Designing built-up member connectors

The Built-up member connectors type (Wizard group Components & calculators, mark prefix BU) designs the welds or bolts that join the parts of a built-up steel member so that the parts act as one member. It covers three kinds of member:

Built-up member inputs #

• Loads: flexural members take the shear V (and, for a partial-length cover plate, the moment M at the section a' from the plate end); compression and tension members the axial force P (shown for reference: the E6 and D4 rules are geometric). Service dead and live loads, a required strength, or load cases.
• Member: the member kind and configuration; the rolled parts (W-shape, channel, angle, WT) from the shape database; the materials of the rolled parts and of the plates.
• Plates (plate girder, box): web depth and thickness, the top and bottom flange plates, and for a box the flange overhang past the outside faces of the webs.
• Cover plates: width and thickness, plates on one or both flanges, which flange is in compression (it selects the E6.2 or the D4 / J3.5 spacing limit), and the partial-length termination (weld across the plate end, extension past the theoretical cutoff).
• Two-shape members: the separation (filler or connector plate thickness), the angle legs back to back, the member length with Kx and Ky, and the number of intermediate connectors (they divide the length into equal spaces a).
• Tie plates: the out-to-out width of the two channels (toes in), the tie plate length, thickness and spacing, and the spacing of the welds or fasteners at each tie plate.
• Connectors: fillet welds (continuous or intermittent: segment length and pitch center to center; one or two fillets per web joint for plate girders and boxes) or bolts (bolts per row, pitch, grade, diameter, joint type, holes); staggered bolts and unpainted weathering steel select the alternative spacing limits.

Built-up member checks #

Flexural members (AISC 360-22 F13.3):

• Section properties from the parts: the neutral axis, Ix, and Q of the part(s) outside each joint.
• Shear flow q = V Q / Ix at each joint (kip/in.).
• Fillet welds: strength 0.60 FEXX × 0.707 w per inch with kds = 1.0 (the weld is parallel to the shear flow), times the number of fillets, times l / s for intermittent welds; the required size in sixteenths (Manual Eqs. 8-2a/b) and the required segment length at the given pitch.
• Base metal: shear rupture 0.60 Fu t of the element whose faces or edge carry the welds (the web of a plate girder or box, the cover plate edge, the W flange tip under a channel cap), Eq. J2-2 and J4.2(b).
• Fillet size limits: Table J2.4 minimum from the thinner part, J2.2b(b) maximum along an edge; intermittent segments at least 4 w and 1-1/2 in. long (J2.2b(e)).
• Bolts: the least of shear, bearing and tearout per bolt (or slip for slip-critical joints), the required pitch s ≤ n φrn / q, the minimum spacing 2-2/3 d.
• Maximum spacing of intermittent welds or bolts: E6.2 at the compression flange (0.75 t √(E/Fy) ≤ 12 in.; staggered 1.12 t √(E/Fy) ≤ 18 in.), D4 / J3.5 at the tension flange (24 t ≤ 12 in.; weathering 14 t ≤ 7 in.).
• Partial-length cover plates: the termination length a' = w with an end weld of at least 3/4 tcp, 1.5 w with a smaller end weld, 2 w without one; the welds in a' (both edges plus the end weld, J2.6 combination) must develop the plate force F = M Q / Ix, and the plate must extend at least a' past the theoretical cutoff. Bolted cover plates must be slip-critical, the bolts in the extension develop F, and the cover plate area may not exceed 70 % of the total flange area.

Compression members (E6):

• Connector spacing: a / ri ≤ 3/4 of the governing slenderness of the built-up member (ri = the least radius of gyration of one component: rz of an angle, ry of a channel or tee), with the number of connectors needed.
• Modified slenderness about the axis that shears the connectors (E6.1): Eq. E6-1 for snug-tight bolts, Eq. E6-2a (a / ri ≤ 40) or E6-2b with Ki = 0.50 (angles), 0.75 (channels), 0.86 (other) for welded or pretensioned connectors. The result (and the snug-tight alternative) is reported for use in the member design (E3 / E4).
• End connection of members that bear on base plates or milled surfaces: weld length ≥ the maximum width of the member, or bolts at ≤ 4 d over 1.5 times the maximum width.
• Outside plates of a plated column: the E6.2 stitch spacing.

Tension members (D4):

• Connector spacing: the component slenderness between connectors a / ri ≤ 300 (User Note, a recommendation).
• Parts in continuous contact: the J3.5 spacing (24 t ≤ 12 in.; weathering steel 14 t ≤ 7 in.).
• Tie plates: length ≥ 2/3 and thickness ≥ 1/50 of the distance between the lines of welds or fasteners, welds or fasteners at the tie plates at most 6 in. apart, and the channel slenderness between tie plates ≤ 300.

Built-up member drawings #

The section shows the parts with every fillet weld in true cross-section (outside the base metal) or the bolts through the plies, the weld symbol (intermittent fillets with their length-pitch, for example 6"-12"), and the part marks. The elevation shows a length of the member broken at both ends: continuous welds or the intermittent segments at their pitch seen face-on with the segment length and pitch dimensioned, the bolts at their pitch, the connectors or tie plates at their spacing, and for a partial-length cover plate the end weld, a' and the extension to the theoretical cutoff.

Built-up member limits #

• The member itself (flexural, compressive or tensile strength) is designed elsewhere; this type designs the connectors and reports the modified slenderness for the compression design.
• Bolted plate girders (flange angles), laced members, perforated cover plates and the shear on intermediate connectors of two-shape compression members are not modelled.
• Welds joining parts at an angle to the shear flow, and loads applied directly to a flange (F13.3: welds that also transfer those loads to the web), are not included; add them to V or check them separately.
• Verification: Design Examples F.14 (continuous and intermittent flange-to-web welds), E.5, E.6 and E.13 (connector spacing and modified slenderness); every other configuration is checked against hand calculations (backend/tests/test_built_up.py).