Degree of bending of concrete-filled rectangular hollow section K-joints under balanced-axial loadings

doi:10.1007/s11709-022-0818-0

Front. Struct. Civ. Eng.

2022, Vol. 16

Issue (4) : 461-477 https://doi.org/10.1007/s11709-022-0818-0

RESEARCH ARTICLE

Degree of bending of concrete-filled rectangular hollow section K-joints under balanced-axial loadings

Rui ZHAO¹, Yongjian LIU^1,²(

), Lei JIANG^1,², Yisheng FU¹, Yadong ZHAO¹, Xindong ZHAO¹

¹. School of Highway, Chang’an University, Xi’an 710064, China
². Research Center of Highway Large Structure Engineering on Safety of Ministry of Education, Xi’an 710064, China

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Abstract

It has been found that the fatigue life of tubular joints is not only determined by the hot spot stress, but also by the stress distribution through the tube thickness represented as the degree of bending (DoB). Consequently, the DoB value should be determined to improve the accuracy of fatigue assessment for both stress-life curve and fracture mechanics methods. Currently, no DoB parametric formula is available for concrete-filled rectangular hollow section (CFRHS) K-joints, despite their wide use in bridge engineering. Therefore, a robust finite element (FE) analysis was carried out to calculate the DoB of CFRHS K-joints under balanced-axial loading. The FE model was developed and verified against a test result to ensure accuracy. A comprehensive parametric study including 190 models, was conducted to establish the relationships between the DoBs and four specific variables. Based on the numerical results, design equations to predict DoBs for CFRHS K-joints were proposed through multiple regression analysis. A reduction of 37.17% was discovered in the DoB, resulting in a decrease of 66.85% in the fatigue life. Inclusively, the CFRHS K-joints with same hot spot stresses, may have completely different fatigue lives due to the different DoBs.

Keywords fatigue assessment K-joint design equations degree of bending fracture mechanics

Corresponding Author(s): Yongjian LIU

Just Accepted Date: 15 April 2022 Online First Date: 27 June 2022 Issue Date: 09 August 2022

Cite this article:

Rui ZHAO,Yongjian LIU,Lei JIANG, et al. Degree of bending of concrete-filled rectangular hollow section K-joints under balanced-axial loadings[J]. Front. Struct. Civ. Eng., 2022, 16(4): 461-477.

URL:

https://academic.hep.com.cn/fsce/EN/10.1007/s11709-022-0818-0
https://academic.hep.com.cn/fsce/EN/Y2022/V16/I4/461

Fig.1 Stress distribution through the chord wall thickness at weld toe.

Fig.2 Geometric parameters of the CFRHS K-joint.

Tab.1 Steel material properties

Tab.2 Concrete mix ratio and material properties

parameter	detail A Ψ = 180° – 135°	detail B ψ = 150° – 50°	detail C ψ = 75° – 30°	detail D ψ = 40° – 15°
joint-included angle (α)
max	90°	Ψ ≤ 105°:60°	40°; 60° for ψ is big	—
min	45°	37.5°; 1/2ψ for ψ is small	1/2ψ	—
bevel angle of brace (ω)
max	—	90°	determined based on the α	—
min	—	10； 45° for Ψ > 105°	10°	—
complete weld
h_e	≥ t_b	≥ t_b for Ψ ≥ 90°; $? t b s i n ψ$ for Ψ ＜ 90°	$? t b s i n ψ$ but ≤ 1.75 t_b	≥2t_b
h_L	$? t b s i n ψ$ but ≤ 1.75 t_b	—	—	—

Tab.3 Details of the weld profile according to the GB 50661-2011 Chinese specification

Fig.3 Details of the weld profile in the GB 50661-2011 Chinese specification. (a) Stepped joints; (b) full-width joints; (c) welding details.

Fig.4 Finite element model.

Tab.4 Mesh sensitivity analysis for a typical joint (β = 0.7, 2γ = 30, τ = 0.75, θ = 30°)

Fig.5 Density of different meshes through the tube thickness. (a) 1 layer; (b) 2 layers; (c) 3 layers; (d) 4 layers; (e) 5 layers; (f) 6 layers.

Fig.6 Boundary and loading conditions.

Tab.5 The extrapolated region as recommended by IIW-XV-E

Fig.7 Extraction of the hot spot stress.

Fig.8 Geometry of specimen and arrangement of strain gauges (unite: mm). (a) General arrangement of truss girder; (b) test joint diagram; (c) measuring-point arrangement of HSS.

Fig.9 Test setup. (a) General arrangement of experiment; (b) local arrangement of experiment.

Fig.10 FE modeling and verification. (a) FE model of the truss; (b) comparison of Load-Displacement curve between FE results and test results; (c) comparison of HSS between FE results and test results.

Tab.6 Specific parameters for parametric analysis

Fig.11 The HSS distribution (β = 0.4, 2γ = 10, τ = 0.75, θ = 45°).

Fig.12 Influence of four variables on hot spot location (a) β; (b) 2γ; (c) τ; (d) θ.

Fig.13 A comparison of the DOB_CFRHS and DOB_CHS (β = 0.4, 2γ = 10, τ = 0.75, θ = 45°). (a) CFRHS K-joint; (b) RHS K-joint.

Fig.14 Influence of β on the DoB under balanced axial force (τ = 0.25, θ = 30°).

Fig.15 Influence of γ on the DoB under balanced axial force (β = 0.7, θ = 45°).

Fig.16 Influence of τ on the DoB under balanced axial force (2γ = 30, θ = 30°).

Fig.17 Influence of θ on the DoB under balanced axial force (β = 0.4, τ = 1).

Fig.18 Error analysis of the DoBs.

Fig.19 A comparison of SCF_CFRHS and SCF_CHS.

Fig.20 A comparison of DoB_CFRHS and DoB_CHS.

Fig.21 Remaining life prediction process for CFRHS K-joints based on fracture mechanics.

Tab.7 Input parameters used for remaining fatigue life prediction of CFRHS K-joints

Tab.8 Remaining fatigue life prediction of CFRHS K-joints

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