About alternate envelope factors
There can be situations where the application of a loading has an unconservative effect on the results.
For example
- a retaining wall loading that applies compression to a floor.
- a cantilever live loading that reduces the internal span moment.
In such circumstances, it is desirable to analyze the structure both with and without the full loading. While you could do this by creating an additional load combination, RAM Concept provides a much simpler solution - Alternate Envelope Factors (AEF).
This beam supports dead loads (not shown) and live loads (shown). The live loading reduces the positive span moment. By using an AEF less than the corresponding load factor, you create a load combination with a reduced live loading. Note that the AEF affects the entire live loading, not just the live load on the cantilever.
Conceptually, RAM Concept considers alternate envelope factors by analyzing the load combination 2L times (where L is the number of loadings) - once for every permutation of load factors and alternate envelope factors for all of the loadings. RAM Concept then envelopes the design strip forces, design section forces and punching shear reactions for all of the load combination analyses. RAM Concept uses these force envelopes later for design purposes. You can also plot the force envelopes or view them in tables.
RAM Concept fully considers any pattern loading effects while considering the load factors.
Note that the general analysis forces that are not used as design forces by RAM Concept - such as standard slab bending moments and deflections - are only stored for the load combination considering the standard load factors.
As stated above, you should only use alternate envelope factors if you fully understand the principle involved. Do not set them to zero without understanding their use. If you are unsure then set them to equal the corresponding load factors.