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Fatigue tests and design of thin CHS–SHS T-joints under cyclic in-plane bending

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Abstract

Agricultural equipments, such as linkage graders, haymakers, swing-ploughs, bale handlers and road transport equipments, such as road trailers, traffic sign supports and lighting poles are manufactured using welded thin-walled (t < 4 mm) hollow section connections. There are currently no fatigue design rules for nodal joints made up of thicknesses less than 4 mm in existing fatigue design standards such as CIDECT Design Guide No.8. Previous research on welded thin-walled joints covered plate-to-SHS (square hollow section) and SHS-to-SHS T-joints. This paper describes fatigue tests on T-joints made up of thin-walled (t < 4 mm) SHS chords and circular hollow section (CHS) braces, namely CHS–SHS T-joints. The joints were tested under constant stress amplitude cyclic in-plane bending in the brace. In all the 18 CHS–SHS T-joints tested, chord-tension-side failure mode was observed. Using the experimental stress concentration factors (SCFs) obtained through stress distribution measurement at weld toes in the chord and SCFs from existing parametric equations, fatigue design recommendations are proposed.

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Abbreviations

β :

Brace diameter to chord width ratio \( \left( {{{d_{1} } \mathord{\left/ {\vphantom {{d_{1} } {b_{0} }}} \right. \kern-0pt} {b_{0} }}} \right) \)

τ :

Brace wall thickness to chord wall thickness ratio \( \left( {{{t_{1} } \mathord{\left/ {\vphantom {{t_{1} } {t_{0} }}} \right. \kern-0pt} {t_{0} }}} \right) \)

σ logN :

Standard deviation of the normal distribution for logN

σr.m1 :

Nominal in-plane bending stress range in the brace

2γ:

Chord width to chord thickness ratio \( \left( {{{b_{0} } \mathord{\left/ {\vphantom {{b_{0} } {t_{0} }}} \right. \kern-0pt} {t_{0} }}} \right) \)

A :

Intercept of S–N curve with the “number of cycles” axis

b 0 :

External width of hollow section chord member

d 1 :

External diameter of hollow section brace member

B :

Inverse of the slope of the SN

CHS:

Circular hollow section

CIDECT:

Committee

CTS:

Chord-tension side

f u,m :

Measured ultimate tensile strength

f y,m :

Measure yield stress

IIW:

International Institute of Welding

N :

Number of cycles to failure

N4:

Number of cycles to an end of test failure criterion

PLC:

Programmable logic controller

R :

Stress ratio, ratio of minimum to maximum algebraic stress in a cycle

SCF max_chord_SHS_SHS :

Maximum parametric equation stress concentration factor at weld toes in the chord for SHS–SHS T-joints under in-plane bending

SCF max_chord_CHS_CHS_Par :

Maximum parametric equation stress concentration factor at weld toes in the chord for CHS–SHS T-joints estimated from parametric equations for SCFs in SHS–SHS T-joints

SCF max_chord_CHS_CHS_Exp :

Maximum experimental stress concentration factor at weld toes in the chord for thin CHS–SHS T-joints estimated from parametric equations for SCFs in SHS–SHS T-joints

SHS:

Square hollow section

S r.hs :

Total hot spot stress range at any hot spot location, usually defined by predetermined lines

S r-nom :

Nominal stress range

t :

Tube wall thickness

t1 :

Wall thickness of brace member

t 0 :

Wall thickness of chord member

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Acknowledgments

The authors would like to thank the following laboratory staff in the Department of Civil Engineering at Monash University for their assistance in this project: Mr. Graham Rundle, Mr. Roy Goswell, Mr. Len Doddrell, Mr. Geoff Doddrell, Mr. Roger Doulis and Mr. Don McCarthy. This Project is sponsored by a CIDECT fund together with OneSteel Market Mills and a Monash University SMURF2 fund. A special thanks to Mr. Hayden Dagg of OneSteel Market Mills for his continuous support and help.

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Correspondence to Fidelis Rutendo Mashiri.

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Mashiri, F.R., Zhao, XL. & Tong, L. Fatigue tests and design of thin CHS–SHS T-joints under cyclic in-plane bending. J Civil Struct Health Monit 3, 129–140 (2013). https://doi.org/10.1007/s13349-013-0042-7

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