design of bracing connections in concentrically braced frames ppt file · web viewconcentrically...
Post on 17-Mar-2018
235 Views
Preview:
TRANSCRIPT
Design of Bracing Connections in Concentrically Braced Frames
Reference Materials
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
Brace End
Brace Net Section Fracture
Gusset PlateUndesired behaviour – Gusset Plate Buckling
Desired behaviour – Gusset Plate Bending and Brace Buckling
Bad Designs of Bracing Connections
HSS Bracing Connections
gusset plate
rectangular HSS bracing member
Check HSS bracing member for limit state of net section fracture
AISC:Ru= Ry Fy Ag
GB50011-2010: 1.2Abrfy
Required axial tension strength of brace for limit state of fracture of the net section
Ru= Ry Fy Ag
Ru = 1.2Abrafy
Critical Net SectionAe = U An
Ae < Ag due to:slot (An < Ag ), andshear lag (U < 1)
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
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
Gusset Plate in Tension 1.2Abrfy/betg <= f
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
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
2t
2t
Concrete floor slab
2t
Concrete floor slab
Styrofoam
2t
>2t
> 2t
>2t
> 2t
Gusset Plate in Compression
Concentric Work Point Location and the Uniform Force Method
The Uniform Force Method
Gusset Plate Design
Beam and Column Web Yielding and Stability Checking
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
Connection at Beam Midspan
Connection at Beam Midspan
Gusset Plate
Ordinary Concentrically Braced Frames
Ordinary Concentrically Braced Frames
Ordinary Concentrically Braced Frames
top related