Lecture Notes #28Design of Gusset plate

1

Professor Guowei MaOffice: 160

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

Gusset Plate

2

• 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

3

Gusset Plate at a Truss Panel Point

4

Gusset Plate at a Truss Panel Point

5

Gusset Plate at a Truss Panel Point

6

Gusset Plate at a Truss Support

7

Design of Gusset Plate

8

• 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

11

• 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

12

tlN wcrc φσφ =

lw: Whitmore effective width

t: Thickness of the gusset plate

Φ: 0.9

σcr: The critical buckling stress

Buckling of the Free or Unsupported Edge

13

Buckling of the Free or Unsupported Edge

14

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

15

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

tlfN wys φφ =

• Design tension or compression yield strength

Tension Failure

16

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

tndlfN holewus )( −=φφ

plategusset theofstrength Tensile : uf0.75 : φ

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

17

0.12*2**

≤

+

+

sss VV

NN

MM

φφφ

Example

18

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

21

1)

mm 6.20630tan1508040

tan40

=°++=

++= θwAAwA Lbl

mm 2.25330tan150280

tan2

=°×+=

+= θwBBwB 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 A

A

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 π

kN 22249247219.0 =×== crc NN φφ

23

3)

kN 4.1458

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

=

××××== −gyt AfN φφ

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 φφ