Axial Load Displacement Research Articles

Axial-Load Resistance of a Novel UHPFRC Grouted SHS Tube-Sleeve Connection: Experimental, Numerical, and Theoretical Approaches

Experimental, numerical, and theoretical analyses were conducted of the axial load resistance of a novel ultrahigh-performance fiber-reinforced concrete (UHPFRC) grouted square hollow section (SHS) tube sleeve connection. The experimental study tested 10 full-scale specimens with varying shear key spacings, grout thicknesses, grout lengths, and volume proportions of steel fiber in the UHPFRC. Two types of failure modes were observed: (1) for the connection with high strength of the grouted part, the failure mode was fracture of the inner tube; and (2) for the connection with lower strength of the grouted part, the failure mode was grout shear crushing with significant bond-slip between grout and steel tube. To understand further the load transfer mechanism of the connection, an advanced three-dimensional (3D) nonlinear finite-element (FE) model was built to simulate the axial load–displacement behavior, state of stress and strain, and crack development of the grout. Based on the test and FE results, a new theoretical model was derived to predict the axial-load resistance of the connection. The proposed model considers the effect of section shape and material parameters, and is applicable to UHPFRC grouted SHS tube sleeve connection with different corner radii. Validation versus the test results showed that the new model can provide reasonably effective and accurate predictions of the axial-load resistance of the novel grouted sleeve connection subjected to tension.

Study on axial compressive performance of HDC-masonry composite elements

High ductile concrete (HDC) is a kind of cement-based composites containing discontinuous short polyvinyl alcohol (PVA) fibers exhibiting strain-hardening performance and high ductility based upon the bridging effect of short fibers. The study reported here investigated the axial compressive performance of HDC-masonry composite columns/walls, which can be used in new masonry constructions. Three different type of masonry specimens, namely short columns, full-scale columns, and walls, were prepared and tested to failure under monotonic concentric axial loads. The experimental results were reported and analyzed in terms of axial load–displacement response, failure mode, strength, stiffness, and energy dissipation capacity of tested members. Overall, the composite effect of HDC improved both load-carrying capacity and peak axial displacement of masonry columns/walls, with effectiveness factors ranging from 1.37 to 2.29 for the peak load and from 1.09 to 1.27 for the peak displacement. Due to the high slenderness ratio of full-scale masonry columns, the full-scale HDC-masonry composite columns showed lower increases in peak load, stiffness, and energy dissipation capacity, compared with short column and wall specimens. The negative influence of high aspect ratio on the axial capacity of HDC-masonry composite members will be weakened by the increased elastic modulus and cross-sectional area. Therefore, the test results obtained from the present study allowed the development of the stability coefficient of unreinforced masonry (URM) structures, using equivalent cross-section approach, for the prediction of the axial load-carrying capacity of composite columns/walls. The analytical model provided a better approximation for the column specimens while gave a conservative prediction for the wall specimens.

Behavior of Quarry Rock Dust, Fly Ash and Slag Based Geopolymer Concrete Columns Reinforced with Steel Fibers under Eccentric Loading

Geopolymer concrete, also known as an earth-friendly concrete, has been under continuous study due to its environmental benefits and a sustainable alternative to conventional concrete construction. The supplies of many source materials, such as fly ash (FA) or slag (SG), to produce geopolymer concrete (GPC) may be limited; however, quarry rock dust (QRD) wastes (limestone, dolomite, or silica powders) formed by crushing rocks appear virtually endless. Although significant experimental research has been carried out on GPC, with a major focus on the mix design development, rheological, durability, and mechanical properties of the GPC mixes; still the information available on the structural behavior of GPC is rather limited. This has implications in extending GPC application from a laboratory-based technology to an at-site product. This study investigates the structural behavior of quarry-rock-dust-incorporated fiber-reinforced GPC columns under concentric and eccentric loading. In this study, a total of 20 columns with 200 mm square cross-section and 1000 mm height were tested. The FA and SG were used as source materials to produce GPC mixtures. The QRD was incorporated as a partial replacement (20%) of SG. The conventional concrete (CC) columns were prepared as the reference specimens. The effect of incorporating quarry rock dust as a replacement of SG, steel fibers, and loading conditions (concentric and eccentric loading) on the structural behavior of GPC columns were studied. The test results revealed that quarry rock dust is an adequate material that can be used as a source material in GPC to manufacture structural concrete members with satisfactory performance. The general performance of the GPC columns incorporating QRD (20%) is observed to be similar to that of GPC columns (without QRD) and CC columns. The addition of steel fibers considerably improves the loading capacity, ductility, and axial load–displacement behavior of the tested columns. The load capacities of fiber-reinforced GPC columns were about 5–7% greater in comparison to the CC columns. The spalling of concrete cover at failure was detected in all plain GPC columns, whereas the failure mode of all fiber-reinforced GPC columns is characterized with surface cracking leading to disintegration of concrete cover.

Study on axial compression mechanical behavior of cold-formed thin-walled C-shaped steel composite wall sheathed with straw board on both sides

To examine the axial compression mechanical behavior of cold-formed thin-walled C-shaped steel (CFS) composite walls sheathed with straw board on both sides (CFSSB composite walls), this study conducted tests on 3 scale-model wall specimens to investigate the failure mode, axial load–displacement responses, and axial load-bearing capacity. The following parameters of the specimens were considered: stud spacing and presence of cement plaster mortar on the surface of the straw board in the specimens. In the tests, one specimen with cement plaster mortar was compared with the other two specimens, and the load–displacement curves and load–strain curves of the three specimens were obtained. The results indicated that the failure mode of the composite wall involved local buckling of the steel stud, partial bending and wrinkles on the straw board. In addition, the restrictive effect of the straw board on the steel frame increased the load-bearing capacity, and the mortar reduced the wrinkles on the straw board. On the basis of these findings, the finite element analysis (FEA) software program ABAQUS was used to analyze the axial compression performance of CFSSB composite walls, and factors affecting the bearing capacity were analyzed, such as the height-thickness ratio of the CFSSB wall, the section thickness of the C-shaped steel, and the stud spacing. A formula for calculating the axial bearing capacity of the CFSSB composite wall based on the test data and FEA results was established. The research conclusions can provide a reference for engineering applications with CFSSB composite walls.

An experimental study on seismic performance levels of highly corroded reinforced concrete columns

AbstractIn the literature, only one empirical model is available as a nondestructive method for the prediction of seismic performance levels of corroded reinforced concrete (RC) columns as a function of the initial corrosion crack width at lower corrosion levels. Because of the ruptured transverse reinforcement bars at higher corrosion levels, the structural behavior may turn brittle in terms of shear failure. Therefore, in this study, higher corrosion levels for a different concrete strength level from that empirical model were studied. To do this, four RC columns were subjected to accelerated corrosion, and the widths of initial corrosion cracks were measured. The corroded RC columns were then tested under combined constant axial load and cyclic lateral displacement excursions. After the cyclic loading test, the actual corrosion levels at each reinforcement bar were obtained by extracting the reinforcement bars from the concrete. Test results showed that the prediction of seismic performance levels of corroded RC columns based on initial corrosion crack widths were limited owing to the nonlinear increase in the crack width with the increase in the corrosion levels. New empirical models were developed to predict the remaining energy capacities and seismic performance levels of the corroded RC columns.

Buckling behaviors of thin-walled cylindrical shells under localized axial compression loads, Part 1: Experimental study

Thin-walled cylindrical shell structure not only shows the highly efficient load carrying capacity but also is vulnerable to buckling instability failure. In practical application, these structures are usually subjected to localized axial compression load, which is a common but complex non-uniform loading case. Until now, the buckling behaviors of thin-walled cylindrical shells under this kind of compression loading condition are still unclear, and there are also few relevant investigations. In order to fill this research gap, in the first part of this series paper the experimental studies on the buckling behaviors of thin-walled cylindrical shells under localized axial compression loads were performed for the first time. The buckling tests of twenty-one steel cylindrical shells were carried out in this paper and some key experimental details were given. The strain curve, axial load–displacement curve, critical buckling load as well as the buckling modes of cylindrical shells under localized axial compression load were systematically discussed. Test results indicated that the localized axial compression load plays a pivotal role in the buckling behaviors of thin-walled cylindrical shell, not matter from the point of view of load carrying capacity, load–displacement curve or buckling mode. The experimental results obtained from this work can be served as a benchmark for related research in this field of buckling analysis of thin-walled cylindrical shells.

The axial compressive behavior of stone-lightweight aggregate concrete-filled steel tubular stub columns

To study the axial compressive mechanical properties of stone-lightweight aggregate concrete-filled steel tubular (SLACFST) stub columns, five circular stone-lightweight aggregate concrete-filled steel tubular (C-SLACFST) and square stone-lightweight aggregate concrete-filled steel tubular (S-SLACFST) stub columns were made by taking the volume replacement ratio of natural gravel aggregate and ceramsite in lightweight aggregate concrete as a variation parameter. After observing their mechanical process and failure modes, the axial load–displacement curves of the specimens were obtained. The influence of gravel replacement ratio on the energy dissipation and stiffness of the specimens was analyzed, and a simplified model for predicting their stiffness degradation was proposed. The plastic damage model was then used to verify those specimens with a finite element, and this model was subsequently adopted in the whole process analysis of these specimens and in finding out the loading relationship between the steel tube and core stone-lightweight aggregate concrete (SLAC). The effects of varying parameters on the compressive behavior of the specimens were investigated, and the extent to which these varying parameters are related to the ultimate bearing capacity of SLACFST was assessed via a grey correlation analysis. Results show that the rigidity of the calculated load–displacement curves in the elastic and elastic–plastic stages is greater than that of the test curves, but the ultimate bearing capacity and peak displacements agree with the test values within an acceptable error. Moreover, the simulated failure modes of the control specimens are the same as the test failure modes. Before reaching the ultimate bearing capacity, the core SLAC made a significant contribution to the bearing capacity of the specimen due to the constraint of steel tube. The negligible influence of gravel replacement ratio on the ultimate bearing capacity of SLACFST specimen. In addition, the nature gravel can inhibit the floating of LAC to a certain extent, so as to achieve the purpose of using SLAC to make SLACFST, reducing the self-weight of the structure while having higher bearing capacity.

Influence of axial force and characteristics of axial force affecting on total knee replacement constraint test

The result of testing for determination of Total Knee Replacement (TKR) Constraint (ASTM F1223) is necessary for surgeons for matching the knee prosthesis with the different degrees of severities of knee osteoarthritis patients. In the knee replacement constraint test, the axial compressive load and translation displacement are the control and the adjusting variables. The magnitude of axial compressive load during testing is affected by the slope of knee bearing surface. According to ASTM 1223 standard, the axial compressive load is not clarifyingly mentioned. Namely, it should be equal 710 N during testing or only in state of initiation. It may lead to testers to perform the test into different two modes which consequently in possibly different constraint result. Therefore, the objective of this research is to clarify the differences in test results when applying two axial compressive load characteristics during testing. The six-axis testing machine (Prosim Universal Joint Simulator) was used to determine the anterior posterior constraint (AP) of fix bearing posterior sacrifice (FB PS) system. Bovine serum was directly applied to the bearing surfaces as a lubricant. An initial axial compressive load 710 N was used. Two axial compressive load characteristics during testing, 1) keeping the axial force at given value as mentioned during testing (load-controlled testing) and 2) with allowing the change in axial compressive load during testing (displacement-controlled test), were used. From the results, the AP load resistance hysteresis loop patterns obtained by both testing modes were similar. The magnitude in forward direction load resistance is higher, while the backward AP load resistance showed the lower, in case of displacement control mode. It resulted in span between AP load resistance was larger. Moreover, the higher constraint in case of displacement control was indicated. Thus, if the test modes are not mentioned in test result, the surgeons will be possibly choosing the wrong TKR for their patient.

Axial Load Behavior of Ultrahigh Strength Concrete-Filled Steel Tube Columns of Various Geometric and Reinforcement Configurations

This paper presents the behavior of concrete-filled steel tube (CFST) columns infilled with fiber-reinforced self-consolidating ultrahigh strength concrete (UHSC) subjected to axial concentric monotonic loading to failure. UHSC is expected to improve ease of fabrication, strength, and ductility of CFST columns. Seventeen columns having varying geometric properties such as tube wall thickness, cross-sectional shape (circular, rectangular, and square), and slenderness were constructed and tested by applying load through both steel tube and concrete core. Circular columns were further distinguished by the presence or absence of main and hoop steel reinforcing bars in the core concrete. Axial load-displacement response, axial/transverse strain development, and failure modes were recorded during the loading history to analyze the performance. Experimental confined concrete strength and axial strength of UHSC-filled CFST columns were compared with those obtained from three suggested analytical models and three code-based design procedures including Eurocode 4, Canadian CAN/CSA S16, and American AISC. Analytical models were found to over-predict the confined concrete strength and the axial strength of CFST columns. Canadian and American codes were found to be most applicable for predicting axial strength of UHSC-filled CFST columns while remaining conservative.

Experimental study on local buckling of high-strength Q960 steel columns at elevated temperatures

High-strength steel has been widely used in many engineering structures owing to its enormous economic benefits. A considerable amount of theoretical and experimental research on the fire resistance of high-strength steel structures has been reported. Most of the research has focused on the mechanical properties of steel and the overall buckling behavior of members, but less work has been done on the local buckling behavior, which is often observed in steel structures subjected to actual fires. Moreover, very few design provisions in codes and standards are available for calculating the local buckling capacity of steel columns under high temperatures. In this study, eight welded H-section columns (groups A and B) made of high-strength Q960 steel were tested under axial compression at ambient and elevated temperatures to investigate their local buckling behaviors. By considering different buckling zones, heating temperatures, and heating methods, the load–axial displacement, load–lateral deflection, and local buckling zone of steel columns were recorded. Compared with the ambient temperature test results, the ultimate load of group A specimens at 480 and 632 °C decreased by 26.1% and 57.2%, respectively, and the ultimate load of group B specimens at 472 and 683 °C decreased by 28.5% and 74.2%, respectively. The critical buckling temperature of the columns in transient-state testing was higher than that in steady-state testing under the same load conditions. A finite element model was established using the ABAQUS finite element software and was validated by the test results. The experimental values were compared with the design methods proposed in Eurocode 3 (EC3). The results reveal that EC3 is unsuitable for calculating the local buckling capacity of H-section Q960 steel columns at elevated temperatures.

Local–overall interactive buckling behaviour of 800 MPa high-strength steel welded H-section members under axial compression

In this study, three different types of columns (i.e. columns with a low width-to-thickness ratio of the plates, columns with a high height-to-thickness ratio of the web, and columns with a high width-to-thickness ratio of the flange) are designed to investigate the buckling behaviour of welded H-section columns fabricated from 800 MPa high-strength steel (HSS). Different buckling behaviours are established, including the load–axial displacement curves, relationships between the local out-of-plane displacement and overall lateral displacement, and ultimate loads of the columns. Current specifications, such as ANSI/AISC and Eurocode 3, are evaluated using the experimental results of this study. It is concluded that ANSI/AISC and Eurocode 3 slightly underestimate the ultimate load of 800 MPa HSS welded H-section members under axial compression. Numerical analyses are performed to estimate the buckling behaviours of 800 MPa HSS welded H-section members under axial compression, and the model is verified using the experimental results in this study. The effects of several parameters (i.e. the slenderness ratio, width-to-thickness ratio of the flange, and height-to-thickness ratio of the web) on the buckling behaviour are investigated. Finite element analyses are carried out for 94 different models, and a more accurate model for estimating the ultimate load of welded H-section members fabricated from 800 MPa HSS is developed. Existing experimental data for HSS columns are collected, and reliability analyses are performed for ANSI/AISC, Eurocode 3, and the proposed model.

Research on Biomechanical Application of Fracture Reduction Fixator Based on Finite Element Analysis

This article uses CAXA 3D solid design software to model the fracture reduction fixator, and assemble the model according to the requirements of clinical medicine. Obviously apply 50N, 100N, 150N, 200N axial load to the model, and obtain the relationship between axial load force and displacement. The stiffness of the model calculated by SPSS23.0 statistical analysis software is 88.5N/mm. The stiffness of the fracture reducer measured by the biomechanical model was 85.4N/mm, and the ratio between the two was 1.037, which was within the error range. Prove that the model and calculation method established in this study can provide reference for clinical medicine.

Numerical analysis of square concrete-filled double skin steel tubular columns with rubberized concrete

Structural engineers have assessed the possibility of replacing part of natural aggregates with rubber particles in concrete in recent years to obtain sustainable structural members. It has been confirmed that the use of rubber particles can enhance ductility and energy absorption capacity of concrete. By contrast, the compressive capacity of rubberized concrete (RuC) is usually lower than the normal concrete (NC). Confining RuC with steel tubes can be considered as an appropriate solution for reaching to a ductile member with adequate strength. This paper, therefore, investigates the behavior of rubberized concrete-filled double skin steel tubular (RuCFDST) short columns by performing a series of nonlinear finite element (FE) analyses. The developed FE models were verified against the experimental test results by comparing the axial load–displacement curves, ultimate axial strength, and failure mechanism of specimens. The validated FE model was used to investigate the effects of geometric and material properties on the behavior of RuCFDST columns with 5%, 15%, and 30% rubber contents, and to compare the performance of RuCFDST and concrete-filled double skin steel tubular (CFDST) columns. The results showed that using RuC for filling square CFDST columns could significantly enhance the ductility. By contrast, CFDSTs presented greater axial strengths than RuCFDSTs. Reduced confining stresses between the outer tube and the concrete core were displayed when RuC was applied compared to CFDST.

Incremental load transfer analysis of an energy pile under arbitrary mechanical and thermal loads

This paper describes a new incremental approach to simulate the axial load–displacement response of energy piles. A load transfer approach is used to model the interaction of pile with surrounding soil, the underlying layers, and the superstructure. Interface springs are nonlinear–hyperbolic and Masing’s rule applies to model their hysteresis behaviour. Mechanical and thermal loads are incrementally applied to the pile using an iterative finite difference method. This strategy makes it possible for both mechanical and thermal loads to have arbitrary time histories during analysis. The self-weight of the energy pile can also be considered. The simulation results are found to compare favourably with published experimental results from field and laboratory testing of three energy piles. The effects of amplitudes of mechanical load and temperature change as well as those of the stiffness of the pile extremities on the thermomechanical response of the pile and the position of the null point are evaluated and discussed. The simulations show that the thermal-induced axial force due to a unique temperature change was greater for an energy pile under lower amounts of mechanical load. It is found that the effect of the end restraining condition on the response of the energy piles is more considerable during the heating processes than during the cooling processes. More restrained pile–superstructure connection also results in more thermal-induced axial force in the energy pile. The null point is always located closer to the stiffer extremity of the energy pile.

Behaviors of welded hollow spherical joints strengthened by unidirectional annular ribs

Welded hollow spherical joints are comprehensively used in spatial steel structures. However, the original joints cannot meet the strength requirements in some conditions, such as the corrosion, the fire and the change of structural load. Therefore, it is necessary to explore effective methods of strengthening the joints to maintain the durability and safety of the structures. This paper proposes and investigates the method of strengthening welded hollow spherical joints using unidirectional annular ribs. Experiments were conducted to study the failure modes, axial load–displacement curves and ultimate bearing capacity under axial compressive and tensile load. Nonlinear finite element (FE) model was established and verified to study the failure mechanism and bearing capacity of the test joints using ABAQUS. Based on the accurate FE model, parametric studies were performed to study the influence of the thickness and height of unidirectional annular rib, the dimensions of the steel tubes and the welded hollow spheres on the capacity of the joints. Practical design formulas were proposed based on the test and the FE analysis. The conclusions presented in this study can provide theoretical and numerical basis for the design of welded hollow spheres strengthened with unidirectional annular ribs in spatial steel structures.

Local buckling of corroded cold-formed steel stub columns

Cold-formed steel (CFS) is widely used as the load-carrying members in infrastructure engineering. However, CFS structure, which has been in the corrosive environment for a long time, is often difficult to avoid corrosion. Five corroded CFS stub columns with different corrosion degrees were tested under axial compression and the material properties of the coupon specimens were obtained by monotonic tensile tests. The thickness and initial geometric imperfection were measured using a dial indicator and an ultrasonic thickness gauge, respectively. The failure modes, the relationship between the axial load and lateral displacement, strain and mechanical parameters of the corroded CFS stub columns were discussed. A numerical study was undertaken using validated finite element models. Finally, the design rules for the corroded CFS columns were analyzed. The results indicated that the yield strength and ultimate strength reduction factor for corrosion decreased linearly with respect to the thickness loss ratio and the elastic modulus reduction factor for corrosion decreased nonlinearly with the thickness loss ratio. The axial displacement corresponding to the axial strength and the axial strength decreased with the increase of the thickness loss ratio. The axial strength predicted by the North American Specification (NAS) were more accurate than that predicted by the Chinese Technical Specification (CTS).

Design method of short circular FRP-steel composite tubed RC columns under eccentric compression

A FRP-steel composite tubed reinforced concrete (F-STRC) column is fabricated by wrapping FRP sheets around a steel tubed reinforced concrete (STRC) column. To date, few studies focus on the design method of F-STRC columns under eccentric compression. A fibre-based numerical model was developed in this paper to simulate the axial load versus lateral displacement curves, based on which the calculation method for the sectional load bearing capacity was developed through the section analysis. However, the developed method is relatively complicated and inconvenient for practical design. Thus, on the basis of parametric studies, the concrete stress in the compression zone was equivalent to rectangular block and calculation methods for the equivalent stress block factors were proposed. A simplified design method was proposed for F-STRC columns under eccentric compression and generally in good agreement with the predicted results of section analysis.

WITHDRAWN: Dimension effect on the seismic behaviour of column by varying effective length-depth ratios

Abstract In the past few years, the seismic vulnerable zones are getting increased in India which increases the importance of the seismic study. The objective of this study is to assess the seismic behavior of the column with different effective length to depth ratio. By varying effective length to depth ratio under the seismic load, the seismic behaviors of columns have been found out. To choose the optimum and safest effective length to depth ratio, the building model has been created and fully analyzed under the seismic load by using STAAD.Pro. The effective length to depth ratio has been chosen as 7.5, 6, 5, 4.28, 3.75, and 3.33. The variation of axial load, Bending Moment & nodal displacement has been plotted against the location of the column. The suitable effective length by depth ratio of the column to withstand under the seismic load safely and also the economical size out of the chosen 6 ratios has been found out.

Experimental investigation of damaged square short RC columns with low slenderness retrofitted by CFRP strips under axial load

The aim of this study is to develop the retrofitting details, which will increase axial ultimate load capacity, stiffness, displacement ductility ratios, and energy dissipation capacities of short reinforced concrete (RC) low-slenderness columns to avoid adverse effects on earthquake performance. The main variables examined in the experimental study are the Carbon Reinforced Fiber Polymer (CFRP) strip width used for retrofitting, the distance between CFRP strips, the use of the anchor at the overlap zone in the CFRP strips, and the placement of the CFRP strips horizontally or vertically to the column axis. For these purposes, eleven square short RC columns with a dimension of 150x150x500 mm (with low slenderness ratio: λ = 11.5) were produced. The columns were damaged up to 50% of their axial load carrying capacity, then retrofitted with CFRP strips in different ways. The short RC columns with low slenderness ratio were tested under monotonic axial loading until they failure. By obtaining the axial load–displacement graphs of the test specimens, the ultimate axial load capacity, initial stiffness value, displacement-ductility ratios, and energy dissipation capacities are calculated and interpreted. It has been found that the most successful retrofitting detail is obtained when CFRP strips are placed perpendicular to the column axis, and CFRP fan-type anchors are used in the strip overlap region.

Numerical investigation of HSC column under axial and flexural loading using 3D-NLFEA

High strength concrete (HSC) has been widely used as material for Reinforced Concrete (RC) column in high rise building in the past two decades. However, ductility of HSC column was one of the main concerns in design. The ductility of HSC column is much lower compared to normal-strength concrete. To increase the ductility of HSC column, the use of adequate transverse reinforcement can be used. In this paper, numerical investigation of HSC column available in the literature is modelled using an inhouse finite element package called 3D-NLFEA. The modelled specimen consisted of HSC columns with dimension 305 m x 305 m x 1473 mm and is subjected to constant axial load and incremental displacement control which act as a shear load up to failure. From the comparisons with the available test results, it was found out that the prediction using 3D-NLFEA agrees well with the test results. This paper also discusses the yield point location of bars in the load-deflection curve, length of bar that yields, buckling of compression bar, and concrete which cracked or crushed.