By default, CAESAR II will not recommend occasional load cases to the user, and it is up to the user to determine these load cases that will be checked against the occasional allowable stresses. The CAESAR II Applications guide covers the a few examples on occasional load cases which are commonly used. Here is an example of those occasional load cases given for a particular model, and how they were generated for wind loads.
In this model I have two separate vectors for wind, in the X and Z directions respectively. I want to consider the occasional load of wind on my model, and in CAESAR there are a few interstitial cases that need to be set up in order to do this.
First I will have to synthesize the stress applied from the wind load by itself, and then combine this "wind stress" to the sustained load case, per the recommendation in B31.3. (Note: these load case combinations for wind are also valid for B31.1)
My first step is to open up my model, go to my first node, and apply the "Wind/Wave" type.
This will give me the Wind/Wave dialog, that allows a wind or wave force to be applied to the nodes in my model. Due to the propagation of parameters within CAESAR, I only have to apply the Wind/Wave parameter to the first node in my model, and the effect will be propagated to the entire model. I'm also going to use a wind shape factor of 0.6, which determines how much force is applied to the model, that is based on the cylindrical shape of the pipe. A larger shape factor would contribute a larger wind force.
Now I can error check my model, and go to my static load case editor:
I'm going to go to the Wind Loads tab at the top, and configure some values to get two different wind vectors applied to this model. A couple things to keep in mind about this dialog:
1. After I've configured the wind values and the vector it will be applied on, I'll be able to switch between my four different wind loads with this arrow.
2. I can copy the wind vector with the "Copy Wind Vector" option, and then just change values (like wind direction) on the new vector.
3. Currently we can use ASCE 7-05 for wind load generation, however 7-10 will be utilized in CAESAR 2016.
4. Keep in mind the Basic Wind Speed here is in ft/sec, and will need to be converted if you are coming from miles/hr.
Now that I have my wind loads generated, I need to apply them with load cases to my model.
The first step is to apply the wind loads to the OPE load case. I would like to consider wind gusts in two separate directions, so I'm going to create two more OPE load cases with wind defined. Now my L2 and L3 cases contain the loads and displacements of my piping system while it is under a wind load. I'm not determining any stresses yet, just looking at the physical effect of wind as it is applied on the system.
Next the stress from the wind by itself has to be synthesized by itself, by adding in load cases L5 and L6. Keep in mind that I skipped load case L4 to add in L5 and L6 - this is because load case combinations, which are those that are referenced with "L" numbers, have to be after all your other load cases in this list.:
Now I can generate the load cases that we can validate against the occasional allowables. Load cases L7 and L8 have now been added, and given the OCC stress type. But there's one last page for us to configure. I'm now going to go to the Load Case Options tab.
I've made a few changes to these options that will help me understand my report output. For example, I've suppressed output of the L5 and L6 load cases, since those will not be checked against any type of an allowable, so I am not interested in reviewing those results. They were only created to help me synthesize load cases L7 and L8. Notice the combination method for L7 and L8. I changed the combination method to be Scalar, instead of Algebraic. This allows the stresses from the Sustained case and my occasional case to be summed in a signed fashion. So if the stresses from sustained were 100 psi, and occasional was 100 psi, the overall stress in this case would be 200 psi with the scalar combination.
That's it! For additional wind loads, I would have to repeat these same steps to my load case editor.
I can now review my analysis and take a look at the stresses extended report for load case 7 or 8, and review the results.