Bracing Systems
Wall Bracing for Pre-Engineered Steel Buildings
Definition: Wall bracing is a system of diagonal rods, cables or angles in the side or endwall bays of a steel building. It carries longitudinal forces collected by the roof bracing down to the foundations and keeps the frames aligned during and after erection.
Key facts
- Commonly X-bracing with rods or cables in selected bays.
- Braced bays usually match roof braced bays.
- Base reactions include uplift and shear that the foundation must resist.
- Openings in braced bays may need portal bracing instead.
- Endwall bracing is used where endwalls are post-and-beam.
Role in the structure
Roof bracing delivers forces to the eave line. The side wall bracing then carries them diagonally down to the base of the columns, where they are resisted by the anchor bolts and foundations. Endwall bracing performs a similar role for forces across the building in post-and-beam endwalls.
How do longitudinal forces reach the ground?
The roof bracing truss delivers forces to the eave strut at braced bays. The wall diagonals carry the force down to the column bases, while the columns act as the truss verticals.
At the bases, anchor bolts and foundations resist the horizontal shear and the vertical uplift or compression generated by the bracing. The foundation engineer uses these reactions.
What about doors in braced bays?
Diagonals block openings. If a braced bay must contain a door, the bracing can be moved to another bay, split into higher bracing above the door, or replaced with portal bracing.
Planning door positions early helps the engineer place bracing where it does not interfere with operations.
When is endwall bracing used?
In post-and-beam endwalls, wind across the building is resisted by the side frames and the endwall bracing working together. Diagonals in the endwall carry forces to the foundation.
Rigid-frame endwalls do not normally need endwall diagonals because the frame resists lateral loads itself.
How many braced bays does a building need?
Short buildings often need only one braced bay in each side wall, usually at or near the ends. Longer buildings, buildings with cranes and buildings in high seismic or wind regions commonly need more, so that forces do not have to travel too far along the eave strut.
Where an expansion joint divides a long building, each part is braced on its own. The number and position of braced bays are decided by the project engineer to the governing code and shown on the erection drawings.
Does wall bracing affect cladding and finishes?
Rods and cables sit inside the girt line, so they are normally hidden behind the wall panels or a liner. Where walls are exposed internally, the bracing remains visible and can be painted to match the frame.
Bracing must not be fixed to or pierced by services, and racking or partitions should be kept clear of the diagonals so that they stay taut and effective.
Materials & coatings
- Threaded steel rods with hillside washers and nuts.
- Galvanized steel cables with fittings.
- Angles or hollow sections for compression bracing.
Design considerations
- Longitudinal wind and seismic forces.
- Location of braced bays relative to doors.
- Base reactions for foundation design.
- Crane longitudinal forces.
- Seismic system requirements.
Fabrication
- Cut and thread rods or prepare cables.
- Punch column webs or flanges for bracing.
- Supply hillside washers and nuts.
Erection
- Install wall bracing with roof bracing in the first bay.
- Use bracing to plumb the frames.
- Retain temporary bracing until permanent bracing is complete.
Inspection & quality
- Check all diagonals are present and tight.
- Verify base connections and anchor bolts in braced bays.
- Check frames are plumb along the length.
What to include in your RFQ
- Door and opening positions along side walls.
- Bays where bracing is not acceptable.
- Seismic and wind data.
3D model & IFC of this component
Rotate the model, isolate the component and download its IFC4 file for your BIM coordination model.
IFC entity: IfcMember (BRACE). Illustrative geometry for coordination and learning. Final member sizes come from the project design.
Frequently Asked Questions
Can bracing go behind racking?
Yes, if racking does not attach to or interfere with the diagonals.
Why do braced bay foundations get extra load?
Bracing reactions add shear and uplift at those columns.
Can I remove a diagonal temporarily?
Not without engineering review and an approved temporary bracing plan.
Engineering content is general guidance. Every World Steel building is designed by qualified engineers to the code and loads of the project.
