By M. Thomas Ferrell

This article will presentdetails that will accommodatemill and shop tolerances of struc-tural members, as well as provid-ing for material ductility. It willalso present limit state strengthconsiderations for both momentconnections with field weldedbeam flanges and field boltedflange plates.

MOMENT CONNECTIONWITH FIELD WELDED

BEAM FLANGES(FIGURE 1)

1. The connection plates must bethe same grade of material asthe weak axis moment beam.

2. The connection plate has beenextended ¾” minimum beyondthe column flange to provide bet-ter toughness and ductility.AISC’s Manual of SteelConstruction (LRFD) VolumeII—Connections, pages 10-60through 10-65, has summarizedresults of nine simulated weakaxis FR moment connection testsperformed by Driscoll, et. al., toaid in selection of details toensure ductility.

3. The top connection platethickness is equal to tf plus ¼”.This additional thickness is nec-essary to accommodate toler-ances for fabrication and beamflange tilt. Note that the bottomof this connection plate isaligned with the bottom of thebeam top flange.

Modern Steel Construction / March 1998

4. The bottom connection platethickness is equal to tf plus 3/8”.This is necessary to accommo-date tolerances for fabricationand beam flange tilt plus possi-

ble overrun/under-run in thebeam depth. Note that the cen-terline of this connection plate isaligned with the centerline of thebottom flange of the beam.

MOMENT CONNECTIONSTO COLUMN WEBS

nection plates must be designedfor shear stresses due to theeccentricity from the neutralaxis of the bolt group to the edgeof the column flange. If a columnweb doubler is required due to astrong axis moment beam, thenthe additional stresses from theshear plate must be consideredin determining the thickness ofthe web doubler plate.

MOMENT CONNECTIONSWITH BEAM FLANGEPLATES (FIGURE 2)

1. It is not necessary for theflange plates to be the samegrade of material of the weakaxis moment beam.

2. Oversized holes should beused in the flange plates to allowfor mill tolerances in the columnbeam. These connections withoversized holes must be designedas slip critical. If tension controlbolts are used, if possible use abolt gage that will allow bolts atthe bottom flange to be tightenedfrom inside of the beam flange.In many cases, this is not possi-ble due to beam flange widthsand beam depths.

3. Shims must be provided at thetop or bottom flanges to accom-modate fabrication and mill tol-erances for flange tilt plus possi-ble overrun/under-run in beamdepths. Fabricators normallyprefer the shims to be at the bot-tom flange due to restrictions onprogramming of shop equipment.If shims are provided at the topflange, the detail can be providedto serve as a deck support (figure3).

4. The flange plates must bedesigned for tension yielding,tension rupture, and compres-sion strength.

5. The flange bolts must bedesigned for shear strength.

6. The beam design flexuralstrength with regard to net sec-tion must be determined toassure that the net beam sectionis adequate without reinforcing.

Modern Steel Construction / March 1998

5. The welds for connectionplates to the column flangesmust be designed for shearforces. These welds may also besubjected to tensile/compressionand shear forces when theseplates serve as stiffener platesfor a strong axis moment beam.Use fillet welds where possible.It is good practice to deducttwice the weld size from thelength of plate available forwelding so that the welds do notterminate at the edges of theplate or column flange. If calcu-lated stresses are transferredthrough the welds at the columnweb, then back-up stiffenerplates must be provided.

6. Bolts for the shear plate tobeam web are normally locatedoutside of the column flanges.This practice simplifies beamerection and allows access totighten the bolts with use of animpact wrench. Short slotsshould be used in the plate andstandard holes in the beam web.Flange welds should be complet-ed before the bolts are tightened.The short slots will “hold” top ofbeam elevation and allow forweld shrinkage to occur at theflange welds. The bolts aredesigned for shear forces only(no eccentricity). The welds forthe shear plate-to-column webare designed for shear only. Thewelds for the shear plate-to-con-

7. The welds for the flange platesto the column flanges/webs aredesigned using the same criteriaused for the connection plates forthe field welded flange momentbeams in figure 1.

8. The web shear plate design isthe same as for the field weldedflange moment beams.

This article is adapted from apaper by M. Thomas Ferrell,P.E., for the 1998 National SteelConstruction Conference. Ferrellis President of FerrellEngineering, Inc., a specialtystructural engineering firm locat-ed in Birmingham, AL.