Specification Design Example
Given: The exterior bearing walls of a project have a uniform roof uplift load of 250 plf, a roof bearing height of 40' above the top of the foundation, and use wall plates made of southern pine. The designer has determined that the dead load of the floors above requires anchorage to the foundation and would like to space the URS at 4' on center and limit the URS to a maximum deflection of 0.20" based on project-specific parameters. (Tables 1–4 available on the following three pages of this guide.)
Step 1 — Determine the demand load on each URS run.
(250 lb./ft.) (4 ft.) = 1,000 lb. per URS rod run
Step 2 — Choose a shrinkage take-up device and determine the deflection for the URS rod run.
From Table 3, the URS4-RTUD has a deflection of 0.164" < 0.20"
Note: For demand loads (PD) or rod run lengths (L) not listed in Table 3, Table 2 can be used to calculate URS deflection for any load and run length.
Step 3 — Specify the rod run: rod diameter, shrinkage compensation device, length and spacing.
URS4-RTUD — 40'–0" @ 48"
Step 4 — Specify the URS rod run anchorage.
You may download the free Anchor Designer Software or use the Anchoring and Fastening Systems for Concrete and Masonry catalog.
Step 5 — Specify the appropriate hurricane tie connector to resist the roof member uplift.
The H2.5A hurricane tie capacity is greater than 500 lb. (assumes trusses @ 2 ft. o.c.).
Step 6 — Specify a connection to prevent top plate rotation.
See Top Plate-to-Stud Rotation Restraint to determine the required top-plate rotation restraint connection force. If a tie is specified at every other stud (32" o.c.), then this force is 333 lb. An H2.5A is a good choice since these are already being used for roof-to-top-plate connections.