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Design and Construction of Lifting Beams

Design and Construction of Lifting BeamsDAVID T. RICKERL ifting Beams (also known as spreader Beams ) are used toassist in the hoisting process. Most erectors and riggersaccumulate an assortment of Lifting Beams during the courseof time. Some common profiles are shown in Fig. basic Lifting beam is shown in Fig. 1A. Thisarrangement provides two places of attachment to the objectbeing lifted, thus avoiding the possibility of overstressing if asingle attachment were used. This also allows for a straightpull on the object rather than an oblique pull as would resultif chokers alone were used. This is sometimes important tominimize unwanted erection stresses or to prevent reversal ofstress in certain portions of the lifted object.

4 13 16 2 1 3 19.0 25 5¾ 2 2 4 5 16 314 35 6¾ 3¼ 2¼ 5 45.0 55* 8 4 2¾ 6 83.6 85** 8½ 5 3¼ 6½ 139 * Screw pin and bolt type only. ** Bolt type only. NOTE: Proof load is 2.2 Times safe working load. Minimum ultimate strength is 6 Times the safe working load. Fig. 6. Forged chain shackles. where a is the least plate width at side of hole (in.)

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Transcription of Design and Construction of Lifting Beams

1 Design and Construction of Lifting BeamsDAVID T. RICKERL ifting Beams (also known as spreader Beams ) are used toassist in the hoisting process. Most erectors and riggersaccumulate an assortment of Lifting Beams during the courseof time. Some common profiles are shown in Fig. basic Lifting beam is shown in Fig. 1A. Thisarrangement provides two places of attachment to the objectbeing lifted, thus avoiding the possibility of overstressing if asingle attachment were used. This also allows for a straightpull on the object rather than an oblique pull as would resultif chokers alone were used. This is sometimes important tominimize unwanted erection stresses or to prevent reversal ofstress in certain portions of the lifted object.

2 For instance, theoblique pull in Fig. 2A may cause excess compression in thetop chord of the truss at a time when that chord is laterallyunbraced. The arrangement in Fig. 2B will help to alleviatethis tendency and optimum choker locations can be chosen tominimize the stresses during the erection 1B illustrates the type of Lifting beam that mightbe employed in Fig. 2B. The beam has multiple holes at theDavid T. Ricker is a structural engineer in Payson, for attachment to the object to be hoisted, thusproviding a large range of adjustment. This arrangement willalso prevent the object from tilting excessively should thehook be slightly off-center of the balance point.

3 Figure 1 Cshows a Lifting beam which has good versatility in location ofattachments. This is useful if the objects to be lifted varygreatly in size and weight. Figure 1D shows a Lifting beamused in an inverted position. Although this condition isrelatively rare, there are occasions when it is necessary, suchas when two cranes must lift a very heavy object which isbeyond the capacity of a single crane. The inverted liftingbeam enables the cranes to share the load. Figure 1E shows alifting beam made for a special purpose and is constructedentirely of plate material. Figure 1F depicts anotheradaptation which permits the lower shackles to be oriented90 to their usual position.

4 Figure 3A shows a multiple liftingbeam arrangement such as might be used to support a longlimber object. Figure 3B illustrates a Lifting beam fitted witha chain-fall in order to provide some adjustment if the objectmust be jockeyed into position. By varying the lengths ofchokers a fixed-tilt Lifting beam can be made as depicted inFig. 3C. Expressed in terms of variables noted in Fig. 3C thesling lengths can be calculated using the following formulae:short sling length: LaHHa1222=++(sin) long sling length: LaHHa2222=++(sin) Dimension H is commonly selected as approximately the a QUARTER / 1991149 Occasionally non-symmetrical Lifting Beams are requiredto hoist objects which are of peculiar shape or have oddweight distribution.

5 Figure 3D shows such an torsion loads are rare in Lifting Beams . If it issurmised that torsion stresses must be addressed, the liftingbeam can be strengthened by adding a plate at each end ofthe wideflange section as in Fig. 14A or by adding side platesto box the section as in Fig. 14B. The AISC publication,Torsion Analysis of Steel Members,3 will be of value intorsion Lifting beam can also be used as a "strong back" toprovide multiple Lifting points on a relatively flexible object(See Fig. 4A.) Some Lifting Beams are made with a bottomlug aligned directly below the top lug so that, if the needarises, an occasional straight pick can be made without theinconvenience of having to remove the Lifting beam.

6 (See ) This is but a small sample of Lifting beam possibilitiesand their elements commonly associated with Lifting beamsare hooks, shackles, chokers, and slings. Shackles are used toconnect the lines to the Lifting Beams . Shackles come invarious patterns and capacities and typical examples areshown in Figs. 5 and 6. The loads shown in these tablesrepresent average industry loads and are for comparisonpurposes only. The capacities of specific rigging componentsmust be verified by the user. Chokers are often used to wraparound the object to be lifted and are usually fastened to theunderside of the Lifting beam by means of shackles. Slingsare used to suspend the Lifting beam from the main hook.

7 SeeFigs. 7 and 8 for various choker and sling are rarely attached directly to a Lifting beambecause the hole required in the lug plate would need to beexcessively large (or oblong) and the required edge distanceon the Lifting lug would be too great to accommodate thehook profile. However, hooks are often used with shackles oroblong rings. Hooks with safety latches which prevent theshackles or lines from escaping the throat of the hook shackle properties most significant to this discussionare: load capacity, diameter of pin (or bolt ), inside width ofjaws, length of shackle, diameter of flange. (See Fig. 9A.)The width of jaw limits the thickness of the lug plate.

8 Thelength of shackle controls the maximum edge distanceavailableABFigure the plate edge. The diameter of the shackle flangeinfluences the minimum distance of the pin hole from the faceof the Lifting beam. In Fig. 9B the minimum dimension X isthe sum of the flange radius and the weld size plus a smallallowance for clearance and fabrication variances. There isno reason to make dimension X overly large except in caseswhere it is desired to increase the effective length of the lugplate weld. An excessive X dimension needlessly increasesthe Z dimension, shown in Fig. 13, which may diminish thecapacity of the Lifting beam. Note that for certain cablelocations the moment in the Lifting beam is increased by theamount of H Z as, for example, in Fig.

9 Diameters and lengths of of chokers and slingsshould, of course, be compatible with the capacities andgeometry of the Lifting beam. Refer to Fig. 2B. The angleshould preferably be between 45 and 90 with 60 being acommon figure. An angle less than 45 usually requiresexcessively long slings and an angle greater than 90 resultsin needlessly high sling lug plate with its pin hole is an important componentof the Lifting beam assembly. Tests have indicated that theratio of pin diameter to hole diameter has little influence onthe ultimate strength of the lug In the unlikelyevent that the pin completely fills the hole in theSAFEWORKINGLOAD(Tous)L(in)W1(in.)

10 W2(in.)PINDIAM.(in.)OUTSIDEOF EYEDIAM.(in.)WEIGHT(lbs)3 2111611116 3 3 5 2 *10 47 2 610185**1358 3 6 179* Screw pin and bolt type only** bolt type onlyNOTE: Proof load is times safe working load. Minimum ultimatestrength is 6 times the safe working 5. Forged anchor JOURNAL / AMERICAN INSTITUTE OF STEEL CONSTRUCTIONlug plate, the plate must be checked for bearing capacity. Thediameter of the hole in the Lifting lug should be at least 116in. greater than the largest pin (or bolt ) diameter which isanticipated. However, it is not necessary to have the pin fitsnugly in the hole. In fact, the pins are apt to be rough castand not perfectly round. More often than not, the pin may beconsiderably smaller than the hole.


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