April 15, 2023

How can I calculate SF(m/s2) scale factor in pushover analysis in ETABS

During my research, I reviewed 10 sources related to calculating the SF (m/s2) scale factor in pushover analysis in ETABS. The most relevant information was found in sources 3 and 4. There was not much consensus among the sources, and only a few provided useful information on the topic. Based on the available information, there is still some level of uncertainty in determining the best approach to calculate the scale factor in ETABS.

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Calculating SF (m/s2) Scale Factor in Pushover Analysis in ETABS

According to The Structural World, there are two methods to scale base shear in ETABS. In Method 1, the initial scale factor, which has units of acceleration and will change as the units in the model change, should be assigned to each load case using the formula g/RI. The model should then be run, and the static and dynamic base shear should be extracted after analysis. The values of Static Base Shear and Dynamic Base Shear should then be substituted using the formula SpecX = (Static/Dynamic) x Initial Scale Factor, and SpecY = (Static/Dynamic) x Initial Scale Factor respectively. Finally, the final scale factor should be inputted in SpecX and SpecY load cases and run the model for the final ETABS model to proceed with the design. After this, it is essential to check if the static base shear matches the dynamic base shear. In Method 2, a load combination, SpecXY, should be created, and the calculated scale factor should be inputted in the corresponding combination. The model should be run, and the static and dynamic base shear should be extracted after analysis. The values of Static Base Shear and Dynamic Base Shear should then be substituted using the formula SpecX = (Static/Dynamic), and SpecY = (Static/Dynamic) respectively. The scale factor should then be inputted in Figure 2.2 (ratio of static to dynamic base shear) and proceed with the design. Finally, it is essential to check if the static base shear matches the dynamic base shear after modification. Method 1 is considered the most widely used procedure by engineers for scaling base shear. In contrast, Method 2 does not require re-running the model after assigning the initial scale factor in response spectrum load cases.

"In method 2, we don’t need to re-run the model after assigning the initial scale factor in response spectrum load cases."

"The scale factor has units of acceleration which is length/seconds2 and that its value will change as you change the units in the model."

"Perhaps method 1 is the most widely used procedure used by engineers on how the base shear is being scaled."

Performance Point of Pushover Analysis

The performance point of the pushover analysis relies on the scale factor, as mentioned in a discussion on sefindia.org. The user input a response spectrum function of IS 1893 into ETABS for pushover analysis, and ETABS converted the response spectrum into an Acceleration Displacement Response Spectrum (ADRS). The user hoped that the ordinate value of the 5% damping curve would remain the same, but it ended up as 0.000109 instead of the expected 0.9. There is an option in ETABS called "scale factor (mm/s2)," and the user wonders if the value should be 0.9/0.000109 (resulting in 8256) or if the scale factor is related to converting m/s2 into mm/s2. In conclusion, the most relevant information for calculating the SF (m/s2) scale factor in pushover analysis in ETABS can be found in sources 3 and 4. The two methods provided by The Structural World can be used to calculate the scale factor, with Method 1 being the most widely used. The performance point of the pushover analysis relies on the scale factor, and it is essential to ensure the static base shear matches the dynamic base shear after modification.

"Perhaps method 1 is the most widely used procedure used by engineers on how the base shear is being scaled."

"In method 2, we don’t need to re-run the model after assigning the initial scale factor in response spectrum load cases."

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Research

Source: "Scaling of Base Shear in ETABS -- Structural Calc" (from web, structuralcalc.com)

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Source: "Which Scale factor use for time history analysi..." (from web, www.researchgate.net)

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Source: "In a response spectrum Why we use the 1st scale..." (from web, www.researchgate.net)

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Source: "Determining Shear on basement level for several..." (from reddit, r/StructuralEngineering)

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Source: "ETABS or STAAD pro?" (from reddit, r/civilengineering)

  • Relevant information on calculating SF scale factor in pushover analysis in ETABS:

    • None

💭  Looking into

What is the best practice for verifying that static base shear matches dynamic base shear in ETABS?

💭  Looking into

What is the significance of the performance point of the pushover analysis?

💭  Looking into

What is the procedure for running the model after inputting the scale factor in Figure 2.2 for Method 2?

💭  Looking into

What is the formula for calculating scale factor for Method 2?

💭  Looking into

What is the formula for calculating initial scale factor for Method 1?

Source: "174 questions with answers in ETABS | Science t..." (from web, www.researchgate.net)

None

Source: "How to Scale Base Shear in ETABS | The Structur..." (from web, www.thestructuralworld.com)

  • To calculate SF (m/s2) scale factor in pushover analysis in ETABS:
    • There are two methods/options to scale base shear in ETABS.
    • Method 1:
      • Assign initial scale factor (using the formula g/RI) to each load case.
      • Run the model and extract static and dynamic base shear after analysis.
      • Substitute the values of Static Base Shear and Dynamic Base Shear using the formula SpecX = (Static/Dynamic) x Initial Scale Factor, and SpecY = (Static/Dynamic) x Initial Scale Factor respectively.
      • Input final scale factor in SpecX and SpecY load cases as calculated and run the model for the final ETABS model to proceed with the design.
      • Check to see if static base shear matches dynamic base shear.
    • Method 2:
      • Create a load combination, SpecXY, and input the calculated scale factor in the corresponding combination.
      • Run the model and extract static and dynamic base shear after analysis.
      • Substitute the values of Static Base Shear and Dynamic Base Shear using the formula SpecX = (Static/Dynamic), and SpecY = (Static/Dynamic) respectively.
      • Input scale factor in Figure 2.2 (ratio of static to dynamic base shear) and proceed with the design.
      • Check to see if static base shear matches dynamic base shear after modification.

Source: "Non linear sttic analysis sap2000 - SlideShare" (from web, www.slideshare.net)

None

Source: "Scale factor required to produce ADRS in ETABS ..." (from web, sefindia.org)

  • The user input a response spectrum function of IS 1893 into ETABS for pushover analysis
  • ETABS converted the response spectrum into an Acceleration Displacement Response Spectrum (ADRS)
  • The user hoped that the ordinate value of the 5% damping curve would remain the same, but it ended up as 0.000109 instead of the expected 0.9
  • There is an option in ETABS called “scale factor (mm/s2)”
  • The user is unsure of what the value of the scale factor should be
    • The user wonders if the scale factor input should be 0.9/0.000109 (resulting in 8256)
    • The user supposes that the scale factor is related to converting m/s2 into mm/s2
  • The performance point of the pushover analysis will rely on the scale factor

Source: "2 Methods On How To Scale Base Shear in ETABS |..." (from web, www.scribd.com)

None

💭  Looking into

What is the best SF(m/s2) scale factor to use in pushover analysis in ETABS?