Axial Compressive Strength Research Articles

Confinement-based direct design method for fibre reinforced polymer confined CFST short columns

The paper presents a detailed analysis of the behaviour of circular and square concrete filled steel tube (CFST) short columns strengthened externally with carbon or glass fibre reinforced polymer sheets (CFRP or GFRP, respectively). A thorough review of existing test information is presented and discussed, and the most salient parameters in terms of the overall strength are identified. There are a large number of influential and inter-related parameters which affect the load-carrying capacity, including the geometry, cross-sectional shape, type of steel, concrete strength, boundary and loading conditions, and type of FRP. It is shown that existing design approaches do not reliably predict the strength for the full range of possible parameters. Therefore, this paper proposes a new design model to calculate the axial compressive strength of FRP-confined concrete filled steel tubular (CFST) short columns with either a circular or square cross-section. The method accounts for the various complexities which affect the behaviour, yet presents a user-friendly, performance-based design expression. It is based on an evaluation of the lateral confining pressure provided by the both the FRP and the steel tube to the concrete core. This is employed in the confinement-based direct resistance calculations. The paper validates the approach by comparing its capacity predictions with a large database of experimental results and alternative design models available in the literature. The results show that the proposed model provides much accurate strength predictions with greater reliability for the full range of parameters examined, than existing methods.

Preparation and properties of silica/hydroxyapatite whiskers porous ceramics scaffold

To investigate the preparation and properties of the novel silica (SiO 2)/hydroxyapatite (HAP) whiskers porous ceramics scaffold. The HAP whiskers were modified by the SiO 2 microspheres using the Stöber method. Three types of SiO 2/HAP whiskers were fabricated under different factors (for the No.1 samples, the content of tetraethoxysilane, stirring time, calcination temperature, and soaking time were 10 mL, 12 hours, 560℃, and 0.5 hours, respectively; and in the No.2 samples, those were 15 mL, 24 hours, 650℃, and 2 hours, respectively; while those in the No.3 samples were 20 mL, 48 hours, 750℃, and 4 hours, respectively). The phase and morphology of the self-made HAP whisker and 3 types of SiO 2/HAP whiskers were detected by the X-ray diffraction analysis and scanning electron microscopy. Taken the self-made HAP whisker and 3 types of SiO 2/HAP whiskers as raw materials, various porous ceramic materials were prepared using the mechanical foaming method combined with extrusion molding method, and the low-temperature heat treatment. The pore structure of porous ceramics was observed by scanning electron microscopy. Its porosity and pore size distribution were measured. And further the axial compressive strength was measured, and the biodegradability was detected by simulated body fluid. Cell counting kit 8 method was used to conduct cytotoxicity experiments on the extract of porous ceramics. The SiO 2 microspheres modified HAP whiskers and its porous ceramic materials were prepared successfully, respectively. In the SiO 2/HAP whiskers, the amorphous SiO 2 microspheres with a diameter of 200 nm, uniform distribution and good adhesion were attached to the surface of the whiskers, and the number of microspheres was controllable. The apparent porosity of the porous ceramic scaffold was about 78%, and its pore structure was composed of neatly arranged longitudinal through-holes and a large number of micro/nano through-holes. Compared with HAP whisker porous ceramic, the axial compressive strength of the SiO 2/HAP whisker porous ceramics could reach 1.0 MPa, which increased the strength by nearly 4 times. Among them, the axial compressive strength of the No.2 SiO 2/HAP whisker porous ceramic was the highest. The SiO 2 microspheres attached to the surface of the whiskers could provide sites for the deposition of apatite. With the content of SiO 2 microspheres increased, the deposition rate of apatite accelerated. The cytotoxicity level of the prepared porous ceramics ranged from 0 to 1, without cytotoxicity. SiO 2/HAP whisker porous ceramics have good biological activity, high porosity, three-dimensional complex pore structure, good axial compressive strength, and no cytotoxicity, which make it a promising scaffold material for bone tissue engineering.

Mechanical properties evaluation of metacarpophalangeal joint prosthesis with new titanium-nickel memory alloy: a cadaver study

ObjectiveNi-Ti memory alloys are unusual materials for hard-tissue replacement because of their unique superelasticity, good biocompatibility, high strength, low specific gravity, low magnetism, wear resistance, corrosion resistance and fatigue resistance. The current study aims to evaluate its mechanical properties and provide biomechanical basis for the clinical application of the prosthesis.MethodsTen adult metacarpophalangeal joint specimens were randomly divided into a prosthesis group (n = 5, underwent metacarpophalangeal joint prosthesis) and a control group (n = 5, underwent sham operation). Firstly, the axial compression strength was tested with BOSE material testing machine to evaluate its biomechanical strength. Secondly, these specimens were tested for strain changes using BOSE material testing machine and GOM non-contact optical strain measurement system to evaluate the stress changes. Thirdly, fatigue test was performed between groups. Lastly, the mechanical wear of the metacarpophalangeal joint prosthesis was tested with ETK5510 material testing machine to study its mechanical properties.ResultsAxial compression stiffness in the prosthesis group was greater than that in the control group in terms of 30 ° and 60 ° flexion positions (P < 0.05). There was no statistically significant difference between two groups with regards to axial compression stiffness and stress change test (P > 0.05). In the fatigue wear test, the mean mass loss in the prosthesis group’s prosthesis was 17.2 mg and 17.619 mm3, respectively. The mean volume wear rate was 0.12%. There was no statistically significant difference in the maximum pull-out force of the metacarpal, phalangeal, and polymer polyethylene pads between the prosthesis group and the control group specimens.ConclusionsNi-Ti memory alloy metacarpophalangeal joint prosthesis conforms to the biomechanical characteristics of metacarpophalangeal joints without implants, and the fatigue strength can fully meet the needs of metacarpophalangeal joint activities after joint replacement.

Optimization of the rice husk ash production process for the manufacture of magnesium silicate hydrate cements

Different types of amorphous, silica-rich materials can be employed as supplemental cementitious materials (SCM) in Portland cement compositions that are more common. SCMs react with Ca(OH)2 in the presence of Portland cement and a water solution to create calcium silicate hydrate (C–S–H). When produced under specific circumstances, rice husk ash (RHA) contains a high concentration of amorphous silicon dioxide and is utilized as SCM in Portland cement formulations. Similar to this, materials high in amorphous silica, like RHA, encourage the production of hydrated magnesium silicate gels (M-S-H) in reactive magnesium aqueous solutions. Studies examining RHA's capacity to generate M-S-H under various temperature settings, however, are scarce. For the creation of cellulose-reinforced cementitious composites, M-S-H cements, which have superior mechanical qualities and reduced alkalinity (pH 9–10) as compared to Portland cement, are a suitable option. Because of this, the current study assesses the hydration reaction of magnesium oxide with silica produced from RHA and processed by various heat treatments (500, 550, 600, and 650 °C) to generate M-S-H. There were tests for mechanical stability, electrical conductivity, calorimetry, XRD, TG, pH, and more. As benchmarks, compositions containing MgO and commercially active silica (SF) were employed. The findings demonstrate that, in comparison to previous thermal treatments, RHA generated at 500 °C (RHA500) enabled the creation of an increased M-S-H concentration. The axial compressive strength of this composition (MgO/RHA500) in the initial phases is comparable to that of the reference composition (MgO/SF). Since the paste consisting of MgO/RHA500 had the lowest pH values at 30 days of curing, even when compared to the pH of the reference composition MgO/SF (pH 10.04), the calcination of RHA at 500 °C is also the best treatment to lower the alkalinity of the created system. The MgO/RHA500 composition's decreased alkalinity will enable the RHA generated at lower temperatures to be applied in a new way. The RHA, which is already a by-product of the agro-industrial sector with some added value, serves as a predecessor for the creation of M-S-H cement, which will promote both technical and environmental benefits for non-conventional cementitious materials.

Experimental Analysis on the Feasibility of Bamboo Reinforcement in Concrete Mix Design and Comparison with Steel Reinforced Concrete

Besides being chief construction ingredients, concrete and steel produce a high amount of CO2, and high energy consumption promotes global warming. To evade this problem, green and low energy consuming alternative is required. Rapid growing time with the least period to attend optimum strength made bamboo a new immerging mainstream constituent in construction. Bamboo, as one of the probable alternate structural materials, not only promises a sustainable and sturdy option but also reduces the environmental carbon footprint. In this research, article authors replaced steel reinforcement in concrete with bamboo. To establish bamboo as a construction material, a concrete beam of 200 mm × 500 mm is made in which bamboo bars of diameter 20 mm are used with a variation of 1 to 4% of the reinforcement area. Various tests were performed to provide the feasibility of bamboo as construction materials after 28 days of curing, in which test results were found promising. The impact test shows only 25% of wear and tear. Also, bamboo reinforced concrete (BRC) without changing cross sections provided 50% axial compressive strength compared to steel reinforced concrete (SRC). However, in the tensile test, BRC outperformed SRC by providing 50% more resistance against tensile load. Authors also performed rate analysis between SRC and BRC to find that it almost reduces 18% of the cost at a small scale. Hence here, comparative research is provided, and the authors believe that it would pave the road on which forthcoming researchers will walk to reach the destination of finding an alternate, sustainable, and green construction material in the form of bamboo.

Experimental and numerical investigation on strengthening mechanism of rib-reinforced round-over-round RCFDST column jointed with steel beam under cyclic loading

This paper involved both experimental and numerical investigations on the behaviour of twelve types of recycled-concrete filled double-skin steel tubular (RCFDST) structures subjected to the cyclic loading with reinforced ribs at the column–steel beam joints, of which the damage pattern and seismic performance were analysed by varying the ratio of beam–column flexural linear stiffness, axial compression ratio, hollow ratio, type and strength of the concrete, and the length of ribs. The results indicate that the specimens primarily exhibited the damage pattern of the plastic hinge at both ends of the beams, and that the horizontal load–displacement hysteresis curves with full loop at the top of the column were observed. Moreover, the structures composed of recycled concrete from 40 MPa to 60 MPa presented no reduction in ultimate load as well as the joint ductility to those of the ones with normal concrete. Regarding the performance of RCFDST, the optimal ratio of beam–column flexural line stiffness (ki) is found in the range of 1.0 to 1.5. This study demonstrated that the recycled concrete made from the industrialized aggregate formed by crushing waste concrete from road bases has potential application prospects in Concrete-filled double skin steel tubular (CFDST) structures due to its low cost and good seismic performance, including high ultimate load capacity and low energy consumption.

Stress–strain model of steel fibre-reinforced alkali-activated slag cementitious material after high-temperature exposure

Steel fibres can reduce the shrinkage of alkali-activated slag cementitious material (AASCM) and improve their strength. Therefore, it is of great significance to accurately predict the stress–strain relationship of steel fibre-reinforced AASCM after exposure to high temperatures to promote this green building material. The effects of temperature and steel fibres on the axial compressive strength, elastic modulus, peak compressive strain, and stress–strain curve of the AASCM were analysed. The test results showed that after exposure to high temperatures, there were two compression failure modes of AASCM: tensile failure and shear failure. After exposure to 200 °C, 400 °C, 600 °C and 800 °C, the average strength loss rate of AASCM was 38.8%, 58.2%, 75.8% and 90.1%, respectively. Below 600 °C, the steel fibre has a positive effect on the compressive strength, elastic modulus and peak compressive strain of AASCM, with the optimal volume fraction being 1.5%. Based on the test data, the existing models are compared and analysed. And a model for predicting the compressive strength, peak strain, elastic modulus and stress-strain relationship of steel fibre-reinforced AASCM was proposed.

Failure criteria and microstructure evolution mechanism of the alkali–silica reaction of concrete

Abstract In this study, the influence of two distinct reactive aggregate dosages on the alkali–silica reaction (ASR) of concrete was investigated. The expansion ratio, axial compressive strength, splitting tensile strength, and relative dynamic elastic modulus (RDEM) of concrete were considered as the main parameters to study the failure criteria of concrete induced by ASR at 40°C. Microscopic experiments, such as scanning electron microscopy and X-ray computed microtomography, were applied to analyze the damage induced by ASR on the concrete prisms and the propagation of internal cracks of the reactive aggregates in nanospace. The results showed that the two ranges can be used as the failure criteria produced by the ASR of concrete containing 3 and 6% dosages of reactive aggregates at 40°C, respectively, when the RDEM of concrete was reduced to 70‒75% and 85‒90%. Additionally, the results of CT indicated that microcracks tended to extend from the initial defects of aggregate to the cement slurry. Meanwhile, ASR gel packed with the pores, which reduced the porosity. It was noteworthy that the adhesive force between the ASR gel and the cement matrix after filling pores could not make up for the loss of the mechanical properties of concrete.

Comparative study of carbon and glass fiber reinforced polymer composites for the confinement of concrete columns

This study deals with the comparison of unconfined concrete specimens with carbon fiber reinforced polymer (CFRP) and glass fiber reinforced polymer (GFRP) confined concrete specimens using epoxy as matrix. Initially, CFRP, GFRP and epoxy laminates were prepared for the analysis of various mechanical properties like tensile strength, flexural strength and fracture toughness. From the test results, CFRP and GFRP laminates exhibit better properties than neat epoxy laminate. Axial compressive strength, energy absorption characteristics, failure modes of the confined specimens are analyzed. Comparing with unconfined specimens, it is noticed that the axial load carrying capacity of GFRP confined specimens increased by 23%. While the CFRP confined specimen is compared, a considerable enhancement of 57% was noticed with a confinement effectiveness of 1.57. It is observed that confinement by the FRPs can also increase the fracture energy and ductility index significantly, which can avert the catastrophic failure of the structures.

Experimental and Numerical Analysis of Axial Behavior of Triaxial Woven Fabric Confined Concrete Columns

Continuous efforts are being made to improve plain concrete compressive strength and ductility by applying carbon, glass fiber, or hybrid-reinforced epoxy resin composites. The investigation centers on analyzing the axial compressive strength and strain, compressive stress–strain behavior, failure morphology, and crack evolution of the reinforced cylinders. Besides the experiments, non-linear finite element analysis was performed using the finite element (FE) package ABAQUS 2021. The test results indicate that carbon fiber triaxial woven fabric (TWF-C) confinement result in the most significant improvement of 118% in compressive stress than the concrete specimens. On the other hand, glass fiber triaxial woven fabric (TWF-G) confinement shows the highest enhancement of 161% in ductility. The mechanical properties of the sample utilizing glass fiber as the weft yarn and carbon fiber as the warp yarn (TWF-GC2) exhibit superior improvements of 22% in compressive stress and 8% in axial strain compared to the sample using glass fiber as the warp yarn and carbon fiber as the weft yarn (TWF-CG2). Samples with glass fiber as weft yarn show gradual cracks during loading, while carbon fiber as weft yarn show instantaneous damage. The numerical finite element models accurately predict the experimental results of the tested specimens in this study. There were 1.2~3% and 5~10% discrepancies for compressive stress and axial strain, respectively, between experimental and FE results. Overall, the results suggest that Triaxial woven fabric confinement is a valuable technique to improve the strength and strain of concrete and that the type of fibers used could be tailored for appropriate performance characteristics.

Study on the mechanical properties of self-compacting recycled aggregate concrete using CFB slag as fine aggregate

To reveal the influence of CFB slag on the mechanical and expansion properties of self-compacting recycled aggregate concrete (SCRAC), five SCRACs with different CFB slag replacement amounts were made, the cubic compressive strength test, the splitting tensile strength test, the axial compressive strength test, and the dry shrinkage test were carried out. The failure processes and failure forms of SCRAC under compression and tension were observed. The effects of the influence of the CFB slag replacement rate on the basic mechanical properties of SCRAC were analyzed. The conversion relationship between various mechanical indicators of SCRACs was explored. The drying shrinkage performance of SCRAC was tested using the grey theory. The test results indicate that the compressive failure of SCRAC using CFB slag as fine aggregate is similar to that of SCC. The results show that the cubic compressive strength, splitting tensile strength, and axial compressive strength of self-compacting recycled concrete are the highest when the sand replacement ratio of CFB slag is 10%. The proposed conversion relationship between the cubic compressive strength of SCRAC and other mechanical properties indexes has high accuracy. GM (1, N) model and grey correlation analysis were established to analyze the influencing factors of drying shrinkage of SCRAC. The drying shrinkage deformation of SCRAC using CFB slag as fine aggregate has a hyperbola relationship with time, and a lower CFB slag sand replacement rate can compensate for the shrinkage of SCRAC.

Compressive–Flexural Failure Mechanism and Bearing Capacity Calculation of Over-Ranging Tapered CFDST Members for Support Structures of Offshore Wind Turbines

Upon the higher requirement on high-performance structures of large-scale supporting structures of offshore wind turbines, the systematic analysis on the compressive-flexural behavior and ultimate bearing capacity of tapered concrete-filled double skin steel tubular (CFDST) members designed by over-ranging parameters was performed. Investigating the entire-process mechanism, e.g., the moment–deformation response, stress development, interaction stress, and subassembly contribution, was based on the finite element (FE) analysis, where the moment–deformation curve can be distinguished by four characteristic points, and the transverse local buckling of outer tube partly weakens distribution height of interface pressure in compression zone compared to that in tension zone. Influences of material strengths and geometric parameters were examined by the parametric study, e.g., increasing tapered angle (ψ) slightly reduces the bearing capacity; the higher axial compression ratio (n) contributes a noteworthy action on the post-peak behavior and carrying capacity, e.g., the bearing capacities at n = 0.9 and n = 0.5 reduce by 64.14% and 18.44% compared to capacity at n = 0.1, respectively; influence of Do/to ratio is more significant than Di/ti ratio. Subsequently, the modified cross-sectional stress integration (CSI) method was proposed to predict the moment–strain (M-ε) curves of tapered CFDST members; meanwhile, a confined concrete model with transverse confinement stress as an explicit parameter was modified, and influences of different confined concrete models on predicting M-ε curves were compared. Finally, design methods based on the modified CSI method and limit state method were proposed as a simplified calculation method to determine the correlative relationship of axial compressive strength and moment-resisting capacity (N-M curve).

Numerical simulation and theoretical analysis on RECC ring beam joints for RECC-encased CFST composite columns

The failure mechanisms of reinforced engineered cementitious composite (RECC) ring beam joints were numerically analysed using finite element (FE) software of ATENA. The failure mode, load-carrying capacity, ductility, and distribution of the strain in the steel reinforcement were comprehensively investigated. The simulation results showed that the RECC ring beam significantly contributed to the mechanical property of the joint. Part of the circumferential reinforcement in the ring beam contributed to the shear strength and improved the strength of the core ECC by the restraint effect. A total of 46 specimens were subsequently investigated to examine the influences of the circumferential reinforcement ratio, stirrup ratio, axial compressive ratio, tensile properties and compressive strength of ECC on the seismic behaviour of RECC ring beam joints. Finally, a simplified softened strut-and-tie model was proposed to predict the shear-carrying capacity of the RECC ring beam joint.

Comparative study on mechanical and environmental properties of coal gangue sand concrete

To reduce the adverse impact of coal gangue heaping and save natural resource, artificial coal gangue sands are utilized as fine aggregates in the concrete preparation. The mechanical and environmental properties of coal gangue sand concrete were studied experimentally and theoretically by considering concrete strength grades (C30, C50) and replacement ratios (0, 25%, 50%, 75%, 100%). The results show that coal gangue sand will weaken the adhesion performance of the transition zone between cement mortar and coarse aggregate. The elastic modulus and axial compressive strength of coal gangue sand concrete were decreased by increasing the replacement ratio regardless of concrete grade. When the replacement ratio is 100%, the elastic modulus and axial compressive strength of C30-grade concrete were reduced by 2.9% and 12.6% respectively whilst the values of C50-grade concrete were 5.0% and 21.5% respectively. Based on the tested results, the prediction formulas of the mechanical properties and the uniaxial compressive stress–strain model of the coal gangue sand concrete under different replacement ratio are proposed. Through life cycle assessment, it is found that the replacement ratio of the coal gangue sand is negatively correlated with environmental impact and willingness to pay (considering transport cost), and positively correlated with willingness to pay (without considering transport cost). The balance point is defined by the environmental influence of coal gangue sand concrete when the willingness to pay (considering transport cost) of coal gangue sand concrete under different replacement ratio is equal. According to the tested results, the prediction formula of the balance point under different transport distance is proposed. When the consistent transportation distance of gangue sand and natural sand exceeds 140 km, the utilization of coal gangue sand can produce good environmental benefits.

Hierarchical Cellulose Aerogel Reinforced with In Situ-Assembled Cellulose Nanofibers for Building Cooling.

The development of new structural materials for passive daytime radiative cooling (PDRC) of buildings will significantly reduce global building energy consumption. Cellulose aerogels are potential PDRC materials for building cooling, but the cooling performance and mechanical strength of cellulose aerogels are considered as challenges for their practical applications. Herein, a bio-inspired hierarchically structured cellulose aerogel (HSCA) was fabricated through an assembly strategy assisted by a high-voltage electrostatic field. The HSCA possesses outstanding PDRC performance and moderate mechanical strength owing to aligned hierarchical porous network microstructures reinforced with in situ-assembled crystalline cellulose nanofibers. Promisingly, the HSCA achieves a max cooling temperature of 7.2 °C and exhibits 1.9 MPa axial compressive strength. There was no significant cooling performance degradation after the hydrophobically modified HSCA was placed outdoors for 3 months. A simulation of potential cooling energy savings shows that by using HSCA as the building envelopes (side wall and roof), it can save 52.7% of cooling energy compared to the building baseline consumption. This new strategy opens up the possibility of developing advanced functionally regenerated cellulose aerogel, which is expected to provide a revolutionary improvement in aerogel materials for building cooling.

Axial compressive behavior of circular composite columns with external confinement

With the advance of externally confined composite columns, a generic model that can predict the ultimate axial compressive strength of both circular concrete-filled steel tube (CFST) and concrete-filled double skin steel tubes (CFDST) short columns with external confinement is very attractive. For this purpose, a rich experiment database of composite columns is assembled, guides to build up this database are outlined, and its limitations are also summarized. Based on some fundamental considerations, a simple formula for estimating ultimate axial compression of circular composite short columns is proposed first. The hoop and longitudinal stresses of outer and inner (if any) steel tubes are then determined by the stress analysis, from which the assumption frequently used in previous studies that the sandwiched concrete in a CFDST column is under uniform confinement is demonstrated to be unreasonable. Besides, the additional external confining pressure provided by external confinement in the form of steel spirals, rings, jackets, or tie bars is thoroughly investigated. Further, to comprehend the triaxial strength of infilled concrete in both CFST and CFDST columns, a novel concept of equivalent confining stress that can reflect both uniform and non-uniform confinement effects is defined, with which a modified Power-law failure criterion is established. Model validations illustrate that this generic model can reasonably estimate the strength of externally confined CFST and CFDST columns. Although it currently slightly underestimates the strength of ring-enhanced CFDST columns, this limitation can be easily overcome by recalibrating some coefficients without rebuilding the proposed framework.

Shear behaviour of SWSS-SCC beams reinforced with GFRP bars and Stirrups: Experimental and analytical investigations

This paper presents a study of shear behaviour of sea-water and sea sand self-compacting concrete (SWSS-SCC) beams reinforced with glass fibre reinforced polymer (GFRP) bars and stirrups. Nine full-scale beams were conducted and tested under four-point loading up to failure. The investigated experimental variables were the shear-span ratio, configuration of GFRP stirrups, type of the concrete, longitudinal reinforcement ratio and beam depth. The crack pattern, failure mode, load–deflection response, load–strain response and shear capacity of concrete beams were discussed. It is evident in the test results that the ultimate shear capacity of test specimens is enhanced by reducing the shear-span ratio, using the GFRP stirrups, improving the longitudinal FRP reinforcement ratio and increasing the beam depth. The shear behaviours of SWSS-SCC beam reinforced by GFRP bars and stirrups were found to be similar to that of fresh-water and river sand self-compacting concrete (FWRS-SCC) beam. The ultimate shear capacity of the test beams was predicted by the theoretical models reported in the literature. In addition, the effect of the experimental parameters on shear capacity was discussed and the theoretical models of shear strength were evaluated based on the summarized database. It is found that the nominal shear strength is barely affected by the axial compressive strength and is optimal when the longitudinal reinforcement ratio is about 2%. The CSA-S806 2012 specification has more accurate prediction results for the shear capacity of concrete beams reinforced with FRP bars and stirrups.

Materials Characteristics of Soil-cement Samples under Various Maintenance Conditions

Subsidence of embankment foundation at the approach roadway is quite common in South Vietnam because natural soil layers are high water content and low bearing capacity. Soil-cement columns could be a potential method to deal with foundation subsidence. A critical issue is to determine proper soil-cement mixtures, mainly depending on maintenance conditions. In this study, materials characteristics of soil-cement samples are experimentally tested under various maintenance conditions. To achieve the objective, first, we drill to get natural soil samples at various depths for different boreholes located in southern Vietnam. Second, soil samples are used to fabricate soil-cement cylinder samples. Third, a set of fabricated samples are maintained under various environmental conditions for 7, 14, and 28 days. Last, experimental tests are conducted to test axial compressive strength to evaluate the effects of environmental parameters on strength development. The result reveals that the proportion of soil cement should be properly designed for soil layers to maximize the performance of the soil-cement column.

Axial compressive strength predictive models for recycled aggregate concrete filled circular steel tube columns using ANN, GEP, and MLR

In recent years, recycled aggregate concrete (RAC) has been used as a suitable solution to solve the problems related to the disposal of construction waste and contribute to sustainable environmental development. However, RAC has defects such as low modulus of elasticity and low compressive bearing capacity, which limits the use of RAC only in non-structural cases. Using composite columns in construction is an excellent way to overcome this limitation. Thus, increasing the use of these columns makes it possible to predict their compressive strength to assist in their design. As part of this study, several artificial intelligence algorithms, including the ANN, the GEP, and the MLR, have been analyzed to predict the compressive strength of recycled aggregate concrete-filled circular steel tubes (RACFCST). A total number of 103 valid experimental data were collected from earlier investigations and the models were trained by 75% of them; the rest were considered for testing. RACFCST's compressive strength was investigated as the target of the models. In addition, the proposed models were evaluated by contrasting them to code equations like ACI, Eurocode, AIJ and DL/T to determine whether or not they were valid and whether or not they were predictable. The findings of this research suggested that all three models utilized in this investigation produced accurate predictions when compared to the results of the experiments. As a consequence, the values of R2 in all three models were greater than 0.9, but the ANN model, which had an R2 value of 0.993, demonstrated the highest level of accuracy. While among design code equations, DL/T with R2 equal to 0.957 showed the best performance in predicting the results.

Experimental study of the behavior under axial compression of steel tube confined concrete with a circular hollow section (STCC-CHS)

A new type of steel tube confined concrete columns (STCC) in which the outer steel tube only confines the core concrete and does not directly bear the axial load. Based on this, a new type of steel tube confined concrete with a circular hollow section (STCC-CHS) column was presented in this article. It demonstrated high strength and relatively light weight, high economic efficiency and promises easy installation. Axial compression tests were conducted to quantify the effects of the diameter-thickness ratio and the hollow ratio on the failure modes, the ultimate strength in axial compression, strain and stiffness. Constraint effects and ductility were also analyzed. The test results show that the outer steel tube effectively delays local buckling failure. The smaller the hollow ratio and the smaller the diameter-thickness ratio, the greater a column's bearing capacity. The observed ultimate compressive strength is compared with STCC and CFDST components. The experimental data are used to test the utility of the recommended formulas for predicting the axial bearing capacity of such columns, with several different models of the confined concrete strength.