Hollow Section Joints in Trusses

Wardenier RHS Joints - Oslo Course 2009

Hollow Section Joints in Trusses

Intro Joints & Behaviour


Trusses


Most common Combinations of sections

for trusses

Brace Chord Joint

CC

RR

CR

RI

CI


Hollow Section Trusses

a. Warren truss

b. Pratt truss

c. Vierendeel truss

d. truss with cross braces

Warren Type : K-joints

Pratt Type : N-joints

Vierendeel Type : T-joints

Cross brace Type : KT - joints

X - joints


Basic Types of Joints


Definition of eccentricity (joint design)


Definition of Gap and Overlap


Definition of Load capacity ultimate load)

Maximum

or load at a

3%d0 or 3%b0

deformation


Further: Service ability criteria

•• Deformation < 1% chord width or chord diameterDeformation < 1% chord width or chord diameter

•• crack initiationcrack initiation


A : chord face plastification

B : chord punching shear

C : brace effective width

D : chord shear failure

E : local buckling brace

F : local buckling chord

Failure Modes

e.g. for

RHS K gap joints


Symbols used (e.g. for K-Joints) d

b

h

t

e

g

0

1

2

β γ θ τ

b0

h0

t0 θ2

b2 d2

h2 h1

b1 d1

θ1

t2 t1

g

+e

N1 N2

N0

1 2

0


For Square Hollow Sections:

T and X-joints:

K gap joints:

KT joints:

For Rectangular Hollow Sections, include rectangularity,

e.g. for K gap joints:

0

1

b

b=β

0

21

2 b

bb +=β

0

321

3b

bbb ++=β

0

2211

4b

hbhb +++=β

Joint parameters

b0

h0

t0 θ2

b2 d2

h2 h1

b1 d1

θ1

t2 t1

g

+e

N1 N2

N0

1 2

0


0

0

0

0

t

bor

t

d2 =γ

0b

hi=η

00

0

yfA

Nn

⋅=

0t

ti=τ

Joint parameters

b0

h0

t0 θ2

b2 d2

h2 h1

b1 d1

θ1

t2 t1

g

+e

N1 N2

N0

1 2

0


Truss Behaviour

• Assume pin ended Joints but only if :

- the governing elements (joints or members) have

sufficient deformation/rotation capacity

If loads between the joints: assume continuous chords


Truss Behaviour

For Vierendeel trusses: use moment joints

(stiffness is important)


General Design Aspects for Trusses

• Depth h ≅ 1/10 to 1/16 L; generally 1/15 L

• pin jointed members if critical parts (members or joints)

have sufficient rotation capacity → secondary moments can

be neglected for static design

• if possible: center lines noding

• gap joints preferred above overlap joints (tolerances)

• optimize chords, however considering joint strength

• consider the joint strength always in the conceptual design


- end preparation

- fitting (tolerances)

- welding

Gap joints vs Overlap joints

ggapoverlap


Multiplanar trusses


Joint strength related to that for uniplanar jointsbut additional:

- Geometrical effect

- Loading effect

(see left)

Multiplanar Truss Behaviour


Hollow Section Joints in Frames

Types of Joints


Bolted joint to a fin plate


Bolted joint to a T stub


Bolted joint to a welded I section stub


Single sided bolted joint


Welded RHS beam to column joints


Stiffened beam to column joints


Basic behaviour of Hollow Section Joints


• follow the forces

• identify potential failure locations

• deform the structure under the acting loads

• consider the local stiffness and the material behaviour

• identify the possible failure modes

General approach


Example: Plate to RHS joint


Example

• plate

• weld

• chord (lamellar tearing)

• chord (face plastification)

• chord (punching shear)

• chord (side wall failure) (yielding, crippling)

Possible failure locations


Example

Plate to RHS chord joint - plate failure


Example

Plate to RHS chord joint - weld failure

Weld failure should be

avoided

(yielding only possible

over a small distance)


Example

Plate to RHS chord joint - chord lamellar tearing

No photo for this failure mode


Example

Plate to RHS chord joint - other chord failure modes

chord

punching shear

side wall yielding

chord face plastification


Plate to RHS joint (plate failure)

Different stiffness for q1 and q2


Plate to RHS joint(plate failure)

Stress and resulting deformation

1. Method:

Consider the

deformations under a

uniform stress



Compatibility

Resulting stress

pattern in plate


Stress and resulting deformation for a rigid plate

2. Method:

Plate stiffness >>

stiffness RHS face



a: ductile →redistribution of stresses

b: brittle →failure at reaching in one

point the ultimate stress

Effect of material


Stress pattern at failure (material a)


Chord side

wall failure

Other failure modes e.g. side wall failure


The end of the

lectures on:

introduction into

the joint behaviour


IIW (2008) Relation to the Basic Types of Joints

0.5N sinθ

0.5N sinθ

θ

N

N cosθ

=

0.5N sinθ

θ

0.5N

0.5N cosθ

0.5N sinθ

θ

+

0.5N

0.5N cosθ

Example: Checking of a K joint with imbalanced brace loads

Hollow Section Joints in Trusses

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