Truss Design

A truss is a structural framework of straight members connected at joints, typically used for long-span roofs, bridges, transmission towers, and lattice structures. Per IS 800:2007, trusses are analysed as pin-connected systems where all members are assumed axial-only (tension or compression, no bending). Common types: (1) King-post truss — simplest, single vertical member, span 5-8 m. (2) Queen-post truss — two vertical members, span 8-12 m. (3) Pratt truss — diagonals in tension, verticals in compression; span 10-30 m. (4) Howe truss — diagonals in compression, verticals in tension; opposite of Pratt. (5) Warren truss — alternating triangles; span 15-40 m. (6) Vierendeel truss — rectangular openings without diagonals; relies on rigid joints; specialty applications.

Design per IS 800: (a) Load analysis — gravity (dead + live + roof load), wind (uplift and lateral), seismic, snow (in applicable regions). (b) Member sizing for axial load — tension or compression. Tension members: gross-area yield + net-area block shear; angle members may need single-bolt reduction factor. Compression members: buckling check with appropriate effective length factor. (c) Joint design — bolts or welds at gusset plates. (d) Lateral stability — bracing system to prevent out-of-plane buckling of compression members. (e) Deflection check — typically span/250 to span/400 depending on use. Indian truss applications: (1) Industrial sheds (PEB) — most common; spans 15-30 m. (2) Stadium roofs (long-span trusses, atria). (3) Transmission line towers (lattice trusses). (4) Bridge superstructure (steel truss bridges). (5) Greenhouse and agricultural structures.