Axial Compression Tests Research Articles

Axial Compression Performance Test and Bearing Capacity Calculation Method of Square Steel Tube–Timber–Concrete Composite L-Shaped Columns

The square steel tube–timber–concrete composite L-shaped columns are lighter in weight due to the inclusion of wood and exhibit superior seismic performance. This combination not only reduces transportation and labor costs but also enhances earthquake resistance. The wood contributes lightness and flexibility, the steel provides strength, and the concrete offers excellent compressive performance, thereby achieving an optimized design for performance. To investigate the axial compression performance of square steel tube–timber–concrete composite L-shaped short columns, axial compression tests were conducted on eight groups of L-shaped columns. The study examined ultimate load, failure modes, load–displacement relationships, initial stiffness, ductility, and bearing capacity improvement factors under different slenderness ratios, steel tube wall thicknesses, and wood content rates. The results show that the mechanical performance of the composite columns is excellent. Local buckling of the steel tube is the primary failure mode, with ‘bulging bands’ forming at the middle and ends. When the wood content reaches 25%, the synergy between the steel tube, concrete, and wood is optimal, significantly enhancing ductility and bearing capacity. The ductility of the specimen increased by 31.1%, and the bearing capacity increased by 4.14%. The bearing capacity increases with the steel tube wall thickness but decreases with increasing slenderness ratio. Additionally, based on the Mander principle and considering the partitioned constraint effects of concrete, a simplified calculation method for the axial compressive bearing capacity was proposed using the superposition principle. This method was validated to match well with the test results and can provide a reference for the design and application of these composite L-shaped columns.

Axial Compressive Behavior and Calculation Model for Axial-Compressive-Load-Carrying Capacity of Locally Corroded RC Short Columns

The individual effects of the main reinforcement corrosion and stirrup corrosion on the axial compressive behavior of reinforced concrete (RC) columns were evaluated through axial compression tests on 10 full-scale short columns. The primary experimental parameters were the corrosion location and the corrosion ratio of the steel bar. The electrochemical accelerated corrosion method was applied on nine of the columns, including three columns corroded in the main reinforcement, three columns corroded in the stirrup, and three columns corroded in both the main reinforcement and stirrup. The full-field displacement of the column and strain of concrete were evaluated using a non-contact 3D-DIC (digital image correlation) technique. The results indicated that, with the increase in the main reinforcement corrosion ratio, the width of the longitudinal corrosion crack increased. The transverse corrosion cracks appeared when the stirrup corrosion ratio is larger than 8%, and the increase in stirrup corrosion ratio increased the crack number, but had little effect on the crack width. Compared to the non-corroded RC column, the peak load of specimens with main reinforcement corrosion ratios of 8.02%, 9.01%, and 19.27% decreased by 10.53%, 13.56%, and 19.77%, respectively, and that of the specimens with stirrup corrosion ratios of 7.08%, 12.33%, and 24.36% decreased by 11.59%, 12.07%, and 17.15%, respectively. The axial-compressive-load-carrying capacity of RC columns decreased almost linearly as the corrosion ratio of the main reinforcement increases, while it exhibited an approximately bilinear degradation as the corrosion ratio of the stirrups increases. The stirrup corrosion ratio had less effect on the axial compressive loading capacity of the RC column when it was larger than 7.5%. A model for calculating the axial-compressive-load-carrying capacity of the corroded RC short columns was developed based on the impact mechanisms of the corroded main reinforcement and stirrups on the columns’ axial compressive behavior. The calculated results closely matched the test data, demonstrating that the proposed model can reliably predict the residual load-carrying capacity of corroded columns.

Effects of undulating printing paths on axial compressive behaviors of 3D-printed continuous fiber-reinforced multi-cell thin-walled structure

Thin-walled structures are widely used in passive safety systems of the vehicles because of their excellent lightweight and stable progressive deformation behavior. Recently, continuous fiber 3D printing technique has been successfully applied in the manufacturing of thin-walled structures, providing a promising path to meet increasing requirements for energy absorbers as vehicle speed increases. This paper proposed a range of novel undulating printing paths to fabricate two kinds of continuous Kevlar fiber reinforced multi-cell thin-walled structures (CFMSs) with different cross-section shapes, named MT1 and MT2, respectively. For each type of CFMS, three different printing paths (moving back and forth between two layers) were designed to manufacture CFMS with the wall thickness comprised of only a single deposited line. The axial compressive tests were conducted to investigate the compressive response of CFMSs. It was found that undulating printing paths affect both the mechanical behavior and collapse mode of CFMSs. During the compression process, MT1 and MT2 printed with path 3 showed progressively folding deformation modes (differed from the progressive crushing mode of composite laminated thin-walled structures). Thus, compared to MT2 printed with path 1 and path 2, which exhibit global buckling, MT1 and MT2 printed with path 3 exhibited more stable energy absorption performance. Besides, although the local failure mode in different CFMSs caused by the same path was similar, the same printing path had different influences on the axial compressive properties of different CFMSs.

Comparative study of failure mechanism of CFRP partially confined normal strength concrete (NSC) and UHPC cylinders under axial compression

Ultra-high performance concrete (UHPC) holds significant potential in marine structures due to its superior compressive strength and enhanced durability in comparison to normal strength concrete (NSC). Carbon fiber-reinforced polymer (CFRP) confinement has been proven to improve these properties further. However, the compressive behavior of CFRP-confined UHPC, especially for partial confinement, presents complexities arising from the intricate interaction mechanism between UHPC and wrapped CFRP strips. To address this issue, the present study conducted axial compression tests accompanied by digital image correlation (DIC) analyses. Failure modes, stress-strain behavior, hoop strain distribution, and cracking evolution of CFRP partially confined NSC/UHPC were elucidated, thereby uncovering the underlying load transfer mechanism between NSC/UHPC and wrapped CFRP strips. Research outcomes show that the enhancement in compressive strength fcc/fco (0.99 ∼ 1.43) and strain εcu/εco (1.51 ∼ 2.59) of CFRP partially confined UHPC is relatively lower than the NSC counterparts (1.28 ∼ 2.98 and 3.82 ∼ 15.14, respectively). Moreover, lower hoop strain efficiency εh,rup/εfrp can be found for CFRP partially confined UHPC compared to NSC (0.61 vs. 0.86). These phenomena were primarily attributed to the localized shear-cracking pattern and low dilation behavior of confined UHPC. Based on the experimental results, the elucidation of the underlying load transfer mechanism between UHPC/NSC and wrapped CFRP strips provides valuable insights into comprehending the compressive behavior of CFRP partially confined UHPC. Finally, the “arching effect” is found to exhibit limited effect on the ultimate condition’s prediction of partially confined UHPC according to the failure mechanism and Li et al.’s model can reliably predict the ultimate conditions among the existing models.

Axial compressive properties of GFRP-reinforced PVC-based glued wood-plastic composites column

Wood-plastic composites (WPCs) are environment-friendly materials, which are always used in decoration engineering and outdoor engineering. However, WPCs cannot be directly used as bearing structural members especially columns for their poor tensile and compressive properties and great creep under long-term loading. This study presented an innovative approach of using glass fiber reinforced polymer (GFRP) to reinforce PVC-based glued WPCs short columns. Three effective reinforcement methods were proposed: embedding GFRP bars, wrapping GFRP sheets around the outer surface, and GFRP bars and sheets compound reinforcement. Axial compression tests were conducted to evaluate the load-bearing capacity and deformability of the columns. The results showed that the outer GFRP sheets effectively inhibited the cracking of adhesive layers, leading to a remarkable enhancement in ductility and stiffness of the WPCs columns. Moreover, the ultimate bearing capacity of GFRP bars/sheets compound reinforced columns increased by over 140%. Finite element (FE) analysis was employed to investigate the influence of GFRP reinforcement methods, aiming to obtain the optimal design solution of WPCs columns. A theoretical formula was established to calculate the axial compressive capacity of GFRP-reinforced WPCs columns, and its accuracy was validated through experimental tests and FE modeling.

Research on axial compression behavior of cold-formed steel built-up T-shaped columns

A series of axial compression tests were conducted on cold-formed steel (CFS) built-up T-shaped columns consisting of three identical single-limb sections connected by longitudinally arranged high-strength bolts and filler plates at the webs. At first, the buckling behavior, failure mode, ultimate bearing capacity, and load response curves of columns are analyzed. Subsequently, finite element models of tested columns were then developed and validated to provide a base for conducting parametric studies of built-up T-shaped columns with different slenderness ratio, web height to plate thickness ratio and bolt spacing. Finally, the design methods in the Chinese code GB50018–2002 and AISI S100–16 specifications for predicting the resistance of the built-up T-shaped columns were evaluated by using both the test and numerical results. The study shows that the current design procedure in AISI S100–16 are unstable in predicting the resistance of the built-up T-shaped columns within a certain range of overall slenderness ratio, while the provisions in the Chinese code GB50018–2002 are overly conservative. Hence, a reliable design procedure is proposed based on the the Effective Width Method (EWM) in the Chinese code GB50018–2002 equations obtained from the paper. The strength predictions of the proposed design procedure match well with those of experimental studies in the literature and the experimental and numerical studies of this paper.

Axial compressive behavior and capacity prediction of concrete-filled cold-formed lipped channel PEC stub columns

The stability and capacity of thin-walled steel columns can be considerably upgraded by filling concrete into hollow spaces surrounded by cold-formed lipped channel (CLC) and external battens. However, there is limited experimental data available, especially for the axial compression behavior of concrete-filled CLC partially encased composite (PEC) columns. This paper aims to investigate the compressive behavior of CLC-PEC short columns and presents an analytical model for predicting the axial capacity of the column. The study explores the influences of cross-sectional dimensions and external batten plate configurations on the compressive performance of CLC-PEC columns through axial compression tests conducted on 12 short column specimens. The results indicate that the failure modes of the specimens involve localized concrete spalling on the exposed side at the lower part of the column, along with a elephant foot-shaped buckling of the cold-formed steel lipped channel. The damage surface of the confined concrete was obtained by circumferential cutting of the buckling location. The findings highlight the significant influence of the character of the CLC section on the ineffectively confined area at the failure surface, with a dumbbell-shaped effective confinement zone revealing the presence of a highly confined area. Based on the calibrated failure surfaces, a numerical model-based study of the axial stress distribution in the concrete core was then carried out to estimate the confinement effect of the columns under peak loading. The study employed multiple regression analysis to quantify the area ratio of the confined zone to the concrete core based on finite element analysis (FEA) results from 143 CLC-PEC columns. The proposed model was evaluated against test results and found to be more reliable than axial compression loads based on the superposition strength method. The proposed axial capacity of short columns takes into account the slenderness ratio of each member.

Comparison of Three Internal Fixation Constructs for AO/OTA 33-A3 Distal Femoral Fractures: A Biomechanical Study.

To compare the biomechanical performance of three internal fixation constructs for AO/OTA 33-A3 distal femoral fractures. Thirty AO/OTA 33-A3 synthetic distal femoral fracture models were constructed and randomly divided into three groups. Group A (dual-plate construct) was fixed with a medial locking plate combined with a less invasive stabilization system (LISS). Group B was fixed with a retrograde femoral nail (RFN) combined with an LISS (RFN + LISS construct), and Group C was fixed with a retrograde tibial nail (RTN) combined with an LISS (RTN + LISS construct). The axial displacement, axial stiffness, torsional displacement, torsional stiffness and maximum failure load of different internal fixation constructs were recorded and statistically analyzed. In the axial compression test, the average stiffness of Group C was significantly higher than that of Groups A and B, and the average displacement of Group C was significantly smaller than that of Groups A and B. In the torsion test, the torsion degree of Group C was significantly lower than that of Groups A and B, and Group C had a higher torsional stiffness than Groups A and B. In the axial compression failure test, the average ultimate load (a displacement greater than 5 mm) of Group C was significantly higher than that of Groups A and B. The biomechanical strength of the RTN combined with a plate is higher than that of the RFN combined with plate and dual-plate constructs, which can be used as an internal fixation option for the treatment of comminuted distal femoral fractures.

Manuscript title: Experimental investigations of concrete-filled double skin steel tube column-column grouted connection under axial compression

This paper presents a novel grouted connection joint for prefabricated CFDST columns. In order to ascertain the reliability of this grouted connection, axial compression tests were conducted on 24 CFDST columns with grouted connections and 3 CFDST columns without grouted connections. The test parameters were grout strength, casing tube length, and length-to-diameter ratio. The results showed that the stub columns failed due to local buckling and the slender columns failed due to global buckling with significant lateral flexural deformation. CFDST columns with grouted connections exhibited a similar or even higher ultimate bearing capacity and much higher later bearing capacity than conventional CFDST columns. The ultimate bearing capacity of CFDST columns with grouted connections is influenced by the casing tube length and the length-to-diameter ratio. The increase in casing tube length leads to an increase in bearing capacity, while an increase in length-to-diameter ratio results in a decrease. Enhancing the grout strength does not significantly improve the ultimate bearing capacity. Furthermore, the effects of each test parameter on the stiffness, strength and ductility of the CFDST column-column grouted connections were evaluated. Finally, by considering the interaction between components and the impact of casing tube length on bearing capacity, a prediction equation for the ultimate bearing capacity of CFDST column-column grouting connections was developed. This equation can offer accurate predictions with an average error of less than 1 % to provide a reference for the joint design.

Effect of Pulp Chamber Access, Instrumentation, Obturation, and Restoration on the Fracture Resistance of Endodontically Treated Canine Teeth in Dogs.

Veterinary studies documenting the effect of endodontic treatment on tooth fracture resistance are scarce. The objective of this ex vivo study was to evaluate the effects of mesial access preparation and restoration, as well as pulp chamber access, instrumentation, obturation, and restoration, on the fracture resistance and characteristics of canine teeth in dogs. Sixty-five dog canine teeth were divided into 4 groups: 1. Standard endodontic treatment through a mesial access only; 2. Treatment as per group 1, adding an incisal access, instrumentation and obturation of the pulp chamber, and restoration of the access; 3. Treatment as per group 2, without pulp chamber obturation or restoration of the incisal access; and 4. Untreated teeth. The fracture resistance and characteristics of each group were documented using axial compression testing, angled 45° disto-occlusal to the long axis of the crown. The maximum force prior to fracture in groups 1, 3, and 4 were not statistically different, demonstrating that restored mesial and incisal accesses with pulp chamber instrumentation did not statistically affect fracture resistance. However, obturated and restored group 2 teeth demonstrated decreased fracture resistance compared to all other groups (P < .001). Additionally, 26.7% of group 1 teeth sustained complicated crown fractures, while 100% of group 2 teeth fractured within the obturation or restorative materials, preventing pulp exposure in these cases. Although the cause and clinical importance of decreased tooth fracture resistance following pulp chamber obturation and restoration remains unknown, it may provide protective value for maintaining a coronal seal in the event of tooth fracture.

Experimental study on axial compression performance of steel tube confined concrete after freeze-thaw cycles

To investigate the axial compression performance of steel tube-confined concrete short columns subjected to freeze-thaw cycles, this study fabricated 30 specimens. Subsequently, axial compression tests were conducted on these specimens after exposure to freeze-thaw cycles. The experimental setup accounted for variations in parameters such as the number of freeze-thaw cycles, concrete strength grade, aspect ratio, and relative slip damage at the interface. The results indicate that, regardless of the presence of relative slip damage at the interface between the steel tube and concrete, the failure mode of the short column remains consistent for a given diameter-to-thickness ratio. Furthermore, it was found that the circumferential constraint coefficient significantly influences the failure mode while exhibiting minimal sensitivity to freeze-thaw degradation. As the number of freeze-thaw cycles increases, there is a notable reduction in load corresponding to the inflection point on the load-lateral deformation relationship curve. Concurrently, although there is an overall slight decrease in longitudinal stress ratios, transverse stress ratios exhibit an increase. To validate the trends regarding how freeze-thaw cycles affect longitudinal and transverse stress ratios, we employed a self-designed program for their calculation.

Five states of reduction in OTA/AO A1.3 intertrochanteric fractures of the femur a biomechanical study

ObjectiveThis study aims to analyze the differences in mechanical stability of OTA/AO 31A1.3 intertrochanteric fractures under various reduction conditions.MethodsTwenty standard synbone artificial femur test bones were selected for the OTA/AO 31A1.3 intertrochanteric fracture model. The models were divided into five groups according to their reduction state: positive support, neutral support, negative support, varus fixation, and valgus fixation, with four specimens in each group. All models were fixed using PFNA intramedullary fixation and subjected to static axial compression tests. The subsidence displacement of the proximal femur under different loads and the axial stiffness of the model were measured to verify the mechanical stability of the OTA/AO 31A1.3 intertrochanteric fracture under different reduction conditions.ResultsAfter the static axial compression test, the proximal femoral subsidence displacement in the positive support and neutral support groups was lower than that in the negative support, valgus fixation, and varus fixation groups (p < 0.001). The axial stiffness of the model was highest in the positive support group. Significant differences in subsidence displacement and axial stiffness were found between the groups (p < 0.001). The positive support group demonstrated the best mechanical stability, while the varus fixation group showed the poorest performance.ConclusionPositive support of the medial cortex can be regarded as the best reduction state for OTA/AO 31A1.3 intertrochanteric fractures, suggesting that this approach should be preferred during surgery to enhance mechanical stability and improve clinical outcomes. Conversely, varus fixation should be avoided due to its inferior stability.

Axial buckling resistance of cold-formed steel built-up I-section wall panels with single- and double-layer sheathing configurations: experimental and analytical studies

ABSTRACT This paper presents experimental investigation of the axial behaviour of built-up (BU) (I-section) cold-formed steel doubly-symmetric channel with single-/double-layer sheathing on both sides configuration. Fifteen (15) monotonic concentric axial compression tests were performed on 7-BU sections with single-layer sheathing, 7-BU sections with double-layer sheathing, 1-BU section stud without sheathing. The experiments aim to enumerate ultimate axial strength, buckling interactions, failure pattern and strength enhancement due to sheathing for BU section stud members. The novelty of the study is that, for the first time an attempt is made to investigate the axial behaviour of single-/double-layer sheathed BU section panels using seven different sheathing boards. Results indicate large range of deformation behaviour, with local-global and distortional-global interaction buckling phenomena. Failure is also observed due to failing of screws in specimens with sheathing of thickness ≥ 9 mm and modulus of elasticity > 6400MPa. Also, for the first time, efficacies of four semi-analytical methods based on rational extension of direct strength method (DSM) are presented. Results suggest the insufficiency of current AISI design specifications, whereas predicted results obtained using the new modified DSM methodology are within the adequate variation range as the adopted methodology considers desired buckling interaction. The efficacy of the recommended design methodology is verified through reliability analysis.

Compressive behavior of manufactured sand recycled coarse aggregate concrete-filled steel tubular short columns

To study the mechanical properties of manufactured sand recycled aggregate concrete-filled steel tubular (RACFST) columns, a total of 81 square short RACFST column specimens with different types of manufactured sand and natural sand were created and subjected to axial compression tests. The variables included sand type, core concrete strength, slenderness ratio, and steel tube thickness. The failure mode, axial load-displacement curve, axial compressive capacity, and deformation capacity of the specimens were analyzed in detail. The results indicate that the failure mode of the specimen is generally waist drum-type failure and shear-type failure, and both of them are local buckling. The load-displacement curve of the manufactured sand specimen is similar to that of the natural sand specimen, but the steel tube of the manufactured sand specimen yields later than that of the natural sand specimen. Generally, the limestone manufactured sand specimen has the highest axial compressive capacity and the best ductility ratio, while the pebble manufactured sand specimen has an axial compressive capacity similar to the natural sand specimen but a lower ductility ratio. The effects of concrete compressive strength, slenderness ratio, and steel tube thickness on specimens with manufactured sand are similar to those with natural sand. Based on the results of this experimental study, a formula for calculating the axial compressive capacity of square RACFST columns is provided.

Experimental Performance Study on Axial Compressive Load-Bearing Capacity of Steel Slag Micropowder Ecotype UHPC of Short Columns Steel Pipe

In order to study the axial compression performance of steel pipe concrete short columns filled with steel slag micronized ultra-high-performance concrete (UHPC), this paper designs 27 steel pipe UHPC short columns for axial compression test and compares and analyzes the axial compression performance of the specimens in terms of the damage mode, the deformation curve, and the coefficient of strength enhancement, which is aimed at investigating the differences in the actual load-bearing performance of steel pipe UHPC short columns through changes in the aspect ratio, concrete type, and steel content rate, and so on. The purpose of this paper is to compare and analyze the axial compressive performance of the specimens in terms of damage mode and strength enhancement factor in order to investigate the difference in the actual bearing capacity performance of steel pipe UHPC short columns through the changes in length-to-diameter ratio, concrete type, and steel content. The test results show that the axial compressive performance of steel slag powder steel pipe UHPC short columns is greatly affected by the L/D ratio and steel content; the specimen bearing capacity increases with the increase in the wall thickness of the steel pipe and decreases slightly with the increase in the L/D ratio, and the steel fibers can effectively improve the deformation of the concrete so as to enhance the composite effect with the steel pipe; the contribution of the core UHPC to improve the value of bearing capacity accounts for a higher percentage when UHPC with 1% steel fiber dosage and 20% coarse aggregate dosage gave the best uplift with no change in the type of steel pipe. In this paper, the axial compression test bearing capacity results of steel slag micro powder steel pipe UHPC short column are compared with the calculated bearing capacity results of domestic and international specifications and analyzed from the perspectives of perimeter compression strength, steel fiber mixing of core concrete, and the relevant parameter design suggestions for high-strength steel pipe concrete specimens are put forward.

Study on the evolution rules of coal deformation and failure characteristics caused by multiple mining disturbances

During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall “wavy” variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters.

Study on the mechanical property and durability of alkali-activated seawater and sea sand recycled aggregate concrete

This study investigates the potential of Alkali-Activated Seawater Sea Sand Recycled Aggregate Concrete (ASSRAC) as a novel sustainable construction material. By utilizing recycled aggregates from construction and demolition waste, seawater, sea sand, and alkali-activated materials such as fly ash and blast furnace slag, this innovative concrete aims to mitigate carbon emissions from cement production and optimize resource usage. The impact of recycled aggregate replacement rate, water-to-binder ratio, and sand type on the compressive strength of ASSRAC was examined through analysis of variance. Cylindrical axial compression and prism flexural tests were conducted to evaluate the long-term performance of ASSRAC under seawater immersion. The results indicate a decrease in compressive strength with higher recycled aggregate replacement rates and water-to-binder ratios, with recycled aggregates being the primary weak link. Additionally, increasing the water-to-binder ratio hampers hydration by diluting alkali activators, weakening polycondensation reactions. Under seawater immersion, ongoing reactions foster denser C-(A)-S-H structures, enhancing compressive strength and elastic modulus over time. Moreover, higher recycled aggregate replacement rates result in improved ductility, attributed to reactions between the old mortar on recycled aggregate surfaces and slag/fly ash at interfaces. For specimens immersed for 0 and 90 days, most theoretical models accurately predict results, except for the CEB-FIP model, which only accurately reflects the stress-strain curve at 180 days. The seawater-sea sand group's flexural strength initially exceeds that of the freshwater-river sand group due to accelerated early hydration, but this advantage diminishes over time due to high salt content.

Axial compressive properties of round bamboo-fiber reinforced phosphogypsum composite short columns

Bamboo is an ideal green building material with excellent mechanical properties. Phosphogypsum (PG) is a kind of solid waste residue which is in urgent need of resource utilization and has been used as construction material. In this paper, a kind of round bamboo-fiber reinforced phosphogypsum composite short column was proposed. Axial compression tests of pure bamboo columns, bamboo columns filled with phosphogypsum inside, bamboo columns with phosphogypsum outside and bamboo columns with phosphogypsum inside and outside were carried out to explore the failure mode and mechanical properties of the short columns. The effects of the parameters include bamboo node, hose hoops, size of the bamboo tube and the strength of phosphogypsum on the mechanical properties of the short columns were analyzed, and the theoretical calculation method of the bearing capacity of the short columns was put forward. The results show that the bamboo nodes and hose hoops can improve the bearing capacity, initial stiffness and ductility of the column. The larger the size of the bamboo tube, the better the mechanical properties of the short column. The bearing capacity of round bamboo—phosphogypsum composite short column is higher than that of pure bamboo column. The ductility of bamboo columns with phosphogypsum outside is obviously higher than that of pure bamboo columns. The finite element analysis results are in good agreement with the test results. The theoretical calculation method of the bearing capacity of columns considering the strength reduction coefficient, the bamboo node effect coefficient and the constraint effect in this paper has high accuracy.

Experimental and model evaluation of cyclic compressive performance for RAC-filled BFRP tube composite columns

The mechanical properties of recycled aggregate concrete (RAC) can be significantly enhanced in RAC-filled fiber-reinforced-polymer (FRP) tube composite columns. However, the cyclic compressive behavior of this type of composite columns has been scarcely studied. In this study, a series of cyclic axial compressive tests were conducted on RAC-filled basalt-FRP (BFRP) tube composite columns, and the effects of confinement level (number of BFRP layers) and RA replacement ratio were investigated. The test results indicate that, compared to RAC columns, the compressive capacity and deformability of RAC-filled BFRP tube composite columns increased significantly under cyclic loading. The compressive strength and ultimate strain of BFRP-confined RAC reached 1.42–3.98 times and 2.88–21.53 times those of unconfined RAC, respectively. The compressive strength and ultimate strain under cyclic loading were generally close to those under monotonic loading, with the compressive strength ratios averaging 1.052 and the ultimate strain ratios averaging 1.031. The enhancement efficiency of BFRP confinement increased progressively with increasing confinement level and/or RA replacement ratio. The envelope curves of the cyclic stress-strain curves resembled the stress-strain curves under monotonic loading. The reloading modulus (Ere) and residual modulus (Eun,0) continuously decreased as the unloading strain (εun) increased, while the plastic strain (εpl) increased almost linearly with εun. The values of Ere, Eun,0 and εpl were affected by the confinement level and RA replacement ratio. Finally, typical theoretical models for FRP-confined concrete were used to evaluate the cyclic stress-strain curves of RAC-filled BFRP tube composite columns.

Effects of load and high temperature on uniaxial compressive properties of desert sand concrete

In order to explore the influence of load and high temperature on the uniaxial compressive properties of desert sand concrete (DSC), the axial compressive strength test of desert sand concrete after different loads and temperatures was carried out, and the stress-strain curve was measured. The influence of load level, temperature grade and cooling method on the mass loss rate, ultrasonic velocity and uniaxial compressive performance of desert sand concrete after high temperature was analyzed. The results show that as the temperature increases, the mass loss rate of desert sand concrete gradually increases, the axial compressive strength gradually decreases, the peak strain increases significantly, the stress-strain curve tends to be flat, and the elastic modulus decreases continuously. The "pseudoplastic platform" near the axial compressive strength of the stress-strain curve of desert sand concrete after high temperature is more obvious. Based on the two-stage constitutive model of concrete, the constitutive model of desert sand concrete considering the influence of temperature and load level is established. The research results can provide technical support for the performance evaluation of desert sand concrete after high temperature.