Designing a vertical bracing gusset (UFM)

The Vertical bracing gusset (UFM) type (Wizard group Truss & bracing, mark prefix VB) designs a diagonal brace connected by a gusset plate at a beam-to-column joint. The gusset is fillet welded to the top flange of the beam. At the column flange (or web) it is either fillet welded or bolted through an end plate, two clip angles or a single plate. The brace force is shared between the two gusset edges and the beam-to-column connection by the Uniform Force Method (UFM) of AISC Manual Part 13.

Bracing gusset inputs #

• Loads: the brace force P (tension positive), the beam end reaction R, and the axial transfer force A in the beam. Enter them as required strengths (the default), service loads, ASCE 7 combinations or load cases. Tick Brace force reverses to check the brace force in both tension and compression (seismic or wind bracing).
• Beam and column: the W shapes and their materials, and whether the gusset is on the column flange or the column web. For the column web, ec = 0 (Manual Part 13).
• Brace: double angle (back to back on the gusset), single angle, WT (flange on the gusset), a rectangular or round HSS slotted for the gusset, or a W-shape with its web in the gusset plane (see W-shape braces). Also enter the material, the connected angle leg, and the bevel as a vertical and a horizontal leg (for example 12 and 9 9/16). Brace clearance sets the gap between the brace end and the beam flange and column face.
• Brace connection: bolted (lines, bolts per line, pitch, gage, end distances on the brace and the gusset) or welded (fillet size and length; slotted HSS are always welded).
• Gusset and UFM: the thickness and material. The length along the beam and the height along the column are sized automatically unless you enter them. Further inputs:
  • the setback from the column face and the corner clip;
  • the UFM case;
  • optional lengths of the interface connections (when they are shorter than the gusset edges);
  • the fillet sizes on each edge, which are welded on both faces of the gusset;
  • the gusset buckling K (0 means automatic) and the buckling length rule;
  • whether the Whitmore width may extend beyond the gusset edges;
  • the gusset shape: a corner plate, optionally with its column-side free edge cut parallel to the brace at a set distance from the bolt line, or a flat bar on the brace line (special case 3 only, AISC Design Guide 29 Ex. 5.8).
• Gusset to column: Welded to the column (the default) or bolted to the column:
  • End plate: the plate is welded to the gusset edge and bolted to the column with two bolts per row at the cross-centre gage. Enter the plate thickness and width; the setback must be at least the plate thickness.
  • Double clip angles: the angles are welded to the gusset (C-shaped welds) and bolted to the column through the outstanding legs.
  • Single plate: the plate is welded to the column and bolted to the gusset with one line of bolts. Enter the distance from the column face to the bolt line. For each, enter the bolts (grade, diameter, threads, holes, rows, pitch) and the element material and fillet. The bolt rows are centred on the gusset-to-column connection length.
• Gusset to beam: Welded to the beam flange (the default) or Bolted to a tab plate welded to the beam (see Gusset bolted to tab plates on the beam).
• Beam-to-column connection: Required forces only (the default) reports the forces. Choose Double angles, Single plate or Shear end plate to design it here:
  • double angles: bolted or welded to the beam web, bolted or welded to the column; the angle size and material;
  • single plate: welded to the column, bolted to the beam web (one or two bolt lines, the distance from the weld line to the bolts);
  • shear end plate: welded to the beam web, bolted to the column;
  • the bolts (grade, diameter, threads, pretensioned), the rows and spacing, the edge distance, the distance from the top of the beam, the gage at the column, the welds and the beam setback.

Gusset bolted to tab plates on the beam #

Use this when the gusset cannot be welded to the beam in the field, as at a truss chord (AISC Design Guide 29 Example 5.11). A tab plate is welded to the beam flange along both faces, and the gusset laps it and is bolted to it. The tab is as long as the gusset-to-beam connection.

Enter:

• the tab thickness, material and fillet;
• the bolts: grade, diameter, threads, bearing or slip-critical (with the slip class), and the holes in the tab and the gusset. Oversized holes need slip-critical bolts;
• the bolts per line along the beam, the number of lines, the pitch and the line spacing;
• the distance from the beam flange up to the centroid of the bolt group;
• the edge distance.

The UFM forces on the beam edge act at the flange. ILX checks:

• the bolt group, by the instantaneous center method with the force applied at the flange. Each bolt takes the least of slip, bolt shear, and bearing or tearout on the tab and the gusset. Tearout uses the edge distance for every bolt, as the guide does;
• the tab plate along the bolt line:
  • shear and tension yielding and rupture;
  • flexure from the moment Hb × (flange to bolt centroid);
  • the Neal interaction of moment, normal force and shear, for yielding and for rupture;
• the tab-to-beam welds, without the 1.25 ductility factor. Design Guide 29 omits it here because bolt slip lets the force redistribute.

ILX still checks the gusset along its beam edge, and the beam web under the gusset force. The drawing shows the tab face-on with its bolts. Section A-A shows the gusset lapped on the tab.

W-shape braces #

Choose W-shape as the brace shape. The brace web lies in the plane of the gusset. Pick one of two connections (AISC Design Guide 29):

• Web WT splices (Example 5.5). Two WTs, one on each face, lap the brace web and the gusset with their flanges; their stems stand out. The bolts are in double shear. Enter the tee size and material, the bolt lines and gage, the bolts per line, the pitch on the gusset (s) and on the brace web, the end distances, and the gap between the gusset end and the brace end.
• Flange plates (Example 5.11). A plate on the outside of each brace flange is bolted to the flange and slotted over the gusset, then fillet-welded to the gusset on both faces of the plate along the slot. Enter the plate width, thickness, material, fillet, weld length and the slot clearance. The bolt lines and bolts per line are per flange. Slip-critical bolts with oversized holes in the plates are allowed.

ILX checks:

• the brace in tension: yielding, rupture and block shear. The shear lag factor U is the larger of 1 − x̄/l and the Table D3.1 Case 7 value. For a web connection x̄ is that of half the W; for a flange connection it is that of the WT.
• the bolts on each side: per bolt the least of shear, bearing and tearout on each ply, and slip when slip-critical.
• the tees: yielding, rupture (U = 1 − ȳ/l) and block shear out to the flange edges.
• the plates: yielding, rupture at the bolts and at the gusset slot, and the plate-to-gusset welds. Each half plate carries P/4 at a quarter of the net plate width from the slot (instantaneous center method).
• the gusset: block shear and the Whitmore section. For web tees the section is at the first gusset bolt row, with width g + 2 l tan 30°. For flange plates it is at the weld ends, with width d + 2 tpl.

The brace end is placed by Brace clearance. Design Guide 29 places it by its own detailing, so the Whitmore width that runs into the beam or column web can differ.

How the UFM forces are found #

• Geometry. eb is half the beam depth. ec is half the column depth for a column flange, or 0 for a column web. tan θ is the horizontal leg of the bevel divided by the vertical leg (θ is measured from the vertical). α̅ and β̅ are the centroids of the gusset-to-beam and gusset-to-column connections. α̅ is measured from the column face and β̅ from the beam flange face.
• General case. With β = β̅, Manual Eq. 13-1 gives α = eb tan θ − ec + β tan θ. Then r = √((α + ec)² + (β + eb)²) (Eq. 13-6). The interface forces are Vc = βP/r, Hc = ec P/r, Vb = eb P/r and Hb = αP/r (Eqs. 13-2 to 13-5).
• Auto-sizing. When the gusset is sized automatically and Auto size for α = α̅ is on, ILX picks the gusset length (or raises its height) so that α̅ matches α, which leaves no moment on the interfaces.
• Moment on the gusset-to-beam edge. When α ≠ α̅, that edge carries Mb = Vb (α − α̅). You can set a small eccentricity that is treated as negligible. This is the Manual's prescribed-geometry analysis with the gusset-to-beam edge taken as the more rigid one (Eqs. 13-20 to 13-22), the default General case.
• Prescribed geometry, other edge. For a gusset of given size (enter its length and height, or the connection lengths) two more choices follow Manual p. 13-14:
  • Moment on the gusset-to-column edge (the column edge is the more rigid): α = α̅ and β = (α̅ − K) / tan θ with K = eb tan θ − ec (Eqs. 13-21, 13-23). The column edge carries Mc = Hc (β − β̅) (Eq. 13-24) and the beam edge none.
  • Minimised eccentricities (both edges equally rigid): α and β minimise ((α − α̅)/α̅)² + ((β − β̅)/β̅)² on the line of Eq. 13-1: α = (K′ tan θ + K (α̅/β̅)²) / D and β = (K′ − K tan θ) / D, with D = tan² θ + (α̅/β̅)² and K′ = α̅ (tan θ + α̅/β̅) (Eqs. 13-25 to 13-29). Both edges carry a moment, Mb = Vb (α − α̅) and Mc = Hc (β − β̅).

  The column-edge moment goes into the gusset section, its welds and, at a column flange, the column web (as Ne = Hc + 4 Mc / L). A bolted gusset-to-column connection takes it as the normal force Hc + 6 Mc / L on its bolt rows. With an auto-sized gusset (α̅ = α, β̅ = β) the three choices give the same forces.

• Special case 1. The work point is at the gusset corner. Then Vc = P cos θ, Hc = 0, Vb = 0 and Hb = P sin θ, and the beam must be designed for Hb eb.
• Special case 1, Design Guide 29 form. The work point is still at the gusset corner. The guide keeps the concentric UFM forces and adds the couple M = P e of the offset brace line, with e = eb sin θ − ec cos θ (DG29 §4.2.2):
  • H′ = (1 − η) M / (β + eb) and V′ = (M − H′ β) / α;
  • the column edge gets Hc + H′ and Vc + V′, and the beam edge gets Hb − H′ and Vb − V′;
  • η = Zb / (Zb + 2 Zc) at a column flange (you can enter it), and η = 1 at a column web;
  • the beam must carry the extra couple η M, and the column (1 − η) M / 2 above and below.

  The guide recommends this form over the Manual's.

• Special case 2. A part ΔVb of Vb (all of it by default) moves to the gusset-to-column edge. The gusset-to-beam edge then carries Mb = ΔVb α.
• Special case 3. There is no gusset-to-column connection: β = 0 and α = eb tan θ − ec.
• Special case 4 (Manual pp. 13-10 to 13-12, Fig. 13-6). The gusset is bolted to a single plate welded to the column, with the bolts outside the column flanges. Choose Single plate as the gusset-to-column connection; at a column web set the setback so the gusset starts outside the flange tips. ILX:
  • takes ec from the column centreline to the bolt line (column face + column face to the bolt line);
  • finds α = eb tan θ − ec + β tan θ with β = β̅ (Eq. 13-15);
  • starts the gusset-to-beam weld x = sh/2 + leh + ¾ in. past the bolt line (Eq. 13-17; one bolt line, sh = 0, leh the plate's edge distance; the ¾ in. is an input) and, when the gusset is auto-sized, makes it lw = 2 (α − x) long so that α̅ = α (Eq. 13-16);
  • adds the couple Fr = Vb ec / (eb + β) (Eq. 13-18): Hc + Fr on the column edge, Hb − Fr on the beam edge, and the moment Fr β on the gusset-to-beam edge (Eq. 13-19). The beam-to-column axial force includes Fr.

  When the beam web is bolted to the same plate (as in Fig. 13-6), design that plate for both bolt groups; ILX designs the gusset bolts and the beam-to-column connection separately. The beam flange is coped clear of the plate.

• Beam-to-column connection. The connection must carry the shear R + Vb (− ΔVb) and the axial force A ± Hc. ILX designs for the larger value, |A| + |Hc|, in tension and in compression (Design Guide 29 checks this envelope). In special case 3 at a column flange the connection also carries the moment Vb ec, taken as an extra axial force 4 Vb ec / L on the connection of length L (Design Guide 29 Example 5.4).

Local web shear in the beam and column (Sabelli et al. 2021) #

The gusset delivers Hc to the column and Vb to the beam as local shear in their webs. Sabelli, Saxey, Li and Thornton (2021, AISC Engineering Journal 58(4)) check that shear and adapt the UFM to keep it within the members' strength. The Local web shear section of the editor turns this on. It is off by default, since the Manual's UFM does not require it. It is always on when you choose the virtual dimension r or a bypass factor λ other than 1.

• Inputs (all default to 0, the paper's base case):
  • Column shear from frame action Vcol and beam shear from frame action VBMF. The gravity shear Vg is the beam end reaction R of each load combination;
  • the available shear strengths of the column and the beam (0 = AISC 360-22 G2.1 of the rolled shape; enter a larger value for a web doubler) and of the beam-to-column connection (0 = the beam's own);
  • the vertical brace component on the gusset across the beam and the horizontal component on the gusset across the column, which share the member's strength (Eqs. 22 to 25).
• Effective strengths. VefCol = φVn − Vcol (Eq. 17), VefBm = φVn − Vg − VBMF (Eq. 18), VefConn = φRn − Vg − VBMF ≤ VefBm (Eq. 19) and UC = VefConn / VefBm (Eq. 20). With a second gusset each strength is shared in proportion to the brace components (Eqs. 22 to 25). For ASD, Vn/Ω replaces φVn.
• Checks.
  • Section C1, the column at the beam flange: Hc ≤ VefC (Eq. 16);
  • section B1, the beam and its connection at the column: Vb ≤ UC VefB (Eq. 27);
  • sections C2 and B2, at the middle of each gusset edge: Vmid = N/2 + M/e ≤ VefC or VefB, with e half the connection length (Eqs. 31, 32, 37, 38);
  • beam and column web local yielding and crippling under the more heavily loaded half of each edge, on a bearing length of half the connection (Eqs. 46, 47);
  • the gusset thickness at each edge by von Mises (Eqs. 44, 45).

  The steps also give the paper's design aids: the shortest edge lengths (Eqs. 33, 39, 78) and the member strengths a given gusset needs (Eqs. 35, 42, 43).

• Virtual dimension r (UFM case: Virtual dimension r from member shear). The UFM forces are taken from the smallest r that keeps the column and the beam within their effective strengths: r ≥ max(ec P / VefC, eb P / (UC VefB)) (Eqs. 26 to 29), then α = r sin θ − ec and β = r cos θ − eb (Eqs. 10, 11). Enter the gusset size; its edges then carry Mc = Hc (β − β̅) and Mb = Vb (α − α̅) (Eqs. 30, 36). You can give a larger r instead (p. 230). ILX also keeps r at least max(ec / sin θ, eb / cos θ), so α and β are not negative.
• Bypass factor λ (default 1, no bypass). The UFM takes λ P, and the rest, (1 − λ) P, goes straight to the column: HcBP = (1 − λ) P sin θ, VcBP = (1 − λ) P cos θ and McBP = HcBP (eb + β̅) − VcBP ec (Eqs. 48 to 50). The edge totals are HcTot = λ Hc + HcBP, VcTot = λ Vc + VcBP, McTot = λ Mc − McBP and λ Hb, λ Vb, λ Mb (Eqs. 68 to 74). They replace the UFM forces in every check, including the welds, J10 and the beam-to-column connection. The steps give the largest λ that keeps the beam within its strength (Eq. 52). The authors do not recommend λ below 0.6, and the report says so. λ applies to the general case, the prescribed-geometry cases and the virtual dimension r.

Bracing gusset checks #

• Brace end (in tension). These checks are the same as the Tension member end type:
  • tensile yielding, and rupture with the Table D3.1 shear lag;
  • block shear of the brace and of the gusset;
  • bolts (shear, bearing, tearout, slip) or welds (strength, base metal, sizes, length);
  • spacing and edge distances.
• Gusset at the brace. In tension, Whitmore yielding, plus Whitmore rupture when the brace is bolted. In compression, Whitmore buckling with Thornton's lengths. K is 0.5 for a corner gusset supported on two edges (Design Example II.C-2), or 1.2 for special case 3. For compression, ILX also recommends limiting the free edge to 0.75 √(E/Fy) t.
• Each interface. On the gusset section, normal yielding (N + 6M/L ≤ φ Fy t L) and shear yielding (φ 0.60 Fy t L), plus a combined (von Mises) check. For the fillet welds on both faces, the design force is the larger of the peak stress and 1.25 × the average stress (Manual Part 13 ductility factor), with the directional strength increase. The Table J2.4 minimum size is also checked.
• Beam web under the gusset (J10.2 yielding and J10.3 crippling, for either sense of the brace force), and the column web under Hc (column flange connection). For the column, Gusset near the column end (Spec. J10.2, J10.3) and Column end to the gusset-to-column connection (Beam and column) set the member-end condition: cleared (default), Eqs. J10-2 and J10-4; ticked, Eq. J10-3 when the distance is ≤ d and Eqs. J10-5a/b when it is < d/2. The report states the distance and the equation.
• Bolted gusset-to-column connection (for the interface forces Vc and Hc; AISC Design Guide 29 Ex. 5.1, 5.5 and 6.1b):
  • the bolt group: per bolt, the least of the bolt shear and the bearing or tearout on the element and the column;
  • in tension, the bolts in tension with shear (J3-3a / J3-3b) and prying of the end plate or angle legs and of the column flange (Manual Part 9);
  • the element in shear (yielding and rupture) and block shear; for angles, the tearout of the gusset under the angle welds; for a single plate, its tension and the bolt group by the instantaneous-center method;
  • the welds to the end plate, angles or single plate, without the 1.25 ductility factor (the element is flexible).
• Single bolt line. The gusset block tears out down the bolt line and across to the nearest free edge (Design Guide 29 Ex. 5.4 and 5.8).
• Beam-to-column connection. With a connection chosen, ILX designs it with the same checks as the Double angle, Single plate or Shear end plate type, for the shear and the axial force above. This includes bolts in combined tension and shear, prying of the angles or end plate and of the column flange, the welds at the load angle, block shear, and the column web. The checks are listed as Beam-to-column …. On a column web, ILX also checks the Design Guide 29 "oil-can" yield line of the web under the transfer force. With Required forces only, ILX reports the forces; design the connection with one of those types.

Seismic (SCBF) mode #

Set Seismic design to SCBF to design the connection of a special concentrically braced frame, as AISC Design Guide 29 Example 6.1a does. The brace force you enter is then replaced by the expected strengths of the brace (AISC 341-22 F2.3 and F2.6c):

• Tension: Ry Fy Ag. AISC 341-22 F2.6c.1(b) lets you use the largest tension the system can deliver to the brace, found by analysis, when it is less. Enter it as Max. brace tension the system can deliver (at the LRFD or ASD level); ILX uses the lesser of the two. Leave it at 0 to use Ry Fy Ag.
• Compression: the lesser of Ry Fy Ag and (1/0.877) Fne Ag, with 1/0.877 = 1.140 (Design Guide 29 rounds it to 1.14). Fne is the Chapter E buckling stress with Ry Fy in place of Fy (341-16 and Design Guide 29 call it Fcre), for the brace length you give (end to end, that is the work-point length less the two pull-offs) and K. With no length, the compression is Ry Fy Ag.
• Post-buckling: 0.3 times the expected compression (AISC 341-22 F2.3(b)). It is a third load case. It does not govern the connection itself, but it is reported with the others.
• For ASD all three are divided by 1.5 (αs). The beam reaction R and the transfer force A stay as entered.

Ry and Rt default to AISC 341-22 Table A3.2 (Table A3.1 in 341-16; the values are the same):

The reinforcing plates use the plate rows. The editor shows the table value for the brace grade under the Ry input. You can type your own values; they replace the table.

The mode adds these checks:

• Net-section reinforcement (slotted rectangular HSS). The brace's effective net area must be at least its gross area. You can add two reinforcing plates, one on each wall parallel to the gusset. ILX adds them to An and to the shear-lag x̄. The brace rupture is then checked at Rt Fu Ae. The plate welds (two along the plate, over the length a, and one across it) must develop Ry Fy Ar of each plate. The plate's Fy must be at least the brace's.
• Brace yielding (information only). The expected strengths are what the connection must carry, not the brace. The brace itself is designed for the brace force from your analysis (AISC 341-22 F2.6c.1(a) Exception), outside this connection. ILX shows the brace's gross yielding against the brace force you entered, for information. It does not change the status.
• Net section, other braces. Braces other than a slotted rectangular HSS must also have an effective net area at least equal to their gross area. Their rupture is checked at Rt Fu Ae.
• Gusset hinge zone. AISC 341-22 F2.6c.3(b) asks for rotation capacity at the brace end; the Commentary (Fig. C-F2.18) shows clearance models for it. Choose the one ILX enforces with Hinge-zone clearance enforced; the other is reported as an advisory:
  • 2t linear (the default, as Design Guide 29 Ex. 6.1a). The brace end must stop at least 2 tp past Point A. Point A is the end of the beam or column edge that lies farthest along the brace. ILX's gusset is rectangular, so a large gusset can push Point A far out. If the check fails, the message gives the pull-off the brace needs and the brace clearance that works with the gusset size on auto. Increase the brace clearance, or make the gusset smaller. A gusset shaped to stop its edges short of the brace, as in DG29 Example 6.1a, is not modeled.
  • 8t elliptical (corner gussets, Fig. C-F2.18(b), Roeder et al. 2011). The restrained gusset edges are drawn as a quarter ellipse through the ends of the beam and column edges, centred at the end of the beam edge and the top of the column edge. The brace end must lie at least 8 tp inside it, that is inside the ellipse whose semi-axes are 8 tp shorter. The report gives the offset of the brace-end corner nearest the restrained edges.
  • A gusset restrained along the beam only (special case 3, flat bar) has no corner ellipse: the 2t check stays enforced, and ILX reports the 6t horizontal clearance (brace end at least 6 tp from the beam flange, Fig. C-F2.18(c), drawn for midspan gussets) for information.
• Moment-release beam splice (optional). Two splice plates in the beam near the column carry the beam shear R to the column face. ILX checks the eccentric bolt group (IC method, eccentricity from the column face, every bolt at its least strength), plate shear yielding and rupture, plate flexure at the first bolt line, and the Manual Part 10 tmax ductility limit.
• Brace slenderness. With a brace length, Lc/r must not exceed 200 (AISC 341-22 F2.5b(a)).
• Built-up braces (double angles). Enter the number of stitch connectors. ILX spaces them evenly, a = L/(n + 1), and checks a/ri ≤ 0.4 Lc/r, at least two connectors and none in the middle quarter of the brace (F2.5b(b)). The connectors themselves are not designed; the report gives the tensile strength of one angle they must match.
• Brace buckling (F2.6c.3). Choose how the connection accommodates it. Rotation (the default) is the hinge zone above. Flexure designs the connection for 1.1 Ry Mp / αs of the brace about its critical axis: ILX checks the gusset's weak-axis plastic moment over the Whitmore width, and the hinge-zone checks become advisories.
• Gusset-to-flange welds (F2.6c.4). By default the welds of the gusset to the beam flange and to the column flange must have 0.6 Ry Fy tp / αs of shear strength per unit length (the 341-22 User Note gives about 0.74 tp for A572 Grade 50 and 0.62 tp for A36 with E70 double fillets). Choose Exception to design them instead for the edge forces of the expected compression combined with the gusset's weak-axis flexural strength. ILX reduces the weak-axis plastic moment by the Neal interaction for those forces and resolves it on the two fillets with a lever arm of tp + 2w/3 (its own model of the Exception; the report shows each step).
• Beam-to-column connection (F2.6b, F3.6b, F4.6b). Choose (a) a simple connection that can rotate 0.025 rad (the default; the moment-release splice provides it), (b) a moment connection for the lesser of 1.1 Ry Mp / αs of the beam and Σ 1.1 Ry Fy Z / αs of the columns (with Column continues above the joint on, two column sections), or (c) an OMF connection to E1.6b(c). For (b) and (c) ILX reports the required moment with the UFM forces; the shear connection types designed here do not provide it, so set the beam-to-column type to none and design the moment connection with the FR moment connection type.
• Bolted joints (D2.2). Holes must be standard or short slots across the load; oversized holes are accepted only in one ply of a slip-critical brace joint. Every bolt is pretensioned with Class A (or better) faying surfaces; ILX checks the brace joint type and asks for it on the drawings where the joint is designed in bearing. Brace bolt bearing and tearout follows D2.2(a): deformation at service considered (2.4 d t Fu) by default, or the D2.2(a) Exception (3.0 d t Fu) where the demand is an expected brace strength.
• V-braced bays and multi-tiered frames. Tick these to get the F2.4b beam requirements, F2.3 Exception (d) (the expected brace tension on the beam limited to the expected compression, your choice) and the F2.4e requirements (with the torsional moment 1.1 Ry Mp / αs of the brace) in the report.
• Protected zones (F2.5c). The report lists them, and the elevation hatches the gusset, the brace end over the brace depth and, for a V-braced beam designed with Exception (d), the beam next to the gusset edge.

Other braced-frame systems #

Seismic design also offers:

• OCBF (F1.6a). The brace force you enter must be the overstrength seismic load effect. Limit the force to the expected brace strength applies the F1.6a Exception: at most Ry Fy Ag / αs in tension and min(Ry Fy Ag, Fne Ag) / αs in compression. In a V-braced bay the brace must satisfy Lc/r ≤ 4 √(E/Fy) (F1.5b).
• EBF (F3.6c). Enter the brace force from the capacity-limited analysis of F3.3. If the brace resists part of the link end moment, tick it: the connection must then be a fully restrained moment connection, which this gusset connection is not, and the report flags it.
• BRBF (F4.6c). Enter the steel core yield strength Pysc and the factors β and ω from the brace qualification tests. The connection is designed for ω Ry Pysc / αs in tension and β ω Ry Pysc / αs in compression. Enter Ry = 1 when Pysc comes from the measured yield stress (F4.2a Exception). The report adds the F4.6c.2 gusset bracing note and the F4.5c protected zone.

Bracing gusset drawings #

The elevation shows:

• the column and beam with breaks, and the gusset outline;
• the brace and its bolts or welds;
• the interface weld symbols and the work lines meeting at the work point;
• the bevel, eb and the gusset dimensions;
• the Whitmore section, drawn hidden;
• a note with the brace force, α, β, ec and the beam-to-column forces;
• the beam-to-column connection when it is designed: the angles or plate, their bolts and welds, with callouts;
• in a seismic mode (SCBF, BRBF), the protected zones hatched, with a note.

Section B-B shows the brace on the gusset. On screen, Section A-A shows the gusset welded to the beam flange (or lapped on the tab plate).

Bracing gusset verification #

The UFM forces are checked against AISC Design Examples V14.1:

• II.C-3, all four cases (general and special cases 1, 2 and 3);
• II.C-2: the UFM forces, the gusset-to-beam weld with the 1.25 factor, beam web yielding and crippling, the beam-to-column forces, and Whitmore buckling.

Both examples use W braces with claw angles, which ILX does not design. A surrogate brace carries the force, and only the rows that do not depend on the brace are compared. Design Guide 29 Example 5.2 (special case 1, the guide's η form) is compared in full. The W braces of Examples 5.5 (web WT splices) and 5.11 (flange plates) are compared too: the brace, the bolts, the tees or plates and their welds, and the Whitmore section. Rows with 1 in. bolt holes are 1 to 3 % lower, because of the hole difference described below.

AISC Design Guide 29 Examples 5.1 to 6.1b are also compared, including the bolted gusset-to-column end plate (5.1, 5.3), clip angles (5.5, 5.7) and single plate (6.1b), the single-line gusset block shear (5.4) and the flat-bar gusset (5.8), and the tab plate of Example 5.11 (bolt group, tab plate and Neal interaction). For 1 in. bolts ILX uses the 1-1/8 in. hole of AISC 360-22, so two shear rupture rows are 2 to 3 % lower than the guide (360-10, 1-1/16 in.). The beam-to-column connections of 5.1 (end plate), 5.4, 5.5 and 5.8 (double angles) and 6.1b (single plate) are compared too. Two differences are documented: Example 5.8 halves the column web for bolt bearing (ILX uses the full web for a one-sided connection), and Example 6.1b takes the single-plate block shear over the full plate length (ILX is 14 % lower). The seismic rows of Example 6.1a are compared in the SCBF mode: the expected strengths (1,060 and 783 kips), the reinforcing-plate net area and welds, and the moment-release splice flexure (2,840 kip-in.).

The local web shear option is compared with Design Examples 1 and 2 of Sabelli et al. (2021), LRFD (the paper has no ASD example). In Example 1 (beam web doubler) these agree within 1 %: r = 27.9 in., α = 14.2, β = 8.80, the edge forces 146 / 119 / 149 / 234 kips, Mb = 479 kip-in., Vmid = 72.8 and 118 kips, and tg = 0.390 and 0.460 in. Mc (100 kip-in.) is within 2 %, because the paper rounds β before it. In Example 2 (bypass, λ = 0.592) these agree within 1 %: r = 34.2 in., HcTot = 202, VcTot = 222, McTot = −1,310 kip-in., Vmid = 62.6 and 88.5 kips, and tg = 0.897 in. The design aids of the unreinforced Example 1 (Eqs. 35, 42, 43: 101, 135 and 150 kips) are compared too.

Bracing gusset limits #

• W-shape braces with claw angles are not designed (web WT splices and flange plates are). A gusset bolted to a tab plate is drawn with its edge on the flange, not raised to the tab bolts. The chord-to-chord tab plate of Design Guide 29 Example 5.11 (Tab Plate C) is a beam-to-column connection and is not designed. The beam-to-column connection is designed for the beam alone; one end plate shared by the beam and the gusset (Design Guide 29 Example 5.1) is not modelled.
• The beam-to-column axial force is |A| + Hc; the frame-action reduction of Design Guide 29 (Hc − HD + A) is not applied (conservative).
• The column web under the gusset-to-column bolt tension (the Design Guide 29 yield line) is noted, not checked.
• The brace member itself (compression buckling), the beam (axial Hb and any moment) and the column are designed separately.
• The UFM is concentric: the brace work line passes through the work point at the beam and column centrelines (or at the gusset corner for special case 1). A work point anywhere else (Design Guide 29 Fig. 4-13) is not offered.
• Special case 4 uses one bolt line on the single plate (sh = 0 in Eq. 13-17). No published example uses the Manual's special case 4 or the prescribed-geometry options of Eqs. 13-23 to 13-29; they are verified by hand calculations, and the brace term of the gusset-to-column force against Design Guide 29 Example A.1.
• Local web shear (Sabelli et al. 2021): the haunch method (the gusset as part of a moment connection, Eqs. 57 to 67, 75, 76) is not implemented. The two gussets above and below the beam are designed one at a time, with the other one's brace component entered to share the strength. For Eqs. 46 and 47 ILX uses the more heavily loaded half of the edge, which equals the paper's Vmid when the moment loads the far half.
• Chevron (V and inverted-V) gussets are a separate type: see Designing a chevron bracing gusset.