# Ram Concept - Load combinations - Alt. Envelope factor

I am trying to create a service load combination to consider 75% of wind load from two wind directions on my roof slab. I want to know if this set up would cover all the combination listed below.

D+0.45Wx+0.45Wz
D+0.45Wx-0.45Wz
D-0.45Wx-0.45Wz

D-0.45Wx+0.45Wz
0.6D+0.45Wx+0.45Wz
0.6D+0.45Wx-0.45Wz
0.6D-0.45Wx-0.45Wz
0.6D-0.45Wx+0.45Wz

• Every permutation of load factors and alternate envelope factors for all of the loadings are included with the load combination defined. As a result, all of the load combinations in your list will be covered.

• You could use live load patterns to accomplish the same thing. It seems better to use alternate envelope factors as the default combinations are already set up to cover that condition and you would not need to devote one of the 10 permitted patterns to account for that condition.

It is common to produce net axial forces in design sections for gravity load cases, especially in models with beams or slab areas with varying thickness/surface elevation. Refer to the web page below for more discussion. When that happens, there may be a net compression force under dead load that decreases reinforcement requirements for axial-flexure interaction compared when the net compression is ignored. Use of 0.9 for an alternate load factor is a good way to ensure that you are not overestimating the dead load and the benefit of the net compression load.

Table 15 in the RAM Concept Manual has a good summary of how the maximum and minimum context envelope results are determined for all cases.

RAM Concept T-Beams and Axial Forces [TN] - RAM | STAAD | ADINA Wiki - RAM | STAAD | ADINA - Bentley Communities