The collapse of reinforced concrete buildings during earthquakes can result in significant loss of property and life. Often such collapses are caused by concrete column axial failure. The authors of

"Rotation-Based Shear Failure Model for Lightly Confined RC Columns" (J. Struct. Engr., 2012:1267–1278) introduced a model for the deformation at onset of shear failure for a class of reinforced concrete columns. As part of the study, the authors investigated how y = maximum sustained shear (Vmax, in kN) is influenced by x q= transverse-reinforcement yield stress (MPa)and x2= concrete cylinder compressive strength (MPa). \text { (a) } \mathbf{a}+b_{1} x_{1}+b_{2} x_{2}, \text { (b) } \mathrm{a}+b_{1} x_{1}+b_{2} x_{2}+b_{3} x_{1} x_{2}, \text { and } \text { (c) } a+b_{1} x_{1}+b_{2} x_{2}+b_{3} x_{1} x_{2}+b_{4} x_{1}^{2}+b_{5} x_{2}^{2} Be sure to specify all function coefficients. For each function, also include the coefficient of multiple determination and interpret its value.