Calculate roof-level seismic wall-tie tension demand and compare it with a headed or L-bolt tension capacity. The model uses a horizontal pair of anchors, with one-half of the increased pair force assigned to each holdown. Wall tie anchors do not carry gravity loads in this module.
Quick start
- Select ASD or LRFD and the headed or L-bolt anchor type.
- Select bolt diameter and enter embedment, bolt spacing, masonry strength, and steel yield and tensile strengths. Enter the leg length eb for an L bolt.
- Enter wall height H1 and parapet height H2 in feet, wall weight in psf, Sds, Ka, and Ie.
- Enter wall-tie spacing in inches. This is the spacing between tie assemblies, separate from spacing between the two anchor bolts.
- Run the model and review both Anchor Bolt Calculations and Wall Tie Calculations, then the demand/capacity summary.
Wall-tie demand
The program calculates pressure as the greatest of 0.4 × Sds × Ka × Ie × Wp, 0.2 × Ka × Ie × Wp, and 5 psf. Wp is the wall weight per square foot entered on the form.
The tributary height is H2 + H1/2. Pressure multiplied by this height and tie spacing/12 gives the LRFD force at a tie assembly. The module applies a 1.4 increase and divides by two to obtain the required force per holdown. ASD force is 0.7 times the LRFD force. Ka is an input; it is not derived from a diaphragm span in this module.
Anchor capacity and spacing
Supported bolt diameters are 1/2, 5/8, 3/4, 7/8, and 1 inch. The program uses the corresponding threaded areas 0.142, 0.226, 0.334, 0.462, and 0.606 in², rather than the gross circular area. Steel tensile strength used in the calculation is limited to the least of Fu, 1.9Fy, and 125,000 psi.
Effective embedment lb equals entered embedment for headed bolts and entered embedment minus bolt diameter for L bolts. The calculation checks lb against max(4d, 2 in) and clear spacing s − d against max(d, 1 in). Invalid dimensions stop the calculation.
For the two-bolt pair, overlapping tension projection reduces the area assigned to each bolt by one circular segment. When s is at least 2lb there is no overlap, and the program uses πlb² without the overlap calculations.
The governing tension capacity is the least applicable masonry breakout, steel tension, and L-bolt pullout capacity. Pullout is excluded for headed bolts. Shear capacity and tension/shear interaction are not calculated.
Results, diagrams, and reports
The summary compares force per holdown with anchor capacity on the selected ASD or LRFD basis and reports the D/C ratio. Green indicates an acceptable ratio and red indicates failure. LRFD output includes the reminder to obtain LRFD holdown values from the manufacturer catalog; the module does not select a proprietary holdown.
Click a diagram to open an enlarged, nonmodal view. Press Escape while that diagram window has focus to close it. The printed report includes design criteria, anchor capacities, required holdown capacity, detailed calculations, and diagrams.
The anchor model assumes side-face installation away from wall ends and openings and does not calculate edge-truncated projected areas. It does not check top-of-wall anchors, wall adequacy, or the remainder of the diaphragm connection.