Experimental and Analytical Behavior of Square CFDST Column Blind Bolted to Steel Beam Connections

Jingfeng Wang,Lei Guo 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.2

In recent years, steel or composite beam-column connections adopting blind fasteners have drawn increasing praise due to the rapid development of assembled steel structures. However, limited researches have paid attention to the experimental and analytical behavior of concrete filled double-skin steel tube (CFDST) column blind bolted joints. For investigating the structural performance and seismic behavior of this type of connection, cyclic tests on blind bolted joints to square CFDST columns were carried out to explore the effects of column hollow ratio and end plate type. Finite element analytical modelling of the semi-rigid joint was performed considering complex contact interactions and material models. Good agreement between the test and analytical results was observed in terms of the failure modes and the hysteretic behavior. Substantial parametric analyses were conducted on typical CFDST column connections to observe the influence of parameters including strength of steel tube, column hollow ratio and bolt pretension force. Furthermore, certain constructional measures commonly employed in engineering practice were also discussed. It was concluded that the CFDST column blind bolted to the steel beam joint has favorable seismic behavior and is feasible for application in high-intensity earthquake regions.

Analytical Performance and Design of CECFST Column Assembled to PEC Beam Joint

Jingfeng Wang,Zhihan Hu,Lei Guo,Bo Wang,Yonggan Yang 대한토목학회 2021 KSCE JOURNAL OF CIVIL ENGINEERING Vol.25 No.7

Concrete-encased concrete-filled steel tube (CECFST) columns and partially encased composite (PEC) beams are both steel-concrete composite members which have outstanding advantages and have been applicated in some engineering constructions. This paper makes an attempt to employ blind bolting technique to assemble CECFST columns to PEC beams. For the purpose of exploring the mechanical performance of this type of assembled joints, firstly, a nonlinear finite element (FE) model was established and validated, where complicated contact interaction was taken into consideration. Plenty of parametric analysis were adopted to find out the effect of ten parameters on strength and initial stiffness of the assembled joint. Numerical analysis showed that mechanic behavior is notably affected by axial load ratio, width and thickness of end-plate, bolt pretension force, bolt diameter, and steel ratio of CECFST column. Full-range analysis was then carried out to observe stress and strain developments and failure modes. Load transfer mechanism in CECFST column was also studied. Design methods to estimate the flexural capacity and initial stiffness of the connections were proposed in accordance with the component models. In comparison, it could be concluded that the calculation results fit well with the analytical results, which confirms that the design formulas could provide a favorable basis in practical design.

Fatigue performance and life prediction methods research on steel tube-welded hollow spherical joint

Qi Guo,Ying Xing,Honggang Lei,Jingfeng Jiao,Qingwei Chen 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.1

The grid structures with welded hollow spherical joint (WHSJ) have gained increasing popularity for use in industrial buildings with suspended cranes, and usually welded with steel tube (ST). The fatigue performance of steel tube-welded hollow spherical joint (ST-WHSJ) is however not yet well characterized, and there is little research on fatigue life prediction methods of ST-WHSJ. In this study, based on previous fatigue tests, three series of specimen fatigue data with different design parameters and stress ratios were compared, and two fatigue failure modes were revealed: failure at the weld toe of the ST and the WHSJ respectively. Then, S–N curves of nominal stress were uniformed. Furthermore, a finite element model (FEM) was validated by static test, and was introduced to assess fatigue behavior with the hot spot stress method (HSSM) and the effective notch stress method (ENSM). Both methods could provide conservative predictions, and these two methods had similar results. However, ENSM, especially when using von Mises stress, had a better fit for the series with a non- positive stress ratio. After including the welding residual stress and mean stress, analyses with the local stress method (LSM) and the critical distance method (CDM, including point method and line method) were carried out. It could be seen that the point method of CDM led to more accurate predictions than LSM, and was recommended for series with positive stress ratios.

Modelling and experiment of semi rigid joint between composite beam and square CFDST column

Lei Guo,Jingfeng Wang,Meng Zhang 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.34 No.6

Semi-rigid connections with blind bolts could solve the difficulty that traditional high strength bolts were unavailable to splice a steel/composite beam to a closed section column. However, insufficient investigations have focused on the performance of semi-rigid connection to square concrete filled double-skin steel tubular (CFDST) columns. In this paper, a component model was developed to evaluate the mechanical behavior of semi-rigid composite connections to CFDST columns considering the stiffness and strength of column face in compression and column web in shear which were determined by the load transfer mechanism and superstition method. Then, experimental investigations on blind bolted composite joints to square CFDST columns were conducted to validate the accuracy of the component model. Dominant failure modes of the connections were analyzed and this type of joint behaved semi-rigid manner. More importantly, strain responses of CFDST column web and tubes verified that stiffness and strength of column face in compression and column web in shear significantly affected the connection mechanical behavior owing to the hollow part of the cross-section for CFDST column. The experimental and analytical results showed that the CFDST column to steel-concrete composite beam semi-rigid joints could be employed for the assembled structures in high intensity seismic regions.

Component based moment-rotation model of composite beam blind bolted to CFDST column joint

Lei Guo,Jingfeng Wang,Wanqian Wang,Zhaodong Ding 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.38 No.5

This paper aims to explore the mechanical behavior and moment-rotation model of blind bolted joints between concrete-filled double skin steel tubular columns and steel-concrete composite beams. For this type of joint, the inner tube and sandwiched concrete were additionally identified as basic components compared with CFST blind bolted joint. A modified moment-rotation model for this type of connection was developed, of which the compatibility condition and mechanical equilibrium were employed to determine the internal forces of basic components and neutral axis. Following this, load transfer mechanism among the inner tube, sandwiched concrete and outer tube was discussed to assert the action area of the components. Subsequently, assembly processes of basic coefficients in terms of their stiffness and resistances based on the component method by simplifying them as assemblages of springs in series or in parallel. Finally, an experimental investigation on four substructure joints with CFDST columns for validation purposes was carried out to capture the connection details. The predicted results derived from the mechanical models coincided well with the experimental results. It is demonstrated that the proposed mechanical model is capable of evaluating the complete moment-rotation relationships of blind bolted CFDST column composite connections.

Study and design of assembled CFDST column-beam connections considering column wall failure

Lei Guo,Jingfeng Wang,T.Y. Yang,Wanqian Wang,Binggen Zhan 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.39 No.2

Currently, there is a lack of research in the design approach to avoid column wall failure in the concrete filled double skin steel tubular (CFDST) column-beam connections. In this paper, a finite element model has been developed and verified by available experimental data to analyze the failure mechanism of CFDST column-beam connections. Various finite element models with different column hollow ratios () were established. The simulation result revealed that with increasing  the failure mode gradually changed from yielding of end plate, to local failure of the column wall. Detailed parametric analyses were performed to study the failure mechanism of column wall for the CFDST column-beam connection, in which the strength of sandwiched concrete and steel tube and thickness of steel tube were incorporated. An analytical model was proposed to predict the moment resistance of the assembled connection considering the failure of column wall. The simulation results indicate that the proposed analytical model can provided a conservative prediction of the moment resistance. Finally, an upper bound value of  was recommend to avoid column wall failure for CFDST column-beam connections.

Community Discovery in Weighted Networks Based on the Similarity of Common Neighbors

Miaomiao Liu,Jingfeng Guo,Jing Chen 한국정보처리학회 2019 Journal of information processing systems Vol.15 No.5

In view of the deficiencies of existing weighted similarity indexes, a hierarchical clustering method initializeexpand-merge (IEM) is proposed based on the similarity of common neighbors for community discovery inweighted networks. Firstly, the similarity of the node pair is defined based on the attributes of their commonneighbors. Secondly, the most closely related nodes are fast clustered according to their similarity to form initialcommunities and expand the communities. Finally, communities are merged through maximizing themodularity so as to optimize division results. Experiments are carried out on many weighted networks, whichhave verified the effectiveness of the proposed algorithm. And results show that IEM is superior to weightedcommon neighbor (CN), weighted Adamic-Adar (AA) and weighted resources allocation (RA) when usingthe weighted modularity as evaluation index. Moreover, the proposed algorithm can achieve more reasonablecommunity division for weighted networks compared with cluster-recluster-merge-algorithm (CRMA)algorithm.

Efficient Greedy Algorithms for Influence Maximization in Social Networks

Lv, Jiaguo,Guo, Jingfeng,Ren, Huixiao Korea Information Processing Society 2014 Journal of information processing systems Vol.10 No.3

Influence maximization is an important problem of finding a small subset of nodes in a social network, such that by targeting this set, one will maximize the expected spread of influence in the network. To improve the efficiency of algorithm KK_Greedy proposed by Kempe et al., we propose two improved algorithms, Lv_NewGreedy and Lv_CELF. By combining all of advantages of these two algorithms, we propose a mixed algorithm Lv_MixedGreedy. We conducted experiments on two synthetically datasets and show that our improved algorithms have a matching influence with their benchmark algorithms, while being faster than them.

Influence of Oxidized Starch and Modified Nano-SiO₂ on Performance of Urea-Formaldehyde (UF) Resin

Lu Wu,Jingfeng Guo,Zhiyong Zhang,Shu Zhao 한국고분자학회 2017 폴리머 Vol.41 No.1

In this work, the nano-SiO₂ was firstly modified by silane coupling agent (3-aminopropyltriethoxysilane), meanwhile the dispersion of nanoparticles was studied with transmission electron microscope (TEM). Then urea-formaldehyde (UF) resins were synthesized and modified with the compound modifier made of different ratio of modified nano-SiO₂ and oxidized starch. All the products were characterized with Fourier transform infrared spectroscopy (FTIR). Free formaldehyde content and bonding strength were measured as the main standard of the performance of the resin. The other performances of modified UF resins were also analysized by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The results showed that the modification could effectively reduce the free formaldehyde content, from 0.49 to 0.19%, and enhance the bonding strength, from 0.90 to 2.06 ㎫.

Community Discovery in Weighted Networks Based on the Similarity of Common Neighbors

Liu, Miaomiao,Guo, Jingfeng,Chen, Jing Korea Information Processing Society 2019 Journal of information processing systems Vol.15 No.5

In view of the deficiencies of existing weighted similarity indexes, a hierarchical clustering method initialize-expand-merge (IEM) is proposed based on the similarity of common neighbors for community discovery in weighted networks. Firstly, the similarity of the node pair is defined based on the attributes of their common neighbors. Secondly, the most closely related nodes are fast clustered according to their similarity to form initial communities and expand the communities. Finally, communities are merged through maximizing the modularity so as to optimize division results. Experiments are carried out on many weighted networks, which have verified the effectiveness of the proposed algorithm. And results show that IEM is superior to weighted common neighbor (CN), weighted Adamic-Adar (AA) and weighted resources allocation (RA) when using the weighted modularity as evaluation index. Moreover, the proposed algorithm can achieve more reasonable community division for weighted networks compared with cluster-recluster-merge-algorithm (CRMA) algorithm.