The shear frame shown in Figure $($a$)$ is constructed of rigid girder and flexible columns. The frame supports uniformly distributed load of total weight of $120$kN and the frame is subjected to step force with a ramp as shown in Figure $($b$)$ at the girder level. Determine the horizontal stalic displacement at l$=0\mathrm{.}75$s$.$

E $=200$GPa and damping can be assured as zero. Moment of inertia of end columns and center column

are $3\mathrm{.}4465$e$-$Smm$^2$ and $7\mathrm{.}07$e$-5$mm$"$ respectivcly.