(Answered): (a) A full water tank is supported on an 80-ft-high cantilever tower. It is idealized as an SDF sys ...

(a) A full water tank is supported on an 80-ft-high cantilever tower. It is idealized as an SDF system with weight w= 100 kips, lateral stiffness k= 4 kips/in., and damping ratio = 5%. The tower supporting the tank is to be designed for ground motion characterized by the design spectrum of Fig. 6.9.5 scaled to 0.5 g peak ground acceleration. Determine the design values of lateral deformation and base shear. (b) The deformation computed for the system in part (a) seemed excessive to the structural designer, who decided to stiffen the tower by increasing its size. Determine the design values of deformation and base shear for the modified system if its lateral stiffness is 8 kips/in.; assume that the damping ratio is still 5%. Comment on how stiffening the system has affected the design requirements. What is the disadvantage of stiffening the system? (c) If the stiffened tower were to support a tank weighing 200 kips, determine the design requirements; assume for purposes of this example that the damping ratio is still 5%. Comment on how the increased weight has affected the design requirements.