1. CMAA SPECIFICATION NO. SPECIFICATIONS FOR TOP RUNNING BRIDGE AND GANTRY TYPE. MULTIPLE GIRDER ELECTRIC OVERHEAD. particular, CMAA 70 – Specifications for Top Running Bridge & Gantry Overhead Traveling Cranes and CMAA 74 – Specifications for Top. CMAA ecificationI anufac Associatio For Electric Overhead Traveling Cranes Errata Sheet CMAA Specification #70,Revised Under
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CMAA 70 - Download as PDF File .pdf) or read online. cRANE MANUFACTTURERS. Home; CMAA Preview Secure PDF. ℹ Add to Cart. Printed Edition + PDF; Immediate download; $; Add to Cart. CMAA SPECIFICATION FOR TOP RUNNING BRIDGE AND GANTRY TYPE MULTIPLE GIRDER ELECTRIC OVERHEAD TRAVELING CRANES.
Section 1. Revised to specifically address crane runways Section 1. Lr defined for cantilevered runway Sections. Revised Section for operational wind loading. Sections 3. Reference to stress levels removed. Table 3. Revised the Table to specify types of testing required for certain weld types. Figure 3. Updated Section 3.
Revised design factor equations Section 3. Revised Section for proportions for welded box girders. Section 3. Revised to include errata issued for edition. Revised to add lateral deflection limits Sections 3. Revised to limit stresses to Case 2 Allowables Section 3.
Revised wording for bridge rail splices. New Section for Gantry Stability. Sections 4. Revised gear quality classification Section Section 5. Revised Section for Resistors Section 5. New Section for lightning protection. Section 5. New Sections for power circuit limit switches. Revised Section for Inverters Section 5. New Section for Collision Avoidance Section 5.
The crane runway shall be designed with sufticient strength and rigidity to prevent detrimentallateral vertical deflection. Gantry and other types of special cranes may require additional considerations. Flexible conductor systems shall be designed and installed in a manner to minimize the eftects of flexing, cable tension, and abrasion. Runway conductors are normally furnished and installed by the downloadr unless otherwise specified. The conductors shall be properly supported and aligned horizontally and vertically with the runway rail.
The conductors shall have sufticient ampacity to carry the required current to the crane, or cranes,when operating with rated loado The conductor ratings shall be selected in accordance with Article of the National Electrical Codeo For manufactured conductor systems with published ampacities, the intermittent ratings may be used.
The ampacities of fixed loads such as heating, lighting, and air conditioning may be computed as 2. The nominal runway conductor supply system voltage, actual input tap voltage, and runway conductor voltage drops shall result in crane motor voltage tolerances per Section 5. In a crane inquiry the runway conductor system type should be specified and jf!
Individual hoist units shall have their rated capacity marked on their bottom block. In addition, capacity label should be marked on the hoist body. The totallifted load shall not exceed the rated capacity of the crane bridge. Load on individual hoist or.
When determining the rated capacity of a crane, all accessories below the hook, such as load bars, magnets, grabs, etc. Structural parts shall be designed according to the appropriate limits as per Chapter of l specification. Mechanical parts shall be designed according to Chapter of this specification. AII other load carrying parts shall be designed so that the calculated static stress in the material, based on rated crane capacity, shall not exceed 20 percent of the published average ultimate strength of the material.
This limitation of stress provides a margin of strength to allow for variations in the properties of materials, manufacturing and operating conditions, and design assumptions, and under no condition should imply authorization or protection for users loading the crane beyond rated capacity. Due regard shall be given in the design for operation, accessibility, interchangeability and durability of parts.
The coating may consist of an number of coats of primer and finish paint according to the manufacturer's standard or as otherwise specified.
When feasible, the trolley should be placed on the assembled crane bridge, but it is not required to reeve the hoisting rape. AII parts of the crane should be carefully match-marked. AII exposed finished parts and electrical equipment are to be protected for shipment. If storage is. Detail drawings are normally not fumished. Before putting the crane in. The crane service classification closely as possible. Load spectrum is a mean effective foad, which is unifonnly distributed over a probability scale and applied to the equipment at a specified frequency.
The selection of the properly sized crane component to perlorm a given function is detennined by the varying load magnitudes and given load cycles which can be expressed in terms of the mean effective load factor. Operation with no lifted load and the weight of any attachment must be included.
The sum total of the load probabilities P must equal 1. Mean effective load factor. Used to establish crane service class only ;"". The cranes can be classified into loading groups according to the service conditions of the most severely loaded part of the crane. The individual parts which are clear1y separate from the rest, or fonning a self contained structural unit, can be classified into different loading groups if the service conditions are fully known. This service class covers cranes which may be used in installations such as powerhouses, public utilities, turbine rooms, motor rooms and transformer stations where precise handling of equipment at slow speeds with long, idle periods between lifts are required.
Capacity loads may be handled for initial installation of equipment and for infrequent maintenance. This service covers cranes which may be used in repair shops, light assembly operations, service buildinr-c;.
Loads may vary fro" load to occasional full rated loads with two to five lifts per hour, averaging ten feet per lift. This service covers cranes which may be used in machine shops or papermill machine rooms, etc. In this type of service the crane will handle loads which average 50 percent of the rated capacity with 5 to 10 lifts per hour, averaging 15 feet, not over 50 percent of the lift at rated capacity. This service covers cranes which may be used in heavy machine shops, foundries. In this type of service, loads approaching 50 percent of the rated capacity will be handled constantly during the working periodo High speeds are desirable for this type of service with 10 to 20 lifts per hour averaging 15 feet, not over 65 percent of the lifts at rated capacity.
Applications may include magnet, bucket, magnet'bucket combination cranes for scrap yards, cement milis, lumber milis, fertilizer plants, container handling, etc. Applications may include custom designed specialty cranes essential to performing the critical work tasks affecting the total production facility.
These cranes must provide the highest reliability with special attention to ease of maintenance features. TABLE 2.
Other suitable materials may be used provided that the parts are proportioned to comparable design factors. Allowable weld stress es for load combination cases 2 and 3, Sections 3. The manufacturer shall specify the type and the construction to be fumished.
The loads acting on the structure are divided into three different categories. AII of the loads having an influence on engineering strength analysis are regarded 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, crane componen. Load effects, such as operating wind loads, skewing forces, snow loads, temperature effect, loads onwalkways, stairways, platforms and handrails are classed as additionalloads and are only considered for the general strength analysis and in stability analysis.
Other loads such as collision, out of service wind loads, and test loads applied during the load test are regarded as extraordinary loads and except for collision and out of service wind loads are not part of the specification.
Seismic forces are not considered in this design specification. However, if required, accelerations shall be specified at the crane rail elevation by the owner or specifier. The allowable stress levels under this condition of loading shall be agreed upon with the crane manufacturero , 3.
The vertical inertia forces include those due to the motion of the cranes or crane components and those due to lifting or lowering of the hoist loado These additional loadings may be included in a simplified manner by the application of a separate factor for the dead load DLF and for the hoist load HLF by which the vertical acting loads, the member forces or the stress es due to them, must be multiplied.
This factor applies to the motion of the rated load in the vertical direction, and covers inertia forces. The hoist load factor is 0. The inertia forces occur during acceleration or deceleration of crane motions and depend on the driving and braking torques applied by the drive units and brakes during each cycle.
The inertia forces during acceleration and deceleration shall be calculated in each case with the trolley in the worst position for the component being analyzed. Wind load WLO. Unless otherwise specified. The wind load on the trolley shall be considered as equally divided between the two girders. Where multiple surfaces are exposed to the wind, such as bridge girders, where the horizontal distance between the surfaces is greaterthan the depth ofthe girder, the wind area shall be considered to be 1.
For single surfaces. When two wheels or two bogies roll along a rail, the horizontal forces normal to the ral, and tending to skew the structure shall be taken into consideration. The horizontal forces shall be obtained by multiplying the verticalIDad exerted on each wheel or bogie by coefficient S'k which depends upon the ratio 01 the span to the wheel base. This is the maximum wind that a crane is designed to withstand during out of service condition.
The speed and test pressure vares with the height of the crane above the surrounding ground leve', geographicallocation and degree of exposure to prevailing winds See ASCE 7 -Iatest revision as applicable. Specialloading 01the crane structure resulting Irom the bumper stops, shall be calculated with the crane at 0. Load suspended from lifting equipment and free oscillating load need not be taken into consideration. Where the load cannot swing, the bumper effect shall be calculated in the same manner, taking into account the value of the loado The kinetic energy released on the collision of two cranes with the moving masses of M" M2' and a 40 percent maximum traveling speed 01 VT, and VT2 shall be detennined from the l0wing equation: The bumper forces shall be distributed in accordance with the bumper characteristics of the motion of the structure with the trolley in its worst position.
The twisting moment due to the starting and stopping of bridge motors shall be considerad as the starting torque of the bridge motor at percent of fullload torque multiplied by the gear ratio between the motor and cross shaft. Torsional moment due to vertical forces acting eccentric to the vertical neutral axis 01 the girder shall be considered as those vertical forces multiplied by the horizontal distance between the centerline of the forces and the shear center 01 the girder.
Due to Lateral Loads: The torsional moment due to the lateral forces acting eccentric to the horizontal neutral axis of the girder shall be considered as those horizontal forces multiplied by the vertical distance between the centerline of the forces and the shear center of the girder.
Longitudinal Distrlbutlon 01 the Wheel Load. Local stresses in the rail, rail base, flanges, welds, and in the web plate due to wheelload acting normal and transversely to the rail shall be determined in accordance with the rail and flange system. Case 1: Case 2: Case 3: The analysis for proving safety against local buckling and lateral and torsional buckling of the web plate and local buckling of the rectangular plates forming part 01 the compression member, shall be made in accordance with a generally accepted theory of the strength of materials.
See Section 3. The average allowable compression stress on the cross section afea 01 axially loaded compression members susceptible to buckling shall be calculated when KUr the largest effective sJenderness ratio 01 any segment is less than Cc: On the cross section 01 axially loaded compression members susceptible to buckling shall be calculated when KUr exceeds Cc:. Members subjected to both axial compression and bending stresses shall be proportioned following requirements: J' --!
For restrained compression members in trames braced against joint transJation and not subject to transverse foading between their supports in!
For compression members in trame braced against joint translation in the plane of loading and subjected to transverse foading between their supports, the value 01 Cm may be determined by rational analysis. However, in fieu of such analysis, the following values may ,but not less than 0.
Allowable Stress Range -Repeated LOId Members and fasteners subject to repeated load shall be designed so that the maximum stress does not exceed that shown in Sections 3. The minimum stress is considered to be negative if it is opposite in sign to the maximum stress. The categories are described in Table 3. The allowable stress range is to be based on the condition most nearly approximated by the description and sketch. See Figure 3.
TABLE 3. Buckllng Local Buckling or Crlppllng 01 Flat Plates The structural design of the crane must guard against local buckling and lateral torsional buckling of the web plates and cover plates of girder. For purposes of assessing buckling, the plates are subdivided into rectangular panels of length "a" and width obR.
The length "a" of these panels corresponds to the center distance of the full depth diaphragms or transverse stiffeners welded to the panels. It is not the intention of this specification to enter into further details of this problem.
For a more detailed and complex analysis such as evaluation of elastically restrained edges, continuity of plate, and determination of the coefficient of restraint, reference should be made to specialized literature. If the resulting the value is above the proportionallimit, buckling is said to be inelastic.
For inelastic buckling, the critical stress shall be reduced to: Deslgn Factors In the case of elastic buckling: The design factor DFB requirements of buckling are as follows: Uh should not exceed 25 Ub should not exceed 65 bit and hit to be substantiated by buckling analysis. Aa 3 lo Dlaphragms and Vertical Stiffeners The spacing 01 the vertical web stiffeners in inches shall not exceed the amount given by the 10rmula: This moment 01 inertia does not include additional requirements, i1 any, 10r local moments.
Stiffener elements shall be proportioned to the provisions 01Section 3. AII diaphragms shall bear against the top coyer plata and! The thickness of the diaphragm plata shaH be sufficient to resist the troIey wheel load in bearing at the allowable bearing stress on the assumption that the wheelload is distributed over a distance equaJ to the width 01 the rail base plus twice the distance 1rom the rail base fa the top of the diaphragm plate.
Short diaphragms shall be placed between full depth diaphragms so that the maximum distance between adjacent diaphragms willlimit the maximum bending stress in the trolley rail without VIF forces to 18 ksi for 'oad combination Case 1, Section 3.
Vertical inertia forces shall not be considered in determining deflection. Welded Torsion Box Glrders. Torsion girders, with the bridge rail over one web plata, are to be designed with the trolley wheelload assumed to be distributed over a distance of the web plate as indicated in Section 3. For box girders having compression flange areas no more than 50 percent greater than that of the tension flange, and with no more that 50 percent difference between the Breas 01the two webs, the shear center may be assumed to be at the centroidal axis 01 the cross section.
Single Web Girders. Single web girders include wide flange beams, standard I beams, or beams rein10rced with plate, or other structural configurations having a single web. Where necessary, an auxiliary girder or other suitable means should be provided to support overhanging loads to prevent undue torsional and lateral deflections. The maximum ,. Al For cases 2 and 3, proportion where: Box section girders built up 01 two beams, either with or without reinforcing flange platas, shall be designed according to the same design data as for box section girder cranes for stress and deflection.
End trucks may be of the rotating axle or fixed axle type as specified by the crane manufacturero. The bridge end trucks should be constructed of structural steel or other suitable material. Provision shall be made to prevent the end truck from dropping more than one inch in case of axle failure. Guards shall be provided in front of each outside wheel and shall project below the top of the runway ral.
Load combinations and basic allowable stresses are to be in accordance with Sections 3. When specified, a footwalk with a handrail should be provided. The handrail shall be at least 42 inches high and provided with an intermediate railing. Footwalk shall have a slip-resistant walking surface and shall be protected on all exposed edges by a suitable roe guardo AII footwalks shall be designed for a live load of 50 pounds per square foot.
For allowable stresses, use stress level 2, Section 3. It shall be so located as not to interfere with the hook approach. The operator's cab shall be open type for indoor service unless otherwise specified. The cab sha C.. AII bolts for supporting member connections should be in shear.
Cab shall be provided with an audible warning device and tire extinguisher. Provision shall be made in the operator's cab for placement of the necessary equipment, fittings. AII cabs should be provided with a seat unless otherwise specified. The controllers or their operating handles are located as shown in Section 5.
FRAMES The trolley trame shall be constructed of structural steel and shall be designed to transmit the load to the bridge rails without deflection which will impair functional operation of machinery. Load combinations and allowable stresses are to be as specified in Sections 3. Bridge rails shall be joined by standard joint bars or welded. The ends of non-welded sections shall be square and sections joined without opening between ends.
Provision shall be made to prevent creeping of the bridge rails. Bridge rails shall be securely fastened in place to maintain center distance of rails. Bridge and runway rails should be in accordance with Table 4.
End ties are to be provided between girders when deemed necessary tor stability ot the girders. When equalizer bridge trucks are incorporated in the crane design, the end ties shall be ot rigid construction and ot adequate strength to resist all ot the above loads.
Flexiblity ot the end tie is necessary when equalizing provisions are not employed. Due consideration should be given to the various types of loading conditions and the resulting stresses, which shall not exceed the values as stated in Section 3. Zinc causes stress corrosion in A and should not be used.
Allowable bolt stresses for load combination Cases 2 and 3, Sections proportioned in accordance with Sections 3. Design of leg, end tie, strut, and si" members shall conform to applicable sections of this specification.
In arder to facilitate a measure of durability ,Ioad and service factors shall be used to determine the mea n effective load in a service classifK:: The mechanical formula. The maximum load used in the above formula shall be established by using the rated load and applicable dead loads, so positioned as to result in the maximum reaction on the component under consideration. The minimum load to be used shall be established by the dead load of the bridge and or trolley only.
For Kw factors of trolley and bridge wheel assemblies and axle bearing selection, see Section 4. The machine service factor Cdlisted in rabie 4. Stress concentration factors can be obtained from data in stress concentration factors by R.
Peterson see Section 1. TABLE 4. Cara shall be taken to minimiza changas in geometry that may cause stress concentrations. The trame shall be designed for rated loado The rated load stress shall not exceed 20 percent of the average ultimara strength of the material used. Where stress concentrations exist, the stress as amplified by the appropriate amplification factor with due consideration for impact and service shall not exceed the endurance strength of the material used.
Other materials agreed upon by the manufacturar and recognized as suitable for the appfication may be used, provided the parts are proportionate to give appropriate design 1actors. The hook shall be of rolled steel, forged steel or a material agreed upon by the manufacturer and recognized as suitable for the application. The hook shall be desgned based on the rated loado The hook rated load stress shall be calculated considering the rated toad on the hook using: Straight beam theory with the calculated combined stresses not to exceed 20 percent of the material's average ultimate strength.
Modi1ied curved beam theory with the calculated combined stresses not to exceed 33 percent 01 the material's average ultimate strength. Plastic theory or testing with the combined stress es not to exceed 20 percent of the stress produced by the straightening load as obtained by test or calculation by this theory.
The hook shank stress shall be calculated considering the rated load and shall not exceed 20 percent of the materal's average ultimate strength. At points of geometric discontinuities, the calculated stress as amplified by the appropriate stress ampli1ication factor with due consideration for impact and service shall not exceed the endurance strength.
Load block sheave pins and trunnions shall be designed per the applicable Section 4. An overload limiting device is normally only provided when speci1ied. Such device is an emergenl;Y device intended to permit the hoist to litt a freely suspended load within its rated capacity, but prevents fitting of an overload that would cause permanent damage to a properly maintained hoist, trolley or crane. Variables experienced within the hoist system, such as, but not limited to, acceleration of the loads.
The over1oaddevice 18actuated only by loads incurred when lifting a freely suspended load on the hook. Therefore, an overload device cannot be relied upon to render the hoisting mechanism inoperative if other sources, such as but not limited to, snagging of the load, two blocking of the load block. The overload limit device is connected into the hoisting control circuit and, therefore. The rated capacity load plus the load block weight divided by the number of parts of rope shall not exceed 20 percent of the published breaking strength of the rope except rapes used for holding or lifting molten metal which shall not exceed The wire rape construction shall be as specified by the crane manufactureroWhen extra strength steel or wire center rope is used, the crane manufacturer's specifications shall so state.
Wherever exposed to temperatures at which fibre cores would be damaged, ropes having an independent wire-rope. The fleet angle of the rape should be limited to 1 in 14 slope 4 degrees as shown in Figure 4.
The fleet angle of the rape should be limited to 1 in 12 slope 4 degrees45 minutes as shown in Figure 4. The CMAA recornmended sheave and drum to rope diameter ratlos have been found by experience tI give satisfactory performance over a wide range of applicatlons.
Wlre rope is considered a consumabll maintenance item. The wire rape maintenance interval will tend to be lengthened by: Smaller sheaves may cause an increase in rope mantenance. The pitch diameter of equalizer sheaves should not be less than one-half of the diameter of running sheaves, and also shall not be less than 12 times the rope diameter when using 6 x 37 class rape or 15 times the rope diameter for 6 x 19 class rope. When special clearance, limitations.
The drum material shall be as specified by the crane manufacturer. Welded steell. If a welded drum is used, refer to Table 2.
Stresses shall be evaluated usng criteria defined in Section 3. The drum shall be so designed that not less than two wraps of hoisting rope will remain on each anchorage when the hook is in ts extreme low position, unless a lower limit device is provided, in whch --case no les s than one wrap shall remain. No overlap of the rope shall be permitted when the hook is at its high point. Grooving should be right and left hand unless otherwise specified by the crane manufacturero. Recommended minimum drum groove depth is.
Recommended mnimum drum groove ptch is either 1. Table 4. Smaller drums may cause an increase in rope maintenance. When special clearance, lift or low headroom is required, it may be necessary to de viate from these limitatons. When worm gearing s used for travel drives, consideraran should be given to its backdriving characteristcs. AII gears and pnions shall be constructed of material of adequate strength and durablty to meet the requirements for the intended class of service.
For the purpose of ths specification, hoist gearing strength and durablity shall be based on the horsepower required to lift the rated loado Travel gearing strength and durability shall be based on the motor name plate rating. Due consideration shall be given to the maximum brake torque which can be applied to the drive. Also, consideration shall be given to the fact that gearing for travel drives transmit a larger porton of the available motor torque than gearing for hoist drives.
For the purpose of this specification, the horsepower formulae may be written: Allowable strength horsepower[ Npd ] Pa. Crane class factor S,. For Cd, refer to Section 4. These factors are not to be used in sizing any commercial gearboxes. AII commercial gearboxes are to be sized according to gearbox manufacturer's recommendations.
Means shall be provided to insure adequate and proper lubrication on all gearing. AII gearing not enclosed in gear cases which may constitute a hazard under normal operating conditions shall be guarded with provision for lubrication and inspection. Guards shall be securely fastened. Each guard shall be capable of supporting the weight of a pound person without distortion, unless the guard is located where it is impossible to step on.
Anti-friction bearings shall be selected to give a minimum rife expectancy based on full rated speed as. Due consideration shall be given to the selection of the bearing in the event a crane is used for a limited time at an increased service class such as: Example-'during 4. Sleeve bearings shall have a maximum allowable unit bearing pressure as recommended bythe bearing manufacturer.
AII bearings shall be provided with proper lubrication or means of lubrication. Bearing enclosures should be designed as lar as practicable to exclude dirt and prevent leakage of oil or grease. This brake shall be applied directly to the motor shaft or some other shaft in the hoist gear train. Hoist holding brakes shall have minimum torque ratings, stated as a percentage of the rated load hoisting torque, at the point where the holding brake is applied as follows: Hoist holding brakes shall have thermal capacity for the frequency of operation required by the service.
Hoist holding brakes shall be provided with means to compensate for lining wear. Each independent hoisting unit of a crane that handles molten materials shall have one of the following arrangements: Each brake shall have a minimum torque rating equal to rated load hoisting torque at the point where the brake is applied.
If the hoist unir has a mechanicalload brake or a controlled braking means that provides emergency braking in the lowering direction upon loss of power, only one holding brake is required. The holding brake shall have a minimum torque rating equal to percent of the rated load hoisting torque at the point where the brake is applied.
Each independent hoisting unit of a crane, except worm-geared hoists, the angie of whose worm is such as to prevent the load fr? Control braking means shall be mechanical, hydraulic, pneumatic or electric power such as eddy current, dynamic, regenerative or counter torque. AII methods must be capable of maintaining controlled lowering speeds. The inherent regenerative controlled braking means of a squirrel cage motor may be used if the holding brake is designed to meet the additional requirement of retarding a decending load upon power removal.
Hoist control braking means shall have thermal capacity for the frequency ot operation required by the service. Trolley Brakes. On cab operated non-skeleton cranes with cab on trolley, a trolley brake shall be provided having torque capability to stop the trolley motion within distance in feet aquel to 10 percent of retad load speed in feet per minute when traveling at rated speed with rated loado On cab-operated non-skeleton cranes with cab on bridge, a trolley brake or non-coasting mechanical drive may be provided when specified.
When provided, the brake or noncoasting mechanical drive shall meet the stop travel distance requirements of Section 4. It a trolley parking brake is provided. A drag brake may be applied to hold the trolley in a desired position on the bridge and to eliminate creep with the power off. On cab-operated non-skeleton cranes. If a bridge parking brake is provided. On cranes designed with high speed and high acceleration rates, consideration provide braking means to achieve proportionally high deceleration rates.
Foot operated brakes shall require an applied force of not more than 70 pounds to develop rated brake torque. Brake pedals, latches, and levers should be designed to allow release without the exertion of greater force than was used in applying the brake. Brakes should be applied by mechanical, electrical, pneumatic.
AII foot-brake pedals shall be constructed so that the operator's foot will not readily slip off the pedal. Foot-operated the pedal. The foot-brake pedals should be so located that they are convenient to the operator at the controls. If parking brakes are provided on the bridge or trolley, they shall not prohibit the use of a drift point in the control circuito. Bridge drives shall consist ot one ot the tollowing arrangements. For the number of driven wheels tor a specific acceleration rate-refer to the electrical Section 5.
A-1 Drive: A-2 Drive: The motor is connected to a self-contained gear reduction unit kxated near the center of the bridge. The truck wheels shall be driven through gears pressed and keyed on their axles or by gears fastened to, or integral with, the truck wheels and with pinions mounted on the end sections of the crossshaft.
The end sections of the cross-shaft shall be connected by suitable couplings. A-3 Drive: The motor is located at the center of the bridge and is connected to the cross-shaft and the gear reduction units with suitable couplings.
Self-contained gear reduction units located near each end of the bridge shall be either directly connected to the wheel axle extension or connected to wheel axles by means of shafts with suitable couplings. A-4 Drive: The motors are located near each end of the bridge without torque shafts.
The motors shail be connected to self-contained gear reduction units. The gear reduction units shaJlbe applied to the truck wheels by means of either suitable shafts and couplings or directly mounted to the wheel axle shaft extension.
Another variation of this drive would separate the high speed aro final reductions by locating the motors near each end of the bridge without torque shafts. The motors will be connected to selfcontained high Speed gear boxes which will drive the truck wheels through gears pressed and keyed on their axles or by gears fastened to the truck wheels, and with pin ions mounted on the end section on the shaft from the high speed gear box and the final reduction shall be connected by means of suitable shafts and couplings.
A-5 Drive: The motor is located near the center of the bridge and is connected to a self-contained gear reduction unit located near the center of the bridge.
A-6 Drive: The motors are located near each end of the bridge and connected with a torque shaft. On the drive end, the motors shall be connected to self-contained gear reduction units by suitable couplings. The output of the gear reduction units shall be connected directly to the truck wheel axle by means 01 suitable shafts and couplings. AII shafts, except the bridge cross-shaft sections which do not carry gears, should be cold rolled shafting quality or better.
The shaft diameter and method of support shall be as specified by the crane manufacturero The bearing spacing for rotating shafts less than rpm shall not exceed that calculated per: The types 01 drive referred to on the table are as defined in Section 4. The allowable angular deflection is expressed in degrees perfoot. In addition the total angular deflection produced by the motor torque in Table 4. AII shafting shall be designad to meet the stresses encountered in actual operation.
For the purposes of this specification, the strength shall be based on the torque required to lift the rated 'Dad for hoist machinery and the motor nameplate rating for drive machinery.
Due consideration shall be given to the maximum brake torque which may be applied to the shaft. When significant stresses are produced by other forces, these forces shall be positioned to provide the maximum stresses at the section under consideration. Impact shall not be included. Combined direct axial and bending with torsional shear: For simply loaded shafting, bending and torsional stresses are maximum on the outer fibf of the shaft and must be combtned.
The transverse shear stresses are maxlmum 00 h neut of the shaft and combine with the torsional stresses but not with the bending stresses. This check is an addition to those in section 4. This is accomplished by applying an appropriate stre amplification factor to the respective nominal stresses not combined as determined in Section 4.
Shafting in bearing must be checked for operating conditions. This bearing stress must not exceed 20 percent of the minimum yield for oscillating shafting when not limited by the bushing material. Cross-shaft couplings, other than flexible type, shall be steel or minimum ASTM Grade A48, latest edition, Class 40 cast iron or equal material as specified by the crane manufacturer. The type of coupling other than flexible may be compression, sleeve or flange type. Flexible couplings shall be the crane manufacturer's standard type.
Motor couplings shall be as specified by the crane manufacturero. Bridge wheels may have either straight treads ortapered treads assembled with the large diameter toward the center of the span. Trolley wheels should have straight treads. Drive wheels shall be matched pairs within 0. When flangeless wheel and side roller assemblies are provided, they shall be of a type and design recommended by the crane manufacturer. WheeIs shall be heat treated onIy If Other suitable materials may be used.
Due consideration shall be given to the brittleness and impact strength of the material used. Slzlng of Wheels and Rails. Wheels shall be designed to carry the maximum wheel load under normal conditions without undue wear. The maximum wheelload is that wheelload produced with trolley handling the rated load in the position to produce the maximum reaction at the wheel, not including VIF. When sizing wheels and rails, the following parameters shall be considered. The values in the table are established by the product of D x W x K.
Other cranes may require special considerations. The factors shown at ton capacity may be used for capacities above 1aO-tons.
Sf TW. TA8LE 4. The speed factor C. These factors are obtained from the following formulas:. The wheel service factor Smis equal to 1.
This factor recognizes that the interaction between rail and wheel is more demanding in terms of durability than well aligned and lubricated interaction of machined parts. Tapered tread wheels may have a clearance ayer the rail head of percent of the clearance provided for straight tread wheels as recommended by the crane manufacturer.
When rotating axles are used. BETH l' ARA-A These bumpers, when used, sha" have the following minimum characteristics: Have energy absorbing ordissipating capacity to stop the crane when traveling with poweroff direction at a speed of at least 40 percent of rated load speed.
Be capable of stopping the crane not including load block and lifted load unless guided vertical'y at a rafe of deceleration not to exceed an average of 3 leer per second per second when traveling with power off in either direction at 20 percent of rated load speed. Be so mounted that there is no direct shear on bolts upon impacto Bumpers shall be designed and installed to minimize parts falling from the crane in case of breakage or loosening of bolted connections. When more than one crane is located and operated on the same runway, bumpers shall be provided on their adjacent ends or on one end of one crane to meet the requirements of Sections 4.
It is the responsibility of the owner or specifier to provide the crane manufacturer necessary for proper bumper design includes: Number of cranes on runway, bridge speed, approximate weight, etc. Height of runway stops or bumper above the runway rail. Clearance between cranes and end of runway. Trolley Bumpers -A trolley shall be provided with bumpers or other means of equivalent effect, unless the trolley is not operated near the ends of trolley travel, or is restricted to a limited distance of the bridge girder and there is no hazard of striking any object in this limited area.
These bumpers. Have energy absorbing or dissipating capacity to stop the trolley when traveling with power off in either direction at a speed of at least 50 percent of rated 'Dad speed. Be capable of stopping the trolley not including load block and lifted load unless gu;ded vertical'y at arate of deceleration not to exceed an average of 4.
Be so mounted that there is no direct shear on bolts upon impacto Bumpers shall be designed and installed to minimize parts falling from the trolley in case of breakage.
When more than one trolley is operated on the same bridge, bumpers shall be provided on their adjacent ends or on one end of the trolley to meet the requirements of Sections 4. Trolley stops shall be provided at the limit of the trolley travel, and shall engage the tu" surface of the bumper.
Stops are located at the limits of the trolley and bridge travel and shall engage the tull surface of the bumper. Stops engaging the tread of the wheeJare not recommended.
Cranes for alternating current power supplies may be equipped with squirrel cage and wound rotor motors with compatible control for single speed, multi -speed or variable speed operation.
Cranes for direct current power supplies, or altemating current power supply rectified on the crane, may be equipped with series, shunt or compound wound motors with compatible control for single speed or variable speed operation. The crane manufacturer shall furnish and mount sIl electrical equipment, conduit and wiring, unless otherwise specified.
If it is necessary to partially disassemble the crane for shipment, all conduit and wiring affected shall be cut to length and identified to facilitate reassembly. Bridge conductors, runway collectors and other accessory equipment may be removed for shipment. Designs not in accordance with these standards may be specified. AC induction motors may be wound rotor slip ring or squirrel cage single speed or multi-speed types.
DC motors may be series, shunt. AC Motors used wlth Inverters: Motors shall be AC Induction Iow slip type. Motor construction shall be TENV. TEFC, motor with independent blower, or open drip proof type. Motor insulation should be Class F rated and should be thermally protected with sensor embedded in the motor winding.
Motor selection shall be based on proper horsepower calculation for the drive of the required service class. The motor's duty rating should be based on the service class and on the speed range required for the application. Motor Insulatlons. Unless otherwise specified by the crane manufacturer. TABLE 6. C DEG. C, the permissible winding temperature rise must be decreased by the same amount, or may be decreased per the applicable NEMA Standards.
C ambient temperature unless otherwise specified by the downloadr. Motors shall be provided with anti-friction bearings. Voltage Motor rated voltage and corresponding nominal system voltage shall be in accordance with Table 5. Voltage Source and 3. Al SE Std. Maximum -AC from Rated Voltage motor input voltage. AII AC induction motors with rated frequency and balanced voltage applied shall be capabJe of accelerating and running with rated hook load at plus or minus 10 percent of rated motor voltage, but not necessarily at rated voltage performance values.
Performance will not necessarily be the same as when the motor is operating with a balanced voltage at the motor terminals. DC motors shall be capable of accelerating and running with rated hook load with applied armature and field voltages up to and including percent of the rated values of the selected adjustable voltage power supply.
Performance will not necessarily be in accordance with the standards for operation at rated voltage. Operation at reduced voltage may result in unsatisfactory drive performance with rated hook load such as reduced speed, slower acceleration.
Protective devices may operate stopping the drive in order to protect the equipment. Operation at eJevated voltages may result in unsatisfactory operation. Prompt corrective action is recommended; the urgency for such action depends upon many factors such as the location and nature of the load and circuits involved and the magnitude and duration of the deviation of the voltage.
These conditions should be reviewed based on the type of drive used. Motor Time Ratlngs Unless otherwise specified by the crane manufacturero the minimum accordance with Table 5. Squlrrel cage motors shall have high startlng torque, low starting current and h91 slip at tull load, similar fo NEMA Design D, unJess otherwise specified by the crane manufacturero Motor size selection: The motor size selection involves torque and thermal considerations.
The motor rating of any drive, hoist or horizontal travel, using either AC or DC power, is basically fhe mechanical horsepower with considerations for the effect of control, ambient temperatura, and service class. This includes all items applicable to the hoist such as the downloadr's Jifted load, which includes downloadrfumished attachments and crane manufacturers furnished items including the hook block and attachments. TABLE 5.
The values of gear efficiency shown apply primarily to spur, herringbone, and are not intended for special cases such as worm gearing. Reduction of E by.. Ropes Supporting One Hook Block Double Reeved 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 Single Reeved 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 The hoist motor shall be selected 50 that its horsepower following formula: For AC wound rotar systems, magnetic or sta tic control, with secondary permanent slip resistors.
For example, this may require larger trame, largar horsepower, torced cooling, etc. Latitude is permitted in selecting the nearest rated motor horsepower, ayer or under the required horsepower, to utilize commercially available motors. In either case, due consideration must be given to proper performance of the drive.
The travel motor shall be selected so that the horsepower rating is not less than that given by the following formula: For reference see Table 5. Table 5. For guidance, see Table 5. See Table 5. Load Speed Feet per Sec. The acceleration rate shall not exceed the values shown in Table 5. Dry Rails per Secoon. TABlE 5. IThe recommended values shown for Class E are based on a maximum of 30 percent time on and a maximum of 25 cycles per hour of the drive.
A cycle for a bridge or trolley consists of two 2 moves one 1 loaded and one 1 unloaded. For drive duty higher than this basis, it is recommended that duty cycle methods of analysis be used. Fordrive duty higherthanthis methods of analysis be used. Compute the free running bridge motor horsepower HP F at rated load and rated speed.
OO V 2 where Vw is the wind velocity mph. Proper speed control, acceleration and braking without wind. Bridge speed. Avoidance of wheel skidding which could likely occur under no load, low percent driven wheels and wind conditions. Sufficient braking means to maintain the bridge braking requirements as defined in Section 4. The gear ratio should be selected to provde the specified drive speed with rated load on the hook, for the actual system used.
Variations from the calculated gear ratio is permissible to facilitate the use of standard available ratios, provided that motor heating and operational performance is not adverseiy affected.
The actual fullload drive speed may vary a maximum of: Types of electrical brakes for hoist and traverse motions shall be specified by the crane manufacturero Refer to Section 4.
Holding brakes shall be applied automatically when power to the brake is removed. On hoists equipped with two electric holding brakes, a time delay setting of one brake may be included.