Analysis and design of demountable circular CFST column-base connections

Dongxu Li,Jia Wang,Brian Uy,Farhad Aslani,Vipul Patel 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.5

In current engineering practice, circular concrete-filled steel tubular (CFST) columns have been used as effective structural components due to their significant structural and economic benefits. To apply these structural components into steelconcrete composite moment resisting frames, increasing number of research into the column-base connections of circular CFST columns have been found. However, most of the previous research focused on the strength, rigidity and seismic resisting performance of the circular CFST column-base connections. The present paper attempts to investigate the demountability of bolted circular CFST column-base connections using the finite element method. The developed finite element models take into account the effects of material and geometric nonlinearities; the accuracy of proposed models is validated through comparison against independent experimental results. The mechanical performance of CFST column-base connections with both permanent and demountable design details are compared with the developed finite element models. Parametric studies are further carried out to examine the effects of design parameters on the behaviour of demountable circular CFST column-base connections. Moreover, the initial stiffness and moment capacity of such demountable connections are compared with the existing codes of practice. The comparison results indicate that an improved prediction method of the initial stiffness for these connections should be developed.

Assessment of titanium alloy bolts for structural applications

Dongxu Li,Brian Uy,Jia Wang,Yuchen Song 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.4

This paper explored the viability of utilising titanium alloy bolts in the construction industry through an experimental programme, where a total of sixty-six titanium alloy (Ti/6Al/4V) bolts were tested under axial tension, pure shear and combined tension and shear. In addition, a series of Charpy V-notch specimens machined from titanium alloy bolts, conventional high-strength steel bolts, austenitic and duplex stainless steel bolts were tested for impact toughness comparisons. The obtained experimental results demonstrated that the axial tensile and pure shear capacities of titanium alloy bolts can be reasonably estimated by the current design standards for steel structures (Eurocode 3, AS 4100 and AISC 360). However, under the combined tension and shear loading conditions, significant underestimation by Eurocode 3 and unsafe predictions through AS 4100 and AISC 360 indicate that proper modifications are necessary to facilitate the safe and economic use of titanium alloy bolts. In addition, numerical models were developed to calibrate the fracture parameters of the tested titanium alloy bolts. Furthermore, a design-based selection process of titanium alloy bolts in the structural applications was proposed, in which the ultimate strength, ductility performance and corrosion resistance (including galvanic corrosion) of titanium alloy bolts was mainly considered.

Behaviour and design of Grade 10.9 high-strength bolts under combined actions

Dongxu Li,Brian Uy,Jia Wang,Yuchen Song 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.35 No.3

The use of high-strength steel and concrete in the construction industry has been gaining increasing attention over the past few decades. With it comes the need to utilise high-strength structural bolts to ensure the design load to be transferred safely through joint regions, where the space is limited due to the reduced structural dimensions. However, research on the behaviour of high-strength structural bolts under various loading combinations is still insufficient. Most of the current design specifications concerning high-strength structural bolts were established based on a very limited set of experimental results. Moreover, as experimental programs normally include limited design parameters for investigation, finite element analysis has become one of the effective methods to assist the understanding of the behaviour of structural components. An accurate and simple full-range stress-strain model for high-strength structural bolts under different loading combinations was therefore developed, where the effects of bolt fracture was included. The ultimate strength capacities of various structural bolts obtained from the present experimental program were compared with the existing design provisions. Furthermore, design recommendations concerning the pure shear and tension, as well as combined shear and tension resistance of Grade 10.9 high-strength structural bolts were provided.

Behaviour and design of high-strength steel beam-to-column joints

Dongxu Li,Brian Uy,Jia Wang 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.31 No.3

This paper presents a finite element model for predicting the behaviour of high-strength steel bolted beam-tocolumn joints under monotonic loading. The developed numerical model considers the effects of material nonlinearities and geometric nonlinearities. The accuracy of the developed model is examined by comparing the predicted results with independent experimental results. It is demonstrated that the proposed model accurately predicts the ultimate flexural resistances and moment-rotation curves for high-strength steel bolted beam-to-column joints. Mechanical performance of three joint configurations with various design details is examined. A parametric study is carried out to investigate the effects of key design parameters on the behaviour of bolted beam-to-column joints with double-extended endplates. The plastic flexural capacities of the beam-to-column joints from the experimental programme and numerical analysis are compared with the current codes of practice. It is found that the initial stiffness and plastic flexural resistance of the high-strength steel beam-to-column joints are overestimated. Proper modifications need to be conducted to ensure the current analytical method can be safely used for the bolted beam-to-column joints with high-performance materials.

Application of a Hybrid Orthogonal Function System on Trademark Image Retrieval

Xiaochun Wang,Yena Wang,Honglei Sun,Dongxu Qi (사)한국CDE학회 2013 한국CAD/CAM학회 국제학술발표 논문집 Vol.2010 No.8

Owing to an increase in the number of trademark images, evaluating a new trademark’s distinctiveness has become a challenge. This paper proposes a new class of orthogonal moment functions based on the W-system of degree one and applies the proposed W-moments on trademark retrieval. W-system of degree one is a hybrid function system on interval [0,1] consisting of piecewise linear functions with multi-level jump discontinuities, and has great advantage in representing information with discontinuities and describing disjointed or articulated contour shape. The W-moment is easy to compute due to the concise expression of the basis functions of the Wsystem of degree one. Furthermore, the new moments eliminate the need for numerical approximations, since the basis set is orthogonal on the discrete domain of the image coordinate space. These properties make W-moments preferable to the conventional orthogonal moments, and can be used to accurately reconstruct the objects, especially, objects group. So the W-moments are suitable for describing complex shape consisting of multiple disjointed curves, such as trademark images. In this paper, the W-moment is applied on trademark retrieval. The W-moments are first derived from the trademark image, the similarity between query and trademark in the database is then evaluated using the Euclidean distance between their W-moment feature vectors, and the trademark retrieval is finally accomplished by comparing the similarities. The experiments are conducted on MPEG-7 CE2 and a self-constructed trademark data set to test the proposed moments. Comparison experiment results show that the new moments give preferable retrieval results and it is feasible and efficient in practical application.

Progressive collapse analysis of stainless steel composite frames with beam-to-column endplate connections

Jia Wang,Brian Uy,Yuchen Song,Dongxu Li 국제구조공학회 2020 Steel and Composite Structures, An International J Vol.36 No.4

This paper carries out the progressive collapse analysis of stainless steel composite beam-to-column joint sub-models and moment-resisting frames under column removal scenarios. The static flexural response of composite joint sub-models with damaged columns was initially explored via finite element methods, which was validated by independent experimental results and discussed in terms of moment-rotation relationships, plastic hinge behaviour and catenary actions. Simplified finite element methods were then proposed and applied to the frame analysis which aimed to elaborate the progressive collapse response at the frame level. Nonlinear static and dynamic analysis were employed to evaluate the dynamic increase factor (DIF) for stainless steel composite frames. The results suggest that the catenary action effect plays an important role in preventing the damaged structure from dramatic collapse. The beam-to-column joints could be critical components that influence the capacity of composite frames and dominate the determination of dynamic increase factor. The current design guidance is non-conservative to provide proper DIF for stainless steel composite frames, and thus new DIF curves are expected to be proposed.

Moment-rotation relationship of hollow-section beam-to-column steel joints with extended end-plates

Jia Wang,Haiming Zhu,Brian Uy,Vipulkumar Patel,Farhad Aslani,Dongxu Li 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.29 No.6

This paper presents the flexural performance of steel beam-to-column joints composed of hollow structural section beams and columns. A finite element (FE) model was developed incorporating geometrical and material nonlinearities to evaluate the behaviour of joints subjected to bending moments. The numerical outcomes were validated with experimental results and compared with EN1993-1-8. The demountability of the structure was discussed based on the tested specimen. A parametric analysis was carried out to investigate the effects of steel yield strength, end-plate thickness, beam thickness, column wall thickness, bolt diameter, number of bolts and location. Consequently, an analytical model was derived based on the component method to predict the moment-rotation relationships for the sub-assemblies with extended end-plates. The accuracy of the proposed model was calibrated by the experimental and numerical results. It is found that the FE model is fairly reliable to predict the initial stiffness and moment capacity of the joints, while EN1993-1-8 overestimates the initial stiffness extensively. The beam-to-column joints are shown to be demountable and reusable with a moment up to 53% of the ultimate moment capacity. The end-plate thickness and column wall thickness have a significant influence on the joint behaviour, and the layout of double bolt-rows in tension is recommended for joints with extended end-plates. The derived analytical model is capable of predicting the moment-rotation relationship of the structure.

Relationship between Dynamic Tensile Strength and Pore Structure of Saturated Concrete under Lateral Pressure

Hao Wang,Li-cheng Wang,Bahman Ghiassi,Yupu Song,Le Zhou,Dongxu Hou 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.3

The dynamic properties of concrete in two states (saturated and dry) were compared and analyzed through a series of dynamic biaxial tensile-compressive (T-C) experimentals. All specimens were subjected to constant biaxial T-C stress ratios (0.5:-1, 0.25:-1, 0.1:-1, 0.05:-1 and 1:0 respectively) at different strain rates (10−5s−1 to 10−2s−1 ). It was found that the biaxial T-C ultimate strengths of both kinds concrete closely relate to the lateral pressure of the specimen, and the independent tensile and compressive strength increases with the increase of strain rate. In the case of exerting lateral pressure, the failure states of specimens show same manner as that of the uniaxial tensile specimens, which indicates that the specimens were completely fractured under tensile loading. The test results show that the biaxial T-C strength of saturated concrete is lower at strain rates of 10−5s−1, whereas it is higher at the other three strain rates (10−4s−1, 10−3s−1 and 10−2s−1). This distinct difference indicates that saturated concrete is more rate sensitive under lateral pressure. Through mechanical analysis the article explains the reason of this phenomenon is mainly dued to the beneficial tensile stress of the pore water surface and the Stefan effect. Meanwhile, the strength prediction expression of saturated concrete was established under the condition of stress ratio and strain rate are considered simultaneously.

Analysis of demountable steel and composite frames with semi-rigid bolted joints

Jia Wang,Brian Uy,Dongxu Li 국제구조공학회 2018 Steel and Composite Structures, An International J Vol.28 No.3

This paper presented an integral design procedure for demountable bolted composite frames with semi-rigid joints. Moment-rotation relationships of beam-to-column joints were predicted with analytical models aiming to provide accurate and reliable analytical solutions. Among this, initial stiffness of beam-to-column joints was derived on the basis of Timoshenko’s plate theory, and moment capacity was derived in accordance with Eurocodes. The predictions were validated with relevant test results prior to further applications. Frame analysis was conducted by using Abaqus software with material and geometrical nonlinearity considered. Variable lateral loads incorporating wind actions and earthquake actions in accordance with Australian Standards were adopted to evaluate the flexural behaviour of the composite frames. Strength and serviceability limit state criteria were utilized to verify configurations of designed models. A wide range of frames with the varied number of storeys and bays were thereafter programmed to ascertain bending moment envelopes under various load combinations. The analytical results suggest that the proposed approach is capable of predicting the moment-rotation performance of the semi-rigid joints reasonably well. Outcomes of the frame analysis indicate that the load combination with dead loads and live loads only leads to maximum sagging and hogging moment magnitudes in beams. As for lateral loads, wind actions are more crucial to dominate the design of the demountable composite frames than earthquake actions. No hogging moment reversal is expected in the composite beams given that the frames are designed properly. The proposed analysis procedure is demonstrated to be a simple and efficient method, which can be applied into engineering practice.

Initial stiffness and moment capacity assessment of stainless steel composite bolted joints with concrete-filled circular tubular columns

Jia Wang,Brian Uy,Dongxu Li 국제구조공학회 2019 Steel and Composite Structures, An International J Vol.33 No.5

This paper numerically assesses the initial stiffness and moment capacity of stainless steel composite bolted joints with concrete-filled circular tubular (CFCT) columns. By comparing with existing design codes including EN 1993-1-8 and AS/NZS 2327, a modified component method was proposed to better predict the flexural performance of joints involving circular columns and curved endplates. The modification was verified with independent experimental results. A wide range of finite element models were then developed to investigate the elastic deformations of column face in bending which contribute to the corresponding stiffness coefficient. A new design formula defining the stiffness coefficient of circular column face in bending was proposed through regression analysis. Results suggest that a factor for the stiffness coefficient of endplate in bending should be reduced to 0.68, and more contribution of prying forces needs to be considered. The modified component method and proposed formula are able to estimate the structural behaviour with reasonable accuracy. They are expected to be incorporated into the current design provisions as supplementary for beam-to-CFCT column joints.