chapter 5design of permanent joints

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Chapter 5: Design of Permanent Joints

(Welded Joints)

 5.0 Introduction

5.1 Butt and Fillet Welds

5.2 Stresses in Welded Joints in Torsion

5.3 Stresses in Welded Joints in Bending

IntroductionA weldment is fabricated by welding

together a collection of metal shapes, cut to particular configurations.

During welding, the several parts are held securely together, often by clamping or jigging.

The welds must be precisely specified on working drawings, and this is done using the welding symbol, as standardized by the American Welding Society (AWS).

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3The arrow of this symbol points to the joint to be welded. 

The body of the symbol contains as manyof the following elements as are deemed necessary:

Reference lineArrowBasic weld symbols as in Figure 1Dimensions and other dataSupplementary symbolsFinish symbolsTail Specification or process

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Basic weld symbols 

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Fillet welds:•The number indicates the leg size; the arrow should point only to one weld when both sides are the same• the symbol indicates that the welds are intermittent and staggered 60 mm along on 200 mm centres.

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Weld is go around 

Butt or groove welds

• square butt-welded(b) single V (c) double V (d) single bevel 

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Special groove welds(a) T-joint (b) U and J welds (c) corner weld (d) edge weld 

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The average normal stress, σ = F / hlStress due to shear loading, τ = F / hl

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A transverse fillet weld 

hl

F

hl

F 414.1

707.0==τ

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Parallel fillet welds

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τ’ = V/Awhere V = shear forceA = throat area of all welds

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Secondary shear, τ’’ = Mr / J Where: r = distance from the centroid of weld group to the point in the weld of interestJ = second polar of moment of area

The throat width of a fillet weld is 0.707h,

The relationship between J and the unit value isJ = 0.707 h Ju

Where h = weld sizeJu found by conventional methods for an area having unit width

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Torsional properties of fillet weld 

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Work out the example 9-1 (page 467)

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Exercise:The figure shows a welded steel bracket loaded by a static force F. Estimate the factor of safety if the allowable shear stress in the weld throat is 120 MPa.

Answer: N = 3.57

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The shear force produces a primary shear in the welds of magnitude

τ’ = V/AWhere: V = shear force

A = throat area of all welds

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The second moment of areaIu = bd2 / 2

 The second moment of area based on weld throat area,

I = 0.707 h Iu = 0.707 h bd2 / 2 The nominal throat shear stress

τ = M c / I =

For bending properties of fillet welds, refer to Table 9-2 (Page 470-471)

bdh

M

hbd

Md 414.1

2707.02

2=

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Work out the example 9-4 (page 476)

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~ END ~Thank you for your kind

attention.