Axial Curves Research Articles

An integral for self inductance of thin wires

Abstract I propose an elegant method of calculating the self inductance of a thin wire of arbitrary shape. The inductance is broken to into two parts - the inductance of a straight wire of the same length and cross section, and the remainder, the “curve inductance” due to the shape of the axial curve. The curve inductance is finite and can be calculated from a double integral by subtracting the straight wire singularity inside the integrand. Unlike all other methods, this does not involve a small parameter, and can be applied to any curve knowing its arc length parameterization. We use the circular arc and helix as examples and find that the integral is fast and accurate. The limits of the approximation are investigated for touching parallel wires.

Study on eccentric compressive performance of circular double skin concrete filled steel tube connected by thread through inside lining tube

Connection method of lengthening the steel tube of circular hollow sandwich concrete-filled steel tube by inside lining tube and thread is proposed. Twelve circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube are designed and fabricated using the length of the thread along the axial direction, the working height of the thread, and the position of the thread as parameters; In addition, one unconnected specimen and two welded specimens also are designed and fabricated to conduct controlled experimental research. The test phenomena and failure modes, axial compressive load-compression curve, axial compressive load-lateral deflection curve, and axial compressive load-strain in steel tube curve, as well as bearing capacity, strength reservation, deflection curve shape, lateral stiffness, ductility and plane section assumption are analyzed. The research results indicate that, within the parameter range studied, the thread connection through inside lining tube is reliable before tripping, and the experimental phenomenon of specimens connected by thread is basically consistent with that of the unconnected specimens. The axial compressive load-compression curve and axial compressive load-lateral deflection curve of all specimens can be approximately divided into elastic stage, elasto-plastic stage, and descending stage. The peak load of all specimens is relatively close, while although experiencing almost the same loading process, the strength reserve of the specimens connected by thread is insufficient. During the entire loading process, the shape of the deflection curve of all specimens is close to the sine half wave curve, and the distribution of longitudinal strain in the steel tube along the height of the middle cross-section basically conforms to the plane section assumption. Calculation method for bearing capacity of circular hollow sandwich concrete filled steel tubular beam-column connected by thread through inside lining tube is suggested.

Comparison of indentation test results and well-logging data for estimation of uniaxial compressive strength and Young’s modulus

Indentation test results and well-logging data are indirect methods of estimating Young’s modulus (E) and uniaxial compressive strength (UCS). The current study compared the results of indirect methods for a well in an oil field in southern Iran. The indentation tests were conducted by an indenter with a diameter of 260 µn on over 500 drill cuttings. The axial load versus displacement curve was used to determine the indentation modulus (IM) and critical transfer force (CTF) for each drill cutting. Indentation tests were performed perpendicularly and parallel to the weakness surface and were determined CTFV, IMV, CTFP, and IMV. The shear and compressive wave velocity (VS and VP ) for the well-logging data were determined and the UCS and static Young’s modulus (Esta.) were determined. Empirical equations for UCS-CTFV, UCS-CTFP, UCS-IMV, UCS-IMP, Esta-CTFV, Esta-CTFP, Esta-IMV, and Esta–IMP were proposed. It was determined that the relationships between UCS-CTFV and Esta-CTFV were more valid and meaningful than the other relationships. Therefore, it is suggested that the indentation test be performed perpendicular to drill cuttings with a weakness surface. The results showed that the values obtained for CTFV and IMV were 20% higher than for CTFP and IMP.

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.

Study on the compressive strength and failure mechanism of fiber-reinforced polymer green filling materials

The utilization of industrial solid waste in the preparation of geopolymer filling materials offers benefits such as low carbon emissions and resource conservation showcasing broad application prospects. In this study, geopolymer filling materials are prepared using calcium carbide slag, slag, fly ash, and tailings, with the addition of 12 mm polypropylene fibers to enhance their strength and toughness. Conducting UCS experiments to investigate the effects of different calcium carbide slag content, fiber content, and water-solid ratio on the UCS of the materials; Utilizing SEM-EDS and XRD techniques to analyze the mechanisms of strength formation in filling materials and the mechanisms of fiber toughening and crack resistance at the micro level; Establishing a uniaxial compression test model using discrete element PFC 3D software and combining digital speckle technology to visually analyze the sample's failure process. The research results indicate that the stimulation of slag and fly ash by calcium carbide slag results in a large amount of C-(A)-S-H gel, effectively promoting the bond between aggregate and fiber, with the UCS of the samples gradually increasing with the addition of calcium carbide slag. With the increase in fiber content, the UCS of the samples shows a trend of first increasing and then decreasing, with the optimal fiber content being 6 ‰. The fibers exist in the matrix in the form of anchor rods and a three-dimensional network structure, playing a good reinforcing role and effectively inhibiting the expansion and development of cracks; The crack morphology of the samples in the PFC 3D numerical simulation process is close to the digital speckle failure morphology, and the axial load-displacement curve in the numerical simulation aligns well with the indoor test results. The research results can provide theoretical guidance for the preparation of fiber-reinforced green filling materials using all solid waste.

A New Self-Sensing Fiber Optic Anchor to Monitor Bolt Axial Force and Identify Loose Zones in the Surrounding Rock of Open TBM Tunnels.

TBM has been widely used in underground engineering and construction, but there is no precedent for the application of open TBM in the inclined shafts of coal mines, which brings new challenges to the support system. The distribution of the axial forces on anchors and the range of loosening of the surrounding rock are crucial considerations in tunnel support design. Existing methods for measuring the axial forces in anchors and determining the extent of loosening in the surrounding rock typically remain at the inspection level, lacking long-term and real-time monitoring capabilities. This paper presents a new self-sensing anchor with embedded optical fibers (made using an improved stirrer) and proposes an intelligent tunnel rock monitoring system. The paper also outlines a method for identifying loosening zones in surrounding rock based on monitoring data and theoretical analysis. Installing self-sensing anchors in the deep sections of the rock surrounding a tunnel provides three-dimensional, round-the-clock real-time monitoring of the axial forces acting on the anchors, using new technology and methods to recognize the deformation characteristics of loosening zones within the surrounding rock. This new self-sensing fiber optic anchor was first applied to an open TBM tunneling project in an inclined shaft in the Kekegai coal mine, and monitoring data indicate that self-sensing optical fiber anchors can accurately reflect stress patterns in real time. The axial force curve can be divided into four segments: the borehole area, the loosening zone, the stable zone, and the anchoring zone. Consequently, it accurately identifies the thickness of loosening zones at different positions within the tunnel's surrounding rock. This information is compared and verified against results obtained from bolt dynamometers and borehole inspection. On this basis, an intelligent monitoring system was established to provide a basis for making engineering construction decisions, which makes tunnel construction smarter and helps technicians timely adjust TBM driving and support parameters.

Three-dimensional continuum point cloud method for large deformation and its verification

This study presents a strong form based meshfree collocation method, which is named Continuum Point Cloud Method, to solve nonlinear field equations derived from classical mechanics for deformed bodies in three-dimensional Euclidean space. The method and its implementation are benchmarked against a nonlinear vector field using manufactured solutions. The analysis of mechanical fields firstly focuses on the study of St. Venant Kirchhoff and compressible neo-Hookean materials. Results for various initial boundary value problems are presented, including benchmark cases involving unidirectional tension and simple shear. Subsequently, the study concludes with an analysis of a displacement-controlled simulation of a compressible neo-Hookean material, specifically a bar that is pulled to 50% of its original length and rotated 90°. The pure tension case yields a 1.5% error in displacement between computed and expected values and a combined tension and torsion loading case provides further insight into material behavior under complex loading conditions. The resulting normal axial and transverse stress-strain curves are also presented. Finally, the consistency and robustness of the proposed nonlinear numerical schemes are successfully demonstrated through various numerical experiments.

Axial compressive behavior of CFRP-confined rubber concrete-encased H-shaped steel hybrid columns

The use of rubber particles as aggregate replacement in concrete production (i.e., rubber concrete) is thought to be an efficient way to dispose of end-of-life rubber products. However, the use of rubber aggregates in concrete generally leads to reduced strength and stiffness as well as early cracking in concrete. Consequently, the practical use of rubber concrete has mainly been limited to non-structural applications. In this paper, a novel compressive component, termed carbon fiber-reinforced polymer (CFRP)-confined rubber concrete-encased H-shaped steel hybrid column (FRuCSC), is proposed for the structural application of rubber concrete. This novel hybrid column consists of an external CFRP tube, an encased H-shaped steel, and rubber concrete filled in between. The axial compressive behavior of FRuCSCs was investigated through combined axial compression tests and theoretical analyses. The test results indicate that FRuCSCs with a rubber replacement ratio of no more than 50 % possess excellent axial load-carrying capacity and ductility. Owing to the confinement offered by the external CFRP tube and encased H-shaped steel, the strength and ductility of the filled rubber concrete improved significantly. Furthermore, by modifying an existing axial stress-strain model of FRP-confined rubber concrete, the axial load-strain curves and axial-lateral strain curves of FRuCSCs with a rubber replacement ratio of no more than 50 % can be accurately predicted.

Expansion deformation mechanism and cracking behaviours of chromium-coated zirconium alloy cladding at room temperature

The deformation of the cladding tube triggered by the expansion of the internal plug is used to investigate the hoop deformation behaviour of the Cr-coated zirconium alloy cladding tube at room temperature. A thin-walled pressurized cylinder model is used to transform the axial load-displacement curve working on the expansion plug into the hoop stress-strain curve working on the cladding tube, and it is found that the Cr coating can be able to restrain the cladding tube from hoop deformation. Observation of the Cr-coated cladding tube after different amounts of hoop deformation revealed that the strain corresponding to the generation of the first crack was a ranged from 0.48 % to 0.59 %, the density of cracks started to grow very fast and then entered a saturation stage. The fracture strength of the Cr coating and maximum interfacial shear strength when the Cr coating crack density reaches saturation were calculated by the shear-lag model. Twins and a large number of dislocations were generated in the Zr matrix and a small number of dislocations in the Cr coating after the hoop deformation. The behaviour of crack initiation and propagation occurring in Cr coating is revealed.

Axial compressive behavior of partially encased composite reactive powder concrete columns after high-temperature exposure

Replacing ordinary concrete in partially encased concrete (PEC) columns with high-strength and durability reactive powder concrete (RPC) significantly improves their axial capacity and suppresses local buckling of the steel section. To study the axial mechanical performance of partially encased composite reactive powder concrete (PEC-RPC) columns after exposure to high temperatures, axial compression tests of eight PEC-RPC column specimens were designed and conducted. Thermal response, failure modes, axial load-vertical displacement curves, and strain-axial strain curves of different specimens were observed considering the effects of link spacing, cross-sectional dimensions, constant temperature duration, and cooling methods. Results indicate: PEC-RPC columns exhibited whitening on the surface of RPC after high-temperature exposure, specimens with the largest link spacing experienced RPC peeling due to concentrated thermal stress, exacerbated by spraying water, which created a stress difference between the surface and the interior, resulting in RPC peeling. The deeper the thermocouple was embedded, the lower the measured temperature. Additionally, due to the significantly lower thermal conductivity of RPC compared to steel, the temperature at measurement points within the RPC is much lower than that at the steel web. The failure mode of PEC-RPC columns after axial loading was characterized by the crushing of RPC and local buckling of section steel. The larger the link spacing, the more prone it was to multi-layer buckling, and columns with larger cross-sectional sizes tended to exhibit shear failure. The characteristic value of mechanical performance showed higher sensitivity to cross-sectional dimensions, but relatively lower sensitivity to link spacing and constant temperature duration. As the cross-sectional dimensions increased from 150×150 mm to 250×250 mm, the peak load, residual bearing capacity, stiffness, and ductility increased by 72.51–164.86 %, 89.8–173.6 %, 61.85–151.47 %, and 13.72–31.46 %, respectively. Finally, based on partition constraint theory and superposition principle, a simplified method for calculating the axial mechanical performance of PEC-RPC columns after exposure to high temperatures was proposed.

Performance of lightweight coconut shell concrete-filled circular steel tube columns under axial compression

The current study aimed to use coconut shell concrete, a structural lightweight concrete, as an infill material in concrete-filled steel tube (CFST) columns and test it under axial compression. Testing was done on eighteen short, intermediate and long coconut shell CFST columns and six normal-weight CFST short columns for comparison. For both types of columns, the axial load-displacement curves and modes of failure were examined. By varying the length-to-diameter and diameter-to-thickness ratios, the axial capacity of steel tubes filled with coconut shell concrete was assessed. The composite action was verified from the results of the confinement index, strength index and the contribution of the coconut shell concrete as infill concrete. Structural efficiency and energy absorption of the lightweight CFST column was contrasted with its counterpart column. The contribution of coconut shell concrete to the strength of the CFST column was the highest at 61.36% and more significant than that of normal-weight CFST columns. The coconut shell CFST columns were 23.63% lighter than the normal-weight columns, contributing to its higher structural efficiency. These columns also had 8.12% more energy absorption than normal-weight columns. Hence, the results of this investigation revealed that coconut shell concrete has the potential to be utilized in CFST columns. Further, compared to the experimental ultimate loads, the predictions made by the existing codes, EC4 and ANSI/AISC 360 are conservative.

Axial compression performance of rubberized concrete-filled steel tubular stub columns after fire exposure: Experimental investigation and calculation models

Rubberized concrete (RuC) has emerged as a promising eco-friendly solution for structural elements, offering improved energy dissipation, damping characteristics, and ductility. Incorporating rubber particles into concrete-filled steel tubular (CFST) columns presents an environmentally conscious alternative for various structural applications. However, understanding its performance post-fire is crucial for safe design application, an area currently lacking comprehensive research. This study investigates the structural behavior of sixteen axially loaded circular RuCFST columns after exposure to fire. The columns, with diameters of 219 mm and 377 mm, are filled with normal concrete and RuC, containing 5 %, 15 %, and 30 % replacement of natural fine and coarse aggregate with rubber particles. Following ISO-834 fire standards, the specimens undergo elevated temperatures and subsequent application of compressive axial loads to determine their post-fire behavior. Analysis includes examination of failure modes, temperature-time relationships, axial load-deformation curves, and strain and stress development in the columns. Microstructural analysis using scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) is conducted to study internal morphology before and after exposure to high temperatures. Results indicate non-uniform and nonlinear distributions of maximum temperatures across cross-sections, with historical temperature affecting residual capacity more significantly with increased rubber content and decreased column size. Load-bearing capacities decrease by up to 30 % and 22 % for small and large RuCFST columns, respectively, after exposure to fire. Residual axial stiffness also declines, with reductions of nearly 55 % and 42 % for small and large columns, respectively. In contrast, ductility improves in fire-exposed specimens, with columns having a 30 % rubber replacement ratio showing the highest enhancement. A novel method for calculating post-fire residual load capacity based on the average historical maximum temperature is introduced, demonstrating high accuracy and offering a valuable tool for assessing and reinforcing RuCFST columns after fire exposure.

Combined axial load-biaxial bending interaction method for L-shaped CFSP shear walls

This paper reports the development of axial load and biaxial bending interaction method for L-shaped concrete-filled steel plate (CFSP) composite shear walls based on fiber section analysis model using the uniaxial constitutive relationship of materials. Owing to the complex interaction between the two perpendicular wall limbs (web and flange) of an L-shaped shear wall, the contour shape of the My-Mz curve is asymmetric. Linear transformation was employed to reduce the asymmetry of the contour shape, eliminate the influence of dimension, and perform parametric analysis. The analysis results indicate that when 0° ≤ θ(neutral axis angle) ≤ 90°, the influence of width-to-thickness ratio (hw1/bw) and shape coefficient (γ) on the coefficient that controls the contour shape (α) was negligible. The effect of shape coefficient (γ), steel content ratio (ρ), compressive strength of unconfined concrete (fc0), and yield strength of steel plate (fyp) on α is not significant for −180° ≤ θ ≤ −90°. Further, simplified equations were suggested to determine α. The axial load-moment interaction curve expressions for distinctive loading directions were determined by establishing the calculation method for the curve's characteristic points (axial load capacity, bending capacity, boundary points). Subsequently, the characteristic points were combined with the contour shape of the axial load-moment interaction curve derived by fitting the finite element simulation data to generate the axial load-moment interaction curve equations. A design approach was finally formulated based on the equations for the biaxial moment capacity curve and the axial load-moment interaction curves of the characteristic loading directions.

Eccentric compression behavior of partially CFRP wrapped seawater sea-sand concrete columns reinforced with epoxy-coated rebars

The combined use of seawater sea-sand concrete (SSC), epoxy-coated rebar (ECR) and fiber-reinforced polymer (FRP) can achieve significant economic and environmental benefits in coastal infrastructure constructions. Thus, this paper first presents an experimental and analytical study on the eccentric compression behavior of partially carbon FRP (CFRP) wrapped SSC columns reinforced with ECR. The effects of load eccentricities, thickness of CFRP strips, clear spacing ratios, and slenderness ratios were comprehensively analyzed. Test results show that as the eccentricity increased from 60 mm to 120 mm, the increment of load capacity of partially CFRP wrapped columns reduced by 27.6 % to 17.1 %. Moreover, a larger lateral deflection was detected for the specimens with a relatively high slenderness ratio, which results in an obvious second-order effect and further aggravates the nonlinearity of axial load-bending curves, especially for the specimens under a small eccentricity. In addition, an eccentricity-dependent stress-strain model for concrete was developed under FRP strip-steel hoop composite confinement, and the lateral deflection formula of eccentrically loaded columns was also derived based on force equilibrium analysis. Finally, a new theoretical formula incorporating the effect of the slenderness ratio was also presented for the determination of load and moment capacity of the partially CFRP wrapped columns based on section analysis. By comparing with the test results, the developed model exhibits satisfactory accuracy.

Axial Compressive Behaviours of Coal Gangue Concrete-Filled Circular Steel Tubular Stub Columns after Chloride Salt Corrosion.

The axial compressive behaviours of coal gangue concrete-filled steel tube (GCFST) columns after chloride salt corrosion were investigated numerically. Numerical modelling was conducted through the static analysis method by finite element (FE) analysis. The failure mechanism, residual strength, and axial load-displacement curves were validated against tests of the coal gangue aggregate concrete-filled steel tube (GCFST) columns at room and natural aggregate concrete-filled steel tube (NCFST) columns after salt corrosion circumstance. According to the analysis on the stress distribution of the steel tube, the stress value of the steel tube decreased as the corrosion rate increased at the same characteristic point. A parametric analysis was carried out to determine the effect of crucial variation on residual strength. It indicated that material strength, the steel ratio, and the corrosion rate made a profound impact on the residual strength from the FE. The residual strength of the columns exposed to chloride salt was in negative correlation with the corrosion rate. The impact on the residual strength of the column was little, obvious by the replacement rate of the coal gangue. A simplified design formula for predicting the ultimate strength of GCFST columns after chloride salt corrosion exposure was proposed.

Bearing Capacity Characteristic Analysis of Anti-floating Bolts in Unsaturated Soil Based on Mindlin Solution

AbstractBased on Mindlin solution and the theory of unsaturated soil mechanics, the theoretical solutions of shear stress and axial force distribution in the elastic stage of full-length binding-type anti-floating bolts were derived, and the bearing capacity characteristics of such bolts and the influencing factors were analyzed. In this paper, the design parameters of anti-floating anchor in a negative two-floor basement of a commercial square are substituted into the formula derived in this paper. The results show that, in unsaturated soil, the shear stress and axial force of the full-length bonded anti-floating anchor are distributed along the total length of the anchor, but neutral points appear in both of them, which is mainly due to the reduction of the axial force and shear stress of the anti-floating anchor caused by the matric suction. The formula derived in this paper is used to analyze the factors affecting the bearing capacity of anti-floating anchor bolt in unsaturated soil. The results show that: the greater the elastic modulus of soil mass, the greater the peak value of shear stress curve, the closer the peak value is to the head of anchor bolt, and the greater the axial force decline rate. With the increase of anchor solid diameter D, the peak value of shear stress decreases, the peak value moves backward, the neutral point moves forward, the negative shear stress value increases, the decline rate of axial force distribution curve decreases, but the negative axial force increases. With the increase of the additional shear stress τ0, the peak value of the shear stress curve decreases, the peak value moves to the hole of the anchor rod, the neutral point moves to the hole, the negative shear stress increases, the decline rate of the axial force distribution curve increases, and the negative axial force increases.

Density dependent constitutive model for Bi-2212 powder compression deformation

Bi-2212 HTS materials are fabricated into multi-filamentary wires via powder-in-tube (PIT) method followed by proper heat treatment to obtain superconductivity, but how to predict the large compression deformation behaviors of the Bi-2212 powder is critical to design the processing of the Bi-2212 HTS wire. Drucker Prager/Cap (DPC) model was the most commonly used model for powders including Bi-2212 with soil-like mechanical behavior to consider its shear failure as well as hydrostatic compression. However, the parameters for DPC Cap evolve with densities change and the original model is inadequate to precisely describe the densification process of Bi-2212 powder with large strain. In this study, the modified DPC model with density dependent parameters was introduced for Bi-2212 powder compressions by measuring the failure strength and hydrostatic compressive behavior under different density states. The DPC yield surface was plotted with an evolution trend of non-linear outward expansion with density increased. FEM model of uniaxial compression based on the as-introduced model was built with subroutine VUSDFLD applied. The distribution of Mises stress and relative density were analyzed. The axial stress-density curve for FEM and experimental results were normalized and quantitively evaluated by Mean Square Error (MSE). The introduced model shows good convergence and could match the experimental results well with normalized MSE of 0.000207 and Root Mean Square Error (RMSE) of 0.0144, indicating the mean error percentage of 1.44%. The model introduced in this article provides supports toward large strain deformation simulation of Bi-2212 powder.

Prediction of the axial strain development curve of soft clay under dynamic triaxial conditions based on LSTM

The dynamic triaxial test results of soft clay show that a long-term cyclic traffic load lead to significant deformation of soft clay. Considering that the dynamic triaxial test data of soft clay under cyclic loading have apparent time series characteristics, the long short-term memory (LSTM) model can be used to predict the deformation law of soft clay. Through a dynamic triaxial test of Shanghai soft clay, time series data, such as axial stress, pore water pressure, and axial strain were obtained to establish the sample data of the LSTM model. The LSTM model is then used to predict the axial strain development curve. The results showed that the LSTM model had a good fitting precision for the sample data under different dynamic stresses and frequencies, and its accuracy was above 97% in all conditions. The prediction results can reproduce the fluctuation law of the axial strain under cyclic loads and can be used to study elastic and plastic strains. The research results can provide technical support for disaster prevention and control in soft clay.

Seismic Performance of Prefabricated Reinforced Concrete Structure Beam Joints Based on the Internet of Things

Abstract Because buildings are easily damaged and collapsed by earthquake disasters, a study on the seismic performance of prefabricated reinforced concrete beam joints based on the Internet of Things has been proposed. Side joints with the largest bottom column section and the largest axial compression ratio of 100 m high prefabricated reinforced concrete structure were selected for the test. The test loading scheme is completed through the test loading device and the test loading system. An logging while drilling wave is selected as the test-simulated seismic wave, and the column axial force, hysteresis curve, displacement point, strain force, and crack position are taken as the main measurement contents. To do this, the DH-3816 data collection was completed based on the Internet of Things and the test data were recorded by DH-3816 data acquisition system. The results show that the proposed method consumes much energy and has high ductility under a low cycle reciprocating load. The bearing capacity in yield state, limit state, and failure state is better, and the degradation trend of strength and stiffness is gentler. Fuzzy optimization is used to test the viability of the proposed mechanism and the results are promising.

Residual behavior of UHPC-filled Q690 high-strength steel tubular members after axial impact

Structures may suffer from accidental impact loads during the service life. While most impacts will not destroy structures completely, quantifying their residual behavior after impact is crucial for evaluating the damage and then providing recommendations for repair or removal. This may greatly reduce the time and economic losses caused by impacts. Hence, this study experimentally and numerically investigated the residual behavior of UHPC-filled high-strength steel tube (UHPC-FHST) members subjected to axial impact. Parameters including impact energy, steel ratio, specimen length, and steel grade (Q690 and Q355) were carefully considered. After tests, different failure modes and axial load-displacement curves were obtained. The residual ratio (β), a ratio of the bearing capacity of a damaged specimen to that of a specimen without impact, was employed to assess the damage level of UHPC-FHST members after axial impact. Tests showed that UHPC-FHST members have excellent axial impact resistance, high residual strength, and high residual ratio, especially under low-energy impact conditions. β decreases rapidly and linearly with increasing nominal strain and then stabilizes after a certain value. A finite element (FE) model was thereafter established and benchmarked by the available test results, where two analysis steps were established to continuously simulate the impact and residual compression processes. The FE results demonstrated a great agreement with the tests, which could provide a reference for further investigations in related studies.