Example 232

A one-storey two-bay semirigid braced frame of a low-rise building is shown in Figure 23.11. The spacing between the frames is 10 m. The roof dead load is 1.25 kN/m2 and the snow load is 1.82 kN/m2. The secant stiffness of the beam-to-column connections obtained from experimental tests associated with the connection rotation 6 0.02 radians are 2.8 x 1010Nmm/radand 1.7 x 1010Nmm/radforbeamsBCandCE, respectively. The rotational stiffnesses of the column bases are 3.0 x 109 N mm/rad for columns AB and DC and 1.75 x 109 N mm/rad for column EF. The diagonal bracing is to be designed as a tension-only member with pinned ends. It is required to find the bending moment distribution ofthe frame and axial loads ofthe columns for the load case of dead load plus live load by using the modified moment distribution method.

Load calculation:

The uniformly distributed nominal dead load is 10 m x 1.25 kN/m2 = 12.5 kN/m The uniformly distributed nominal snow load is 10 m x 1.82 kN/m2 = 18.2 kN/m Gravity load case (dead load + snow load):

w = 1.2D + 1.6L = 1.2 x 12.5 + 1.6 x 18.2 = 44.12 kN/m

Properties of cross-sections: Beam: W530 x 85, Ibx = 485 x 106mm4; Column: W250 x 33, Icx = 48.9 x 106mm4

0 0

Post a comment