Lecture Notes #28Design of Gusset plate

1

Professor Guowei MaOffice: 160

Tel: 61-8-6488-3102Email: ma@civil.uwa.edu.au

Gusset Plate

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Flat structural elements used to connect adjacent

members meeting at truss panel joints and at diagonal

brace connections.

Help transmit loads from one member to another.

Maybe welded or bolted to the members meeting at the

joints.

Minimum thickness used in design practice is usually 10

mm.

Gusset Plate at a Diagonal Brace

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Gusset Plate at a Truss Panel Point

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Gusset Plate at a Truss Panel Point

5

Gusset Plate at a Truss Panel Point

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Gusset Plate at a Truss Support

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Design of Gusset Plate

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For diagonal bracing connection, several connection

interfaces must be designed:

diagonal brace-to-gusset connection gusset-to-column connection beam-to-column connection

At truss joints, the gusset plates connect the web

members to the chord members

The centroidal axes of the members meeting at the joint

coincide at one point, called the work point (WP)

Design of Gusset Plate

9

Moment may be induced in the gusset plate and the

adjoining members if it is not feasible to have a common

WP

Shear and axial stresses

Whitmore effective width, lw Projecting lines at an angle of spread of 30 on both

side of the connection starting from the first row of bolts

to the last row of bolts

For welded connections, projected on both sides of the longitudinal weld to the end of the weld

Design of Gusset Plate

10

Effective gross area

Whitmore effective width, lw times the plate thickness, t End of the bracing member or truss web member

terminates at least a distance of 2t away from the re-

entrant corner of the gusset plate at the gusset-to-column

interfaces

Above requirement can be relaxed for connections subject

to monotonic or static loading

Out-of-Plane Buckling

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Unbraced length, Lg the larger of the length of the plate between adjacent

lines of bolts parallel to the direction of the axial

compression force, or the length of the plate along the

centroidal axis of the diagonal brace or truss web

member between the end of the brace or truss web

member and the connected edge of the gusset plate.

Buckling is assumed to occur over a plate width equal to

the Whitmore effective width, lw

Out-of-Plane Buckling

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tlN wcrc =

lw: Whitmore effective width

t: Thickness of the gusset plate

: 0.9

cr: The critical buckling stress

Buckling of the Free or Unsupported Edge

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Buckling of the Free or Unsupported Edge

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Ef

Lt yfg5.0

Gusset plate under monotonic or static loading

Gusset plate subject to cyclic (or seismic) loading

Ef

Lt yfg33.1

Yielding of Gusset Plate

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Tension yielding is the most desirable form of failure because of the ductility associated with this failure mode

tlfN wys =

Design tension or compression yield strength

Tension Failure

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Tension failure of the gusset plate due to fracture at a bolt line within the Whitmore effective area

tndlfN holewus )( =

plategusset theofstrength Tensile : uf0.75 :

lineeach for force axial applied the lar toperpendicu holesbolt ofNumber : n

holebolt ofDiameter : holedLeast desirable form of failure because of the sudden and brittle nature of this failure mode

Combined Actions

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0.12*2**

+

+

sss VV

NN

MM

Example

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For the truss joint shown below, the gusset plate is made of

Grade 400 steel with a yield stress fy= 400 MPa, and tensile

strength fu=520 MPa assuming a M20 bolts of Property Class

4.6, determine

i) Whitmore effective width for the gusset plate on diagonal

web members A and B

ii) Compression buckling capacity of the gusset plate on

diagonal member A

iii)Tension capacity of the gusset plate on diagonal member B

19

16 mm thick

Gusset plate

271 kN

271 kN

376 kN

20

75 mm

40

Solution

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1)

mm 6.20630tan1508040

tan40

=++=

++= wAAwA Lbl

mm 2.25330tan150280

tan2

=+=

+= wBBwB Lbl

22

2) mm 75=gL

433 mm 5.70519)16)(6.206(121

121

=== tlI wAA

mm 62.4)16)(6.206(

5.70519===

AIr AA

2.1662.4

75==

A

g

rL

75 mm

206.6 mm

kN 24721N 104721.2

)1075()105.70519)(10200(14.3

7

23

1292

2

2

=

=

==

ecr l

EIN

kN 22249247219.0 === crc NN

23

3)

kN 4.1458

)102.253)(1016()10400)(9.0( 336

=

== gyt AfN

Tension yielding capacity of the gusset plate on the diagonal element B

Tension capacity of the gusset plate due fracture

kN 5.133110)2222.253)(1016()10520)(85.0)(9.0(

85.0336

=

=

=

uut AfN

Lecture Notes #28Gusset PlateGusset Plate at a Diagonal BraceGusset Plate at a Truss Panel PointGusset Plate at a Truss Panel PointGusset Plate at a Truss Panel PointGusset Plate at a Truss SupportDesign of Gusset PlateDesign of Gusset PlateDesign of Gusset PlateOut-of-Plane BucklingOut-of-Plane BucklingBuckling of the Free or Unsupported EdgeBuckling of the Free or Unsupported EdgeYielding of Gusset PlateTension FailureCombined ActionsExampleSlide Number 19Slide Number 20SolutionSlide Number 22Slide Number 23