Values of strength obtained in this way usually range from 2000 to 6000 psi, the most common value being of the order of 3000 psi - a value which is often used for purposes of general discussion. Compressive stress is expressed symbolically as
σ = P / A
in which σ = compressive stress in psi
P = applied load in lb
A = cross sectional area in square inch
3.2 Tensile strength
following formula is adopted for tensile strength –
P = compressive load on the cylinder
L = length of the cylinder
L = length of the cylinder
D = diameter of the cylinder
In which σ = stress in the fiber farthest from the neutral axis, psi
M = bending moment at the section, lb-in.
I = moment of inertia of the cross section, in.
c = distance from neutral axis to farthest fiber, in.
3.3 Flexural strength
When concrete is subjected to bending, tensile and compressive stresses and in many cases direct shearing stresses are developed [3]. The most common plain-concrete structure subjected to flexure is a highway pavement, and the strength of concrete for pavements is commonly evaluated by means of bending tests on 6 by 6 inch beam specimens. Flexural strength is expressed in terms of “modulus of rupture”, which is the maximum tensile (or compressive) stress at rupture computed from the well-known flexure formula
σ = Mc / I
In which σ = stress in the fiber farthest from the neutral axis, psi
M = bending moment at the section, lb-in.
I = moment of inertia of the cross section, in.
c = distance from neutral axis to farthest fiber, in.
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