design of bracing connections in concentrically braced frames ppt file · web viewconcentrically...
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Design of Bracing Connections in Concentrically Braced Frames
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Reference Materials
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Design of Seismic-Resistant Steel Building Structures
Prepared by:Michael D. EngelhardtUniversity of Texas at Austinwith the support of theAmerican Institute of Steel Construction.
Version 1 - March 2007
3. Concentrically Braced Frames
Reference Materials
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Brace End
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Brace Net Section Fracture
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Gusset PlateUndesired behaviour – Gusset Plate Buckling
Desired behaviour – Gusset Plate Bending and Brace Buckling
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Bad Designs of Bracing Connections
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HSS Bracing Connections
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gusset plate
rectangular HSS bracing member
Check HSS bracing member for limit state of net section fracture
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AISC:Ru= Ry Fy Ag
GB50011-2010: 1.2Abrfy
Required axial tension strength of brace for limit state of fracture of the net section
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Ru= Ry Fy Ag
Ru = 1.2Abrafy
Critical Net SectionAe = U An
Ae < Ag due to:slot (An < Ag ), andshear lag (U < 1)
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Ru= Ry Fy Ag
Limit state: fracture of net section (0.75) Ae (Rt Fu) ≥ Ry Fy Ag
OR:For A500 Gr B rectangular HSS:
14.1ksi583.175.0
ksi464.1AAg
e
Need to Reinforce Net Section (Ae need not exceed Ag )
ut
yy
g
e
FRFR
AA
75.0
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Reinforcing net section of bracing member....
I recommend that net section to be reinforced such that yielding occur in the brace member, not at the connection
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Gusset Plate in Tension 1.2Abrfy/betg <= f
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Pu= Ry Fy Ag
1.2Abrfy
Also check block shear rupture of bracing member....
Lt = design wall thickness of HSS
Pn = (0.75) ( 4 L t x 0.6 x 64.2 ksi) ≥ 1.4 x 46 ksi x Ag
tA557.0
L g = minimum length of welded overlap
needed based on block shear rupture in HSS bracing member
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For "pinned" end braces: flexural plastic hinge will form at mid-length only. Brace will impose no bending moment on connections and adjoining members.Must design brace connection to behave like a "pin"
PP
PP
Plastic Hinge
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2t
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2t
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Concrete floor slab
2t
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Concrete floor slab
Styrofoam
2t
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>2t
> 2t
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>2t
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> 2t
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Gusset Plate in Compression
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Concentric Work Point Location and the Uniform Force Method
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The Uniform Force Method
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Gusset Plate Design
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Beam and Column Web Yielding and Stability Checking
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1.1 Ry Pn
Ry Fy Ag
Check gusset buckling, beam web crippling, etc.
Check gusset yield, gusset net section fracture, gusset block shear fracture, local beam web yielding, etc.
Beam Midspan
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Connection at Beam Midspan
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Connection at Beam Midspan
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Gusset Plate
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Ordinary Concentrically Braced Frames
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Ordinary Concentrically Braced Frames
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Ordinary Concentrically Braced Frames