7/16/2019 E410 - LUG Exercise

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E410 Design - Lifting Lug and Bracket - Prof. D. Andrews - January 2008

Introduction

During manufacture it is often necessary to lift and move large objects betweenmachining operations. Sometimes this involves an overhead crane, and a sling or liftingattachments would be employed. For safety reasons, such attachments are required tohave a limit on the maximum load that can be applied (safe working load).

Lifting Lug Design

The large plate, shown in Figure 1 (page 2), is an example where a temporary liftingattachment is needed. The plate would ultimately be used with the attachmentremoved. One approach is to weld on a temporary attachment. The general form of the attachment, known as a lug, is given in Figure 1, but not dimensioned.The lug is welded to one face of the plate, half way along and centred on point A asshown in Figure 1. Lifting would be achieved by a lifting device (e.g. crane)

connected to the pin inserted in the lug. Using the material data shown below,together with the plate dimensions given in Figure 1, dimension and give detailedcalculations for:

(a) The pin diameter (Ø=D)(b) The lug dimensions (H, L, b)(c) The weld of the lug to the plate (A = weld area)

Plate Steel Density = 7830 kg/m3 ,Pin and lug Mild steel Yield stress = 200 MPa , Weld metal Yield stress = 195 MPa

N.B. Other methods of lug design must not be used.

Bracket Design

If the plate were lifted directly from the pin through the lug then it would not hangvertically. This could make subsequent positioning of the plate for further operationsmore difficult. In order to avoid this inconvenient it may be important that the plate islifted vertically.

(d) Design a device (bracket) to allow vertical lifting of the plate. Detailedcalculations are not required for this part of the exercise.

Stress Analysis

For the shear stress in the pin, the tensile stress on the lug net section, the shear stressdue to pin pull out from the lug, and the shear stress in the pin, use the following:

Stress = Force / Area (1)

For pin bending:3

32=stressfibreExtreme D M  π   (2)

where  M  is the bending moment calculated assuming that the pin is in three point bending, with the plate load applied at the centre of the lug, and reacted by theconnections to the lifting device on each side of the lug, and  D being the pin diameter.For the lug bending:

2

6=stressfibreExtreme bd  M  (3)

E410 - Exercise 1 - Deadline: 2 pm on 1st Feb. ’08 - www.ucl.ac.uk/~ucemlca/E410 - 1/2

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where  M  is the bending moment calculated using the distance from the pin centre tothe plate surface, b is the lug thickness, and d  is the lug height measured parallel tothe plate.

Hints

Make the following assumptions:(a) The Tresca yield criterion is appropriate.(b) The safety factor is three.(c) The weld is a fillet weld with equal leg lengths.

Use the following simplification: the plate would hang at an angle to the vertical, thismakes calculations difficult. To simplify the analysis, carry out separatecalculations for the two limiting cases: the full force being parallel to the plateand the full force being perpendicular to the plate.

Check the following stresses in the order given.

(a) In the pin.○ The shear stress.○ The extreme fibre stress due to pin bending.

(b) In the lug, for the force in both directions.○ The tensile stress in the net section.○ The shear stress due to pin pull out on sections on either side of the pinfrom the centre line to the surface.

(c) In the lug, for the force parallel to the plate.○ The extreme fibre stress due to lug bending.

(d) In the weld connection, for the working load in both directions: perpendicular and parallel to the plate. ○ The shear stress on the minimum area.

Figure 1 - Plate and lifting lug.

E410 - Exercise 1 - Deadline: 2 pm on 1st Feb. ’08 - www.ucl.ac.uk/~ucemlca/E410 - 2/2