Hello everyone,
I am modeling a steel frame stand for holding a heavy steam casing. This stand will be used inside a factory, therefore only dead load and seismic load are analyzed. The profile of the stand and its post design are shown below: the pinned connections for the cross bracings only have one row and are not designed to transfer moments.
I had some difficulties with the long cross bracing members retaining the shape of the stand in the longitudinal direction. The two cross bracings are connected to the posts of the stand by non-slip critical bolted connected. Therefore, they are not intended to take any moments and the moments at these connections are released. Since the bracings are longer, their mid-points were pinned together so that their slenderness ratio are within the acceptable range.
We modeled the two long bracings as continuous members with a pin in the mid points. But our client wanted us to release the moments in the pin connection because the pin is not a rigid type of connections that could transfer moments. I tried to set them as truss members and it ended up with huge displacements in the mid points.
My question is:
1. What type of connection should I use for the pin at their mid points? Should I combine the two mid points or use separate mid points and then compare their displacements? Why there are huge displacements if I used "TRUSS" member?
2. What are the differences between TRUSS members and the beam members with X-, Y-, and Z- directions released? For this analysis, both the long cross bracings and short cross bracings are connected to the posts by non-slip critical connections. So they are not taking the moments. Which type of elements should I use?
I am attaching the codes from STAAD below. If our STAAD expert could have a look at it, I will really appreciate. Thanks a lot, :)
Fiona
STAAD SPACE START JOB INFORMATION ENGINEER DATE 03-Apr-17 END JOB INFORMATION INPUT WIDTH 79 UNIT METER KN JOINT COORDINATES 1 0 0 0; 2 0 0.3683 0; 3 0 0.6477 0; 4 0 0.8001 0; 5 0 2.2479 0; 6 0 3.3782 0; 7 0.229108 0 2.04457; 8 0.229108 0.3683 2.04457; 9 0.229108 0.6477 2.04457; 10 0.229108 2.2479 2.04457; 11 0.229108 3.3782 2.04457; 12 2.48054 3.3782 1.05979; 13 2.59715 1.4478 2.04457; 14 2.59715 1.4478 2.04457; 15 4.96519 0 2.04457; 16 4.96519 0.3683 2.04457; 17 4.96519 0.6477 2.04457; 18 4.96519 2.2479 2.04457; 19 4.96519 3.3782 2.04457; 20 5.1943 0 0; 21 5.1943 0.3683 0; 22 5.1943 0.6477 0; 23 5.1943 0.8001 0; 24 5.1943 2.2479 0; 25 5.1943 3.3782 0; MEMBER INCIDENCES 1 1 2; 2 2 3; 3 3 4; 4 4 5; 5 5 6; 6 2 8; 7 5 9; 8 10 3; 9 7 8; 10 8 9; 11 9 10; 12 10 11; 13 12 6; 14 12 11; 15 13 9; 16 10 14; 17 16 8; 18 4 23; 19 12 19; 20 14 17; 21 18 13; 22 12 25; 23 15 16; 24 16 17; 25 17 18; 26 18 19; 27 21 16; 28 17 24; 29 22 18; 30 20 21; 31 21 22; 32 22 23; 33 23 24; 34 24 25; START USER TABLE TABLE 1 UNIT INCHES KIP TUBE STRAIGHTBRACING 7.6875 8 3 0.375 56.5479 11.1182 29.314 6 2.25 END UNIT INCHES KN DEFINE MATERIAL START ISOTROPIC STEEL E 132258 POISSON 0.3 DENSITY 0.00125885 ALPHA 1.2e-005 DAMP 0.03 TYPE STEEL STRENGTH FY 163.355 FU 263.096 RY 1.5 RT 1.2 ISOTROPIC CONCRETE E 14011.9 POISSON 0.17 DENSITY 0.000386106 ALPHA 1e-005 DAMP 0.05 TYPE CONCRETE STRENGTH FCU 17.7929 ISOTROPIC RIGID_STEEL E 1.32258e+010 POISSON 0.3 DENSITY 1.25885e-006 ALPHA 1.2e-005 DAMP 0.03 END DEFINE MATERIAL MEMBER PROPERTY AMERICAN 1 TO 5 9 TO 12 23 TO 26 30 TO 34 TABLE ST PIPE OD 8.625 ID 7.625 UNIT INCHES KIP MEMBER PROPERTY AMERICAN 6 TO 8 27 TO 29 TABLE ST C5X9 MEMBER PROPERTY AMERICAN 18 UPTABLE 1 STRAIGHTBRACING 17 TABLE ST W4X13 MEMBER PROPERTY AMERICAN 13 14 19 22 PRIS YD 2.5 15 16 20 21 TABLE ST C6X8 UNIT INCHES KN CONSTANTS MATERIAL STEEL MEMB 1 TO 12 15 TO 18 20 21 23 TO 34 MATERIAL RIGID_STEEL MEMB 13 14 19 22 UNIT INCHES KIP SUPPORTS 1 7 PINNED 15 20 FIXED BUT FX FZ MX MY MZ UNIT INCHES POUND MEMBER OFFSET 7 START 0 0 4.3125 28 END 0 0 4.3125 8 START 0 0 -4.3125 29 END 0 0 -4.3125 21 START -4.3125 0 0 16 START 4.3125 0 0 7 END 0 0 -4.3125 28 START 0 0 -4.3125 8 END 0 0 4.3125 20 END -4.3125 0 0 18 START 4.3125 0 0 18 END -4.3125 0 0 17 START -4.3125 0 0 15 17 END 4.3125 0 0 29 START 0 0 4.3125 6 27 START 0 0 4.3125 6 27 END 0 0 -4.3125 16 END 0 0 0 20 START 0 0 0 UNIT INCHES KIP MEMBER RELEASE 6 TO 8 17 27 TO 29 START MX MY MZ 6 TO 8 17 27 TO 29 END MX MY MZ 13 14 19 22 END MX MY MZ UNIT MMS NEWTON MEMBER TRUSS 15 16 20 21 UNIT INCHES POUND LOAD 1 LOADTYPE None TITLE WEIGHT OF STEAM CASING UNIT INCHES KIP SELFWEIGHT Y -1.41 JOINT LOAD 12 FY -60.7 UNIT MMS NEWTON LOAD 2 LOADTYPE None TITLE SEISMIC LOAD SELFWEIGHT X -0.21 JOINT LOAD 12 FX -56714.8 LOAD 3 LOADTYPE None TITLE 1.4 X DEAD LOAD REPEAT LOAD 1 1.4 LOAD 4 LOADTYPE None TITLE 1.0 X DEAD LOAD + 1.0 X SEISMIC LOAD REPEAT LOAD 1 1.0 2 1.0 UNIT INCHES KIP PERFORM ANALYSIS PRINT ALL CHANGE PARAMETER 1 CODE CANADIAN FYLD 50 MEMB 1 TO 5 9 TO 12 18 23 TO 26 30 TO 34 UNIT MMS NEWTON PARAMETER 4 CODE CANADIAN FU 364.754 MEMB 1 TO 8 11 TO 32 34 PARAMETER 5 CODE CANADIAN FYLD 248.211 MEMB 6 TO 8 15 TO 17 20 21 27 TO 29 CHECK CODE ALL FINISH