I am trying to solve a structure where the superstructure is a mix of RCC and steel and the substructure is of RCC, and it is partially resting on a river. So while trying to run the analysis, I am getting the error as "PROBABLE CAUSE NEGATIVE DIAGONAL =>LDLT MTX".
I tried to apply partial release of MZ and MY, but did not solve my problem.
Also, I am getting an error "PROBABLE CAUSE SINGULAR-ADDING WEAK SPRING" which I am clueless what to do about it.
Can anyone else help me with this problem? It is a bit of an urgent piece of work
Frame members like 170, 371, 372, 373, etc. are resting on truss members like 370, 369, 368, etc.
Truss members have no ability to resist loads in shear, so, the loads like selfweight from those frame members cannot be carried by those truss members. That is what is producing the instability warnings.
You need to
a) remove the truss specification which will convert them to frame members which have the ability to resist shear
or
b) add members (similar to 171 and 172 in the attached figure) to the truss assembly to transmit loads from those beam to the lower levels.
Answer Verified By: Arindom Bora
Hello, I made some changes and reduced quite a bit of warning and errors.
But some of the sections have failed. So, I was checking on trying different sizes. So, while I defined some of the members as Cold-formed Steel sections, I am getting a warning as " WARNING: DESIGN OF SECTION FOR MEMBER # 160 IS NOT SUPPORTED."
Then an error as " ERROR: MEMBER DESIGN FAILED FOR MEMBER 160"
What should I do about it?
Your original model did not have any cold-formed sections, so we presume you have added them to your modified model.
In STAAD, cold formed sections can be designed only to cold-formed steel codes. For example, the American cold-formed sections can be designed only to the AISI code. Indian cold-formed sections can be designed only to the IS801 code.
If you attempt to design a cold-formed section to a code meant for hot-rolled sections like AISC 360, or IS800, you will encounter those messages. Same is true of prismatic sections - ones specified using the YD and ZD parameters. Those cannot be designed to any steel code.
If you need an answer more specific to your model, please upload the modified model.