A concrete beam fixed at both ends is modelled using four solid (brick) 3D finite elements as shown in Figure Q1. Solid elements consider only node translations as degrees of freedom. The Young's modulus is E = 30,000MPa and Poisson's ratio is v= 0.1. The structure is strengthened using four truss elements (1-8,5-8, 1'-8', 5'-8') placed on the sides. y Z 1' X 2' 3' 6 2m 4' 7 2m 8 5' 9 2m 2m 2m 10 Figure Q1 (a) What is the size of the structure stiffness matrix before and after removing the rows and columns corresponding to the boundary conditions shown in Figure Q1. [6] (b) Calculate the det(J) for one of the four brick elements as well as one of the truss elements using the physical interpretation of the det(J). Include units in your answer.