The design of timber structure is totally based on working stress method. Due to which, we don’t use factored load. We design the member by considering service loads / Working loads.

In Boxed Column, there is hollow portion inside timber planks but in built-up column the hollow portion is either entirely empty or filled. All boxed column are built-up columns but all built-up columns are not boxed columns.

IS 800:2007, General Construction in Steel (Design of Steel Structure)

IS 875 (Part 1), 1987 – For Dead Loads

IS 875 (Part 2), 1987 – For Live/Imposed Loads

IS 875 (Part 3), 1987 – For Wind Loads

IS 875 (Part 4), 1987 – For Snow Loads

IS 875 (Part 5), 1987 – For Special Loads and Combinations

IS 1983 (Part 1) – Criteria for earthquake resistant design of structures (General Provisions and Buildings)

IS 1983 (Part 2) – Criteria for Earthquake Resistant Design of Structures (Liquid Retaining Tanks)

In I section/ Channel section purlin, wind load is considered as normal to roof and gravity load is considered as vertically downward from CG, so multiply by load factor to find factored load.

IS 800:2007 is silent about the design of angle section purlin.Note: In angle section purlin, both wind load and gravity load (dead + live) are assumed to be normal to the roof truss. So, calculated load is taken as factored load. (not multiplied by Gamma_f)

Peak gust velocity averaged over a short time interval of about 3 seconds and corresponds to mean heights above ground level in an open terrain (Category 2). Basic wind speeds have been worked out for a 50 year return period.

The ratio of rise to span of truss represents the pitch in roof truss.

• Span is Large
• Loads are heavy
• Bending Moment is very high.
• Load cannot be carried by rolled section economically.
• Even I-section with cover plate also become insufficient to support the loads.
• Need deeper sections having higher stiffness to carry heavy loads.