Longbang Qing

Longbang Qing
Hebei University of Technology · Civil Engineering

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68
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Publications

Publications (68)
Article
In this study, the toughness enhancement of aligned steel fibers in cement-based composites was mainly characterized. Three-point bending fracture tests with different fiber orientations and fiber volume contents were performed; additionally, crack propagation processes of random and aligned steel fiber reinforced cement-based composites (SFRCs and...
Article
To maximize the reinforcement of steel fibers in cement-based composite specimens, both the orientation and volume fraction of the steel fibers were optimized according to the principal tensile stress everywhere in the specimen, which is defined as Adaptively Distributed Steel Fiber Reinforced Cement-based Composites (AD-SFRC). In this investigatio...
Article
Self-healing concrete is a new material with the ability to autogenously heal cracks. Self-healing by encapsulated healing agents has been widely studied, while the influence of the space distribution of capsules or short glass tubes on healing capacity has seldom been addressed. This study investigated how to improve the self-healing capacity of s...
Article
The maximum resistance rate principle (MRRP) is proposed to characterise the unstable of quasi-brittle fracture. Under quasi-static loading conditions, the unstable fracture of quasi-brittle materials occurs when the resistance rate reaches its maximum value. Firstly, the whole fracture process of the single edge cracked specimen was calculated, an...
Article
In this study, the stochastic characteristics of the fracture process zone (FPZ) of concrete are analysed. The impacts of specimen size on the critical crack opening displacement, the distribution of cohesive stress, and the critical length of FPZ are studied, and calculations are performed for the stochastic energy consumption curve of concrete. T...
Article
Full-text available
Aligning steel fibers is an effective way to improve the mechanical properties of steel fiber cementitious composites (SFRC). In this study, the magnetic field method was used to prepare the aligned hooked-end steel fiber cementitious composites (ASFRC) and the fracture behavior was investigated. In order to achieve the alignment of steel fibers, t...
Article
Full-text available
From the perspective of improving the self-healing method in construction, a tubular healing fiber was adopted as a container to improve the encapsulation capacity, which was available using a micro-capsule as a container. Knowing the direction of the stresses to which structure members are subjected, this research investigated the influence of ali...
Article
An experimental method, based on the modified two‐parameter model and digital image correlation technique, was proposed for determining the mixed mode fracture toughness (KI+II) of concrete. Three‐point bending tests on notched concrete beam specimens of different sizes, maximum aggregate sizes, and aggregate volume contents were conducted, and the...
Article
Experimental research was carried out to evaluate the comparative fracture performance of random steel fiber-reinforced composite (SFRC) and aligned steel fiber-reinforced composite (ASFRC). The desired direction of steel fiber in the fresh cementitious mortar was achieved by the electromagnetic field. Three-point bending tests were conducted on ge...
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Full-text available
Mixed-mode fracture experiments were conducted on aligned steel fibre reinforced cementitious composite (ASFRC) and ordinary steel fibre reinforced cementitious composite (SFRC) three-point bending beams. Mixed-mode fracture performances of the ASFRC and SFRC specimens were studied by changing the crack offset distance. The fracture processes of th...
Article
In this study, a full-field aligned steel fiber reinforced cementitious composites (FASFRC) prism specimen was designed, prepared and tested. The special feature of the FASFRC is the orientation of steel fibers in the specimen is consistent with the principal stress when apply flexural loading to the specimen. In order to optimise the design of the...
Article
Full-text available
The Grey Relation Entropy (GRE) theory is used to analyze the sensitive pore size that affects the compressive strength of concrete. The relationship between the strength and pore structure is revised based on the sensitivity coefficient. The revised model is used to calculate the compressive strength of concrete. In order to verify the validity of...
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Full-text available
Based on fracture extreme theory (FET), the size effect on initial fracture toughness \(K_{\mathrm{I}}^{\mathrm{ini}}\) and unstable fracture toughness \(K_{\mathrm{I}}^{\mathrm{un}}\) of concrete for three-point bending beam was investigated. Nine groups of geometrically similar specimen were simulated to obtain peak load and critical crack mouth...
Article
Full-text available
The article “Uniaxial tensile behavior of aligned steel fibre reinforced cementitious composites”, written by “Longbang Qing, Kelai Yu, Ru Mu, John P. Forth”, was originally published electronically on the publisher’s Internet portal (currently SpringerLink) on 25 June 2019 without open access.
Article
Two theoretical methods were developed to determine the tensile strength ft of concrete using wedge splitting specimens based on nil-stress intensity factor (nil-SIF) criterion and force equilibrium theory, respectively. With the fracture extreme theory (FET), only experimental peak load of one specimen was needed and did not require the measuremen...
Article
An automatic discontinuous deformation measurement (DDM) approach was proposed to evaluate full-field deformations during the crack propagation process based on the digital image correlation (DIC) method. The color speckle pattern and crack identification procedure were applied at first in the DDM approach to obtain the region of interest (ROI) in...
Article
A modified non-linear hinge model (NLHM) was proposed to predict the crack propagation of cementitious composites. Based on the toughness criterion and the weight function method, the fracture processes of normal concrete and aligned steel fiber reinforced concrete (ASFRC) were analytically determined. For normal concrete, the P–CMOD curves of the...
Article
Full-text available
By applying an external uniform magnetic field to a fresh cement mixture during casting, an aligned steel fibre reinforced cementitious composites (ASFRC) was prepared. This investigation compares the performance of ASFRC with its counterpart—ordinary steel fibre reinforced cementitious composite (SFRC) containing randomly distributed steel fibres....
Article
An arc bending notched specimen was used to determine the mechanical and fracture parameters of concrete in this study. Compared with the traditional arc bending notched specimen, the lateral thrust generated at the bottom supports in the specimen can counteract the influence of self-weight on the crack propagation. Therefore, relative stable crack...
Article
Based on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at...
Article
Concrete pipes are widely used in municipal structures and vulnerable to cracking and leakage when subjected to external load. To improve the mechanical properties and hence increase the cracking resistance of the pipe, steel fiber reinforced cement-based composite pipe specimens with steel fibers annularly distributed along the circumferential dir...
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Full-text available
The study of the mechanical properties of sea ice benefits the parameterization of sea-ice numerical models and the optimization of engineering design. Deformation measurement of sea ice has been seen as the essential foundation for the study of these properties. However, this measurement has proved to be difficult due to the complex and nonhomogen...
Article
A general theoretical framework for determining the fracture parameters of concrete was presented based on fracture extreme theory (FET). The method for determining tensile strength ft and initial fracture toughness KIini was established using nil-stress intensity factor (nil-SIF) criterion and initial fracture toughness criterion, respectively. Us...
Article
Concrete tensile strength and fracture toughness are two important material constants that should be independent of specimen size, geometry or type. In this study, on the basis of the improved boundary effect model, independent tensile strength and fracture toughness of concrete, which are unaffected by the specimen type, were determined by using v...
Article
This study is aimed at exploring the mechanism of the reinforcement of aligned steel fibers on the mechanical properties of cement-based composite by acoustic emission (AE) signal analysis. Flexural tests were carried out and the results shown that the flexural strength of aligned steel fiber reinforced cement-based composite (ASFRC) increases by a...
Article
A normal distribution methodology is proposed by considering variations in fictitious crack growth Δa fic at notch-tip in concrete specimens at peak load P max due to heterogeneous aggregate structures. The variation in Δa fic leads to normal distributions in measured tensile strength f t and fracture toughness K IC . These normal distributions wit...
Article
Full-text available
We took advantage of digital image correlation to measure the full-field deformation of sea ice in a uniaxial compression experiment in situ. The characteristics of failure mode, nonlinear behavior and crack propagation are all captured by the strain field of specimens. To our knowledge, this is the first attempt to experimentally capture sequentia...
Article
Shear behavior is one aspect of the fundamental mechanical performance of steel fiber reinforced cement-based composites. In order to investigate the influence of fiber orientation on the shear properties of steel fiber reinforced cement-based composites, the shear behavior of aligned steel fiber reinforced cement-based composites (ASFRC) and conve...
Article
A method for determining the stochastic cohesive law of concrete was developed using a parallel spring model. This method is based on the energy consumption equivalence between stochastic damage and fracture and assumes that the micro-spring failure strain is a lognormal stochastic variable. The stochastic cohesive laws of dam concrete and wet-scre...
Article
A theoretical method for determining the tensile strength ft of concrete was proposed based on the experimental loads in fracture tests. Using the fracture extreme method, only the initial cracking load Pini and the peak load Pmax were required to be measured. The experimental data from three-point bending notched beams and wedge splitting specimen...
Article
Steel fiber reinforced cementitious composites(SFRC) were treated as composite material, which consists of steel fiber and cement mortar. The whole process of tensile fracture for aligned steel fiber reinforced cementitious composites(ASFRC) was simulated on the basis of extended finite element method(XFEM). Mixed congruence algorithm was used to g...
Article
The aim of this work is to present an approach, inspired by the way in which a compass needle maintains a consistent orientation under the action of the Earth's magnetic field, for manufacturing a cementitious composite reinforced with aligned steel fibers. Aligned steel fiber reinforced cementitious composites (ASFRC) were prepared by applying a u...
Article
A simplified extreme method and corresponding model are developed for determining the initiation toughness of dam concrete. Based on the extreme method, we derive an analytical expression for the initiation toughness of wedge splitting specimens and a simplified extreme method for determining the initiation toughness of dam concrete. This simplifie...
Article
A theoretical method for determining the effective fracture toughness KICe and tensile strength ft of concrete was proposed based on the fictitious crack model. With the fracture extreme theory (FET), only the experimental peak load of one specimen in fracture test is required for the calculation. The application of the proposed method was illustra...
Article
Full-text available
This simplified extreme method and corresponding model was developed for determining the initial toughness of dam concrete. Based on the extreme value method, the analytical expression of the initial toughness of wedge splitting specimen was deduced, and a simplified extreme method for determining the initial toughness of dam concrete was establish...
Article
A theoretical method to determine the initial fracture toughness KI ini of concrete for central-notched split-tension specimens was developed based on the extreme theory. In this method, the KI ini, critical crack tip opening displacement CTODc, and half critical effective crack extension Δɑc could be obtained by the experimental peak load of a sin...
Article
The three-point bending tests on notched beams with different steel fibre volume fractions and different specimen sizes were conducted. The resistances to crack initiation of randomly distributed steel fibre reinforced cementitious composite (SFRC) and aligned steel fibre reinforced cementitious composite (ASFRC) were studied. Based on the load-cra...
Article
Based on physical model tests of a classical concrete gravity dam, a macro-meso structure finite element model of dam bodies was developed that takes the concrete in the region of crack propagation as inhomogeneous materials at meso level and adopts an extended finite element method to simulate the whole propagation process in the dam. Crack propag...
Article
The characteristics of the cohesive zone at crack tips throughout the fracture process were studied based on the initial fracture toughness (IFT) criterion and cohesive crack model. Single-edge notched beams with different sizes, subjected to three-point bending, were used as specimens, and the length of the cohesive zone at crack tips, the cohesiv...
Article
An approach of aligning steel fibers in cement mortar using external uniform electromagnetic field is presented, which is the rotating process of steel fiber driven by magnetic force to overcome the viscous impeding of the mortar. Using the approach, the aligned steel fiber reinforced cement mortar (ASFRC) is prepared. Then the orientation distribu...
Article
Full-text available
According to the concept of the permissible damage scale, the strain in front of the crack tip were obtained as three-order series based on the stress expressed by William series, the analytical solution of the permissible damage scale was derived based on the stress relaxation method. Taking the three-point bending concrete beam specimen with fini...
Article
Based on the Wallin model and fracture mechanics theory, a simple power law expression of the effective K-R model for steel fibre reinforced cement-based composites was presented. To validate this model, a three-point bending beam fracture test with different sizes and different steel fibre distributions was carried out. It is shown that the power...
Article
Full-text available
A simplified method for determining the initial fracture toughness of dam concrete was examined in this study based on the linear regression theory. It determines initial cracking load using a P-Δ curve of load versus crack opening displacement, which is linear before cracking and takes a sudden drop in linear correlation coefficient at cracking st...
Article
A simplified approach to obtain the double-K fracture parameters of concrete for three-point bending beams was proposed based on the extreme method. With the proposed method, the double-K parameters can be easily obtained by the experimental peak load. This method requires fewer parameters or tests than the double-K method and the peak load method....
Article
Full-text available
Based on energy consumption equivalence between damage and fracture, a micro-spring stochastic damage model was established with the assumption that the micro-spring failure strain is lognormal distribution and further the method of constructing the cohesive law of concrete was studied. The specific expressions of the cohesive laws of dam concrete...
Article
The fracture processes of concrete were described by a cohesive crack model based on initial toughness criterion. The corresponding analytical method to predict the instability state was proposed. In this model, the initial toughness was adopted as the crack propagation criterion and the weight function method was used to calculate the stress inten...
Article
The effects of tensile softening curve parameters on the crack propagation P-CMOD and P-CTOD curves were analyzed using a calculation method which adopted the initial fracture toughness as the crack propagation criterion. The results showed that: the whole process of the P-CMOD and P-CTOD curves were affected by the tensile softening curve paramete...
Article
An interfacial spring element model (ISEM) is employed to simulate the strength of concrete under uniaxial compressive loading. In this model, the concrete was considered as a composition consisting of aggregate, matrix, interfacial transition zone (ITZ) and initial defects in ITZ at meso level. The distribution and contents of the initial defects,...
Article
A three-dimensional model of dam-water-interaction system was built. Three different materials were used to model the dam, and the acceleration response of arch dam under the observed seismic waves was simulated. The results show that the dynamic reactions of the arch dam under observed earthquakes can well match the monitoring values, which means...
Article
Full-text available
A kind of crack with similar characteristics has been discovered on the upstream surface of super-high arch dam. In this paper, the reason of cracking was analyzed by the three-dimensional finite element method. It is found that the stress concentration of concrete near the water-stop structure led to the concrete initial cracking in the process of...
Article
Full-text available
In this paper, the crack stability and crack propagation regularity of the upstream surface of super-high arch dam along the water-stop structure were analyzed in the framework of fracture mechanics. According to fracture toughness of dam concrete, the relationship between the crack propagation length and the allowable water pressure was studied. F...
Article
Based on the classical three-wave method theory of the SHPB/SHTB device, a correction method for the dynamic tensile deformation measurement is proposed. The method can effectively avoid the signal interference caused by the threaded connection and transition part between the incident (transmitted) bar and the specimen. Dynamic tensile and compress...
Article
Full-text available
Based on Paris' displacement formula and by considering the role of cohesive stress in the fracture of concrete, a theoretical expression for crack opening displacement of three-point bending notched beams is derived. Then, with the initial fracture toughness taken as the criterion of crack initiation, the derived expression is applied in simulatin...
Article
In this paper, a definition of a representative volume element (RVE) based on the meso-structure of concrete, as well as a method for determining the RVE size of concrete is proposed by means of statistical analyses of the mesoscale structural characteristics of concrete. The voxel concept is employed to calculate the statistical variable of a volu...
Article
Full-text available
The paper proposed a method to generate the finite element mesh of concrete at meso level semi-automatically. And an aggregate meshing computer program, AggMesh, was developed by C++ language. Since it avoids the judgment of node coincidence in contact surface between aggregates and mortar through meshing process, the approach can greatly increase...
Article
A method for simulating the whole fracture process of concrete has been developed and it is able to consider the criterion initial fracture toughness and cohesive stress. Taking the wedge-splitting specimen as an example, the corresponding crack propagation P-CMOD curve was obtained. Based on the existing experimental data, the effects of cohesive...
Article
Based on the fictitious crack model, fracture process of concrete is studied in this paper. Taking the tensile fracture model for the center of an infinite plate for an example, and by expressing the opening displacement in fracture process zone in a polynomial, the distributions of displacement and cohesive stress in the fracture process zone are...
Article
Based on the concept of cohesive crack and taking initial fracture toughness as a fracture initiation and propagation criteria, the calculation method of a concrete fracture process zone length is developed. The fracture process zone length in the Mode I Crack with different initial crack lengths and fracture toughness are calculated and the result...
Article
The logarithmic spiral curved arch dam (LSCAD) is a new type of dam. Based on mathematic equations developed for the arch rings of the LSCAD and automatic mesh generation techniques, a mesh generation system for the LSCAD was constructed. Differnt design patterns, including strategy pattern, façade pattern, CAD-mesh separation pattern and embedded...
Article
In this study, an interfacial spring element model with random defects was constructed based on the four-phase material model of concrete, which consists of aggregate, matrix, interfacial transition zone (ITZ), and initial defects distributing randomly within the ITZ. The ITZ is modeled by linear spring element of zero length. Simulation of concret...
Article
Full-text available
This paper proposes a theoretical expression for the ultimate relationship between the crack gauge monitoring data and steel stress gauge ones in dam concrete, based on the equation for crack width of reinforced concrete member, when the cracks expanded to the crack-control steel. In addition, a practical method is developed for analyzing and deter...
Article
The optimal search problem for a randomly moving target perturbed by a Brownian motion is considered in this paper. Firstly, an optimal control model for the search problem is introduced. Based on the principle of optimality, the search problem is then transformed to an equivalent problem of deterministic distributed parameters system, represented...
Article
Extending the ring signature scheme for individual person, a novel ring signature scheme for general subsets of a group is proposed. In the scheme, the members of signing subset firstly construct a group including themselves, then construct a set of subsets including the signing subset, namely the authorized subsets. The signature is generated by c...
Article
In order to distribute the power of verifying the signature of a message, this paper proposed a new (T, N) threshold shared verification signature scheme with specified receiving groups. The signature can only be verified by the cooperation of T or more individuals out of N group members. The scheme is on the basis of Shamir's threshold secret shar...
Article
In order to prolong the network lifetime, energy-efficient protocols should be designed to adapt the characteristic of wireless sensor networks. Clustering Algorithm is a kind of key technique used to reduce energy consumption, which can increase network scalability and lifetime. This paper studies the performance of clustering algorithm in saving...

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Project
The present project plans to adopt the combination of experimental study, theoretical analysis, and numerical simulation to conduct a deep and systematic study on such scientific problems as the size effect rule of fully-graded hydraulic concrete fracture criteria, fracture initiation mechanism, and the entire process of damage fracture. Through fracture tests of concrete members meeting different types of similarity ratios, the study will analyze the size effect rule of fully-graded hydraulic concrete macro fracture parameters, will establish a calculation method for the similarity ratio of fully-graded hydraulic concrete fracture parameters, and will ascertain the conversion formulas among fully-graded hydraulic concrete, wet screening concrete, one-graded concrete, and two-graded concrete fracture parameters. The fracture initiation state of the fully-graded hydraulic concrete will be recorded with high-speed photography to study the fracture initiation mechanism and analyze its size effect. Based on the technologies related to Digital Image Correlation, the morphological characters of the fracture process zone of the fully-graded hydraulic concrete will be quantitatively described. The whole dynamic process of extension and development of the fracture process zone of the fully-graded hydraulic concrete will be studied.The three-dimensional random defective interface spring element model will be adopted to simulate the entire microscopic fracture process of the fully-graded hydraulic concrete; consequently, the fracture size effect mechanism of the fully-graded hydraulic concrete will be explained from a microscopic perspective. The current study focuses on the similarity ratio of the fracture criteria of the fully-graded hydraulic concrete and on the evolution process of the entire fracture and mechanism processes. The micro mechanism study on fracture initiation and extension as well as the expected results can provide data for the theoretical analysis of 300 m-graded high-arch dam construction, including cracking-risk evaluation, fracture stability analysis, and safety evaluation, among others.