Analytical calculation method for the axial equivalent elastic modulus of laminated FRP pipes based on three-dimensional stress state

Li Chen,Darong Pan,Qilin Zhao,Li-Cheng-Xi Huang,Liang Chen,Wei Xu 국제구조공학회 2021 Structural Engineering and Mechanics, An Int'l Jou Vol.77 No.1

In engineering design, the axial equivalent elastic modulus of laminated FRP pipe was mostly calculated by the average elastic modulus method or the classical laminated plate theory method, which are based on relatively simplified assumptions, and may be not accurate enough sometimes. A new analytical calculation method for the axial equivalent elastic modulus of laminated FRP pipe was established based on three-dimensional stress state. By comparing the results calculated by this method with those by the above two traditional analytical methods and the finite element method, it is found that this method for the axial equivalent elastic modulus fits well not only for thin-walled pipes with orthotropic layers, but also for thick-walled pipes with arbitrary layers. Besides, the influence of the layer stacking on the axial equivalent elastic modulus was studied with this method. It is found that a proper content of circumferential layer is beneficial for improving the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers, and then can reduce its material quantity under the premise that its axial stiffness remains unchanged. Finally, the meso-mechanical mechanism of this effect was analyzed. The improving effect of circumferential layer on the axial equivalent elastic modulus of the laminated FRP pipe with oblique layers is mainly because that, the circumferential fibers can restrain the rigid body rotations of the oblique fibers, which tend to cause the significant deformations of the pipe wall units and the relatively low axial equivalent elastic modulus of the pipe.

Experimental and theoretical research on the compression performance of CFRP sheet confined GFRP short pole

Li Chen,Qilin Zhao,Kebin Jiang 국제구조공학회 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.2

The axial compressive strength of unidirectional FRP is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. In order to restrain the lateral expansion and splitting of GFRP, and accordingly heighten its axial compressive bearing capacity, a project that to confine GFRP pole with surrounding CFRP sheet is suggested in the present study. The Experiment on the CFRP sheet confined GFRP poles showed that a combined structure of high bearing capacity was attained. Basing on the experiment research a theoretical iterative calculation approach is suggested to predict the ultimate axial compressive stress of the combined structure, and the predicted results agree well with the experimental results. Then the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure are also analyzed basing on this approach.

Experimental investigation of novel pre-tightened teeth connection technique for composite tube

Fei Li,Qilin Zhao,Haosen Chen,Longxing Xu 국제구조공학회 2017 Steel and Composite Structures, An International J Vol.23 No.2

A new composite tube connection method called the pre-tightened teeth connection technique is proposed to improve the composite tube connection efficiency. This paper first introduces the manufacturing process of the proposed technique. It then outlines how the mechanical properties of this technology were tested using four test groups. The factors that influence the load-bearing capacity and damage model of the connection were analyzed, and finally, the transfer load mechanism was investigated. The following conclusions can be obtained from the research results. (1) The new technique improves the compressive connection efficiency by a maximum of 79%, with the efficiency exceeding that of adhesive connections of the same thickness. (2) Changing the depth of teeth results in two types of damage: local compressive damage and shear damage. The bearing capacity can be improved by increasing the depth, length, and number of teeth as well as the pretightening force. (3) The capacity of the technique to transfer high loads is a result of both the relatively high interlaminar shear strength of the pultruded composite and the interlaminar shear strength increase provided by the pre-tightening force. The proposed technique shows favorable mechanical properties, and therefore, it can be extensively applied in the engineering field.

Structural Health Monitoring of Shanghai Tower Considering Time-dependent Effects

Zhang, Qilin,Yang, Bin,Liu, Tao,Li, Han,Lv, Jia Council on Tall Building and Urban Habitat Korea 2015 International journal of high-rise buildings Vol.4 No.1

This paper presents the structural health monitoring (SHM) of Shanghai Tower. In order to provide useful information for safety evaluation and regular maintenance under construction and in-service condition, a comprehensive structural health monitoring (SHM) system is installed in Shanghai Tower, which is composed of a main monitoring station and eleven substations. Structural responses at different construction stages are measured using this SHM system and presented in this study. Meanwhile, a detailed finite element model (FEM) is created and comparison of results between SHM and FEM is carried out. Results indicate that the time-dependent property of concrete creep is of great importance to structural response and the measured data can be used in FEM updating to obtain more accurate FEM models at different construction stages. Therefore, installation of structural health monitoring system in super-tall buildings could be considered as an effective way to assure structural safety during the construction process.

Experimental and theoretical research on the compression performance of CFRP sheet confined GFRP short pole

Chen, Li,Zhao, Qilin,Jiang, Kebin Techno-Press 2011 Structural Engineering and Mechanics, An Int'l Jou Vol.40 No.2

The axial compressive strength of unidirectional FRP is generally quite lower than its axial tensile strength. This fact decreases the advantages of FRP as main load bearing member in engineering structure. In order to restrain the lateral expansion and splitting of GFRP, and accordingly heighten its axial compressive bearing capacity, a project that to confine GFRP pole with surrounding CFRP sheet is suggested in the present study. The Experiment on the CFRP sheet confined GFRP poles showed that a combined structure of high bearing capacity was attained. Basing on the experiment research a theoretical iterative calculation approach is suggested to predict the ultimate axial compressive stress of the combined structure, and the predicted results agree well with the experimental results. Then the influences of geometrical parameters on the ultimate axial compressive stress of the combined structure are also analyzed basing on this approach.

Experimental and Theoretical Study of the Torsional Mechanism of a Hybrid FRP-aluminum Triangular Deck-truss Structure

Dongdong Zhang,Qilin Zhao,Fei Li,Feng Li 대한토목학회 2016 KSCE JOURNAL OF CIVIL ENGINEERING Vol.20 No.6

This paper investigates the torsional mechanism of a hybrid FRP-aluminum triangular deck-truss structure composed of modular structural units. A pure torsion test was conducted on a 6-m cantilever specimen to characterize the structural responses. Based on the experimental results and structural layout, a simplified analytical model is established to predict the torsional stiffness of the hybrid triangular deck-truss structure. The derivation procedures and formulae are experimentally calibrated, finding that the formulae can be conveniently used with satisfactory accuracy. It is ultimately confirmed that the torsional center of the entire triangular truss collocates with the center of the orthotropic deck. The external torsional moment is primarily resisted by the FRP lower chords and the aluminum longitudinal beams, particularly for the FRP lower chords which should be given a great consideration in the torsion design.

Research on the mechanical properties of membrane connections in tensioned membrane structures

Yingying Zhang,Qilin Zhang,Yang Li,Lu Chen 국제구조공학회 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.6

As an important part, the connections generally are important for the overall behavior of the structure and the strength and serviceability of the connection should be ensured. This paper presents the mechanical properties of membrane connections in tensioned membrane structure. First, the details of common connections used in the membrane structure are introduced. Then, the common connections including membrane seam, membrane-flexible edge connection and membrane-rigid edge connection are tested and the corresponding failure mechanisms are discussed. Finally, the effects of connection parameters on the connection strength are investigated and proper connection parameters are proposed. The strength reduction factors corresponding to different connection types are proposed, which can be references for the design and analysis of membrane structures.

Solving Truss Topological Optimization with Discrete Design Variables via Swarm Intelligence

Bin Yang,Qilin Zhang,Han Li 대한토목학회 2015 KSCE JOURNAL OF CIVIL ENGINEERING Vol.19 No.4

Structural topological optimization is the most general form of structural optimization and one of the most challenging research problems in this field is to find optimized layouts with minimization of compliance (maximization of stiffness) for a given total mass of the structure discretized by truss members in terms of discrete design variables, which has not been well solved by evolutionary algorithms. Particle Swarm Optimization (PSO) is a new paradigm of Swarm Intelligence which is inspired by concepts from ‘Social Psychology’ and ‘Artificial Life’. PSO is particularly a preferable candidate to solve highly nonlinear, non-convex and even discontinuous problems and has been applied to many different kinds of optimization problems. The motivation of this paper is to use the Modified Lbest based PSO (MLPSO) and geometrical consistency check tightly connecting to the ground structure approach to break through in this kind of optimization problems. In order to handle discrete design variables, rounding-off strategy is used in this paper. Furthermore, external quadratic penalty function is chose to deal with constraints. Through a popular benchmark test, two kinds of MLPSO exhibited competitive performance due to improved global searching ability.

Strength Prediction of a Single Tooth Bound to Composite Pre-tightened Tooth Connection (PTTC) Joints based on Different Failure Criteria

Yifeng Gao,Fei Li,Qilin Zhao,Jiangang Gao,Yubo Hu 대한토목학회 2019 KSCE Journal of Civil Engineering Vol.23 No.8

A method capable to predict the strength of single tooth bound to composite pre-tightened tooth connection (PTTC) joints is presented. The proposed method uses four representative failure criteria: max-stress, Tsai-Hill, Tsai-Wu and Hashin. The characteristic length method is also used to obtain prediction strengths. Three types of experiments of single PTTC joints were conducted using the following variations: 1) tooth depth, 2) tooth length, and 3) pre-tightened force. The experimental results were compared with the two-dimensional failure envelope diagram calculated using the four representative failure criteria. The physical nature and the strength predictive ability of each criterion were investigated. The obtained results show that the shear failure mode of single PTTC joint was accurately predicted by all four failure criteria. However, the Tsai-Wu criterion when compared to Maximum Stress, Tsai-Hill and Hashin criteria, exhibits better accuracy regarding the prediction strength of single PTTC joints, this is due to the fact that the Tsai-Wu criterion reflects more accurately the increase in the interlaminar shear strength caused by the transverse compressive stress.

Research on the mechanical properties of membrane connections in tensioned membrane structures

Zhang, Yingying,Zhang, Qilin,Li, Yang,Chen, Lu Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.6

As an important part, the connections generally are important for the overall behavior of the structure and the strength and serviceability of the connection should be ensured. This paper presents the mechanical properties of membrane connections in tensioned membrane structure. First, the details of common connections used in the membrane structure are introduced. Then, the common connections including membrane seam, membrane-flexible edge connection and membrane-rigid edge connection are tested and the corresponding failure mechanisms are discussed. Finally, the effects of connection parameters on the connection strength are investigated and proper connection parameters are proposed. The strength reduction factors corresponding to different connection types are proposed, which can be references for the design and analysis of membrane structures.