Defining Ec8 Seismic Analysis In Robot - Example.doc

Defining EC8 seismic analysis in Robot – short step-by-step description of the simple typical case. 1. Defining modal analysis load case using Analysis Type/ New.

2. Defining added masses using Loads/Load definition or conversion of loads to masses using appropriate dialogue

3. Running analysis and checking participation mass for each horizontal direction. If 90% is not reached for both horizontal directions X and Y (table Dynamic Analysis Results with appropriate columns added) increasing the number of modes in modal analysis parameters and running analysis again. Continuing this procedure until

appropriate number of modes is found. It can be also done automatically when using Seismic mode or Seismic (Pseudo mode) mode in Modal Analysis Parameters and specifying there Participation masses as active – in such case Robot will automatically increase the number of modes until the demanded participation percentage is reached.

4. Defining seismic analysis EC8 using Analysis Type/ New. Specifying code parameters and selecting Direction definition

5. Selecting the method of creating combinations between directions – on European market usually Newmark combinations are used. Specifying the type of combinations between modes (usually CQC) used for each direction in combinations between directions.

6. Running analysis 7. Defining design combinations (manual or automatic ones) considering static load cases and dynamic combinations Additional notes:

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In case of using signed quadratic combinations it will be necessary to set main modes for each of directions. Usually the main criterion to select such modes is their contribution to participation mass for given direction – this contribution can be checked in Dynamic Analysis Results with appropriate columns added

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Robot by default stores results for single modes. In case of big models it can be better from the point of view of amount of results and speed to store only results of combinations of modes – it can be changed in Job Preferences/ Structure Analysis/ Results Save. In case of big models it can be also useful to filter modes (to be set in parameters of seismic spectral analysis) and to use pseudo-mode approach (to be set in parameters of modal analysis – analogous to Ritz vector approach in SAP) Signed combinations are the method to avoid the effect of using quadratic combinations i.e. loosing the information concerning sign of loads, moments, displacements etc. This information can be important as concerns for instance the relation between sign of normal force (tension/compression) and sign (direction) of bending or as concerns the change of sign of moment along members. Signed quadratic combinations are calculated according to formulas (with assumption that coefficients are equal to 1) given below:

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  R S / i 3  R S / j 3  R S / k 3  RQS1  sign XS / i  Y S / j  ZS / k    R  RY RZ  X 

R   R   R  S /i 3 X S /i X

R

S/ j 3 Y S/ j Y

R

S /k 3 Z S/k Z

R

  R S / i 3  R S / j 3  R S / k 3   sign XS / i  Y S / j  ZS / k    R  RY RZ  X 

R   R   R 

  R S / i 3  R S / j 3  R S / k 3  RQS 3  sign XS / i  Y S / j  ZS / k    R  RY RZ  X 

R   R   R 

S Q2

R

S/i 3 X S /i X

R

S /i 3 X S /i X

R

S/ j 3 Y S/ j Y

R

S/ j 3 Y S/ j Y

R

S/k 3 Z S/k Z

R

S/k 3 Z S/k Z

R

S Q4

R

  R S / i 3  R S / j 3  R S / k 3   sign XS / i  Y S / j  ZS / k    R  RY RZ  X 

R   R   R  S /i 3 X S /i X

R

S/ j 3 Y S/ j Y

R

S/k 3 Z S/k Z

R