Axial Compression Tests Research Articles

Axial compression tests on CFRP strengthened CFS plain angle short columns

A comprehensive test program was performed to experimentally investigate the effect of CFRP strengthening on the axial strength and stability of CFS plain angle short columns subjected to monotonic axial compression. A total of 28 specimens were tested by varying the CFRP strengthening configurations for different column heights. Both uni-directional (CF_UD) and bi-directional (CF_BD) CFRP were considered. The influence of various parameters such as the type of CFRP, fiber orientation, and number of CFRP layers was investigated and discussed in detail. For single layer (ply) of CFRP, CF_UD-0° strengthening configuration resulted in maximum increase of axial capacity by 58.33% and 45.72% (in comparison to bare steel specimens), corresponding to 0.5 m and 1.0 m column lengths respectively. All the bare steel and skin-strengthened specimens failed predominantly due to torsional–flexural buckling mode. Additional layer of CFRP wrapping was found to enhance the axial capacity further and CF_UD-0°/BD was found to possess greater capacity in the case of double layer of CFRP. Adopting cardboard in-fill in addition to CF_UD-0° wrap has prevented the torsional mode of buckling and resulted in a peak increase of axial capacity by 192.55% and 240.61% corresponding to 500 mm and 100 mm long specimens, respectively.

A study of dimensional effects on the stress characteristics of Yunnan pine shafts considering seismic strain rates

Abstract The mechanical properties of wood are affected by member size and loading rate. Axial compression tests with different seismic strain rates and sizes of specimens were carried out to investigate the static and dynamic dimensional effects of Yunnan pine timber. And obtained load-displacement curves, compressive strength, modulus of elasticity, peak strain and Poisson’s ratio. Weibull’s weakest chain theory, Bazant’s law of dimensional effects and Carpinteri’s law of multiple fractal dimensional effects were used to analyze the dimensional effects on the compressive strength of wood, and to establish a wood strength model that takes strain rate effects and dimensional effects into account. The results showed that the compressive strength, elastic modulus, and Poisson’s ratio of Yunnan pine wood exhibit both size and strain rate effects. Under the coupling effect of strain rate effect and size effect, the size effect of Yunnan pine wood strength decreases with increasing strain rate, while the strain rate effect increases with increasing size. A size effect model for compressive strength of wood considering strain rate effect based on three theories and experimental data can well describe the dynamic size effect of Yunnan pine wood strength.

Experimental Study on the Mechanical Properties of Recycled Spiral Steel Fiber-Reinforced Rubber Concrete

Recycled rubber (RR) and recycled spiral steel fiber (RSSF) were added to plain concrete (PC) to prepare recycled spiral steel fiber rubber concrete (SSFRC) with matrix strengths of C30, C40, and C50. Strength tests on the PC, rubber concrete (RC), and SSFRC were carried out, including the cube compressive strength, splitting tensile strength, and flexural strength. The effects of RSSF and RR on the mechanical properties of concrete were analyzed. Simultaneously, the stress–strain curve of the SSFRC was obtained through axial compressive testing, and the toughness of SSFRC was evaluated by three indexes: the tensile compression ratio, bending compression ratio, and toughness index. The results show that adding RR to PC results in a decrease in the mechanical properties of concrete with different matrix strengths, and the addition of RSSF can make up for the strength loss of the rubber. The mechanical strength of SSFRC with different matrix strengths increased first and then decreased with the increase in RSSF content. The cubic compressive strength reached its peak value when the content of RSSF was 1%, and the splitting tensile strength and flexural strength reach their peak values when the content of RSSF was 1.5%. RSSF works best with rubber particles at the right dosage to further increase the toughness of the concrete. When the rubber content is 10%, and the RSSF content is 1.5%, the mechanical strength enhancement effect of SSFRC is at its best, and the toughness is also at its best.

3D woven tubular composites with bamboo‐structures for enhanced energy absorption: Designing, manufacturing and performance analysis

Abstract3D woven tubular composites (3D‐WTC), known for their lightweight and high‐strength characteristics, are widely used in various energy‐absorbing components. To enhance the energy absorption capacity of 3D‐WTC, this study conducted a mechanical analysis of bamboo tube structures and proposed concentric circular nested biomimetic structures with “single tube + double ribs” and “double tubes + double ribs.” 3D woven tubular composites with bamboo‐structures (3DWTC‐Bamboo) were fabricated using the vacuum‐assisted resin transfer molding (VARTM) process. Axial compression tests were conducted using a universal testing machine to reveal and discuss the energy absorption capacity and failure modes of 3DWTC‐Bamboo. The results showed that 3DWTC‐Bamboo with a “double tube + double ribs” concentric circular nested biomimetic structures performed exceptionally, with a peak load of 28.93KN and specific energy absorption of 7.74 J·g−1. The failure mode was a hybrid of “rib folding + tube wall buckling.” Finally, finite element analysis of the stress distribution during the compression of 3DWTC‐Bamboo was conducted using ABAQUS, which validated the experimental results. In summary, this work provides a reference for structural innovation in 3D‐WTC and further expands its application in the field of energy absorption.Highlights Propose “single tube + double ribs” and “double tubes + double ribs” structures. Introducing the “rib” structures to enhance the local strength/stiffness. Test results show that 3DWTC‐Bamboo has great potential in energy absorption. The “ribs” can increase the local strength/stiffness of the tube structures.

Axial-compression performance and numerical-simulation analysis of steel tube coal gangue concrete column

Coal gangue is a solid waste produced in the process of coal mining, excessive accumulation will occupy land and pollute the environment. It is one of the most effective means to realize comprehensive utilization of coal gangue by replacing some aggregates in concrete and applying it to engineering structures. In this paper, based on C30 concrete, by changing the replacement rate of coal gangue, slenderness ratio, and steel pipe wall thickness, 17 Coal gangue concrete-filled steel tubular (CGC-FST) columns were designed and made, and the axial compression tests were carried out. The results show that the failure mode of the CGC-FST column is similar to that of CFST, and the annular band shear buckling occurs on the wall of the steel pipe, and the higher the slenderness ratio, the more the number of buckling in the middle. With the increase of coal gangue substitution rate, the ultimate bearing capacity of the CGC-FST column decreases gradually, and the ductility of the specimen decreases slightly. The increase in slenderness ratio reduces the ultimate bearing capacity of the member, the failure form changes from material failure to stable failure, and the material properties are not fully utilized. The most obvious way to improve the bearing capacity and ductility of gangue steel tube members is to increase the steel content. Through the finite element simulation analysis of more working conditions of the CGC-FST column, the calculation formula of the bearing capacity of the CGC-FST column is fitted, which can effectively predict the bearing capacity of the CGC-FST column in a certain range.

Investigation on three-dimensional printed prosthetics leg sockets coated with different reinforcement materials: analysis on mechanical strength and microstructural

Previous research has primarily focused on pre-processing parameters such as design, material selection, and printing techniques to improve the strength of 3D-printed prosthetic leg sockets. However, these methods fail to address the major challenges that arise post-printing, namely failures at the distal end of the socket and susceptibility to shear failure. Addressing this gap, the study aims to enhance the mechanical properties of 3D-printed prosthetic leg sockets through post-processing techniques. Fifteen PLA + prosthetic leg sockets are fabricated and reinforced with four materials: carbon fiber, carbon-Kevlar fiber, fiberglass, and cement. Mechanical and microstructural properties of the sockets are evaluated through axial compression testing and scanning electron microscopy (SEM). Results highlight superior attributes of cement-reinforced sockets, exhibiting significantly higher yield strength (up to 89.57% more than counterparts) and higher Young’s modulus (up to 76.15% greater). SEM reveals correlations between microstructural properties and socket strength. These findings deepen the comprehension of 3D-printed prosthetic leg socket post-processing, presenting optimization prospects. Future research can focus on refining fabrication techniques, exploring alternative reinforcement materials, and investigating the long-term durability and functionality of post-processed 3D-printed prosthetic leg sockets.

Axial Compression Tests for Circular Concrete-Filled Steel Tube (CFST) Columns with Notch Imperfection

Axial Compression Tests for Circular Concrete-Filled Steel Tube (CFST) Columns with Notch Imperfection

Experimental study on axial compression behavior of square pultruded GFRP tubular stub column

To investigate the influence of aspect ratio and width-to-thickness ratio on the axial compression behavior of square pultruded glass fiber-reinforced polymer (GFRP) tubular stub columns, axial compression tests were conducted on 12 GFRP tubular columns. The mechanical properties of the GFRP tubular columns, including load-bearing capacity, initial stiffness, compressive toughness, and ductility coefficient, were analyzed. The test results reveal that all GFRP tubular columns exhibit crushing failure, with specific failure modes, including mid-section fracture and longitudinal tearing along the corners of the columns. The load-bearing capacity is negatively correlated with the aspect ratio and width-to-thickness ratio. The initial stiffness negatively correlates with the aspect ratio, and the compressive toughness negatively correlates with the width-to-thickness ratio. The Hashin damage criteria for the C3D8R solid element was developed by utilizing the explicit finite element subroutine ABAQUS-VUMAT to analyze the axial compression behavior of GFRP tubular columns. Through parameter analysis, the relationship between the load-bearing capacity and fiber orientation was obtained, and an empirical equation for predicting the load-bearing capacity of the GFRP tubular column was proposed.

Effect of recycled coarse aggregate model arrangement mode on the axial compressive performance of MRCAC

The paper presents the results of studies on based the universal morphology of recycled coarse aggregates in reality, an idealized model of recycled coarse aggregates was prepared using stones. Axial compressive strength tests were conducted on prism-shaped specimens of Modeled Recycled Coarse Aggregate Concrete (MRCAC), which were prepared with different old cement mortar coverages and aggregate arrangements. Through comparison with experimental data, the reliability of the finite element analysis model was determined. It was found that the arrangement of MRCA had a significant impact on the failure characteristics and elastic modulus of MRCAC. Thus, different arrangement modes affected the stress distribution within the specimens, resulting in significantly different axial compressive strength.

Design Method for Local Buckling Resistance of Double Steel Plate–Concrete Composite Walls with Stiffening Ribs and Tie Plates

An ordinary double steel plate–concrete composite wall (ODSC wall) is composed of core concrete, the faceplates, and shear connectors such as studs, etc. Based on an ODSC wall, a new type of stiffened double steel plate–concrete composite wall (SDSC wall) is conceived by incorporating additional stiffeners and tie plates on the internal surface, which aims to improve the local stability of the faceplates. In the authors’ previous study, a series of axial compression tests were conducted on the SDSC walls. The SDSC walls in the test showed better mechanical performance, as the presence of stiffeners changed the buckling deformation mode and significantly improved the corresponding local buckling stress and ultimate strength. In this paper, a comprehensive summary of the prior research on SDSC walls is provided, and the effect of the constructive parameters on the local stability is discussed. The results reveal that the modified formula of the critical stress can degrade to the Euler formula when the stiffener-to-stud spacing ratio (i.e., a/B ratio) approaches infinity. What is more, the analysis model is also applicable for DSC walls with enclosed side plates, and the proposed formula can predict the buckling stress of the SDSC walls with different a/B ratios. In addition, according to the analysis of the numerical simulation, a design approach for SDSC walls to prevent local buckling is provided, which is applicable in practical engineering applications.

Experimental study on performance of reinforced concrete short columns repaired and strengthened with Basalt fiber ultra-high-performance concrete (BF-UHPC)

To explore the reinforcement effectiveness of basalt fiber UHPC repair materials on concrete structures, this study designed four types of wrapping materials for C40 concrete short columns (inner columns), and formed four types of composite short columns. Axial compression tests were conducted on these specimens to analyze the effects of wrapping material type, wrapping material thickness, and protective layer thickness on bearing capacity. Additionally, a model for axial compressive bearing capacity of short column specimens, based on the Mander model and relevant parameter modifications, was established. The results show that: (1) All designed short column specimens showed brittle failure in the experiment, and the brittle failure phenomenon during the experiment is like that of ordinary concrete short columns constrained by stirrups. (2) The type of wrapping material and the thickness of the wrapping layer are important factors affecting the axial compressive bearing capacity of the entire short column. (3) Adding an appropriate amount of basalt fiber and nano-silica significantly enhances the reinforcing and repairing capabilities of the repair material, thereby improving the load-bearing capacity of the repaired concrete columns. (4) Based on the Mander model and the correction of correlation coefficients, a model for axial compressive bearing capacity of short column specimens was established.

Experimental and numerical research on the uniaxial behavior of the stiffened circular concrete-filled steel tube stub columns

In large-span bridges or high-rise buildings, CFST columns with large width-to-thickness ratio are often adopted, which require proper stiffening measures to improve the mechanical behaviors. This paper presents a comparative study of circular CFST stub columns with different stiffening methods, including longitudinal stiffeners (cross-shaped, T-shaped and ordinary type), additional reinforcement and headed studs. Axial compression tests have been conducted to investigate the effects of different stiffening methods on the failure mode, ultimate strength and ductility of the circular CFST stub columns. Finite element models are established to simulate the columns’ behaviors and conduct parametric studies. Based on test and simulation results, an axial bearing capacity prediction model for circular CFST stub columns stiffened by longitudinal stiffeners is proposed. It is demonstrated that the failure modes of the steel tube and core concrete are changed by the longitudinal stiffeners. The longitudinal steel stiffeners as well as reinforcing cage can effectively improve the axial bearing capacity and ductility of the columns. The latter is more efficient in promoting the bearing capacity while the former is more efficient in improving the ductility and residual strength. A combination of the additional stirrups and the ordinary stiffeners will be a more economical choice. In addition, the proposed formula gives better prediction accuracy compared to the equations in various design codes.

Finite Element Simulation Parameter Calibration and Verification for Stem Cutting of Hydroponic Chinese Kale

The finite element simulation is a valid way for the rapid development of the root-cutting mechanism for hydroponic Chinese kale. The stem of the hydroponic Chinese kale was simplified as a transverse isotropic elastic body, and axial compression, three-point bending, and shear tests were performed. The ANSYS/LS-DYNA19.2 software was adopted for stem shear simulation, and the regression equation of the maximum simulated shear force was established. The optimized mechanical parameters were determined by minimizing the deviation between the maximum shear force obtained from the simulation and test. The three-dimensional scanning method was employed to establish the geometric model of the hydroponic Chinese kale stem. The cutting finite element simulation model and test platform were constructed. Displacement, deformation, and force measured from simulation and test were compared. Through measurement and simulation calibration, an axial elastic modulus of 6.22 MPa, axial Poisson’s ratio of 0.46, radial elastic modulus of 3.56 MPa, radial Poisson’s ratio of 0.44, radial shear modulus of 0.8 MPa, and a failure strain of 0.08 were determined. During the cutting simulation and test, the resulting maximum displacement deviations of the marking points on the end of the stem were 0.68 mm along the X-axis and 2.83 mm along the Y-axis, while the maximum deviations of the cutting and clamping force were 0.49 N and 0.77 N, respectively. The deformation and force variation laws of the kale stem in the cutting simulation and test process were basically consistent. It showed that the mechanical parameters calibrated by the simulation were accurate and effective, and the stem cutting simulation results with the finite element method were in good agreement with that of the cutting test. The study provided a reference for the rapid optimization design of the root-cutting mechanism for hydroponic Chinese kale harvest.

Unstable Vancouver B1 periprosthetic femoral fracture fixation: A biomechanical comparison between a novel C-shaped memory alloy implant and cerclage wiring.

To compare the biomechanical stability of a novel, C-shaped nickel-titanium shape memory alloy (SMA) implant (C-clip) with traditional cerclage wiring in the fixation of a Vancouver B1 (VB1) periprosthetic femoral fracture (PFF). In total, 18 synthetic femoral fracture models were constructed to obtain unstable VB1 fracture with an oblique fracture line 8 cm below the lesser trochanter. For each model, the distal portion was repaired using a 10-hole locking plate and four distal bi-cortical screws. The proximal portion was repaired using either three, threaded cerclage wirings or three, novel C-shaped implants. Specimens underwent biomechanical testing using axial compression, torsional and four-point bending tests. Each test was performed on three specimens. The C-clip was statistically significantly stronger (i.e., stiffer) than cerclage wiring in the three biomechanical tests. For axial compression, medians (ranges) were 39 (39-41) and 35 (35-35) N/mm, for the C-clip and cerclage wiring, respectively. For torsion, medians (ranges) were, 0.44 (0.44-0.45) and 0.30 (0.30-0.33) N/mm for the C-clip and cerclage wiring, respectively. For the four-point bending test, medians (ranges) were 39 (39-41) and 28 (28-31) N/mm; for the C-clip and cerclage wiring, respectively. Results from this small study show that the novel, C-shaped SMA appears to be biomechanically superior to traditional cerclage wiring in terms of stiffness, axial compression, torsion and four-point bending, and may be a valuable alternative in the repair of VB1 PFF. Further research is necessary to support these results.

Compression performance of FRP bar-reinforced seawater sea-sand concrete encased FRP-wrapped steel tube columns

This paper developed a new type of composite column made of fibre-reinforced polymer (FRP) bar-reinforced seawater sea-sand concrete (SWSSC)-encased FRP-wrapped steel tubes, which is suitable for maritime engineering. In this composite form, the inner steel tube was isolated to the chloride ions by wrapping with an FRP sheet, and FRP bars were employed to reinforce the exterior SWSSC. To avoid/delay the occurrence of internal steel tube buckling, two measures were implemented, that is, filling with ordinary concrete, and bundling and welding using four hollow small-sized steel tubes. The compression performance was explored by axial compression and eccentric compression tests, and three experimental variables were set, including the steel tube thickness (2.5 mm and 5 mm), number of steel tubes (0, 1 and 4), and eccentricity (20 mm, 40 mm and 60 mm). The test results showed that increasing the thickness of the steel tube could improve the bearing capacity and lateral deformation of specimens (e.g., from 32.66 MPa to 36.99 MPa), whereas the number of steel tubes had a minor positive effect on the specimens. Meanwhile, the bearing capacity of the specimens decreased with increasing eccentricity of the eccentric compression test from 41.51 MPa to 36.99 MPa. Finally, a calculation method was proposed to predict the peak eccentric strength of specimens, which can provide a reference for the design of this kind of composite column.

Experimental study of energy‑absorbing and support characteristics of glass microsphere-filled steel tube columns under uniaxial compression.

An innovative energy-absorbing and bearing structure was proposed, which incorporated the coupling of glass microspheres with a metal tube. Glass microsphere-filled steel tube (GMFST) column, consisting of external steel tube and inner glass microspheres, was expected to give full play to the energy-absorbing and load-bearing capacities of the particle while restricting particle flow from collapsing, thereby enhancing the overall structural strength. Four groups of steel tubes and the GMFST specimens were designed and subjected to axial compression tests at four different loading rates to investigate the performance of the structure. These tests aimed to analyze the deformation mode, mechanical response, and energy absorption capacity of the GMFST columns under quasi-static to low-speed compression conditions. The results indicated that the deformation process and failure mode of GMFST columns were similar to those of hollow steel tubes, albeit with a different post-buckling mode. Filling the steel tubes with glass microspheres reduced the load fluctuation range, moderated load-displacement curves, and exhibited a strain rate strengthening effect. The GMFST columns demonstrated superior energy absorption capacity, with significant increases in crush force efficiency, the averaged crush force, and the total absorbed energy, particularly in terms of subsequent support capacity. The load-increasing reinforcement properties enabled GMFST columns to overcome the limitations associated with the unstable post-buckling path of energy‑absorbing damping structure, exhibiting outstanding load-bearing performance and stability in the later stages. The results provided valuable guidelines for designing and engineering high-performance GMFST columns, serving as a new type of energy-absorbing and supporting structure.

Reusing Egyptian in-situ construction &demolition waste(CDW)to produce sustainable concrete.Investigation of compressive &bond strengths using steel & glass fiber reinforced polymer(GFRP)rebars

ABSTRACT This research paper presents the effect of using recycled concrete aggregate (RCA), from the Egyptian construction waste, in different proportions on the bond performance between concrete and its internal reinforcement, where two types of reinforcement were used: a- steel reinforcing bars, and b- glass fiber reinforced polymer (GFRP) bars. 72 samples of concrete were prepared and tested with replacement ratios for natural aggregate (NA) with RCA: 0, 20, 40, 60, 80, and 100 %. The samples were divided into 150 mm cubes to conduct axial compression tests, and pull-out samples to investigate the effect of replacement ratios on the bond between concrete with steel and GFRP rebars. Results showed that concrete loses 26% of its compressive strength after replacing NA with 100% RCA. The results of the pull-out test for steel samples showed 30% higher bonding than GFRP samples. A slight decrease in bond was observed between the control and the tested samples, where the steel and GFRP samples showed a decrease of 5% and 9%, respectively, over the control samples for each, at a replacement percentage of 100%. It was also clear that the steel reinforcement bars had a stronger bond with the concrete, and this can be attributed to the stronger mechanical interlocking of the steel ribs than their counterparts in the GFRP. Failure patterns showed the crushing of concrete with steel bars, in contrast to the GFRP bars, which showed slipping from within the concrete with failure of the ribs in many samples.

Experimental study on axial compression performance of unbonded prestressed mortise-tenon precast concrete mid joint

This paper presents an unbonded prestressed mortise-tenon precast concrete (MTPC) structure, where the beam-column joints are connected by mortise and tenon construction and are tightly crimped using longitudinal prestressed steel strand. It has the advantages of no wet works, easy on-site assembly, short construction period and can be disassembled. First, the structure and assembly method of MTPC joints were introduced. Five full-scale models of MTPC mid joints and one full-scale model of cast-in-place joint were produced. Then the axial compression test was carried out on these models. According to the test results, the damage mode and axial bearing capacity of the MTPC mid joint were analyzed. The analysis results show that the mortise and tenon construction of MTPC joint can effectively transfer the axial compression load, and its axial compression load bearing capacity is about 37%–46% of that of the cast-in-place joint. Unlike cast-in-place joint, there is an obvious compaction stage in MTPC joint under the axial compression. The damage of MTPC joint is concentrated in the beam-column joint area, and the main damage mode is short column damage. The weakest part of the joint is the lower column mortise, which is weakened by the small cross-sectional area and shear-compression force state. The MTPC joint is sensitive to the construction error and assembly error, which will cause the joint to be in eccentric force state and lead to the decrease of its bearing capacity. Finally, this paper proposes a method to calculate the axial compression bearing capacity of MTPC mid joint.

Axial Compression Bearing Capacity of Bolted Drum-Shaped Spherical Shell Joints: Experimental and Numerical Analysis

Bolted drum-shaped spherical shell joints (BDSSJs) represent a type of joint applicable to space grid structures. These joints merge the benefits of both bolted spherical joints and welded hollow spherical joints, embodying features such as a compact size, favorable centerline alignment with members, a high degree of adjustability, and high installation efficiency. Through unidirectional axial compression tests on specimens of BDSSJs, this study examines the stress distribution, force transmission pathways, ultimate bearing capacity, and failure modes of the joint, thereby determining its bearing capacity and presenting a bearing capacity calculation formula for such joints. By establishing a finite element model with parameters identical to the experimental specimens, this study analyzes the force and deformation of BDSSJs under unidirectional compression, identifying the high-stress areas during the compression process of BDSSJs. The findings of this study provide a basis for the practical engineering application of such joints, as well as theoretical support for subsequent dynamic performance into BDSSJs.

Experimental and theoretical analysis of FRP-confined square lightweight aggregate concrete columns under axial compression

The structure of an FRP-confined square lightweight aggregate concrete (LWAC) column was investigated, and it was found to significantly decrease the self-weight while improving the deformation capacity and bearing capacity. Twelve FRP-confined LWAC columns and three unconfined LWAC columns underwent monotonic axial compression tests. The influences of the FRP thickness and type on the compressive performance, stressstrain relationship and strain cloud maps were investigated based on digital image correlation (DIC) technology. Both types of FRP materials demonstrated a noticeable enhancement in both the strength and deformation capacity of LWAC, with CFRP having the greatest effect on strength and BFRP having the greatest effect on ductility. Compared to LWAC columns without confinement, the compressive strength of LWAC confined by BFRP or CFRP increased by 9.4∼21.9% and 24.9∼53.3%, respectively, and the ultimate strain increased by 10.6–14.2 times and 8.0–10.9 times, respectively, with increasing the thickness of FRP. DIC technology was used to accurately measure changes in the strain and the crack development of the specimens, thereby obtaining an accurate rupture strain of the FRP material. The existing models were evaluated using test data, and new models were proposed for FRP-confined square LWAC.