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

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

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

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)

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

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

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

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

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

Types of Welds Groove weld Fillet weld Plug weld Slot weld

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

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

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

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

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

Types of Welds

Welded Joints They are classified as: Butt Joint is groove-welded Lap Joint is fillet-welded

Welded Joints Tee Joint can be fillet-welded or groove-welded Corner Joint

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

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

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.

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

Welding processes Metal Arc Welding 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 Metal Arc Welding 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 Metal Arc Welding

Shielded Metal Arc Welding (SMAW) Welding processes Shielded Metal Arc Welding (SMAW) 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) Welding processes Shielded Metal Arc Welding (SMAW)

Submerged Arc Welding (SAW) Welding processes Submerged Arc Welding (SAW) 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) Welding processes Submerged Arc Welding (SAW)

Flux Cored Arc Welding (FCAW) Welding processes Flux Cored Arc Welding (FCAW) 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) Welding processes Flux Cored Arc Welding (FCAW)

Metal-Arc Inert Gas (MIG) Welding Welding processes Metal-Arc Inert Gas (MIG) Welding 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 Welding processes Metal-Arc Inert Gas (MIG) Welding

Tungsten-Arc Inert Gas (TIG) Welding Welding processes Tungsten-Arc Inert Gas (TIG) Welding 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 Welding processes Tungsten-Arc Inert Gas (TIG) Welding

Important considerations Welding processes Important considerations 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 Welding processes Important considerations 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 Welding processes Important considerations A fillet weld that is too small compared with the thickness of the material being welded is affected adversely during cooling. The amount of heat required to deposit a small weld is not sufficient to produce appreciable expansion of the thick material, and as hotter weld contracts during cooling it is restrained by being attached to the cooler material and tensile stresses produce, may cause crack of the weld.

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.

Standard Welding symbols Fillet Weld

Standard Welding symbols Fillet Weld

Standard Welding symbols Fillet Weld

Standard Welding symbols Fillet Weld

Standard Welding smbols Fillet Weld Unequal legs

Standard Welding symbols Groove Weld

Standard Welding symbols Groove Weld

Standard Welding symbols Groove Weld

Standard Welding symbols Plug & Slot Weld

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.

Stresses In Welds f = P / (LTe)

Stresses In Welds 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 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. P 2 / 4

Stresses In Welds 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 Load sharing of P, between two longitudinal fillet & one transverse fillet weld depends either on: Proportional to their length if welds are of same size. Proportional to the area for different size weld.

Stresses In Welds 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. Joint is elongated in direction of load to produce a more uniform transfer of stress These concentrations are of no consequence for static loads, but they are significant where fatigue is involved.

Specifications for Welded Connections 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 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 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.

Code Requirements AISC/ASD AISC/LRFD 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 AASHTO AREA 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

Code Requirements

Code Requirements

Code Requirements

Code Requirements

Design Problem

Example Problem 1 - ASD

Example Problem 1 - ASD

Example Problem 1 - ASD Final Design

Example Problem 1 - ASD

Example Problem 2 – LRFD

Example Problem 2 – LRFD

Example Problem 2 – LRFD

Example Problem 2 – LRFD

Example Problem 3 – LRFD

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.

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.

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.

Example Problem 3 – LRFD

Example Problem 3 – LRFD 10” Final Design

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