Computer study-Influence of supports on frame behavior.

(a) Using the RISA-2D computer program, compute the initial elastic deflection at midspan of the girder in Figure P8.44, given that the support at \(D\) is a roller. For the computer analysis, replace the tapered members by 3 -ft-long segments of constant depth whose properties are based on each segment's midspan dimensions; that is, there will be 9 members and 10 joints. When you set up the problem, specify in GLOBAL that forces are to be computed at three sections. This will produce values of forces at both ends and at the center of each segment. To account for cracking of the reinforced concrete, assume for girder \(B C D\) that \(I_{e}=\) \(0.35 I_{G}\); for column \(A B\) assume \(I_{e}=0.7 I_{G}\) (compression forces in columns reduce cracking). Since deflections of beams and one-story rigid frames are due almost entirely to moment and not significantly affected by the area of the member's cross-section, substitute the gross area in the Member Properties Table.

(b) Replace the roller at support \(D\) in Figure P8.44 by a pin to prevent horizontal displacement of joint \(D\), and repeat the analysis of the frame. The frame is now an indeterminate structure. Compare your results with those in part (a), and briefly discuss differences in behavior with respect to the magnitude of deflections and moments.

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9' "22 22" 22" B -16" P = 24 kips 18'- D 16 12 varies