What it checks
The module designs tension hairpins at the column bases of a metal building. It calculates the force in each leg based on the factored horizontal thrust and the leg angle. The design method uses strength design with a tension steel phi of 0.90.
The sequence of checks determines the minimum number of hairpins required to carry the thrust. It verifies that the leg capacity exceeds the leg force. The module then calculates the required lap length for the Class B lap with the slab bars, considering whether the hairpin acts as a top bar in a thick slab.
Inputs
- Thrust - Factored horizontal thrust at one column base (kips).
- Geometry - Hairpin bar size (No. 3 to No. 11), number of hairpins (0 for fewest), leg angle from line of thrust (degrees), and inside width of the U (in).
- Spacing - Centre-to-centre spacing of adjacent hairpins (in) and spacing of the slab bars being lapped (in).
- Depth - Depth of the hairpin bar centre below the slab top (in).
What it reports
- Leg Force - Force in one leg (kips), compared against the leg capacity.
- Leg Capacity - phi Ab fy of one leg (kips).
- Required Lap - Required lap of a leg with the slab bars (in), based on Class B requirements.
- Leg Length - Leg length along its axis (in) and the value rounded to the next whole inch for the drawing.
- Projection - Projection of a leg on the line of thrust (in).
- Sideways Run - Sideways run of a leg (in).
- Bend Diameter - Inside bend diameter used (in), which is not less than 6 db.
- Overall Length - Overall length of a hairpin from the back of the bend to the leg tips (in).
- Tip Width - Distance between the two leg centrelines at the tips (in).
- Slab Bars - Number of slab bars to lap with each leg so the slab bars can carry the leg force.
Code references
The engine cites ACI 318-19 §25.4 and §25.5.2 for the Class B lap with the slab bars. It applies a tension steel phi of 0.90. The inside bend diameter is referenced to Table 25.3.1, ensuring it is not less than 6 db.
Limits
The module assumes the frame pushes each column base outward and that the slab-on-grade building carries that thrust in the slab. It does not design the anchor bolts or the slab reinforcement independently, only the hairpins and their lap. Results are engineering aids; the engineer of record is responsible for the design.