Please wait a minute...

Frontiers of Structural and Civil Engineering

Front. Struct. Civ. Eng.    2020, Vol. 14 Issue (5) : 1215-1231
Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints
Peng DENG1,2(), Boyi YANG2, Xiulong CHEN2, Yan LIU1,2
1. Shandong Provincial Key Laboratory of Civil Engineering Disaster Prevention and Mitigation, Shandong University of Science and Technology, Qingdao 266590, China
2. College of Civil Engineering and Architecture, Shandong University of Science and Technology, Qingdao 266590, China
Download: PDF(3406 KB)   HTML
Export: BibTeX | EndNote | Reference Manager | ProCite | RefWorks

A method for strengthening damaged tubular steel T-joints under axial compression by wrapping them with carbon fiber-reinforced polymer (CFRP) sheets was proposed and evaluated. The influence of the CFRP strengthening on the failure mode and load capacity of T-joints with different degrees of damage was investigated using experiments and finite element analyses. Five T-joints were physically tested: one bare joint to obtain the peak load and corresponding displacement (D1m), two reinforced joints to provide a reference, and two pre-damaged then retrofitted joints to serve as the primary research objects. The ratio of the pre-loaded specimen chord displacement to the value of D1m was considered to be the degree of damage of the two retrofitted joints, and was set to 0.80 and 1.20. The results demonstrate that the maximum capacity of the retrofitted specimen was increased by 0.83%–15.06% over the corresponding unreinforced specimens. However, the capacity of the retrofitted specimen was 2.51%–22.77% lesser compared with that of the directly reinforced specimens. Next, 111 numerical analysis models (0.63≤b≤0.76, 9.70≤g≤16.92) were established to parametrically evaluate the effects of different geometric and strengthening parameters on the load capacity of strengthened tubular T-joints under different degrees of damage. The numerical analysis results revealed that the development of equivalent plastic strain at the selected measuring points was moderated by strengthening with CFRP wrapping, and indicated the optimal CFRP strengthening thickness and wrapping orientation according to tubular T-joint parameters. Finally, reasonable equations for calculating the load capacity of CFRP-strengthened joints were proposed and demonstrated to provide accurate results. The findings of this study can be used to inform improved CFRP strengthening of damaged tubular steel structures.

Keywords tubular T-joint      carbon fiber-reinforced polymer      degree of damage      numerical analysis      equivalent plastic strain     
Corresponding Author(s): Peng DENG   
Just Accepted Date: 25 August 2020   Online First Date: 18 September 2020    Issue Date: 16 November 2020
 Cite this article:   
Peng DENG,Boyi YANG,Xiulong CHEN, et al. Experimental and numerical investigations of the compressive behavior of carbon fiber-reinforced polymer-strengthened tubular steel T-joints[J]. Front. Struct. Civ. Eng., 2020, 14(5): 1215-1231.
E-mail this article
E-mail Alert
Articles by authors
Xiulong CHEN
Fig.1  Specimen configuration and dimensions.
Fig.2  CFRP installation methods: (a) wrapping orientation of 0°/90° and (b) wrapping orientation of 45°/135°.
specimen degree of pre-damage chord brace β CFRP sheets
d0× t0 (mm) l0 (mm) d1× t1 (mm) l1 (mm) wrap orientation layer lc (mm)
T1-6 194 × 6 1180 127 × 6 464 0.65
T1-CV6 [0°/90°] 2 682
T1-CF6 [45°/135°] 2 682
T1-D80-CV6 0.80D1m [0°/90°] 2 682
T1-D120-CF6 1.20D1m [45°/135°] 2 682
Tab.1  Test specimens
member tensile yield stress, fy (N/mm2) ultimate tensile stress, fu (N/mm2) fy/fu elongation, d (%)
brace 325 476 0.683 17.85
chord 334 480 0.696 21.32
Tab.2  Material properties of steel
material type tensile strength (MPa) tensile modulus (GPa) thickness (mm) breaking elongation (%)
CFRP (SKO-I-300) 4900 240 0.111 1.7
Tab.3  Material properties of CFRP
material type viscosity (MPa·s) epoxy value (eq/100 g) organic chlorine (eq/100 g) inorganic chlorine (eq/100 g)
adhesive (E-51) 2000–2500 0.48–0.54 0.02 0.001
Tab.4  Technical parameters of epoxy resin E-51
material type compressive strength (kg/cm2) punching strength (kg/cm2) flexural strength (kg/cm2) tensile strength (kg/cm2) viscosity (MPa·s) volume resistivity (W·cm)
hardener (593) 1266 8–12 859 375 100±50 9 × 1013
Tab.5  Technical parameters of Hardener 593
Fig.3  Test setup.
Fig.4  Layout of LVDTs.
Fig.5  Failure modes of test specimens: (a) T1-6; (b) T1-CV6; (c) T1-D80-CV6; (d) T1-D120-CF6.
specimen P1m (kN) P1rm (kN) P2m (kN) (P1r(2)mP1m)/P1m (%) D1m (mm) D1rm (mm) Dpre (mm) D2m (mm)
T1-6 239.71 5.82
T1-CV6 256.70 7.10 8.64
T1-CF6 246.00 2.90 8.03
T1-D80-CV6 244.49 2.10 4.65 7.79
T1-D120-CF6 241.23 0.84 6.98 6.66
Tab.6  Test results
Fig.6  Load-displacement curves during first step loading.
Fig.7  Load-displacement curves during second step loading.
Fig.8  Mesh sensitivity evaluation of specimen T1-CV6.
Fig.9  Meshes of (a) T-joint specimens and (b) CFRP sheets.
Fig.10  FE model boundary conditions and loading methods.
Fig.11  (a) Numerical simulation and (b) test deformation of T1-6; (c) numerical simulation and (d) test deformation of T1-CV6.
Fig.12  Comparison of numerical and experimental load-displacement curves of (a) undamaged specimens and (b) retrofitted specimens.
group variable evaluated chord brace γ β CFRP sheets degree of damagea)
d0 (mm) t0 (mm) d1 (mm) t1 (mm) qf
qf 194 6 127 6 16.17 0.65 0/90
0.111 240 0.50D1m,
t0 194 6
127 6 16.17 13.86
0.65 0/90 0.111 240
d0 168 180 194 203 6 127 6 14.00 15.00
16.17 16.92
0.76 0.71
0.65 0.63
0/90 0.111 240
tc 194 6 127 6 16.17 0.65 0/90 0.111 0.167 240
Ec 194 6 127 6 16.17 0.65 0/90 0.111 240 360 480 600
Tab.7  Value of dimensional variables for the parametric study
Fig.13  Distribution of measuring points on the (a) chord elevation and (b) chord section.
Fig.14  Equivalent plastic strain at measuring points on (a) T2-6 and (b) T2-CV6 at different concave chord displacements.
group specimen P1m (kN) P1rm (kN) P2m (kN) P2m/P1m (%) P2m/P1rm (%) D1m (mm) D1rm (mm) D2m (mm)
T2 T2-6 229.78 7.43
T2-CV6 255.82 10.59?
T2-D50-CV6 237.28 103.26? 92.75 ?8.65
T2-D80-CV6 235.19 102.35? 91.94 ?9.49
T2-D120-CV6 221.69 95.39 86.66 24.78
T2-D150-CV6 218.41 95.05 85.38 25.25
T2-D200-CV6 215.67 93.86 84.31 29.85
T3 T3-CF6 250.07 8.53
T3-D50-CF6 231.46 100.73? 92.56 7.75
T3-D80-CF6 228.99 99.66 91.57 ?7.89
T3-D120-CF6 207.70 90.39 83.06 22.02
T3-D150-CF6 205.22 89.31 82.07 23.09
T3-D200-CF6 202.51 88.13 80.98 26.98
T4 T4-CS6 253.74 9.78
T4-D50-CS6 235.01 102.28? 92.62 8.01
T4-D80-CS6 232.81 101.32? 91.75 ?8.59
T4-D120-CS6 218.63 95.15 86.16 22.15
T4-D150-CS6 215.32 93.71 84.86 23.57
T4-D200-CS6 213.05 92.72 83.96 27.01
Tab.8  Comparison of specimens in groups T2, T3, and T4
Fig.15  Load-displacement curves of T2 group specimens.
Fig.16  Equivalent plastic strain of specimens with different CFRP wrapping orientations.
Fig.17  (a) Load-displacement curves of groups T5–T8 and (b) the brace buckling failure of T7-D120-CV8.
Fig.18  (a) Load-displacement curves of group T9–12 and (b) the punching shear failure of T12-D120-CV6.
group specimen tc
T13 T13-6 0.111 229.78 7.43
T13-CV6 255.82 10.59
T13-D50-CV6 237.28 103.26 92.75 ?8.65
T13-D80-CV6 235.19 102.35 91.94 ?9.49
T13-D120-CV6 221.69 ?96.48 86.66 24.78
T13-D150-CV6 218.41 ?95.05 85.38 25.25
T13-D200-CV6 215.67 ?93.86 84.31 29.85
T14 T14-CV6 0.167 262.14 11.27
T14-D50-CV6 244.29 106.31 93.19 18.59
T14-D80-CV6 242.36 105.47 92.45 19.48
T14-D120-CV6 240.63 104.72 91.79 23.19
T14-D150-CV6 239.07 104.04 91.19 22.96
T14-D200-CV6 237.00 103.14 90.41 26.75
Tab.9  Comparison of maximum capacity and corresponding displacement in groups T13 and T14
Fig.19  Load-displacement curves of specimens in groups T13 and T14.
Fig.20  Equivalent plastic strain at measuring points under different CFRP thickness.
Fig.21  Load-displacement curves of specimens with a pre-damage displacement of 1.20D1m.
Fig.22  Relationship between degree of damage and correction coefficient.
specimen degree of pre-damage Ffrp (kN) Fdfrp (kN) Fnum (kN) difference (%)
334.91 300.39
284.49 257.77
277.77 241.92
Tab.10  Comparison of bearing capacities obtained from FE models and proposed equation
1 G Shi, W J Zhou, Y Bai, C C Lin. Local buckling of 460 MPa high strength steel welded section stub columns under axial compression. Journal of Constructional Steel Research, 2014, 100(Sep): 60–70
2 G Shi, J J Wang, Y Bai, Y J Shi. Experimental study on seismic behavior of 460 MPa high strength steel box-section columns. Advances in Structural Engineering, 2014, 17(7): 1045–1059
3 H Qu, J S Huo, C Xu, F Fu. Numerical studies on dynamic behavior of tubular T-joint subjected to impact loading. International Journal of Impact Engineering, 2014, 67(May): 12–26
4 L Zhu, Q M Song, Y Bai, Y Wei, L M Ma. Capacity of steel CHS T-joints strengthened with external stiffeners under axial compression. Thin-walled Structures, 2017, 113(Apr): 39–46
5 W P Li, S G Zhang, W Y Huo, Y Bai, L Zhu. Axial compression capacity of steel CHS X-joints strengthened with external stiffeners. International Journal of Impact Engineering, 2014, 67(May): 12–26
6 M M K Lee, A Llewelyn-Parry. Offshore tubular T-joints reinforced with internal plain annular ring stiffeners. Journal of Structural Engineering, 2004, 130(6): 942–951
7 J Yang, Y B Shao, C Chen. Static strength of chord reinforced tubular Y-joints under axial loading. Marine Structures, 2012, 29(1): 226–245
8 N Hossein, L Y Mohammad Ali, A Hamid. Static performance of doubler plate reinforced tubular T/Y-joints subjected to brace tension. Thin-walled Structures, 2016, 108(Nov): 138–152
9 Y S Choo, J X Liang, G J van der Vegte, J Y R Liew. Static strength of doubler plate reinforced CHS X-joints loaded by in-plane bending. Journal of Constructional Steel Research, 2004, 60(12): 1725–1744
10 T C Fung, T K Chan, C K Soh. Ultimate capacity of doubler plate-reinforced tubular joints. Journal of Structural Engineering, 1999, 125(8): 891–899
11 H Qu, A L Li, J S Huo, Y Z Liu. Dynamic performance of collar plate reinforced tubular T-joint with precompression chord. Engineering Structures, 2017, 141: 555–570
12 Y Su, W Y Li, X Y Wang, T J Ma, L Ma, X M Dou. The sensitivity analysis of microstructure and mechanical properties to welding parameters for linear friction welded rail steel joints. Materials Science and Engineering A, 2019, 764: 138251
13 CECS (China Association for Engineering Construction Standardization). Technical Specification for Strengthening Concrete Structures with Carbon Fiber Reinforced Polymer Laminate CECS146: 2003(2007). Beijing: China Planning Press, 2007 (in Chinese)
14 ACI 440R07. Report on Fiber-reinforced Polymer (FRP) Reinforcement for Concrete Structures. ACI, 2007
15 M Lesani, M R Bahaari, M M Shokrieh. Experimental investigation of FRP-strengthened tubular T-joints under axial compressive loads. Construction & Building Materials, 2014, 53: 243–252
16 H Peng, J R Zhang, S P Shang, Y Liu, C S Cai. Experimental study of flexural fatigue performance of reinforced concrete beams strengthened with prestressed CFRP plates. Engineering structures, 2016, 127(Nov.15): 62–72
17 J G Teng, J W Zhang, S T Smith. Interfacial stresses in reinforced concrete beams bonded with a soffit plate: A finite element study. Construction & Building Materials, 2002, 16(1): 1–14
18 M A Zaki, H A Rasheed, T Alkhrdaji. Performance of CFRP-strengthened concrete beams fastened with distributed CFRP dowel and fiber anchors. Composites. Part B, Engineering, 2019, 176: 107117
19 M M A Kadhim, Z J Wu, L S Cunningham. Experimental and numerical investigation of CFRP-strengthened steel beams under impact load. Journal of Structural Engineering, 2019, 145(4): 04019004
20 A Benachour, S Benyoucef, A Tounsi, E A Adda bedia. Interfacial stress analysis of steel beams reinforced with bonded prestressed FRP plate. Engineering Structures, 2008, 30(11): 3305–3315
21 A Shaat, A Fam. Axial loading tests on short and long hollow structural steel columns retrofitted using carbon fibre reinforced polymers. Canadian Journal of Civil Engineering, 2006, 33(4): 458–470
22 K A Harries, A J Peck, E J Abraham. Enhancing stability of structural steel sections using FRP. Thin-walled Structures, 2009, 47(10): 1092–1101
23 M Lesani, M R Bahaari, M M Shokrieh. Numerical investigation of FRP-strengthened tubular T-joints under axial compressive loads. Composite Structures, 2013, 100: 71–78
24 M Lesani, M R Bahaari, M M Shokrieh. FRP wrapping for the rehabilitation of Circular Hollow Section (CHS) tubular steel connections. Thin-walled Structures, 2015, 90: 216–234
25 Y G Fu, L W Tong, L He, X L Zhao. Experimental and numerical investigation on behavior of CFRP-strengthened circular hollow section gap K-joints. Thin-walled Structures, 2016, 102: 80–97
26 J Aguilera, A Fam. Retrofitting tubular steel T-joints subjected to axial compression in chord and brace members using bonded FRP plates or through-wall steel bolts. Engineering Structures, 2013, 48: 602–610
27 L Zahedi, A Vatani Oskouei. A numerical study on steel tubes wrapped with CFRP Laminates: Carbon Fibre Reinforced Polymers applications on offshore marine structures. International Journal of the Constructed Environment, 2013, 3(3): 75–86
28 R H Haddad. Hybrid repair configurations with CFRP composites for recovering structural performance of steel-corroded beams. Construction & Building Materials, 2016, 124: 508–518
29 Y F Wu, C Yun, Y Y Wei, Y W Zhou. Effect of predamage on the stress-strain relationship of confined concrete under monotonic loading. Journal of Structural Engineering, 2014, 140(12): 04014093
30 K D Dalgic, M Ispir, A Ilki. Cyclic and monotonic compression behavior of CFRP-jacketed damaged non-circular concrete prisms. Journal of Composites for Construction, 2016, 20(1): 04015040
31 Y Z Gong, M T Liu, H Li, T Tan. Flexural behavior of existing damaged RC plate girders strengthened with CFRP sheets. Journal of Tianjin University (Science and Technology), 2018, 51(12): 1246–1252 (in Chinese)
32 N Kenta, F Chikako, N Tsutomu. Damage mechanism of existing RC slabs with reinforcing steel plate. MATEC Web of Conferences, 2019, 258: 05011
33 P Gao, J Wang, Z Y Li, L Hong, Z L Wang. Effects of predamage on the compression performance of CFRP-confined rectangular steel reinforced concrete columns. Engineering Structures, 2018, 162: 109–120
34 S Vanlanduit, J Vanherzeele, R Longo, R Guillaume. A digital image correlation method for fatigue test experiments. Optics and Lasers in Engineering, 2009, 47(3–4): 371–378
35 T Rabczuk, T Belytschko. Cracking particles: A simplified meshfree method for arbitrary evolving cracks. International Journal for Numerical Methods in Engineering, 2004, 61(13): 2316–2343
36 T Rabczuk, T Belytschko. A three-dimensional large deformation meshfree method for arbitrary evolving cracks. Computer Methods in Applied Mechanics and Engineering, 2007, 196(29–30): 2777–2799
37 T Rabczuk, G Zi, S Bordas, H Nguyen-Xuan. A simple and robust three-dimensional cracking-particle method without enrichment. Computer Methods in Applied Mechanics and Engineering, 2010, 199(37–40): 2437–2455
38 H Nguyen-Xuan, T Rabczuk. Adaptive selective ES-FEM limit analysis of cracked plane-strain structures. Frontiers of Structural and Civil Engineering, 2015, 9(4): 478–490
39 C P Pantelides, J Nadauld, L Cercone. Repair of cracked aluminum overhead sign structures with glass fiber reinforced polymer composites. Journal of Composites for Construction, 2003, 7(2): 118–126
40 J D Nadauld, C P Pantelides. Rehabilitation of cracked aluminum connections with GFRP composites for fatigue stresses. Journal of Composites for Construction, 2007, 11(3): 328–335
41 A Fam, S Witt, S Rizkalla. Repair of damaged aluminum truss joints of highway overhead sign structures using FRP. Construction & Building Materials, 2006, 20(10): 948–956
42 CMC (China Ministry of Construction). Technical specification for welding of steel structure of building JGJ81-2002. Beijing: China Architecture and Buildings Press, 2002 (in Chinese)
43 SAC (Standardization Administration of China). Metallic Materials-Tensile testing-Part 1: Method of Test at Room Temperature GB/T 228.1-2010. Beijing: China Standards Press, 2010 (in Chinese)
44 M A Msekh, N H Cuong, G Zi, P Areias, X Zhuang, T Rabczuk. Fracture properties prediction of clay/epoxy nanocomposites with interphase zones using a phase field model. Engineering Fracture Mechanics, 2018, 188: 287–299
45 K M Hamdia, M A Msekh, M Silani, T Q Thai, P R Budarapu, T Rabczuk. Assessment of computational fracture models using Bayesian method. Engineering Fracture Mechanics, 2019, 205: 387–398
46 Y Bao, T Wierzbicki. On fracture locus in the equivalent strain and stress triaxiality space. International Journal of Mechanical Sciences, 2004, 46(1): 81–98
47 T H Zhou, W C Li, Y Guan, L Bai. Damage analysis of steel frames under cyclic load based on stress triaxiality. Engineering mechanics, 2014, 31(7): 146–155 (in Chinese)
48 F F Liao. Study on micro fracture criterion of steel and its prediction for connections ductile fracture. Dissertation for the Doctoral Degree. Shanghai: Tongji University, 2012 (in Chinese)
49 W Wang, F F Liao, Y Y Chen. Ductile fracture prediction and post-fracture path tracing of steel connections based on micromechanics-based fracture criteria. Engineering mechanics, 2014, 31(3):101–108, 115 (in Chinese)
50 Z Y Shen. Calculation of the ultimate load bearing capacity of the junction of straight welded pipe. Steel structure, 1991, 14(4): 34–38 (in Chinese)
Related articles from Frontiers Journals
[1] Mohammad Abubakar NAVEED, Zulfiqar ALI, Abdul QADIR, Umar Naveed LATIF, Saad HAMID, Umar SARWAR. Geotechnical forensic investigation of a slope failure on silty clay soil—A case study[J]. Front. Struct. Civ. Eng., 2020, 14(2): 501-517.
[2] Yaqiong WANG, Yunxiao XIN, Yongli XIE, Jie LI, Zhifeng WANG. Investigation of mechanical performance of prestressed steel arch in tunnel[J]. Front. Struct. Civ. Eng., 2017, 11(3): 360-367.
[3] Zhiming ZHAO, Xihua WANG. Evaluation of potential failure of rock slope at the left abutment of Jinsha River Bridge by model test and numerical method[J]. Front Struc Civil Eng, 2013, 7(3): 332-340.
[4] Xiaojia CHEN, Yuanlin WANG. Experimental and numerical study on microcrack detection using contact nonlinear acoustics[J]. Front Arch Civil Eng Chin, 2009, 3(2): 137-141.
[5] DU Baisong, GE Yaojun, ZHOU Zheng. An analytical method for calculating torsional constants for arbitrary complicated thin-walled cross-sections[J]. Front. Struct. Civ. Eng., 2007, 1(3): 293-297.
[6] LOU Menglin, LI Yuchun, LI Nansheng. Analyses of the seismic responses of soil layers with deep deposits[J]. Front. Struct. Civ. Eng., 2007, 1(2): 188-193.
[7] YUE Zhongqi. Digital representation of meso-geomaterial spatial distribution and associated numerical analysis of geomechanics: methods, applications and developments[J]. Front. Struct. Civ. Eng., 2007, 1(1): 80-93.
Full text