Soon after the construction of a single-story structure, shown below as the "as-built structure", the designer finds a major mistake in the design seismic displacement estimation. Upon reanalyzing the structure, the designer calculates that the 0.4 sec period, 5% of the critical damped "as-built" structure has a roof drift ratio greater than 1% under the design-basis earthquake. In other words, the designer calculates that at the roof level the structure sways more than 3 cm (= 300 cm x 1%), and as such, poses pounding hazard to neighboring buildings. To fix the problem, the designer suggests installing a massless rigid stiffener linking the columns at mid-height (see sketch shown as the "retrofitted structure"). The rigid stiffener is connected to the columns rigidly, i.e. columns do not rotate at the stiffener level. As a reviewer, you are asked to check both claims. Using the provided design acceleration spectra, which is for 5% of the critical damped structure like the structure being reviewed, a. check if the "as-built" structure has a roof drift exceeding 3 cm; b. check if the suggested "retrofitted structure" has a roof drift less than 3 cm. ngid se 3 m PSA, Pedo-ccteration ) 10 O.F 1 0.01 1 04 (as-built structure) 02 1 1 00+4 I 1 I 0.01 DS 200000 Period(s) added maisiss ngd sener retrofimed aucture Design Acceleration Spectra 1 1 1.5 m 1.5 m