FIGURE 63. Vibrating bent.quired at the top to cause a horizontal displacement of one unit. Since the girder is consid-
ered to be infinitely rigid, the elastic curves of the columns are vertical at the top. Let/=
frequency; k = spring constant; M= total mass of girder and bodies supported by girder.
Using cases 22 and 23 in the AISC Manual, we see that when A = 1, the horizontal re-
actions are R 1 = UEI 1 IL^3 ; R 2 = 3E(1.3/0/(1.2I)^3 - 2.26EI 1 IL^3 k = R 1 + R 2 = 14.26EI 1 IL^3.
- Compute the frequency of vibration
Use the equation/= (\l27r)(k/M)^0 -^5 = (1/2^(14.26EI 1 IML^3 )^05 = 0.6Ql(EI 1 IML^3 )^05 Hz.