Fatigue Behavior of Welded Aluminum Light Poles - Menzemer

Fatigue Behavior of Welded Aluminum Light
Poles
Historical Perspective and Design Recommendations
DR. CRAIG C . MENZEMER
COLLEGE OF ENGINEERING
THE UNIVERSITY OF AKRON
JULY 2009

Objectives
• Brief, historical perspective on aluminum fatigue design provisions
• Existing fatigue data for welded aluminum light pole support details
• Review research program sponsored by HAPCO at The University of
Akron
• Fatigue test results from HAPCO research program
• Parametric studies and fracture mechanics evaluation
• Age old questions – how much, how long, are you sure…..
• Design recommendations

Historical Perspective
• 1986 First fatigue design specification published by the Aluminum
Association i in the U.S.
• 1986 Specification based on primarily small scale fatigue specimens
• Prior to the mid 1970’s, most fatigue data held by private and
government laboratories
• Effort started in the 1970’s to develop a fatigue data bank.
Collaborative effort started with European colleagues.
• Full – scale welded aluminum specimens evaluated during the 1980’s
in Europe and the U.S.
• Data sharing and extensive analysis resulted in current Aluminum
Association and ECCS fatigue design specifications
• Current provisions utilize stress range and detail type as the primary
variables that determine fatigue life for welded aluminum structures.

Historical Perspective – Questions / Answers
• “Ray Minor Database” – since the late 1960’s relatively low failure rate
for aluminum luminaire i poles
• What failure rate is acceptable
• Are the statistical limits adequate for an acceptable failure rate
• Resistance versus load and design philosophy.

Fatigue Test Results
ATLSS Fatigue Data Compared to ADM Provisions
100
Mean Curve, CategoryC, Aluminum Design Manual 2000
nge (ksi)
Stress Ra
10
Other Test Data
Mean Curve, Category D, Aluminum Design Manual 2000
Run-Out Data
Lower Limit, Category D, Aluminum Design Manual 2000
1
1.0E+04 1.0E+05 1.0E+06 1.0E+07
Cycles to Failure, N

HAPC and UA Fatigue Test Program
• Comparative set of tests for cantilever type samples with two different
base support details.
• Poles inserted into bored shoebase castings and welded top to bottom
Shoe base
Through Plate

Project Components
35
Stress (ksi)
30
25
20
15
24.5%
27.6%
27.6%
26.25%
10-0.188
10-0.25
10-0.3125
10-0.375
10
5
0
0 1 2 3 4 5
Plate Thickness (in)
7
6
m m
C rack length m
5
4
3
2
38 MPa_t=25.4
38 MPa_t=76.2
38 MPa_shoe base
1
0
0.E+00 2.E+05 4.E+05 6.E+05 8.E+05 1.E+06
Fatigue life, N

Publications
• Azzam, D. and Menzemer, C. C.
• Residual Stress Measurement of Welded Aluminum Light Pole Supports, The Journal of
Structural Engineering, ASCE, Volume 132, No. 10, October 2006, pp. 1603 – 1610.
• Azzam, D. and Menzemer, C. C.
• Fatigue Behavior of Welded Aluminum Light Pole Support Details, The Journal of Structural
Engineering, ASCE, Volume 132, No. 12, December 2006, pp. 1919 – 1927.
• Azzam, D. and Menzemer, C. C.
• Numerical Study of Stiffened Socket Connections for Highway Signs, Traffic Signals and
Luminaire Structures, accepted, The Journal of Structural Engineering, ASCE, Vol. 134, No. 2,
February 2008, pp. 173-180.
• Azzam, D. and Menzemer, C. C.
• Fatigue Life Assessment of Welded Aluminum Light Pole Structures, Bridge Structures:
Assessment, Design and Construction, Taylor and Francis, Vol. 3, No. 1, March 2007, pp. 81-90.
• Azzam, D., Menzemer, C. C. and Srivatsan, T.
• Fracture Mechanics Evaluation of the Fatigue Behavior of Welded Aluminum Light Poles,
Journal of Materials Engineering and Performance, to be submitted.

Fatigue- Test Results Shoe base
Stress
s rang e, ksi
100
Shoe base fatigue test t results
Lower Limit, Category D, Aluminum Design Manual, 2005
Lower Limit, Category E, Aluminum Design Manual, 2005
Lower Limit, Category E', Aluminum Design Manual, 2005
10
CAFL, 3.3 ksi
1
0.1
S =
29.698
0.1368
N −
CAFL, 2.5 ksi
CAFL, 1.9 ksi
CAFL, 1.0 ksi
1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Cycles to failure, N

Fatigue Test Results Through Plate
Stress
s rang ge, ks
i100
10
1
Through plate fatigue test results
Lower Limit, Category D, Aluminum Design Manual, 2005
Lower Limit, Category E, Aluminum Design Manual, 2005
Lower Limit, Category E', Aluminum Design Manual, 2005
S
= 43 N
− 0.1262
CAFL,2.5 ksi
CAFL,1.9 ksi
CAFL,1.0 ksi
CAFL,0.8 ksi
0.1
1.E+04 1.E+05 1.E+06 1.E+07 1.E+08
Cycles to failure, N

Butterfly Trend
Gage 2
Gage 3
ang e , k si
tress R
S
2.8
2.4
2
1.6
1.2
0.8
0.4
0
-0.4
-0.8
-1.2 12
-1.6
-2
-2.4 24
4.5 ksi
33 3.3 ksi
Gage 1
Gage 2
Gage 3 - Opposite
to bolt
Gage 4
Gage 5
Gage 6
2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 3.8 4
Elapsed time, sec

Fatigue Limits – Welded Aluminum Structures
Aluminum Association, ECCS/ENV, BS
10
Runout Fatigue Data - ATLSS / UA
ECCS/ENV (23 Mpa, 3.34 ksi)
BS8118 (20 Mpa, 2.9 ksi)
Aluminum Association (3.2 ksi)
Shoe-base details
1
10E+06 1.0E+06 10E+07 1.0E+07 10E+08 1.0E+08

Suggested Specification Provision
• Construction - Fillet
Welded Connections
• Application - Fillet welded
tube to integrally stiffened cast
base connection.
• CAFL - Current D 2.5 ksi
• CAFL - New Category 3.2 ksi
• Detail - Base metal at a pair of
circumferential fillet welds at least
0.48 D apart in the tubes
longitudinal direction. Tubes shall
be fit to a base with non-tapered
bore. Fillet welds shall be sufficient
to develop the static strength of the
tube and be placed in the following
order: weld the top of the base and
tube followed by the end of the
tube and bottom of base. The base
shall be for a top mounted
luminaire and short mast arms
that result in a dead load stress of 5
ksi or less.

Questions