The next step is to run the Building Analysis with the Eigenvalue Analysis option also ticked, as shown below. These setting adjustments will have a big impact on the calculated periods, so must be applied appropriately. Before running the Building Analysis, you must ensure that you have already adjusted the Stiffnesses and the Live Load Participation Factor as discussed previously. This can be done by going to Building > Parameters > Lateral Loading > Live Load Participation Factor (n), as shown below.ġ.5 Determine the Fundamental Periods In Orion, the Fundamental Periods of the building can be determined using the Eigenvalue Analysis option within the Building Analysis. You then need to apply the derived value to your Orion model. This factor can be determined by referring to UBC97 1630.1.4. However, the simpler guidance is to use the same adjustment factor (typically 1.0) in all member types.Īpplying UBC97 Seismic Loads to an Orion model Adjust the Live Load Participation Factorġ.4 Adjust the Live Load Participation Factor Another important value that needs to be defined is the Live Load Participation Factor, which controls the storey mass to be considered in the Eigenvalue Analysis, and hence affects the frequencies determined. For design to the British Standards, then if you believe that the adjustments make a reasonable allowance for the creep/cracking in each member type, then there is no reason not to use them.
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In terms of design, if you were designing to the American codes, then you would use the adjustment factors suggested by the design code (which would be the same/similar). The cracked/un-cracked status of the columns and walls is up to you to determineįor further guidance on the stiffness factors to be used, please refer to UBC97 1910.11.1. Slabs are not part of the 3D Building Analysis model, so adjustment to the slab stiffness is not relevantģ. If the walls in the model are to be meshed (FE Walls), then adjustment to the I value is meaningless you must adjust the E valueĢ.
These stiffness adjustments can be made in Orion by going to Run > Building Analysis > Model Options > Stiffnesses, as shown below.ġ.
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Standard Training Manual - available from C:\Program Files\CSC\Orion\18\Help Engineers Handbook - available from C:\Program Files\CSC\Orion\18\Help and the Help menu within Orion Orion Help document - available from the Help menu within Orionġ.3 Adjust the stiffnesses of the model To accurately calculate the fundamental periods of your structure, the stiffnesses of the structural elements beams, columns and walls need to be adjusted in-line with the code being followed in this case, UBC97. For further guidance on this, please refer to:
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This document is only intending to show you how to assess the effects of the equivalent static forces on an Orion model.ġ.2 Build the model Once you have accepted the Equivalent Static Force method as an appropriate way of assessing your structure for seismic forces, the next stage is to build your Orion model. If you are intending to use UBC97 alongside BS8110 for the design of your structure, some engineering judgement will be required. It should also be noted that BS8110 does not include any seismic design checks or guidance. Please note: If you wish to use a method other than the Equivalent Static Force method, then the following guidance document is not appropriate. 16ġ.1 Analysis method Equivalent Static Force The following guidance document will show you how to apply the Equivalent Static Force method to an Orion model, taking the seismic loads from UBC97 with BS8110 Design. 16ġ.11 Limitations of the design - Important. 12ġ.9 Apply the seismic lateral loads in Orion.
6ġ.6 Calculate the vertical distribution of seismic force. 5ġ.4 Adjust the Live Load Participation Factor. 5ġ.3 Adjust the stiffnesses of the model. 1 1.1 Analysis method Equivalent Static Force. Applying UBC97 Seismic Loads to an Orion model Analysis method Equivalent Static Forceġ.0 Applying UBC97 Seismic Loads to an Orion modelĬontents 1.0 Applying UBC97 Seismic Loads to an Orion model.
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