Plain Concrete Structures Research Articles

Numerical Integration Study of Penetration and Blasting Damage for Composite Underground Protective Structure with Reinforcement Layers

In response to the increasing threat of powerful earth-penetrating weapons, underground protective structures typically employ composite structural systems with reinforced steel layers. However, current numerical studies often simplify the entire structural system to plain concrete when assessing damage effects, and penetration and blasting processes are treated separately using a restart method. In this paper, we adopt an integrated simulation approach to analyze the resistance performance of composite protective structures with reinforcement layers. The results reveal significant differences in failure modes between plain concrete and reinforced concrete protective structures. The diameter of the steel bars and the spacing between mesh layers notably impact the penetration and blasting damage. Based on the results of a parameter analysis, we propose a method for optimizing the design of reinforcements in composite underground protective structures. The results of the study show the following: (1) The penetration and blast damage patterns of EPWs on plain concrete and composite protective structures with reinforcing mesh are significantly different. Compared to the plain concrete layer, the composite protection structure can effectively resist the damage of EPWs. (2) With the increase in reinforcement diameter, the decrease in reinforcement mesh spacing, and the increase in reinforcement dosage, the penetration depth gradually decreases; the amount and range of the blast damage also decrease accordingly. (3) Under the condition of the same reinforcement ratio, reducing the number of layers of reinforcement mesh, increasing the diameter of reinforcement, and configuring the reinforcement on the top of the protective structure as much as possible can improve the performance of the protective layer against penetration. At the same time, the reasonable arrangement of the reinforcement mesh can also enhance the ability of the protective structure to resist blasting damage.

Degradation analysis of dynamic properties for plain concrete structures under mixed-mode fracture conditions via an improved cohesive crack approach

The present work investigates the crack-induced degradation of the dynamic characteristics in plain concrete elements subjected to mixed-mode fracture conditions. Specifically, a discrete fracture model, based on an inter-element cohesive approach, has been improved and implemented into a 2D finite element framework to evaluate the progressive variation of the static and dynamic properties as the damage level increases. The obtained numerical results highlight the effectiveness of the proposed model in determining the load-carrying capacity and the degradation of natural vibration frequencies during damage propagation, demonstrating its applicability in the framework of structural health monitoring.

Size Effect of Synthetic Fibre Reinforced Concrete – Investigation using a Semi-Discrete Analytical Beam Model

Abstract The size effect is a well-known characteristic of concrete structures. However, in the case of fibre-reinforced concrete (FRC), this issue is not thoroughly explored. Most design recommendations of FRC neglect the size effect or handle the behaviour of FRC structures in case of different structural sizes similar to plain concrete structures (assuming FRC is a homogeneous material). The aim of this paper is to show that the size effect of FRC can be divided, the share of the concrete matrix and the fibres in the size-dependent properties is separable. For the size effect research fifteen synthetic macro fibre reinforced concrete and six plain concrete beam specimens were prepared and tested in three different sizes and then evaluated with the semi-discrete analytical (SDA) model. The analysis of the experimental specimens has shown that the size effect significantly influences the concrete material in the case of FRC with softening material behaviour, but the residual loadbearing capacity which mainly arise from the local bridging effect of fibres is essentially independent of the structural size. It is also shown in this paper that the two defining parameters of the SDA model is independent of the structural size, so the model provides an excellent tool in case of the design of real-sized FRC structures.

Crack Width – Seismic Intensity Relationships for Concrete Gravity Dams

ABSTRACT Seismic assessment of plain concrete structures like gravity dams is generally conducted based on cracking. The responses of two types of gravity dams, i.e. the conventional and roller compacted concrete (RCC), were investigated in this study using a discrete element tool coupled with special reservoir elements. Using incremental dynamic analysis, the relationship between the seismic intensity measures and crack widths on the U/S face of the monolith was obtained. The damage accumulation on conventional and RCC dams was different: The cumulative cracking on the upstream face of the monolith correlated well to a seismic intensity measure representing base shear.

Safety Evaluation of Plain Concrete Lining Considering Deterioration and Aerodynamic Effects

With an increase in the service time of high-speed railway tunnels, various defects caused by construction-quality defects in the secondary lining begin to appear. How to evaluate the safety of such tunnels and take countermeasures is very important for the safe operation of tunnels. Based on the load-structure method and a numerical simulation, this paper studied the short-term and long-term safety of the missing section of anti-crack reinforcement mesh in the plain concrete lining of a high-speed railway mountain tunnel. The short-term safety evaluation considered the influence of negative pressure caused by aerodynamic effects. The long-term safety evaluation considered the combined influence of the surrounding rock and concrete deterioration and the negative pressure and concrete fatigue damage caused by aerodynamic effects. The results showed that under the negative pressure generated by aerodynamic effects, the minimum tensile safety factor of the lining in the defective section increased by 3.8%, while the minimum compressive safety factor of the lining decreased by 7.9%. The negative pressure generated by the aerodynamic effects had little impact on the short-term safety of the lining in the defective section. During the long-term safety evaluation, the overall safety of the defective section decreased significantly, and the minimum tensile and minimum compressive safety factors of the lining decreased by 59.4% and 66.8%, respectively. The calculation results for the initial design do not meet the long-term design requirements and cannot guarantee the long-term safe operation of the tunnel. Finally, two new strengthening methods of galvanized steel mesh-short bolts and galvanized corrugated steel plate-short bolts were proposed to strengthen the defective section of the concrete lining, so as to improve the ultimate bearing capacity and toughness of the plain concrete lining structure.

Improved plastic-damage cap model for shear behavior predictions of plain and reinforced concrete members

In this article, an improved continuous surface cap model (ICSC) with isotropic plastic-damage algorithms is proposed, namely to predict more accurately the shear behavior of both plain and reinforced concrete members. For this, a suitable yield surface is implemented and the critical shear-to-compression transition parameter in the ductile damage law is scrutinized and determined. Firstly, the mathematical framework of the plastic-damage cap model is summarized, namely the formulations in plasticity, the returning mapping algorithms of cutting plane and the isotropic damage law. Then, the proposed constitutive parameters in ICSC model are presented. The plastic-damage algorithms flowchart is presented and described, and the new proposed ICSC model is implemented in the software LS-DYNA. Next, the proposed ICSC model is validated against the original CSC model (MAT159 in LS-DYNA) and also against the previously improved CSC model with crack closure behavior developed by the authors. For this, several simulations using the three CSC models are performed and the results are compared with experimental results, which involve single concrete element under various loading conditions, plain concrete structure under direct shear load and simply supported reinforced concrete (RC) beams with or without stirrups under a center-point load. The results are presented and discussed. They show the superiority of the proposed ICSC model for the prediction of the ultimate concrete behavior at the material level, and a better prediction of the shear behavior for plain concrete and reinforced concrete beams.

Experimental study on the elastic-plastic dynamic response of shallow-buried corrugated steel-plain concrete composite structures under long-duration plane blast wave loading

To study the elastic-plastic dynamic response characteristics of shallow-buried corrugated steel-plain concrete (CSPC) composite structures under long-duration plane blast loads, a series of tests were conducted in a large confined blast-resistant test facility using the plane charge explosion technique (PCET), and the dynamic response and deformation laws of CSPC arches, reinforced concrete (RC) arches and plain concrete (PC) arches under different blast loads were comprehensively compared and analyzed. The test results show that under this test condition, the plane air shock wave overpressure peak with the increase in charge is basically a linear growth, but the shock wave pressure duration of action and impulse growth rate gradually decreased, the test device simulated by the explosion shock wave pressure duration of the maximum action time of more than 340 ms. Comparing the differences in the dynamic response of the three structures, it was found that when the peak long-duration shock wave overpressure acting on the structure reached 0.09 MPa, the PC model had plastic deformation, and the combined reinforced concrete and CSPC structure exhibited fully elastic deformation. When the peak shock wave overpressure reaches 0.238 MPa, the RC model begins to show plastic deformation. When the peak shock wave overpressure increased to 0.315 MPa, all models produced significant plastic deformation. The deformation resilience of the CSPC composite structure under the above-mentioned blast shock wave load is greater than that of RC and PC structures, which have good deformation recovery ability and can effectively reduce the damage to the structure by blast shock. On the contrary, the peak structural vibration acceleration caused by the blast shock wave is greater in the CSPC combined structure than in the RC and PC structure, and the deformation rebound and oscillation of the corrugated steel plate is the main way of impact energy dissipation. The results of the study provide an experimental basis for the simulation of long-duration plane blast waves and the optimal design of CSPC blast-resistant structures.

Greener and sustainable self-compaction concrete: A review on performance at elevated temperatures

Self-compacting concrete (SCC), highly flow-able engineer-friendly concrete that have moderate viscosity, low yield stress, good segregation resistance, and high deformability. SCC is a composition of high amounts of cement, mineral admixtures, fine aggregate, water, super-plasticizer, and coarse aggregate. Mineral admixtures obtained from agricultural and industrial by-products and or waste materials are primarily used as filler materials and or pozzolanic materials for increasing the slurry or cementitious paste in SCC. Many high-rise concrete structures or plain concrete structures and or reinforced concrete structures are nowadays constructed by using SCC. Hence, considering its fresh and hardened properties, materials used, and importance in the construction industry, understanding the behaviour of SCC after exposure to elevated or high temperatures is of utmost importance and gaining attention. In SCC, explosive spalling was mainly caused by the stress developed, water to binder ratio and cement binder ratio. Higher amounts of powder content in SCC reduced the porosity and made SCC more vulnerable and susceptible to spalling. The strain values of SCC are enhanced by the increase in temperature. Higher reduction in strength values are observed with non-destructive testing than destructive tests. The scanning electron microscope of SCC revealed that the stiffness ratio between aggregates and cement matrix reduced with elevated temperature, which results in reducing the interaction transition zone. Finally, from the literature review, it may be concluded that the degradation mechanism of SCC when subjected to elevated temperatures is similar to the conventional concrete.

An energy-based elastoplastic damage model for concrete at high temperatures

Although structural concrete is widely used in civil engineering, the proper modeling of its thermo-mechanical behavior remains a challenging issue for the academic and engineering communities due to the complexity involved in the underlying micro-cracking process. In this work, the previous thermodynamically consistent energy-based elastoplastic damage model is extended to concrete at high temperatures, with the aim to describe the material nonlinear behavior and provide numerical predictions of concrete structures. Both the thermal expansion and transient creep strain are incorporated in the kinematics. Within the framework of continuum damage mechanics, two mechanical damage variables that lead to a fourth-order damage tensor are introduced to describe stiffness degradation of concrete under predominant tension and compression, respectively. Moreover, temperature-dependent mechanical properties are adopted to describe the thermal degradation and the thermo-mechanically coupled behavior of concrete at high temperatures. The plastic flow is described by the effective stress space plasticity and the evolution laws for the mechanical damage variables are driven by the conjugate elastoplastic damage energy release rates. The proposed model is validated by several benchmark experiments of plain concrete and then applied to reinforced concrete (RC) structures. The well agreement between the numerical predictions and experimental results indicates that the proposed model is promising in quantifying the global responses and assessing the safety of plain concrete and RC structures at high temperatures.

A modified applied element model for the simulation of plain concrete behaviour

A modified applied element model to simulate the behaviour of plain concrete continuum structures including discrete cracking is proposed in this study. In the classical applied element model, Poisson effects are fully ignored. To remediate this issue, diagonal elements are introduced to include the Poisson effect, and the constitutive parameters are rigorously determined using the Cauchy–Born rule and the hyper-elastic theory. The formulation is validated for linear elastic problems and the consistency and convergence behaviour of the numerical approach is shown. Tensile softening formulation using the concept of fracture energy is utilised for the nonlinear range. In this range, the approach is validated using the classical benchmark tests with pure tensile, split-tensile, combined shear-tensile and bending dominated push-over loading. The load–displacement behaviour and crack response were captured successfully, showing the proposed methodology can be used to quantify discrete cracks on large systems, such as dam monoliths, from initiation to significant damage levels.

Application of Nondestructive Testing Technology in Quality Evaluation of Plain Concrete and RC Structures in Bridge Engineering: A Review

The development and application of nondestructive testing technology for prestressed reinforced concrete structures in the field of infrastructure construction were summarized in this study via the analysis of relevant literature worldwide. The detection methods, detection principles, and detection instruments in quality evaluation of prestressed reinforced concrete structures were analyzed and compared, based on which, acoustic emission detection technology, impact echo detection technology, ultrasonic detection technology, infrared thermography detection technology, ground-penetrating radar detection technology, piezoelectric transducer detection technology, and X-ray detection technology were summarized. Additionally, the advantages, disadvantages, and application scope of each detection method were focused upon and analyzed comparatively. It is indicated that further improvement in the detection visualization, accuracy, and efficiency for most nondestructive testing technologies is available by optimizing the algorithm and combining artificial intelligence technology with neural network deep learning, precise positioning, and imaging analysis of the quality defects in prestressed reinforced concrete structures. The results of this study can provide technical reference for the further application and research of nondestructive testing technologies in the quality inspection of prestressed reinforced concrete structures.

Intelligent Classification Method for Tunnel Lining Cracks Based on PFC-BP Neural Network

Tunnel lining crack is the most common disease and also the manifestation of other diseases, which widely exists in plain concrete lining structure. Proper evaluation and classification of engineering conditions directly relate to operation safety. Particle flow code (PFC) calculation software is applied in this study, and the simulation reliability is verified by using the laboratory axial compression test and 1 : 10 model experiment to calibrate the calculation parameters. Parameter analysis is carried out focusing on the load parameters, structural parameters, dimension, and direction which affect the crack diseases. Based on that, an evaluation index system represented by tunnel buried depth (H), crack position (P), crack length (L), crack width (W), crack depth (D), and crack direction (A) is put forward. The training data of the back propagation (BP) neural network which takes load-bearing safety and crack stability as the evaluation criteria are obtained. An expert system is introduced into the BP neural network for correction of prediction results, realizing classified dynamic optimization of complex engineering conditions. The results of this study can be used to judge the safety state of cracked lining structure and provide guidance to the prevention and control of crack diseases, which is significant to ensure the safety of tunnel operation.

Blast Vibration Control in A Hydropower Station for the Safety of Adjacent Structure

The transverse cofferdam in Xiangjiaba hydropower station was a water retaining concrete structure with a length of 126 m, a width of 12 m, and a height of 25.2 m, consisting of masonry, plain concrete structure (PC), and roller compacted concrete (RCC), which had to be demolished by blasting after the dam was built. There were many precise instruments nearby the cofferdam which had strict restrictions on blasting vibration. Therefore, the cofferdam was divided into six blasting regions, including land blasting and underwater blasting. Blasting parameters and blasting network structure were accurately designed and continuously optimized through blast-induced vibration test results. At nine measurement points in different locations, 57 blast vibration data were recorded. Consequently, 1386 holes with an explosive weight of 9641.3 kg were detonated in land blasting. The highest levels of vibration were recorded as 8.74 cm/s in the desilting tunnel on the right of the cofferdam. The explosives up to 11887.7 kg were detonated in an underwater blasting. According to the analysis of the law of vibration attenuation, the blast vibration value was reduced to 7.65 cm/s. The results showed that the research on the attenuation law of blasting vibration can effectively increase the charge weight per delay and control the blast-induced vibration. Consequently, the peak particle velocity (PPV) of underwater blasting could be predicted by analyzing the PPV of land blasting in same structure, which provided the basis for the design of underwater blasting parameters. A reliable method for cofferdam demolition in hydropower station was proposed, which provided a reference for similar projects.

Fully-coupled hydro-mechanical cracking using XFEM in 3D for application to complex flow in discontinuities including drainage system

The presence of uplift pressures in cracked plain concrete hydraulic structures is a major concern for their durability, serviceability and stability. To assess the performance of cracked structures several mechanical and hydraulic response parameters must be computed. This paper presents the development, implementation and application of a new nonlinear combined segregated fully-coupled hydromechanical model for application to non-planar 3D hydraulic fractures where complex flow is occurring. The eXtended Finite Element Method (XFEM) formulation is used, as it facilitates the computation of the crack aperture as well as the application of water pressure on crack surfaces for the simulation of hydraulic fracture initiation and propagation. To take into consideration the effects of drainage in numerical modeling and simulation, two coupled (multi-physics) finite element models are used; (1) one for the uplift pressures where a hydraulic mesh with refinement around drains is used, and (2) one for the mechanical response coupled with the computation of the unsaturated interstitial seepage problem. The two subproblems are solved using a partitioned procedure, as they have different resolution requirements. Finally, the mechanical mesh and the hydraulic mesh have non-matching discrete interfaces that must be coupled while respecting the equilibrium of the applied loads. Applications of the proposed hydromechanical constitutive model and numerical solution strategy to different problems are presented on a wedge splitting test and a full scale gravity dam including multiple drainage configurations. A case study adapted from a real dam is also given with a complex 3D non-planar discontinuity surface.

Numerical simulations of crack path control using soundless chemical demolition agents and estimation of required pressure for plain concrete demolition

In demolition process of large concrete structures, the non-explosive methods can be advantageous in reducing noise, vibration, and dust emission compared to the conventional explosive methods. One of the representative non-explosive methods is the injection of soundless chemical demolition agents (SCDAs) into the holes drilled in concrete structures and further expansion of the SCDAs. In the current paper, a computational framework was established and applied to simulate crack initiation and propagation caused by slow expansion of the SCDAs in plain concrete structures from a theoretical perspective. Using the concrete damaged plasticity model for semi-infinite structures, we first determined a proper domain size for the demolition simulation and then investigated a cost-effective spacing of the SCDA holes arranged horizontally or vertically. The interaction between the SCDAs was examined in terms of the minimum expansion pressure required to form cracks connecting the SCDAs. Furthermore, we found an equation for the minimum expansion pressure required to control a U-shaped crack path as a function of SCDA spacing and concrete compressive strength.

Application of Acoustic Emission Method and Impact Echo Method to Structural Rehabilitation

The paper is concerned with the technical aspects of the appraisal and retrofitting process of fire damaged reinforced concrete structures. The assessment of fire damaged structures is carried out along lines similar to those of the appraisal of existing structures. In practice, constructions are most often assessed by destructive tests in-situ and on core bore specimens. In addition to destructive tests, damaged structures are also assessed by non-destructive ones. The present paper shows the use of non-destructive methods of measurement using the acoustic-emission and impact-echo methods. Acoustic emission provides valuable data on the structural integrity of a material. This method has a significant potential to be used for in-situ monitoring and evaluation of the current state of structures. An impact-echo method is based on impact-generated stress waves that propagate through concrete and are reflected by internal flaws and external surfaces. Impact-echo can be used to determine the location and extent of flaws such as crack delamination, voids, honeycombing and deboning in plain, reinforced, and post-tensioned concrete structures. The paper presents a possible rehabilitation plan based on the potential results obtained by these non-destructive methods.

Nonlinear dynamic analysis of arch dams considering contraction joints

Arch dams are massive plain concrete structure, their stability and security are usually controlled by the tensile behavior and cracking of concrete. They are constructed as vertical monolithic cantilever elements separated by contraction joints filled with mortar. This contribution consists of the evaluation of the performance and the reliability of nonlinear joints numerical models used in the finite element open source code “Code-Aster.” These contraction joints can only transfer limited tensile stresses between the adjacent cantilever monoliths. Relative motions of the cantilever monoliths during an earthquake induce the opening, closing, and sliding of the contraction joints, resulting in significant dissipation of the seismic input energy. For these reasons, Nonlinear Time History Analysis is carried out in order to locate and estimate the probable damages of the structure in the form of joints opening. The numerical results obtained from nonlinear time history analysis show that the contraction joints opening releases the tensile stresses in the arch, but increases the compressive stresses in the arch and the vertical stresses in the cantilevers. The increase in the compressive stresses in the arch can lead to the crushing of the concrete, and to the increase of vertical stresses in the cantilevers which can exceed the tensile strength of the concrete arch, resulting in the apparition of tensile cracks along the horizontal joints. High tensile stresses may also appear along the Dam–Rock interface causing cracks along the contact surface.

A novel experimental method to characterise the shear strength of concrete based on pre-stressed samples. A comparison with existing techniques

Mode II shear fracture process can be observed in plain-concrete structures exposed to intensive loadings such as shock, blasting or projectile-impact. It is the reason why the quasi-static and dynamic shear fracturing properties of concrete need to be investigated. In previous works performed by Forquin and coauthors a passive confining cell was applied to PTS (Punch-Through-Shear) specimens in a similar way than in quasi-oedometric compression tests where metallic ring are used as passive confinement. However the change of confining level during the sample loading constitutes a main drawback of this technique. In the present work a novel testing method is proposed based on a pre-stressing of the sample. To do so, the concrete specimen is inserted into pre-stressed metallic cell. During the unloading stage confining stresses are transferred to the ligament of the sample. In a second stage, a differential displacement applied to the central part of the sample toward the side parts produces a shearing of the ligament. The experiments performed in static and dynamic conditions (SHPB testing) allow the shear response of concrete to be determined over a wide range of strain-rates. In the present communication, the testing technique and obtained results are compared to the obtained data with the previous experimental method.

Adaptive Crack Modeling with Interface Solid Elements for Plain and Fiber Reinforced Concrete Structures.

The effective analysis of the nonlinear behavior of cement-based engineering structures not only demands physically-reliable models, but also computationally-efficient algorithms. Based on a continuum interface element formulation that is suitable to capture complex cracking phenomena in concrete materials and structures, an adaptive mesh processing technique is proposed for computational simulations of plain and fiber-reinforced concrete structures to progressively disintegrate the initial finite element mesh and to add degenerated solid elements into the interfacial gaps. In comparison with the implementation where the entire mesh is processed prior to the computation, the proposed adaptive cracking model allows simulating the failure behavior of plain and fiber-reinforced concrete structures with remarkably reduced computational expense.

Seismic assessment of small to medium spans plain concrete arch bridges

There are numerous old arch bridges in Iran that have been used as railway bridges for more than 70 years. Field load testing of old railway bridges in km-23 and km-24 of Tehran–Qom railway have revealed important characteristics of the bridges and have proven that there is still a large capacity under service load. Since most of these bridges are not designed for earthquake excitation, seismic vulnerability of these structures is uncertain. This fact necessitates the investigation of the earthquake resistance of these kinds of bridges. In this paper, seismic performance of bridges is assessed by the pushover analysis. These bridges are plain concrete arch structures with different span length and mechanical properties which have been built 70 years ago. The results of dynamic load tests are used to calibrate a finite element model of the bridges in which a plain strain analysis is carried out. Using non-linear static analysis method, suggested by several modern standards, the capacity curves of the structures and non-linear demand spectrum are obtained. The choice of control nodes in the pushover analysis and their influences on seismic performance of plain concrete arch bridges are investigated. The crown, centre of mass and a virtual point are selected as control nodes and it is demonstrated that the capacity curves are almost identical in all control node cases. Finally, the demand levels of the bridges are determined and compared with capacity curves. The results show that the earthquake resistance of these kinds of bridges totally depends on material properties and geometry of the structures.