Load Carrying Capacity of Composite Bars:

You have study how a whole load applied on a composite bar is shared by different components of a composite. Though this is surely enlightenment on the behaviour of composite bars, we ought to learn more to apply the concept in practically more useful way. i.e., we have to learn

1. what shall be the total load which a composite bar can carry, and

2. to carry a given load, how must a composite bar be proportioned.

For this cause, we must know the strength of each of material and also we must be able to compute the stresses induced in the several components of a composite bar.

Already we have learnt the compatibility condition that the axial deformations undergone by all of the components of a composite bar must be equal.

As the lengths of components are also equivalent, the strain in each of component must also be equal. Taking the strain of the composite bar as ε, stress in any component might be expressed as

                           σ_i = E_i  × ε

or         σi = ( E_i/ E₁) × E₁  × ε

or         = m_i    × E₁   × ε

Since, E₁ × ε = σ₁, then we can write

σ_i = m_i  × σ₁

Eq. shows the relationship that the stress induced in any component of a composite bar must be proportional to its elastic modulus or modular ratio. The stress in steel, σ_s, shall be 18 times the stress in concrete. You must have seen this by yourself, if you had divided the load shared by each of member by its area of cross section. Using Eq. saves some of computational effort.