Staad pro member specification

The default connection between 2 members, or between a member and an element in STAAD is one where all the 3 forces and all the 3 moments (torsion, bending moments, shears and axial force) can be fully transmitted across that connection. This is usually achieved in practice by fully moment resistant connections in steel, or monolithically constructed beams columns in concrete.

If the connection is such that one or more of those forces and moments cannot be transmitted, you have to communicate that information using MEMBER RELEASEs at the "START" or "END" node of the beam or column whose end has such a connection. A shear connection is such an example. The degrees of freedom FX through MZ that you release are based on the local axis of the member at whose end the release is specified.

An example on using this is available in Example problem 1 of the Application Examples section of the Help menu. See section 5.22.1 and the figures in Section 1.19 of the Technical Reference manual for additional information.

In STAAD's Modeling Mode, if you go to the General-Spec page on the left side of the screen, there is a button called "Beam" on the right side which will bring up a dialog box with Release as a tab. Follow the prompts.

Sometimes, releasing the moments by 100% can lead to instabilities. In such cases, you could simulate a semi-rigid connection by specifying a partial moment release. For example, on member 75, at its start node, a connection where  95% of the MX stiffness is released, 75% of the MY stiffness is released, and 50% of the MZ stiffness is released is specified as

MEMBER RELEASE

75 START MPX 0.95 MPY 0.75 MPZ 0.50

The number you specify alongside the terms MPX, MPY, MPZ or MP specify the extent of the release. Thus, a smaller number signifies a smaller release, a larger number signifies a larger release.

Only the moment degrees of freedom can be "partially" released. Force degrees of freedom cannot.

thanks biwatosh.

Dear,

kindly clear some of my doubts;;;;

> suppose that i have simply supported beam with concentrated load at the centre.in first case if to apply load , i divide the member at mid point and apply the load at that node as nodal load.

the result i get is different for both the members. e.g. utilization ratio etc

in second case if i apply member load and give that load at the centre, then i t will consider whole member as a one. now it will shows the utilisation ratio for whole member.

if any of the method used( as above) in actual appication will be fine or we have to consider second case only?

please reply as i have done some boom analysis in which i always used first case. I am confused now if they might have given me wrong results.

.

thanks sanjay

When you segment the member into parts, the default unbraced length of each part is the segment length. When you model a longer member, the default unbraced length is longer and this has a big impact on the interaction or utilization ratio in most cases.  

I do find it peculiar that you said you got a different interaction ratio for the two half-segments in the first case, however. Assuming those segments are the same length, have the same end fixity, and the same internal forces, I would expect the interaction ratios of the two halves to match. If you want to attach your .std file I, or one of the others on the Forum, could clarify.

Thanks for the posts, Biswatosh and Seth.