Creates earthquake spectra (horizontal and vertical) according to the Mexico's Earthquake Resistant Design code.
As with every other earthquake loading analysis, the object is to calculate the shear force at the center of mass of each vessel element. After the shear force at each elevation is known, the moments are accumulated to the base, leg or lug support.
You should begin the analysis by calculating the weights and centroidal distances of all vessel elements. It is very important to model the structure in sections that are appropriate in length. For cylinders, this value is about 10 or 12 feet (3 m). This ensures that the software has enough information to calculate the natural period of vibration with sufficient accuracy.
Using the input data and calculated earthquake weights and natural frequency, CAESAR II determines the values from table 3.1 of the Mexican Seismic Code.
The values are:
|
ao |
Spectral coordinate used in computing a |
|
c |
Spectral coordinate used in computing a |
|
Ta(s) |
Period value used in computing a |
|
Tb(s) |
Period value used in computing a |
|
r |
Exponent used in computing a |
For group A structures, the values of the spectral ordinates ao and c are multiplied by 1.5.