Concrete Failure Mode Research Articles

Group resistances of tensile-loaded anchored-bolted connections with CFST columns: Tests, simulations, and theoretical models

The performance of the connections in concrete-filled steel tubular (CFST) columns fabricated with a group of two anchored blind-bolts under tensile forces is evaluated. Based on the bolt group arrangement, two sets of experiments, comprising eight full-scale specimens, were tested. Test parameters include the presence of concrete, bolt anchorage length, pitch distance, and gauge distance. Further, numerical models were developed, which, after validation, were used for parametric studies. Key findings indicate that bolt gauge distance, anchorage length, concrete grade, and column cross-section slenderness significantly influence the connection behaviour, but pitch distance has the least influence. Tube and concrete failure modes, as well as critical gauge and pitch distances, are identified, which govern tube deformation and concrete crushing zones. Finally, a bi-linear theoretical model is developed that can provide a fair prediction of the connection strength and stiffness.

Influences of Pre-Existing Fissure Angles and Bridge Angles on Concrete Tensile Failure Characteristics: Insights from Meshless Numerical Simulations.

The existence of cracks is a key factor affecting the strength of concrete. However, traditional numerical methods still have some limitations in the simulation of crack growth in fissured concrete structures. Based on this background, the numerical treatment method of particle failure in smoothed particle hydrodynamics (SPH) is proposed, and the generation method for concrete meso-structures under the smoothed particle hydrodynamics (SPH) framework is developed. The concrete meso-models under different pre-existing micro-fissure inclinations and bridge angles (the inner tip line of the double pre-existing micro-fissure is defined as a bridge, and the angle between the bridge and the horizontal direction is defined as the bridge angle) were established, and numerical simulations of the crack propagation processes of concrete structures under tensile stress were carried out. The main findings were as follows: The concrete meso-structures and the pre-existing micro-fissures all have great impacts on the final failure modes of concrete. The stress-strain curve of the concrete model presents four typical stages. Finally, the crack initiation and propagation mechanisms of fissured concrete are discussed, and the application of smoothed particle hydrodynamics (SPH) in crack simulations of fissured concrete is prospected.

Mechanical Properties and Mesoscopic Numerical Simulation of Local Weakening in High-Performance Concrete after 10 Years of Alkali Solution Immersion

The natural environment in the high-altitude regions of Northwest China is extremely harsh, characterized by numerous salt lakes. The high concentrations of chloride salts, sulfates, and alkali metal ions in these areas can induce alkali–silica reactions (ASRs) in concrete. These reactions generate harmful gel within the concrete, causing expansion and cracking, which significantly impacts the durability of concrete structures. This study investigates the evolution of the mechanical properties in high-performance concrete (HPC) under long-term ASR by incorporating different admixtures and varying the equivalent alkali content. A three-dimensional random aggregate mesoscopic model was used to simulate static compression tests under various operational conditions. Non-destructive testing methods were utilized to determine the expansion rate, internal, and surface damage variables of the concrete. The experimental results indicate that the 10-year expansion rate differs from the 1-year rate by approximately 1%, and under long-term ASR mitigation measures, the internal damage in the HPC is minimal, though the surface damage is more severe. As the equivalent alkali content increases, the compressive strength of the concrete cubes decreases, initially rising before falling by 5–15% over time. The HPC with only air-entraining agent added exhibited better mechanical performance than the HPC with both air-entraining and corrosion inhibitors added, with the poorest performance observed in the HPC with only a corrosion inhibitor. A relationship was established between the surface and internal damage variables, with the surface damage initially increasing rapidly before stabilizing as the internal damage rose. Numerical simulations effectively describe the damage behavior of HPC under static uniaxial compression. Comparisons with actual failure morphologies revealed that, in the cube compression tests, crack propagation directly penetrated both coarse and fine aggregates rather than circumventing them. The simulations closely matched the experimental outcomes, demonstrating their accuracy in modeling experiments. This study discusses the compressive mechanical properties of concrete under prolonged ASR through a combination of experimental and simulation approaches. It also delves into the impact of surface damage on the overall mechanical performance and failure modes of concrete. The findings provide experimental and simulation support for the concrete structures in regions with high alkali contents.

Macro-Meso Damage Analysis of Tunnel Lining Concrete under Thermal-Mechanical Coupling Based on CT Images.

The mechanical properties and failure modes of concrete are controlled by its mesoscopic material composition and structure; therefore, it is necessary to study the deterioration characteristics of tunnel lining concrete under fire from a mesoscopic perspective. However, previous studies mostly analyzed the damage and failure process from a macro-homogeneous perspective, which has certain limitations. In this paper, a thermal-mechanical coupling test device was modified to simulate the state of concrete under tunnel fire conditions. Combined with CT technology, the macroscopic properties and mesoscopic characteristics of concrete were observed. Features were obtained, such as the change in compressive strength under fire, as well as mesoscopic deterioration characteristics. The damage variable D was defined to quantify mesoscopic damage, and the link between mesoscopic deterioration characteristics and macroscopic performance was established, which can be used to predict compressive strength loss through mesoscopic characteristics.

Deterioration performance analysis of recycled brick concrete subjected to freezing and thawing effect

This study employed experimental and finite element modeling approaches to systematically investigate the mechanical damage mechanisms of recycled brick aggregate concrete (RAC) under freeze-thaw cycling conditions. The investigation encompassed analyses at three hierarchical levels: macroscopic, mesoscopic, and microscopic. The influence of recycled brick aggregate (RA) replacement rate and the number of freeze-thaw cycles on RAC's apparent state and mechanical performance was examined at the macroscopic level. Utilizing equipment such as electron microscopes, a comprehensive observation was conducted from mesoscopic and microscopic perspectives to elucidate the evolving patterns of the cementitious matrix, RA, and the interfacial transition zone (ITZ) within RAC during the freeze-thaw cycling process. On the one hand, more excellent internal space was inherent in RA compared to NA, enabling it to effectively accommodate the volumetric expansion resulting from water freezing. It contributed to mitigating the damage to concrete caused by freeze-thaw cycles. On the other hand, RA's rough and porous characteristics facilitated the infiltration of cement particles into its internal structure, forming a robust ITZ with RA. Concurrently, a numerical simulation of RAC's freeze-thaw cycling process was presented. This simulation generated coupled damage maps and load-deflection curves for RAC under various conditions, encompassing different levels of RA replacement rates, freeze-thaw cycle counts, and loading modes. The research results indicated that the inclusion of RA adversely affects the mechanical properties of concrete while concurrently altering the concrete's failure mode and the propagation pathways of internal cracks. Nevertheless, it was worth noting that the introduction of RA, despite diminishing the mechanical performance of concrete, effectively mitigates the rate of performance degradation during the freeze-thaw cycling process. A favorable equilibrium between freeze-thaw resistance and mechanical performance could be achieved when the replacement rate of RA for natural aggregates (NA) fell within the range of 10–30 %. By employing a finite element model to simulate the flexural performance of RAC after freeze-thaw cycles, the deviation range between the simulated and measured values fell within the range of 5.00–8.23 %. This affirmed the model's fitting solid capability and validated its effectiveness in analyzing the RAC structure's freeze-thaw-load coupled damage and lifespan prediction.

Failure behavior and strength deterioration model of high-performance concrete under coupled elevated temperature, biaxial constraint and impact loading

This research investigates the effects of high temperatures, multiaxial stress constraints, and impact loads on the failure behavior and strength deterioration of high-performance concrete. Combined with scanning electron microscopy and ultrasonic testing, the microscopic deterioration characteristics of thermally damaged concrete were revealed. Dynamic compression tests were performed on concrete, after exposed to elevated temperatures (from 25 °C to 750 °C), using a true triaxial Hopkinson pressure bar test system. The study analyzes the effect of temperature and strain rate on dynamic failure behaviors of concrete under biaxial stress constraints. The study establishes models for predicting the evolution of dynamic strength deterioration and strain rate. Additionally, the research discusses the mechanisms of influence of stress constraint states on the dynamic increasing factor (DIF) and failure modes of concrete. Results indicate that concrete's strength under biaxial stress constraints increases with the load rate and is hardened or weakened by changes in temperatures (taking 300 °C as a demarcation point). The strain rate effect of concrete becomes more significant with increasing temperature. Stress constraint states significantly affect the dynamic strength of concrete, and the DIF of concrete grows quasi-linearly with the logarithm of strain rate at different temperatures. Under biaxial stress constraints, concrete is dominated by oblique shear failure, and damage is less severe with the increase in the intermediate principal stress σ2. Macro-fractures are unlikely to appear under true triaxial stress constraints.

Long-term mechanical performance of high fluidity fiber reinforced concrete modified by metakaolin

To clarify the long-term strength and toughness of metakaolin (MK) and steel fiber (SF) modified concrete with higher fluidity and water/binder ratio, a series of tests including slump tests, compression tests, splitting tests, digital image processing and Scanning Electron Microscope (SEM) tests were performed on MK-SF concrete cured for 7–360 days. Results reveal that the slump of fresh concrete decreased with an increase in the MK and SF replacement rates. Moreover, the impact of MK on the slump of steel fiber reinforced concrete (SFRC) was more pronounced when combined with a lower water/binder ratio, resulting in increased viscosity. At the pre-peak stress region of the strain-stress curve, the compressive strength fc, tensile strength ft, Young’s modulus Ec, elastic modulus E0, and tensile strain at peak stress εt-max of high fluidity MK-SF concrete increased with increasing MK and SF admixing ratio, regardless of curing age. Notably, the coupling effects of MK and SF became more prominent after long-term curing. Without MK incorporation, the effects of SF and curing time on the above indices were relatively implicit. At the post-peak stress region of strain-stress curves, there existed a residual stage. The inclusion of MK significantly improved the long-term residual strength and strain of SFRC. Additionally, the toughness index Mc, which represents the total area of the compressive strain-stress curve containing both the pre-peak and post-peak regions, also exhibited substantial development with curing time, primarily attributed to the incorporation of MK and SF. The coupling of MK and SF led to a transformation of the concrete failure mode from brittle to ductile. Regression analysis reveals that a linear equation adequately described the long-term relationships of fc-ft, fc-Ec, fc-E0, fc-Mc, and fc-εt-max in MK-modified SFRC. Based on the testing data, a relative strength or toughness index λ and a new generalized hyperbola model were proposed to predict the long-term mechanical behavior mentioned above. Through crack morphology and microstructure analysis, the distinct roles of MK and SF in the composite material were examined.

Investigation on the change of shear strength of concrete with cold joint under the action of sulfate dry–wet cycles

Large-volume concrete structures in the saline areas of Western China often have cold joint structural surfaces due to the improper handling of construction joints, dividing them into old and new layers of concrete. In this sulfate-rich environment, the shear strength of concrete with cold joint and the evolution pattern of its composition with the sulfate dry–wet cycles are particularly important in assessing the quality of the interface between old and new concrete bond surfaces. Therefore, in this paper, direct shear tests and microscopic scans were performed on concrete specimens with cold joint at different pouring age intervals and numbers of sulfate dry–wet cycles. The mechanism of the effect of both on the shear strength and failure mode of concrete was analyzed. Results show that the sulfate dry–wet cycles of erosion and the age interval have significant effects on the shear strength of the cold with cold joint and their components. As the number of sulfate dry–wet cycles increased, the shear dilation of concrete specimens with cold joints under direct shear action was reduced, the internal friction angle initially increased and then decreased for specimens with a short pouring interval (0–0.25 day), and the reduction of the internal friction angle of the specimens with a long pouring age interval (0.25–28 days) was nonlinear. The shear dilation of the specimen increased, and the internal friction angle decreased nonlinearly with the increase of the pouring interval. In addition, the failure criterion of specimens transformed from the bilinear Mohr–Coulomb criterion before erosion to the linear Mohr–Coulomb criterion under the action of sulfate dry–wet cycles.

Influence of end friction confinement on dynamic mechanical properties and damage evolution of concrete by coupled DEM-FDM method

This paper presents a quantitative evaluation of the effect of end friction on the dynamic mechanical response and damage evolution of concrete based on the coupled Discrete Element Method (DEM) - Finite Difference Method (FDM) method. Considering the heterogeneity of concrete, a three-phase meso-scale model of concrete (mortar, aggregate and interfacial transition zone) is constructed by DEM, and the crushability, real geometry and random distribution of aggregates are considered by combining 3D scanning techniques and the “ball-clump-cluster” method. Meanwhile, the split Hopkinson pressure bar (SHPB) device is constructed by FDM, and the interface deformation coordination between the concrete sample and metal rods is realized by coupling algorithm. On this basis, the quantitative effects of end friction on the stress–strain response, dynamic increase factor (DIF), damage distribution and failure mode of concrete are investigated. The results indicate that the dynamic compressive strength increases significantly when the interfacial friction coefficient μi increases from 0 to 0.1, and the interfacial friction enhancement effect weakens significantly when >0 μi.1. With the increase of strain rate, the friction contribution coefficient tends to decrease. The end friction has a significant effect on the distribution of microcracks in the axial direction. The end friction confinement changes the local stress state and damage distribution of concrete, which is beneficial to improve the compressive strength of concrete.

An improved meshless method for modeling the mesoscale cracking processes of concrete containing random aggregates and initial defects

Traditional kernel functions in SPH has been improved to realize the simulations of progressive cracking processes; The generation method of meso properties in concrete has been proposed, and the “region searching” algorithm has been developed. Uniaxial tension numerical simulations of concrete specimens with different initial defects and aggregate percentages are carried out, results show that the initial defects and aggregate percentages have great impacts on concrete failure modes. The rationality of the improved method is verified by comparing with previous experimental and numerical results, and future research directions should focus on the developments of multi-field coupling 3D parallel MSC-IKSPH programs.

The evolution of the shape of composite dowels

Abstract Composite dowels have opened new possibilities for engineers designing composite structures. The fundamental and most important characteristic of composite dowels is the shape of the cutting line. It is important to understand why only one particular shape of the cutting line is used in bridge engineering, while so many different shapes have been investigated by many researchers. The essential part of the process of developing composite dowels – the development of the shape of the cutting line – is presented in this paper. The influence of the steel web thickness is presented, and technological problems of steel fabrication are highlighted. The role of empirical experience from the first bridges, push-out tests, and finite element simulations is presented. Assumptions for numerical procedures are given. The distinction between the steel failure and concrete failure modes is introduced for composite dowels. The paper presents how the concept of “shape” was divided into “shape,” “ratio,” and finally “size,” and how, because of the fatigue problems in bridges, all the three factors have emerged to result in the form of shapes that can satisfy the requirements for bridges. Research leading to the invention of the first version of the clothoidal shape is presented.

Research on the True Triaxial Mechanical Properties of Concrete under the Coupling Action of High Temperature and Biaxial Unequal Lateral Pressure.

Based on engineering practice and practical needs, this paper takes ordinary concrete specimens as the research object, and adopts a high-temperature true triaxial loading test system to carry out high-temperature uniaxial and true triaxial static compression tests of concrete under high-temperature conditions. By comparing with normal temperature conditions, this paper analyzes the influence of the coupling effect of high-temperature and biaxial unequal lateral pressure on the static mechanical properties of concrete. By analyzing the experimental data, we reached a series of conclusions and carried out theoretical research on this basis. High temperatures can significantly affect the uniaxial static pressure strength characteristics, deformation characteristics, and failure mode of concrete. When the temperature exceeds 400 °C, the compressive strength decreases significantly, the peak strain increases sharply, and the plasticity of concrete is further enhanced. The coupling effect of high-temperature deterioration and lateral pressure strengthening makes the true triaxial mechanical properties of concrete change significantly; 0.6:0.2 and 400 °C are the turning points of side pressure ratio and temperature that affect the change law of the true triaxial mechanical properties of concrete, respectively. Based on the study of the high-temperature deterioration factor and lateral pressure strengthening factor, this paper further puts forward a concrete strength formula under the coupling action of high temperature and biaxial unequal lateral pressure. It was verified that the formula has a high accuracy.

Mesoscale Study on Splitting Tensile Damage Characteristics of Concrete Based on X-ray Computed Tomography and Digital Image Correlation Technology.

In this paper, the mesoscale damage properties of concrete and mortar were studied experimentally under Brazilian disc splitting tensile tests combining X-ray computed tomography (CT) and digital image correlation (DIC) technology. Considering the factors of water/cement ratios and loading rates, the influence of meso components on the macro tensile properties and failure modes of concrete were studied. The experimental results and analysis indicate that the following: (1) the existence of coarse aggregate makes the tensile strength of concrete lower than that of mortar and reduces the sensitivity of tensile strength to the loading rates; (2) the failure modes of mortar and concrete Brazilian discs differ in the crack initiation positions and localization phenomena. Under high loading rates, the local failure plays a critical role in the strength improvement of concrete; (3) for concrete, interface failure and mortar failure are the main failure modes under low loading rates, whereas aggregate failure gradually becomes the main failure mode with increasing loading rates. The decrease in water/cement ratios improves the strength of the mortar matrix and interfacial bonding performance, leading to more serious aggregate damage and higher strength.

Behavior of confined concrete columns with HSSSWR meshes reinforced ECC jacket under uniaxial compression

This paper presents experimental and analytical studies on the uniaxial compressive properties and failure mechanics of confined concrete columns with a novel strengthening system, high-strength stainless steel wire rope (HSSSWR) meshes reinforced engineering cementitious composite (ECC) jacket. The effects of the formula of ECC, spacing of lateral HSSSWRs and concrete strength were considered in this experimental study. Test results showed this strengthening system can confine concrete columns effectively due to good bond performance between the jacket and concrete, which changed the concrete failure mode from brittleness to ductile failure and resulted in effective improvements in bearing capacity, deformation capacity, ductility and energy absorption capacity. Multiple fine cracks were observed in the confined concrete columns, which indicated the excellent crack-width controlling ability of the jacket. By embracing path-independence assumption and modifying the relationship of hoop strain and vertical strain for concrete columns confined by HSSSWR meshes reinforced ECC jacket, an analytical model for predicting the load–displacement curve of the HSSSWR meshes reinforced ECC confined concrete columns was developed. The predicted results by using the proposed analytical model were found in good agreement with the experimental results.

Numerical simulation of influence of coarse aggregate crushing on mechanical properties of concrete under uniaxial compression

Coarse aggregate crushing has a significant impact on concrete deformation and failure characteristics. The coarse aggregate geometries with actual shapes are imported and the mesoscopic model of concrete is established in the discrete element method. The effect of coarse aggregate crushing on the mechanical properties of normal concrete and high-strength concrete during the uniaxial compression test is investigated. The findings reveal that: (1) The coarse aggregate crushing affects the concrete stress–strain curve. Increasing the content of crushable coarse aggregates can reduce the concrete’s peak stress and peak strain. (2) The changing trend of compressive strength of normal concrete and high-strength concrete is different as the percentage of crushable coarse aggregates increases. (3) Normal concrete is more affected by coarse aggregate crushing than high-strength concrete. The compressive strength of normal concrete can be reduced significantly with less crushable coarse aggregates. (4) Coarse aggregate crushing changes the failure mode of concrete. The cracks inside the concrete can extend through the crushable coarse aggregates. In conclusion, it is beneficial to obtain a more realistic deformation failure mode of the concrete by considering the crushing of the coarse aggregate during the uniaxial compression test.

An experimental study and failure mechanism analysis on dynamic behaviors of plain concrete under biaxial compression-compression

In order to explore the dynamic mechanical properties of concrete under biaxial compression-compression, a true triaxial instrument was used to conduct an experimental study on the dynamic mechanical properties of plain concrete under biaxial compression-compression. Eight different lateral compressive stresses (0 MPa~14 MPa) and four strain (10−5/s, 10−4/s, 10−3/s and 10−2/s) rate were considered. From this, the effects of lateral compressive stress and loading strain rate on the biaxial compression-compression properties of concrete were compared and analyzed by obtaining the failure modes, principal compressive stress-strain curves and related mechanical characteristic parameters of plain concrete under different loading conditions. The research results show that: with the increase of lateral compressive stress, the failure modes of concrete were developed from columnar failure at low lateral compressive stress to sheet-like failure at high lateral compressive stress. With the increase of lateral stress, the development trend of concrete failure mode decreased gradually under the influence of strain rate. With the increase of lateral compressive stress, the variation range of concrete principal compressive stress decreased first and then tended to be relatively stable under the influence of strain rate. With the increase of strain rate, the increase range of concrete principal compressive stress decreased under the influence of lateral compressive stress. The influence mechanism of lateral compressive stress and strain rate on biaxial compression-compression performance of concrete was analyzed. Meanwhile, based on Kupfer biaxial compression failure criterion, a biaxial compression dynamic failure criterion model considering the effect of loading strain rate on plain concrete was proposed. The research results provided an important theoretical basis for the application and development of concrete engineering.

Failure modeling of concrete: A peri-dynamical approach with bond-based correspondence to bi-scalar damage model

Concrete is a special quasi-brittle material, in which both the tensile and compressive nonlinearity play an important role, especially when working with steels. To capture the failure behavior of concrete, a peridynamic (PD) approach that shows great advantages in modeling discontinuities and cracks is employed in the present paper. Based on the simplest PD model, a bond-based correspondence framework is established instead of reconstructing the constitutive relations, which provides a general and direct way for classical constitutive models incorporation. To derive the mapping function, the strain energy density equivalence is conducted and further simplified for computational efficiency. Under the correspondence framework, a thermodynamically consistent damage model, namely the bi-scalar plasticity-damage model is incorporated in for concrete failure modeling. Corresponding to the separate consideration of tensile and compressive behavior in the model, the topologic damage is developed accordingly, which combines both the advantages of PD and damage mechanics. The proposed model is then demonstrated by the simulation of experiment, including both the plain concrete and reinforced concrete cases. The results indicate that the proposed model retains the original simplicity but greatly improves the capability for concrete failure modeling, with which different failure modes of concrete can be well reproduced.

Numerical and Experimental Investigation of Anchor Channels Subjected to Tension Load in Composite Slabs with Profiled Steel Decking

In curtain wall applications, anchor channels are frequently installed near the edge of composite slabs with profiled steel decking. The complex concrete geometry of these floor slabs affects the capacity of all concrete failure modes, but there are currently no guidelines or investigations available on this topic. The main objective of the present research is to investigate how the position of anchor channels and the complex slab geometry influence the tensile capacity of anchor channels. For this purpose, an extensive numerical parametric study was performed using the 3D nonlinear FE code MASA, which is based on the microplane constitutive model. In order to validate the numerical results, an experimental program was carried out for some of the configurations possible in practice. Based on the results, recommendations are given for the reduction in the tensile capacity of anchor channels in composite slabs with profiled steel decking.

Effect of nano-SiO2 and nano-CaCO3 on the static and dynamic properties of concrete

Three kinds of nano-concrete, i.e., 2.0% nano-SiO2 doped, 2.0% nano-CaCO3 doped and 1.0% nano-SiO2-1.0% nano-CaCO3 co-doped concretes (NS, NC, NSC) were prepared for a study on static property and dynamic property under different strain rates (50–130 s−1) using HYY series hydraulic servo test system and Φ100 mm split Hopkinson pressure bar test system, and a comparison with plain concrete (PC) as well. The results have shown that under static load, as compared with PC, NC has both strength and elastic modulus increased obviously, while NS has strength decreased and elastic modulus increased, and under dynamic load, there is an obvious strain rate effect for the dynamic compressive strength, impact toughness, energy dissipation and impact failure mode of concrete. Under the same strain rate, the dynamic compressive strength, peak strain, impact toughness and energy dissipation of NC are significantly increased, while its dynamic elastic modulus is decreased. Compared with PC, NS has dynamic compressive strength, peak strain, impact toughness and energy dissipation decreased, and dynamic elastic modulus increased, NC has static and dynamic mechanical properties improved, NS has static and dynamic mechanical properties weakened, and NSC is between PC and NC in static and dynamic mechanical properties, but generally improved. Doped with nano-CaCO3, NC has compactness improved, weak areas reduced, and pore size distribution optimized, while doped with nano-SiO2, NS has obvious internal weak areas, with pore structure degraded.

Dynamic mechanical properties of hybrid fiber reinforced concrete

In this study, the dynamic mechanical properties of hybrid fiber reinforced concrete (HFRC) are analyzed with respect to failure mode, dynamic increase factor (DIF), and peak strain by means of a SHPB testing apparatus. The factors that influence the dynamic mechanical properties include fiber type and fiber content. It is concluded that the best dynamic mechanical properties of fibers are CS-PHFRC at medium and low strain rates and AS-PHFRC at a high strain rate. Within a certain range, the higher the fiber content is, the larger the DIF of the corresponding HFRC and the more obvious the increase in dynamic compressive strength. AS-CSHFRC improves the dynamic compressive deformability of the HFRC. The polypropylene fiber causes plasticity, as shown in the failure mode of concrete. The Ottosen nonlinear elastic model, modified by introducing the damage factor, can better describe the dynamic mechanical properties of HFRC.