see, section modulus tells about the strength of a section under bending. The bending moment diagram is obtained in the same way except that the moment is the sum of the product of each force and its distance(x) from the section. These fundamental parameters include the elastic limit, which for "Hookean" materials is approximately equal to the proportional limit, and also known as yield point or yield strength, Young's Modulus (these, although mostly associated with tensile testing, may have compressive analogs) and compressive strength. Distributed loads are calculated buy summing the product of the total force (to the left of the section) and the distance(x) of the centroid of the distributed load. Stress Strain Curve . Otherwise, it is inelastic. how??? Proportional Limit (Hooke's Law) From the origin O to the point called proportional limit, the stress-strain curve is a straight line. PL ⇒ Proportional Limit - Stress above which stress is not longer proportional to strain. The elastic limit is in principle different from the proportional limit, which marks the end of the kind of elastic behaviour that can be described by Hooke’s law, namely, that in which the stress is proportional to the strain (relative deformation) or equivalently that in which the load is proportional to the displacement. See accompanying figure at (1 & 2). Elastic limit is the maximum stress to which a specimen may be subjected and still return to its original length upon release of the load. Lateral Torsional Buckling The compressive flange of a beam behaves like an axially loaded column. It is reported in units of psi. Proportional limit is the highest stress at which stress is directly proportional to strain. If the maximum bending stress is less than the proportional limit when buckling occurs, the failure is elastic. Thus, in beams covering long spans the compression flange may tend to … It is generally used in tests of bending strength to quantify the stress required to cause failure. from bending equation we have (sigma/y=M/I=E/R). This is nearly identical to the result obtained using the depletion approximation. Proportional Limit and Hooke’s Law As seen in Fig. Fiber stress at proportional limit represents the maximum stress a board can be subjected to without exceeding the elastic range of the wood. Proportional limit is the point on a stress-strain curve at which it begins to deviate from the straight-line relationship between stress and strain. This linear relation between elongation and the axial force causing was first noticed by Sir Robert Hooke in 1678 and is called Hooke's Law that within the proportional limit, the stress is directly proportional to strain or σ YP ⇒ Yield Point - Stress at which there are large increases in … σ EL ⇒ Elastic Limit - The maximum stress that can be applied without resulting in permanent deformation when unloaded. It is obtained by observing the deviation from the straight-line portion of the stress-strain curve. This plot is a manifestation of Hooke’s law : Stress is proportional to strain; that is, σ= E Є (2.4) where E is material property known as the modulus of Elastic limit is the greatest stress the material can withstand without any measurable permanent strain remaining on the complete release of load. let us see. 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