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This study evaluates the potential of using the material extrusion (MEX) process for recycling waste tire rubber (WTR). By investigating the process parameters, mechanical behaviour and morphological characterisation of a thermoplastic polyurethane-waste tire rubber composite filament (TPU-WTR), this study aims to establish a framework for end-of-life tire (ELT) recycling using the MEX technology.

The research assesses the impact of various process parameters on the mechanical properties of the TPU-WTR filament. Hysteresis analysis and Poisson’s ratio estimation are conducted to investigate the material’s behaviour. In addition, the compressive performance of diverse TPU-WTR triply periodic minimal surface lattices is explored to test the filament suitability for printing intricate structures.

Results demonstrate the potential of the TPU-WTR filament in developing sustainable structures. The MEX process can, therefore, contribute to the recycling of WTR. Mechanical testing has provided insights into the influence of process parameters on the material behaviour, while investigating various lattice structures has challenged the material’s capabilities in printing complex topologies.

This research holds significant social implications addressing the growing environmental sustainability and waste management concerns. Developing 3D-printed sustainable structures using recycled materials reduces resource consumption and promotes responsible production practices for a more environmentally conscious society.

This study contributes to the field by showcasing the use of MEX technology for ELT recycling, particularly focusing on the TPU-WTR filament, presenting a novel approach to sustainable consumption and production aligned with the United Nations Sustainable Development Goal 12.

This study aims to enhance the understanding of fiber-reinforced polymer (FRP) applications in partially confined concrete, with a specific focus on improving economic value and load-bearing capacity. The research addresses the need for a more comprehensive analysis of non-uniform vertical strain responses and precise stress–strain models for FRP partially confined concrete.

DIC and strain gauges were employed to gather data during axial compression tests on FRP partially confined concrete specimens. Finite element analysis using ABAQUS was utilized to model partial confinement concrete with various constraint area ratios, ranging from 0 to 1. Experimental findings and simulation results were compared to refine and validate the stress–strain model.

The experimental results revealed that specimens exhibited strain responses characterized by either hardening or softening in both vertical and horizontal directions. The finite element analysis accurately reflected the relationship between surface constraint forces and axial strains in the x, y and z axes under different constraint area ratios. A proposed stress–strain model demonstrated high predictive accuracy for FRP partially confined concrete columns.

The stress–strain curves of partially confined concrete, based on Teng's foundation model for fully confined stress–strain behavior, exhibit a high level of predictive accuracy. These findings enhance the understanding of the mechanical behavior of partially confined concrete specimens, which is crucial for designing and assessing FRP confined concrete structures.

This research introduces innovative insights into the superior convenience and efficiency of partial wrapping strategies in the rehabilitation of beam-column joints, surpassing traditional full confinement methods. The study contributes methodological innovation by refining stress–strain models specifically for partially confined concrete, addressing the limitations of existing models. The combination of experimental and simulated assessments using DIC and FEM technologies provides robust empirical evidence, advancing the understanding and optimization of FRP-concrete structure performance. This work holds significance for the broader field of concrete structure reinforcement.

Recently, the repairing of reinforced concrete (RC) structures attracted great research attentions, but the research interests were mainly concentrated on common repairing types. To this end, in this paper, a repairing of pre-loaded RC beams strengthened by aramid reinforcement polymers (AFRP) is presented. Furthermore, the purpose of this paper is to study the behavior of pre-loaded RC Deep beams under sustained load. The AFRP has many advantages such as controlling stresses distribution around the openings, controlling failure modes, and enhancing the structural capacity of pre-cracked RC beams.

Four specimens were experimentally tested: one specimen without strengthening, which is considered as control specimen, one strengthened specimen using AFRP without pre-cracking and two specimens subjected to pre-cracking load before prior to AFRP application. Furthermore, after validation of experimental data by using ANSYS software, a parametric study was conducted to investigate the effect of pre-damage level on shear capacity of RC beams. For pre-cracked beams, loading was first applied until the cracking stage, followed by specimen repairing with epoxy injection, and then the specimens were loaded again until failure point.

The result showed that pre-damage level and AFRP strengthening have great influence on the ultimate strength and failure mode. In addition, the results obtained from experimental tests were compared with those from numerical validation with ANSYS and showed good agreement.

Based on ACI guidelines, an analytical equation for calculating the shear strength of strengthened RC beams with openings subjected to pre-damage was then proposed, and the calculated results were compared with those from the tests, with differences not exceeding 10%.

This paper aims to propose an effective dynamic calibration and compensation method to solve the problem that the statically calibrated force sensor would produce large dynamic errors when measuring dynamic signals.

The dynamic characteristics of the force sensor are analyzed by modal analysis and negative step dynamic force calibration test, and the dynamic mathematical model of the force sensor is identified based on a generalized least squares method with a special whitening filter. Then, a compensation unit is constructed to compensate the dynamic characteristics of the force measurement system, and the compensation effect is verified based on the step and knock excitation signals.

The dynamic characteristics of the force sensor obtained by modal analysis and dynamic calibration test are consistent, and the time and frequency domain characteristics of the identified dynamic mathematical model agree well with the actual measurement results. After dynamic compensation, the dynamic characteristics of the force sensor in the frequency domain are obviously improved, and the effective operating frequency band is widened from 500 Hz to 1,560 Hz. In addition, in the time domain, the rise time of the step response signal is reduced from 0.29 ms to 0.17 ms, and the overshoot decreases from 26.6% to 9.8%.

An effective dynamic calibration and compensation method is proposed in this paper, which can be used to improve the dynamic performance of the strain-gauge-type force sensor and reduce the dynamic measurement error of the force measurement system.

This paper presents the experimental and numerical results of the bending properties of low-height prestressed T-beams. The purpose is to study the bearing capacity, failure state and strain distribution of low-height prestressed T-beams.

First, two 13 m-long full-size test beams were fabricated with different positions of prestressed steel bundles in the span. The load–deflection curves and failure patterns of each test beam were obtained through static load tests. Secondly, the test data were used to validate the finite element model developed to simulate the flexural behavior of low-height prestressed T-beams. Finally, the influence of different parameters (the number of prestressed steel bundles, initial prestress and concrete strength grade) on the flexural performance of the test beams is studied by using a finite element model.

The test results show that when the distance of the prestressed steel beam from the bottom height of the test beam increases from 40 to 120 mm, the cracking load of the test beam decreases from 550.00 to 450.00 kN, reducing by 18.18%, and the ultimate load decreases from 1338.15 to 1227.66 kN, reducing by 8.26%, therefore, the increase of the height of the prestressed steel beam reduces the bearing capacity of the test beam. The numerical simulation results show that when the number of steel bundles increases from 2 to 9, the cracking load increases by 183.60%, the yield load increases by 117.71% and the ultimate load increases by 132.95%. Therefore, the increase in the number of prestressed steel bundles can increase the cracking load, yield load and ultimate load of the test beam. When the initial prestress is from 695 to 1,395 MPa, the cracking load increases by 69.20%, the yield load of the bottom reinforcement increases by 31.61% and the ultimate load increases by 3.97%. Therefore, increasing the initial prestress can increase the cracking load and yield load of the test beam, but it has little effect on the ultimate load. The strength grade of concrete increases from C30 to C80, the cracking load is about 455.00 kN, the yield load is about 850.00 kN and the ultimate load is increased by 4.90%. Therefore, the improvement in concrete strength grade has little influence on the bearing capacity of the test beam.

Based on the experimental study, the bearing capacity of low-height prestressed T-beams with different prestressed steel beam heights is calculated by finite element simulation, and the influence of different parameters on the bearing capacity is discussed. This method not only ensures the accuracy of bearing capacity assessment, but also does not require a large number of samples and has a certain economy. The study of prestressed low-height T-beams is of great significance for understanding the principle and application of prestressed technology. Research on the mechanical behavior and performance of low-height prestressed T beams can provide a scientific basis and technical support for the design and construction of prestressed concrete structures. In addition, the study of prestressed low-height T-beams can also provide a reference for the optimization design and construction of other structural types.

When the reinforced concrete beams are reinforced by bonding steel plates to the bottom, excessive use of steel plates will make the reinforced concrete beams become super-reinforced beams, and there are security risks in the actual use of super-reinforced beams. In order to avoid the occurrence of this situation, the purpose of this paper is to study the calculation method of the maximum number of bonded steel plates to reinforce reinforced concrete beams.

First of all, when establishing the limit failure state of the reinforced member, this paper comprehensively considers the role of the tensile steel bar and steel plate and takes the load effect before reinforcement as the negative contribution of the maximum number of bonded steel plates that can be used for reinforcement. Through the definition of the equivalent tensile strength, equivalent elastic modulus and equivalent yield strain of the tensile steel bar and steel plate, a method to determine the relative limit compression zone height of the reinforced member is obtained. Second, based on the maximum ratio of (reinforcement + steel plate), the relative limit compression zone height and the equivalent tensile strength of the tensile steel bar and steel plate of the reinforced member, the calculation method of the maximum number of bonded steel plates is derived. Then, the static load test of the test beam is carried out and the corresponding numerical model is established, and the reliability of the numerical model is verified by comparison. Finally, the accuracy of the calculation method of the maximum number of bonded steel plates is proved by the numerical model.

The numerical simulation results show that when the steel plate width is 800 mm and the thickness is 1–4 mm, the reinforced concrete beam has a delayed yield platform when it reaches the limit state, and the failure mode conforms to the basic stress characteristics of the balanced-reinforced beam. When the steel plate thickness is 5–8 mm, the sudden failure occurs without obvious warning when the reinforced concrete beam reaches the limit state. The failure mode conforms to the basic mechanical characteristics of the super-reinforced beam failure, and the bending moment of the beam failure depends only on the compressive strength of the concrete. The results of the calculation and analysis show that the maximum number of bonded steel plates for reinforced concrete beams in this experiment is 3,487 mm². When the width of the steel plate is 800 mm, the maximum thickness of the steel plate can be 4.36 mm. That is, when the thickness of the steel plate, the reinforced concrete beam is still the balanced-reinforced beam. When the thickness of the steel plate, the reinforced concrete beam will become a super-reinforced beam after reinforcement. The calculation results are in good agreement with the numerical simulation results, which proves the accuracy of the calculation method.

This paper presents a method for calculating the maximum number of steel plates attached to the bottom of reinforced concrete beams. First, based on the experimental research, the failure mode of reinforced concrete beams with different number of steel plates is simulated by the numerical model, and then the result of the calculation method is compared with the result of the numerical simulation to ensure the accuracy of the calculation method of the maximum number of bonded steel plates. And the study does not require a large number of experimental samples, which has a certain economy. The research result can be used to control the number of steel plates in similar reinforcement designs.

The use of recycled coarse aggregate in concrete structures promotes environmental sustainability; however, performance of these structures might be negatively impacted when it is used as a replacement to traditional aggregate. This paper aims to simulate recycled concrete beams strengthened with carbon fiber-reinforced polymer (CFRP), to advance the modeling and use of recycled concrete structures.

To investigate the performance of beams with recycled coarse aggregate concrete (RCAC), finite element models (FEMs) were developed to simulate 12 preloaded RCAC beams, strengthened with two CFRP strengthening schemes. Details of the modeling are provided including the material models, boundary conditions, applied loads, analysis solver, mesh analysis and computational efficiency.

Using FEM, a parametric study was carried out to assess the influence of CFRP thickness on the strengthening efficiency. The FEM provided results in good agreement with those from the experiments with differences and standard deviation not exceeding 11.1% and 3.1%, respectively. It was found that increasing the CFRP laminate thickness improved the load-carrying capacity of the strengthened beams.

The developed models simulate the preloading and loading up to failure with/without CFRP strengthening for the investigated beams. Moreover, the models were validated against the experimental results of 12 beams in terms of crack pattern as well as load, deflection and strain.

This paper aims to investigate the responses of single piles and pile groups due to tunneling-induced ground movements in a two-layered soil system. The analyses mainly focus on the additional single pile responses in terms of bending moment, lateral deflection, axial force, shaft resistance and pile settlement. Subsequently, a series of parametric studies were carried out to better understand the responses of single piles induced by tunneling. To give further understanding regarding the pile groups, a 2 × 2 pile group with two different pile head conditions, namely, free and capped, was considered.

Using the PLAXIS three-dimensional (3D) software, a full 3D numerical modeling is performed to investigate the effects of ground movements caused by tunneling on adjacent pile foundations. The numerical model was validated using centrifuge test data found in the literature. The relevance of the 3D model is also judged by comparison with the 2D plane strain model using the PLAXIS 2D code.

The numerical test results reveal that tunneling induces significant displacements and internal forces in nearby piles. The magnitude and distribution of internal forces depend mainly on the position of the pile toe relative to the tunnel depth and the distance between the pile and the vertical axis of the tunnel. As the volume loss increases from 1% to 3%, the apparent loss of pile capacity increases from 11% to 20%. By increasing the pile length from 0.5 to 1.5 times, the tunnel depth, the maximum pile settlement and lateral deflection decrease by about 63% and 18%, respectively. On the other hand, the maximum bending moment and axial load increase by about 7 and 13 times, respectively. When the pile is located at a distance of 2.5 times the tunnel diameter (Dt), the additional pile responses become insignificant. It was found that an increase in tunnel depth from 1.5Dt to 2.5Dt (with a pile length of 3Dt) increases the maximum lateral deflection by about 420%. Regarding the interaction between tunneling and group of piles, a positive group effect was observed with a significant reduction of the internal forces in rear piles. The maximum bending moment of the front piles was found to be higher than that of the rear piles by about 47%.

Soil is a complex material that shows differently in primary loading, unloading and reloading with stress-dependent stiffness. This general behavior was not possibly being accounted for in simple elastic perfectly plastic Mohr–Coulomb model which is often used to predict the behavior of soils. Thus, in the present study, the more advanced hardening soil model with small-strain stiffness (HSsmall) is used to model the non-linear stress–strain soil behavior. Moreover, unlike previous studies THAT are usually based on the assumption that the soil is homogeneous and using numerical methods by decoupled loadings under plane strain conditions; in this study, the pile responses have been exhaustively investigated in a two-layered soil system using a fully coupled 3D numerical analysis that takes into account the real interactions between tunneling and pile foundations. The paper presents a distinctive set of findings and insights that provide valuable guidance for the design and construction of shield tunnels passing through pile foundations.

Fused deposition modeling (FDM) is an extensively used additive manufacturing method with the capacity to build complex functional components. Due to the machinery and environmental factors during manufacturing, the FDM parts inevitably demonstrated uncertainty in properties and performance. This study aims to identify the stochastic constitutive behaviors of FDM-fabricated polylactic acid (PLA) tensile specimens induced by the manufacturing process.

By conducting the tensile test, the effects of the printing machine selection and three major manufacturing parameters (i.e., printing speed S, nozzle temperature T and layer thickness t) on the stochastic constitutive behaviors were investigated. The influence of the loading rate was also explained. In addition, the data-driven models were established to quantify and optimize the uncertain mechanical behaviors of FDM-based tensile specimens under various printing parameters.

As indicated by the results, the uncertain behaviors of the stiffness and strength of the PLA tensile specimens were dominated by the printing speed and nozzle temperature, respectively. The manufacturing-induced stochastic constitutive behaviors could be accurately captured by the developed data-driven model with the R² over 0.98 on the testing dataset. The optimal parameters obtained from the data-driven framework were T = 231.3595 °C, S = 40.3179 mm/min and t = 0.2343 mm, which were in good agreement with the experiments.

The developed data-driven models can also be integrated into the design and characterization of parts fabricated by extrusion and other additive manufacturing technologies.

Stochastic behaviors of additively manufactured products were revealed by considering extensive manufacturing factors. The data-driven models were proposed to facilitate the description and optimization of the FDM products and control their quality.

To understand the seismic behavior of reinforced concrete (RC) beams confined by corroded stirrups, low-reversed cyclic loading tests were carried out on seven RC beam specimens with different stirrup corrosion levels and stirrup ratios to investigate their mechanical characteristics.

The failure mode, hysteresis behavior, skeleton curves, ductility, stiffness degradation and energy dissipation behavior of RC specimens are compared and discussed. The experimental results showed that the restraint of concrete provided by corroded stirrups is reduced, which leads to a decline in seismic performance.

For the specimens with the same ratios of stirrup, as the corrosion level increased, the load-carrying capacity, stiffness, plastic deformation capacity and energy-dissipation capacity dropped significantly. Compared with the uncorroded specimen, the failure modes of specimens with high corrosion level changed from ductile bending failure to brittle failure. For the specimens with the same levels of corrosion, the higher the stirrup ratio was, the stronger the restraint effect of the stirrups on the concrete, and the seismic behavior of the specimens was obviously improved.

In this paper, a total of seven full-size RC beam specimens at joints with different stirrup corrosion levels and stirrup ratios were designed and constructed to explore the influences of corrosion levels and stirrup ratios of stirrups on the seismic performances. The failure modes, strain of reinforcement, hysteretic curves, skeleton curves, stiffness degradation and ductility factor of RC specimens are compared and discussed.