— David Wagner 2007/09/03 11:57

Solve the following problems from your textbook using the changes indicated. Solutions to some of these problems are available under practice problems in WebCT.

Change the roof cover from 5-ply with gravel to 3-ply with gravel. Change the truss weight from 9 lb/ft to 12 lb/ft. Change the plywood in the roof from ½” to ¾”.

a. Roof dead load D in psf

b. Second-floor dead load D in psf

*It looks like the 150 psf figure in the textbook is incorrect

c. Basic (i.e. consider roof slope but not tributary area) unit roof live load L_r in psf

Roof is flat so no reduction. ; 12 ≤ 20 ≤ 20✔

Change the ridge beam spans from 20 ft to 25 ft.

a. Tributary area to the ridge beam

Assume gables do not support significant roof weight.

325 sf

b. Roof live load L_r in lb/ft

17.5 psf

455 lb/ft

For the snow load assume the structure located in Childress, TX. Maintain the same exposure.

Figure 2.B, standard residential occupancy, heated building, a ground snow load of 70 psf, and Exposure C terrain with a fully exposed roof. Find the design snow load S in psf on a horizontal plane.

• The ground snow load looks to be about p_g=10 psf.
• Category II → I=1.0
• Exposure factor C_e=0.9
• Thermal factor C_t=1.0

6.3

Change the snow load from 25 psf to 30 psf.

The roof structure in Fig. 2.D and a 25 30-psf design snow load specified by the building official.

a. Uniformly distributed snow load S in lb/ft for

a1. 2×4 subpurlin 480

a2. 4×14 purlin 4800

a3. 6-3/4 x 33 glulam beam 30000

b. Tributary snow load S to column C1 in k 30000

Change the beam spans from 26 ft to 28 ft and the tributary width from 16 ft to 18 ft.

An interior beam supports the floor of a classroom in a school building. The beam spans 26 28 ft. and the tributary width is 16 18 ft. Dead load = 20psf.

a. Basic floor live load L₀ in psf

b. Reduced floor live load L in psf

504 sf; K_LL=2

1008 ≥ 400 → 29 psf

L > 0.5L₀✔

c. Uniformly distributed total load to the beam in lb/ft

1372

d. Compare the loading in part c with the alternate concentrated load required by the Code. Which loading is more critical for bending, shear and deflection?

w=1372 lb/ft is numerically larger than the P=1000 lb concentrated load specified in the code.

Part a ONLY. No changes. Hint: use Example 2.8.

The enclosed building in Fig. 2.E is a two-story essential facility located near Denver, Colorado. Wind Exposure C applies.

a. The design wind pressures in both principal directions of the building for main wind force-resisting systems.

Roof angle: 15º Building height: 28.25'

P_s30=90; Category IV → I=1.15; K_zt=1.0 (Assume at least one criterion is not met);

λ=1.3825;

1.6 p_s30