Elastic-plastic Stage Research Articles

Seismic behavior of composite interior joints of prefabricated H-shaped steel reinforced concrete column - steel beam

To better meet the requirements of building industrialization, this study proposes a Modular Prefabricated Composite Interior Joint (MPCIJ), which consists of node modules, prefabricated H-shaped steel–concrete columns, and steel beams. The failure process and characteristics of three MPCIJ joints under low cyclic reciprocating loading are analyzed. Seismic behaviors such as skeleton curve, hysteresis curve, ductility deformation, energy dissipation, strength, and stiffness degradation of MPCIJ are studied. The variable parameters of three MPCIJ specimens are the stiffness ratios (beam to column). The test results show that with increasing beam to column stiffness ratio, MPCIJ specimens gradually develop from clear beam end bending failure to joint shear failure and column end compression-bending failure. Each node has experienced the elastic stage, the elastic–plastic stage, and the failure stage. Load-displacement curves of MPCIJ specimens are relatively full, showing high bearing capacity and strong energy consumption. The average equivalent viscous damping coefficient ranges between 0.30 and 0.37, and the average ductility coefficient ranges between 3.60 and 4.25, which meets the seismic performance requirements. The beam to column stiffness ratio exerts less influence on the strength degradation coefficient and stiffness degradation coefficient of MPCIJ specimens, and their performance degradation ability remains relatively stable. In summary, the MPCIJ specimen offers high bearing capacity and good seismic performance. At the same time, the influence of the internal welding quality of the joint module cannot be ignored, and the weld strength should be strictly guaranteed during processing.

Accounting for physically nonlinear deformation of the shell under flat loading based on the finite element method

On the basis of the theory of small elastic plastic deformations obtained at the loading step in the curvilinear coordinate system of the relationship between stress increments and strain increments, which are implemented in the matrix of shell stiffness under flat loading In this paper, algorithms for obtaining physically nonlinear relations at the loading step in finite element calculations of shells under flat loading are developed.On the basis of relations of deformation theory of plasticity the equations of connection between increments of stresses and increments of deformations at flat loading in elastic plastic stage of work are received. The coefficients of proportionality are obtained when using the strain diagram of the material. The found defining relations are implemented in the algorithm of forming the stiffness matrix of the finite element of the shell under flat loading. Specific examples show the effectiveness of the developed algorithms for the calculation of the shell with a flat loading beyond the elasticity limits.

Mechanical and damage mechanisms of reinforced ultra high performance concrete under tensile loading

Understanding the tensile mechanism of reinforced ultra high performance concrete (RUHPC) is important for structural design and application of ultra high performance concrete (UHPC). In this study, the direct tensile test accompanied with crack width detection and acoustic emission (AE) source locating were conducted on RUHPC specimens with the longitudinal reinforcement ratios of 0%, 2.3% and 4.6%. Two types of RUHPCs were studied: high strain hardening RUHPC (HSH-RUHPC) and strain softening RUHPC (SS-RUHPC). Experimental results included the tensile stress (load)-strain curves, the crack width-strain curves and the AE source distribution maps under tensile loading. The tensile mechanisms were elaborated from two aspects. From the view of mechanical mechanism, during Stage I (the elastic stage) and Stage II (the elastic-plastic stage): (1) HSH-RUHPC had a globally uniform stress distribution while the steel rebar in SS-RUHPC changed from total elastic state to partial yielding and finally to partial strain hardening; (2) the reduction of the tensile strength of UHPC was observed in RUHPC, which was more obvious with the higher reinforcement ratio. From the view of damage evolution mechanism based on AE analysis method at the micro level: (1) HSH-RUHPC exhibited a homogeneous damage distribution owing to its multiple-micro-cracking mode before steel yielding; (2) SS-RUHPC showed several damage concentrations at crack positions after UHPC softening due to its several-macro-cracking mode. Meanwhile, Gini index was proved to be an effective parameter to evaluate the distribution nonuniformity of the internal damages of RUHPC.

Bearing Capacity of Stone-Lightweight Aggregate Concrete-Filled Steel Tubular Stub Column Subjected to Axial Compression

The objective of this research was to investigate the axial compression performance of stone-lightweight aggregate concrete-filled steel tubular (hereafter referred to as SLCFST for simplicity) stub columns. Ten specimens, five circular SLCFST (C-SLCFST) stub columns and five square SLCFST (S-SLCFST) stub columns, were tested using replacement ratios of normal gravel aggregate of between 0% and 100%, in increments of 25%. The influence of replacement ratio on axial compression performance and failure mode, ultimate bearing capacities and peak displacements was analysed. The results were compared, and show that under axial compression loading, strength damage occurs in SLCFST stub columns. The working process of SLCFST stub columns can be divided into four parts: an elastic stage, an elastic-plastic stage, a gentle descent stage and a plastic stage. The ultimate bearing capacities of the specimens were calculated and analysed based on existing design codes. By introducing the influence parameter of normal gravel replacement ratio, mathematical models for predicting the complete stress-strain compression curves of C-SLCFST and S-SLCFST stub columns were developed and verified.

Experimental investigation of square stainless steel tubular stub columns after elevated temperatures

The behaviour of square stainless steel tubular (SSST) stub columns after elevated temperatures under axial compression is presented in this paper. A total of sixty specimens were tested, including forty-eight SSST stub columns at elevated temperatures cooled in air, nine SSST stub columns at elevated temperatures cooled in water and three SSST stub columns at ambient temperature. A total of twelve square CFSST stub columns were carried out load-strain tests. The main parameters explored in the test include thickness (1.0 mm, 1.2 mm, 1.5 mm), high temperature duration (30 min, 60 min, 90 min, 120 min), temperature ranging from 400 °C to 1000 °C and cooling methods. This paper presents the failure modes, ultimate load-bearing capacity, load-strain curves, load versus displacement curves, initial stiffness at the elastic stage and ductility of the specimens. It was found that high temperature has the greatest influence on the ultimate load-bearing capacity of the columns, and the cooling methods also have some effect on it. As the elevated temperature specimens subjected increased, the percentage decrease in load-bearing capacity had an obvious increase, the ductility became worse and the initial compressive stiffness slightly decreased. The crack resistance of the specimens improved after elevated temperature. The axial deformation versus load curves had an obvious elastic-plastic stage as the elevated temperature duration increased to 120 min. Based on the experimental results, a formula was proposed to calculate the ultimate load-bearing capacity of SSST stub columns after elevated temperatures.

COMPARATIVE ANALYSIS OF THE BUCKLING FACTOR OF THE STEEL ARCH BRIDGES

The dominant axial compressive force makes the arches become extremely sensitive to the loss of stability. Their stability analysis was first initiated in the late 20th century. The first stability research of single arches was carried out inplane at the elastic stage of the arches. Later the behaviour of arches in the elastic-plastic stage, the initial stresses and geometric imperfections before the arch buckles were also assessed, the effective length of the arches and the out-of-the-plane arch strength conditions were being identified as well as the effect of the temperature on the stability of the arch. The expression of the critical force of the arches connected by vertical hangers with a chord and its dependant elements were defined by Petersen in the late 20th century. The design methodology for the formal design of arches connected by vertical hangers with a stiffening girder is presented in Annex D of the Eurocode 1993-2. Nevertheless, the area of application and the main assumptions are not defined. The first part of the comparative analysis identifies the assumptions for arch bridge modelling under which the buckling factor β dependence curves in Figure D.4 of Annex D to Eurocode 1993-2 can be applied. In the second part a comparison of the the normative βEC factor value and the one established by the numerical experiment with the increase in the number of hangers and change in the hanger network form is presented.

Study of the Ultimate Bearing Capacity of Concrete-filled Steel Tube K-Joints

To study the ultimate bearing capacity of Concrete-Filled Steel Tube (CFST) K-joints, theoretical analysis and numerical simulation methods were adopted. A finite element model of a K-joint was established and verified with test data. Based on this model, the failure modes of the K-joint were studied. The results showed that the load-displacement curves of CFST K-joints can be divided into three stages: an elastic stage, an elastic-plastic stage and a failure stage. There were two types of failure modes for K-joints: local buckling failure at the connection between a branch pipe and the main pipe due to compression and tearing failure at the connection between a branch pipe and the main pipe due to tensile forces. The factors that influence the ultimate bearing capacity of CFST K-joints were studied, and the results were as follows. The ultimate bearing capacity increased as the radius-thickness ratio of the main pipe, radius-thickness ratio of the branch pipes and gap between branch pipes decreased. Additionally, the ultimate bearing capacity of the CFST K-joints increased with increasing core concrete grade, outer diameter ratio and thickness ratio between the branch pipe and main pipe. As the angle between the axis of the branch pipe and the axis of the main pipe increased, the ultimate bearing capacity initially decreased and then increased. As the axial pressure level in the main pipe increased, the ultimate bearing capacity of the K-joint initially increased and then decreased. A positive linear correlation was observed between the growth coefficient of the ultimate bearing capacity and the scaling factor. Moreover, the ultimate bearing capacity of CFST K-joints can be significantly improved by using core concrete. Finally, formulas for the ultimate bearing capacity of K-joints under different failure modes were proposed, and the results provide a reference for the design of CFST arch bridges.

Size- and Temperature-Dependent Collision and Deposition Model for Micron-Sized Sand Particles

Sand ingestion and deposition in gas turbine engine components can lead to several operational hazards. This paper discusses a physics-based model for modeling the impact, deposition, and sticking of sand particles to surfaces. The collision model includes both normal and tangential components of impact. The normal collision model divides the impact process into three stages, the elastic stage, the elastic–plastic stage, and full plastic stage, and the recovery process is assumed to be fully elastic. The adhesion loss in the recovery stage is described using Timoshenko's model and Tsai's model, and shows that the two models are consistent under certain conditions. Plastic deformation losses of surface asperities are also considered for particle–wall collisions. The normal impact model is supplemented by an impulse-based tangential model, which includes both sliding and rolling frictions. Sand properties are characterized by size and temperature dependencies. The predicted coefficient of restitution (COR) of micron-sized sand particles is in very good agreement with experimental data at room temperature and at higher temperatures from 1073 K to 1340 K. The predicted COR decreases rapidly at temperatures above 1340 K. There is a strong interplay between the size-dependent properties of micron sand particles and the temperature dependency of yield stress on the collision and deposition characteristics. This is the first physics-based high temperature model including translation and rotation of micron-sized sand particles with sliding and rolling modes in the gas turbine literature.

Mechanical performance of sand-lightweight concrete-filled steel tube stub column under axial compression

In order to study the axial compression performance of sand-lightweight concrete-filled steel tube (SLCFST) stub columns, three circular SLCFST (C-SLCFST) stub column specimens and three SLCFST square (S-SLCFST) stub column specimens were fabricated and static monotonic axial compression performance testing was carried out, using the volume ratio between river sand and ceramic sand in sand-lightweight concrete (SLC) as a varying parameter. The stress process and failure mode of the specimens were observed, stress-strain curves were obtained and analysed for the specimens, and the ultimate bearing capacity of SLCFST stub column specimens was calculated based on unified strength theory, limit equilibrium theory and superposition theory. The results show that the outer steel tubes of SLCFST stub columns buckled outward, core SLC was crushed, and the damage to the upper parts of the S-SLCFST stub columns was more serious than for C-SLCFST stub columns. Three stages can be identified in the stress-strain curves of SLCFST stub columns: an elastic stage, an elastic-plastic stage and a plastic stage. It is suggested that AIJ-1997, CECS 159:2004 or AIJ-1997, based on superposition theory, can be used to design the ultimate bearing capacity under axial compression for C-SLCFST and S-SLCFST stub columns; for varying replacement ratios of natural river sand, the calculated stress-strain curves for SLCFST stub columns under axial compression show good fitting to the test measure curves.

Axial capacity of reactive powder concrete filled steel tube columns with two load conditions

Reactive powder concrete (RPC) is a type of ultra-high strength concrete that has a relatively high brittleness. However, its ductility can be improved by confinement, and the use of RPC in composite RPC filled steel tube columns has become an important subject of research in recent years. This paper aims to present an experimental study of axial capacity calculation of RPC filled circular steel tube columns. Twenty short columns under axial compression were tested and information on their failure patterns, deformation performance, confinement mechanism and load capacity were presented. The effects of load conditions, diameter-thickness ratio and compressive strength of RPC on the axial behavior were further discussed. The experimental results show that: (1) specimens display drum-shaped failure or shear failure respectively with different confinement coefficients, and the load capacity of most specimens increases after the peak load; (2) the steel tube only provides lateral confinement in the elastic-plastic stage for fully loaded specimens, while the confinement effect from steel tube initials at the set of loading for partially loaded specimens; (3) confinement increases the load capacity of specimens by 3% to 38%, and this increase is more pronounced as the confinement coefficient becomes larger; (4) the residual capacity-to-ultimate capacity ratio is larger than 0.75 for test specimens, thus identifying the composite columns have good ductility. The working mechanism and force model of the composite columns were analyzed, and based on the twin-shear unified strength theory, calculation methods of axial capacity for columns with two load conditions were established.

Mechanical properties and finite element analysis of walnut under different cracking parts

In order to reduce mechanical damage and improve extraction quality of walnut kernel during walnut cracking, the Wen-185 walnut cultivar was selected as the research object, and the mechanical properties of walnut under different cracking parts were assessed by combining compression tests and finite element analysis (FEA) method. The compression test results showed that the relationships between rupture force and deformation of walnut were nonlinear, and the cracking process of shell mainly consisted of three stages (elastic stage, plastic stage and composite elastic-plastic stage). The best method to crack walnut was the spherical compression, and the peak value of rupture force and corresponding deformation were 211.83 N and 1.68 mm, respectively. In condition of spherical compression, the shell-breaking rate, first-grade kernel rate and whole kernel rate were (91.67±2.89)%, (88.33±2.89)%, (80.00±5.00)%, respectively. The FEA results indicated that spherical compression was also the suitable way to rupture walnut, which resulted in the obvious propagation trends of shell cracks and further a better integrity of extracting walnut kernel. Therefore, the spherical contact form between walnut and cracking parts may be considered to design the structural shape of key components of walnut cracking machines, which was consistent with the analysis of compression test results. The comparison between experiment results and FEA results showed that the established FEA model can be used to analyze the mechanical properties of walnut. The research results can provide references for the structural design and optimization of key components of cracking machines for walnut or other nut crops. Keywords: walnut, mechanical damage, compression tests, mechanical properties, finite element analysis DOI: 10.25165/j.ijabe.20181106.3309 Citation: Zhang H, Shen L Y, Lan H P, Li Y, Liu Y, Tang Y R, et al. Mechanical properties and finite element analysis of walnut under different cracking parts. Int J Agric & Biol Eng, 2018; 11(6): 81–88.

A design method of viscoelastic damper parameters based on the elastic-plastic response reduction curve

The traditional design method of the elastic response reduction curve (ERRC) was used to design the parameters of the viscoelastic damper (VED), where the plastic behavior of the primary structure is neglected. Considering the structural plastic behavior, in this study, a direct design method is proposed to obtain the parameters of VEDs based on the elastic-plastic response reduction curve (EPRRC), which can illustrate the relationship between damper parameters and the response reduction effect in the elastic-plastic stage. First, the ERRC is developed to the EPRRC, and the differences between them are compared using the displacement and acceleration response difference ratios, which demonstrate an overestimated response reduction effect of VEDs in the elastic-plastic stage using the ERRC. Then, the corresponding design procedures are given based on the EPRRC by referring to the direct displacement-based design theory. Finally, a benchmark model is used to illustrate the effectiveness of this proposed design method by conducting a time history analysis. The analysis results indicate that the target story drift of the structure can be satisfied under different earthquake intensities using VEDs. Thus, based on this study, the development of the EPRRC can be considered worthwhile, and the proposed design method of VED parameters is easy to implement and is effective.

Thermodynamic and mechanical properties of Cu–Zr–Al–Ti bulk metallic glasses

The thermodynamic and mechanical properties of Cu46Zr46-xAl8Tix (x = 0, 1, 2, and 3 at.%) bulk metallic glasses (BMGs) were investigated. The experimental results indicate that the Cu46Zr46Al8 and Cu46Zr45Al8Ti1 alloys achieve good glass formation ability (GFA), whereas that of both Cu46Zr44Al8Ti2 and Cu46Zr43Al8Ti3 alloys are weak. The thermogravimetric curve is nonlinear from the glass transition temperature to the completion of crystallization temperature and may be related to the reaction of disordered atoms and oxygen and nitrogen atoms. The Cu46Zr45Al8Ti1 BMG with the work-hardening ability in these alloys has a large yield strength of 1870 MPa and a fracture strength of 2060 MPa. The average incubation time of the serrated flow in the elastic–plastic stage with the high work-hardening index is 1.3706 s, which is higher than that of the plastic deformation stage (0.9398 s) with the low work-hardening index. The nonlinear thermogravimetric curve of the supercooled liquid region and the average incubation time of the serrated flow are crucial to further understand the oxidizability and nitriding capacity of the disordered atoms and the mechanism of plastic strain in the metallic glass field.

Experimental Research on Prestressed Carbon Fiber Reinforced Plastic Reinforced Concrete Decks

A new type of bridge deck structure with prestressed Carbon Fiber Reinforced Plastic Reinforced (CFRP) tendons was designed. Flexural performance tests on the prestressed concrete bridge deck with CFRP tendons were conducted. The cracking and ultimate loads of such bridge deck and the stress states and failure modes of the CFRP tendons were systematically analyzed. Results showed that the bending force process of unbonded prestressed CFRP tendon bridge deck with ordinary steel bars in the tension zone can be divided into three stages, namely, initial elastic loading state, elastic-plastic stage from the appearance of cracks to ordinary steel yielding in the tensile area, and rapid deformation development and destruction stage during tension bearing of the CFRP tendons. The failure modes of unbonded prestressed CFRP tendon bridge deck were caused by the rapid deformation development due to the low modulus of CFRP tendons, and the extension of cracks and crushing failure of concrete were due to the decreased area of effective compressive concrete. The fractures were mostly equidistant parallel cracks. The cracks slowly developed in the early stage, whereas they rapidly developed after ordinary steel yielding.

Seismic performance of a repaired thin steel plate shear wall structure

A multi-ribbed grid of channels can effectively restrain the deformation of an embedded steel plate shear wall, improving the elastic stiffness of the overall structure while enhancing its energy dissipation capacity. Aone-bay, two-story specimen was tested under low cycle reversed loading in two stages. After being damaged in Stage I, the structure was repaired by anchoring the multi-ribbed channel grid. The structure was then loaded to destruction. To investigate the changes in performance of the structure due to reinforcement, comparison and analysis of the structure were conducted for the two stages. The results indicate that in the elastic stage, when the repaired structure is in its normal service state, the deformation of the steel plate is effectively restrained, and the elastic stiffness and energy dissipation capacity is improved. In the elastic-plastic stage, the failure mode of the structure is reasonable, and the hysteresis loop is full as the multi-ribbed channel grid effectively restrains the pinching phenomenon. Based on the results of the experiment, finite element models were established. According to the finite element analysis, the yield load, initial stiffness, and maximum lateral force bearing capacity of the repaired structure improved significantly.

Dynamic impact behaviors and constitutive model of super-fine stainless wire reinforced reactive powder concrete

The dynamic impact behavior of super-fine stainless wire (SSW) reinforced reactive powder concrete (RPC) was studied through split hopkinson pressure bar test with the strain rate range from 94/s to 926/s in this paper. The modification mechanisms of SSW to the dynamic impact performance of RPC were revealed via computed tomography and scanning electron microscope analysis. Experimental results showed that the dynamic impact compressive strength of SSW reinforced RPC increases with the strain rate. The dynamic increase factor of compressive strength is decreased and the strain-rate strengthening effect of RPC is weakened by SSW. The maximum dynamic peak strain of SSW reinforced RPC reaches up to 34,070 µε at the strain rate of 305/s. The limit strain of RPC is decreased because of the lateral confinement effect of SSW. The stress-strain curves of SSW reinforced RPC include elastic stage, elastic-plastic stage and descending stage. The addition of SSW leads 43.5% and 58.2% of increase in dynamic impact toughness and impact dissipate energy of RPC, respectively. Increasing SSW volume fraction makes more SSW to inhibit the generation and propagation of cracks in RPC, thus leading to the decrease of destruction degree. The formation of inter-anchored interface among bundling SSW increases the resistance of RPC to crack development. The dynamic impact constitutive model established on the basis of revised visco-elastic and damage theory can well describe the stress-strain relationship of SSW reinforced RPC at different strain rates, in which the strain threshold is governed by strain rate and SSW volume fraction simultaneously.

Role of layered structure in ductility improvement of layered Ti-Al metal composite

Layered Ti-Al metal composite (LMC) was designed and fabricated by hot-rolling and annealing of pure Ti and Al sheets. The as-prepared composite exhibits high tensile ductility, being superior to any individual Ti or Al sheets. The stress/strain evolution and fracture behavior of the LMC were analyzed by in-situ observations during the tensile deformation. Three deformation stages of LMC were clearly observed by neutron diffraction: elastic stage, elastic-plastic stage and plastic stage. It is found that stress partitioning at the elastic-plastic deformation stage improves the strain balance of LMC, but leads to an internal stress accumulated at the interface. Additionally, a strain-transfer from Ti to adjacent Al layers relieves the strain localization of Ti layers in LMC, which improves the ductility of Ti. Both stress partitioning and strain localization of Ti layers facilitate the nucleation of cracks at a low macro strain. However, the crack propagation is constrained by layered structure. In terms of the Al layers, the constrained micro-cracks relieve the stress concentration in Al layer and improve the ductility of Al layers, so that cracking indirectly affects the plastic deformation behavior of LMC, then improving its entire ductility. This work provides a new structural strategy towards simultaneously improving strength and ductility to develop high performance LMC by structural design.

Research on the Load-slip Properties of Corrugated Rib Connectors’ Push-out Test

The failure characteristic and load-slip performance of corrugated rib connectors under static load were investigated using the push-out test combined with Finite Element Analysis (FEA). The results obtained from experiment and FEA indicate that the shear bearing capacity of the corrugated rib connectors are closely relate with the key factors including cubic strength of concrete (fcu), the open area of the steel plate (Ac1), perforated rebar tensile yield strength (fy) and Cross-sectional area (Ay), horizontal projection area of corrugated rib (= dwhw). In elastic stage, the overall shear stiffness of the corrugated rib connector are mainly affected by the shear stiffness of the concrete bars. And in elastic-plastic stage, the shear stiffness of the concrete bars and perforated rebar pronouncedly influence the overall shear stiffness of the corrugated rib connector. Finally, a linear model and a power law model for the load-slip behavior at elastic stage and elastic-plastic stage are provided based on the regression statistical analysis, respectively.

In-situ tensile testing of ZrCu-based metallic glass composites

ZrCu-based bulk metallic glass composites (BMGCs) are well known for their plastic deformability, superior to traditional metallic glasses (MGs), which is attributed to a unique dual-phases structure, namely, the glassy matrix and unstable B2 phase. In the present study, in-situ tensile testing is used to trace the deformation process of a ZrCu-based BMGC. Three deformation stages of the BMGC, i.e., the elastic-elastic stage, the elastic-plastic stage, and the plastic-plastic stage are identified. In the elastic-elastic and elastic-plastic stages, the yield strength and elastic limit are major influenced by the volume fraction of the B2 crystals. In the plastic-plastic stage, the B2 phase stimulates the formation of multiple shear bands and deflects the direction of shear bands by disturbing the stress field in front of the crack tip. The deformation-induced martensitic transformation of the metastable B2 phase contributes to the plasticity and work hardening of the composite. This study highlights the formation and propagation of multiple shear bands and reveals the interactions of shear bands with structural heterogeneities in situ. Especially, the blocking of shear bands by crystals and the martensitic transformation of the B2 phase are critical for the mechanistic deformation process and illustrate the function of the B2 phase in the present BMGCs.

An analytical analysis of the pullout behaviour of reinforcements of MSE structures

Pullout tests are usually employed to determine the ultimate bearing capacity of reinforced soil, and the load-displacement curve can be obtained easily. This paper presents an analytical solution for predicting the full-range mechanical behavior of a buried planar reinforcement subjected to pullout based on a bi-linear bond-slip model. The full-range behavior consists of three consecutive stages: elastic stage, elastic-plastic stage and debonding stage. For each stage, closed-form solutions for the load-displacement relationship, the interfacial slip distribution, the interfacial shear stress distribution and the axial stress distribution along the planar reinforcement were derived. The ultimate load and the effective bond length were also obtained. Then the analytical model was calibrated and validated against three pullout experimental tests. The predicted load-displacement curves as well as the internal displacement distribution are in closed agreement with test results. Moreover, a parametric study on the effect of anchorage length, reinforcement axial stiffness, interfacial shear stiffness and interfacial shear strength is also presented, providing insights into the pullout behaviour of planar reinforcements of MSE structures.