ENGINEERING – TRUCTURAL ENGINEERING — TEEL CALCULATOR
Bracing Frame Drift
A precise tool.
What is the Bracing Frame Drift & How does it work?
Lateral drift in steel braced frames governs the serviceability of a structure. Excessive story drift can cause non‑structural damage, affect occupant comfort, and lead to code violations. Engineers therefore limit drift to a fraction of the story height, typically 0.5 % to 1 % depending on the occupancy and design standards.
A braced frame resists horizontal forces through a combination of beam‑column joints and diagonal or X‑braces. The overall lateral stiffness of the system is the sum of the stiffness contributed by each brace in every story. By approximating each brace as a linear spring, the total stiffness can be expressed as the product of brace stiffness and the number of stories, assuming similar geometry and material properties throughout the height.
The computed drift is then compared to the allowable drift limit, (Delta_{allow}), prescribed by the relevant code. If (Delta le Delta_{allow}), the braced frame satisfies the serviceability requirement; otherwise, the designer must increase stiffness, add additional bracing, or reduce the applied loads.
\Delta = \frac{P ; h}{K ; n}
Delta = story drift (in)
P = applied lateral load (kN)
h = story height (in)
K = brace stiffness (kN/in)
n = number of stories
P = applied lateral load (kN)
h = story height (in)
K = brace stiffness (kN/in)
n = number of stories
Parameters
Result
—
Frequently Asked Questions
What is the typical allowed story drift percentage?
The typical allowed story drift percentage ranges from 0.5% to 1%, depending on occupancy and design standards.
How does a braced frame resist horizontal forces?
A braced frame resists horizontal forces through beam-column joints and diagonal or X-braces.
What factors affect the overall lateral stiffness of a braced frame?
The overall lateral stiffness is influenced by the design and material properties of the beams, columns, and braces.
Why is it important to limit story drift in steel braced frames?
Excessive story drift can cause non-structural damage, affect occupant comfort, and lead to code violations.
How do engineers calculate the lateral drift of a braced frame?
Engineers use specific formulas considering factors like load, stiffness, and geometry to calculate lateral drift.
What are the consequences of exceeding the allowed story drift limit?
Exceeding the limit can result in structural damage, reduced occupant comfort, and potential code non-compliance.
Can you explain the role of diagonal braces in a braced frame?
Diagonal braces provide additional lateral stiffness and help distribute loads more effectively within the frame.
Results are for informational purposes only and do not constitute professional advice.