Oasys GSA Documentation

# Analysis Wizard : Footfall Analysis

This page defines the analysis parameters. If no modal dynamic analysis results are present, this option is disabled and this page cannot be opened.

# Definition

Modal analysis task

If more than one set of modal dynamic analysis results exist it needs to know which set of results are to be used. If only one modal dynamic analysis task is available, it will be used by the analysis.

Excitation Method

  1. Self excitation - the excitation node will be the same as response node, i.e. only excite the response node itself for obtaining its response (maximum response may be missed)
  2. Full excitation - Rigorous - excite all the specified excitation nodes for each of the response nodes. For a large model, this will take very long time for the analysis to complete.
  3. Full excitation - Rigorous (exclude response node) - excite all the specified excitation nodes for each of the response nodes but exclude the response node. For a large model, this will take very long time for the analysis to complete.
  4. Full excitation - Fast - use search technique to determine the nodes to be excited for each of the response nodes in order to reduce the computing time (maximum response may be missed, but better than self excitation)

Response Nodes

Node list to define the nodes that the responses will be calculated in the analysis. Responses will not be available if the nodes are not included in the response node list.

Excitation Nodes

Node list to define the nodes that will be excited for evaluation of the response of the response nodes. If search technique is used, only a selection of the nodes, that will generate large response at the response nodes according to search technique, will be excited to evaluate the responses of the response nodes. If self excitation method is used, the definition of excitation nodes is not required, so it will be greyed out.

Number of Footfalls

The number of footfalls to be considered in the analysis.

Walker (mass or weight)

The mass/weight representing a sample walker

Direction of Responses

The direction of response in the GSA global axis direction. It can be in Z (vertical), X, Y or XY plane (horizontal). Note that it is the response direction in GSA global axis, not the Basicentric axes of the human body described in BS6472 and BS6841.

Frequency weighting curve

The Frequency Weighting Curve (FWC) is used in calculating the response factors. Standard and user defined curves can be used.

The following standard frequency weighting curves are available in GSA: , and . These weightings are defined in BS 6841:1987, a document which also describes how they might be applied to comfort, perception, health and so on. These defined weightings have been adopted and applied in various ways in other subsequent BS documents, as summarised below in the case of the assessment of human exposure to vibration in buildings.

  • Wg is the weighting adopted in BS6472:1992 for the assessment of human exposure to vertical vibrations in buildings. It is presented as a base curve with a multiplier corresponding to the response factor metric in the frequency range 1-80 Hz. The horizontal weighting is also presented as a base curve which is similar to the Wd weighting and is shown in the frequency range 1-100 Hz.
  • Wb is the weighting specified in BS6472-1:2008 for the assessment of human exposure to vertical vibration in buildings; Wd is the corresponding weighting for horizontal vibration. The weighting functions are presented in the form of charts showing the weighting curves in the frequency range 0.1 to 100 Hz.

Excitation forces (DLFs)

This defines the way of the structure to be excited (the dynamic Load Factor to be used). The options are:

  • Walking on floor (AISC SDGS11) – AISC Steel Design Guide Series, Floor Vibration Due to Human Activity.
  • Walking on floor (AISC SDGS11 2nd ed) – AISC Steel Design Guide Series, Floor Vibration Due to Human Activity.
  • Walking on floor (CCIP-016) – Arup method.
  • Walking on floor (SCI P354) – SCI P354 – Design of Floors for Vibration: A New Approach.
  • Walking on stair (AISC SDGS11 2nd ed) – AISC Steel Design Guide Series, Floor Vibration Due to Human Activity.
  • Walking on stairs (Arup) – Arup method.
  • Walking on stairs (SCI P354) – SCI P354 – Design of Floors for Vibration: A New Approach. method is used.
  • Running on floor (AISC SDGS11 2nd ed) – AISC Steel Design Guide Series, Floor Vibration Due to Human Activity.
  • User defined Dynamic Load Factor – from the ‘Dynamic Load Factor’ table

Walking Frequency

Defines the range (minimum & maximum) of walking frequencies to be considered in the analysis.

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