experimental study on mechanical behavior and failure

Experimental Study on Mechanical Behavior and Failure Mechanism of

Transmission Tower Structures ---Review and Reflect from the perspective of Resilience

Li Sun Institute of Structural Engineering

Chair of Structural Dynamics and Earthquake Engineering Prof. Dr. Božidar Stojadinović

Electric Power Supply System: an Infrastructure Network

Users Transmission and Distribution Generation

Research Background ◆Damage due to extreme ice load Rare ice disaster in South China in 2008

by courtesy of CMA

Research Background

Failure due to unbalanced tension in cables Failure due to cable disconnect

Jiangxi Province

by courtesy of Prof. Qiang Xie

Zhejiang Province

Failure due to unbalanced cable tension

by courtesy of Prof. Qiang Xie

Research Background

◆Damage due to extreme wind load Xuyu, JiangSu Province, 2005

by courtesy of Prof. Qiang Xie

Research Background

Outline ◆Test Program

◆Discussion on some issues

◆Reflection on test results

◆Conclusions and future works

Diaphragm

Diaphragm

Diaphragm

2:3 1:2

1. Test Program ◆ Test prototypes

Pw

C Gi Mw Gi T G1 G2

L L L Pw Pw

general load wind load ice load

◆ Loading types

reaction frame

distribution beam oil jack

rigid foundation anchor bolt

rigid stand

grooves testing pedestal

rigid box beam

◆ Laboratory loading setup

wind-resistance

3.45

m

Tongji University, Shanghai

Six specimens

Two pairs of Double-panel specimens

One pair of Single-panel specimens

One pair

Another pair

ice-resistance

wind-resistance ◆ Test specimens

◆ The principal failure mode --- Out-of-plane deformation….

by courtesy of Prof. Qiang Xie

How long is the buckling length?!

2. Discussion on some issues

◆ Are the tests of individual sub-assemblages are indicative of the overall behavior of the system?

◆ Are the cumulative second order effects have a significant impact on the buckling load distribution to individual members?

3. Reflection on test results

◆Why did the observed damage occur?

Principal failure mode: out-of-plane deflection and buckling

The location of tower stiffening diaphragms was not adequate

The design principles for distributing stiffening diaphragms in the tower body should be revisited

◆How the out-of-plane deflection of diagonal bracings negatively affect the stability performance of the tower structure?

¬ From three perspectives:

I. Considering the main leg…

II. Considering the diagonal bracings…

III. Considering the INTERACTION between the main leg and the diagonal bracings…

0 400 800 1200 1600 20000

20

40

60

80

100

120

140

121110

9

605958

f suw

f    suo

0.9f    suw

G1 (

kN)

ε (10-6)

 57 58 59 60 9 10 11 12

without diaphragm with diaphragm57

I. Considering the main leg…

0 20 40 60 80 100 120 140-2

0

2

4

6

8

10

12

14  without diaphragm

with diaphragm  

D (m

m)

G1 (kN)0 15 30 45 60 75 90 105

-1

0

1

2

3

4

5

6  without diaphragm

with diaphragm  

D (m

m)

G1 (kN)

Ⅱ. Considering the diagonal bracing…

Axially loaded member…

single-panel double-panel

D

Ⅲ . Considering the INTERACTION between the main leg and the diagonal bracing…

0 200 400 600 800 10000

400

800

1200

1600

2000

2400

Pw

G1

ε (10-6)

 57 58 59 60 9 10 11 12

ε (1

0-6)

G2

121110

9

605958

without diaphragm with diaphragm57

0 5 10 15 20 25 30 350

4

8

12

16

20

24

28

32

Pw(k

N)

D(mm)

 without diaphragm  with diaphragm

◆What is the difference of load-carrying capacity? The case of wind resistance

Pw

Pw

0 2 4 6 8 10 120

20

40

60

80

100

120

140

 without diaphragm  with diaphragm

G1(

kN)

D(mm)0 1 2 3 4 5 6 7 8

0

20

40

60

80

100

120

 without diaphragm  with diaphragm

G1(

kN)

D(mm)

The case of ice resistance

double-panel single-panel

◆What is the difference of load-carrying capacity?

G1

G1

Conclusions: ◆ The out-of-plane deflection of diagonal bracing is

“critical” but difficult to avoid; ◆ The stability performance of both the individual member

and the overall tower structure is remarkably influenced by the out-of-plane deflection of diagonal bracings;

◆ Adding diaphragms on the vulnerable panels of tower structure would be a practical and effective retrofitting strategy.

4. Conclusions and Future Work

Future work: 1.  Investigation of dynamic response 2.  Risk-informed performance analysis existing power network updated power network

retrofit existing component(s) updated Component(s) most cost-effective

Thank you for your attention! Looking forward to working with all of you…

Tel: +41 44 633 06 33

Email: sun@ibk.baug.ethz.ch

Any question? Or comments?