Modern buildings with lightweight floors and open-plan layouts are more prone to footfall-induced vibration, especially when using sustainable materials like cross-laminated timber (CLT). Accurate footfall analysis is essential to ensure comfort, performance, and reliability, as clients expect quiet, stable spaces.
Figure 1 - Maximum response factor contours across a floor.
Effective analysis demonstrates that your design will perform as intended, supporting both quality and comfort without compromising cost or sustainability.
Step 1. Build a robust model
Capture enough of the structure to reflect its dynamic behaviour, including adjacent elements that affect stiffness. Avoid conservative static assumptions and select appropriate material properties.
The footfall design guides recommend using the instantaneous Young’s modulus for concrete, normally 10-20% higher than the long-term value used in static analysis. For profiled slabs or CLT, define orthotropic properties based on manufacturer data or industry guidance. And for composite floors, capture composite action by using effective stiffness, correct mass distribution, and realistic connection assumptions.
Boundary conditions significantly affect analysis; for slabs, CLT, or precast planks, confirm panel support and fixity where relevant. Also, adjust for overlapping self-weight in slabs and beams to ensure accurate mass distribution.
Step 2. Perform a modal analysis
When defining the loads for your modal analysis, ensure only a small percentage, for example 10% of non-permanent loads like superimposed or live are considered in your modal analysis. Likewise, to cover all sensitive cases, the number of modes should cover all frequencies up to 10 - 15 Hz. Validate modal shapes visually and numerically to ensure realistic dynamic behaviour. Then progress to defining your footfall analysis task.
Figure 2 – Modal shape and undeformed meshed geometry of a floor.
Step 3. Define the right footfall analysis parameters
Table 1 - Guidance for defining footfall analysis tasks.
Step 4. Interpret your results correctly
Both resonant and transient response factors, derived from frequency-weighted RMS (Root Mean Square) acceleration, tend to be the key metric, though velocities and accelerations may also be relevant.
Compare your results against comfort criteria in Steel Construction Institute or Concrete Centre guidance, ISO 10137, or relevant guidance for your project and region.
Figure 3 – Transient (top) and resonant (bottom) response factor contours.
Step 5. Refine and iterate
If your results are unsatisfactory, refine your structure, loading or analysis parameters.
Choosing the right footfall analysis tool
While the principles apply universally, software can make or break your workflow and confidence in the results. Oasys GSA streamlines footfall analysis, offering powerful excitation methods, standard frequency weighting, default code-based forces, and flexible damping, all in one intuitive environment..
Figure 4 – Footfall analysis wizard overview in Oasys GSA.
GSA provides with powerful visualisation tools like results contours, deformed shapes, annotated diagrams, charts or tables to help you interpret and verify your analysis with confidence.
Figure 5 – Example footfall analysis results charts in Oasys GSA.
GSA seamlessly connects
with Grasshopper to help you easily build models, define footfall analyses, run them, and extract, post-process and generate custom views of the results.
References