Implemented Suggested 12/18/2018 by Seth Greenberg

6

votes

Load Combinations in Construction Staging

I want to determine the maximum forces on a structure during an entire construction sequence. It is not necessarily true that the maximum loads on a given member, support, or elastic link will be greatest at the final step of the construction sequence. MIDAS Civil currently provides the min/max loads during erection, but I need to create load combinations to satisfy the Australian code (AS5100). 

I need to create linear combinations of:
Steel dead load
Concrete dead load (per AS5100, steel and concrete have different dead load factors)
Superimposed (composite) dead load
Construction wind load
Construction live load

For wind and live load, I need to envelope a number cases, since it is unclear which one will govern.

Presumably, such a feature would be beneficial for satisfying any building code. In addition, one should be able to import these combination into the section design tools already in MIDAS.


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To add to this more than 3 load cases would be needed to separate the results when using construction staging. There are other loads applied during construction that have load factors different to dead load. For instance in AASHTO the sentimental girder construction load combinations (Table 5.14.2.3.3-1) have different load factors for construction equipment, construction live load, wind, and thermal gradient among other things.

These are not permanent loads so they would be activated and deactivated in the staging, but even for just dead loads its useful to be able to separate the self weight from superimposed dead loads (surfacing, barriers etc.). The current limitation of 3 load cases in insufficient to do this.

For the non permanent loads like wind and snow we would still need to activate these loads in one stage, and then deactivate them in a dummy stage before continuing the construction sequence otherwise the effects would get locked in. It would be useful if you could specify if a load case as permanent, meaning as the construction goes on the load stays there unless deactivated or temporary, meaning it is only applied at the specified stage and does not effect subsequent stages and is not factored into creep, shrinkage, PT elastic losses, etc. This way we wouldn't need to create extra stages for deactivation.
12/18/2018 2:46 AM

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