WWhen working on a steelconstruction project, theStructural Engineer ofRecord (SER) can createan economical structure

that is fabricator and erector friendly, es-pecially with good communication andteamwork on the project design and con-struction teams.

If the fabricator designs the connec-tions, sealed calculations usually need tobe submitted to the SER for review. Also,the load criteria need to be given on thecontract documents. For moment and ax-ially loaded connections, the actual de-sign load or a percentage of themember’s capacity is given. For shearconnections, one of three methods (or acombination) is used:➜➜ The actual beam shear loads are given.➜➜ A beam shear-load schedule for differ-

ent beam depths are given. ➜➜ The SER specifies that the shear load

will be determined based on a per-centage of the beam’s uniform distrib-utive load capacity (UDL). If a beam shear-load schedule or a

percentage of UDL is given, the actualcriteria specified by the SER should sat-isfy the required loading. However, thecriteria should not be so conservative asto unnecessarily create the need for ex-cessive typical shear connections (morethan two vertical rows of bolts or morethan full-depth connections).

For the most economical structure, itis preferred that shear loads be given ondrawings for every beam. There are alsoconditions where a beam shear-loadschedule or the UDL method do notapply and actual loads should be given: ➜➜ At beams with concentrated loads

near the beam end.➜➜ At beams sized for serviceability re-

quirements rather than strength re-quirements.

➜➜ At infill beams that support a rela-tively small area.

➜➜ At beams with axial load.At relatively short beams, the UDL

method usually gives overly conserva-tive shear loads, and an upper-limit shearload or the actual beam shear loadshould be given.

Below are some recommendations forcost-effective connection design that alsocould reduce problems in the field:

11.. At bolted flange-plated connections,the flange plate should not be thesame width as the beam flange.

Allow at least a ½” difference on each sideof the flange plate at bolted flange-platedconnections. If bolt holes misalign in thefield, there will be a sufficient shelf di-mension to place longitudinal fillet weldsto compensate for the missing bolts.

22.. Use oversized holes in beam momentand brace connections.

At flange-plated moment connections orbrace connections with slip-critical bolts,oversized bolt holes are often preferredover standard bolt holes. Although stan-dard holes give a greater bolt capacity,oversized holes permit more erection tol-erance and reduce field problems. Typi-cally, oversized holes are used in thedetail material and standard holes in themain member.

33.. Group similar connections rather thanhave several different connections.

Connections on a project should be asuniform as possible to save fabricationtime and reduce the possibility of errors.

44.. Limit the number of bolt diameters toone size (a maximum of three sizes ifnecessary).

This reduces field errors as well as fabri-cation errors with drill lines that havemanually changed spindles. Some fabri-

cators/erectors keep at least a ¼” differ-ence between bolt sizes to prevent uncer-tainty.

55.. Avoid different grade bolts with thesame diameter.

66.. Use bolted connections instead offield-welded connections.

Bolted connections are quicker to erectand less costly. Welded connection delaysresult from the absence of a qualifiedwelder or welding platforms, or coldwindy weather.

77.. Try to use fillet welds instead of par-tial-penetration or full-penetrationwelds.

Fillet welds are less expensive, since nobase-metal preparation is needed. Also,partial- and full-penetration welds usuallyrequire more weld metal and inspection.

88.. Limit the maximum fillet weld size to5/16” (especially in the field).

This is the maximum-size weld that canbe completed in a single pass using theshielded-metal arc-welding (SMAW)process. Smaller, longer welds are pre-ferred over larger, shorter welds.

99.. Avoid overhead welding.

The preferred welding positions are flatand horizontal. Overhead welding is diffi-cult, costly and generally yields lower-quality welds. For single-pass SMAW filletwelds, it can take four times as long aswelding in the flat or horizontal position.

1100.. Use full-penetration welds onlywhen necessary.

Full-penetration welds cost more thanpartial-penetration or fillet welds due toincreased material preparation, testingrequirements, weld-metal volume andmaterial distortion. Use fillet welds (pro-

May 2004 • Modern Steel Construction

30 GGoooodd RRuulleess ffoorr CCoonnnneeccttiioonn DDeessiiggnn

By Carol Drucker, S.E.

Practical tips for designing economical, fabricator- and erector-friendly steel connections

vided that the fabricator does not deter-mine them excessively large) or partial-penetration welds when joint strength isadequate for the applied load. Full-pene-tration welds at HSS members are diffi-cult due to the need for backing bars.

1111.. Consider finishing to bear.

For connections with high compressiveloads, it could be more economical to fin-ish the steel to bear and provide AISC’sminimum-required weld size instead oftransferring the compressive forcethrough large fillet or groove welds.When steel is to be finished to bear, itmust be indicated on the connection de-tail. The detail also should call for thebeam flanges to be square to the beamweb. In detailing, stiffeners might need tobe longer than d-2tf for beam overrun indepth and variation in beam-flangethickness. Per AISC Specification SectionM, gaps not exceeding 1/16” are permittedin bearing connections.

1122.. Avoid excessive connections.

Connections should be designed to ac-tual load requirements. The SER shouldnot specify that connections be designedfor the members’ full capacity if not nec-

essary. Excessive connections increaseconstruction cost and the possibility ofproblems in the field. Over-welding candamage the steel.

1133.. Specify only prequalified welds.

The welding procedure specification(WPS) for a weld not American WeldingSociety (AWS) prequalified must betested. To avoid the cost, time and confu-sion of qualification, use only prequali-fied welds.

1144.. Minimize weld volume at full- andpartial-penetration welds.

The weld configuration with the least weldvolume is the most economical. For weldconfigurations with double-sided prepara-tion, consider the additional cost of mate-rial preparation, since it could offset thecost savings of less weld metal. For full-penetration welds, it is economical to prepone side of plates with a thickness less than1” and to prep both sides of plates with athickness greater than or equal to 1”.

1155.. Provide proper clearance forbolted and welded connections.

AISC’s LRFD Manual of Steel Construction,3rd Edition, Parts 7 and 8, give the neces-sary clearances for bolted and welded

connections.

1166.. Specify slip-critical bolts onlywhen necessary.

Slip-critical bolts are not always needed atmoment and brace connections, and bear-ing bolts might be acceptable in standardholes. The RCSC (Research Council onStructural Connections) Specification,Section 4.3 gives criteria for slip-criticaljoints, which are more costly than bearingjoints due to additional installation, in-spection and faying-surface preparation.Also, more or larger bolts are needed forreduced bolt strength. In certain condi-tions, fabricators/erectors might preferslip-critical bolts for oversized holes andgreater erection tolerance.

If slip-critical joints and bolts areneeded, the steel detailer must indicatethem on the erection and shop drawings.The detailer should indicate masking re-quirements in the bolt-hole area to keepthe faying surface free of coatings frominadvertent overspray of unqualifiedpaint.

1177.. Allow bearing bolts at the shearconnection of flange-welded mo-ment connected beams.

At directly welded moment connectionsor flange-plated moment connectionswelded to the supported beam, bearingbolts can be used in the beam-web shearconnection. Since the flange weld and theweb bolts are not on the same faying sur-face, the web bolts do not need to be slip-critical. (See AISC’s LRFD SpecificationCommentary, Section J1.9). Also, sincethe web bolts will be installed prior to thecompletion of the flange weld, the webbolts should be in bearing.

1188.. Limit the maximum bolt diameterto 11/8” diameter.

Bolts with diameters greater than 11/8”are difficult to tighten, not commonlyused, and costly. ASTM A490 boltsgreater than 1” diameter have a disad-vantage in slip-critical connections withoversized or slotted holes. Hardenedwashers with a 5/16” minimum thickness(standard washers are 5/32” thick) are re-quired to cover oversized and short-slot-ted holes in outer plies. See RCSCSpecification Section 6.2.

1199.. Avoid slotted holes in platesthicker than the bolt diameter.

Slots in thick plates are hard to punchand must be flame-cut, which is difficultand costly. Standard holes or oversized

Modern Steel Construction • May 2004

Use shear plate connections at beam-to-column flange-plated moment connections (see tip 20).

holes are preferred.

2200.. Use shear plate connections atbeam-to-column flange-platedmoment connections.

If flange plates need to be welded to acolumn flange, a shear-plate connectionis preferred. Since the column needs to bepositioned in the shop for the flange-plate welds, the shear plate can be readilywelded.

At fully restrained moment connec-tions, a typical shear-plate connectioncan be designed for shear only (and ec-centricity in the shear connection can beignored). The joint rotation is consideredresisted by the flange connections.

2211.. Use double-angle connections atdirectly welded beam-to-columnmoment connections.

To avoid double-cutting the beam, dou-ble-angle connections (bolted to the col-umn) are preferred over shear-plateconnections at directly welded momentconnections. At directly welded momentconnections, the beam flange typically isset back ¼” from the face of the columnflange for welding purposes. If a shear-plate connection is used, the beam webneeds to be set back ½” to clear the shear-plate welds, and the beam needs to bedouble-cut. However, for double-angleconnections, the beam-web set-back canbe reduced to permit a single beam cut.

2222.. Allow for field adjustment in onedirection only at bolted connec-tions.

If slotted holes are needed at a boltedconnection for field adjustment, the ad-justment should be in only one direction.This permits adjustment in one directionwhile the adjustment in the other direc-tion is made.

2233.. Cope or block beams instead ofcutting flush and grinding smooth.

It is less costly to cope or block a beam. Ifthe beam flange must be cut flush, thenspecify grinding smooth only whenneeded.

2244.. For shear-plate connections toHSS columns, use face-mountedsingle-plate connections insteadof through-plate connections.

Avoid through-plate shear connections,which cost more than face-mounted sin-gle-plate connections. AISC’s HollowStructural Sections Connections Manualdiscusses face-mounted single-plate con-

nections and how to evaluate them. Face-mounted single-angle connections arealso economical shear connections to HSScolumns.

2255.. At beam-to-HSS column momentconnections, use direct momentconnections when possible.

Moment connections in which the beam’sflanges or flange plates are welded di-rectly to the face of the HSS column arethe most economical moment connectionto an HSS column. It is preferred overcut-out plate (doughnut) or through-plate connections. If the resistance of thedirect moment connection is insufficient,then a cut-out connection is preferred toan expensive through-plate connection.

The limit states for direct momentconnections are given in the HSS Specifi-cation in AISC’s LRFD Manual of SteelConstruction, 3rd Edition. They includeeffective flange width, and yielding, crip-pling, and punching shear and bucklingof the side walls. The HSS Specificationdoes not include the limit state for yield-ing of the HSS face given in equations (5-2) and (5-3) in AISC’s HSS ConnectionsManual. Based on conversations withAISC, this limit state was omitted due tolimited testing and does not need to beconsidered.

2266.. Clearly show column stiffener anddoubler requirements.

The SER should check columns for stiff-eners and doublers, and if possible, in-crease column sizes to eliminate requiredcolumn reinforcement (especially dou-blers). If the fabricator is responsible forchecking the columns, the actual beamdead, live and wind moments are neededat the time of bidding to determine therequired reinforcing or alternate columnsizes.

Sometimes typical details on the SER’sstructural drawings can include prob-lems, such as:1. Stiffeners might be provided unneces-

sarily.2. It is unclear if the stiffener material is

Grade 36 or Grade 50.3. The stiffener weld size is not given.4. The full-penetration field welds could

be excessive.5. It is unclear if the SER checked if col-

umn doublers are needed.If no information is shown on the con-

tract documents, it might be assumed in-correctly that no column reinforcing isneeded.

Consider bolted HSS bracing connections (see tip 29).

May 2004 • Modern Steel Construction

2277.. For simple shear connections,allow the fabricator to choose theAISC standard shear connectionthat is most economical for theirshop.

Each fabricator has a preference for astandard shear connection, based onshop equipment, ease of erection andspecified shear reactions. Usually, anyAISC standard shear connection is ac-ceptable. Concerns about shear-plateconnections or single-angle connectionsat laterally unbraced beams are due tothe low torsional resistance of these con-nections. However, most beams are later-ally braced due to the attachment ofmetal deck or perpendicular beams.

2288.. At W-shape brace connections,connect only the brace flanges tothe gusset plate.

For ease of erection and fabrication, it ispreferred that only W-shape flanges con-nect to the gusset plate. If the gusset plateand the web of the brace are not the samethickness, then filler plates are necessaryat the web connection. If the web needsto be connected, connect it on one side sothe brace can be erected easily from it. Ifonly the brace flanges are connected, thesection must be checked for shear lag.

2299.. Consider bolted HSS brace con-nections.

HSS braces commonly are shown slottedand welded to the gusset plate. To elimi-nate the need to field-weld the HSSbrace, the HSS brace can be bolted to thegusset plate. A welded tee end or a slot-ted HSS/gusset-plate connection couldbe used. Design procedures for both con-nections are in AISC’s HSS ConnectionManual. To eliminate connection eccen-tricity, side plates also can be used.

3300..Whether using ASD or LRFD, con-sider information in AISC’s LRFDManual that can simplify connec-tion design and increase connec-tion capacity.

1. Appendix J gives the fillet-weldstrength-increase equation for weldsloaded at an angle relative to the lon-gitudinal axis of the weld.

2. Eccentrically loaded bolt-group andweld-group tables for loads applied atan angle from the vertical position. �

Carol Drucker, S.E, P. E. is a principal atDrucker Zajdel Structural Engineers inNaperville, IL. She can be reached atcarol@dzse.com.

Modern Steel Construction • May 2004

Cope or block beams instead of cutting flush and grinding smooth (see tip 23).

For more information on connec-tion design, see the article “57Tips for Reducing ConnectionCosts” by Victor Shneur, P.E., inthe July 2003 issue of ModernSteel Construction (available on-line at www.modernsteel.com).

Also, check out AISC’s newDetailing Cards, available by call-ing 800.644.2400 or by visitingwww.aisc.org/bookstore for $30for AISC members ($60 for non-members). AISC Detailing Cardsare a quick and handy referencefor the shape, gage, and strengthproperties of steel sections andconnectors.