Prediction of natural frequency of free spanning subsea pipelines
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2010
- Type: Text , Journal article
- Relation: International Journal of Steel Structures Vol. 10, no. 1 (2010), p. 81-89
- Full Text: false
- Reviewed:
- Description: Free spans or suspended spans normally occur in subsea pipelines due to the irregularity of seabed and/or the scouring action of sea water. A problem of significance to the free spans of subsea pipeline is that currents or waves flowing across pipelines can shed vortices and induce vibration which may cause fatigue damage to the pipelines. Natural frequencies of free spans are required when solving vibration amplitude and cyclic stresses in the free span. The natural frequency is usually calculated with simplified equations, where factors such as boundary conditions and axial forces are not accurately taken into account. In this study, the influence of boundary conditions, mass of hydrocarbon products, axial force, and multiple spans on the natural frequencies of pipeline are investigated and corresponding suggestions are provided for frequency calculation.
Fatigue experiments on CFRP repaired welded thin-walled RHSTO-RHS cross-beam connection
- Authors: Xiao, Zhigang , Zhao, Xiao , Mashiri, Fidelis
- Date: 2008
- Type: Text , Conference paper
- Relation: Proceedings of the Tenth International Symposium on Structural Engineering for Young Experts (ISSEYE-10) p. 971-978
- Full Text: false
- Reviewed:
- Description: Cracked thin-walled rectangular hollow section (RHS)-to-RHS cross-beam connections are repaired with carbon fibre reinforced polymer (CFRP) composites and constant amplitude fatigue experiments are conducted on them. A pilot test is first conducted on a square hollow section (SHS)-to-SHS T-connection to explore an effective method of applying CFRP. Due to the “peel off” effect at the corner region of the SHS-to-SHS specimen, early debonding appears in the pilot test which only results in a small increase in fatigue life. Circumferential or transverse restraining CFRP patches are added in the RHS-to-RHS cross-beam specimens which prevent early debonding successfully and lead to significant increase in fatigue life.
Fatigue testing of subsea pipeline steel connections under combined actions
- Authors: Liu, Huihua , Zhao, Xiao , Xiao, Zhigang
- Date: 2010
- Type: Text , Conference paper
- Relation: Incorporating Sustainable Practice in Mechanics of Structures and Materials - Proceedings of the 21st Australian Conf. on the Mechanics of Structures and Materials p. 649-654
- Full Text: false
- Reviewed:
- Description: This paper describes a set of experimental tests of subsea pipeline steel connections under combined forces: one set of force is fatigue load, which is the simulation of the variation caused by currents or waves flowing across pipelines; another set of force is hoop force, which is constant tension force introduced by internal and external pressures. The steel connections are made of two steel plates joined together by single-sided girth welds. One central notch is machined on the weld toe. The specimens under combined forces are compared with those subjected to fatigue loads alone. It is found that the hoop force could affect the fatigue life of subset pipeline steel connections and also reduce the initiation angle of the crack propagation.
A boundary element analysis of fatigue crack growth for welded connections under bending
- Authors: Chen, Tao , Xiao, Zhigang , Zhao, Xiao , Gu, Xianglin
- Date: 2013
- Type: Text , Journal article
- Relation: Engineering Fracture Mechanics Vol. 98, no. (2013), p. 44-51
- Full Text: false
- Reviewed:
- Description: Transverse fillet welded joints and circular hollow section (CHS)-to-plate welded connections were analyzed to obtain crack growth life under bending. Based on a 3D boundary element model, an initial semi-elliptical surface crack was embedded at the weld toe. Thereafter, crack propagation was performed with Paris’ law and strain energy density criterion. This method discards the assumption of constant aspect ratio of crack shape during propagation stage. Numerical results were compared with the experimental results in the literature. It is found that numerical analysis is reliable and the boundary element method is suitable for estimating the fatigue crack growth life.
Fatigue strength evaluation of transverse fillet welded joints subjected to bending loads
- Authors: Xiao, Zhigang , Chen, Tao , Zhao, Xiao
- Date: 2012
- Type: Text , Journal article
- Relation: International Journal of Fatigue Vol. 38, no. (2012), p. 57-64
- Full Text: false
- Reviewed:
- Description: Three methods of fatigue strength evaluation, i.e., the hot spot stress (HSS) method, 1 mm stress method and linear elastic fracture mechanics (LEFM) method, are used to evaluate the fatigue strength of transverse fillet welded joints in bending and the results are compared with those of fatigue experiments. It is found that the HSS is overly conservative in predicting the fatigue strength of fillet welded joints in bending. The 1 mm stress catches the geometric influence of attachments very well. A reference strength range is suggested for applying the 1 mm stress method to the fatigue strength evaluation of fillet welded joints in bending on the base of analysing available test data. LEFM is an established method for fatigue strength evaluation of welded joints and its applicability is much dependent on the ease and accuracy of quantifying the stress intensity factor (SIF) along the crack front. In this study, the SIF of fillet welded joints in bending is estimated in different ways and the resulting fatigue strengths are compared with fatigue test data.
Fatigue behaviour of CFRP strengthened steel plates with different degrees of damage
- Authors: Yu, Qian Qian , Chen, Tao , Gu, Xianglin , Zhao, Xiao , Xiao, Zhigang
- Date: 2013
- Type: Text , Journal article
- Relation: Thin-Walled Structures Vol. 69, no. (2013), p. 10-17
- Full Text: false
- Reviewed:
- Description: An experimental and analytical study was conducted to further investigate the effectiveness of the carbon fibre reinforced polymer (CFRP) plates in extending fatigue life of steel structures. Different lengths of artificial cracks were introduced to represent different degrees of fatigue damage. The experimental results demonstrated that the CFRP patches could effectively slow down the crack growth and prolong the fatigue life. A theoretical model was developed to predict the fatigue life of tested specimens. Thereafter, a parametric study was carried out to investigate the fatigue behaviour of steel plates with a wider range of damage degrees. This study extends the understanding of CFRP repair at different stages of crack propagation and provides some useful suggestions for the strengthening method.
Tests on CFRP repaired welded thin-walled cross-beam connections
- Authors: Xiao, Zhigang , Zhao, Xiao , Tong, L.
- Date: 2010
- Type: Text , Conference paper
- Relation: Proceedings of the 5th International Conference on FRP Composites in Civil Engineering (CICE 2010) p. 903-906
- Full Text: false
- Reviewed:
- Description: Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fibre reinforced polymer (CFRP) composites and constant amplitude fatigue experiments are conducted on the repaired specimens. In the previous pilot test on a T-connection of square hollow sections (SHS), early debonding happened in the corner region due to peeling effect. In this study, circumferential or transverse restraining CFRP patches are applied in the corner region which prevent early debonding and lead to significant increase in fatigue life. Furthermore, the addition of strengthening steel plates has further increased the flexural stiffness and fatigue life of the cracked specimens.
CFRP repaired welded thin-walled cross-beam connections subject to in-plane fatigue loading
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2012
- Type: Text , Journal article
- Relation: International Journal of Structural Stability and Dynamics Vol. 12, no. 1 (2012 2012), p. 195-211
- Full Text: false
- Reviewed:
- Description: Cracked cross-beam connections made of thin-walled rectangular hollow sections (RHS) are repaired with carbon fiber-reinforced polymer (CFRP) sheets. Constant amplitude fatigue experiments are conducted on the repaired specimens. A pilot test is conducted on a T-connection of square hollow sections (SHS) to explore the effective method of applying CFRP. Due to the peeling effect at the corner region of the SHS-to-SHS connection, early debonding happens in the pilot test that only results in a slight extension in fatigue life. In the following experiments of repairing RHS-to-RHS cross-beam connections, circumferential or transverse restraining CFRP patches are applied in the corner region that prevents early debonding successfully and leads to significant increase in fatigue life. Finally, an improvement is made with the addition of steel strengthening plates that increase both the flexural stiffness and fatigue life of the cracked specimens significantly. The proposed retrofitting method may be useful for repairing other similar fatigue-cracked welded tubular connections.
Stress analyses of free spanning subsea pipelines with finite element method
- Authors: Xiao, Zhigang , Zhao, Xiao
- Date: 2008
- Type: Text , Conference paper
- Relation: Proceedings of the Tenth Int. Symp. on Structural Engineering for Young Experts (ISSEYE-10) Vol.1 p. 305-309
- Full Text: false
- Reviewed:
Modified stress intensity factor equations for semi-elliptical surface cracks in finite thickness and width plates
- Authors: Peng, Yang , Tong, Lewei , Zhao, Xiao , Xiao, Zhigang
- Date: 2011
- Type: Text , Conference paper
- Relation: The Twelfth East Asia-Pacific Conference on Structural Engineering and Construction p. 2601-2608
- Full Text: false
- Reviewed:
- Description: Weld defects and severe variation of shape near the welds cause high stress concentration at weld toes or weld roots. This high stress concentration reduces fatigue lives of welded structures. A stress intensity factor (SIF) which includes this effect increases the accuracy of fatigue lives prediction. A magnification factor is commonly used to multiply the SIF of semi-elliptical surface cracks to account for the stress concentration effect in welded connections. Yamada and Hirt model is one of these methods. Comparison between Yamada & Hirt SIF equations and Newman & Raju SIF equations are applied to SIF of semi-elliptical surface cracks. The results suggest that Yamada & Hirt SIF equations are valid when the crack aspect ratio is less than 0.6. New empirical SIF equations are developed based on Yamada & Hirt SIF equations. The newly derived SIF equations are verified by comparing with experimental data.
Formula for SIF of cracked steel plates strengthened with CFRP plate
- Authors: Yu, Qian Qian , Zhao, Xiao , Chen, Tao , Xiao, Zhigang , Gu, Xianglin
- Date: 2012
- Type: Text , Conference paper
- Relation: 22nd Australasian Conference on the Mechanics of Structures and Materials, ACMSM 2012 p. 537-540
- Full Text: false
- Reviewed:
- Description: Fatigue loading will lead to crack initiation and crack growth in steel structures where stress concentration exists. Fatigue life of aged steel members can be extended significantly with carbon fiber reinforced polymer (CFRP) repair. Stress intensity factor (SIF) is a key parameter to calculate the fatigue life and analyze the progress of crack development. There is a lack of knowledge of SIF for cracked steel plate with different degrees of damage strengthened with CFRP. This paper aims to fill this knowledge gap. The SIF formula is developed based on the classical SIF solution and James-Anderson method by considering two correction factors, representing the effect of load share effect in composite system and the effect of initial damage degree, respectively. It is demonstrated that the SIF formula proposed in the paper is applicable to SIF estimation of strengthened center cracked steel plate with different degrees of damage.
Experimental study on repair of steel plate with different damage degrees subject to fatigue loading
- Authors: Yu, Qian Qian , Zhao, Xiao , Al-Mahaidi, R. , Xiao, Zhigang , Chen, Tao , Gu, Xianglin
- Date: 2014
- Type: Text , Conference paper
- Relation: 7th International Conference on Bridge Maintenance, Safety and Management, IABMAS 2014 p. 879-884
- Full Text: false
- Reviewed:
- Description: Recent research on the use of carbon fibre reinforced polymer (CFRP) materials in steel structures has demonstrated their potential for fatigue crack repair and corresponding convenience in construction. However, most previous tests focused on the specimen with a small notch or slot. There is limited study on the improved fatigue behavior of steel plates with different initial degrees of damage. This paper presents an experimental program on notched steel plates with different initial crack lengths repaired with CFRP laminates. Particular attention was paid to simulate the various initial degrees of damage using multiple lengths of slots, including 2%, 10%, 20%, 30% and 40% of the plate width. CFRP reinforcement with different elastic moduli and different configurations were adopted. The fatigue crack propagation was monitored by the "beach marking" technique and crack propagation gauges. The test results indicated that this retrofitting method was applicable to specimens at all stages of crack propagation to retard the crack propagation and prolong the fatigue life. Increasing the elastic modulus of CFRP laminate and covering the initial cracks could lead to more significant strengthening effects
Crack propagation prediction of CFRP retrofitted steel plates with different degrees of damage using BEM
- Authors: Yu, Qian Qian , Zhao, Xiao , Chen, Tao , Gu, Xianglin , Xiao, Zhigang
- Date: 2014
- Type: Text , Journal article
- Relation: Thin-Walled Structures Vol. 82, no. (2014), p. 145-158
- Full Text: false
- Reviewed:
- Description: Although carbon fibre reinforced polymer (CFRP) materials have proven effective in strengthening steel structures especially when used to improve fatigue behaviour, further study is required to investigate their effectiveness when applied at different stages of crack propagation in steel elements. This paper presents a numerical study on CFRP retrofitted steel plates with different degrees of damage using the boundary element method (BEM). The numerical results compared well with the experimental data, which demonstrated that the BEM is reliable for crack propagation analysis of CFRP laminate retrofitted steel plates. Finally, a parametric analysis was conducted to investigate the influence of bond length, bond width, CFRP stiffness and adhesive shear modulus on stress intensity factor (SIF) values. © 2014 Elsevier Ltd.
A boundary element analysis of non-load-carrying cruciform welded joints strengthened with FRP materials
- Authors: Chen, Tao , Zhao, Xiao , Gu, Xianglin , Xiao, Zhigang
- Date: 2012
- Type: Text , Conference paper
- Relation: International Conferences on Advances in Steel Structures 2012 p. 1405 - 1412
- Full Text: false
- Reviewed:
Evaluation of stress intensity factor for CFRP bonded steel plates
- Authors: Yu, Qian Qian , Zhao, Xiao , Xiao, Zhigang , Chen, Tao , Gu, Xianglin
- Date: 2014
- Type: Text , Journal article
- Relation: Advances in Structural Engineering Vol. 17, no. 12 (2014), p. 1729-1746
- Full Text: false
- Reviewed:
- Description: Recent studies on the application of carbon fibre reinforced polymer (CFRP) materials to defected steel structures have demonstrated the potential for significant reduction of stress intensity factor (SIF) values at crack tips leading to extended fatigue lives. However, most of the previous research relied on experimental and numerical methods, which were either expensive or time-consuming. In this paper, the SIF values at crack tips of steel plates strengthened with bonded composite materials were evaluated using linear elastic fracture mechanics. The analysis was based on the classical solution of SIF values of plain steel plates, considering load share effect and geometry correction factor change resulted from the overlay patch. The effect of different parameters were demonstrated and compared with experimental results, including initial damage degrees of specimens, geometric and mechanical properties of retrofitting materials and bond locations. Good agreement with the experimental data indicated that this approach could conservatively predict the SIF values with reasonable accuracy. A parametric study on variables including the CFRP modulus, the bond width and bond length was conducted based on this method to further investigate their effect on the SIF values.
Fatigue behaviour of CFRP-strengthened thin-walled RHS-to-SHS cross-beam connections
- Authors: Xiao, Zhigang , Zhao, Xiao , Borrie, Daniel
- Date: 2012
- Type: Text , Conference paper
- Relation: 14th International Symposium on Tubular Structures, ISTS 2012 p. 345-350
- Full Text: false
- Reviewed:
- Description: Cross-beam connections are widely used in welded thin-walled structures made of rectangular or square hollow sections mainly due to the connection's requiring less welding and no member cutting. Re-welding or bolted splicing are not suitable for repairing or strengthening fatigue cracked cross-beam connections. In this research, a new method using Carbon Fibre Reinforced Polymer composites (CFRPs) is proposed. Repair/strengthening are conducted for thin-walled RHS cross-beam connections at different levels of fatigue damage before constant amplitude fatigue experiments are conducted again on the specimens. Fatigue test results of unstrengthened intact connections are also presented for the purpose of comparison. The results show that the proposed retrofitting method is effective in repairing/strengthening fatigue-damaged thin-walled cross-beam connections when the connections are not severely cracked.
Dynamically controlling exterior and interior window coverings through IoT for environmental friendly smart homes
- Authors: Karmakar, Gour , Roy, Soma , Chattopadhyay, Gopinath , Xiao, Zhigang
- Date: 2017
- Type: Text , Conference proceedings , Conference paper
- Relation: 2017 IEEE International Conference on Mechatronics, ICM 2017; Gippsland, Australia; 13th-15th February 2017 p. 487-491
- Full Text: false
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- Description: Energy saving using smart home is of paramount importance to reduce heating and cooling energy consumption, and promote sustainable environment. Awnings and blinds have exhibited their effectiveness to reduce heating gain in summer and cooling loss in winter, respectively. Awnings are more effective to reduce heat gain in summer than blinds, while the opposite is true in winter. There exist many approaches in the current literature to remotely control flat curtains and blinds. However, up to our knowledge, no automatic technique is available in the literature, which can dynamically control the orientation of an exterior covering so that it can act like a blind in winter and an awning in summer. In this paper, we propose an automatic on-demand system to control the orientation and size of such exterior covering, and the turning air conditioners, heaters and lights on and off considering the rate of change of room temperature, and its lighting condition. We also discuss the properties and design of such exterior covering. A simulation model was developed to analysis the performance of our approach in terms of energy savings both in summer and winter. © 2017 IEEE.
- Description: Proceedings - 2017 IEEE International Conference on Mechatronics, ICM 2017
Numerical analysis of stress intensity factor in cracked steel plates strengthened with CFRP plate
- Authors: Yu, Qian Qian , Xiao, Zhigang , Zhao, Xiao , Chen, Tao , Gu, Xianglin
- Date: 2012
- Type: Text , Conference paper
- Relation: Sixth International Composites Conference ACUN-6 p. 187 - 191
- Full Text: false
- Reviewed:
Numerical study on the compression-bending response of grouted connections in offshore structures
- Authors: Chen, Tao , Fang, Qi , Zhang, Chihai , Li, Weichao , Xiao, Zhigang
- Date: 2021
- Type: Text , Journal article
- Relation: Journal of Constructional Steel Research Vol. 185, no. (2021), p.
- Full Text: false
- Reviewed:
- Description: Grouted connections (GCs) are widely used to link the substructures and towers for offshore wind turbines and transfer various loads from the turbine and tower to the substructure. Extremely complex stresses are developed in these composite connections formed with steel pipes and grout fillings. This paper presents a numerical study, using ABAQUS, on the mechanical response of GCs under axial compression coupled with bending. The effect of axial load ratio on the moment-rotation responses, contact stress between steel pipes and grout, as well as compositions of flexural capacity. Further study is conducted on the stress distribution in the grouted connection under axial compression coupled with bending, and the stress distribution was derived with python script. Analysis shows that, axial load ratio plays a non-negligible role and the distribution of contact stress differs from that recommended by current design guide. These should be considered with caution in industrial design. In addition, this paper also proposes a method to derive the contact stress from numerical model constructed with Abaqus. The results show that contact pressure and shear keys provide the main components for the flexural capacity and the sum of Mp and Mshear-keys accounts for about 75% of the total capacity. And the values of the non-uniform coefficient of shear keys ηsk are all larger than 0.75 which shows that the force distribution between shear keys is extremely uneven. The outputs of this paper provide a further understanding of the GCs subject axial compression coupled with bending. © 2021 Elsevier Ltd
Fatigue evaluation of grouted connections subjected to Markov matrix based random loading
- Authors: Huang, Xiaoming , Chen, Tao , Chen, Ke , Yuan, Guokai , Xiao, Zhigang
- Date: 2022
- Type: Text , Journal article
- Relation: Marine structures Vol. 86, no. (2022), p. 103295
- Full Text: false
- Reviewed:
- Description: Grouted connections in offshore wind turbines often experience random cyclic loadings due to harsh marine environment and are prone to fatigue damage. It is significant to evaluate their fatigue life for the durability of the offshore wind turbine. In this study, a fatigue evaluation exercise of grouted connection of wind turbine structure with finite element method is completed based on standards of Det Norske Veritas, i.e., DNVGL-ST-0126 and DNVGL-RP-C203. Loadings of variable amplitude summarized in the format of Markov matrix are firstly separately applied to the grouted connection models, and refined finite element models were analyzed to obtain stress states of the materials at critical locations. Hot spot stresses of welded shear keys and nominal stresses of grout were calculated and their damage indices were then accumulated for predominant loading directions. Furthermore, an integrated program has been designed to make the process of fatigue assessment convenient and efficient. Finally, fatigue evaluation is conducted for the grouted connection based on the proposed method. The process was applied to the grouted connection of an actual wind turbine and the results indicated that the damage indices are less than 1/3. The proposed method can serve as a useful tool for the actual engineering design of grouted connections. •A fatigue evaluation method for grouted connections was proposed based on finite element analyses with Markov matrix loads.•An integrated program was developed to facilitate the extensive finite element modeling and fatigue damage evaluation.•Critical locations of the model under axial force, horizontal force, and bending moment were discussed.•Fatigue damage contours are plotted to show the extent of damage of the grouted connection in different directions.