Chapter 9site.iugaza.edu.ps/mhaiba/files/2013/09/Welding...Permanent-Joints.pdf · Chapter 9 Welding and the Design ... Fillet weld ... American Institute of Steel Construction (AISC)

Chapter 9 Welding and the Design

of Permanent Joints

9/28/2013 10:22 PM

Dr. Mohammad Suliman Abuhaiba, PE 1

Chapter Outline

9/28/2013 10:22 PM

Dr. Mohammad Suliman Abuhaiba, PE

2

Welding Symbols

Welding symbol standardized by AWS

Specifies details of weld on machine drawings

Fig. 9–4

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Welding Symbols

Arrow side of a joint is the line, side, area, or near

member to which the arrow points

The side opposite the arrow side is the other side

Shape of weld is shown with the symbols below

Fig. 9–2

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Welding Symbol Examples

Weld leg size of 5 mm

Fillet weld

Both sides

Leg size of 5 mm

On one side only (outside)

Circle indicates all the way around

Intermittent and staggered 60 mm long on 200

mm centers



Fig. 9–5



Fig. 9–6


Welding Symbols

Fig. 9–1

Tensile Butt Joint Simple butt joint loaded in tension or compression

Stress is normal stress

Throat h does not include extra reinforcement

Reinforcement adds some strength for static loaded joints

Reinforcement adds stress concentration and should be ground off for fatigue loaded joints

Fig. 9–7a

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Shear Butt Joint

Simple butt joint loaded in shear

Average shear stress

Fig. 9–7b

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Transverse Fillet Weld

Joint loaded in tension

Weld loading is complex

Fig. 9–8

Fig. 9–9

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Summation of forces

Law of sines

Solving for throat thickness t

Fig. 9–9

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Nominal stresses at angle q

Von Mises Stress at angle q

Fig. 9–9

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Largest von Mises stress occurs at q = 62.5º with value of

s' = 2.16F/(hl)

Maximum shear stress occurs at q = 67.5º with value of

tmax = 1.207F/(hl)

Fig. 9–9

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Experimental Stresses in Transverse Fillet Weld

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Figure 9–10: Stress distribution in fillet welds: (a)

stress distribution on legs as reported by Norris; (b)

distribution of principal stresses and maximum shear

stress as reported by Salakian

Transverse Fillet Weld Simplified Model

No analytical approach accurately predicts the experimentally

measured stresses.

Standard practice is to use a simple and conservative model

Assume the external load is carried entirely by shear forces on the

minimum throat area.

By ignoring normal stress on throat, the shearing stresses are

inflated sufficiently to render the model conservative.

By comparison with previous max shear stress model, this inflates

estimated shear stress by factor of 1.414/1.207= 1.17.

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Parallel Fillet Welds

Same equation also applies for simpler case of simple

shear loading in fillet weld

Fig. 9–11

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Fillet Welds Loaded in Torsion

Fillet welds carrying both

direct shear V & moment M

Primary shear

Secondary shear

A is throat area of all welds

r is distance from centroid

of weld group to point of

interest

J is second polar moment of

area of weld group about

centroid of group

Fig. 9–12

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Example of Finding A and J

Rectangles represent throat areas. t = 0.707 h

Fig. 9–13

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Example of Finding A and J

t3 terms will be very

small compared to b3

and d3, Usually

neglected

Leaves JG1 and JG2 linear

in weld width

Can normalize by

treating each weld as a

line with unit thickness t

Results in unit second

polar moment of area,

Ju

Since t = 0.707h,

J = 0.707hJu

Fig. 9–13

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Table 9–1: Common Torsional Properties of Fillet Welds


Table 9–1: Common Torsional Properties of Fillet Welds


Example 9–1

Fig. 9–14


Example 9–1

Fig. 9–15

Example 9–1

Dr. Mohammad Suliman Abuhaiba, PE Fig. 9–15


Example 9–1

Shigley’s Mechanical Engineering Design

Fig. 9–15


Example 9–1


Example 9–1

Fig. 9–16


Example 9–1

Fig. 9–16

Stresses in Welded Joints in Bending FBD of beam would show a shear-force reaction V and a moment M

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

Moment M induces a horizontal shear stress component in the welds. Treating the two welds as lines, the unit second moment of area to be

Fig. 9–17

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The model gives the coefficient of 1.414, in contrast

to the predictions of Sec. 9–2 of 1.197 from

distortion energy, or 1.207 from maximum shear.

The conservatism of the model’s 1.414 is not that it

is simply larger than either 1.196 or 1.207, but the

tests carried out to validate the model show that it

is large enough.

The second moment of area in Eq. (d) is based on

the distance d between the two welds.

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Stresses in Welded Joints in Bending


Table 9–2: Bending Properties of Fillet Welds





Strength of Welded Joints

The matching of electrode properties with those of parent metal is

usually not so important as:

Speed

Operator appeal

Appearance of the completed joint.

Select a steel that will result in a fast, economical weld.

Best results will be obtained if steels having a UNS specification

between G10140 & G10230 are chosen.

These steels have a tensile strength in the hot-rolled condition in

the range of 60 to 70 kpsi.

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Table 9–3: Minimum Weld-Metal Properties

AWS specification code numbering system for electrodes

E prefixed to a four- or five-digit numbering system

First two or three digits designate approximate tensile strength

Last digit includes variables in the welding technique, such as current supply

Next-to-last digit indicates welding position: flat, or vertical, or overhead


American Institute of Steel Construction (AISC) code for building

construction:

Permissible stresses are based on yield strength of material instead of

ultimate strength

The code permits the use of a variety of ASTM structural steels having

yield strengths varying from 33 to 50 kpsi

The code permits the same stress in the weld metal as in the parent

metal.

For these ASTM steels, Sy = 0.5Su

Table 9–4 lists formulas specified by the code for calculating these

permissible stresses for various loading conditions

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Table 9-4: Stresses Permitted by AISC Code for

Weld Metal

For tension, n = 1/0.60 = 1.67. For shear, n = 0.577/0.40 = 1.44, using

the distortion-energy theory.


The electrode material is often the strongest material present.

If a bar of AISI 1010 steel is welded to one of 1018 steel, the weld

metal is actually a mixture of the electrode material and the 1010

and 1018 steels.

A welded cold-drawn bar has its cold-drawn properties replaced

with the hot-rolled properties in the vicinity of the weld.

Check the stresses in the parent metals.

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The AISC code, as well as the AWS code, for bridges includes

permissible stresses when fatigue loading is present.

For structures covered by these codes, the actual stresses cannot

exceed the permissible stresses; otherwise the designer is legally

liable.

Codes tend to conceal the actual margin of safety involved.

The fatigue stress-concentration factors listed in Table 9–5 are

suggested for use.

These factors should be used for the parent metal as well as for the

weld metal.

Table 9–6 gives steady-load information and minimum fillet sizes.

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Fatigue Stress-Concentration Factors

Kfs appropriate for application to shear stresses

Use for parent metal and for weld metal

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Table 9–5: Fatigue Stress-Concentration Factors, Kfs


Example 9–2

Fig. 9–18


Example 9–2


Example 9–2


Example 9–3

Fig. 9–19


Example 9–3


Example 9–3


Example 9–3


Example 9–3


Example 9–4

Fig. 9–20


Example 9–4


Example 9–4


Example 9–4


Example 9–5

Fig. 9–21


Example 9–5


Example 9–5


Fig. 9–22

Example 9–6


Example 9–6


Example 9–6

First Exam

On Tuesday 1/10/2013 at 11:00

Tested Material: Chapter 9

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60

Practice Problems

1, 5, 9, 16, 20, 24,

28, 34, 45, 51

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Documents

Chapter 9site.iugaza.edu.ps/mhaiba/files/2013/09/Welding...Permanent-Joints.pdf · Chapter 9 Welding and the Design ... Fillet weld ... American Institute of Steel Construction (AISC)