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By: Prof Dr. Akhtar Naeem Khan chaircivnwfpuet.pk

2. WeldingTypes of weldsWelded JointsWelding processesNomenclature of weldsWelding symbols. Topics to be Addressed. 3. Stresses in WeldsSpecifications for WeldsCode RequirementsDesign Examples. Topics to be Addressed. 4. Welding. It is a process of joining parts by means of heat

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By: Prof Dr. Akhtar Naeem Khan chaircivnwfpuet.pk

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    1. 1 By: Prof Dr. Akhtar Naeem Khan chairciv@nwfpuet.edu.pk

    2. 2 Welding Types of welds Welded Joints Welding processes Nomenclature of welds Welding symbols Topics to be Addressed

    3. 3 Stresses in Welds Specifications for Welds Code Requirements Design Examples Topics to be Addressed

    4. 4 Welding It is a process of joining parts by means of heat & pressure, causes fusion of parts. OR Heating metal to fusion temperature with or without addition of weld metals. Code & specification: American Welding Society (AWS)

    5. 5 Types of Welds Welds are classified according to their shape and method of deposition into: Groove Weld Fillet Weld Plug Weld Slot Weld

    6. 6 Types of Welds Groove Weld is made in opening between two parts being joined.

    7. 7 Types of Welds Fillet Weld triangular in shape, joins surfaces which are at an angle with one another.

    8. 8 Groove welds are more efficient than fillet welds. Have greater resistance to repeated stress and Impact loaded. Hence preferable for dynamically loaded members. Groove welds require less weld metal than fillet weld of equal strength. But fillet welds are often used in structural work. WHY ? Types of Welds

    9. 9 But fillet welds are often used in structural work WHY ? Partly because many connections are more easily made with fillet welds and Partly because groove welds require the member of structure to be cut to rather close tolerances. Types of Welds

    10. 10 Types of Welds Plug Weld is made by depositing weld metal in a circular hole in one of two lapped places.

    11. 11 Types of Welds Slot Weld similar to plug but the hole is elongated.

    12. 12 Types of Welds

    13. 13 Welds are classified according to the position of weld during welding as Flat Horizontal Vertical Overhead Types of Welds

    14. 14 Flat: Executed from above, the weld face approximately horizontal. Types of Welds

    15. 15 Horizontal: Similar to Flat weld but weld is harder to make. Types of Welds

    16. 16 Vertical: Longitudinal axis of weld is vertical. Types of Welds

    17. 17 Overhead: Welding is done from underside of the joint. Types of Welds

    18. 18 Types of Welds

    19. 19 Welded Joints They are classified as: Butt Joint is groove-welded

    20. 20 Welded Joints

    21. 21 Welding processes There are three methods of Welding: Forge welding Resistance welding Fusion welding

    22. 22 Welding processes Forge welding: It consists of simply heating the pieces above certain temperature and hammering them together

    23. 23 Welding processes Resistance welding Metal parts are joined by means of heat and pressure which causes fusion of parts. Heat is generated by electrical resistance to a current of high amperage & low voltage passing through small area of contact between parts to be connected.

    24. 24 Welding processes Fusion welding: Metal is heated to fusion temperature with or without addition of weld metal Method of connecting pieces by molten metal Oxyacetylene welding Electric arc welding

    25. 25 Arc is a sustained spark between a metallic electrode and work to be welded. At the instant arc is formed the temperature of work and tip of electrode are brought to melting point. As the tip of electrode melts, tiny globules of molten metal form. Welding processes

    26. 26 The molten metal, when exposed to air combines chemically with oxygen & nitrogen forming oxides & nitrides, which tend to embrittle it & less corrosive resistant. Tough, ductile weld are produced if molten pool is shielded by an inert gas, which envelops molten metal & tip of electrode. Welding processes

    27. 27 Welding processes

    28. 28 When an arc is struck between the metal rod (electrode) and the work piece, both the rod and work piece surface melt to form a weld pool. Simultaneous melting of the flux coating on the rod will form gas and slag which protects the weld pool from the surrounding atmosphere. Shielded Metal Arc Welding (SMAW)

    29. 29 Shielded Metal Arc Welding (SMAW)

    30. 30 A bare wire is fed through welding head at a rate to maintain constant arc length. Welding is shielded by blanket of granular fusible material fed onto the work area by gravity, in an amount sufficient to submerge the arc completely. In addition to protecting weld from atmosphere, the covering aids in controlling rate of cooling of weld. Submerged Arc Welding (SAW)

    31. 31 Submerged Arc Welding (SAW)

    32. 32 It utilizes the heat of an arc between a continuously fed consumable flux cored electrode and the work. The heat of the arc melts the surface of the base metal and the end of the electrode. The metal melted off the electrode is transferred across the arc to the work piece, where it becomes the deposited weld metal. Shielding is obtained from the disintegration of ingredients contained within the flux cored electrode. Flux Cored Arc Welding (FCAW)

    33. 33 Flux Cored Arc Welding (FCAW)

    34. 34 MIG Welding refers to the wire that is used to start the arc. It is shielded by inert gas and the feeding wire also acts as the filler rod. Metal-Arc Inert Gas (MIG) Welding

    35. 35 Metal-Arc Inert Gas (MIG) Welding

    36. 36 The arc is started with a tungsten electrode shielded by inert gas and filler rod is fed into the weld puddle separately. The gas shielding that is required to protect the molten metal from contamination is supplied through the torch. Tungsten-Arc Inert Gas (TIG) Welding

    37. 37 Tungsten-Arc Inert Gas (TIG) Welding

    38. 38 Large fillet welds made manually require two or more passes. Each pass must cool, and slag must be removed before next pass. Most efficient fillet welds are those which can be made in one pass. Important considerations

    39. 39 Largest size can be made in one pass depends upon welding position & should not exceed the following. 5/16 Horizontal or overhead 3/8 Flat position 1/2 Vertical position Thickness of weld = Thickness of material 1/16 Important considerations

    40. 40 Important considerations

    41. 41 Nomenclature of Welds The part of weld assumed to be effective in transferring stress is Throat. The faces of weld in contact with the parts joined is called its Legs.. For equal-legged fillet weld throat is 0.707s, where s is leg size.

    42. 42 Standard Welding symbols

    43. 43 Standard Welding symbols

    44. 44 Standard Welding symbols

    45. 45 Standard Welding symbols

    46. 46 Standard Welding smbols

    47. 47 Standard Welding symbols

    48. 48 Standard Welding symbols

    49. 49 Standard Welding symbols

    50. 50 Standard Welding symbols

    51. 51 Stresses In Welds Groove weld may be stressed in tension, compression, shear, or a combination of tension, compression and shear, depending upon the direction and position of load relative to weld.

    52. 52 Stresses In Welds f = P / (LTe)

    53. 53 The load P in Fig is resisted by shearing force P/2, on the throat of each fillet weld. f = (P /2) / (LTe) Stresses In Welds

    54. 54 It is customary to take the force on a fillet weld as a shear on the throat irrespective of the direction of load relative to throat. Stresses In Welds

    55. 55 Tests have shown that a fillet weld transverse to the load is much stronger than a fillet weld of same size parallel to the load. Stresses In Welds

    56. 56 Load sharing of P, between two longitudinal fillet & one transverse fillet weld depends either on: Stresses In Welds

    57. 57 Any abrupt discontinuity or change in section of member such as notch or a sharp reentrant corner, interrupts the transmission of stress along smooth lines. Stresses In Welds

    58. 58 Welding electrodes are classified on the basis of mechanical properties of weld metal, Welding position, type of coating, and type of Current required. Each electrode is identified by code number EXXXXX. E stands for Electrode and each X represents number. Specifications for Welded Connections

    59. 59 First two or three numbers denote the tensile strength in Ksi. Next No. position in which electrode can be used. e.g. 1: all positions, 2: flat & horizontal fillet welds, 3: flat welding only Last No. denotes type of covering, type of current & polarity. Specifications for Welded Connections

    60. 60 Example: E7018 means Tensile strength 70 Ksi 1 means can be used in all positions 8 means it is iron-powder, low-hydrogen electrode used with A.C or D.C but only in reverse polarity. Specifications for Welded Connections

    61. 61 AISC/ASD Allowable stress in welded connection is given in Table 2-21 AISC/LRFD Design strengths of welds are given in Table 2-22 with resistance factor ?. Code Requirements

    62. 62 AASHTO Allowable stress are more conservative than AISC. e.g. 0.27Fu for fillet weld, Fu is tensile strength of electrode but not less than tensile strength of connected part. AREA Allowable shear stress on fillet welds are given as function of base material and strength of weld metal. e.g. A36. Electrode or electrode-flux combinations with: 60,000 psi tensile strength 16,500 psi 70,000 psi tensile strength 19,500 psi Code Requirements

    63. 63 Code Requirements

    64. 64 Code Requirements

    65. 65 Code Requirements

    66. 66 Code Requirements

    67. 67 Code Requirements

    68. 68 Design Problem

    69. 69 Example Problem 1 - ASD

    70. 70 Example Problem 1 - ASD

    71. 71 Example Problem 1 - ASD

    72. 72 Example Problem 1 - ASD

    73. 73 Example Problem 2 LRFD

    74. 74 Example Problem 2 LRFD

    75. 75 Example Problem 2 LRFD

    76. 76 Example Problem 2 LRFD

    77. 77 Example Problem 3 LRFD

    78. 78

    79. 79 Example Problem 3 LRFD The weld is assumed as lines of unit width. f = M/S = 6M/bh2 since b = 1 and h = L therefore L = 6M/f where f is the demand, equating to the capacity we get the given equation. The weld is assumed as lines of unit width. f = M/S = 6M/bh2 since b = 1 and h = L therefore L = 6M/f where f is the demand, equating to the capacity we get the given equation.

    80. 80 Example Problem 3 LRFD Due to the return at the top, the COG is shifted slightly to top. For the return (as in the numerator) the product of area and centriod is ignored as it will be a very small value. Due to the return at the top, the COG is shifted slightly to top. For the return (as in the numerator) the product of area and centriod is ignored as it will be a very small value.

    81. 81 Example Problem 3 LRFD The direct shear acts as shear for the weld along the length. The tension component due to moment is perpendicular to the weld, however it is added to the shear as welds are always design for shear.The direct shear acts as shear for the weld along the length. The tension component due to moment is perpendicular to the weld, however it is added to the shear as welds are always design for shear.

    82. 82 Example Problem 3 LRFD

    83. 83 Example Problem 3 LRFD

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