Design of Beam-Column Connections in Steel Moment Frames

Observed Damage to Steel Moment Frames in the 1994 Northridge Earthquake

Observed Damage to Steel Moment Frames in the 1994 Northridge Earthquake

Typical Moment Frame Connection Detail Prior to 1994

The SAC Steel Project www.sacsteel.org

• Funded by FEMA• Over 6 years to 2000• $12m research funding• Participated by 100s of

practicing engineers, university researchers, contractors, materials suppliers, inspectors and building officials

Output of the SAC Steel Project

Prequalified Connection Detail by FEMA 350

Welded Unreinforced Flanges, Welded Web Connection (WUF-W)

Welded Unreinforced Flanges, Bolted Web Connection (WUF-B)

Recommended Weld Access Hole Detail

Typical Details of the Joint Panel Zone - Continuity Plate and Column Web Doubler Plate

Design Procedure of the WUF-B Connections

Beam-Colum Connection Recommended in GB50011-2001: WUF-B Connection – Beam Parallel to Column Web

• Column through, joint panel zone in the column • The 2 welds between the beam flanges and the columns flange must be CJP groove welds• The beam web to column flange connection by high strength friction grip bolts via a column

connection plate• The weld between the column flange and the column connection plate shall be fillet weld both

sides, >=5mm, and to develop the full shear strength of the connection plate. If the plate exceeds 16mm in thickness, use double bevel CJP groove welds

• Continuity plates and beam flanges equal thickness and equal strength

Beam-Colum Connection Recommended in GB50011-2001: WUF-B Connection – Beam Perpendicular to Column Web

Design Process – Step 1 Design Connection for Bending

• Mu >= 1.3Mp

• Mp = full plastic moment capacity of the plastic hinge of the beam (column through), or of the column (beam through)

• Mu = Bending moment resistance capacity of the joint connection provided by the flange connections and based on the design strength of connection

• If column through and if CJP groove welds are used to connect the beam flanges to the column, this overtrength requirement is considered met

Eurocode 8 Provisions

Design Process – Step 2 Design Connection for Shear

• Vu >= 1.2(2Mp/ln)+VGb

• Mp = full plastic moment capacity of the plastic hinge of the beam (column through), or of the column (beam through)

• ln = clear span of beam• VGb=(seismic weight UDL)ln/2, shear force at beam

ends, determined by considering static equilibrium of the isolated beam under the seismic weight UDL

• Vu = Shear resistance capacity of the joint connection provided by the web connection and based on the design strength of connection

Design Process – Step 3 Calculate the Required Panel Zone Thickness and Determine if a Doubler Plate is Needed

• The shear stress in the panel zone bounded by the flanges of the column and the continuity plates shall meet t = y(Mpb1 + Mpb2)/Vp<=4fyv/3, as well as t = (Mb1 + Mb2)/Vp<=(4/3)fv/gRE

• Vp = hbhctp is the volume of the panel zone, tp is the panel zone thickness >=(hb + hc)/90

• y = 0.6 for Seismic Resistance Class 3 and 4, 0.7 for Seismic Resistance Class 1 and 2

• Mb1 and Mb2 = the factored bending moments of beams at the two sides of the joint panel

• gRE=0.75• fv = design shear strength of steel• fyv = 0.58fy, is the yielding stress in

shear of steel material

Beam-Column Joint Panel Zone

Doubler Plate if Required

Design Process – Step 4 Design the Shear Tab and the HSFG Bolts

• To resist the connection shear force demand 1.3(2Mp/l) • FEMA 350 recommends that the bolts should be designed for

bearing• Chinese code recommends the following for checking the shear

resistance of HSFG bolts: Nvb = 0.75nAn

bfub

• Nvb = shear resistance provided by one HSFG bolt

• n = number of cross sections resisting shear in the bolt• An

b= net cross section area of bolt• fu

b = tensile strength of bolt material