huangyhg

how to work 2d problem in risa 3d
could someone please help out,
i was trying to work a 2d problem in risa 3d..the answers were way out then expected.
could someone please help me out..

if i'd have to guess, i'd say make sure you're defining your
the direction of the ridiculousness of the answers will tell you where the problem is. what results did you get, and what did you expect?
as implied in the previous post, i would look to the supportpoint restraints and/or
also - watch your restraints - reactions.....
sometimes you have to lock the z direction if you are working in x and y.
and if you are having trouble figuring this out - might suggest you take a user course....
i have issues with the support restraint's.
if simply supported i would restrain
reactions in x, y, z
but should i restraint my moments too in y and x...
is there a good reference where i can look for such support conditions
is your frame in the x-y plane?
if so, only restrain moments in the z direction (at both supports). restrain translation in x,y, and z directions at the first support and restrain translation in y, and z at the second support.
that should give you appropriate restraints.
is this a beam or a frame or something else?
often one of the problems is a torsional restraint missed.
if you have a simply-supported beam, you have to restrain the torsional moment as well as translation or you'll have a rigid-body mode (twisting) that will cause instability in your model. adding these restraints can sometimes lead to odd/unexpected results in the reactions, especially when you're accustomed to 2d analyses. you'll have to investigate these results so that you can develop a feel for what is a result of the math in the program solver and what is significant.
check risa's help file. in my experience it is a good source of information.
i want to do frame analysis but started with simple beam analysis , of beams who's solution i know...
but the result's we quite off from know results..
structuraleit or other's, could you please correct me if i am wrong:
for frame analysis" only restrain moments in the z direction (at both supports). restrain translation in x,y, and z directions at the first support and restrain translation in y, and z at the second support"
considering a beam with restrain on z direction means a fixed beam ...for simply supported beam i have to restrain translation in x, y, z...might have to restrain moment in x direction. to get results..
then when i do a frame analysis, with pinned at support should not i fixed my moments in y direction instead of z direction, if my y coordinate is pointing upward..
and x to right..
finally i would appreciate if any one has tutorials of risa 3d ver 5.0d
i have version 6.
mike mccann
mccann engineering
for 2-d frame problems, restrain vertical torsion in one support.
- restrain horizontal and vertical translations in the same support.
restrain vertical and out of plane translations in the second support.
staed79,
assuming you're working in the xy plane, use the "all" boundary condition to set the bc for z, x rotation and y rotation to "fixed". you can do this by entering all for the joint label in the "joint boundary conditions" spreadsheet. this will lock all your joints from out of plane displacements or rotations. the risa help file will have more on this.

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