Civil Engineering/truss column
QUESTION: dear prof
i would like to ask you about design and analysis truss steel columns using sap, the structure is mainly RC, it is a museum, in the right facade of the building there are truss steel columns each of them looks like communication steel tower, those steel columns are located on graded step ground and they are fixed to a hollow concrete boxes, those columns are connected to the top roof of the building (story 7) and to the bottom of the building the graded base, those trusses steel columns carry the loads transferred to them from the roof of story 7 (the top story) and i should study them against earthquake loading using etabs or sap, i do not know where to put the base shear and in etabs we usually define mass of source , in this case , how and where can i define mass of source , and how can i study this trusses steel columns against earthquake, if there is a reference i will be regretful.
ANSWER: Dear Farah
I suggest you to define the lumped mass you would result from the architectural maps, independent of the structural arrangement. Then you could decide which of the joints must be considered as the mass concentration location. You can send me the details and plans and maps to my e-mail so that I can help you better.
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QUESTION: DEAR PROF
THANK YOU FOR YOUR INTEREST
I WOULD LIKE TO ASK YOU ABOUT THE CONNECTION BETWEEN TRUSSES STEEL COLUMN AND CONCRETE WALL AND CONCRETE SLAB
SUPPOSE THAT I HAVE 12 MODULE OF TRUSS STEEL COLUMN WHICH ARE LOCATED ON GROUND AND ARE CONNECTED FROM THE TOP POINT OF EACH ONE BY THE CONCRETE SLAB IN THE TOP STORY OF THE BUILDING, WHAT ABOUT THE CONNECTION BETWEEN THE COLUMN AND THE SLAB, SHOULD I MODEL THEM RIGID OR SEMI RIGID OR PINNED,
AND ABOUT THE BEAMS IN THE SLAB, SHOULD I RELEASE THE MOMENTS IN THE PERIMETER SIDE OF THE BUILDING WHEN THE CONNECT TO THE COLUMN.
THE COLUMNS ARE 21 METER HEIGHT AND HAVE TRIANGULAR HORIZONTAL BRACING EACH 3 METERS HEIGHT AND K BRACING VERTICALLY
SHOULD I JOIN THE POINTS OF EACH HORIZONTAL BRACING WITH DIAPHRAGM, TACKING INTO ACCOUNT THAT THE MASS IS CONCENTRATED IN THE ROOF OF THE TOP STORY (7 STORY) SO THE SOURCE OF MASS IS IN THE STORY 7
WHAT ARE THE MOMENTS RELEASE WHICH I MUST DO TO MATCH THE REAL BEHAVIOR
OF THE STEEL COLUMN
I APPRECIATE YOUR INTEREST
ANSWER: Dear Farah
Normally the columns are interconnected with beams and girders and the slab is connected to the beams. All joints in same level of slabs must be diaphragmed. The type connection of beams to the trussed columns shall be pinned unless you use a specific connection detail.
Please let me know about any doubt.
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QUESTION: dear prof
thank you for your quick response
i would like to ask you about the local axes of the point of the support in sap, when and in any cases should i rotate the local axes of the support,
and what does it mean when we rotate the local axes of the support say for example rotate local axes about z = 26 , and about y direction = 180
what that means if this support is hinge so restrains u1, u2, u3.
if there is a reference explain easily the local axes of the support and the rotate and the effect on the restrained displacements.
again thank you
Suppose you define an element ( say a H section) between 2 arbitrary joints ( A and B). The software assumes the 1 , 2 and 3 axis of the element in an specific order: (1) axis along the direction of joints A to B, (2) axis along the height of the profile and (3) axis along the direction orthogonal to the plane of (1) and (2).
You must know and be aware of these axis and the loading in each direction. What happens if the position of the member is different than what the software assumes? You shall change the axis orientation using a combination of rotation of (2) and (3) axis.
The (1), (2) and (3) axis are called local axis.
U1 , u2 and u3 directions of joints are called global axis which are different from local axis but they can be in same direction of some members axis. The displacements of joints are calculated in this axis system.
Please let me know about any doubt you would have.