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Method 1: Pre-Engineered Runs | Canada

The following is an example of how pre-engineered runs are specified from this catalogue.

The Designer shall determine the cumulative overturning tension and compression forces at each floor. The ATS components (Strong-RodTM threaded rod and bearing plates) are selected on the basis of the factored tension forces. The designer should then select the lumber at the ends of the shearwall on the basis of the factored forces. Note that the compression forces are typically greater than the tension forces due to combinations of additional forces such as dead and live load.

Simpson Strong-Tie Anchor Tiedown System component capacities are selected to meet or exceed the design forces provided and determined by the Designer. Simpson Strong-Tie has not confirmed and is not responsible for any of the design, engineering, calculations or derivation of the structural forces related to the building.

The Designer is responsible for evaluating the effects of lumber shrinkage and ATS elongation on shearwall drift. Please refer to page 13 of the catalogue for information regarding shearwall drift.

For simplicity of the design and installation, it is recommended that the Designer group similar runs together.

Given: NBCC 2015
Wall geometry and shear forces as shown in Figure 1 below
Douglas Fir–Larch wall plates
2x4 nominal wall thickness
0.30 m floor thickness

Step 1

Determine the cumulative overturning and incremental forces based 15kN on the applied storey shear:

The moment arm is the distance between the centerline of compression members and centerline of tension members. For symmetrical post configurations, this is typically the distance between tension rods on each end of the shearwall. For tension loads, gravity loads have not been included.

C-L-SRSCAN18-pg39-A-Tension_Equation C-L-SRSCAN18-pg39-B-Tension_Equation C-L-SRSCAN18-pg39-C-Tension_Equation

Determine the incremental overturning forces at each level. These are typically the difference in the cumulative forces at the stories above and Storey below. These forces are generated at each level, and are transferred into the rod by the bearing plate and nut.

Incremental OT Force roof = 12.30kN
Incremental OT Force L3 = 34.84 − 12.3 = 22.54kN
Incremental OT Force L2 = 65.57 − 34.84 = 30.73kN
Figure 2 below shows the load path at level 2.

figure-2-method-1-Specify-Pre-Engineered-Runs
figure-1-method-1-Specify-Pre-Engineered-Runs

Determine the cumulative compression forces in the studs at the end of the shearwalls.

P = Forces due to gravity loads.
Cumulative OT Compression L1 = T1 + 5 + 10 + 10 = 90.57 kN
Cumulative OT Compression L2 = T2 + 5 + 10 = 49.84 kN
Cumulative OT Compression L3 = T3 + 5 = 17.30 kN

Step 2

Select system and verify tension capacities

Try: TDS3-7/8 (see page 46 of the catalogue).

C-L-SRSCAN18-p40-D

Step 3

Select compression members (see pages 29-33 of the catalogue).

C-L-SRSCAN18-p40-E

For the top floor, assume Designer opts to use bridge block termination with a single 2x4 cripple stud and a single 2x4 king stud on either side.

Step 4

Determine the nailing requirement for shear transfer from the cripple stud to the king stud.
Assume 16d common nails (0.162" dia. x 31⁄2"), side-member thickness of 38.1 mm (11⁄2"), main-member penetration of 38.1 mm (11⁄2"), D.Fir-L members, and short-term loading (KD = 1.15)
Factored lateral resistance of each nail is 1.29 kN (290 lb.) as per CSA 086-14 Clause 12.9.4
Compressive force in each cripple = 12.30 / 2 = 6.15 kN
Number of nails required = (6.15 kN) / (1.29 kN / nail) = five 16d common nails for each cripple stud to king stud
Alternatively, Simpson Strong-Tie SDWS screws can be used for shear transfer when more than one cripple stud per wall cavity side is required:
Assume SDWS22400DB (0.22" x 4") screws or otherwise the same conditions as above
Factored lateral resistance of each screw is 1.73 kN (390 lb.) as per F-SDWSSDWH flier
Number of screws required = (6.15 kN) / (1.73 kN / screw) = four SDWS22400DB screws for each cripple stud to king stud

For worst-case scenarios (where compressive load nears compressive resistance of studs), see page 34 of the catalogue.

Step 5

Total vertical displacement of each storey, or between restraints, meets the total vertical displacement limit of 0.30" or 7.6 mm because the pre-engineered run TDS3-7/8 uses regular-strength rod. As discussed on page 13 of the catalogue, the prescriptive limit can be waived if the building design conforms to the calculation procedures in CSA O86-14 Engineering Design in Wood (Clause 11.7.1), APEGBC Technical and Practice Bulletin, or the Mid-Rise Wood- Frame Construction Handbook Special Publication SP-57E by FPInnovations.

tds3-method-1-Specify-Pre-Engineered-Runs