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Structural Load Case Optimization

The document discusses a new "Range Add" combo feature in SAP2000 and ETABS software that allows engineers to efficiently model and analyze pattern loading scenarios. The Range Add combo considers all possible permutations of individual load cases acting alone or together to determine the maximum and minimum responses, avoiding the need to define many individual additive combinations. It works by listing the individual load cases and computing the maximum and minimum results by adding positive and negative values respectively across all contributing cases.

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373 views8 pages

Structural Load Case Optimization

The document discusses a new "Range Add" combo feature in SAP2000 and ETABS software that allows engineers to efficiently model and analyze pattern loading scenarios. The Range Add combo considers all possible permutations of individual load cases acting alone or together to determine the maximum and minimum responses, avoiding the need to define many individual additive combinations. It works by listing the individual load cases and computing the maximum and minimum results by adding positive and negative values respectively across all contributing cases.

Uploaded by

curvedbrain
Copyright
© Attribution Non-Commercial (BY-NC)
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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SAP2000 (and ETABS soon)

New Range Add Combo (Enveloping Add) For pattern loading, such as the most extreme response over all possible combinations of individually loaded bays in a multi-story building

The beam below has 8 separate Load Cases, each of which loads a 1/8 length of the beam. Load Case 2 is shown

Moment diagram for an Algebraic-Add Combo. All 8 Load Cases are added together, equivalent to uniform load on the entire beam

Moment diagram for an Enveloping Combo. All 8 Load Cases are considered independently, only one acting at a time. Max and Min are shown

For pattern type-loading, we want the envelope of:


Any single load case (same as the envelope combo previously shown), 8 permutations Any pair of load cases, 28 permutations Any three load cases, 56 permutations Any four load cases, 70 permutations Any five load cases, 56 permutations Any six load cases, 28 permutations Any seven load cases, 8 permutations All eight cases (same as the additive combo previously shown), 1 permutation

For a total of 255 possible permutations!

In the past, we would have had to define 255 additive combos, plus one more combo that envelopes them all.

Now we can define a single Range Add combo to get the same results:

Simply list the 8 load cases as we would for adding or enveloping The computation starts with zero for Max and Min For each contributing case:
Positive values add to the Max Negative values add to the Min

If the contributing case is another combo:


Positive Max values add to the Max Negative Min values add to the Min

The result represents a range of results that always includes zero The specification is easy, the computation is quick

Moment diagram for a single Range Add Combo. All 8 Load Cases are included. Equivalent to 255 additive and 1 enveloping combo

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