Second moment of area "I" and deflecton relationship 1. The problem statement, all variables and given/known data What I value will halve the beam deflection 2. Relevant equations I = bd^3 / 12 and y max = - 5wL^4 / 384EI 3. The attempt at a solution Transpose y max = - 5wL^4 / 384EI to: I = - 5wL^4 / 384Ey max This makes the value of I (2nd moment of area) double to achieve a halved deflection. Is this just a commonly known relationship? Obviously I'm not inferring that the beam CSA be doubled, only 'I', and I'm also aware that when thinking of CSA, it takes approximately 26% of a rectangular beam depth increase to halve deflection.