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The concrete-filled square steel tubular (S-CFST) structure has been widely used as a resistance system against earthquakes due to its good seismic performance. However, the application of the S-CFST structure is limited by its complex joint formulation. To overcome this shortcoming, a sleeve semirigid joint has been proposed, while its seismic performance has not been well examined. This study aims to discuss the behavior of sleeve joints with different parameters under low cyclic loading. The analysis results show that the simulation results of the finite element model established by ABAQUS were in good agreement with the experimental results, which further verified the good energy dissipation performance of the sleeve joint, and gave the design suggestions of the joint under different parameters to promote the engineering application of this type of joint. [ABSTRACT FROM AUTHOR]

The main drive sealing system of shield tunneling machine is one of the key systems of the shield tunneling machine, the performance of the main drive sealing ring directly affects the performance of the shield tunneling machine. An orthogonal test scheme was established for the main structural parameters of lip seal ring which affect the sealing performance of the shield machine's main drive. The finite element analysis software ABAQUS was used to establish the calculation method of opening pressure difference and contact width in the working process of main drive sealing ring of shield machine. According to the orthogonal test scheme,the opening pressure difference and the contact width were simulated, and the calculation results were analyzed by variance.The results show that the lip height and the lip thickness of the lip sealing ring have a significant effect on the opening pressure difference, the lip curvature and the lip height have significant effects on the contact width.According to the sealing requirements and analysis results,the optimal structure of the seal ring with a lip curvature of 17 mm, a lip height of 22.35 mm, a compression amount of 7.1 mm, and a lip thickness of 5 mm is obtained. After structural optimization,the opening pressure difference is reduced by 33% and the contact width is reduced by 23%. [ABSTRACT FROM AUTHOR]

Development of experimental studies in bond behavior between deformed bar and concrete under complex stress conditions in the last 2 decades is significantly affecting the concrete design specification. This article presents a rib-scale finite element model (FEM) to study the bond behavior of deformed bar in concrete under lateral tensions. In this model, detailed modeling including the reinforcing bar ribs and the concrete keys in contact region is realized with real geometric parameters. At the concrete–bar interface, surface-to-surface contacts with tie constraints are used and relative sliding or separation between contact surfaces are inhibited; adhesion between concrete and deformed bar is ignored. A user-defined subroutine named VUSDFLD in ABAQUS software was incorporated into the concrete damaged plasticity (CDP) model to acquire more accurate concrete constitutive relations. The FEM is calibrated using pullout test data from published papers. The simulation results show that all specimens failed in splitting mode. The lateral tension is an adverse factor on the bond property between steel bar and concrete, both the ultimate bond strength and the slip at the peak bond stress decrease with the increase of the lateral tensions. Comparison of computational simulation with the experimental data indicates that the proposed model gives a reasonable prediction of the bond stress–slip curves as well as the concrete crack patterns. [ABSTRACT FROM AUTHOR]

• Reliable 3D finite element models are developed for FRP-confined concrete-encased cross-shaped steel columns (FCCSCs). • An in-depth understanding on the complex confinement mechanism of FCCSCs is achieved. • The effects of key parameters on the mechanism and behaviour of FCCSCs are thoroughly examined. Fibre-reinforced polymer (FRP)-confined concrete-encased cross-shaped steel columns (FCCSCs) are an emerging type of hybrid columns. In an FCCSC, the concrete is subjected to combined confinement from the steel section and the FRP tube, leading to an enhanced load capacity and excellent ductility of the column. While several recent experimental studies have demonstrated the excellent structural performance of FCCSCs, the complex confinement mechanism behind their structural behaviour has not been clarified or thoroughly examined. This paper presents a comprehensive study aiming to investigate the confinement mechanism of FCCSCs. In this paper, the experimental observations of FCCSCs are first summarized, followed by three-dimensional FE modelling of the columns. The FE models, after being verified against the test results in various aspects, are used for a systematic parametric study. In this study, the complex interaction between the three components of FCCSCs (i.e., FRP tube, steel section and concrete) is illustrated explicitly and the effects of key parameters (i.e., flange width, flange thickness, web thickness and FRP tube thickness) are examined separately and thoroughly, leading to an in-depth understanding of the confinement mechanism of FCCSCs. In particular, through the examination on the distribution of steel flange-to-concrete normal pressure, it is shown quantitatively that the variations of the dimensions of the steel section in a practically wide range have only marginal effects on its confinement to the concrete, while the increase of FRP tube thickness tends to reduce the confinement effect from the steel section. [ABSTRACT FROM AUTHOR]

• The cracking behaviors of corroded RC beams were emphatically analyzed. • Extended finite element method (XFEM) was adopted to simulate the cracking developments. • A user-defined element (UEL) was developed to represent the degraded bond response. Chloride-induced corrosion of reinforcement has been recognized as one of the most predominant causes of structural degradation. In this paper, experimental and numerical investigation was conducted to study the degraded shear performance of reinforced concrete beam. The corrosion of reinforcements, crack patterns, and structural behaviors of corroded specimens with various corrosion levels accelerated by the impressed current method were analyzed. The test results indicated that the corrosion-induced crack patterns have a close relationship with the level of reinforcement corrosion. Moreover, an obvious degradation of shear performance of corroded RC beams in terms of initial stiffness, cracking loads, ultimate bearing capacity, post-peak behavior, and energy dissipation capacity was observed, which became more pronounced as the corrosion level increased. When a severe corrosion level (η a ≥ 12%) was encountered, the failure mode could even be changed from the shear-compression failure into a much more brittle diagonal splitting failure. In parallel, to numerically simulate the propagation of the main diagonal crack faithfully, the extended finite element method (XFEM) specified with an exponential softening traction-separation relationship was adopted. Moreover, to investigate the effect of corrosion-induced bond degradation, a user-defined element (UEL) was also developed to represent the interfacial bond response. The reasonable agreement between the numerical simulation and experimental results proved the feasibility of the proposed approach. [ABSTRACT FROM AUTHOR]

A sound finite element model is essential for the nonlinear structural analysis of FRP tube-confined UHPC columns, wherein an accurate constitutive model to characterize the mechanical behavior of UHPC under passive constraints is of utmost importance. This study presents a refined finite element modeling methodology for the UHPC-filled FRP tube column. The constitutive model for UHPC under passive constraint is developed, in which the yield criterion, hardening/softening law, plastic flow rule, and damage evolution law are determined based on the experimental results of UHPC under multiaxial loading conditions. Furthermore, a solid element model of FRP tube with definable layer information is utilized to simulate the behavior of FRP tubes under complex stress states. The proposed finite element model is implemented in ABAQUS and verified through available experimental results. The results indicate that the proposed model can accurately predict the stress–strain behavior of confined UHPC with varying fiber and coarse aggregate contents, and describe the damage progression of UHPC and FRP tubes. Particularly, the interaction process between FRP and UHPC can be well reflected. The proposed finite element model serves as a paradigm for numerical analysis of UHPC-filled FRP tube elements and provides a reference for simulations of UHPC structures. [ABSTRACT FROM AUTHOR]

Magnesium (Mg) is a potential biomaterial suitable for developing biodegradable orthopaedic implants, especially as internal fixators for fracture fixation at non-load bearing skeletal sites. However, Mg alone cannot provide sufficient mechanical support for stable fracture fixation at load bearing sites due to its rapid degradation in the early stage after implantation. In consideration of the strengths and weaknesses of Mg, we developed an innovative magnesium/titanium (Mg/Ti) hybrid fixation system for long bone fracture fixation and investigated the fixation efficacy. The finite element analysis (FEA) results indicated that the Mg/Ti hybrid fixation system provided sufficient mechanical support for fracture fixation at load-bearing skeletal site. As a proof-of-concept, we performed a “Z-shaped” open osteotomy at the mid-shaft of rabbit tibia. For comparison, the animals were divided into two groups: Mg/Ti group (fixated with Mg screws and Ti fixators) and Ti control group (fixated with Ti screws and Ti fixators). The radiographic, four-point bending mechanical test, histological and histomorphometric analysis were postoperatively performed in a temporal manner up to 12 weeks. Both X-ray and micro-CT images of the Mg/Ti group showed a larger callus (14.7% at 3rd week and 24.8% at 6th week, n = 5–7, p < 0.05) in the regions of interest (ROIs) over time, especially at the opposite cortex of the fixation plate. At the 12th week post-operation, the biomechanical test result indicated that the rabbit tibia in the Mg/Ti group healed better and the overall mechanical strength was approximately 3-fold higher (n = 8, p < 0.05) than that at 6th week. Furthermore, the FEA revealed that the Mg/Ti group had a higher mechanical strength (19.5% at week 6 and 31.5% at week 12) at the specified ROI and resulted in an earlier and faster endochondral ossification (68.0% at week 3 and 71.4% at week 6) with a higher expression of osteocalcin (54.0%) and collagen I (34.2%) than the Ti control group (n = 4, p < 0.05). Further evaluation suggested that a higher expression of calcitonin gene-related peptide (CGRP), a known osteogenic neuron peptide, in the fracture callus of the Mg/Ti group might be a major underlying mechanism of enhanced fracture healing attributed to the release of Mg ions during the degradation of Mg screws. [ABSTRACT FROM AUTHOR]

This paper presents a modified concrete damaged plasticity model (CDPM) based on ABAQUS, in order to accurately simulate the mechanical responses of steel-polypropylene hybrid fiber reinforced concrete (HFRC). The modifications mainly include the determination of fiber effect-dependent parameters in terms of damage evolution, yield criterion, hardening/softening law and plastic potential. The influences of respective parameter on the numerical results are discussed in detail. Subsequently, the CDPM with refined parameters is validated by independent experimental results having various fiber reinforcement indexes in both material scale and structural scale, where the mechanical behavior of FRC material under multiaxial loadings and the seismic performance of HFRC column subjected to cyclic loadings are respectively simulated. The close agreements between numerical predictions and test results solidly substantiate the applicability of the modified model, which serves as a solid foundation for accurate simulation of FRC behavior using ABAQUS. [ABSTRACT FROM AUTHOR]