Encased Columns:
Sometimes structural sections are encased in masonry or concrete. This improves its slenderness ratio and thus enhances its strength. It also increases its durability and attack from harmful chemicals or fumes. However the IS: 800 stipulates some conditions to be fulfilled by them:
(a) The steel section have to be symmetrical (single I or double channel back to back).
(b) The whole dimension of the steel section must not be greater than 750 × 450 mm (750 parallel to web).
(c) The column shall be unpainted and solidly encased in ordinary dense concrete of minimum M-15 grade with 20 mm aggregates.
(d) The minimum width of solid casing to be (b0 + 100) where b0 is the width of steel flange (mm).
(e) A surface and edges of the column should have a concrete cover of not less than 50 mm.
(f) The casing is efficiently reinforced with steel stirrups or binders (minimum 5 mm dia) at a minimum pitch of 150 mm, so arranged as to pass through the centre of the covering of the edges and outer faces of the flanges and supported by at least 4 longitudinal spacing bars.