Handbook of Structural Steel Connection Design and Details

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3.11.1 High Connection Demands

3.11.2 Stress Concentrations

10.5.5 Force Transfer Mechanism for Through-Beam Connection Detail10.5.6 Tentative Design Provisions for Through-Beam Connection Detail10.6 Notations (For Sec 10.3)

David R Williams, P.E Principal, Williams Engineering Associates, Virginia Beach,

Virginia (Chap 6)

Akbar R Tamboli, P.E., F.ASCE, is a consultant at Thornton Tomasetti in New York He has

been a senior project engineer with CUH2A in Princeton, New Jersey, a company that

specialized in architecture, engineering, and planning He has also been a vice president andproject manager at Cantor-Seinuk Group PC, Consulting Engineers, in New York, where hewas the principal consulting engineer on a number of noteworthy projects, including MorganGuaranty Bank Headquarters at 60 Wall Street and Salomon Brothers World Headquarters,Seven World Trade Center

Mr Tamboli was senior vice president and principal at Thornton Tomasetti, where hedesigned and managed several award-winning projects, including Random House WorldHeadquarters in New York; the University of Pennsylvania’s Perelman Center for AdvancedMedicine and Roberts Proton Therapy Center; Janelia Research Campus of the Howard

Hughes Medical Institute in Leesburg, Virginia; the Neuroscience Research Center at theNational Institutes of Health in Bethesda, Maryland; and Carrasco International Airport inMontevideo, Uruguay

He designed and managed several concrete and steel projects in Europe, Asia, and theMiddle East Mr Tamboli has also published three engineering handbooks with McGraw-Hill,

including Tall and Supertall Buildings: Planning and Design and Steel Design Handbook:

LRFD Method, and contributed chapters to McGraw-Hill’s Standard Handbook for Civil

Engineers and Building Design and Construction Handbook.

Since the previous edition of this book was published in October 2009, there have been manydevelopments in the various aspects of steel connection design Improved fabrication andconstruction techniques have led to efficient structural connections

The new AISC code provisions for 2016 have been incorporated in this new edition AISCprovisions have been referenced in and made part of the International Building Code

Chapters 1 and 2 have been reworked to reflect the 2016 AISC code provisions Chapter 3

on welding has been completely rewritten to incorporate new welding codes and the 2016AISC code provisions New information has been added on state-of-the-art welding

procedures and special precautions needed for welded joints in seismically active regions.Partially restrained connections, covered in Chap 4, have been evolving and have beenmade part of the AISC code This chapter has been rewritten with several examples

Seismic connection and structural design, addressed in Chap 5, have been improving Thischapter has been revised to reflect the improvements with actual examples

Chapter 6, on structural details, can be found at www.mhprofessional.com/tamboli

New construction and fabrication methods used for recent special structures are described

in Chap 7 Chapter 8, on quality control and inspection, has been completely rewritten Inmany cases, the projects featured in this chapter are international; therefore, both metric andEnglish unit tolerances are given

Chapter 9 on steel decks has been completely updated to meet Steel Deck Institute (SDI)requirements

Users of this handbook are welcome to communicate with the editor regarding any aspect

of the book, particularly suggestions for improvement

Akbar R Tamboli

The need for the Handbook of Structural Steel Connection Design and Details with an LRFD approach was recognized at the time the Steel Design Handbook: LRFD Method was

published

This handbook was developed to serve as a comprehensive reference source for the design

of steel connections using the LRFD method Each topic is written by leading experts in thefield Emphasis is given to provide examples from actual practice Examples are focused togive a cost-effective approach The theory and criteria are explained and cross-references toequations to AISC are given where applicable

The book starts with a discussion of fasteners for structural connections It then goes intothe design of connections for axial, moment, and shear forces Detailed connection designaspects are covered in this chapter

Welded joint design and production are treated as a separate topic, and state-of-the-artinformation on welding is given for use in daily practice How to control weld cracking andjoint distortion is explained for use in general consulting practice Partially restrained

connection design is explained with practical examples

Recent seismic activity has created the need for the design of connections for seismicallyresistant structures These types of connections are covered with detailed examples

Commonly used connection details are shown for use in daily practice by fabricator, detailer,and consulting engineer

Sometimes fabricators and engineers need to design connections for special structures.Actual examples of how to approach these needs are given from real projects which are built

To ensure quality of connection, construction inspection and quality control are vital

Therefore, detailed information on these aspects is given to achieve desired goals

Most steel structures have steel decking To ensure good quality and interaction, steel deckdetails are explained thoroughly

The latest trend in composite construction has created the need for the design of compositeconstruction connections Steel-to-concrete shear wall and composite column connections areexplained in detail to achieve proper interaction and strength

The editor gratefully acknowledges the efforts of contributors in preparing excellent

manuscripts Thanks are due to the management and staff at CUH2A, Inc

The editor and authors are indebted to several sources for the information presented

Space considerations preclude listing all, but credit is given wherever feasible, especially inreferences throughout the book

Users of this handbook are urged to communicate with the editor regarding all aspects ofthis book, particularly any error or suggestion for improvement

Akbar R Tamboli

The editor would also like to acknowledge the help and assistance provided by LaurenPoplawski, sponsoring editor of this handbook, who put forth invaluable support during theprocess of preparing the manuscript Also, thanks go to the many other individuals at

McGraw-Hill and at Cenveo who were responsible for bringing the book to press, includingLynn Messina and Stephen Smith, and Srishti Malasi, project manager

The editor wishes to extend his thanks and appreciation to his wife, Rounkbi, and hischildren, Tahira, Ajim, and Alamgir, for their patience and understanding during the

preparation of this handbook

Connections are an intimate part of a steel structure and their proper treatment is essentialfor a safe and economic structure An intuitive knowledge of how a system will transmit loads(the art of load paths), and an understanding of structural mechanics (the science of

equilibrium and limit states), are necessary to achieve connections which are both safe andeconomic Chapter 2 will develop this material This chapter is based on the bolting and

Specifications: F3125, F3043, and F3111 F3125 is an umbrella specification that includes fourgrades: A325, A490, F1852, and F2280 The AISC Specification divides high-strength boltsinto three groups based on minimum tensile strength Group A bolts have a minimum tensilestrength of 120 ksi and include ASTM F3125 Grades A325, A325M, and F1852, as well asASTM A354 Grade BC Group B bolts have a minimum tensile strength of 150 ksi and

include ASTM F3125 Grades A490, A490M, and F2280, as well as A354 Grade BD Group Cbolts have a minimum tensile strength of 200 ksi and include ASTM F3043 and ASTM A3111.The various grades of F3125 are intended for general structural use, with the use of A354 andA449 fasteners intended only for conditions where the length or diameter limits of F3125must be exceeded F3034 and F3111 are probably best suited to heavily loaded connections.A449 bolts are also permitted to be used where the length and diameter limitations for A325are exceeded They are not included in Group A due to the multiple decreases in tensile

strength based on diameter A307 bolts, which were referred to previously as common bolts, are also variously called machine bolts, ordinary bolts, and unfinished bolts The use of these

bolts is limited primarily to shear connections in nonfatigue applications

FIGURE 1.1 High-strength structural-steel bolt and nut.

Structural bolts can be installed pretensioned or snug tight Pretensioned means that thebolt is tightened until a tension force approximately equal to 70 percent of its minimum

tensile strength is produced in the bolt Snug tight is the condition that exists when all plies are

in contact It can be attained by a few impacts of an impact wrench or the full effort of a manusing an ordinary spud wrench Common bolts (A307) can be installed only to the snug-tightcondition There is no recognized procedure for tightening these bolts beyond this point.Pretensioned structural bolts must be used in certain locations Section J3.1 of the AISCspecification requires that they be used for the following joints:

In all other cases, A307 bolts and snug-tight A325 and A490 bolts can be used

The use of ASTM F3125 structural bolts shall conform to the requirements of the

Research Council on Structural Connections (RCSC) “Specification for Structural JointsUsing Bolts,” 2004 This document contains all of the information on design, installation,inspection, washer use, compatible nuts, etc for these bolts Information on the installation,inspection, washer use, compatible nuts, etc for F3043 and F3111 bolts is contained in theASTM Specifications There is no comparable document for A307 bolts The RCSC “boltspec.” was developed in the 1950s to allow the replacement of rivets with bolts

Many sizes of high-strength bolts are available, as shown in Table 1.1 In general, a

connection with a few large-diameter fasteners costs less than one of the same capacity withmany small-diameter fasteners The fewer the fasteners, the fewer the number of holes to beformed and the less installation work Larger-diameter fasteners are generally favorable inconnections, because the load capacity of a fastener varies with the square of the fastener

preferred Shop and erection equipment is generally set up for these sizes, and workers arefamiliar with them It is also advisable to limit the diameter of bolts that must be pretensioned

to 1⅛ in since this is the largest diameter tension control (TC) bolt available

TABLE 1.1 Thread Lengths for ASTM F3125 High-Strength Bolts

1.2.2 Washer Requirements

Washers are generally not required in snug-tightened joints However, a beveled ASTM F436washer should be used where the outer face of the bolted parts has a greater slope than 1:20with respect to a plane normal to the bolt axis Additionally, an ASTM F436 washer must beprovided to cover the hole when a slotted or oversized hole occurs in an outer ply

Alternatively a in common plate washer can be used to cover the hole

Washers conforming to ASTM F436 are required in pretensioned and slip-critical joints asindicated in Table 1.2

TABLE 1.2 Washer Requirements for High Strength Bolts

As pointed out in a previous section, pretensioned bolts must be used for certain connections.For other locations, snug-tight bolts should be used because they are cheaper with no

reduction in strength The vast majority of shear connections in buildings can be snug tight,and shear connections are the predominate connection in every building

1.2.4 Bearing-Type versus Slip-Critical Joints

Connections made with high-strength bolts may be slip-critical (material joined being

clamped together by the tension induced in the bolts by tightening them and resisting shearthrough friction) or bearing-type (material joined being restricted from moving primarily bythe bolt shank) In bearing-type connections, bolt threads may be included in or excluded fromthe shear plane Different design strengths are used for each condition Also, bearing-typeconnections may be either pretensioned or snug-tight, subject to the limitations already

discussed Snug-tight bolts are much more economical to install and should be used wherepermitted The slip-critical connection is the most expensive, because it requires that the

faying surfaces be free of paint, grease, and oil, or that a special paint be used Hence this type

of connection should be used only where required by the governing design specification, forexample, where it is undesirable to have the bolts slip into bearing or where stress reversalcould cause slippage The 2016 AISC specification requires the use of slip-critical

connections when

(a) Bolts are installed in oversized holes

(b) Bolts are installed in slotted holes with the direction of the load parallel to the slot

(c) Bolts joining the extended portion of bolted, partial-length cover plates, as required inSection F13.3

The RCSC specification further requires slip-critical connections for

(d) Joints that are subject to fatigue load with reversal of the loading direction

(e) Joints in which slip at the faying surfaces would be detrimental to the performance of thestructure

Threads Included in Shear Planes The bearing-type connection with threads in shear planes

is most frequently used Since location of threads is not restricted, bolts can be inserted fromeither side of a connection Either the head or the nut can be the element turned Paint of anytype is permitted on the faying surfaces

Threads Excluded from Shear Planes The bearing-type connection with threads excluded

from shear planes is the most economical high-strength bolted connection, because fewerbolts generally are needed for a given required strength There can be difficulties involved inexcluding the threads from the shear planes when either one or both of the outer plies of thejoint is thin The location of the thread runout or vanish depends on which side of the

Total nominal thread lengths and vanish thread lengths for high-strength bolts are given in

Table 1.1 It is common practice to allow the last ⅛ in of vanish thread to extend across asingle shear plane

In order to determine the required bolt length, the value shown in Table 1.3 should beadded to the grip (i.e., the total thickness of all connected material, exclusive of washers) Foreach hardened flat washer that is used, add in and for each beveled washer, add in Thetabulated values provide appropriate allowances for manufacturing tolerances and also

provide for full thread engagement with an installed heavy hex nut The length determined bythe use of Table 1.3 should be adjusted to the next longer ¼ in length

TABLE 1.3 Lengths to Be Added to Grip

1.2.5 Bolts in Combination with Welds

Due to differences in the rigidity and ductility of bolts as compared to welds, sharing of loadsbetween bolts and welds should generally be avoided However, the specification does notcompletely prohibit it

In welded alterations to structures, existing rivets and high-strength bolts tightened to therequirements for slip-critical connections are permitted for carrying stresses resulting fromloads present at the time of alteration The welding needs to be adequate only to carry theadditional stress

1.2.6 Standard, Oversized, Short-Slotted, and Long-Slotted Holes

The AISC Specification requires that standard holes for bolts be in larger than the nominalfastener diameter up to 1 in diameter and ⅛ in larger than the nominal diameter for larger

construction In computing net area or a tension member, the diameter of the hole should betaken in larger than the hole diameter

Holes can be punched, drilled, or thermally cut Punching usually is the most economicalmethod To prevent excessive damage to material around the hole, however, the maximumthickness of material in which holes are punched full size is often limited as summarized in

Table 1.4

TABLE 1.4 Maximum Material Thickness (in) for Punching Fastener Holes*

In buildings, holes for thicker material may be either drilled from the solid or subpunchedand reamed The die for all subpunched holes and the drill for all subdrilled holes should be

at least in smaller than the nominal fastener diameter

Oversized holes can be used in slip-critical connections, and the oversized hole can be insome or all the plies connected The oversized holes are in larger than the bolt diameterfor bolts ⅝ to ⅞ in in diameter For bolts 1 in in diameter, the oversized hole is ¼ in largerand for bolts 1⅛ in in diameter and greater, the oversized of hole will be in larger

Short-slotted holes can be used in any or all the connected plies The load has to be applied

80 to 100° normal to the axis of the slot in bearing-type connections Short slots can be usedwithout regard to the direction of the applied load when slip-critical connections are used.The short slots for ⅝- to ⅞-in-diameter bolts are larger in length than the bolt diameter Forbolts 1 in in diameter, the length in larger and for bolts 1⅛ in diameter and larger, the slotwill be ⅜ in longer in length

Long slots have the same requirement as the short-slotted holes, except that the long slothas to be in only one of the connected parts at the faying surface of the connection The width

of all long slots for bolts matches the clearance for standard holes, and the length of the longslots for ⅝-in-diameter bolts is in greater, for ¾-in-diameter bolts 1⅛ in greater, for ⅞-in-diameter bolts 1 in greater, for 1-in-diameter bolts 1½ in greater, and for 1⅛-in-diameterand larger bolts, 2½ times diameter of bolt

When finger shims are fully inserted between the faying surfaces of load transmitting parts

of the connections, this is not considered as a long-slot connection

1.2.7 Edge Distances and Spacing of Bolts

Minimum distances from centers of fasteners to any edges are given in Table 1.5

The AISC Specification has provisions for minimum edge distance: The distance from thecenter of a standard hole to an edge of a connected part should not be less than the applicablevalue from Table 1.5

Maximum edge distances are set for sealing and stitch purposes The AISC Specification

limits the distance from center of fastener to nearest edge of parts in contact to 12 times thethickness of the connected part, with a maximum of 6 in For unpainted weathering steel, themaximum is 7 in or 14 times the thickness of the thinner plate For painted or unpainted

members not subject to corrosion, the maximum spacing is 12 in or 24 times the thickness ofthe thinner plate

Pitch is the distance (in) along the line of principal stress between centers of adjacent

fasteners It may be measured along one or more lines of fasteners For example, supposebolts are staggered along two parallel lines The pitch may be given as the distance betweensuccessive bolts in each line separately Or it may be given as the distance, measured parallel

to the fastener lines, between a bolt in one line and the nearest bolt in the other line

Gage is the distance (in) between adjacent lines of fasteners along which pitch is measured

or the distance (in) from the back of an angle or other shape to the first line of fasteners.The minimum distance between centers of fasteners should usually be at least 3 times thefastener diameter However, the AISC Specification permits a minimum spacing of 2⅔ timesthe fastener diameter

Limitations also are set on maximum spacing of fasteners, for several reasons In built-upmembers, stitch fasteners, with restricted spacings, are used between components to ensureuniform action Also, in compression members such fasteners are required to prevent localbuckling

Designs should provide ample clearance for tightening high-strength bolts Detailers who

FIGURE 1.3 Staggered holes provide clearance for high-strength bolts.

FIGURE 1.4 Increasing the gage in framing angles.

Minimum clearances for tightening high-strength bolts are indicated in Fig 1.5 and Table1.6

For connections with high-strength bolts, surfaces, when assembled, including those

adjacent to bolt heads, nuts, and washers, should be free of scale, except tight mill scale Thesurfaces also should be free of defects that would prevent solid seating of the parts, especiallydirt, burrs, and other foreign material Contact surfaces within slip-critical joints should befree of oil, paint (except for qualified paints), lacquer, and rust inhibitor

2 Snug tightening of bolts All high-strength bolts are inserted and made snug-tight

(tightness obtained with a few impacts of an impact wrench or the full effort of a personusing an ordinary spud wrench) While the definition of snug-tight is rather indefinite, thecondition can be observed or learned with a tension-testing device

3 Nut rotation from snug-tight position All bolts are tightened by the amount of nut rotation

specified in Table 1.7 If required by bolt-entering and wrench-operation clearances,tightening, including by the calibrated-wrench method, may be done by turning the boltwhile the nut is prevented from rotating

TABLE 1.7 Number of Nut or Bolt Turns from Snug-Tight Condition for High-Strength Bolts*

Direct Tension Indicator The direct tension indicator (DTI) hardened-steel load-indicator

washer has dimples on the surface of one face of the washer When the bolt is tensioned, thedimples depress to the manufacturer ’s specification requirements, and proper pretension can

be verified by the use of a feeler gage Special attention should be given to proper installation

of flat hardened washers when load-indicating washers are used with bolts installed in

oversize or slotted holes and when the load-indicating washers are used under the turnedelement

the actual length of the bolt This extension will twist off when torqued to the required tension

by a special torque gun The use of TC bolts have increased for both shop and fieldwork,since they allow bolts to be tightened from one side, without restraining the element on theopposite face A representative sample of at least three TC assemblies for each diameter andgrade of fastener should be tested in a calibration device to demonstrate that the device can betorqued to 5 percent greater tension than that required

For all pretensioning installation methods bolts should first be installed in all holes andbrought to the snug-tight condition All fasteners should then be tightened, progressing

systematically from the most rigid part of the connection to the free edges in a manner thatwill minimize relaxation of previously tightened fasteners In some cases, proper tensioning

Welded connections have a rigidity that can be advantageous if properly accounted for indesign Welded trusses, for example, deflect less than bolted trusses, because the end of awelded member at a joint cannot rotate relative to the other members there If the end of abeam is welded to a column, the rotation there is practically the same for column and beam

A disadvantage of welding, however, is that shrinkage of large welds must be considered

It is particularly important in large structures where there will be an accumulative effect

Properly made, a properly designed weld is stronger than the base metal Improperly

made, even a good-looking weld may be worthless Properly made, a weld has the requiredpenetration and is not brittle

Prequalified joints, welding procedures, and procedures for qualifying welders are

covered by AWS D1.1, Structural Welding Code—Steel, American Welding Society (2006).

Common types of welds with structural steels intended for welding when made in accordancewith AWS specifications can be specified by note or by symbol with assurance that a goodconnection will be obtained

In making a welded design, designers should specify only the amount and size of weldactually required Generally, a -in weld is considered the maximum size for a single pass A

⅜-in weld, while only -in larger, requires three passes and engenders a great increase incost

The cost of fit-up for welding can range from about one-third to several times the cost ofwelding In designing welded connections, therefore, designers should consider the worknecessary for the fabricator and the erector in fitting members together so they can be welded

The main types of welds used for structural steel are fillet, groove, plug, and slot The mostcommonly used weld is the fillet For light loads, it is the most economical, because littlepreparation of material is required For heavy loads, groove welds are the most efficient,because the full strength of the base metal can be obtained easily Use of plug and slot weldsgenerally is limited to special conditions where fillet or groove welds are not practical

More than one type of weld may be used in a connection If so, the allowable capacity ofthe connection is the sum of the effective capacities of each type of weld used, separatelycomputed with respect to the axis of the group

Tack welds may be used for assembly or shipping They are not assigned any stress-carrying capacity in the final structure In some cases, these welds must be removed after finalassembly or erection

Fillet welds have the general shape of an isosceles right triangle (Fig 1.6) The size of theweld is given by the length of leg The strength is determined by the throat thickness, the

shortest distance from the root (intersection of legs) to the face of the weld If the two legs areunequal, the nominal size of the weld is given by the shorter of the legs If welds are concave,the throat is diminished accordingly, and so is the strength

FIGURE 1.6 Fillet weld: (a) theoretical cross section and (b) actual cross section.

Fillet welds are used to join two surfaces approximately at right angles to each other Thejoints may be lap (Fig 1.7) or tee or corner (Fig 1.8) Fillet welds also may be used withgroove welds to reinforce corner joints In a skewed tee joint, the included angle of welddeposit may vary up to 30° from the perpendicular, and one corner of the edge to be

connected may be raised, up to in If the separation is greater than in, the weld leg must

be increased by the amount of the root opening A further discussion of this is continued in

Sec 1.3.7

FIGURE 1.7 Welded lap joint.

Groove welds are made in a groove between the edges of two parts to be joined These

welds generally are used to connect two plates lying in the same plane (butt joint), but theyalso may be used for tee and corner joints

Standard types of groove welds are named in accordance with the shape given the edges to

be welded: square, single V, double V, single bevel, double bevel, single U, double U, single J,and double J (Fig 1.9) Edges may be shaped by flame cutting, arc-air gouging, or edge

planing Material up to ⅜ in thick, however, may be groove-welded with square-cut edges,depending on the welding process used

FIGURE 1.9 Groove welds.

Groove welds should extend the full width of the parts joined Intermittent groove weldsand butt joints not fully welded throughout the cross section are prohibited

Groove welds also are classified as complete-penetration and partial-penetration welds

In a complete-joint-penetration weld, the weld material and the base metal are fused

throughout the depth of the joint This type of weld is made by welding from both sides of thejoint or from one side to a backing bar When the joint is made by welding from both sides,

of weld reinforcement

Partial-joint-penetration welds should be used when forces to be transferred are less than

those requiring a complete-joint-penetration weld The edges may not be shaped over the fulljoint thickness, and the depth of the weld may be less than the joint thickness (Fig 1.11) Buteven if the edges are fully shaped, groove welds made from one side without a backing bar ormade from both sides without back gouging are considered partial-joint-penetration welds.They are often used for splices in building columns carrying axial loads only

Plug and slot welds are used to transmit shear in lap joints and to prevent buckling of

lapped parts In buildings, they also may be used to join components of built-up members.(Plug or slot welds, however, are not permitted on A514 steel.) The welds are made, withlapped parts in contact, by depositing weld metal in circular or slotted holes in one part Theopenings may be partly or completely filled, depending on their depth Load capacity of aplug or slot completely welded equals the product of hole area and available design stress.Unless appearance is a main consideration, a fillet weld in holes or slots is preferable

Economy in Selection In selecting a weld, designers should consider not only the type of

joint but also the labor and volume of weld metal required While the strength of a fillet weldvaries with size, the volume of metal varies with the square of the size For example, a ½-infillet weld contains 4 times as much metal per inch of length as a ¼-in weld but is only twice

as strong In general, a smaller but longer fillet weld costs less than a larger but shorter weld

of the same capacity

Furthermore, small welds can be deposited in a single pass Large welds require multiplepasses They take longer, absorb more weld metal, and cost more As a guide in selectingwelds, Table 1.8 lists the number of passes required for some frequently used types of welds.This table is only approximate The actual number of passes can vary depending on the

welding process used Figure 1.10 shows the number of passes and fillet weld strength It can

be seen that cost, which is proportional to the number of passes increases much faster thanstrength

TABLE 1.8 Number of Passes for Welds

Double-V and double-bevel groove welds contain about half as much weld metal as single-V and single-bevel groove welds, respectively (deducting effects of root spacing) Cost ofedge preparation and added labor of gouging for the back pass, however, should be

considered Also, for thin material, for which a single weld pass may be sufficient, it is

uneconomical to use smaller electrodes to weld from two sides Furthermore, poor

accessibility or less favorable welding position (Sec 1.3.4) may make an unsymmetrical

When bevel or V grooves can be flame-cut, they cost less than J and U grooves, whichrequire planning or arc-air gouging

For a given size of fillet weld, the cooling rate is faster and the restraint is greater withthick plates than with thin plates To prevent cracking due to resulting internal stresses, theAISC Specification Section J2.2 sets minimum sizes for fillet welds depending on plate

nominal thickness of the part Another reason is that if weld size and plate thickness are nearlyequal, the plate comer may melt into the weld, reducing the length of weld leg and the throat

exceed 25 percent of the effective length

Subject to the preceding requirements, intermittent fillet welds maybe used in buildings totransfer calculated stress across a joint or faying surfaces when the strength required is lessthan that developed by a continuous fillet weld of the smallest permitted size Intermittent filletwelds also may be used to join components of built-up members in buildings

Intermittent welds are advantageous with light members where excessive welding canresult in straightening costs greater than the cost of welding Intermittent welds often are

sufficient and less costly than continuous welds (except girder fillet welds made with

automatic welding equipment)

For groove welds, the weld lengths specified on drawings are effective weld lengths They

in design calculations to allow for the start or stop weld crater

The AISC Specification requires fillet weld terminations to be detailed in a manner thatdoes not result in a notch in the base metal subject to applied tension loads An accepted

practice to avoid notches in base metal is to stop fillet welds short of the edge of the basemetal by a length approximately equal to the size of the weld In most welds the effect of

stopping short can be neglected in strength calculations A weld that is not stopped short of theedge is not cause for rejection unless the welding results in a harmful notch

The AISC Specification also requires welds to allow deformation to accommodate

assumed design conditions Examples include

• Welds on the outstanding legs of beam clip angle connections are returned on the top of theoutstanding leg and stopped no more than 4 times the weld size and not greater than half theleg width from the outer toe of the angle

• Fillet welds connecting transverse stiffeners to webs of girders that are ¾ in thick or lessare stopped 4 to 6 times the web thickness from the web toe of the flange-to web fillet weld,except where the end of the stiffener is welded to the flange End returns should be indicated

on design and detail drawings

Fillet welds deposited on opposite sides of a common plane of contact between two partsmust be interrupted at a corner common to both welds An exception to this requirement must

be made when seal welding parts prior to hot-dipped galvanizing

If longitudinal fillet welds are used alone in end connections of flat-bar tension members,the length of each fillet weld should at least equal the perpendicular distance between the

welds

In material ⅝ in or less thick, the thickness of plug or slot welds should be the same as thematerial thickness In material greater than ⅝ in thick, the weld thickness should be at leasthalf the material thickness but not less than ⅝ in

The diameter of the hole for a plug weld should be at least equal to the depth of the holeplus in, but the diameter should not exceed 2¼ times the thickness of the weld

Thus, the hole diameter in ¾-in plate could be a minimum of ¾ + = 1 in The depth ofweld metal would be at least ⅝ in > (½ × ¾ = ⅜ in)

Plug welds may not be spaced closer center-to-center than 4 times the hole diameter

The length of the slot for a slot weld should not exceed 10 times the thickness of the weld.The width of the slot should not be less than the thickness of the part containing it plus inrounded to the next larger in, but the width should not exceed 2¼ times the weld thickness.Thus, the width of the slot in ¾-in plate could be a minimum of ¾ + = 1 in The weldmetal depth would be at least ⅝ in > (½ × ¾ = ⅜ in) The slot could be up to 10 × ⅝ = 6¼ inlong

Slot welds may be spaced no closer than 4 times their width in a direction transverse to theslot length In the longitudinal direction, center-to-center spacing should be at least twice the