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1/3Modern Steel Construction July 2003

Victor Shneur, P.E.

Connections can be expen-sive, and they can take a lotof effort to create duringthe design and construc-tion process. How can you

save time and moneyand makeeverybodys work easier when work-ing with connections on fasttrackschedules? Here are some generalguidelines for structural engineers forthe design of economical bolted andwelded connections for columns,

beams and braces.

1.Communication is key. Develop aworking design-build team forfast-track projectswith the fabricatorand erector on board. The main bene-fits are:I Design requirements can be con-

veyed accurately.I Everyones expertise can be utilized.I Detailing can start quickly.I Duplication of work can be avoided.I Revise and Resubmit on ap-

provals is avoided.I All parts work together without

surprises.I Paperwork is minimized.I Your best chance for cost savings.I Good working environment.

2.Connection approvals shouldoccur in a timely manner. Detail-ers need connections immediately forfast-track project delivery. Make ap-proval comments clear. Confusingnotes cause misinterpretation andmore paperwork.

3.Engineers should always provideall end reactions, including shear,moment, torsion and axial end reac-

tions. Drawings that dont show actualend reactions can lead to costly and un-safe connections.

4.Always provide complete loadpaths (including transfer forces)where there are axial forces. Keep loadpaths simple.

5.Favor factored end reactions(LRFD) over service end reactions(ASD).

6.Provide details that clearly repre-sent the design intent. They willeliminate misunderstandings and save

time.

7.Use standard AISC connectionswhen possible.8.Dont be excessively conser-vativeconnections need to with-stand only design loads.

9.Simplify as much as possible. Forexample, make column-base de-tails symmetrical, use the same spacingfor expansion anchors and minimizethe number of sizes of slab edge clo-sures/pour-stops. This expedites thefabrication and erection process and

greatly reduces the number of possiblemistakesand repair costs.

10.Check structural drawings forconstructability issues.11.Review the member sizes forconnection economy:I Preferably, a supportingbeam should

have at least the same depth as thesupportedbeam.

I Dont frame W8 beams into thewebs of heavy W-shapes or plategirders. The thick flanges of theheavier shapes will require exces-

siveand sometimes impossi-blecopes in the W8.

I Favor W12 and W14 sections fortypical gravity columns. The dis-tance between flanges makes webconnections easier.

I Consider using heavier member sizesto eliminate stiffeners (see Tip 18).

I Provide adequate flange width atperimeter members. Provide beamsthat frame slab openings to supportdeck and pour stops, and to weldstuds.

12.Use A36 steel for connectionangles, and plates for typicalconnections.

13.Specify readily available an-chor rods. Often, the rods aredelivered in a rush immediately afterthe contract has been awarded and be-fore communication has been estab-lished between fabricator and engineer.

14.When possible, use standardtolerances established byASTM A6/A6M, the AISC Code of Stan-dard Practice for Steel Buildings and

Bridges (www.aisc.org/code), andAWS. Tighter tolerances will increasecosts and construction time substan-tially.

15.Avoid overly restrictive specifi-cations.16.Dont over-specify detailsyou might not be aware of fab-rication/erection procedures, requiredclearances, etc.

17.Moment connections:I Eliminate when possible. For exam-

ple, you can use a cantilever at the

Tips for ReducingConnection Costs57

A little planning goes a long way, especially with respect to steel connections.

These helpful tips should help you keep bolts from driving you nuts, and welds

from torching your temper.

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2/3July 2003 Modern Steel Construction

roof in lieu of two moment connec-tions to the column.

I Provide actual moments/momentenvelopes and vertical end reac-tions.

I Favor extended end-plate momentconnections. Refer to AISC DesignGuide 4: Extended End-Plate MomentConnections for design information.

I Shop weld short cantilevers.I Moment connections to HSS

columns are usually very expensive.

18.Stiffeners can complicate con-

nections for framing beams.I Specify only when required.I Wherever possible, use partial-

depth stiffeners.I AISCs SteelToolTM Clean Columns

v3.1 can help avoid column stiffen-ers. Its available atwww.aisc.org/steeltools.

I Refer to AISC Design Guide 13: Wide-Flange Column Stiffening at MomentConnections for designing and speci-fying stiffeners.

19.

Favor one-sided shear connec-

tions (single-angle and single-plate), but avoid expensive through-plate connections at HSS columns.

20.Rule of thumb: The morepieces there are in a connectiondetail, the more expensive it is to fabri-cate and erect.

21.Give some thought to the de-sign of column splices:I Do not specify to develop the full

bending strength of the smallershaft. This is not always necessary.

I Use field-bolted column splices formoderate uplift forces.

I Minimize the number of splices, es-pecially for HSS columns. Some-times it is more economical toextend the lower shaft for anotherlevel than to add a splice.

I For W-column splices with PJP orCJP welds at flanges, favor webchannel(s) over temporary flangelugs wherever possible. This willmake detailing, fabrication anderection easier.

22.Design-build projects requireextra attention:

I Complete each released area asmuch as possible.

I Size members conservatively.I Consider using field-welded con-

nections for openings.I Immediately inform fabricator of

the areas of possible substantial re-visions.

23.Provide for tolerancesuseoversized, short-slotted, andlong-slotted holes in bolted connec-tions, and leave extra space for weldedconnections.

24.Make embedded plates a min-imum 6 to 8 larger than re-quired for connections. Field fixes forembedded plates that are mislocatedare time and money consuming.

25.Clearly identify all changesand revisions on designdrawings.

26.When shop or field errors re-quire correction:I Request an as-built report. It clearly

shows the problem and eliminatesmisunderstanding and misinterpre-

tation.I Discuss possible solutions with fab-

ricator or erector.I Keep in mind: labor is expensive,

material is relatively inexpensive.I As a rule of thumb, fast decisions

and approvals are required to con-tinue the work.

I Remember that not every error re-quires correction.

27.Wherever possible, specifybearing joints. It makes themost economical use of bolts, elimi-nates masking or a special paint sys-tem, and reduces installation andinspection requirements.

28.Use snug-tightened joints asmuch as possible.29.Favor -diameter A325 boltsfor typical structures.30.Try to limit bolt diameters to1 or smaller. Larger diametersrequire special equipment, larger spac-ing and edge distance, and special 5/16-thick washers (ASTM F436) for fullypretensioned ASTM A490 bolts.

31.Never use bolts with the samediameter but differentstrengths on a jobit can lead to mis-takes.

32.Use short-slotted holes in out-standing legs of connection an-gles, end plates and single-plateconnections.

33.When loads are large, considerlarger diameter bolts and/orASTM A490 bolts.I Bolt material cost is roughly propor-

tional to strength.

I Higher strength bolts save in con-nection material, hole making, andinstallation cost.

34.Consider excluding boltthreads (X-bolts) for:I Heavily loaded connections where

typical bolt size doesnt give enoughcapacity.

I Shop assembled trusses.I Connections when outer plies are

3/8 thick or larger.

35.Use slip-critical connectionsfor:I

Bracing connections with oversizedor slotted holes.I Field-assembled trusses with over-

sized holes.I Members with short/long-slotted

holes when force applies parallel tothe slots.

I Built-up compression members.I Cyclic loads.

36.Where fully pretensioned boltsare needed, permit the use ofany of the four methods approved byRCSC and AISC:I Turn-of-nut.I Calibrated wrench.I Twist-off-type tension-control bolt.I Direct-tension-indicator.

37.Mechanically galvanizedASTM A325 bolts provide ex-cellent corrosion resistance and requirea minimum overtapping of nuts andeasier pretensioning.

38.Keep your bolt holes as ra-tional as possible:I Dont use different hole sizes in the

same member. It leads to mistakes

Least Weight IsntAlways Least Cost

Heavier ColumnsMinimize Stiffeners

Specify ASTM A36Connection Material

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and slows fabrication because shop

re-tooling is required for the piece.I Dont specify slots in material

thicker than bolt diameter plus 1/8.The AISC Specification doesnt allowpunching holes in such material,and it is difficult to make slots. Agood alternative would be to useoversized holes.

I Use the same oversized holes in allplies if it is possible.

I Use long-slotted holes in girts andany members that must be field-aligned to tolerances other thanstandard steel framing tolerance (forexample, curtain wall connections).

39.Correctly apply AISC require-ments for fillers:I Fillers in slip-critical joints are not

required to be developed.I Fillers up to thick can be used in

bearing joints without reduction instrength.

I Fillers up to thick dont have to bedeveloped if the design shear strengthof the bolts is multiplied by the factor[1 - 0.4(t 0.25)], where t is the totalthickness of the fillers up to .

I Fillers over must be developedby bolts or welds, in or outside ofthe joint.

40.Leave extra holes open. In al-most all cases they dont needto be filled, and filling takes a lot oftime (think labor costs), especially forthick members.

41.Avoid over-welding.I The weld doesnt need to be

stronger than base metal in anycase.

I Excessive welding can cause seriousproblems (distortion, cracking, etc.).This can lead to expensive repairs oreven rejections.

I Weld connection elements for actualforces.

42.Use single-pass fillet weldswhere possible. A 3/8 filletweld requires 44% more material and100% more labor, but it is only 20%stronger than a 5/16 fillet weld.

43.Use AWS D1.1 rules for mini-mum weld size. Per AWSD1.1/D1.1M:2002, Table 5.8, for low-

hydrogen process: Minimum weld

size is dependent upon the thinner ofthe two parts joined.

44.Use intermittent fillet weldswhen possible.45.Use AISC Specification Appen-dix J2.4 for fillet welds. This al-lows an increase in strength of the filletweld based on direction of the force.Note: Per AISC it is also acceptable for ex-tended end-plate moment connections.

46.Favor fillet welds over groovewelds. Groove welds are usu-ally more time consuming.

47.Favor PJP welds over CJPwelds.

48.Allow full-strength connec-tions in lieu of CJP welds instatically loaded structures. Filletwelds up to are more economical.

49.Specify effective throat size orrequired strength for welds.50.Allow the use of groove-welded joints with a prepara-tion that minimizes weld metalvolume.

51.Leave weld access holes open.52.Inspect critical CJP welds withUltrasonic Testing (UT).53.Avoid the weld-all-aroundsymbol. It is expensive, and ina lot of cases its not requiredandsometimes its even prohibited.

54.Avoid shop welding on galva-nized surfaces.55.Layout welds to reduce re-straint, especially for largewelds. This lowers the possibility oflamellar tearing.

56.Favor horizontal and flat posi-

tions. Let gravity work for you.

57.Try to minimize field-weldedconnections and favor field-bolted connections. #

Victor Shneur, P.E. is a chief engineerwith LeJeune Steel Company in Minneapo-lis, MN. He is a member of the AISC Com-mittee on Manuals and Textbooks. Thisarticle was adapted from the paper Mr.Shneur submitted for the 2003 NASCC,How to reduce the cost of common struc-tural steel connections.

Single-Pass FilletsAre Cost-Effective

Member ReactionsSimplify Detailing

Keep Bolt HolesOne Size Per Piece

Slip-Critical JointsOnly When Needed

Favor Fillet WeldsOver Groove Welds

Modern Steel Construction July 2003