1.19 The Washington Monument is an obelisk with a hollow rectangular cross section that tapers along its length. An approximation of the monument geometry is shown in Figure P1.19. The thickness at the base is 4.5 m and at top it is 2.5 m. The monument is constructed from marble and granite. Using a specific weight of 28 kN/m' for these materials, determine the average bearing stress at the base of the monument. 10 m Figure P1.19 169 m. 10 m 17 m 17 m