In this study, a finite cyclic elasto-plastic constitutive model is developed to simulate the cyclic hardening and softening of the low-yield-point steel BLY160. Compared with existing models, an ...improved description of the stress-strain hysteresis loops is achieved by introducing a modified Chaboche kinematic hardening rule and a nonlinear isotropic hardening rule extended with a strain memory surface. In the proposed kinematic hardening rule, the backstress is decomposed into three parts for short, middle, and long ranges, with each of them obeying an Armstrong-Frederick (A-F) evolution rule consisting of a linear hardening and dynamic recovery term. To incorporate the significant effect of the kinematic hardening rule on the shape change in hysteresis loops, a dynamic recovery coefficient is postulated herein to develop with not only the accumulated plastic strain but also the memorized strain range. In addition, a hardening factor is introduced to the linear hardening term to consider the different plastic moduli of monotonic and cyclic deformations. The model parameters are identified in an exquisite manner by discriminating the contributions of the isotropic and kinematic components to the cyclic hardening and softening phenomena, which is implemented through a quantitative evaluation of the tested hysteresis loops. The comparison between the numerical prediction and experimental results indicates that the developed constitutive model can elaborately simulate the cyclic behaviour of the investigated steel. The results demonstrate that the entire evolution process of the stress-strain hysteresis curve characterized by the cyclic hardening and softening, transient Bauschinger effect, and strain-range dependence can be adequately described by the proposed model.
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•The kinematic hardening has a significant influence on the shape change of hysteresis loops.•Obvious different plastic moduli exist between the monotonic and cyclic deformation.•A constitutive model for exquisitely simulating the hysteresis loops is developed.•Strain range dependence is incorporated in both kinematic and isotropic hardening rules.•Quantitative evaluation of the hysteresis loops helps calibration of model parameters.
•The crack spacing of RC members is analyzed using the fracture energy criterion.•The influence of compressive strength on crack spacing is first explained.•The size effect of the crack spacing is ...first examined for RC members.•A simple formula for crack spacing is proposed with a reasonable level of accuracy.
The average crack spacing is a key parameter for an accurate evaluation of the crack width of reinforced concrete (RC) members. According to the test results in the existing literature, both the variations of the concrete strength and the size effect are critical factors influencing the average crack spacing. However, available prediction models for the average crack spacing cannot give satisfactory results in simulating both factors. Based on the finite-element (FE) analysis and the fracture-energy criterion, a theoretical method considering the influence of concrete strength variation and size effect is first proposed. It is assumed that a micro-crack will grow into a visible crack if and only if the energy release exceeds the fracture energy of the effective cracking area. Therefore, the average crack spacing can be predicted by equating the energy release, which is obtained by the three-dimensional FE model of concrete subjected to bond stress, to the fracture energy of the effective cracking area. In addition, from the proposed model, the characteristic length of concrete is found to be the most important material parameter for average crack spacing of RC members. Subsequently, a database including 136 test specimens is established to sufficiently validate the proposed model. The influence of various key factors on the average crack spacing is discussed in detail. Finally, simplified prediction formulas for average crack spacing of RC members are proposed considering both concrete strength variation and size effect. Comparisons indicate that both the proposed theoretical model and the simplified formulas have sufficient accuracy.
•Six innovative shear critical composite shear walls without tie bars were tested.•The shear compression failure for each specimen was observed with notable capacity and ductility.•The influence of ...axial compression ratio and faceplate slenderness ratio was elaborately investigated.•A novel database of 38 composite shear walls was established for shear capacity evaluation.
Many skyscrapers have used the Reinforced Concrete (RC) filled Composite Plate Shear Walls (CPSW). Based on in-plane shear tests on six shear-critical CPSW specimens and a RC shear wall specimen, the behavior of CPSW systems with stud or tie bar connectors, various connector spacings, and various axial compression ratios were reported. In the test program, the Concrete Filled Steel Tubes (CFSTs) are applied for each specimen as boundary elements to simulate the engineering design of CPSW in skyscrapers. This paper presents the test observations, the ultimate capacity, the lateral stiffness, the ductility and the energy dissipation results. Based on the test results, the CPSW specimens with CFST boundary element failed in shear compression failure and the reference RC shear wall failed in shear tension failure. The weld fracture was generally found at boundary element (CFST) in the descending branch. Compared to the RC shear wall, the shear capacity of the CPSW systems were enhanced by 104–129%. The difference between CPSW systems with stud connectors and those with tie bars was insignificant in terms of ultimate capacity. Subsequently, a new database including 38 test specimens was established from the aforementioned test program and available literatures. The database results indicate the compressive capacity of infilled concrete is the dominating factor influencing the shear capacity, instead of the yield capacity of steel. In addition, a design formula for the in-plane ultimate capacity of shear-critical CPSW systems is proposed. Comparisons demonstrated that the proposed model was consistent and exhibited a reasonable level of consistency.
Volumetric additive manufacturing (VAM) enables fast photopolymerization of three-dimensional constructs by illuminating dynamically evolving light patterns in the entire build volume. However, the ...lack of bioinks suitable for VAM is a critical limitation. This study reports rapid volumetric (bio)printing of pristine, unmodified silk-based (silk sericin (SS) and silk fibroin (SF)) (bio)inks to form sophisticated shapes and architectures. Of interest, combined with post-fabrication processing, the (bio)printed SS constructs reveal properties including reversible as well as repeated shrinkage and expansion, or shape-memory; whereas the (bio)printed SF constructs exhibit tunable mechanical performances ranging from a few hundred Pa to hundreds of MPa. Both types of silk-based (bio)inks are cytocompatible. This work supplies expanded bioink libraries for VAM and provides a path forward for rapid volumetric manufacturing of silk constructs, towards broadened biomedical applications.
Digital light processing bioprinting favors biofabrication of tissues with improved structural complexity. However, soft-tissue fabrication with this method remains a challenge to balance the ...physical performances of the bioinks for high-fidelity bioprinting and suitable microenvironments for the encapsulated cells to thrive. Here, we propose a molecular cleavage approach, where hyaluronic acid methacrylate (HAMA) is mixed with gelatin methacryloyl to achieve high-performance bioprinting, followed by selectively enzymatic digestion of HAMA, resulting in tissue-matching mechanical properties without losing the structural complexity and fidelity. Our method allows cellular morphological and functional improvements across multiple bioprinted tissue types featuring a wide range of mechanical stiffness, from the muscles to the brain, the softest organ of the human body. This platform endows us to biofabricate mechanically precisely tunable constructs to meet the biological function requirements of target tissues, potentially paving the way for broad applications in tissue and tissue model engineering.
This paper investigates the dynamic behaviour of an innovative structural system with separated gravity and lateral resisting systems (SGLR system), which is proposed for the prefabricated structures ...in multi-story buildings by enhancing the standardization of beams, under earthquake excitation. The seismic performance of SGLR system is benchmarked against the conventional rigid frame system (RF system) designed with the same maximum inter-story drift ratios, and the influences of connection semi-rigidity on the dynamic responses of SGLR system are focused on. Numerical models are built using the self-developed fiber beam-column elements for composite frames, beam elements for semi-rigid connections and multi-layer shell elements for shear walls based on a six-story prototype structure. The modal analysis indicates that the natural vibration periods of SGLR system are smaller than those of RF system and the connection semi-rigidity will further significantly decrease the periods for the first three orders. Nonlinear time history analysis is conducted under eight sets of ground motions at two different levels in two horizontal directions. The shear walls in SGLR system bear the majority of seismic action with damage concentrated in the bottom. The connection semi-rigidity will decrease the lateral deformation and increase the involvement of the frame part in the lateral resisting mechanism of SGLR system, which can be more significant when the semi-rigidity is higher. SGLR system exhibits better control of inter-story drift ratios considering connection semi-rigidity in low-rise buildings and higher economic efficiency in mid-rise buildings.
•The seismic behaviour of SGLR system is benchmarked against RF system.•Efficient numerical models are built based on a six-story prototype structure.•Modal analysis and nonlinear time history analysis are conducted.•Connection semi-rigidity effect on dynamic responses of SGLR system is focused on.•Influences of building height on seismic performance of SGLR system are studied.
Abstract
Rolling friction pairs in the tower saddle of suspension bridges could significantly reduce the horizontal load that is transferred to the tower. To investigate the dependence of the rolling ...friction coefficient (μ) of a rolling friction pair on the normal load (fn) and the cylinder radius (R), an experiment was conducted where a sandwich-like mechanism measured μ. Based on the μ–fn–R relationship, a numerical model, which used one-dimensional (1D) Gaussian random nonplanar surface representation, was proposed in this research to calculate the overall rolling friction coefficient (μT) of a multiroller plate system. The experimental results showed that the dependence of μ on fn and R could be divided into three stages: (1) roughness; (2) elastic; and (3) inelastic. In addition, μ was proportional to
f
n
/
R in the elastic stage. The proposed numerical model could accurately calculate μT for a multiroller plate system. The μT rose with increasing surface nonplanarity and slightly increased with the number of rollers (N). This clarified that the μ–fn–R relationship and proposed numerical model could help to quickly determine the size of the rollers and the flatness of plates during design and reduce the scale of the experiments required.
Using an antimicrobial susceptibility test (AST) as an example, this work demonstrates a practical method to fabricate microfluidic chips entirely from polypropylene (PP) and the benefits for ...potential commercial use. Primarily caused by the misuse and abuse of antibiotics, antimicrobial resistance (AMR) is a major threat to modern medicine. The AST is a promising technique to help with the optimal use of antibiotics for reducing AMR. However, current phenotypic ASTs suffer from long turnaround time, while genotypic ASTs suffer from low reliability, and both are unaffordable for routine use. New microfluidics based AST methods are rapid but still unreliable as well as costly due to the PDMS chip material. Herein, we demonstrate a convenient method to fabricate whole PP microfluidic chips with high resolution and fidelity. Unlike PDMS chips, the whole PP chips showed better reliability due to their inertness; they are solvent-compatible and can be conveniently reused and recycled, which largely decreases the cost, and are environmentally friendly. We specially designed 3D chambers that allow for quick cell loading without valving/liquid exchange; this new hydrodynamic design satisfies the shear stress requirement for on-chip bacterial culture, which, compared to reported designs for similar purposes, allows for a simpler, more rapid, and high-throughput operation. Our system allows for reliable tracking of individual cells and acquisition of AST results within 1-3 hours, which is among the group of fastest phenotypic methods. The PP chips are more reliable and affordable than PDMS chips, providing a practical solution to improve current culture-based AST and benefiting the fight against AMR through helping doctors prescribe effective, narrow-spectrum antibiotics; they will also be broadly useful for other applications wherein a reliable, solvent-resistant, anti-fouling, and affordable microfluidic chip is needed.
Using an antimicrobial susceptibility test (AST) as an example, this work demonstrates a practical method to fabricate microfluidic chips entirely from polypropylene (PP) and the benefits for potential commercial use.
Two interpenetrated diamondoid coordination networks, Dia-4-M (M= Ni and Co), are synthesized. Both materials exhibit preferential binding of C2H6 over C2H4, because C2H6 molecules can be well ...accommodated within the pores through stronger host–guest interactions. Such C2H6-selective porous materials not only exhibit decent C2H6/C2H4 selectivity but also display ultra-high C2H6 uptake.
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•Reversed selective C2H6/C2H4 separation was due to the enhanced host–guest interaction.•Dia-4-Co exhibits ultra-high C2H6 uptake (103 cm3 g−1).•Exceptional recyclability for Dia-4-Co and Dia-4-Ni.•High purity (99.9%) of C2H4 can be produced in one step under ambient conditions.
The separation of ethane (C2H6) from ethylene (C2H4) is one of the most challenging and important tasks in chemical industry. Herein we report two interpenetrated diamondoid (dia) coordination networks, Dia-4-M M(pba)2 (pba = 4-(4-pyridyl)benzoate); M = Ni or Co), that can directly capture ethane from ethane-ethylene mixtures with reverse C2H6/C2H4 separation. Both materials not only exhibit ultra-high C2H6 uptake (100 cm3 g−1 for Dia-4-Ni; 103 cm3 g−1 for Dia-4-Co) but also display good C2H6/C2H4 selectivity (1.76 for Dia-4-Ni; 2.04 for Dia-4-Co). Such C2H6/C2H4 separation performance was confirmed by dynamic breakthrough experiments. Dia-4-M could extract low concentrated of C2H6 from C2H6/C2H4 mixture (v(C2H6)/v(C2H4) = 1:9 and 1:15) and produce high purity (99.9%) of C2H4 under ambient conditions. The mechanism for selective C2H6/C2H4 separation was clarified through Grand Canonical Monte Carlo (GCMC) simulations and Density functional theory (DFT) calculations. Overall, this research demonstrates that Dia-4-M has a significant potential as effective C2H6-selective adsorbents for the purification of ethylene in practice.
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