Monotonic Axial Loading Research Articles

Crack propagation in TPMS scaffolds under monotonic axial load: Effect of morphology

In this paper, the mechanical behaviour and failure of porous additively manufactured (AM) polylactide (PLA) scaffolds based on the triply periodic minimal surfaces (TPMS) is investigated using numerical calculations of their unit cells and representative volumes. The strain-amplification factor is chosen as the main parameter, and the most critical locations for failure of different types of scaffold structures are evaluated. The results obtained are presented in comparison with a multiple-crack-growth algorithm using the extended finite element method (XFEM), underpinned by the experimentally obtained fracture properties of PLA. The effect of morphology of TPMS structures on the pre-critical, critical and post-critical behaviours of scaffolds under monotonic loading regimes is assessed. The results provide an understanding of the fracture behaviour and main risk points for crack initiation in structures of AM-PLA scaffolds based on typical commonly used types of TPMS, as well as the influence of structure type and external load on this behaviour.

Predicting ultimate strength and axial strain of circular concrete columns having AFRP wraps and tube-encased confinement

The current study performs an in-depth analysis into the reinforcement of circular concrete columns (CCC) using aramid fiber-reinforced polymers (AFRP), focusing on two distinct techniques: wet-layup wrapping and tube-encasement with manufactured shells. The need for improved forecasting models for AFRP-wrapped concrete structures arises from observed inconsistencies and limited accuracy in existing models, which often fail to fully account for key parameters such as confining stiffness and composite strain. Addressing this gap, our study begins with a comprehensive review of prior experimental research, emphasizing the impact of various parameters on the performance of AFRP-wrapped CCC under monotonic axial compressive loading. To build a robust foundation for this investigation, we compiled an extensive database of experimental outcomes from existing literature, encompassing 180 concrete cylinders wrapped by AFRP. Our analysis meticulously evaluates nine different models designed to predict the ultimate compressive strength and axial strain of circular columns reinforced with AFRP. These models are scrutinized for their accuracy, revealing notable discrepancies, particularly when key parameters are overlooked. In response, we introduce new equations that offer more precise predictions compared to previously proposed models. These novel equations are derived from an extensive statistical analysis, ensuring their reliability and robustness. Prominently, our proposed model for compressive strength demonstrated superior performance with a coefficient of determination (R2 = 0.87), a root means square error (RMSE) of 0.29, and a mean absolute error (MAE) of 22.91. Similarly, the proposed strain model showed a high level of forecasting accuracy, with a coefficient of determination (R2 = 0.82), a root mean square error (RMSE) of 2.79, and a mean absolute error (MAE) of 208.69. To validate our findings, we employed the Taylor diagram and probability density function, which provide a detailed comparison of the forecasting accuracy of our proposed models against existing ones. The outcomes of this study not only enhance the understanding of AFRP-wrapped concrete columns but also offer valuable insights for the development of more effective reinforcement techniques. Our findings are expected to contribute significantly to the advancement of structural engineering practices, particularly in the application of AFRP for strengthening concrete structures.

Numerical Modeling of Steel Fiber Reinforced Recycled Concrete Filled Steel Tube Column Under Cyclic Loading

A finite element model (FEM) was created with the aim of analyzing the behavior of steel fiber reinforced recycled concrete (SFRRC)-filled steel tube columns under combined cyclic loading and monotonic axial load. The FEM considered the effect of steel tube confinement on the inner concrete behavior under cyclic loading. The numerical model was described in detail, with a focus on modeling the materials involved (normal concrete, SFRRC, and steel) under cyclic loading. A constitutive concrete model - with and without considering confinement - was based on utilizing a concrete damaged plasticity (CDP) model. The steel tube - concrete core interface was modeled by a surface-to-surface contact. A stress-strain constitutive concrete model, confined by circular steel tubes, was implemented, and validated using experimental results from the literature. The developed FEM considered various parameters: steel tube thickness, volume ratios of steel fibers, besides strengths of both concrete core and the steel tube. The FEM results showed great similarity to the under- cyclic- loading tested columns. The results indicated that the concrete confining pressure must be considered in CDP model. A good correlation between numerical and experimental findings was obvious, including failure modes, and hysteretic curves of load-displacement.

Hemp Fiber-Reinforced Polymers Composite Jacketing Technique for Sustainable and Environment-Friendly Concrete.

This research suggested natural hemp fiber-reinforced ropes (FRR) polymer usage to reinforce recycled aggregate square concrete columns that contain fired-clay solid brick aggregates in order to reduce the high costs associated with synthetic fiber-reinforced polymers (FRPs). A total of 24 square columns of concrete were fabricated to conduct this study. The samples were tested under a monotonic axial compression load. The variables of interest were the strength of unconfined concrete and the number of FRR layers. According to the results, the strengthened specimens demonstrated an increased compressive strength and ductility. Notably, the specimens with the smallest unconfined strength demonstrated the largest improvement in compressive strength and ductility. Particularly, the compressive strength and strain were enhanced by up to 181% and 564%, respectively. In order to predict the ultimate confined compressive stress and strain, this study investigated a number of analytical stress-strain models. A comparison of experimental and theoretical findings deduced that only a limited number of strength models resulted in close predictions, whereas an even larger scatter was observed for strain prediction. Machine learning was employed by using neural networks to predict the compressive strength. A dataset comprising 142 specimens strengthened with hemp FRP was extracted from the literature. The neural network was trained on the extracted dataset, and its performance was evaluated for the experimental results of this study, which demonstrated a close agreement.

Finite element modelling of pipe piles driven in low-to-medium density chalk under monotonic axial loading

Percussive driving in low-to-medium density chalk creates a thin annulus of fully de-structured ‘putty’ chalk around pile shafts and an outer annular zone where fracturing is more intense than in the natural chalk. This damage and the related generation, and subsequent equalisation, of excess pore pressures impacts the piles’ time-dependent axial loading behaviour, as do other ageing processes. This paper presents finite element analyses of open steel tubular piles driven for the recent ALPACA and ALPACA Plus research projects under monotonic axial loading to failure after extended ageing periods. A nonlinear elastic stiffness model with a nonlocal deviatoric strain-based Mohr-Coulomb failure criterion was employed, with different sets of properties to represent the de-structured, fractured chalk and intact chalk. It is shown that the piles’ axial responses are mainly controlled by the puttified chalk annuli. A simplified but efficient means is adopted to impose pre-loading chalk effective stress conditions that explicitly capture the effects of installation damage and subsequent ageing. The potential for strain-softening in the brittle chalk is examined and the effective stress paths developed in representative chalk elements throughout the loading are considered in conjunction with the mobilisation of accumulated deviatoric strains. The simulations indicate 264% higher shaft capacity in compression than in tension, which is mainly attributed to the internal chalk plug.

Confinement of masonry columns with FRCM: A new confined strength formulation and experimental validation

In this work, a wide experimental dataset about the axial behavior of masonry columns confined with Fabric Reinforced Cementitious Matrix (FRCM) jackets (also refered to as TRM - Textile Reinforced Mortar or TRCC - Textile Reinforced Cementitious Composites), that contains the results from 226 confined specimens, was collected. Data were critically analyzed with the aim of identifying the influence of the most important parameters considered within the dataset (i.e., fibers type and number of layers, masonry type and unconfined strength, mortar type and mechanical strength, the effective lateral pressure, etc.). Further, a review of the main models proposed in different Codes and in literature was carried out, which were then applied to the dataset, highlighting some discrepancies in their predictions. Thus, a new formulation for the confined strength of masonry columns was proposed, aiming to consider also some other influencing variables such as the compressive strength of the masonry blocks and that of the mortar joint. Lastly, the validity of the proposal was verified on a new set of experimental results, which were obtained by the authors testing three unconfined and confined clay brick masonry columns. Specimens were subject to monotonic axial loading under displacement control until failure, and stress and strains were monitored continuously during the test. The jacketing system was realized with one layer of glass-based FRCM (GFRCM).

Experimental and analytical model of CFRP-confined spontaneous combustion coal gangue aggregate concrete

In this study, carbon fiber reinforced polymer (CFRP) confined cylindrical concrete specimens were tested under monotonic axial loading. The effects of the replacement ratio of the spontaneous combustion coal gangue aggregate (SCGA) and stiffness of the CFRP confinement on the mechanical properties of concrete were mainly considered. The results showed that the confinement efficiency of CFRP on the concrete decreases with increasing SCGA content. Despite the increase in the confinement stiffness, the confinement efficiency of the CFRP confinement on high-content SCGA concrete (SCGAC) will also be significantly reduced. Evidently, the influence of aggregate properties on confined concrete cannot be ignored. A CFRP-confined analysis model considering the SCGA replacement ratio was established. Through the verification of existing test data, its accuracy meets the requirements.

Influence of GFRP Confining Tube Parameters in Double-Skin Tubular Short Columns under Axial Loading

Abstract Composite construction with steel and concrete has become a widespread solution in modern construction practices because of its inherent properties such as high strength-to-weight ratio, good corrosion resistance, and high stiffness. Concrete-filled fiber-reinforced polymer (FRP) steel double-skin tubular compression members as vertical load–carrying members in buildings helps in optimizing the advantages of three materials: steel, concrete, and FRP. This study investigates the axial compressive behavior of short, concrete-filled glass fiber–reinforced polymer (GFRP) steel double-skin tubular (GSDST) columns and concrete-filled GFRP tubular (CFFT) columns. Parameters such as the number of FRP layers, hollow section ratio (HSR), variation of diameter of the inner steel tube, and the angle of orientation of the fibers have been examined in this investigation. The experimental study was carried out by performing a monotonic axial compressive loading condition. Three different angles of fiber orientation, 0° along the hoop direction, 45°, and 0°/90° with respect to the axis of the column, were adopted in this study. The ultimate load-carrying capacity, axial displacement, axial and horizontal strains, and failure modes were observed. The experimental results indicate that the structural performance of GSDST columns is significantly influenced by GFRP tube thickness, inner steel-tube diameter, and fiber-orientation angle. Maximum displacement was observed in the specimens with high HSR, thus showing a ductile characteristic in the axial load-displacement behavior. The load-carrying ability of the specimens decreased as the HSR increased. The load-carrying capacity of the specimens increased with the increase in outer GFRP tube thickness. This study demonstrates that GFRP tubes can be used efficiently in the construction field as vertical load–carrying components by enhancing the axial behavior of FRP steel double-skin tubular columns.

Experimental Analysis of the Mechanical Response of Masonry Columns Partially Confined with PBO FRCM (Fabric Reinforced Cementitious Mortar) Composites.

An experimental investigation on partially PBO (short of Polyparaphenylenebenzobisthiazole) FRCM (Fiber Reinforced Cementitious Mortar) confined clay brick masonry columns has been conducted. Ten small-scale specimens measuring 445 mm high with a square cross-section of the 250 mm side have been tested under monotonic axial loading until collapse. Two columns were unconfined, while the remaining ones were confined with single-layer PBO FRCM jackets varying the geometric configuration along their height. The vertical spacing ratio sf'/sf, being sf' and sf the center-to-center and the net spacings between two consecutive jackets, respectively, was considered as the key parameter of the confinement configuration. The failure modes, stress-strain curves and peak axial stress and strain values are reported. The experimental results have been compared to the predictions of models found in the Italian guidelines CNR DT 215/2018 and the American ACI 549-R20 standards. The main aspects analyzed involved (i) the evaluation of the effectiveness of partial confinement on the mechanical response of columns, (ii) the definition of the mechanical and geometrical parameters that influence the structural response of partially confined columns, and (iii) the development of appropriate analytical models for the prediction of the resisting capacity of masonry columns partially confined with PBO FRCM.

Seismic Behaviour of CFST Space Intersecting Nodes in an Oblique Mesh

The design of intersecting nodes in high-rise oblique mesh structures is a critical issue. The existing research on the intersecting nodes of oblique meshes mainly focuses on plane intersecting nodes and monotonic axial compression loads. The plane intersecting nodes cannot consider the contribution of the node’s out-of-plane angle and floor beam to the node’s out-of-plane stiffness in actual structures. In this paper, numerical analysis using ABAQUS was conducted to investigate the mechanical performance of space intersecting nodes of oblique meshes (OMSIN) under cyclic axial tension and compression loads, to provide a reference for the engineering application of oblique mesh structures in seismic regions. Six parameters were considered: the space intersecting angle, the plane angle symmetry coefficient, the plane intersecting angle, the out-of-plane constraint restraint, the steel content of the cross-section, and the concrete strength. The study showed that changes in the thickness of the steel tube wall are unfavourable for the uniform transmission of stress. Increasing the space intersecting angle significantly weakened the seismic performance, and the space angle affects the failure mode of the node. Asymmetric arrangements of the upper and lower plane angles caused nonlinear development of out-of-plane. The ultimate load and overall compressive stiffness of the specimen were positively correlated with the plane angle, and vertical constraints should be applied to the node position of components with plane angles greater than or equal to 70°. The out-of-plane constraint was a key factor affecting the seismic performance of the node, and it was proportional to the ultimate load of the component. In structural design, if the aim is to improve the mechanical performance of the component by increasing the steel content, more enormous out-of-plane constraints should be set to control plane external displacement strictly. The concrete strength is proportional to the ultimate axial load and axial stiffness, and its influence on the mechanical performance in the axial tension direction is not significant. Finally, a dimensionless skeleton curve model of the node was established. The existing formula for the bearing capacity of CFST columns was fitted to obtain the calculation formula for the axial yield and ultimate load of the OMSIN under cyclic loads.

Impact of corrosion on axial load capacity of ageing low-strength reinforced concrete columns with different confinement ratios

Many ageing structures in earthquake-prone regions are vulnerable to failure by seismic actions resulting from the poor detailing, environmental degradation and quality of materials used. Insufficient column confinement and corrosion of the embedded reinforcement have been identified as some of the problems existing within such structures. This paper summarises the results of an experimental investigation into ageing low-strength short-reinforced concrete (R.C.) columns with varying confinement levels and degrees of corrosion. The latter is introduced in a controlled manner using electrolysis. In total, thirty short R.C. columns (15 square and 15 circular) with three confinement ratios and steel corrosion loss (0% to ∼30%) were subjected to monotonic axial load. The experimental results showed rebar buckling was more pronounced at higher corrosion rates and in sparsely confined columns. In addition, the load-carrying capacity of the R.C. columns was significantly affected by corrosion and the degree of confinement.

Compressive behaviors of FRP-confined concrete prepared using spontaneous combustion gangue as coarse aggregate

Thirty-six concrete specimens composed of spontaneous combustion gangue (SCG) were tested under monotonic axial loading. To evaluate the mechanical behaviors of fiber reinforced polymer (FRP) confined SCG concrete, different concrete strengths and the glass FRP (GFRP) tube thickness were considered as variables. The compressive strength and ductility were significantly enhanced when the SCG concrete was confined with GFRP tube. In addition, SCG concrete has a specific expansion characteristic, which exhibits apparent volumetric compaction behavior during loading. Based on the existing model, a new design model of FRP-confined SCG concrete that uses piecewise functions was proposed, and its accuracy was verified.

Experimental study on the axial compressive behaviour of steel reinforced concrete composite columns with stay-in-place ECC jacket

Steel Reinforced Concrete (SRC) column made with high strength materials features excellent load-carrying capacity and energy dissipation capacity, but the compromised ductility issue hinders the widespread application in seismic-prone areas. To overcome this weakness, this paper proposes a novel type of steel-concrete composite column by employing Engineered Cementitious Composites (ECC) as the permanent formwork of conventional SRC column. An experimental program was conducted by subjecting seven stub columns to monotonic axial compressive loading. The test variables in this study include the presence of ECC jacket, the presence of embedded structural steel, stirrup spacing and stirrup configuration. The axial performance were carefully analyzed in terms of load-carrying capacity, initial stiffness, post-peak ductility, damage pattern, as well as the full range load-deformation response. The physical tests confirm the potential of ECC jacket to be used as the permanent formwork of SRC columns as to improve both the construction efficiency and structural performance, and the comparison between the test results and analytical predictions demonstrates the applicability of design equation in EN 1994-1-1 and JGJ 138–2016 to predict the axial capacity of ECC-SRC columns.

Finite Element-Based Performance Analysis of Encased Composite Columns under Monotonic Axial Compression Load

This paper presents the results of an investigation into the performance of fully encased composite columns under monotonic axial load using finite element simulation. The damage characteristics and the performance investigation of the specimen were mainly focused on the influence of the compressive strength of concrete and the size of reinforcement. The concrete material was modeled using concrete damage plasticity (CDP), which incorporates the hardening and softening behaviors, and the steel was modeled using metal plasticity. The results obtained from the current study were validated by using previously conducted experimental work and manual calculation based on Eurocode 4. According to the FEA result, damage to the concrete matrix was significantly minimized with the increase in the strength of the concrete. By keeping other parameters constant, an increase in longitudinal reinforcement diameter minimizes the equivalent plastic strain both in structural steel and reinforcement bars. Furthermore, the results showed that the numerical simulation fairly validated the analytical solution.

Experimental and numerical research on cracking characteristics of medium-reinforced prisms under variable uniaxial degrees of elongation

The main objective of this research is to study the phenomenon of cracking in reinforced concrete (R/C) structural elements, particularly the columns and walls (especially the extreme regions of walls, namely the boundary columns). Various parameters affecting cracking phenomena were studied, e.g. load influence, tensile strain, etc. It has to be noted that load application is a monotonic axial tensile loading that simulates the strain condition taking place at the boundary edges of reinforced concrete seismic walls. Specifically, this type of loading simulates the tensile loading that takes place during the first semi-cycle of loading under dynamic seismic events. Experimental research was carried out by the construction and usage of a group of 4 experimental specimens, subjected to different degrees of elongation. This test group examined the tensile parameters and how they affect the cracking. The test specimens in question were all reinforced with the same medium longitudinal reinforcement ratio (2.68 %) and subjected to tensile degrees 10‰, 20‰, 30‰ and 50‰. Significant conclusions are reached on cracking, e.g. its extent, the size of the cracks, their positions, minimum crack width, maximum crack width, average crack width, and number of cracks.

Axial compressive and seismic performance of GFRP wrapped square RC columns with different scales

The seismic and axial compression behavior of columns wrapped with FRP sheets has been studied experimentally and theoretically over the last two decades. However, most tests and models focused on small-scale columns with/without steel reinforcement. To get better understanding of this strengthening technique and to achieve reliable design approaches for practical applications, further studies should be carried out on full-scale columns with FRP wraps considering the influence of internal steel and column size. Due to such knowledge gaps, this study exhibits experimental results of 17 GFRP wrapped square RC column specimens with side lengths of 350 mm, 495 mm, and 700 mm tested under both monotonic axial compressive load and cyclic lateral load combined with constant axial compression. The results indicate that the FRP confinement effect is highly affected by column size in both axial compression and cyclic loading. Moreover, provisions of three design codes GB50367–2013, GB50608-2020, and ACI440.2R-17 on the axial loading capacity of FRP confined concrete columns are reviewed and verified with the test data. It is suggested that the influence of column size should be further considered in the codes to widen the application range of the present provisions. • 17 column specimens with different scales were tested under two loading conditions. • Failure modes and load-strain relationship were obtained and seismic parameters and strain were analyzed. • Influence of size effect on the performance of FRP enhanced columns were discussed. • Calculation method from three design codes were reviewed and verified.

Constitutive model of lightweight aggregate concrete confined by circular steel tube

To study the constitutive model of lightweight aggregate concrete (LAC) constrained by the circular steel tube, the monotonic axial loading test was carried out on steel tube confined LAC (STCLAC) stub columns, considering the effects of the diameter-to-thickness (D/t) ratio (30.4, 19 and 12.7) and steel grade (Q235 and Q355). The test results showed that the steel tubes of STCLAC columns were bulging outward as a whole without local buckling during the loading process. The D/t ratio for the STCLAC column is recommended that be greater than 19.0. Due to friction stress accumulating at the interface between the steel tube and the LAC core, the steel tube is subjected to longitudinal stress. When the confinement factor (ξ) is less than 2.313, the transverse stress of the steel tube reached its yield strength before the peak load, otherwise it reached the proportional stress without yielding. Using the average transverse stresses along the height of the steel tube, this study calculated the equivalent lateral confining stress of the STCLAC column. The calculation formulas of the compressive stress and corresponding strain of confined LAC were proposed based on the test results. And the constitutive model was also proposed, which is more capable of predicting the stress–strain relationship of the constrained LAC by a circular steel tube.

A phase field approach to fracture for hyperelastic and visco-hyperelastic materials applied to pre-stressed cylindrical structures

In this investigation, the mechanical modeling of nonlinear visco-hyperelastic residually stressed materials obtained from an invariant-based constitutive energy framework is coupled with the phase field approach to fracture. The main target regards the extension of the phase field method to simulate pre-stressed cylindrical structures subjected to monotonic axial pulling load upon failure. This formulation is incorporated into a numerical procedure using the Finite Element Method (FEM), in particular, it is implemented in the commercial FE package ABAQUS as a user subroutine UMAT. Results suggest the dependence of the mechanical behavior and the crack pattern of these structures on not only viscous parameters like the relaxation time and the displacement rate, but also on the strength of the residual stress field, which in turn depends on geometrical characteristics of the cylindrical structure such as the radius or the length. A range of solutions related to crack propagation is shown for different cylindrical structures, from azimuthal crack propagation to axial one. The proposed framework aims to provide an extended application for the already-defined visco-hyperelastic formulation by the inclusion of residual stresses.

Mechanical Properties of Rubberised Concrete Confined with Basalt-Fibre Textile-Reinforced Mortar Jackets

This paper presents an experimental investigation of the mechanical properties of rubberised concrete confined with basalt-fibre textile-reinforced mortar (TRM) jackets. The main aim is to evaluate the effectiveness of the TRM confinement scheme on cylindrical rubberised concrete specimens by examining five different mixtures (rubber content ranging from 10.5% up to 42% of the total aggregate volume), including a plain concrete reference mixture. Unconfined and confined specimens with either one or two TRM layers were subjected to monotonic axial loading. The results indicate a decrease in the compressive strength of unconfined concrete as the rubber content increased. The stress–strain curves of rubberised concrete became smoother at the peak as the rubber content increased, also exhibiting increased axial strain capacity post-peak. Rubberised concrete exhibited less brittle failure than plain concrete, accompanied by increased lateral dilation. Confinement with TRM increased the compressive strength, while also enhanced the performance in terms of toughness and axial deformation capacity compared to unconfined concrete. Overall, it is concluded that there is a promising potential for using TRM-confined rubberised concrete in applications with ductility demands and low environmental footprint specifications.

Model pile behavior in calibration chamber under very large number of cycles of axial loading in saturated clay

ABSTRACT The results of a series of displacement-controlled cyclic axial loading tests of model pile in saturated kaolinite clay, carried out in a calibration chamber, are presented. An instrumented pile-probe was used to investigate the evolution of local skin friction and excess pore water pressure during cyclic loading. After a brief description of the experimental setup and the testing procedure, the tests results are presented concerning the response of the probe during installation, initial monotonic axial loading, cyclic loading up to large numbers of cycles (105 cycles) and post-cyclic monotonic axial loading. During cyclic loading, an initial degradation phase of local skin friction followed by a stabilization phase is observed. Generation of excess pore water pressure occurs during the 60 first cycles followed by a dissipation phase. Parametric study showed that, for initial monotonic loadings, maximum tip resistance and local skin friction are proportional to stress level. Furthermore, excess pore water pressure generated during cyclic loading depends both on initial stress level applied to the clay specimen and cyclic displacement amplitude. A peak value of local skin friction resistance has been observed during post-cyclic monotonic loadings.