Study on the Relationship between Fractal Characteristics and Mechanical Properties of Tensile Fracture of Reinforced Concrete Structures

Chenxu Ding,Tianci Xu,Qiyang Chen,Chengguang Su,Pingrui Zhao 대한토목학회 2022 KSCE JOURNAL OF CIVIL ENGINEERING Vol.26 No.5

In the present study, experiments are carried out to investigate the behavior of the tensile crack of the reinforced concrete structure. Moreover, the fracture morphology and mechanical properties of the tensile crack are analyzed with the fractal geometry theory and reverse engineering. The obtained results show that the axial force of the tensile crack increases with the crack sequence. When the crack reaches a stable state, the number of cracks does not change, while the width of the crack increases. It is found that fractures of the structural tensile crack have distinct fractal characteristics and the fractal dimension shows a decreasing trend as the cracking axial force increases. Obtained results show that the correlation between the crack axial force and the fractal dimension of the fracture follows a power function. It is demonstrated that the fractal dimension of the fracture depends on different parameters, including the tensile strength of the concrete, cross-sectional area of the structure, ratio of the elastic modulus of the steel bar to that of the concrete, and the reinforcement ratio. Moreover, the fractal dimension of the tensile crack is calculated to evaluate the tensile force of the structure. Based on the obtained results, it is found that appropriate and timely measurements can avoid the built-in steel bars reaching yield and causing the structure to lose its bearing capacity completely.

Navigation safety domain and collision risk index for decision support of collision avoidance of USVs

Zhou Jian,Ding Feng,Yang Jiaxuan,Pei Zhengqiang,Wang Chenxu,Zhang Anmin 대한조선학회 2021 International Journal of Naval Architecture and Oc Vol.13 No.1

This paper proposes a decision support model for USVs to improve the accuracy of collision avoidance decision-making. It is formed by Navigation Safety Domain (NSD) and domain-based Collision Risk Index (CRI), capable of determining the collision stage and risk between multiple ships. The NSD is composed of a warning domain and a forbidden domain, which is constructed under the constraints of COLREGs (International Regulations for Preventing Collisions at Sea). The proposed domain based CRI takes the radius of NSD in various encounter situations as threshold parameters. It is found that the value of collision risk in any directions can be calculated, including actual value and risk threshold. A catamaran USV and 6 given vessels are taken as study objects to validate the proposed model. It is found that the judgment of collision stage is accurate and the azimuth range of risk exists can be detected, hence the ships can take direct and effective collision avoidance measures. According to the relation between the actual value of CRI and risk threshold, the decision support rules are summarized, and the specific terms of COLREGs to be followed in each encounter situation are given.

Experimental Study on Bond Performances of Track Slab and Mortar Based on DIC Technology

Chengguang Su,Dan Liu,Chenxu Ding,Chuang Gong,Pingrui Zhao,Xueyi Liu 대한토목학회 2018 KSCE JOURNAL OF CIVIL ENGINEERING Vol.22 No.9

In order to guarantee the normal long-time service performance of CRST II slab track, it is necessary to study the interface parameters between track slab and CA mortar layer of CRTS II slab track. Thus the splitting and shearing model test of concrete and mortar bonded composite specimens were conducted. Based on the Digital Image Correlation (DIC) technology, the stress-strain relationship and cohesion model parameters were obtained from the interface displacement and distribution of strain. The results showed that: The displacement and the strain field distribution of the composite specimens as well as the whole interlaminar cracking process of initiation, propagation and failure can be well described with DIC. The bond failure between the track slab and the CA mortar layer is part of the brittle failure, and the normal and tangent interface tension-displacements are both bilinear. The shear strength between the track slab and the CA mortar layer is 1.82 MPa with the peak strain of 2.49 × 10−4 and the secant modulus of 7.30 × 103 MPa; While the shear strength is 2.40 MPa with the peak strain of 6.17 × 10−3 and the secant modulus of 3.89 × 102 MPa. When the shear strain is about 7.5×10-4, the shear stress-strain curve tends to remain stable. At this point, the shear strain is 0.12 times of the peak strain. Parameters of the cohesive zone model between the track slab and the CA mortar layer are suggested as follows: the normal cohesive strength is 1.792 MPa with the interface stiffness of 708.485 MPa/ mm and the critical fracture energy of 0.0252 mJ/mm2; the tangential cohesive strength is 0.956 MPa with the interface stiffness of 63.039 MPa/mm and the critical fracture of 0.018 mJ/mm2.

Parametric Analysis on Elastic Buckling Performance of Low Yield Point Steel Plate Shear Wall with Two-Side Connections

Shenggang Fan,Runmin Ding,Shaoru Zeng,Chenxu Li,Chengliang Liu 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.6

The steel plate shear wall (SPSW) with two-side connections can be arranged fl exibly in the structure, and has no additional infl uence on the column, but its buckling capacity is diffi cult to be deduced directly by thin plate theory. The low yield point SPSW (LYP-SPSW) with two-side connections is proposed in this paper, including unstiff ened LYP-SPSW, cross-stiff ened LYP-SPSW and diagonally-stiff ened LYP-SPSW. The elastic buckling performance and buckling capacity of these three types of LYP-SPSWs are studied by numerical simulation. On the basis of the accurate model, a series of parametric analysis on the key factors were conducted, including the height-to-thickness ratio, the stiff ness ratio of the stiff ener, and the stiff ness ratio of the edge member, which have eff ects on the elastic buckling stress of the LYP-SPSW with two-side connections. The elastic buckling stress of the SPSW can be eff ectively increased by adding stiff eners and edge members, but it is unnecessary to use oversized stiff eners and edge members. Based on a large amount of parametric analysis, simplifi ed formulas for calculating the elastic buckling stresses of the three types of LYP-SPSWs mentioned above are proposed in this paper.

Research on Local Buckling of Stainless Steel Lipped C-Section Beam Around Strong-Axis

Shenggang Fan,Hang Zhou,Zhixia Ding,Chenxu Li,Qinglin Jiang 한국강구조학회 2022 International Journal of Steel Structures Vol.22 No.5

To study the local buckling capacity of stainless steel beams with lipped C-sections under strong axis bending, tensile tests were performed on 12 stainless steel coupons based on S30408 austenitic stainless steel (AISI304) in fl at and corner areas, and mechanical properties and stress–strain curves were obtained. Then, local buckling capacity tests were performed on 6 specimens of stainless steel beams under strong axis bending to determine their mechanical properties and failure mechanism. The failure phenomenon, load–displacement curve, load–strain curve and local buckling capacity were determined. Results show that the failure modes of the specimens are local buckling failure of the fl ange and web at mid-span. Additionally, a refi ned fi nite element analysis model was developed using Python and ABAQUS to simulate and analyse the mechanical performance and local buckling capacity. Then, the analytical results were compared to the test results, and the accuracy of the refi ned model was verifi ed. Then, the refi ned model of the stainless steel C-section beam was simplifi ed including the constraint simplifi cation model, which considered diff erent fl ange constraints and initial imperfections, and the length simplifi cation model, which was based on diff erent length and support constraints. The comparative analysis results showed that the constraint simplifi cation model can simulate the local buckling failure mode more accurately than other models. Additionally, initial imperfections were shown to have little eff ect on the local buckling capacity; however, specimen length and the bearing constraint condition did aff ect the local buckling capacity.