Footfall assessment settings

When you create a new model, global settings for footfall assessment are copied to the model file and become model specific settings applicable to the new model only.

To edit the global footfall settings: click Home > Settings > Footfall Assessment.
- Under each available design guide, the following settings pages are then provided:
  
  Analysis Settings, Analysis Model Options, Concrete Modification Factors and Footfall Checks.
To edit the model specific footfall settings: open a Footfall Analysis View and then click Footfall Analysis > Settings on the ribbon.
- The first model specific page is Settings Sets Management. Subsequent pages are then provided for the available design guides. Each design guide contains one (or more) settings set. Each settings set contains the following sub-pages: Analysis Settings, Analysis Model Options, Concrete Modification Factors.

Settings Set Management

Note: This page is only available in the model specific settings, not the global settings.

From the Design guide list, select the design guide containing the footfall settings sets you want to manage.

A table then lists the available settings sets for the selected design guide.

When a settings set is highlighted in the table, you can change its description by editing the Name field.
Click Add to create a new settings set. The following sub-pages are added beneath the new set in the left hand pane of the dialog:
- Analysis Settings
- Analysis Model Options
- Concrete Modification Factors
When a settings set is highlighted in the table, click Copy to duplicate it to a new settings set.
When a settings set is highlighted in the table, click Remove to remove it. If there is only one settings set it cannot be removed.

Locate the new set in the left hand pane of the dialog to edit its Analysis Settings, Analysis Model Options and Concrete Modification Factors as required.

Analysis Settings

Note: It is anticipated that most users will not need to adjust the default analysis settings.


Item	Description
Extraction Method	Allows you to select the appropriate extraction method for your model. The options are: Automatic (default option): Initially uses the Subspace option to find the lowest modes. If the criteria (either mass or number of modes) is not fulfilled, FEAST is then automatically used to find higher modes until the stopping criteria is fulfilled. Jacobi: An iterative transformation method used to calculate all eigenvalues and eigenvectors. Suitable for small models, but not for medium to large models. Subspace: An iterative simultaneous vector method to calculate the smallest eigenvalues and the corresponding eigenvectors. Suitable for quickly finding the lowest frequencies in medium to large models. FEAST: uses the FEAST algorithm to effectively calculate all the eigenvalues within a specific range. Suitable for any size structure. For more information, see: http://www.ecs.umass.edu/~polizzi/feast/.
Mass Model	Allows you to select how the mass model of the analysis is displayed. The options are: Consistent Lumped
Stopping Criteria	Stopping criteria prevent the analysis from continuing forever. If either of the criteria (Maximum number of modes or Stopping Frequency) are met, the analysis will not look for any more modes.
Modes	Allows you to select one of the following options: Automatic number of modes: If the option is selected, you must specify the mass participation required in each direction. You can optionally specify an initial number of modes that should be close to the actual number required in order to speed up the analysis process. Total number of modes: If Automatic number of modes is cleared, you can specify the total number of modes required. Note that sufficient modes are required to attain the Cut off frequency set in the FAM Footfall Checks properties (typically 20 Hz). With the default number of 100 it will be extremely unlikely modes above this target are not found. However for larger area models it may start to take several minutes to find 100 modes. Hence if analysis speed is felt to be an issue you can consider reducing the target number of modes. For small/normal sized FAMs speed will not be an issue and there is no need to reduce the default number. See also: Cut off frequency in the Footfall checks section below).
Jacobi (Only displayed for the Jacobi Extraction method)	Allows you to adjust the following settings: Maximum number of sweeps: A sweep is a transformation of every off-diagonal in the global matrices. The option allows you to set the maximum number of sweeps allowed. Sweep tolerance: At the end of each sweep, values are checked against the previous sweep results. If the difference is less than the tolerance specified here, the result is converged, and the analysis is complete.
Subspace	Allows you to adjust the following settings: Maximum number of iterations: The number of iterations to perform. Tolerance: At the end of each iteration, values are checked against the previous iteration results. If the difference is less than the tolerance specified here, the result is converged, and the analysis is complete.
FEAST	Allows you to adjust the following settings: Initial search range: Specifies the initial range of values FEAST will search for eigenvalues in. Overestimation multiplier: Specifies the initial guess for the subspace dimension within each range; an overestimate of the predicted number of modes in the range. Maximum modes in range: The maximum number of modes in the range. If more modes are found in a range, the range is split into several smaller ranges. Minimum search range: When a range is smaller than the value specified here, it will no longer be split, even if the maximum number of modes is greater than that allowed.

Analysis Model Options

The options given below generally relate to analysis model guidance in the guides, e.g. connections assumed to be pinned for static design may be assumed to be fixed for footfall assessment.


Column Modeling
Stack height and support	Full height with fixed support (default) Half height with pinned support
Modeled supports	Use fixed support (default) Use modeled support
Attached beam releases	Set to fixed (default) Use modeled releases


Wall Modeling (except bearing walls)
Modeled supports	Use fixed support (default) Use modeled support
Attached beam releases	Set to fixed (default) Use modeled releases


Beam Modeling
Max node spacing	Entered as a ratio of the member length (default 0.5) The purpose of this is to ensure that beam lengths with no meshed slab attached are subdivided to some degree.


Slabs
1-way slabs to be meshed	Select the slab types that are to be meshed in the FAM.
Effective Self Weight Mass from unmeshed slabs	Specified as a proportion (default 0.25)
Composite slab orthotropic properties	By default these are auto calculated based on the thickness, but user defined properties can be adopted if required.


Spandrel Beam Properties (AISC DG11 only)
Major axis stiffness multiplier	Any beams identified as spandrel beams have a multiplier applied to their major axis stiffness for the footfall modal analysis. The default multiplier is 2.5, as this is the value recommended in AISC DG11.

Concrete Modification Factors


Item	Description
modification factors table	These are modification factors specific to the Footfall assessment modal analysis for concrete entities (default for all = 1.0) Different factors can be applied in the model in order to adjust the following properties used in the footfall analysis: Young's modulus, E G: Shear modulus, G Section inertia about local X, I_torsion Section inertia about local Y, I_major Section inertia about local Z, I_{minor -} Section area in compression or tension, Area Section shear area in local Y, A_{parallel to minor} Section shear area in local Z, A_{parallel to major} Shell thickness, t If you make changes to any of the factors, footfall analysis must be repeated.
Factor for increased dynamic stiffness	This factor (default 1.1) is applied to the Young's modulus value for all concrete element types in addition to the E factors specified in the above table, (unless the below option to Use fixed dynamic modulus of elasticity is selected).
Use fixed dynamic modulus of elasticity	When this option is enabled you can specify the value to be used for all concrete entities regardless of their concrete grade (which will otherwise determine their E value). When this option is enabled the Factor for increased dynamic stiffness is not applied.

Footfall Checks (SCI P354)

Note: This page is only available in the global settings, not the model specific settings.

Each Floor Analysis Model (FAM) inherits these values from the global settings as it is created, the values can then be edited in the properties window for any selected FAM.

Refer to SCI P354 for further guidance.


Footfall Checks (SCI P354)
Item	Default	Range	Description
Cut off frequency	20 Hz	1-50	Frequency above which post processing calculations are not performed. Modes with frequencies above this value may be found (see Total number of modes in the Analysis Settings section above) but are not considered in the footfall calculation procedures. A warning is issued if this value is greater than the max modal frequency found. For guidance, refer to SCI P354 Table 6.1: Low frequency floor to high frequency floor cut-off
Consider all modes	On		When selected all modes below the Cut off frequency are considered.
No. of modes	10		This property is only displayed when Consider all modes is cleared. The Cut off frequency is ignored and the number of modes specified here are considered in the footfall post processing instead.
No. of harmonics	4	1 to 4	Not required for transient response.
Pacing frequency	1.80-2.20Hz@0.01	1 to 5Hz	Can be input as a single value or range and increment or series of values.
Walker's weight	76 (kg)	50 to 150 (kg)	Walker's weight.
Length of walking path	30 m	0.1 to 100m	Used in the resonance build up factor of resonant response and in VDV calculations for both resonant and transient response. Larger values result in conservative checks. If not known, provide a reasonable max value for best results.
Length of stride	0.75 m	0.1 to 2 m	Required for VDV
Damping ratio	3%	0 to 100%	The design guidelines provide recommended values of the damping ratio if more accurate values cannot be estimated. Refer to SCI P354 Table 4.1: Critical damping ratios for various floor types ζ
Axis of vibration perception	Z	X, Y, Z	In local coordinate system of the subject person. Only ‘Z’ is available in the current release.
BS 6841 weighting curve	Wb	Wb, Wd, Wg	The BS 6841 weighting curve used in the calculation of Weighting Factor, Wh, in resonant and transient responses.
Target vibration dose value (VDV)	0.2	0.1 to 2.0	The reciprocal of this value gives the number of times in a period that the target VDV is exceeded.
Consider VDV for Pass/Fail	Off		When selected, the pass/fail threshold is determined by the Target number of events in a period.
Target number of events in a period	1000	1 to 1000000	Defines the pass/fail threshold when ConsiderVDV for Pass/Fail is selected.
Target response factor, Rf	4	0 to 100	Unless Consider VDV for Pass/Fail is selected, the pass/fail threshold is determined by this value.
Acceptable hotspots	Off		When selected a General limit, Rf value (default 2.0) is set. Regions with Rf values between the general and upper limits will be given a warning status.

Footfall Checks (CCIP-016)

Note: This page is only available in the global settings, not the model specific settings.

Each Floor Analysis Model (FAM) inherits these values from the global settings as it is created, the values can then be edited in the properties window for any selected FAM.

Refer to CCIP-016 for further guidance.


Footfall Checks (CCIP-016)
Item	Default	Range	Description
Cut off frequency	20 Hz	1-50	Frequency above which post processing calculations are not performed. Modes with frequencies above this value may be found (see Total number of modes in the Analysis Settings section above) but are not considered in the footfall calculation procedures. A warning is issued if this value is greater than the max modal frequency found.
Consider all modes	On		When selected all modes below the Cut off frequency are considered.
No. of modes	10		This property is only displayed when Consider all modes is cleared. The Cut off frequency is ignored and the number of modes specified here are considered in the footfall post processing instead.
No. of harmonics	4	1 to 4	Not required for transient response.
Pacing frequency	1.80-2.20Hz@0.01	1 to 5Hz	Can be input as a single value or range and increment or series of values.
Walker's weight	76 (kg)	50 to 150 (kg)	Walker's weight.
Length of walking path	30 m	0.1 to 100m	Used in the resonance build up factor of resonant response and in VDV calculations for both resonant and transient response. Larger values result in conservative checks. If not known, provide a reasonable max value for best results.
Length of stride	0.75 m	0.1 to 2 m	Required for VDV
Damping ratio	3%	0 to 100%	The design guidelines provide recommended values of the damping ratio if more accurate values cannot be estimated. Refer to Appendix A of CCIP-016 for suggested damping values for different structures.
Axis of vibration perception	Z	X, Y, Z	In local coordinate system of the subject person. Only ‘Z’ is available in the current release.
Target vibration dose value (VDV)	0.2	0.1 to 2.0	The reciprocal of this value gives the number of times in a period that the target VDV is exceeded.
Consider VDV for Pass/Fail	Off		When selected, the pass/fail threshold is determined by the Target number of events in a period.
Target number of events in a period	1000	1 to 1000000	Defines the pass/fail threshold when ConsiderVDV for Pass/Fail is selected.
Target response factor, Rf	4	0 to 100	Unless Consider VDV for Pass/Fail is selected, the pass/fail threshold is determined by this value.
Acceptable hotspots	Off		When selected a General limit, Rf value (default 2.0) is set. Regions with Rf values between the general and upper limits will be given a warning status.

Footfall Checks (AISC DG11)

Note: This page is only available in the global settings, not the model specific settings.

Each Floor Analysis Model (FAM) inherits these values from the global settings as it is created, the values can then be edited in the properties window for any selected FAM.

Refer to AISC DG11 for further guidance.


Footfall Checks (AISC DG11)
Item	Default	Range	Description
Cut off frequency	20 Hz	1-50	Frequency above which post processing calculations are not performed. Modes with frequencies above this value may be found (see Total number of modes in the Analysis Settings section above) but are not considered in the footfall calculation procedures. A warning is issued if this value is greater than the max modal frequency found.
Consider all modes	On		When working to AISC DG11 this option can not be cleared.
Walker's weight	0.084 ton (US) 76 kg (metric)	0.055 to 0.165 ton 50 to 150 kg	Walker's weight.
Damping ratio	3%	0 to 100%	The damping ratio can be estimated using the component values in DG1 Table 4-2 if more accurate values are not available.
Axis of vibration perception	Z	X, Y, Z	In local coordinate system of the subject person. Only ‘Z’ is available in the current release.
Fig. 2-1 AISC DG11	Curve A	A, B , C	When determining the pass/fail status at a given node, the calculated peak acceleration at the dominant frequency is compared to the limiting peak acceleration obtained from the selected curve.