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When a steel beam is encased in cement concrete throughout the entire length, it is called an encased beam. The cased beam is shown in figure below.
As per IS 800 :1984, beams may be designed as encased beams when the following conditions are fulfilled:
a) The section is of a single web and I-shape or of double open channel formed with the webs not less than 40mm apart.
b) The overall dimensions of the steel section do not exceed 750mm x 450mm including the overlapping, where used, the larger dimension being measured parallel to the web.
c) The beam is encased in dense concrete of a minimum grade of M15.
d) The minimum width of solid casing is equal to where is the width of the steel beam flange in mm.
e) The surface and edges of the beam have a minimum cover of not less than 50mm.
f) The casing is effectively reinforced with steel wire at least 5mm diameter in the form of stirrups or binding with a pitch not more than 150mm.
g) The steel cores shall be accurately machined at splices, provision should be made for the alignment of the column.
h) At the column base, suitable arrangement should be made to transfer the load to the footing.
a) The steel beam section carries the entire load.
b) Concrete contributes to the lateral stability of the compression flange for the purpose of determining the permissible stress in compression.
c) The equivalent moment of inertia, about y-y axis is equal to where A is the area of the steel section and may be taken as where being the width of the flange in mm
d) The permissible bending stress determined as above should not exceed 1.5 times that permitted for encased sections.