How to use the bracing member force calculator
A brace turns the story shear from wind or seismic load into an axial force and carries it down to the foundation. Enter the lateral load that one braced bay resists along with the bay width and story height, and the calculator returns the brace angle, work point length, axial force, the vertical component delivered into the column, and the required area for tensile yielding.
The angle drives everything. Axial force equals the lateral load divided by the cosine of the brace angle, so a steep brace sees a larger axial force and pushes a larger vertical component into the column. A shallow brace lowers the axial force but becomes long and slender. Most braced frames end up between 30 and 55 degrees from horizontal.
X-bracing changes the answer by a factor of two. Slender tension-only diagonals buckle out on the compression side, so the tension diagonal alone takes the full story shear. Only when both diagonals are designed as compression members do they share the load.
The required area shown covers gross section tensile yielding with a resistance factor of 0.90. Compression buckling, net section rupture at bolt holes, block shear, gusset plate design and weld sizing all remain, so have a licensed structural engineer confirm the member before the design is finalized.
Frequently asked questions
A brace carries load only along its axis, so the axial force equals the lateral load divided by the cosine of the angle. A shallow angle gives a smaller axial force but a longer member with a worse slenderness ratio, while a steep angle raises both the axial force and the vertical component delivered to the column.
Only if both are designed to act in compression. Slender tension-only rods or angles buckle out on the compression side, so the tension diagonal alone carries the full story shear. Pick the matching option before reading the result.
No. The value shown covers gross section tensile yielding per AISC 360 only. Compression buckling, net section rupture at bolt holes, block shear, and the gusset plate and weld design are separate checks, so have a licensed structural engineer confirm the member.