Guide to Design of Built-up Beams

Design Procedure of the Built-up Beams design

In my earlier articles, we discussed in detail about the “Theory of Built-up Beams“. In this article, we will move a step ahead and understand the concept of the design of Built-up beams.

Here are the simple steps that are to be followed for the design of Built-up Beams.

Step one

The effective span and load required to be carried by the built-up beam are known.

Maximum bending moment and shear force in built-up beams are calculated.

Step two

Value of yield stress (fy) for structural steel is to be assumed.

The permissible bending stress (sigma bc) is calculated.

Step three

The required section modulus (Z) for the given beam section is calculated.

Step four

From the steel table, a trial section for a beam is adopted having the modulus of section (Z) about 25% to 50% in excess of that requirement. The geometrical proportion of beam sections are noted.

Step five

When the depth of the beam is noted, then the usually the practice is to select from ISI handbook No.1 (Steel tables).

The strongest Rolled steel beam that will allow for necessary thickness of power plates at top and bottom.

Step six

The area of power plate required is found out by trial and error method are by;

I = Ibeam + 2(Ap)(h/2)(h/2)

For finding the area, divide the whole equation by h/2.

Step seven

Width of cover plate and thickness are decided with the restriction of outstands.

Step Eight

Check for bending stress/Actual bending compressive stress

(sigma bc)calculated = (maximum bending moment/Gross MI) x Distance of extreme fibre in compression from Neutral Axis

= (M/Ixx)x y1

Actual bending tension stress
sigma bt, cal = (sigma bc)cal x (gross area of tension flange/Net area of tension flange)
= Value should not exceed the permissible bending stress (sigma bc) or (sigma bt) = 0/66fy

Step nine

Check for shear and Deflection