Applies To
	Product(s):	STAAD.Pro
	Version(s):	ALL
	Environment:	ALL
	Area:	Postprocessing workflow
	Subarea:
	Original Author:	Sye Chakraborty, Bentley Technical Support Group

 

When I look at signs of the forces in the Beam End Forces table, I am noticing discrepancies when I look at the All tab vs. when I look at the Envelope tab. For example here are is a screenshot of the All tab within Beam End Forces table. As you can see the axial force Fx is reported as 165.876 kN at node 550 for the load case 1027 and the axial force Fx is reported as -195.077 kN at node 550 for the load case 3002.

However when I look at the Envelope tab within the Beam End Forces table, I see Fx is reported as -165.876 kN for node 550 corresponding to load case 1027 and Fx is reported as +195.077 kN at node 550 for load case 3002. These seem to be in contradiction with what is reported in the All tab above.

Can you please explain why ?

Although it may seem like the signs are not consistent when you look at the All and the Envelope tab within the Beam End Forces table, however if you look at it carefully, you will see that the results are in agreement.

The sign convention followed for reporting the Envelopes is the following

 

As per the above convention, the force 165.876 is tensile ( reported as negative in the Envelope table) and the force 195.077 is compressive (reported as positive in the Envelope table). Now if you look at the sign of the beam end forces in the All tab as shown in your screenshot, you will see the following

For load case 1027,  -165.876 is reported at the start node 547 (indicating tension) and 165.876 is reported at the end node 550 (again indicating tension). Hence the member is subjected to a tensile force of 165.876 kN corresponding to load 1027 which is what the Envelope table also reports. 

Similarly for load case 3002, 195.077 is reported at the start node 547 (indicating compression) and -195.077 is reported at the end node 550 (again indicating compression). Hence the member is subjected to a compressive force of 195.077 kN corresponding to load 3002 which is what the Envelope table also reports.