Reaction is smaller in Envelope Comb than that in Linear Add Comb? 1

[netsonicyxf]

I get reaction from dead load is 9406+1663 kN, max reaction from moving load is 846 kN. The load factor 1.2 for dead load and 1.4 for live load.
The max reaction shall be 1.2*(9406+1663)+1.4*864=14492 kN.

In CSiBrdge 23.3, the reaction from Envelope Comb is 11287 kN, while that in Linear Add Comb is 14492 kN.

According to CSiBridge user manual:

Envelope. A max/min Envelope of the defined load cases is evaluatedfor each frame output segment and object joint. The load casesthat give the maximum and minimum components are used for this combo. Therefore the load Combo holds two values for each outputsegment and joint. The Combo Type can be used for moving loads and any load case wherethe load producing the maximum or minimum force/stress is required.

 

[skewl]

I am not entirely sure I understand your question, so let me know if this doesn't explain your issue.

Envelope combination doesn't add the load cases. It simply shows the max/min value of the governing load cases at each location along the span.

 

[rapt]

I have never used CSiBrdge 23.3, but in RAPT we calculate 2 envelopes,

1 an envelope of moments with co-existing shears/reactions.
2 an envelope of shears/reactions with co-existing moments

The first gives the highest possible moments but not necessarily highest shears and reactions.

Your CSiBrdge 23.3 envelope may be the 1st one above. You would have to check with them.