Local joint flexibility of tubular T/Y-joints retrofitted with GFRP under in-plane bending moment
Introduction
Circular hollow section (CHS) members are extensively applied as the primary components in offshore tubular lattice structures [1]. The CHSs are connected together to form a tubular connection where the profiled ends of secondary members (the braces) are welded onto the circumference of the main member (the chord) [2]. For tubular joints, the local joint flexibility (LJF) happens simply when the joint is under basic loadings such as IPB moment [3]. The LJF causes the growth of the nominal stresses, deflections, and variation the natural frequencies of the structure. In addition, LJF can simply cause plastic failure of the chord wall [4,5].
So far, several methods are proposed for enhancing tubular joints, such as FRP method [[6], [7], [8]], collar plate method [[9], [10], [11]], doubler plate method [[12], [13], [14]], external ring method [15,16], internal ring method [17,18], grout method [19,20], joint can method [21]. Fig. 1 shows a Y-connection retrofitted FRP.
In spite of the important role of the LJF in evaluating the global static and dynamic responses of tubular connections, the LJF of the connections with FRP has not been investigated. Consequently, there is an essential demand for further investment so that more detailed guidelines on the LJF of the connections retrofitted with the FRP which can be formulated.
In this work, in the first step, a FE model was generated. In the FE model, the weld along the chord/brace junction was generated. Besides, using ANSYS contact ability, the interface between the bottom face of the FRP and the outer face of the chord, weld, and brace wall was modeled. In the next step, the precision of the generated FE model was evaluated with the data of three experimental tests and nine models produced by the equation derived by Fessler et al. [22] and three experimental tests carried out by Lesani et al. [23]. After that, 158 FE models were generated to evaluate the efficacy of the FRP sheets (number, length, and orientation), the brace angle (θ), and the joint geometry (θ, β, and γ) on the fLJF of the FRP retrofitted connections (fLJF,frp), and the ratios of the fLJF,frp to the fLJF of the associated un-retrofitted connection (fLJF,u). According to the results of FE models, a full fLJF database was performed and finally, an equation was proposed. This equation reflects the efficacy of the FRP, the brace inclination angle, and connection geometry on the fLJF,frp. Also, the formula is checked with the acceptance standard proposed by the UK DoE [24].
Section snippets
Literature survey
The following two paragraphs evaluate the research works carried out on the LJF of tubular connections, and the research works conducted on the joints retrofitted with FRP.
Determination of the fLJF
The LJF of tubular joints defines as the displacement attributed to the local chord deformation occurred by a unit load. To determine the LJF at the joint junction, the rotation of the joint due to the overall displacement must be removed from the total occurred rotation. The local rotation at the joint can be calculated without taking the beam movement. It obtains the distortion of the circular section which is oval shape in IPB moment [2]. The LJF determines as indicated in Eq. (1).
Details of FE models
In this work, the weld along the chord/brace junction was modeled as stated by the American Welding Society [53]. The details of the weld profile are depicted in Fig. 3 and Table 1. The same as other research works conducted on the LJF in tubular joints [3,[33], [34], [35], [36]], and [[39], [40], [41]], the properties of the weld are the same as the properties of the brace. Also, the SOLID186 element and SHELL 281 element were applied to model the steel members and FRP sheets. A sub-zone mesh
Validation of FE results
The accuracy of FE results should be validated. As far as the authors are aware, no experimental/FE/theoretical data of fLJF for joints retrofitted with the FRP is available in the literature. Due to this reason, the following works are utilized to evaluate the accuracy of the FE model. Three experimental Y-joints in IPB moment reported by Fessler et al. [22], nine Y-joints in IPB moment produced by the formula suggested by Fessler et al. [22], and three experimental T/Y-joints retrofitted with
Characteristics of the parametric study
A total of 158 FE models were created, in the FE software package ANSYS19.0, to evaluate the efficacy of the FRP sheet number, FRP sheet length, FRP sheet orientation, connection geometries, and the angle between brace and chord on the fLJF of the retrofitted T/Y-joints in IPB moment. The parameters include; FRP sheet number (N), FRP length coefficient (η), FRP sheet orientations, the diameter proportion between brace and chord (β), the proportion of the radius to wall thickness of the chord (γ
Parametric formula for the prediction of the fLJF values of the joints under IPB load
Until now, no equation is available to determine the fLJF of connections retrofitted with FRP. Therefore, in this section, by using the results of FE analyses and the statistical software package, SPSS V22, a parametric equation is proposed for this problem.fLJF,GFRP = N−0.178η−0.017β−2.14τ−0.48γ2.025θ1.54; R2 = 0.971Where fLJF,GFRP is the fLJF of the T/Y-connections with FRP. N shows the GFRP sheet numbers. η shows the FRP length coefficient and it is equal to δFRP/d. R2 is the determination
Conclusions
158 FE models were produced to evaluate the efficacy of FRP sheets (length, number, and orientation), the brace inclination angle (θ), and the joint geometry (β, θ, τ, and γ) on the local joint flexibility coefficient (fLJF) of the T/Y-connections retrofitted with FRP in IPB moment. The main conclusions of this paper are as follows:
- (1)
Validation of the FE results using experimental data and empirical equations showed that the FE model can well predict the fLJF of T/Y-joint retrofitted with FRP
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgement
The authors gratefully acknowledge the useful comments of anonymous reviewers on the draft version of this paper.
References (56)
- et al.
Identification of jack-up spudcan fixity by an output-only substructural strategy
Mar Struct
(2012) - et al.
A novel framework for deriving the unified SCF in multi-planar overlapped tubular joints
Mar Struct
(2018) - et al.
Local joint flexibility of completely overlapped tubular joints under in-plane bending
J Constr Steel Res
(2014) - et al.
Experimental and numerical investigation on behavior of CFRP-strengthened circular hollow section gap K-joints
Thin-Walled Struct
(2016) - et al.
Retrofitting tubular steel T-joints subjected to axial compression in chord and brace members using bonded FRP plates or through-wall steel bolts
Eng Struct
(2013) - et al.
Stress concentration factors in tubular T/Y-joints strengthened with FRP subjected to compressive load in offshore structures
Int J Fatig
(2020) Static strength of tubular T/Y-joints reinforced with collar plates at fire induced elevated temperature
Mar Struct
(2019)- et al.
Experimental investigation of a doubler-plate reinforced tubular T-joint subjected to combined loadings
J Constr Steel Res
(2001) - et al.
Experimental study of the axial compressive strength of CHS T-joints reinforced with external stiffening rings
Thin-Walled Struct
(2016) - et al.
Strength of external-ring-stiffened tubular X-joints subjected to brace axial compressive loading
Thin-Walled Struct
(2018)
Study on fire resistance of circular hollow section (CHS) T-joint stiffened with internal rings
Thin-Walled Struct
Strength of ring-stiffened tubular T-joints in offshore structures: a numerical parametric study
J Constr Steel Res
Formulae for hot-spot stress concentration coefficients of concrete-filled CHS T-joints based on experiments and FE analysis
Thin-Walled Struct
Behaviour of grout-filled double-skin steel tubular T-joint subjected to low-velocity impact
Thin-Walled Struct
Static strength of chord reinforced tubular Y-joints under axial loading
Mar Struct
FRP wrapping for the rehabilitation of Circular Hollow Section (CHS) tubular steel connections
Thin-Walled Struct
Local joint flexibility of tubular joints of offshore structures
Mar Struct
Stress analysis of spatial frames with consideration of local flexibility of multiplanar tubular joint
Eng Struct
Nonlinear joint flexibility element for the modeling of jacket-type offshore platforms
Appl Ocean Res
Local joint flexibility element for offshore plateforms structures
Mar Struct
Local joint flexibility of CHS X-joints reinforced with collar plates in jacket structures subjected to axial load
Appl Ocean Res
Local joint flexibility of CHS T/Y-connections strengthened with collar plate under in-plane bending load: parametric study of geometrical effects and design formulation
Ocean Eng
Parametric equations to predict LJF of completely overlapped tubular joints under lap brace axial loading
J Constr Steel Res
Local joint flexibility of completely overlapped tubular joints under out-of-plane bending
Constr Steel Res
Local joint flexibility of tubular joints of offshore structures
Mar Struct
A study on the Local Joint Flexibility (LJF) of two-planar tubular DK-joints in jacket structures under in-plane bending loads
Appl Ocean Res
Local joint flexibility of two-planar tubular DK-joints in OWTs subjected to axial loading: parametric study of geometrical effects and design formulation
Ocean Eng
Geometrical effects on the local joint flexibility of two-planar tubular DK-joints in jacket substructure of offshore wind turbines under OPB loading
Thin-Walled Struct
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