SutranetTower — User Manual

1.Introduction

SutranetTower is a web application by Sutranet for designing lattice telecom towers — either a 3-leg (equilateral-triangular) or 4-leg (square) cross-section, selected under Tower Type. You describe the tower’s geometry, member sizes, bracing, wind environment and antenna loads in a structured form (or as a JSON file), and the app (the list below describes the Indian-code path; for US towers see ANSI/TIA-222-I):

1. Computes wind loads on every section per IS 875 Part 3:2015.
2. Builds the real 3D lattice (legs, diagonals, horizontals) and solves it with OpenSeesPy, a finite-element engine.
3. Checks every member against tension and compression (buckling) capacity per IS 17740:2022 / IS 800:2007.
4. Produces a single self-contained HTML report you can open, share, or archive — and, optionally, a STAAD.Pro .std file for independent cross-checking.

2.Key Concepts

3.Quick Start

1. Open the app at www.sutranet.co.in. Open the Data ▾ menu in the header and click Load Example to start from a working 40 m tower instead of a blank one.
2. In the Tower Builder tab, walk the left-hand tree from the top: Tower Type, Wind Parameters, Analysis Config, Antennas, Mounts & Platforms, Lighting, Signs & Anti-climb, Climbing Ladder, Feed Lines, Ice & Seismic (Ice, Seismic & Tornado on a TIA-222-I tower), then each slope (S1, S2…) and the sections inside it. A required input that is still blank is outlined in red. If you click Run Analysis with one missing, a message names it and the builder opens the node where it is entered.
3. (Optional) Click the ✦ Review Inputs button to get an automated sanity check before you spend time waiting on the solve.
4. Click Run Analysis. The app polls progress every 1.5 s until the job finishes (typically seconds to low minutes, hard-capped at 180 s — see Limitations).
5. Review the report in the Analysis Result tab: start with Summary for the headline max utilisation and drift, then drill into Capacity and Lattice Forces for any overstressed members.
6. Use Data ▾ → Export JSON to save your tower definition, Save the run to keep it in History, and (optionally) download the STAAD .std file for an independent cross-check.

4.Wind Input

Wind loading follows IS 875 Part 3:2015. The design wind speed at any height is:

Vz = Vb × k1 × k2 × k3 × k4
pz = 0.6 × Vz²   (design wind pressure, N/m²)

The Wind Parameters node holds these inputs. The first column gives the builder’s label and, below it, the key in tower.json.

Whether the static method or the gust-factor method (IS 875 Part 3 Cl. 10.2) is used is set under Analysis Config → Wind Method; see section 9.

Wind speed lookup by location

Under Site Location Lookup at the top of Wind Parameters, enter the site’s Latitude and Longitude and click → Lookup. The panel shows the basic wind speed from the IS 875 wind map and the distance to the coast; click ✓ Apply Vb to use the speed, or View on Map to check the location. When the coast is within 60 km the lookup pre-fills Cyclone region with “Yes”, with a note: it cannot tell which coast, so confirm it.

How force coefficients are applied

The Cf table used depends on both the member shape and the tower type (IS 875 Cl. 7.4.3.5):

• Flat-sided (angle) members use Table 33: Cf depends on solidity ratio φ. On a 3-leg tower it is constant for all wind directions; on a 4-leg (square) tower the face→corner increase (Cl. 7.4.3.5(b), 1.0→1.2×) is interpolated linearly by wind angle.
• Round (pipe) members use Table 35 on a 3-leg tower and Table 34 (face vs. corner Cf) on a 4-leg tower. Cf depends on solidity ratio φ and flow regime, set by D×V̄d (shown as DVd), where D is the member diameter and V̄d is the design hourly-mean wind speed at that height (V_b·k1·k2,i·k3·k4, IS 875 Part 3 Cl. 6.4) — not the 3-second gust speed Vz that the pressure uses. The hourly-mean speed is roughly two-thirds of Vz, so more members fall in the higher-Cf regime than a check on Vz would give. Below 6 m²/s the flow is subcritical (higher Cf, ~1.3–1.8); at/above 6 m²/s it is supercritical (lower Cf, ~0.8–1.2).
• Solidity ratio φ is computed per section from the actual projected member areas vs. the gross panel face area — you don’t set φ directly, it falls out of your member sizing.

5.Slopes & Sections

Build the tower top-down or bottom-up in the tree: add Slopes for each taper change, then one or more Sections inside each slope.

6.Member Sections

Each section has a Leg section (leg_section), a Diagonal section (diagonal_section), a Horizontal (ring beam) (horizontal_section) when the bracing pattern places horizontal members, and a section for each tag listed under Redundant members (redundant_sections). If the pattern places horizontals or redundants that have no section, the run is refused unless Auto-Size is on; the diagonal size is never borrowed. Four section types are offered (Section type):

Pipe (CHS)

Solid round bar (S.R.)

Enter the Diameter — Ø ({"type": "solid_round", "od": …}) and an IS 2062 grade. It is checked as a round member (buckling curve ‘a’). A bolt hole in a solid bar is deducted across the full diameter.

Single equal angle (ISA, IS 808:2021)

Double angle (back-to-back)

Same fields as a single angle, plus Gap (gap_mm, back-to-back spacing, default 10 mm), which shifts the combined Iyy via the parallel-axis theorem. On a diagonal, horizontal or redundant, Stitch connectors (IS 17740 Cl. 12.2.2) describes the intermediate connectors: connector type, the largest spacing a_i and the number of intermediate connectors n. The modified slenderness of Cl. 12.2.2(b) is then used. Left as Not declared, the member takes the strictest of the three cases. For two angles connected only at their ends this gives the same slenderness as before; it matters when a member is split at a crossover.

End connection of bracing (IS 17740 Annex F)

Each diagonal, horizontal and redundant has an End connection setting (end_connection). It selects the row of IS 17740 Annex F Table 6 that turns the member’s L/r into the equivalent slenderness KL/r used in its compression check. It does not set the net section in tension; that comes from the connections block.

The table applies to single angles as written. A double angle is treated as concentric: up to L/r 120 KL/r = L/r, and above 120 the row of its end connection. A pipe is checked on its geometric L/r whatever the end connection. A solid round bar with a single-bolt or flattened end takes the eccentric rows, and with a welded or multi-bolt end its geometric L/r. Round bracing also has Leg connection (Annex F-8) (leg_connection): choose Welded directly to leg to use the effective length factors K of Annex F-8; leave it unset, or choose Bolted to leg, for K = 1.0. An end connection value the table does not list is refused. The other choices in the list (gusset only, welded direct to legs) belong to TIA-222-I and are hidden on an IS tower.

Bolt holes & net section

On an IS tower, a member’s bolt holes are described only in the section’s connections block: the bolt line of its entry is used for net-section rupture and block shear (IS 800 Cl. 6.3, 6.4), and {"welded": true} declares a welded end. A member with no entry is checked on gross yield only and the report says so. The older n_bolt_holes / bolt_hole_dia keys on a member are refused on IS towers; they remain in use on TIA-222-I towers. fu (ultimate strength) is taken from the grade.

Connection design (optional)

Each section can carry a bolted-connection check, enabled by the Connection design toggle on that section in the Tower Builder. The spec is edited as a small raw-JSON block; leave a sub-key out to skip that connection. The checks are driven by the factored axial demand that the section’s members actually attract in the analysis (tension for the flange, axial magnitude for bracing), and every result appears in the report’s Connections tab. All checks use IS 800:2007 partial safety factors: γ_m0 = 1.10, γ_m1 = 1.25, γ_mb = 1.25 (bolts), γ_mw = 1.25 (shop weld).

Bolted shear connections — what each field measures

Applies to diag_bracing, horiz_bracing, redundant_bracing and leg_splice — they all share one field set. All dimensions are in millimetres, strengths in MPa.

Ring-flange leg splice — what each field measures

Applies to flange, used when the leg is a pipe (CHS).

Detailing (IS 800 §10.2). Every bolted-shear spec is also checked against the spacing limits the capacity equations assume: minimum end and edge distance (Cl. 10.2.4.2), maximum edge distance 12·t·ε (Cl. 10.2.4.3), and minimum pitch 2.5·d (Cl. 10.2.2). The minimum end/edge distance depends on how the edge was prepared, so edge_type is required and has no default — "sheared" / "hand_flame_cut" give 1.7× the hole diameter, "rolled" / "machine_flame_cut" / "sawn" / "planed" give 1.5×. Omitting it reports the distance as unchecked rather than assuming a factor; an unrecognised value is an error. A detailing violation fails the connection but does not appear in its utilisation ratio, which stays a pure strength figure. A bolt smaller than 12 mm is also reported as a detailing violation (IS 17740 Cl. 13.1.2), on bracing ends, leg splices and ring flanges. Note the Cl. 10.2.3.1 maximum pitch and the corrosive-exposure edge cap are not checked.

JSON schema

The connections object sits on a section, alongside leg_section / diagonal_section / redundant_sections. Every sub-key is optional — omit one to skip that connection entirely. Notation below: (required) means the analysis raises if the key is absent; = value is the default applied when it is.

"connections": {                    // optional, per section

  "flange": {                      // leg splice — PIPE (CHS) leg only
    "n_bolts":          integer (required)   // bolts on the pitch circle
    "d_bolt":           number  (required)   // mm
    "pcd":              number  (required)   // mm, bolt pitch-circle DIAMETER
    "plate_thickness":  number  (required)   // mm
    "plate_od":         number  (required)   // mm, plate outside DIAMETER
    "plate_fy":         number  = 250        // MPa
    "plate_fu":         number  = from plate_fy
    "bolt_grade":       string               // IS 800 Table 1 class, e.g. "8.8"; or:
    "fub_bolt":         number  = 800        // MPa; not with bolt_grade
    "fyb_bolt":         number  = from the class fub_bolt names
    "pretensioned":     boolean = false      // sets β in Cl. 10.4.7 prying
    "weld_throat":      number  = 0          // mm; 0 ⇒ full pen, weld check SKIPPED
    "fu_weld":          number  = 410        // MPa
    "fu_pipe":          number  = from the leg grade
  },                                          // pipe OD/thk/fy come from leg_section

  "leg_splice": {                  // leg splice — ANGLE / DOUBLE-ANGLE leg only
    // …all the bolted-shear fields below, plus:
    "both_legs_connected": boolean (required) // bolts through both legs of the leg angle?
    "bearing_credit":   boolean = false      // true ⇒ halve compressive demand (§10.8)
    "t_ply":            number  = 8.0        // NOTE: 6.4 for the bracing blocks
  },

  "diag_bracing":  { …bolted-shear fields… },   // diagonals
  "horiz_bracing": { …bolted-shear fields… },   // horizontals

  "redundant_bracing":                 // EITHER one shared spec…
      { …bolted-shear fields… }
    // …OR one spec per redundant tag, keyed as in "redundant_sections":
    { "r1": { …fields… }, "r2": { …fields… } }
}

// ── bolted-shear fields (diag_bracing, horiz_bracing,
//    redundant_bracing and leg_splice all share these) ──
    "d_bolt":           number  (required)   // mm
    "d_hole":           number  (required)   // mm, = d_bolt + clearance
    "edge_type":        string  (required if end_dist/edge_dist given)
                                             // "sheared" | "hand_flame_cut"
                                             // "rolled" | "machine_flame_cut" | "sawn" | "planed"
    "bolt_grade":       string               // IS 800 Table 1 class, e.g. "8.8"; or:
    "fub_bolt":         number  = 800        // MPa; not with bolt_grade
    "n_shear_planes":   integer = 2          // 1 = single lap ← usual for redundants
    "threads_in_plane": boolean = true       // false ⇒ shank area, not 0.78·A
    "t_ply":            number  = 6.4        // mm, governing thickness in bearing
    "fy_ply":           number  = 250        // MPa
    "fu_ply":           number  = from fy_ply
    "width_gross":      number  = 0          // mm; 0 ⇒ net-section check SKIPPED
    "end_dist":         number  = 0          // mm; 0 ⇒ inflates bearing k_b
    "edge_dist":        number  = 0          // mm
    "pitch":            number  = 0          // mm, between bolts in line of force
    "n_bolts_line":     integer = 1          // bolts in the line of force
    "gc_mm":            number  (optional)   // bracing blocks only; Cl. 10.4.4.2, never 0

// a welded member end instead of bolt details:
    { "welded": true }

When a plate’s ultimate strength (fu_ply, plate_fu) is not given, it is derived from its fy through the IS 2062 grade map (250→410, 300→440, 310→450, 350→490 MPa; anything else → 410).

A horiz_bracing entry on a section whose bracing pattern places no horizontal member has nothing to check: it is listed as a warning and the report marks it NOT CHECKED.

A complete example

An angle-leg section with per-tag redundant detailing — r1 on M16 and the more heavily loaded r2 on M20:

"connections": {
  "leg_splice": {
    "d_bolt": 20.0, "d_hole": 22.0, "bolt_grade": "8.8",
    "n_shear_planes": 2,            // cover plate each side of the angle
    "t_ply": 8.0, "fy_ply": 250.0, "width_gross": 70.0,
    "end_dist": 40.0, "edge_dist": 38.0, "edge_type": "sheared",
    "pitch": 60.0, "n_bolts_line": 2,
    "bearing_credit": true,         // IS 800 §10.8 full-contact bearing
    "both_legs_connected": true     // required on an angle-leg splice
  },
  "diag_bracing": {
    "d_bolt": 20.0, "d_hole": 22.0, "fub_bolt": 800.0,
    "n_shear_planes": 1,            // single lap onto the gusset
    "t_ply": 8.0, "fy_ply": 250.0, "width_gross": 70.0,
    "end_dist": 40.0, "edge_dist": 38.0, "edge_type": "sheared"
  },
  "redundant_bracing": {            // keys match "redundant_sections"
    "r1": {
      "d_bolt": 16.0, "d_hole": 18.0, "fub_bolt": 800.0, "n_shear_planes": 1,
      "t_ply": 6.0, "fy_ply": 250.0, "width_gross": 50.0,
      "end_dist": 32.0, "edge_dist": 32.0, "edge_type": "sheared"
    },
    "r2": {
      "d_bolt": 20.0, "d_hole": 22.0, "fub_bolt": 800.0, "n_shear_planes": 1,
      "t_ply": 8.0, "fy_ply": 250.0, "width_gross": 70.0,
      "end_dist": 45.0, "edge_dist": 38.0, "edge_type": "sheared"
    }
  }
}

The // comments are for this manual only — strip them, JSON has no comments. A single flat spec is still accepted in place of the {"r1": …, "r2": …} map when every redundant tag shares one detail. Swap leg_splice for flange if the leg is a pipe.

7.Bracing Patterns

Pick a bracing pattern per section from the dropdown (built from the editable bracings.json library). Every face automatically receives the same pattern by rotational symmetry (120° on a 3-leg tower, 90° on a 4-leg tower). Each pattern declares which leg counts it is valid for (applicable_legs) — the dropdown only offers patterns valid for the current Tower Type, and picking an incompatible one is rejected at run time with a clear error.

The shipped library is a deliberately small starter set of four standard patterns. Anything beyond these is user-defined: create your own in the Bracing Library editor and they are saved to your private library (they never modify the shipped set).

Plan bracing (4-leg towers)

A triangular ring is inherently rigid, but a square ring is not — so even-leg (4-leg) towers often need plan bracing: horizontal diagonals across the ring that provide torsional/plan rigidity and also shorten the out-of-plane buckling length of crossover X-braces. In the library editor these appear as Plan Bracing (opposite-face links) alongside the legacy Hip Members (adjacent-face links); both are saved into each pattern’s redundant_links.

The Bracing Library editor

The Bracing Library tab is a single unified 3D editor — you author directly on the live 3D lattice (it replaces the older 2D Face Canvas / Hip / Plan views and the read-only preview). You still design one face — whatever you draw on the reference face is replicated to every other face automatically by rotational symmetry, so a pattern stays leg-count-agnostic. The tab has three regions plus two assistants:

• Pattern list (left) — every pattern with a small 2D thumbnail; + New, Clone, Delete. The list is filtered to patterns valid for the current Tower Type.
• 3D Pattern Editor (centre) — the interactive viewport: drag to rotate, scroll to zoom. Each face carries the fixed corner nodes bot_L, bot_R, top_L, top_R, and faces are labelled F0, F1…. You author by clicking one node then another: two nodes on the same face draw a same-face member; two nodes on different faces draw a cross-face (hip / plan) link with the face offset inferred automatically — there is no separate Hip/Plan mode. Click an existing member or cross-face line to split it with a node. A colour legend below the viewport keys diagonal / redundant / ring / cross-face / leg.
• Editing & controls (right) — the context panels that appear for the current action (draw-member / add-node, member type & OPS element, cross-face link tag, rings and redundant-link lists), plus the two assistants below.
• Pattern Health panel — four live checks (no duplicate members, all nodes connected, no bypassed nodes, all nodes have out-of-plane stiffness) that update as you edit. Fix reds before saving.
• Guidance panel — a rule-based (or AI-backed, if an API key is configured) helper. Click Explain current errors or ask a free-text question about the pattern.

Anatomy of a pattern

A pattern is a small record (stored in bracings.json) built from these pieces:

Step-by-step: creating a custom pattern

1. Open the Bracing Library tab. Start from an existing pattern close to what you want (select it, then edit) rather than a blank face — it’s faster and less error-prone.
2. Set the Tower Type you’re targeting in the Tower Builder first, so the 3D editor shows the correct 3-leg or 4-leg lattice while you work.
3. Place nodes. In the 3D viewport click two existing nodes on the same face; in the panel that appears, drag Position t and click Add Node to drop a node at that fraction along the line between them. For a true X crossing, click ✕ X-intersect Node and then click the four endpoints of the two crossing lines — the app computes their intersection.
4. Draw members. Click one node, then another on the same face; choose Diagonal, Horizontal or Redundant. Click an existing member to change its Type, its OPS element, or (for redundants) its Tag, or to remove it.
5. Split, don’t bypass. If a node sits partway along a member’s path, that member must be drawn as two segments meeting at the node — never as one member that runs past it (see Do’s & Don’ts). Click a member (or a cross-face line) to split it at a node.
6. (4-leg / stiffening) Add cross-face links in the same viewport: click a node on one face, then a node on a different face — the editor makes a Hip (adjacent face) or Plan-bracing (opposite face) link and infers the face offset automatically. Give it a Tag and Save Link. For a full horizontal ring, click the same node label on two adjacent faces and choose ＋ Horizontal ring. Use the F0, F1… face labels to pick the intended adjacent/opposite face deliberately.
7. Watch the Pattern Health panel. Resolve every red item; use Explain current errors for a plain-language fix.
8. Open Pattern Settings & Save: set Name, Aliases, Description, and tick the Applies to (3-leg / 4-leg) boxes. Click Save Pattern (local).
9. Save to server (built-in library for admins, or my patterns for a private copy). The server re-validates with validate_bracing_pattern() and rejects anything invalid. This step is required before the pattern can be used in an analysis.
10. Assign the pattern to a section in the Tower Builder, and give that section a redundant_section for each redundant Tag you used (or enable Auto-Size).

Do’s and Don’ts

8.Antennas & Climbing Ladder

Antennas

Click + Add Antenna Group for each set of identical antennas. A group has an ID, a Type (panel / dish / generic), an Elevation, the Mass per antenna and its size (panel: width, height and depth; dish: diameter; generic: frontal area). The drag coefficient is worked out from the size (IS 875 Part 3 Table 20 for a panel, IS 17740 Annex L Table 7 for a dish); a value in Cd Override replaces it.

Under Mounting positions add one row per physical antenna:

The 3×120° Preset button (4×90° on a 4-leg tower) puts one antenna on each face. Each antenna contributes projected wind area, drag, dead weight and the torsion from its eccentric position at its elevation.

• Mount pipe (optional): the round pole the antenna clamps to — OD (use the actual outside diameter, 60.3 mm for a 2″ NPS pipe), length, C_a (default 1.2) and mass. Its wind area is added to each antenna. Shield behind antenna counts only the length that sticks out beyond the antenna.
• Shielding Factor (optional, 0 to 1, default 1.0): reduces the wind on an antenna on the leeward side of the tower body for each wind direction. It is not applied to dishes, whose coefficients already vary with the wind angle.

A dish must state its Dish type — without radome, with radome, with cylindrical shroud, or grid — on IS and TIA-222-I towers alike; there is no default and the run is blocked until it is chosen. The type selects the coefficient table (IS 17740 Annex L Table 7, or TIA-222-I Annex C). The dish load has three parts: a force along the wind, a force across it, and a twisting moment.

Climbing ladder

Toggle this on to add the climbing ladder, defined by Ladder A_eff, its exposed wind area per metre of height (A_eff_m2_per_m — required, there is no default), its Drag Coefficient Cd (about 1.2), Dead Weight per metre, its Mounting Location (outside_face, inside_face, or inside_axis) with face index and offset, and the elevation range it covers. A ladder inside the tower takes the Shielding Factor Ka (default 0.9); one on the outside face takes 1.0. The Visual Dimensions only change the 3D drawing. On an IS tower the IS 17740 Cl. 7.2.2 climber load of 1330 N is applied at the ladder top; a tower without a ladder carries no live load. The TIA-222-I load combinations carry no live load.

When the tower has an ice case, the ladder needs two more inputs under Ice on the ladder: the total length of rails and rungs in one metre of ladder (about 3.3 for two rails with 0.4 m rungs at 300 mm) and the rail / rung size. The run is blocked until both are entered.

This is the ladder only. Enter a cable tray / feedline ladder under Feed Lines as its own run (custom, component type Flat, with the tray width), and the cables as separate runs. Do not include trays or cables in the ladder’s area, or their wind load is counted twice.

Feed lines

Each Feed Lines run is a group of identical cables on one face, with its elevation range and arrangement. On an IS tower every line’s projected area is counted (IS 17740 Cl. 7.5, C_f 1.2 round / 2.0 flat); the block treatments are TIA-only (T6), so on an IS tower automatic is evaluated as individual and rectangular / round are not offered.

Mounts & Platforms

Mounting frames and platforms can be declared on an IS tower as well as on a TIA-222-I tower, under Mounts & Platforms. The kinds (sector frame, frame assembly, platform), the mount library and the optional 3D drawing are described in T6. On an IS tower you enter each mount’s wind area (EPA) and weight from the manufacturer’s data, and the wind on it is IS 17740 Cl. 7.5 at the same design pressure as the antennas. IS 17740 gives no shielding factor for mounts, so the reductions offered there (three or more frames at one level, low-profile platforms) are the ANSI/TIA-222-I values; the report says so. A platform on an IS tower must state its deck area, which carries the IS 17740 Cl. 7.2.2 live load of 1500 N/m².

Lighting, signs and anti-climb devices

The Lighting, Signs & Anti-climb node is for items that are neither antennas nor mounts. Each row needs an elevation, a mass and a wind area (EPA); zero is allowed, blank is not. With no placement the item acts on the tower axis in every wind direction. Give it a placement on a face or a leg and enter its EPA normal and sideways, and it can also twist the tower. When the tower has an ice case, enter the values in a table by ice thickness instead; a run whose ice thickness goes beyond the table is refused.

9.Analysis Config

The design standard (IS or ANSI/TIA-222-I) is chosen under Tower Type → Design Standard. The Analysis Config node then sets:

• Load Combination Standard (IS towers): IS 17740:2022 Table 2 (the default) or IS 800:2007 Table 4. Member ratios read roughly 7–12% lower on the IS 17740 set than on the IS 800 set (wind factor 1.4 against 1.5, dead load 1.1 against 1.5). Every strength combination of the chosen set, including the gravity-only ones, enters the member checks.
• Wind Method (IS towers): the checkbox Use the gust-factor method (IS 875 Part 3 Cl. 10.2). Off, the static method is used, and the run changes to the gust-factor method by itself only when the first natural frequency is below 1 Hz (IS 17740 Cl. 8.2). On, the wind on the structure and on antennas, ladder and feed lines is the hourly-mean pressure × G(z) whatever the frequency, and K_d, K_a and K_c are not applied. The gust-factor method cannot be combined with a change of terrain upwind; such a run is refused.
• Redundant Member Grade: one grade for every redundant member — IS 2062, or an IS 1161 tube grade when the redundants are pipes; on a TIA-222-I tower an ASTM grade, which is required when the tower has redundant members (there is no ASTM default).
• Auto-Size Members: tick Auto-size members left without a section, then choose whether to size unspecified horizontal and/or redundant members, and the number of Refinement Passes (2–3 is enough). The program picks the lightest IS 1161 pipe or IS 808 angle (AISC shapes on a TIA tower), in the family of the section’s diagonal, that passes slenderness, compression, tension and the minimum bracing resistance; the chosen member is then checked like any other. The run log lists each pick and marks one for which nothing in the catalogue passes (that member then fails its check). The picks are written into the run’s tower file, so reopening the run from History shows them. With Auto-Size off, a horizontal or redundant with no section stops the run; the diagonal size is never borrowed.

The element formulation for each diagonal and horizontal is defined per member in the Bracing Library — every pattern carries its own ops_element (choose corotTruss, Truss, or elasticBeamColumn on each member), so different sections can use different bracing behaviour. It is no longer a single tower-wide toggle in the Config node.

Legs always use elasticBeamColumn (they carry significant bending in addition to axial load and need full beam behaviour). For model-validation work, the per-member choice can be force-overridden from the CLI (not exposed in the UI):

python main.py tower.json --diag-type elasticBeamColumn --horizontal-type elasticBeamColumn --redundant-grade 350

Automatic planar-joint stabilization. Singular “planar-joint” nodes (for example an X/M crossover on a square 4-leg face with no plan bracing) have no out-of-plane stiffness when their bracing is axial-only truss, which would make the stiffness matrix singular. SutranetTower auto-stabilizes these joints — the offending truss bracing is promoted to elasticBeamColumn automatically (the PLS-TOWER / tnxTower approach), so the model stays solvable without manual edits. This is on by default; the analysis log lists exactly which joints were stabilized.

K-brace horizontals on IS towers. A horizontal that a diagonal ends on part-way along its length, with no plan bracing at that node, is modelled as a beam (elasticBeamColumn) on an IS tower, as IS 17740 Cl. 9.1(a)(2) asks for. The analysis log lists these members.

Dynamic wind, seismic & ice loads

(On a TIA-222-I tower see T7 instead.) Three additional IS 17740 load effects. Seismic and ice live under the Ice & Seismic builder node and are off by default; a plain tower report has neither unless you enable them. The gust-factor method is switched on under Analysis Config, and also engages by itself when the tower is flexible.

When enabled, the member-capacity check envelopes over all ultimate cases (wind + seismic + ice), and the report Summary tab gains dedicated dynamic / seismic / ice panels. A red banner also appears whenever f₁ < 1.0 Hz to flag that a dynamic gust-factor analysis is required.

T.US Design — ANSI/TIA-222-I

SutranetTower can design a tower to the US standard ANSI/TIA-222-I instead of the Indian codes. Pick ANSI/TIA-222-I — US LRFD as the Design Standard under Tower Type ("design_standard": "TIA222I" in tower.json) and the whole run follows it: wind loads, load combinations, member strength, connection design, the report and the STAAD export. The 3D finite-element solve itself is the same for both standards.

This chapter covers only what is different on a TIA tower. Everything about geometry, slopes, sections and bracing patterns (sections 5–7) applies unchanged.

T1. Scope

T2. Site inputs (Wind Parameters)

None of these can be looked up by the app for a US site — the location lookup covers India only. Read them from the ASCE 7 Hazard Tool and the project documents.

The directionality factor K_d is fixed at 0.85 for latticed towers (Table 2-2). The IS inputs k1–k4, K_c and the gust factor do not apply and are hidden.

T3. Wind directions

TIA-222-I §2.6.11 requires each wind direction of Table 2-6 to be checked for each face:

• 4-leg (square): face-on and 45° to every face → 0°, 45°, 90° … 315° (8 directions).
• 3-leg (triangular): face-on, 60° and ±90° to every face → every 30° (12 directions).

Directions are measured from the normal to face 0. When you switch a tower to TIA-222-I, or change its leg count, the builder ticks these directions for you. You may add more (every 15°, say).

If you remove some and the tower carries antennas, a ladder, feed lines or mounts — anything that loads one face differently from another — a warning under the direction grid lists the missing directions, with an Add them button, and the report repeats the warning. A bare tower with no attachments is not warned: every face then behaves like face 0.

T4. How the wind load is calculated

qz  = 0.613 × Kz × Kzt × Ks × Ke × Kd × V²          (N/m², V in m/s)
Gh  = 0.85 + 0.15 × (h/45.7 − 3),  kept between 0.85 and 1.00
F   = qz × Gh × (EPA)S
(EPA)S = Cf × [ Df × Af + Dr × Ar × Rr ]

• K_z varies with height and exposure (Table 2-4). It is evaluated at each section’s mid-height.
• C_f depends on the solidity ratio ε of the face: 4.0ε² − 5.9ε + 4.0 (square) or 3.4ε² − 4.7ε + 3.4 (triangular).
• A_f is the projected area of flat members (angles), A_r of round members (pipes, solid bars). Round members are reduced by R_r, which depends on the flow regime.
• D_f, D_r (Table 2-6) depend on where the wind comes from:

  Tower	Face-on	Other tabulated directions
  Square	1.0	45°: 1 + 0.75ε (max 1.2), flat and round
  Triangular	1.0	60°: Df 0.80 · ±90°: Df 0.85 · Dr 1.0 throughout

  A direction between the tabulated ones takes the nearest one.
• Tapered towers (§3.7.1): if the leg slope changes by more than 1° between sections, and the projected legs meet within the tower height, extra load cases are added with the wind pressure reduced above or below that point. They appear as …_ap1hi / _ap1lo cases and feed the capacity check automatically.

T5. Members, materials and strength

Sections and grades

Grades are ASTM names (A572-42/50/55/60/65, A871-60/65, A588, A606, A36, A992, A529-50, A500-B/C). Yield and ultimate strengths are the ASTM minimums. Thickness-dependent reductions are not applied. The Redundant Member Grade under Analysis Config has no ASTM default: a tower with redundant members cannot run until one is chosen, and an IS grade is refused.

End connection of bracing

The end connection sets the bracing’s effective slenderness (Tables 4-4 and 4-5):

The IS-only choices (“partial restraint at one end”, “concentric one end”) are hidden on a TIA tower because Table 4-4 has no row for them.

What is checked

• Compression: φ_cF_crA_g, with local buckling through the effective yield F′_y (§4.5.4.1). Angles use the angle column curve, round members the AISC curve.
• Tension: the lesser of yield on the gross area and rupture on the effective net area (§4.6), with the prescribed shear-lag factor U.
• Slenderness: legs per Table 4-3; bracing per Table 4-4; crossing and K-bracing per Tables 4-6 / 4-7, using the actual connection points in your bracing pattern. A crossover only counts as supported if the plan or hip bracing there is triangulated (Figure 4-2).
• KL/r limits (§4.4.2): legs 150, diagonals and horizontals 200, redundants 250, tension-only members 300.
• Minimum bracing strength (§4.4.1, Tables 4-1 and 4-2): every bracing member is designed for at least the required bracing force from the legs it braces. Hip bracing uses Figure 4-2 note 3 instead. Redundants are usually sized by this minimum rather than by their analysis force.
• Legs in bending (§4.8.1): axial load plus the moment from leg continuity, with the B₁ magnifier.
• Joint eccentricity (§4.4.4.2): if a single-angle brace is connected beyond the centreline of the leg, enter gc_mm in the connection block (T9). Otherwise normal framing is assumed.

Auto-size works on TIA towers too: it picks from the AISC catalogues and checks with the TIA rules above.

T6. Antennas, mounts, feed lines and the ladder

Antennas

Wind force F = q_z · G_h · K_a · C_a · A (§2.6.11.2), at the antenna’s elevation. Panels take C_a from Table 2-8 by their aspect ratio (1.2 to 2.0); dishes use Annex C Tables C-1 to C-4, chosen by the required Dish type, with the force along the wind, the force across it and the twisting moment, all varying with the angle between the wind and the dish axis. K_a is taken as 1.0.

Mounts & Platforms

Add the frames and platforms your antennas hang on under Mounts & Platforms. Their wind area and weight are loaded onto the tower. You enter the EPA and weight from the manufacturer or a catalogue, at one or more ice thicknesses; the app interpolates at the actual ice thickness.

• An antenna can be placed on a mount; it then moves with the mount.
• Frequently used products can be saved to your mount library.
• The optional 3D drawing of a mount is for the viewer only — it never changes a load.
• If you add antennas but no mounts, the report warns that any mount load is missing.

Feed lines

Each Feed Lines run is a group of identical cables on one face. On a TIA tower the cluster treatment can be individual (every line counted), rectangular or round (the group treated as one block, §2.6.11.5), or automatic (the lower of the two per direction). A block is only allowed when the lines really form a cluster — at least two lines, no further apart than three times the larger diameter — and automatic never applies block relief to flat lines. A cable tray or feedline ladder is entered as its own run with a flat component type.

Climbing ladder

Same input as on IS towers (section 8), loaded with the TIA velocity pressure. TIA-222-I load combinations carry no live load, so the climber load is not applied.

T7. Ice, seismic and tornado

All three are under Ice, Seismic & Tornado and are off until you enable them.

If your tower is Risk Category III or IV and you have not added a tornado block, the report warns that §2.9 was not evaluated.

T8. Load combinations

Member capacities are checked against the envelope of every ULS, ICE, EQ and TOR case.

Serviceability (§2.8.2): twist and sway rotation ≤ 4° and horizontal displacement ≤ 3% of height, checked on SLS1 — the 60 mph service loads, whatever your design V. The report’s Direction Summary (base shear, tip drift, reactions), the max tip deflection figure and the PDF reaction table all show this service case and say so. They are not design values: take foundation design forces from the factored cases in the Support Reactions tab. In the STAAD file the service wind is written as its own load cases.

T9. Connection design

Connections are entered as JSON in the section’s Connections box; the placeholder shows a TIA example. The checks follow §4.9: bolt tension, shear and bearing, combined tension and shear, connecting plates, block shear, bracing connections, angle-leg splices (with the §4.8 eccentric-splice check), ring flanges to Annex Q, welds, and U-bolts.

• Every key is checked. A misspelt key stops the run instead of being ignored.
• edge_type (sheared or rolled) is required: the minimum edge distance depends on it.
• Give the bolt strength as bolt_grade (e.g. A325) or bolt_fu.
• A ring flange needs nc or nc_basis (Annex Q, Table Q-1).
• Two keys change the member check as well as the connection: gc_mm in a bracing block (joint eccentricity, §4.4.4.2) and both_legs_connected in a leg splice (raises the shear-lag factor U from 0.80 to 1.00).
• redundant_bracing can be one block for all redundants, or one block per tag ({"r1": {…}, "r2": {…}}).
• Anchor rods, base plates, guy link plates and slip-critical connections are refused.

T10. Report, warnings and STAAD export

• The report opens in US units; the SI / US toggle in its header switches it.
• The Wind, Antennas and Capacity tabs show the TIA quantities and clause references. The Summary tab adds ice, seismic and tornado panels when those loads are enabled.
• The compliance banner at the top of the Summary lists what the app could not decide for you. On a TIA tower it can report: missing wind directions (§2.6.11), antennas with no mounts, the two-period seismic spectrum being used (§2.7.6.1), tornado loads not evaluated (§2.9), a bent main diagonal that needs hip bracing (§4.5.2.3), and a seismic or ice block that failed and was not analysed. Read it before the numbers.
• The STAAD.Pro model is written in FEET / KIP, with the AISC angles as a user table inside the file. Towers with double-angle members cannot be exported. See section 13.

10.Running the Analysis

1. Click Run Analysis. The browser posts your tower JSON plus the analysis config to the server, which spawns the analysis as a background job and returns a job_id.
2. The app polls job status every 1.5 s while a window shows the progress. Status moves through running → done, error or cancelled.
3. On done, the generated HTML report loads automatically into the Analysis Result tab.
4. On error, the status panel shows the reason in the run’s own words (e.g. a missing input, timeout, or memory limit — see Troubleshooting). A run that is refused for a missing or invalid input is not counted against your quota.
5. If the inputs were accepted but the analysis itself failed (for example it did not converge), the report is still shown, with a red ANALYSIS FAILED banner. Such a run cannot be saved or exported.

You can have one run at a time: starting another while one is queued or running is refused. The running window has a Cancel run button that stops it. A cancelled run is still counted against your quota.

When a result is a mechanism

If a load case moves any node of the tower by more than half the tower height, the model is probably a mechanism — for example a bracing pattern with no diagonals. The run continues, but the compliance banner on the report names those load cases and says their results should not be relied on. The 0.5 × height limit is the program’s own, not a code clause. A load case whose result is not a number stops the analysis, and the report is shown with the ANALYSIS FAILED banner.

Opening an older tower file

When you import a file or reopen a History entry made with an earlier version, a notice above the builder lists:

• the inputs the current version requires that the file does not state — for example Risk Category, Cyclone region, k3, Dish type, the ladder’s A_eff, the deck area of an IS platform, the ladder ice inputs or the wind speed with ice;
• any value it filled in exactly from the file itself (a TIA-222-I tower’s risk category, taken from its tornado block or its seismic importance factor);
• defaults that have changed since the file was written: leg base supports are now pinned, the IS 800 bending check is off unless stated, and a TIA-222-I tower with no wind directions now runs every Table 2-6 direction for each face.

The program never guesses an engineering input for you: fill in the listed items and run again. Results may differ from the earlier run. A file written by a newer version of the program is refused.

11.AI / Rule-Based Guidance

Three optional guidance helpers are available. Each is answered by an AI model (Claude) only when the server it runs on has been set up with an API key; otherwise, or when the AI call fails, a fixed rule-based engine answers instead. The live site may run either way, so do not expect AI answers to always be there. The report’s guidance panel shows which engine answered (rule-based or ✦ Claude AI).

Bracing pattern guidance

While editing a custom bracing pattern, get instant feedback on duplicate members, floating nodes, and bypassed nodes, with suggested fixes.

Tower / results guidance

• Before running (✦ Review Inputs in the header): flags widening-with-height geometry, panel heights below 1 m or above 6 m, very thin-walled members (D/t > 50), member thicknesses below the IS 17740 Table 3 minimum, a missing Risk Category or a k1 below the table, a missing cyclone region or terrain category, wind speeds outside a plausible 25–75 m/s range, and antenna/ladder elevations outside the tower height.
• After running (✦ Ask AI, bottom right of the report): type a question or click one of the prompts (Is it safe?, Redesign?, Governing dir?, Drift OK?). It flags max UC > 1.0 (overstressed) or > 0.9 (marginal), drift exceeding the IS 17740:2022 Cl. 10.1.2 limits (3% of height sway, 4° twist), KL/r above the per-role IS 17740 limits (legs 120, diagonals 150, horizontals 200, redundants 250), and identifies the governing wind direction, with suggested next steps (e.g. “increase OD×t of section S3 leg”).

12.Reading the Report

On a TIA-222-I tower the tabs show the TIA quantities instead, and the check is LRFD — see T10. The rest of this section describes the IS report.

The UNITS tile in the strip of headline figures at the top of the report switches the displayed units between SI and US customary (SI ⇄ US), and ↓ Export CSV at the foot of the tables saves every table of the open tab to one CSV file. Read the compliance banner at the top of the Summary before the numbers: it lists the warnings of the run (inputs accepted with a warning, members not checked, load cases that look like a mechanism, and similar). A red ANALYSIS FAILED banner above it means the analysis did not complete.

The 3D viewer in the Geometry tab also has Deflected shape and Force colours toggles that redraw the real lattice at its displaced position (scaled) and colour members by force for the selected wind direction.

Utilisation ratio (UC)

UC = |Applied Force| / Governing Capacity

• Tension: governing capacity = the lowest of gross-section yield T_dg, net-section rupture T_dn and block shear T_db (IS 17740 Cl. 11.1, IS 800 Cl. 6), with the bolt line taken from the section’s connections block. A member with no connection entry is checked on gross yield only; the report says its net section and block shear were NOT CHECKED, and the Summary’s compliance banner names those members.
• Compression: governing capacity = Perry–Robertson buckling capacity per IS 800 Cl. 7.1, γ_m0 = 1.10, using buckling curve ‘a’ (α = 0.21) for CHS/pipe and curve ‘c’ (α = 0.49) for angle / double-angle sections (IS 800 Table 10). Bracing members additionally use the IS 17740 Annex F equivalent slenderness. A slender angle (IS 800 Table 2) is checked on its effective area.
• Bending: only when Bending check on beam elements (IS 800) is on (Tower Type); the leg ratio shown is then the larger of the axial ratio and the combined axial-and-bending ratio.

Tension and compression envelopes are tracked separately per member/section, so a larger tension force can never mask a smaller-but-governing compression case.

Pass/Fail

A member passes when UC ≤ 1.0 and its KL/r is within the per-role limit (IS 17740 with Amendment 1: legs 120, diagonals 150, horizontals 200, redundants 250). Tip drift vs the IS 17740:2022 Cl. 10.1.2 limits (3% of height; 4° rotation) is a serviceability flag, not a strength criterion, but should not be ignored.

13.STAAD.Pro Export

Download a STAAD.Pro .std file of the model your analysis run actually solved — the same geometry, sections and nodal loads — for independent cross-checking or detailed design continuation. Available for IS and TIA-222-I towers. The file is written during the run, so re-run a tower to get a file for it.

• Coordinate system: Z-up; units: METER, KN on an IS tower, FEET, KIP on a TIA-222-I tower
• Sections: IS angles from STAAD’s Indian table; AISC angles as a user table written inside the file (STAAD’s own American table lacks many sizes); pipes and solid bars as prismatic properties. A tower with double-angle members cannot be exported to STAAD.
• All lattice nodes and members, mapped to MEMBER TRUSS (pin-ended, axial only) for Truss/corotTruss elements, or beam members (section properties AX, IZ, IY, IX) for elasticBeamColumn. No shear areas are written, matching the SutranetTower analysis.
• Material: E = 200000 MPa, ν = 0.30, ρ = 7850 kg/m³
• Load cases: LC1 dead load (self-weight + antenna & ladder dead weight), LC2 live/maintenance load (the IS 17740 Cl. 7.2.2 climber load where a ladder is defined, and the platform live load where an IS platform is declared; the case is empty when the tower has neither), LC3+ wind per direction (including per-direction ladder wind); combinations per the selected standard (IS 800:2007 Table 4, IS 17740:2022 Table 2, or TIA-222-I §2.3.2). Ice, seismic, tornado and §3.7.1 pattern cases are not exported.

Choosing the STAAD analysis

Pick the analysis next to Export STAAD.Pro before downloading:

• Match SutranetTower (default) — PDELTA 30 ANALYSIS LARGEDELTA. STAAD reproduces this report: P–Δ is included, P–δ inside members is not. Each load combination is written as its own load case (REPEAT LOAD), because P–Δ results cannot be added together.
• Linear — PERFORM ANALYSIS with STAAD load combinations. A first-order run; light diagonals and small leg moments can differ from this report, which includes leg P–Δ.
• Full P–Δ (incl. P–δ) — PDELTA 30 ANALYSIS SMALLDELTA, STAAD’s own default. It also includes bending within each member, which SutranetTower does not model, so leg moments on heavily loaded legs can read 10–20% higher than this report.

14.Accounts & Quota

If the deployment has Firebase authentication configured, you’ll see a sign-in modal on first visit. Each account has a role (free or admin) and a monthly run quota that resets on the 1st of each month; your remaining quota is shown next to your email in the header. Admins can adjust other users’ quotas.

Ways to sign in

Email verification and the welcome email

When you register with email and password, Firebase sends a link to verify your address, and a notice in the app says so. You can use the app straight away; verifying is not required to run analyses. Once the address is verified, the app sends one welcome email with links to the training videos and this manual. It is sent the next time you sign in or the app refreshes your session, so it can arrive up to an hour after you click the link. A Google account is already verified, so its welcome email is sent when the account is created. The emails come from a new sender and are often filed as spam: check your spam folder and mark them “not spam”. Accounts created before the welcome email existed do not get one.

Forgot your password?

On the Sign In tab, click Forgot password?, enter your account email, and click Send reset link. Firebase emails you a secure link to choose a new password — check your inbox (and spam folder). For privacy the app shows the same confirmation whether or not that email is registered, so the message appearing does not by itself confirm an account exists. Password recovery applies to email/password accounts; if you signed up with Google, sign in with the Continue with Google button instead (your password is managed by Google).

15.Limitations

16.Best Practices

• Start from the example tower and modify incrementally rather than building from a blank slate — it’s a known-valid baseline.
• Run “Review Inputs” before every analysis, especially after large geometry or bracing changes — it catches common modelling mistakes for free.
• Check the Geometry tab first after every run, before trusting any numbers — a wrong bracing pattern or panel count produces a structurally different (and silently wrong) model.
• Keep panel heights moderate (roughly 1–6 m) — very short or very tall panels distort solidity ratio and force-coefficient assumptions.
• Use more/shorter sections at the base, where wind moment and axial load are highest, and fewer/taller sections near the top.
• Cross-check critical designs against the STAAD export, particularly when UC is close to 1.0 or when you’ve switched diagonals to elasticBeamColumn.
• Export your tower JSON after every meaningful change, and Save runs you want to keep — an unsaved run is replaced by your next run.
• Validate custom bracing patterns in the Bracing Library tab before using them in a real tower — fix any duplicate-member, floating-node, or bypassed-node errors immediately.
• Treat AI/rule-based guidance as a second opinion, not a final verdict — always apply engineering judgement on top of it.

17.Troubleshooting

18.Glossary

Bracing editor & geometry

These are the terms used inside the Bracing Library editor and the pattern schema (bracings.json). A pattern is always authored on one face and replicated to every face by rotational symmetry, so most terms describe a single face and how members reach across to their neighbours.

Analysis & code