Why 'i' section beams are preferred than rectangular section?

Question

As we know, in case of rectangular sections the moment of inertia is high and hence the stress it can handle it is also high according to bending moment equation, but why we prefer a i section beam.

Answer 1

Ever try and bolt up a connection or a joint between two pieces inside of an enclosed rectangle ? You need the access and ability to physically bolt two pieces together. Impossible to do in an enclosed rectangle. An I Beam offers savings typically in weight ( weight is money in working with steel ), and an I Beam can be extruded without the need of making a butt weld
as required when rolling a piece of steel into a rectangle. The joint where you start and finish your rectangle must be welded together !!!

Answer 2

take ISMC300 AND A solid ractangular section having same height and width, as far as the strength is concerned , I section stell rolled beam is having same strength,high moment of inertia and less weight .
So, handling is very easy and cheaper also.
I-beams (also known as double-T esp. in Polish and German) are beams with an I- or H-shaped cross-section. The horizontal elements are flanges, while the vertical element is the web. The Euler-Bernoulli beam equation shows that this is a very efficient form for carrying both bending and shear in the plane of the web.

Answer 3

because a rectangular section wastes material since the flanges of the I section take the bending moment and the web takes the shear if properly apportioned. If steel beams were rectangles instead of I shaped, they would be too heavy. Concrete beams are usually cast in place with forms to make rectangular sections. In the field, it is quite difficult or next to impossible to form an I shape beam. But I shaped concrete beams do exist in the form of bridge girders, but these girders are cast in a special yard using specialized materials and equipment.

Even some wood trusses are manufactured in the I shape using 2 x 4 top flanges and plywood webs, called Truss Joists.

Answer 4

The shape of the I cross section maitains a relatively high moment of inertia (in one direction) while reducing weight. It's also much cheaper to form an open channel than a closed rectangular beam.

Answer 5

I Section Beams

Answer 6

They generally support more load with less material.