Ultimate Deformation Capacity Research Articles

Experimental study on the mechanical properties of FRP reinforced shotcrete lining of tunnel in extremely fractured surrounding rock

Tunnel excavation in the southwestern area of China encounters many difficulties caused by the large deformation of extremely fractured surrounding rock, which is the product of high plate tectonic stress. Improving the initial cracking strength and ductility of shotcrete layer is one of the most important means to reduce the frequency of support structure repair, which will improve tunnel construction efficiency and ensure personnel safety. In this case, this paper introduced fiber reinforced polymer (FRP) mesh to replace the steel mesh as reinforcement to optimize the support effect of shotcrete lining. Both large-scale model test and mechanical test are conducted to compare the reinforcement effect between FRP and steel mesh. Research results indicate that replacing steel mesh with FRP can increase the ultimate deformation capacity of tunnel lining by more than four times. The parametric analysis results indicate that increasing the lining thickness, the diameter of the FRP bars and the mesh density have different degrees of effect on improving the stiffness and strength of tunnel lining. The research results can provide reference for relevant projects.

Experimental investigation on the load-bearing capacity and deformation behaviour of the composite lining with polyurethane compressible layer

Lining structures for tunnels in rheological rocks are susceptible to large deformations and damage. Installation of a polyurethane (PU) compressible layer between the primary and secondary lining provides a potential solution to mitigate large deformation hazards. Although the capability of PU-enhanced composite lining in adapting and absorbing large deformation has been found, its underlying load-bearing mechanism and deformation behaviour remain less understood. To fill the gap, large-scale model tests were conducted using a self-designed loading test setup, primarily focusing on the mechanical response of PU-enhanced composite lining. Ten lining specimens with varying thicknesses (25, 37.5, and 50 mm) and densities (50, 100, and 150 kg/m3) of the PU compressible layer were investigated. The digital image correlation (DIC) analysis technique was used to detect real-time deformation and strain fields under loading conditions. Results demonstrated that the PU compressible layer enhanced the ultimate load, toughness, and deformation capacity of the composite lining by an average of 17.6 %, 164.6 %, and 157.4 %, respectively. The load-displacement response of the specimens with PU compressible layer could be categorized into four stages: pre-cracking, post-cracking, strain-hardening, and failure. The primary lining experienced the largest vertical displacements among the specimens with the PU compressible layer, followed by the compressible layer and the secondary lining. Although the specimens exhibited similar progressive failure modes, there were variations in crack distribution and propagation. The analysis of rock-support interaction indicated that increasing the thickness of the PU compressible layer mainly affects the deformation capacity when the secondary lining reaches its elastic limit.

Effect of Textile Layers and Hydroxypropyl Methylcellulose on Flexural Behavior of TRLC Thin Plates

To examine the flexural toughness characteristics of textile-reinforced lightweight aggregate concrete (TRLC), a four-point bending test was conducted to assess the impact of varying numbers of textile layers and the inclusion of hydroxypropyl methylcellulose on the ultimate load-bearing capacity and deformation capacity of TRLC thin plates. Six groups of specimens were prepared for the experiment, and the bending capacity of the thin plates in each group was evaluated. The flexural toughness index was utilized to quantify the bending performance of TRLC thin plates. The findings revealed that increasing the number of textile layers improved the initial cracking load, initial cracking deflection, ultimate load, ductility, and flexural toughness of the thin plates. For the specimens without HPMC, the initial cracking load was increased by up to 36.1%, the ultimate load by up to 40.9%, and the flexural toughness index by up to 292% as the number of textile layers was increased. For specimens doped with HPMC, the initial cracking load was increased by up to 61.7%, the ultimate load by up to 246.7%, and the flexural toughness index by up to 65%. The TRLC thin plate containing hydroxypropyl methylcellulose exhibited a reduced initial cracking load yet displayed a stronger matrix consistency and good flexural toughness. Moreover, the enhancement in the ultimate load of TRLC thin plates with hydroxypropyl methylcellulose was more pronounced with an increased number of textile layers, resulting in a significantly higher number of cracks compared to TRLC without hydroxypropyl methylcellulose and an 11.40-fold increase in the flexural toughness index.

Constant damage inelastic permanent period shift ratios spectra

The phenomenon of elongation of the structural period after earthquake excitation has been widely observed, and elongated period obtained after earthquake excitations can be used for post-earthquake assessment. The inelastic permanent period shift ratio, an indicator representing the degree of stiffness degradation and closely relating to the damage state, is defined as the ratio of the elongated period Tin of single-degree-of-freedom (SDOF) systems after earthquake excitations to the initial period Tel. The objective of this paper is to investigate the inelastic permanent period shift ratios under constant damage performances through nonlinear time-history analysis of SDOF systems, and the modified Park-Ang damage index is employed to characterize the structural damage. Inelastic permanent period shift ratio spectra are statistically constructed considering both the ground motion characteristics (such as site conditions, velocity pulse, magnitude, closet distance, directivity effects, significant duration and frequency contents) and structural parameters (including damage states, hysteretic models, ultimate deformation capacity, energy dissipation factor and postyield ratio). The results showed that the permanent period shift ratio is a reliable damage indicator for assessment of global damage states. The influence caused by ground motions on the estimation of the mean of the permanent period elongation ratio under constant damage performances is limited, while the effects caused by different structural damage and deformation capacity can reach up to approximately 70% and 33%, respectively. An expression for the relationship between the damage index and the permanent period shift ratio is established. Ignoring the differences of structural performances, using the period shift ratios to directly assess the global damage states will lead to erroneous results.

Augmented Data-Driven Machine Learning for Digital Twin of Stud Shear Connections

Existing design codes for predicting the strength of stud shear connections in composite structures are limited when adapting to constant changes in materials and configurations. Machine learning (ML) models for predicting shear connection are often constrained by the number of input variables, resembling conventional design equations. Moreover, these models tend to overlook considerations beyond those directly comprising the connection. In addition, the data used in ML are often biased and limited in quantity. This study proposes a model using AutoML to automate and optimize the process for predicting the ultimate strength and deformation capacity of shear connections. The proposed model leverages a comprehensive dataset derived from experimental studies and finite element analyses, offering an advanced data-driven solution to overcome the limitations of traditional empirical equations. A digital twin model for the static design of pushout specimens was defined to replace existing empirical design codes. The digital twin model incorporates predictions of the geometry model, ultimate strength, and slip as input parameters and provides criteria for evaluating the limit state through a bilinear load–slip curve. This study advances predictive methodologies in structural engineering by emphasizing the importance of ML in addressing the dynamic and multifaceted nature of shear connection behaviors.

Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panel reinforced with FRP bar/grid: Development and flexural performance

In this study, Ultra-High-Strength Engineered Cementitious Composites (UHS-ECC) panels with Fiber-Reinforced Polymer (FRP) reinforcement (i.e., FRP bars and girds) were proposed for the construction of sustainable marine structures. Based on four-pointed bending tests, the mechanical performance of FRP-reinforced UHS-ECC [with 2% polyethylene (PE) fibers] and FRP-reinforced ultra-high-strength concrete (UHSC, without fibers) panels were investigated and compared to understand the composite action between UHS-ECC and FRP. Compared with the FRP-reinforced UHSC panel, the FRP-reinforced UHS-ECC panel showed significantly higher ultimate load (139-173% higher), stiffness, and deformation capacity. It was also found that the use of seawater as the raw material had almost no effect on the mechanical performance of FRP-reinforced UHS-ECC (UHSC) panels. An analytical investigation was conducted to predict the load capacities of the tested panels, and the prediction error was acceptable. For FRP-reinforced UHS-ECC (UHSC) panels, it was revealed that using UHS-ECC to replace UHSC improved the stress transfer and deformation compatibility with FRP because the multiple cracking behavior of UHS-ECC lowered the crack-induced shear stress concentration along the FRP reinforcement. The developed FRP-reinforced UHS-ECC system showed great potential in the construction of durable and sustainable marine infrastructure.

Influence of Steel and Polypropylene Fibers on the Structural Behavior of Sustainable Reinforced Lightweight Concrete Beams Made from Crushed Clay Bricks

Structural lightweight concrete is preferred over traditional concrete due to its ability to reduce the dead load, minimize the size of load-bearing structural members, and provide more economical solutions for foundation deteriorations. This research sheds light on sustainable lightweight concrete using waste crushed clay bricks (CCB) as a lightweight aggregate. To reduce micro-crack propagation of the developed concrete, two types of fiber were implemented and investigated. Steel fibers (SF) with amounts of 0.5% and 1.0% by volume of concrete, and polypropylene fibers (PPF) with amounts of 0.1% and 0.2% by volume of concrete, were employed. Five reinforced concrete beams were made and tested in order to precisely evaluate the structural behavior of the proposed lightweight CCB concrete. Additionally, ABAQUS software for nonlinear finite element analysis has been utilized to simulate the tested beams and compare the numerical model predictions with the experimental findings. The findings revealed that the addition of SF and PPF exhibited a notable influence on enhancing the mechanical characteristics of lightweight CCB concrete. Adding 0.2% PPF increased the ultimate load and deformation capacity at failure by approximately 16% and 24%, respectively. Furthermore, after 28 days, the addition of 0.5% and 1.0% SF enhanced the compressive strength by around 11.7% and 17.6%, respectively. Moreover, a significant level of consistency between the results obtained from the numerical model and the experimental findings was observed. In general, the use of SF and PPF in CCB concrete successfully produced high-quality lightweight concrete with interesting results for use in reinforced concrete beams.

Study on seismic behavior of steel frame joint with external arc diaphragm

The application of External Diaphragm (ED) in steel frame system is able to reinforce the stiffness of joint and provide efficient protection for the critical part of joint. However, due to the limitation of the existing design codes, the inside space of building is affected frequently by the excessive size of the ED. To reduce the size effect of ED, a hysteretic experiment on four steel joint specimens is first carried out in this paper, the effects of the width ratio (the ratio of ED width to beam flange width) and connection type (Bolted web-Welded flange (BW) connection and Full Bolted (FB) connection) are investigated. Then, a numerical analysis is conducted to further explore the influence of the width ratio and the thickness ratio (the ratio of ED thickness to beam flange thickness). The results indicate that the specimen with BW connection exhibits larger stiffness and bearing capacity, but the specimen with FB connection has obvious ascendancy on the ultimate deformation capacity and ductility. Moreover, Changing the width ratio and thickness ratio are unable to cause significant variation on the seismic performance of steel joint if the thickness ratio is larger than 1.25. Therefore, the thickness of the ED is more critical than width to the seismic performance of steel joint. Meanwhile, in the circumstance of the thickness ratio is equal to 1, the width ratio of 0.1 is recommended for the minimum limited value in structure design.

Behavior of large-scale concrete columns reinforced with high-strength and high-toughness steel bars under axial and eccentric compression

In this paper, combined with the current era background of energy saving and emission reduction, low carbon and environmental protection, the mechanical performance of new high-strength and high-toughness steel bars (HSHTSB) in concrete structural members is studied, and HSHTSB is expected to be popularized. To investigate the compression behavior of large-scale concrete columns reinforced with HSHTSB under axial and eccentric compression, thirteen reinforced concrete (RC) columns were designed in this paper, including the five columns under axial compression and the eight columns under eccentric compression. The effects of different types of steel bars, transverse steel bar spacing, the configuration of transverse steel bars, and eccentricity on failure modes, load-deformation curves, load-strain curves, ultimate bearing capacity, deformation capacity, and energy absorption capacity were studied in detail. The results show that the cracks are more uniform for concrete columns reinforced with HSHTSB. When the transverse steel bar spacing is less than 80 mm, concrete columns reinforced with HSHTSB with eccentricity ≤200 mm (including eccentricity = 0) have obvious secondary bearing phenomenon, and significantly improve ductility and energy absorption capacity; HSHTSB as longitudinal steel bars can reach yield strength for RC columns under axial compression. For RC columns under eccentric compression, HSHTSB could not reach yield strength on both the tensile and compression side. For the RC columns of Group II, III, and IV, when the eccentricity increases from 100 mm to 400 mm, the ultimate bearing capacity decreases by 76.1%, 75.2%, and 75.1%, respectively. Different from the ordinary RC columns, the ductility decreases with the increase of eccentricity for concrete columns reinforced with HSHTSB. Compared with ordinary RC columns, the energy absorption capacity and deformation capacity of concrete columns reinforced with HSHTSB under axial compression are increased by 120.9% and 116.9%, respectively. Compared with RC columns using transverse steel bars with single-leg, the energy absorption capacity and ductility for multiple-leg can be increased by 111.5% and 103.2%, respectively. When the eccentricity increases from 100 mm to 400 mm, the ductility for columns of Group II and III decreases by 73.5% and 65.9%, respectively. The use of HSHTSB can save the number of longitudinal steel bars and the transverse steel bar spacing while maintaining the bearing capacity, and further improve the deformation capacity. Based on the section strain analysis, the analytical models of the ultimate bearing capacity for the concrete columns reinforced with HSHTSB were established with high accuracy.

Progressive collapse resistance of RC frames subjected to localized fire

Fire is one of the accidental loads that can cause progressive collapse of buildings. However, the behavior of fire-exposed reinforced concrete (RC) frames to resist progressive collapse are still unclear. Therefore, a numerical study on the RC assembly based on the sequential thermal-mechanical coupling method is conducted. Fire effects on the failure mode, load-resistant capacity, and the evolution of load-resistant mechanisms of the RC frame are captured. The numerical results show that compressive arch action (CAA) and catenary action (CA) can develop in sequence for the specimens exposed to fire within a short fire duration of 30 min. The failure of the specimen is controlled by the fracture of beam rebars near the removed column. However, when the fire duration exceeds 60 min, the specimen is difficult to develop effective CA due to a decrease of over 80% in the tensile strength of the bottom reinforcement. The failure of the specimen is dominated by the fracture of the rebar at the cut-off point of the beam top rebar. Fire lasting for 30 min, 60 min, 90 min and 120 min results in a decrease of 41%, 72%, 77% and 78% in ultimate load, respectively. Increasing the span-depth ratio can upgrade the deformation capacity of the specimen, but it is adverse to the development of CAA. The effects of the reinforcement ratio on the failure mode, the ultimate load and deformation capacity are mild as the fire exposure duration increases.

Parametric study for Y‐shape perfobond shear connection

AbstractThe development process of the composite structures is always an ongoing process, to gain more the benefits of the composite work between steel and concrete. This process has created a wide range of types of shear connections. Different types of perfobond shear connections have been developed to overcome the disadvantages of the conventional headed stud connections. The new types like the Y, puzzle, clothoid, etc. shape perfobond plates have been studied due to their beneficial ultimate resistance and deformation capacity. The Y‐type perfobond rib shear connection is a superior alternative to the conventional perfobond due to its improved performance characteristics, such as higher ductility and stiffness, and greater resistance against uplifting force. In this paper the focus in on Y‐shape perfobond shear connections. A finite element model for a push‐out test has been developed to analyze the influence of structural parameters on the behavior of the connection. The model was verified by the experimental test completed at the Department of Structural Engineering, in Budapest University of Technology and Economics. The FE model was developed on Atena GID software. In this paper the effect of the angle of the inclined Y parts and the geometrical dimensions of the inclined Y parts are analyzed on the resistance, degradation tendencies, deformation capacity and the stiffness of the connection, conclusions are drawn, and beneficial structural details are recommended.

Experimental investigation and numerical simulation of masonry walls designed in different versions of Chinese codes

Masonry structures built in different years according to different Chinese seismic design codes are still widely distributed in China. In order to study the differences in seismic performance of these masonry structures, pseudo static tests are carried out on three masonry walls designed according to different versions of codes, and a numerical simulation method for the masonry walls is established. First, three masonry walls are designed according to different versions of codes, which adopt different confined measures. Pseudo static tests are then conducted on these three masonry walls to obtain their damage development law, hysteresis response, skeleton curve, and energy dissipation capacity, etc. Finally, the numerical simulation method for the masonry walls is established based on the cohesive surface interaction. The results show that the specimen Q-1, which is designed according to TJ11-78 and GBJ 11–89, exhibits sliding failure, and the specimens Q-2 and Q-3, which are designed according to GB50011-2001 and GB50011-2010, respectively, exhibit shear failure. The confined column can effectively prevent sliding failure of masonry walls and make the hysteretic curve fuller. Increasing the longitudinal reinforcement strength and reducing the stirrup spacing in the confined column can increase the ultimate bearing and deformation capacity, as well as the fullness of the hysteretic curve. The proposed numerical simulation method can accurately simulate the cracking and hysteresis response of masonry walls with a skeleton curve error of less than 5%.

Initial stiffness degradation and its effect on seismic capacity of shear wall with high reinforcement volume: An experimental study

Nuclear simulation analyses and field investigations were performed to study the seismic response of the reinforced concrete (RC) walls of the Onagawa NPP Unit 2 reactor building to the Tohoku Region Pacific Coast Earthquake on March 11, 2011 (hereafter referred to as the “March-11 Earthquake”). They indicated that the degree of deformation of the walls remained within the elastic range and did not reach the plastic range. Small residual cracks appeared in the shear walls on some floors, and the observation records of the natural period of the building exhibited stiffness degradation. In addition to the effect of large seismic loads, which are among the factors responsible for such reduced initial stiffness, a correlation between reduced stiffness and deterioration due to aging was recognized in the results of the analyses based on long-term earthquake observation records. The likely factors responsible for deterioration from aging include internal stress and cracks resulting from the drying shrinkage characteristics of concrete. Therefore, we conducted seismic resistance experiment #1, a static load test, to understand the effect of drying shrinkage on the initial stiffness and maximum strength. The results for the specimens subjected to drying showed better agreement with the results of the observation record analysis of the reactor building than those that were not subjected to drying. In addition, because small residual cracks occurred in the reactor building, we conducted seismic resistance experiment #2, a static load test, to understand the effect of such cracks on the ultimate strength and deformation capacity. The test confirmed that the seismic performance of the building after the earthquake was ensured. From the results of these investigations, it is considered that both the drying shrinkage of concrete and large seismic forces from the March-11 Earthquake were factors in the initial stiffness reduction of the Onagawa Unit 2 reactor building. However, there was no significant impact on the seismic performance of the building.

Lateral load resistance of reinforced concrete columns with brittle details

AbstractAnalytical models for shear strength and deformation capacity estimation of reinforced concrete members are essential for the practical implementation of performance‐based seismic evaluation of existing structures and form a key part of current seismic assessment codes (e.g., EN 1998‐3 (2005), (2022), ASCE/SEI 41‐17). Although these models have been derived from regression or calibration of large datasets collected from experimental literature, discrepancy persists between experimental and analytical estimates, especially in cases of members with old‐type detailing. The evident uncertainty about parametric dependencies of the underlying mechanistic problem motivated the present work, where a set of benchmark columns that represent older structural detailing are studied parametrically through advanced finite element simulation. Parameters considered were, the axial load ratio, transverse reinforcement amount and spacing, longitudinal reinforcement ratio, and anchorage/lap splice detailing; results were gauged in terms of the resulting drift ratio (deformation capacity) at the performance limit states and were compared with the Code estimates to evaluate their limits and conservatism. The simulation results were used to vet the assumptions that underlie the simple mechanistic models used in deriving seismic design expressions for yield and ultimate deformation capacities, shear strength, and the rate of its degradation with increasing ductility.

Comparative study on fracture characteristics of carbon and stainless steel bolt material

Bolt fracture often limits the ultimate strength and deformation capacity of bolted connections and leads to overall joint failure. Therefore, the prediction of structural collapse under extreme loads necessitates the incorporation of a reliable fracture model that reflects the observed structural response of bolts. This paper reports a comprehensive experimental and numerical study into the structural behaviour, ductility and fracture characteristics of Grade A4–80 austenitic stainless steel bolts and carbon steel 8.8 bolts in tension, which are commonly used as fasteners in bolted connections. Tensile tests were performed on smooth material coupons machined from both bolt grades to obtain the material response. Thereafter, tensile tests were performed on notched specimens from both grades, allowing the fracture characteristics to be studied over a range of stress triaxialities and the development of an equation relating the plastic strain at fracture to the stress triaxiality. 2D axisymmetric and 3D advanced finite element models were calibrated against the experimental results and damage propagation parameters. The developed numerical models are shown to perfectly replicate the observed experimental behaviour of the tested bolt materials under predominantly tensile loading, including fracture. Both experimental and numerical results confirm the superior ductility of A4–80 bolts over their 8.8 counterparts.

Experimental Study on the Seismic Performance of a Steel Slag CFDST T-Joint

In this paper, a kind of steel slag, concrete-filled double-skin steel tube (CFDST) T-joint is proposed to promote sustainable structural development. In order to examine the seismic performance of the steel slag CFDST T-joint, a series of hysteresis experiments were carried out on 4 CFDST T-joints with the main pipe under axial compression load and the brace pipe subjected to cyclic axial loading. The seismic performance of the CFDST T-joint was experimentally investigated in terms of the failure mode, load–displacement hysteresis relationship, stiffness degradation, energy dissipation and ductility. The effects of the hollow ratio and the steel slag concrete of the CFDST main pipe on the seismic performance of CFDST T-joint specimens were compared and analyzed. The experimental results show that the failure modes of the CFDST T-joint mainly included two kinds of failure, with those being main pipe fracture and joint area compression-bending failure. The seismic performance of the joints could be improved with a 12% ultimate bearing capacity and 54% ultimate deformation capacity with the hollow ratio of the CFDST main pipe increasing from 0 to 0.5. The seismic performance of the joints could be improved with a 54% ultimate deformation capacity by filling the steel slag concrete with a 0.5 hollow ratio.

Progressive collapse resistance of steel frame with beam to column transfer structure under a middle column-removal scenario

The application of Beam to Column Transfer Structure (BCTS) in practical engineering is more frequent to satisfy the requirement of space and economy of modern structure. However, the structure is unavoidable to increase the burden of the column in the lower floor, which will enlarge the risk of the structure subjected to progressive collapse. Hence, in order to explore the performance of the steel frame with BCTS on anti-progressive collapse, a numerical model is established by using Abaqus and it is validated by the test result. Based on that, a parametric analysis is carried out to discuss the effects of the Span to Depth Ratio (SDR) of the beams, and the Axial Compression Ratio (ACR) of the BCTS. The result indicates that the model with larger ACR leads to smaller load bearing capacity and Ultimate Deformation Capacity (UDC). Meanwhile, the model with larger SDR leads to smaller load bearing capacity but larger UDC. Moreover, it is found that it is inadvisable for unduly increasing the SDR to improve the contribution of the Catenary Action (CA) but decrease the contribution of the Flexural Action (FA). In addition, the better performances on progressive collapse can be observed as long as the models with the ACR is not greater than 0.06 in the RDS range from 11 to 19. Thus, the ACR of 0.06 is recommended as the limited value in structure design.

Carbon Footprint between Steel-Reinforced Concrete and UHPC Beams

Due to its superior mechanical and durability performance, ultrahigh performance concrete (UHPC) has gained increasing applications worldwide. While studies have suggested different strategies to design reinforced UHPC beams, their resulting structural behavior is not yet well understood, and their carbon footprint has not been given considerable attention. Based on nonlinear finite element simulations and cradle-to-gate life-cycle analyses, this study compares the performance of two steel-reinforced concrete beams to steel-reinforced UHPC (R/UHPC) beams with the same flexural load capacity but different design strategies. Results show that an R/UHPC beam of the same cross-section but lower reinforcing ratio of a conventional concrete beam could show 166% higher carbon emission and 64% less deformation capacity than a control steel-reinforced concrete beam. On the other hand, a well-designed R/UHPC beam can (1) maintain the carbon footprint; (2) reduce the section size and steel bar usage by 50% and 30%–53%, respectively; and (3) show equivalent or higher service-level stiffness and ultimate deformation capacity.

Seismic behavior of the assembled walls using uniform precast hollow-core concrete panels restrained by cast-in-place boundary elements in single-story buildings

To achieve efficient construction of single-story buildings and increase economic efficiency while ensuring safety, low-cost, easy-to-assemble, and good seismic performance assembled walls using uniform precast hollow-core concrete panels restrained by cast-in-place boundary elements were designed. Through the low-cyclic loading test of three specimens, the safety and reliability of the connection between the components were verified, the good seismic performance of the structure was proved, and the influence of the number (2, 3, 4) of panels contained in the specimens, that is the shear span ratio (SSR) of the specimens, on their seismic performance was investigated. The study found that all specimens finally show shear-slip damage, and with the decrease of SSR, the ultimate shear-bearing capacity of the specimen increases, the deformation capacity decreases, and the energy dissipation capacity increases. Compared with the specimen of 2 panels, the ultimate shear bearing capacity of 3 panels and 4 panels is increased by 39.2% and 88.9% respectively. The ultimate deformation capacity of 2 panels is similar to that of 3 panels, but that of 4 panels is reduced by 23.3%. In addition, these three specimens are simulated using the finite element analysis software ABAQUS. The stress nephogram of each specimen reflects the presence of vertical shear along the thin wall of the circular hole of the panels under horizontal load, and the vertical shear surface will be linked into the shear belt along the diagonal of the specimen. Combined with experiment and finite element simulation, the calculation method of the ultimate lateral bearing capacity of the structure is established. The ratio of the measured value to the calculated value is greater than 1.0, and the maximum relative error of them is only 6.85%, which proves that the calculation method is safe and reliable. The research results of this paper can provide the necessary basis for the engineering application in single-story buildings.

Constitutive relations, mechanical behaviour, and failure criterion of microcapsule-based self-healing concrete under uniaxial and triaxial compression

Microcapsule-based self-healing concrete can autonomously release repairing agents to bond and seal cracks when the material is damaged. It is seen as a promising construction material from the perspective of a sustainable society. In addition, it is important to study mechanical behaviour under complex stress conditions to promote the application of self-healing concrete in engineering structures. This study investigated the constitutive relations, strength and deformation, and failure criterion of the epoxy/urea-formaldehyde microcapsule-based self-healing concrete through uniaxial compression, conventional triaxial compression and true triaxial compression tests, in which the influence of different microcapsule dosages, confinement pressures and the principal stress ratios on the mechanical behaviours was considered. The results showed that the ultimate strength of the specimen decreased with increasing microcapsule dosage under all loading conditions. The lateral pressure significantly promoted the ultimate strength and deformation capacity of the specimen, and this increase mainly depended on the maximum principal stress (σ1) rather than the intermediate principal stress (σ2). By visual checking the failure modes of the specimens, more cracks were observed under the conventional triaxial compression than those under the true triaxial compression. This multi-crack failure mode allowed more core material of microcapsules to enter the microcracks, which accordingly increased the strength of the microcapsule-based concrete.