How to Use Footfall Analysis

Footfall Analysis#

Footfall Analysis calculates the vibration of a storey drawn in one of the project's models. The macro does not draw geometry. Columns, walls, beams, slabs, loads and equipment are drawn on the project's Models tab, and the calculation takes a storey from that model. In the macro you define the guide, the activity, the assessment criteria and the walking or receiver areas.

The details of the method are on the Footfall Analysis page, and the tests of the calculation against the guides' worked examples and other programs are on the verification page.

First analysis#

The steps below are enough to check walking vibration on an office storey whose model is ready.

1. Choose Footfall Analysis in the Calculation Gallery and add it to your project with Start Calculation.
2. Use Pick a Model in the command bar to choose the model the storey is drawn in, and press Use. When the model has more than one storey with a slab, choose the storey to analyse from the Analysis target list in the command bar.
3. In the inspector on the right, choose SCI P354, CCIP-016 or AISC DG11 as the Guide.
4. In the Floor section, choose the row of Damping class that matches the state of the floor.
5. In the Whole-floor criteria section, choose Office as the Room type. This fills the limit and the weighting curve.
6. Press Analyze. When the analysis finishes, the Results view becomes available, and the summary strip shows the worst value of the storey with the verdict PASSED or FAILED.

In this flow a person walks at every point of the storey, and each point is read while it is walked on. Areas are drawn to limit walking to particular places such as a corridor, or to assess part of the storey against its own criterion (Areas).

Creating the calculation and picking a model#

A new calculation has no geometry. The Floor Plan view is empty in that case, and the status bar reads No floor plan.

The Pick a Model window lists the project's models with their names and update dates. Pressing Use takes a copy of the model into the calculation, and the model's name appears in the command bar. The calculation works with this copy. Later changes to the model do not pass into the calculation by themselves.

When the current geometry is taken, the calculation's plan changes and the stored result is no longer current. The analysis has to be run again. When the source model has been deleted, the calculation continues with its own copy of the geometry.

The analysed storey is chosen from the Analysis target list in the command bar or from the model tree in the Floor Plan view. The list appears only when the model has more than one analysis target (a storey with a slab or a stair). Only the areas of the analysed storey enter the calculation. Analysing a stair is described under Stair analysis.

Screen layout#

The screen has four parts.

• Command bar. The Analysis target list, the model controls, Analyze, Analysis Settings, Report, the view switch and the full-screen button.
• Views. Floor Plan, Results and Finite Element Model. The last two open when there is a result. A red dot beside the Results label shows an area that fails its criterion, and an amber dot shows warnings only.
• Inspector. On the right in the Floor Plan view. It shows the properties of the selected area, or the calculation's inputs when no area is selected. The area list sits at the bottom of the inspector.
• Status bar. Shows the state of the analysis, the numbers of nodes and shell elements, the fundamental frequency, the number of modes, the floor classification and the guide. When a problem blocks the analysis, a red Problems cell appears, and pressing it lists the problems.

The floor plan of the footfall calculation is read-only. Selecting an element and right-clicking it opens the Properties panel, which shows the element's card from the model editor in reading mode.

Most inputs carry an information icon. Its window explains what the input is, its options and its counterpart in the guide, for the guide currently chosen.

Guide and facade#

The Guide sets the finite element model as well as the method. The length of the column and wall extensions, the modulus of elasticity of concrete and the facade condition depend on the guide. The details are in the Floor model section of the method page.

When the guide is changed, every value the new guide does not have returns to that guide's default.

A result computed under another guide is not shown. The status bar reads Guide changed, and the Results and Finite Element Model views close. When the previous guide is chosen again, the result reappears.

The Facade option takes the values Not modelled and On the outer outline, and is off by default. When it is on, the guide's condition for the outer edge is applied to the building's outer outline.

Activity and excitation#

The Activity list offers the activities the chosen guide covers.

When you leave an activity, its inputs are kept but not sent. When you return to the same activity, the inputs come back.

The Excitation sets where the source of the vibration is.

Depending on the activity, the inspector shows the following inputs.

When Rotating machines is chosen, the inspector lists the machines on the analysed storey with their names and speeds. Machines are defined on the equipment card in the model, not on this screen (Rotating machines).

Floor#

The Damping ratio can also be typed and must lie between 0 and 0.20. For a typed value the damping class shows Entered by hand. The form's default is 0.03.

Whole-floor criteria#

This section sets the criterion the whole storey is assessed against.

When a room type is chosen, the limit field shows the room type's value as a placeholder. A value typed into the field replaces the room type's value. When neither a room type nor a limit is given, the result is reported without an assessment.

Areas#

Areas are drawn in the Floor Plan view with the buttons the macro adds to the tool rail on the left of the plan. The plan is read-only on this screen. Only areas can be drawn and edited.

To draw an area, click its corners in turn. The polygon closes with the Enter key or a right click. The new area is selected at once and gets a name such as "Area 1". Corners are moved by dragging. The selected area is deleted with the Delete key or with Delete area on its card. Areas are stored in the calculation, not in the model.

When an area is selected, the inspector shows the area's card.

• Walking area. Name and Path length. The path length limits the resonant response that builds up as a person walks along the area, and it is needed for the vibration dose value. This input does not appear for rhythmic activity or under AISC DG11.
• Receiver area. Name and the room type, weighting curve, limit, VDV limit and exposure inputs of the Whole-floor criteria section. An input left blank is taken from the room type.

A receiver area takes the elements it touches in full. When the outline of the area crosses the middle of an element, all nodes of that element enter the assessment. A walking area takes the nodes inside it and on its outline.

Partitions#

Counting the stiffness of partitions takes two steps. Whether a wall stays is a fact about the building and is entered in the model editor. Whether the calculation uses it is chosen in the footfall calculation.

1. In the model editor, select the partition and turn on Permanent wall on its card. The switch appears only on full-height walls. The top of the wall must reach the underside of the beam or slab above it.
2. On the same card, below the masonry unit, give the modulus of elasticity of the wall's material. The value applies to every wall of the same masonry unit.
3. In the footfall calculation, if the model has been updated, choose Take the Newer Geometry from the yellow icon in the command bar.
4. In the Guide section of the inspector, set Partitions to Stiffness of permanent walls and run the analysis.

The walls under the slab are drawn on the storey below and enter the calculation when their tops reach the analysed slab. When the material of a permanent wall has no modulus of elasticity, the analysis does not start and the problems list names the wall. The result notes say how many walls were modelled as shells and how many as springs.

Rotating machines#

A machine is defined on the card of a piece of equipment in the model. To open the equipment card, go to the model's page with Edit Model and select the equipment on the plan.

1. Turn on the Rotating machine switch on the card.
2. Give the Running speed in rpm, or choose it from the Poles table. For a variable-speed machine the Lowest speed is also given, and the analysis sweeps between the two speeds.
3. Choose Force from and give the values asked for.
4. When the machine stands on isolators, choose the Isolation method and give the isolator values.

The isolators are defined by their Static deflection or their Isolator frequency, and the Isolator damping must be given. When the static deflection is given, the isolator frequency is shown on the card as a calculated value.

The Manufacturers' catalogue opens from the Catalogue row of the card. The catalogue can be filtered by equipment type and manufacturer, and each row links to the manufacturer's own document. Choosing a row fills the equipment's weight, height and footprint. A row with force data makes the equipment a rotating machine and fills the force source.

Analysis settings#

The Analysis Settings window holds the settings made once per calculation. Values take effect as they are typed, and the window closes with Close.

Running the analysis#

When Analyze is pressed, the storey is sent to the solver on the server. The button's label becomes Submitting, Queued and Solving in turn. While the analysis runs the inputs are locked, and the previous result stays on screen.

The analysis continues on the server even if you leave the page. When you open the calculation again, the result of the finished analysis is taken, and the status bar reads Finished in background. An analysis cannot be stopped from inside the macro. A running analysis is stopped from the My Analyses page.

When a problem blocks the analysis, the Analyze button is disabled and the Problems cell in the status bar lists the problems. The most common ones are these.

When the server refuses the analysis, a red cell opens in the status bar. Its window lists the reason for the refusal and the suggested remedy as findings, and contains the Try again button.

Reading the results#

The Results view is a single document with a contents list on the left. The summary strip at the top shows the fundamental frequency, the floor classification, the value at the governing point, the governing area with its limit, the governing frequency and the verdict PASSED or FAILED.

Pressing an area's row in the Areas table switches the charts to the worst point of that area.

Finite element model#

The Finite Element Model view shows the model solved in the analysis in three dimensions. The model is downloaded from the server the first time the view opens.

• Mode shapes. The shape of each mode is shown with its frequency and animated with Play.
• Whole-floor maps. The response factor, the resonant and transient response factors, the governing frequency and the governing analysis. Under AISC DG11 the same maps are drawn in %g, and in sensitive-equipment areas as band velocity.
• Area maps. A separate map for each assessed area. The area's limit appears as a step in the colour scale, and the colours change at quarters of the limit.

The map of a response that was not calculated is not shown. For example, a high-frequency floor has no resonant map. Clicking a node lists every result at that node on a card. The Find tool locates a node, frame element or shell element by its number.

The model's visual data is removed from the server after some time. The numerical results then stay in the calculation, and the analysis has to be run again to see the model.

Calculation steps, report and publishing#

The Calculation steps are the last section of the Results view and are produced in every analysis. The steps go from the model's geometry and the vibrating mass through the modes, the classification, the load and the excitation to each area's response and assessment, with their formulas and numerical values. Only the steps of the methods that ran in the analysis are shown.

The Report button is enabled when there is a result, and produces the Floor Vibration Report as a PDF. The report contains, in order:

1. Verdict heading and summary
2. Areas and assessment
3. Floor plan with the assessed areas, and one plan for each load pattern
4. Result maps and the first mode shape
5. Vibration dose
6. Solution and the table of modes
7. Graphs at the governing point
8. Analysis notes and warnings
9. Detailed calculation steps
10. Scope statement

The report is produced from the stored result. For the result maps the model is fetched from the server when the report is produced. When the model's visual data has been removed, the report is produced without maps.

Publish in the page toolbar makes an unchanging copy of the calculation shareable. The published copy contains the results, the inputs, the areas, the floor plan and the interactive finite element model, and recalculates nothing.

Stair analysis#

Analysis target#

When the model has stairs, the Analysis target list in the command bar is split into two groups, Storeys and Stairs. Each stair is listed by name with the levels it runs between (for example "M1 · Ground → 1st floor"). Choosing a stair shows the storey it arrives at in the Floor Plan view. Choosing a storey from the list, or moving to another storey in the model tree, makes the target a floor again.

The stair's model, its bearings and the two guides' stair rules are described on the Footfall Analysis page.

Inputs#

For a stair target the Excitation section, the areas list, the facade, the partitions, the floor type and the Whole-floor criteria section are not shown. CCIP-016 cannot be chosen in the guide list. A Stair section takes the place of the Floor section.

The damping ratio is entered as for a floor. The Welded steel row of SCI P354's damping table is for fully welded steel structures such as stairs. The stair's loads become mass through the mass source in Analysis Settings. The mesh settings do not apply to a stair.

The stair card's warnings, such as a landing that bears on nothing, are shown above the Stair section and do not block the analysis. Problems that block it are listed in the Problems cell of the status bar.

Results#

The summary strip of the Results view shows the fundamental frequency, the response factor $R$ under SCI P354 or the peak acceleration of the descent nearest its limit under AISC DG11, the limit, and PASSED or FAILED.

Points are named by flight, landing and tread (for example "Flight 1, tread 5" or "Landing 1, node 123"). A spiral stair counts as one flight.

The Finite Element Model view has the stair's mode shapes and its result maps under Stair. On the SCI P354 map each tread's $R$ is drawn over all of the tread's nodes and each landing node's value at itself, so the map's largest value is the reported $R$. The AISC DG11 map shows, with the walker where the rule places them, the peak acceleration of the descent nearest its limit at every point, in %g.

Report produces the Stair Vibration Report as a PDF. In order, it contains:

1. Verdict banner and summary
2. Stair assessment
3. Result map and first mode shape
4. Solution and mode table
5. Graphs at the governing point
6. Analysis notes and warnings
7. Detailed calculation steps
8. Scope statement

When results go out of date#

Each result stores a signature of the inputs it was produced from. When the storey, mass source, mesh, guide, activity, areas or criteria change, the result on screen no longer belongs to those inputs. The status bar reads Results out of date, and the analysis has to be run again to update the result.

• Changing an input that the chosen activity or guide does not use does not make the result out of date.
• Changing the interface language does not make the result out of date.
• A calculation saved with an out-of-date result does not store the result.
• When the guide is changed, the result is hidden, and it reappears when the previous guide is chosen again.
• When the model is updated, the result belongs to the calculation's own copy of the geometry until the newer geometry is taken.