The response of two three-story shear frames of to a ground motion is to be computed as a function of time. The properties of the frame are h = 12 ft, m = 100 kips/g, I = 1400 in*, E = 29,000 ksi, and (n = 5%. The ground acceleration data are available in the attachment. (a) Determine the SDF system responses Dn(t) and An(t) using a numerical time-stepping method of your choice with an appropriate At; plot Dn(t) and An(t). (b) For each natural mode, calculate as a function of time the following response quantities: (i) the roof displacement, (ii) the story shears, and (iii) the base overturning moment. (c) At each instant of time combine the modal contributions to each of the response quantities to obtain the total response; determine the peak value of the total responses. For selected response quantities, plot as a function of time the modal responses and total response. (d) Discuss the effect of stiffness of columns on the responses in (c) based on comparison of results of the two frames. m/2 Rigid beams m/2 Rigid beams h El h El/3 EI/3 m m h h 2E1/3 2E1/3 m m h h + THE TITI 77777 2h 2h