Tools › User guides › Steel Roof Truss Designer
The Steel Roof Truss Designer lets you draw a roof truss on a grid (like STAAD) or start from a Pratt, Howe, Fink or flat truss. It works out IS 875 dead, live and wind loads, analyses the truss, chooses angle, channel or ISMB sections to IS 800, designs bolted or welded joints, and designs the RCC column or beam the truss sits on to IS 456.
Open the Steel Roof Truss Designer ›
| Tool | How to use | Typical | Tip |
|---|---|---|---|
| Select | Click a member to change its group (top chord, bottom chord, web), or a node to type exact coordinates. | — | |
| + Node | Click a grid point to add a node. | — | Nodes snap to grid points. |
| + Member | Click two nodes to join them. | — | |
| Support | Click a node: 1st click pin, 2nd roller, 3rd removes it. | Pin one end, roller the other | A truss needs at least one pin and one roller. |
| Delete / Undo / Clear | Remove the clicked item, undo, or clear everything. | — | Clear, then draw any shape you like. |
| Fit grid / Numbers | Zoom to fit; show node and member numbers. | — |
| Field | What to enter | Typical value | Tip |
|---|---|---|---|
| Truss type | Pratt (pitched), Howe (pitched), Fink / W (4 panels), Parallel chord (flat). | Pratt | Diagonals of a Pratt truss are in tension under gravity — economical. |
| Span (m) | Clear span between supports. | 8 – 24 m | |
| Rise (m) | Height at the ridge (depth for a flat truss). | Span/4 to span/6; flat: span/10 – span/15 | |
| Panels | Number of panels (even). | Panel length 1.2 – 2 m | So that purlins sit on the nodes. |
| Grid — spacing across / up, bays across / up | Size of the drawing grid. | 1.5 m × 0.6 m | Only for drawing your own shape. |
| Field | What to enter | Typical value | Tip |
|---|---|---|---|
| Truss spacing (m) | Distance between trusses. | 3 – 6 m | |
| Building length (m) | Length of the shed. | ||
| Height to truss seat (m) | Ground to the level where the truss sits. | 5 – 8 m | Used for wind. |
| Roof access | No access (sheeted roof) or With access. | No access | Live load 0.75 kN/m², less 0.02 per degree above 10°, not below 0.40 (IS 875 Part 2). |
| Roof covering | Colour-coated sheet, GI sheet, PUF panel, AC sheet. | GI 0.63 mm — 0.08 kN/m² | |
| Purlins & sag rods (kN/m²) | Weight of purlins. | 0.10 | |
| Ceiling / services (kN/m²) | Hung loads. | 0 – 0.25 | Truss self-weight is added automatically. |
| Basic wind speed (m/s) | IS 875 Part 3 Annex A. | Kolkata 50, Delhi 47, Mumbai 44 | |
| Terrain | 1 open … 4 city centre. | 2 | |
| k₁ design life | 1.00 (50 years), 1.07 (100 years), 0.92 temporary. | 1.00 | |
| k₃ ground slope | 1.00 flat … 1.36 hill crest. | 1.00 | |
| k₄ cyclone | 1.00 not cyclonic, 1.15 / 1.30 cyclonic coast. | 1.00 | Use 1.15 on the Bengal / Odisha coast for industrial sheds. |
| Wall openings | Under 5 %, 5 – 20 %, over 20 % open. | 5 – 20 % (Cpi ±0.5) | Sheds with large doors: 5–20 %. |
| Field | What to enter | Typical value | Tip |
|---|---|---|---|
| Steel grade (IS 2062) | E250 or E350. | E250 | |
| Top chord / Bottom chord | Double angle, Single angle, Channel ISMC, Beam ISMB. | Double angle | |
| Web members | Single angle, Double angle, Channel. | Single angle | |
| Smallest angle allowed | ISA 40 – 60. | ISA 50×50 | |
| Bottom chord braced every | Lateral bracing interval. | 2 nodes | The bottom chord goes into compression under wind uplift, so bracing matters. |
| Joint type | Bolted or Welded (shop). | Bolted | |
| Gusset plate (mm) | 8 – 16. | 10 | |
| Bolt diameter / grade | M16 – M24; 4.6 or 8.8. | M20, 4.6 | |
| Fillet weld size (mm) | For welded joints. | 6 | Reduced automatically for thin legs. |
After the design runs you can replace the suggested size of any member group with your own choice in section 5 of the results.
| Field | What to enter | Typical value | Tip |
|---|---|---|---|
| Support | Directly on RCC column tops, or on an RCC beam between columns. | On columns | |
| Column width b / depth D (mm) | Column size; D is in the plane of the truss. | 300 × 450 | Columns are taken fixed at the base, free to sway at the top (effective length 2 × height). |
| Beam width / depth (mm), Column spacing (m) | Only when the truss sits on a beam. | 300 × 600, 8 m | Beam designed as simply supported. |
| Other load on the beam (kN/m) | e.g. a brick parapet. | 0 | |
| Concrete / Rebar / Cover | M20–M30, Fe 415/500, cover. | M25, Fe 500, 40 mm | Foundations are not designed here. |
After Analyse & design you get the load summary, member forces for every load combination, the chosen section for each group with its checks (tension, compression, slenderness), bolts or welds at each joint, support reactions and the RCC column or beam design with reinforcement. Save the truss with Save file to reopen it later.
Yes. Press Clear, then use + Node and + Member to draw any shape, and Support to add a pin and a roller.
Wind can lift the roof, which puts the bottom chord in compression. Lateral bracing at every 2 nodes keeps its buckling length short.
No. It designs the steel truss, its connections and the RCC column or beam below. Use the SBC calculator and a footing design for the foundation.