Calculation of the response factor

A question about the calculation of the response factor within RAM Concept: 

When reading the RAM Concept Manual to understand how the response factor is calculated within RAM, the manual states that the baseline acceleration, alpha,RMS = 1 m/s2 (see snapshot below).

When reviewing the associated literature which the vibration analysis in RAM Concept is based off (Concrete Centre & P354), the concrete centre states that the response factor is calculated by dividing the calculated (or measured) RMS acceleration by the baseline acceleration. According to P354 the baseline acceleration is 0.005 m/s2 (see the snapshot below)

And from the concrete centre, the measure acceleration RMS can be evaluated from the graph shown below:

To achieve a response factor of 1, the measured acceleration RMS would be 0.005m/s2, and for frequencies above and below the range of 4-8Hz, this would result in a greater response factor due to a larger measured acceleration. However, I cannot see where a baseline acceleration value = 1m/s2 can be found, as per the RAM manual. Is the information in the RAM Concept manual a typo? Should baseline acceleration value be 0.005m/s2 and the response value limit is =1? Can someone provide an explanation to the calculation of the response factor in RAM please.

Thanks.

  • The alpha,ms parameter referred to in the manual represents the entire base line curve represented with the blue line in the image below and is a range of accelerations for different frequencies. The value of 1 is the unitless "response factor" and not 1 m^2/s. Any acceleration above that curve would coincide with a response factor greater than 1.

    In the vibration analysis, the program determines a response factor using the curve represented by the blue line in the image below for each harmonic frequency. Those individual response factors are then combined using SRSS and those are the values displayed on the Max Response Factor Plan. 

    The lowest or most sensitive acceleration (0.005 m/s^2) on the baseline curve is associated with frequencies between 4-8 Hz as you mentioned. See area marked with the green lines in the image below. If the entire frequency range is between 4-8Hz, then the response factor R would be equal to aw,rms/0.005 as shown in your screen capture above.