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Concrete Design - Alternating Live Loads

Concrete Design - Alternating Live Loads

Concrete Design - Alternating Live Loads

Is there any way in RISA Floor to alternate live loads (to meet ACI requirements) for concrete design?

In typical designs we would have six live load combinations:
Live Load on Odd Spans
Live Load on Even Spans
Live load on Adjacent spans 1-2, 4-5, 7-8, etc.
Live load on Adjacent spans 2-3, 5-6, 8-9, etc.
Live load on Adjacent spans 1, 3-4, 6-7, etc.
Total Live Load

This is required by the ACI code - you cannot ignore it.  If you can't do this in RISA Floor then the concrete design package isn't any use.



RE: Concrete Design - Alternating Live Loads

There are ways to do this, but they are not automated.... nor are they perfect solutions. Essentially this would have to be done "manually".  

What you would do is define a different type of live load for those adjacent bays. Floor offers a number of types of live load (LL, LLS, RL, RLL, SL). You even have OL1 through OL4. Then you can create different load combinations to address the various different live load placement scenarios.  

The program certainly was built around the concept of steel structures. When we added in concrete to the program we did so by merely adding a new member type into the existing design routine. Our thought was that there are a lot of multi-use buildings with some lower concrete levels, but with the upper levels mainly steel.  RISAFloor will do a much better job on these buildings than other programs (IMHO).  But, if you are doing a pure concrete building then this may not be the program for you.  

RE: Concrete Design - Alternating Live Loads


As good as RISA is, I am absolutely floored that it was not designed for this scenario (no pun intended, but I can live with it).

Sounds like suggestion time...

Mike McCann
MMC Engineering


RE: Concrete Design - Alternating Live Loads

This scenario doesn't come into play much for steel structures.  And, RISAFloor was first designed for steel structures. So, any limitations related to concrete stem from that original program architecture.  

At some point, we will re-vamp the program's concrete capabilities to handle this and other concrete specific issues.  But, that's not necessarily as easy as it sounds. Some portions of the concrete code seem to be built around approximate hand calculation methods that are difficult to extend out into 3D finite element solutions.

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