— David Wagner 2007/11/04 16:18

(including preliminary sizes)

The following design details are considered.

• The front windows are assumed to be glass block. Caulking on the top prevents the allowable deflection of the front collar beam from deforming the window.
• Additional beams are used across the long dimension of the structure so there are a total of four roof beams along with the rear masonry wall supporting the rafters.
• A column integral to the central wall extends upward to support the roof beams at midspan.
• Also, supporting columns are placed at ¼- and ¾- points along the interior roof beams so their support is identical to the support of the front collar beam.
• Purlins may be placed between roof beams if the rafters need more lateral bracing.

1. Prepare the site.
2. Pour the foundation.
3. Build masonry walls and columns
4. Build the roof.
5. Pour the slab.

• The roof is standing-seam ceramic-coated steel.
• The roof deck is plywood.
• The rafters are x lumber.
• The roof beams are x glulam.
• The windows are glass block.
• The walls and supporting columns are standard concrete masonry units (CMU).

”…several rest areas on a major road from San Antonio to McAllen, Texas.”

Only LRFD analysis is used. [: Do governing authorities require application of both methods?]

Assume the overhangs are at least 3' on every side, rounded up to a whole number of 4×8 plywood sheets.

• The roof is 45.2×30.2 in plan, nominally 48'x31' a horizontal plane area of 1490 sf.
• The roof slopes 6' over 24' (3-in-12 or 14°), a length of 31.1'. The inclined area is nominally 48×32', 1536 sf.

–Table 1607.1, IBC 2006

The design ground snow load, p_g, ranges from zero to 5 psf in the area of interest. [2006 IBC, Figure 1608.2]

Basic wind speed (3-second gust) ranges from 90 to 105 mph in the area of interest. [2006 IBC, Figure 1609] The largest value is more conservative than the 100 mph gust provided in the project description.

Building Geometry

• h_mean=16 ft; 0.4 h_mean = 6.4 ft; Least horiz. dim. = b=32 ft; 0.1b=3.2 ft
• End zone: a = min(0.4 h_mean, 0.1b) = a=3.2 ft
• End zone length = 2a=6.4 ft

Wind Pressures

[Figure 6-2, ASCE 7-05]

The roof angle depends to a small degree on the dimensions of the roof members and is taken here conservatively as 15°.

• * from Figure 6-2,ASCE 7-05, h≤60', 105 mph design wind speed, 15° Roof Angle, Load Case 1
• †I=1.0 ; Kzt=1.0 ; λ=1.486 ;

from here on

• Zone A: 32.5 psf
• Zone C: 21.8 psf

Earthquake loads include 0.2 second spectral response S_s of 1.4 to 10 (<15 %g), and 1.0 second spectral response S₁ of <2 to 3 (<4 %g) [2006 IBC, Figure 1613.5(1) and (2)]. Since S_s<15 %g and S₁<4 %g, section 11.4.1 of ASCE 7-05, allows the use of seismic design category A.

from here on.

In the shorter dimension, the central dividing wall resists lateral loads.

Since the vertical wind loads are negative, the wind load combination may be neglected.

1.6L + 1.2D
1.6L + 1.2D
1.6L + 1.2D
1.6L + 1.2D

a. Roof joists are 2 x 10 at 16 in. o.c. which directly support the roof sheathing. Loads are (D + S). This is ASD for Hem-fir