEC2) butnot less than 2.5 percent of the vertical load This percentage is to be applied to both the liveand dead loads, exclusive of the end trucks. The live load shall be located in the same positionas when calculating the vertical moment. The moment of inertia of the entire girder sectionabout its vertical axis shall be used to determine the stresses due to lateral forces. The inertiaforces during acceleration and deceleration shall be calculated in each case with the trolley inthe worst position for the component being analyzedAdditional LoadsOperating Wind Load (WLO)Unless otherwise specified, the lateral operational load due to wind on outdoor cranes shall beconsidered as 5 pounds per square foot of projected area exposed to the wind. Where multiplesurfaces are exposed to the wind, and the horizontal distance between the surfaces is greaterthan the depth of the largest surface, the wind area shalt be considered to be 1.6 times trwprojected area of the largest surface. For single surfaces, such as cabs or machinery enclo-sures, the wind area shall be considered to be 1.2 (or that applicable shape factor specifiedASCE 7-Iatest revision) times the projected area.

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3.3.2.33.3.2.3.1

3.3.2.3.2

3.3.2.43.3.2.4.1

Forces due to Skewing (SK)When wheels roll along a rail, the horizontal forces normal to the rail, and tending to skew thestructure shall be taken into consideration. The horizontal forces shaf be obtained by rnultipty-

the vertical load exerted on each wheel by coefficient which upon the ratio thespan to the wheel base. The wheel base is the distance the outermost wheels.

0.200.150.100.05

RATIO = SPANWHEELBASEExtraordinary LoadsStored Wind Load (WLS)This is the maximum wind that a crane is designed to withstand during out of service condition.The speed and test pressure varies with the height of the crane above the surrounding groundlevel, geographical location and degree of exposure to prevailing winds (See ASeE 7-latestrevision as applicable).Collision Forces (CF)Special loading of the crane structure resulting from the bumper stops, shall be calculated withthe crane at OA times the rated speed assuming the bumper system is capable of absorbing theenergy within its design stroke. Load suspended from the lif ting equipment and free oscillatingload need not be taken into consideration. Where the load cannot swing, the bumper effectshall be calculated in the same manner taking into account the value of the load. The kineticenergy released on the collision of two cranes with the moving masses of M I' M2, and a 40percent maximum traveling speed of V T1 and VT2 shall be determined from the following equa-tion:

E=MjM/4Vr: + AVT2)2

2(Mj + M2)The bumper forces shall be distributed in accordance with the bumper characterist ics and thefreedom of the motion of the structure with the trolley in its worst position.Should the crane application require that maximum deceleration rates and/or stopping forcesbe limited due to suspended load or building structure considerations, or if bumper impact ve-locities greater than 40% of maximum crane velocity are to be provided for, such conditionsshould be defined at the time of the crane purchase.Torsional Forces and MomentsDue to the Starting and Stopping of the Bridge MotorsThe twisting moment due to the starting and stopping of bridge motors shall be considered asthe starting torque of the bridge motor at 200 percent of full load torque multiplied by the gearratio between the motor and cross shaft.

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3,3.2.4.2

3.3.2.4.3

3.3.2.5

3,3,2.5,1

3,3,2,5.2

Due to Vertical LoadsTorsional moment due to vertical forces acting eccentric to the vertical neutral axis of theshall be considered as those vertical forces multiplied by the horizontal distance betweencenterline of the forces and the shear center of the girderDue to Lateral Loads:The torsional moment due to the lateral forces acting eccentric to the horizontal neutral axisthe girder shall be considered as those horizontal forces multiplied by the verticalbetween the centerline of the forces and the shear center of tile girder,Load CombinationThe combined stresses shall be calculated for the following cases.Case 1: Crane in regular use under principal loading (Stress Level 1)DL (OLF 8 ) + TL (DLFT ) + LL (1 + HLF) + IFDCase 2: Crane in regular use under principal and additional loading (Stress Level 2)

3,3.2.5.3 Case 3: Extraordinary Loads (Stress Level 3)DL (DLFJ + TL (DLFT ) + LL (1 + HLF) + IFD .; WLO + SK

3.3,2.5.3.1 Crane subjected to out of service windDL + TL + WLS

3.3.2.5,3.2 Crane in collisionDL + TL + LL + CF

3.3.2.5.3,3 Test Loads

3.3.2.63.3,2.6,1

16

CMAA recommends test load not exceed 125 percent of rated load.Local Bending of Flanges Due to Wheel LoadsEach wheel load shall be considered as a concentrated load applied at the center of wheelcontact with the flange (Figure 3.3.2.6-1) Local flange bending stresses in the lateral (x) andlongitudinal (y) direction at certain critical points may be calculated from tile following formulasUnderside of flange at flange-to-web transition ~Point 0:c r : : :, ; - < ( l P(tJ

P

Underside of flange directly beneath wheel contact point ~Point 1:P Po.,

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of

For

-Point

sections-1096 + 1 + O.19?e

= = 3.965- 4835A 3.965e-0.981 -IA79A + 1 120e'1.810 - 1.150)" + 1.060e

t, [:4] [~] for standard'S" sectionwhere: t. published flange thickness for standard "S" section (inches)For parallel flange section (Figure 3.3.2.6-3 & 4)

:=

-2.110 + 1.977A + 0.0076e10.108 7A08A 10.108el0.050 - 0580A + 0.148e2.230 - lAg}" + 1390e

For single web symmetrical sections (Figure 3.3.2.6-2 & 3)2a

:= b - t \f/b ::: section width across flanges (inches)

For other cases (Figure 3.3.2.6-4)

b' :=

where Pt :=

=a =

ab' -distance from centerline of web to edge of flange (inches)

1 7

Load per wheel including HLF (pounds)Flange thickness at point of load application (inches)Web thickness (inches)Distance from edge of flange to point of wheel load application (inches) (Cen-ter of wheel contact)

e = Napierian base = 2.71828 ...The localized stresses due to local bending effects imposed by wheel loads calculated at pointso and 1 are to be combined with the stresses due to the Case 2 loading specified in paragraph3.3.2.5.2 of this Specification.

3.3.2.6.2

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P

Point 1

Figure 3.3.26-1

twP

18

Figure 3.32.6-3

P y P

bFigure 3.3.2.6-2

Point 2

P

Point 1

Point D

Lower Chord of a Box GirderFigure 3.3.2.6-4

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3 . 3 . 2 . 6 . 3

3.3.2.6.4

3.3.2.6.5

the combined stress. the flange bending stresses forof the value calculated per paraqraph 33.2.6.1 web girders are to

The combined stress value (0) obtained by the method prescribed In 3.4.41 shall not exceedthe allowable stress level of 0.66 (j' 0Additionally, in the case of welded plate girders only. the localized stresses on the topside of theflange at the flange-to-web transition (Point are to be combined with the stresses due to theCase 2 loading specified in paragraph 3.3.2.5.2 of this SpecificationThe combined stress value taJ in the weld at Point 2 obtained by the method prescribed inparagraph 3.4.4.2 shall not exceed the allowable weld stress specified in paragraph 3.2 norshall the stress range in the weld exceed the value specified in Table 3.4.7-1 for joint category E.The local flange bending criteria per section 3.3.2.6 is to be met in addition to the generalcriteria of paragraphs 3.3.2.5 and section 3.4.At load transfer points, consideration should be given to lower flange stresses which a-fa notcalculable by the formulas presented in section 3.3.2.6.

3.4 ALLOWABLE STRESSES (aAll)

3.4.13.4.23.4.3

3.4.43.4.4.1

3.4.4.2

STRESS ALLOWABLE ALLOWABLE ALLOWABLE ALLOWABLELEVEL COMPRESSION TENSION SHEAR BEARING

AND CASE STRESS" STRESS STRESS STRESS1 O.60a O.60

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3.4.634.6.1

3.4.6.2

3.4.6.3

20

MemberThe averaqe allowable compression stress on the cross section area of axially loaded cornpres-sion members susceptible to buckling shall be calculated when KLlr (the effective slen-derness ratio of any segment) is less than

[1.. (KLi.r.V ] 0 '2(Cy vpa~=------- _t-. [-35 + 3(KLlr) (KLlrr.;.]8C 8(Cy N

=~V - o ; :The average allowable compression stress on the cross section area of axially loaded cornpression members susceptible to buckling shall be calculated when KLlr (the largest effective slen-derness ratio of any segment) exceeds Cc:

where:

0' =~ 12rr"E23(KLlr)'NMembers subjected to both axial compression and bending stresses shall be proportioned tosatisfy the following requirements:

C r n , O ' b X C ay by ::: 1.0a I e . , [1- O 'd ) 0'a . . . . B>OJ.,

ailwhen a ", ::: 0.15 the following formula may be used:0'; a D > : a b ;a; + q ;0 + a

EW< 1.0

where:KL =r :::Eaypa

effective length factorunbraced length of compression memberradius of gyration of membermodulus of elasticityyield point

= the computed axial stressC Jh computed compressive bending stress at the point under considerationa " = axial stress that will be permitted if axial force alone existeda fj compressive bendinq stress that will be permitted if bending moment alone existed

allowable compression stress from Section 3 .412rr;E

=aNN c-N =:

and

23(KLlrfN1.1 11.0 Case 20.89 Case 3::;,a coefficient whose value is taken to be:

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1. For members in frames to joint translation 0.85For restrained members in frames braced joint translation andsubject to transverse between their supports in the plane of

= 0.6 0.4 [ M) ] but riot less than 0.4where M IM L is the ratio of the srnaller to moments at the ends of that portion of themember unbraced in the of bending under consideration. I 'vl /M2 is positive when th emember is bent in reverse curvature, negative when bent in single curvature.3. For compression members in frame braced against joint translation in the plane of loading

and subjected to transverse loading between their supports, the value of may be deter-mined by rational analysis. However, in lieu of such analysis, the following values may beused:a. For members whose ends are restrained :::0.85b. For members whose ends are unrestrained ::: 1.0

3.4.7 Allowable Stress Range - Repeated LoadMembers and fasteners subject to repeated load shall be designed so that the maximum stressdoes not exceed that shown in Sections 3.4.1 thru 3.4.6, nor shall the stress range (maximumstress minus minimum stress) exceed allowable values for various categories as listed in Table3.4.7-1. The minimum stress is considered to be negative if it is opposite in sign to the maxi-mum stress. The categories are described inTable 3.4.7-2A with sketches shown in Fig. 3.4.7-28.The allowable stress range is to be based on the condition most nearly approximated by thedescription and sketch. See Figure 3.4.7-3 for typical box girders.

TABLE 3.4.7-1ALLOWABLE STRESS RANGE - ksi[ C M A A I J O IN T C A T E G OR YI S e r v i c eI I I I I JClass A B C 0 EI - , I6 3 I 4 9 i 3 5 2 8 2 2 1 5I I

B 5 0 3 9 2 8 2 2 1 8 1 4C 3 7 2 9 2 1 i 1 6 13 1 2D

Stress range values are independent of material yield strength