— David Wagner 2007/12/04 17:09

You have been contacted by TxDOT to design modular restrooms for several rest areas on a major road from San Antonio to McAllen, Texas. The unit shall consist of a timber roof and masonry walls as shown in the attached figures. The roof configuration can be changed to a different timber roof system if you preferred. All structural timber members must satified the NDS 2005 Specifications and all structural masonry elements shall be designed in accordance with the ACI 530-05. The floor slab is going to be 4-inch thick. The bearing capacity of the soil has been estimated to be 5000 psf. The water table is very deep. The structure shall resist a 3-sec gust speed of 100 mph. Only Gr.60 steel is available. Assume a unit weight of soil equal to 120 pcf.–Project Statement by Dr. Diaz

This design addresses only the timber and masonry components of this structure. The roof is made of plywood supported by sawn lumber purlins and glulam roof beams. The rest of the structure is made of standard concrete masonry units (CMU). The only minor changes to the provided drawings is the extension of the central partition wall so it is the same shape as the end walls, and the specification of glass block windows. This report documents the load and resistance factor design (LRFD) of the purlins and roof beam [NDS 2005]. Most of the structure is unreinforced masonry by allowable stress design (ASD), though LRFD is used to design the reinforced lintels [ASCE 5-05, 6-05]. Wind and seismic design follow ASCE 7-05.

• Gravity loads transfer from the roof sheathing to the lumber purlins, to the glulam beams (at the front and in the middle), to the walls, and into the foundation. At the rear, the purlins bear directly on the exterior masonry wall.
• Lateral wind and seismic loads transfer to perpendicular masonry shear walls.