Design of Bracing Connections in Concentrically Braced Frames

Reference Materials

Reference Materials Design of Seismic. Resistant Steel Building Structures 3. Concentrically Braced Frames Prepared by: Michael D. Engelhardt University of Texas at Austin with the support of the American Institute of Steel Construction. Version 1 - March 2007

Brace End

Brace Net Section Fracture

Gusset Plate Undesired 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 GB 50011 -2010: 1. 2 Abrfy Required axial tension strength of brace for limit state of fracture of the net section

R u = R y Fy Ag Ru = 1. 2 Abrafy Critical Net Section Ae = U A n Ae < Ag due to: slot (An < Ag ), and shear lag (U < 1)

$R u = R y Fy Ag Limit state: fracture of net section (0.$

R u = R y Fy Ag Limit state: fracture of net section (0. 75) Ae (Rt Fu) ≥ Ry Fy Ag For A 500 Gr B rectangular HSS: OR: Need to Reinforce Net Section (Ae need not exceed Ag )

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. 2 Abrfy/betg <= f

Also check block shear rupture of bracing member. . L t = design wall thickness of HSS Pu = R y Fy Ag 1. 2 Abrfy Pn = (0. 75) ( 4 L t x 0. 6 x 64. 2 ksi) ≥ 1. 4 x 46 ksi x Ag = minimum length of welded overlap needed based on block shear rupture in HSS bracing member

P P Plastic Hinge P P 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"

2 t

2 t

2 t Concrete floor slab

2 t Concrete floor slab Styrofoam

> 2 t t >2

>2 t

> 2 t

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

$Beam Midspan Check gusset yield, gusset net section fracture, gusset block shear fracture, local$

Beam Midspan Check gusset yield, gusset net section fracture, gusset block shear fracture, local beam web yielding, etc. R y Fy Ag Check gusset buckling, beam web crippling, etc. 1. 1 Ry Pn

Connection at Beam Midspan

Gusset Plate

Ordinary Concentrically Braced Frames