This article aims to investigate the structural response of a novel type of composite concrete columns in which the conventional steel bars are replaced in the main longitudinal direction with small ...circular-section steel tubes infilled with cementitious grouting material (CGM). In this study, 24 circular cross-sectional reinforced concrete columns with different transverse reinforcement configurations were tested under varied eccentric axial loads (in two series with variable slenderness ratios). The type of columns (short with a height-to-diameter ratio of 4.41 or long with a ratio of 10.29), the type of reinforcement (steel bars of 16 mm diameter, steel tubes of 16 mm outer diameter infilled with CGM or steel tubes of 25.4 mm outer diameter infilled with CGM), the spiral pitch (50 or 75 mm), and the eccentricity of the applied load (25 or 50 mm) are the main test parameters included in the experimental program. The remarkable compression and tension strengths of confined CGM in comparison to concrete inspired the idea of embedding CGM within small steel tubes. Furthermore, economic factors support replacing a portion of the conventional steel material with cementitious grouting material. To evaluate the impact of the steel reduction resulting from CGM embedment within the steel tubes, the specimens' load capacity, strain, and deformation were investigated. The outcomes demonstrated that CGM-filled steel tubes are a promising and economically feasible solution for lowering the amount of steel used in column members. The findings demonstrated that the load-carrying capability of both the short and long-tested columns reinforced with 25.4 mm diameter CGM-infilled steel tubes was marginally greater than that of the columns reinforced with 16 mm diameter steel bars by 7%. Furthermore, specimens reinforced with 16 mm outer diameter steel tubes, where the wall area of the steel tube is only 30% of the area of a steel bar with the same diameter, provide an ultimate capacity ranging from 62% to 77% of the columns reinforced with steel bars with a 16 mm diameter. The capacity of the specimens decreased as the slenderness ratio and the eccentricity of the applied load increased, while the tested column's lateral deformation increased. In the meantime, a notable enhancement in the specimen's load capacity was seen with the reduction of the spiral pitch from 75 to 50 mm.
•Cementitious grouting material-filled steel tubes were proposed as an alternative to traditional steel bars in composite concrete columns.•The advantage of steel tubes is demonstrated by the higher strength gain for concrete within tubes as opposed to concrete with steel spirals alone.•The axial and lateral stiffness of all tested columns showed a considerable decrease as the eccentricity and slenderness ratio increased.
This paper is focused on stainless steel square and rectangular hollow section (SHS and RHS) slender members loaded by a combination of compressive force and the bending moment. The study presents ...tests on 20 members, including initial imperfection measurements and material coupon tests. The tests take into consideration uniaxial bending to the major axis. The data obtained from the experimental study were subsequently used for validating an FE numerical model. A comprehensive numerical parametric study was carried out on all three common structural stainless steel groups: austenitic, ferritic and duplex. The cross-section slenderness and the cross-section aspect ratio (h/b), the non-dimensional member slenderness, the material stress–strain diagram (yield strength, ultimate strength, degree of non-linearity) and the ratio between the compressive force and the bending moment were set as the main parameters. Results of the numerical parametric study were compared with some of the existing procedures for stainless steel beam–column design. The main focus is on the proposal developed by Zhao et al., which is the procedure expected to be used in the new EN 1993-1-4. Although the method published by Zhao et al. has shown good prediction ability, a new design approach was proposed and its suitability demonstrated by a reliability study. The method is believed to be more general, as it uses a single formula for all grades of stainless steel, and also covers the effect of the section Class on the interaction between axial force and bending moment.
•20 tests of stainless steel SHS and RHS beam–columns were conducted.•Numerical model was created, validated and used for a numerical parametric study.•Based on the numerical data, existing design procedures were compared.•A new general stainless steel SHS/RHS beam–column design procedure was developed.
Uniaxial compressive strength (UCS) is often an indispensable parameter for the engineering geological assessment. The specimen geometry has a significant influence on such determination in the ...laboratory. Previous laboratory test results confirm that the laboratory-determined rock strength generally decreases with the increase in the slenderness ratio, which has been shown to be attributing to the end friction effects. In the present study, by numerically investigating the effect of slenderness ratio (i.e., shape effect) on the strength and deformation behavior of an intrusive crystalline rock based on the discrete element method, the key underlying microscopic factors contributing to this slenderness effect are examined in detail. A loading scheme is carried out on a grain-based model to simulate a series of uniaxial compression tests on specimens possessing different slenderness ratios. The findings reveal that the Young's modulus remains almost unchanged with the increase in the slenderness ratio. The UCS gradually decreases, which is in good agreement with previous laboratory test results. The numerical results further reveal that the change of rock strength in response to the slenderness ratio is mainly associated with the stress distribution and micro-cracking pattern inside the model. As the slenderness ratio gradually increases, the stress in the model becomes more uniformly distributed and the micro-cracking becomes less prominent but more homogeneous. The chance of finding an effective failure pathway (i.e., a macroscopic fracture) is higher, thus resulting in a lower rock strength. Our simulation results not only offer a plausible microscopic explanation for the progressive decrease of laboratory-determined rock strength with the increase in the slenderness ratio, but also provide insights on practical applications such as hard rock pillar design of underground openings.
•Influence of slenderness ratio effect on rock strength is numerically investigated.•Uniaxial compressive strength decreases with the increase in slenderness ratio.•Strength change against slenderness ratio is associated with stress distribution.•The chance of finding an efficient failure pathway is higher in taller models.
•Tree slenderness coefficient (TSC) of Chinese fir in relation to biotic and climatic variables was explored.•TSC variance explained by biotic variables was 59% much larger than climate variables ...2.8%.•MAT was the dominant climatic factor manipulating TSC values.•Trees grown in less dense stands were more stable than those grown in dense stands.
Tree slenderness coefficient (TSC) is an important measure of tree stability. Generally, trees with higher TSC values are prone to snow, icing, and wind damage than trees with smaller TSC values. Chinese fir (Cunninghamia lanceolata (Lamb.) Hook.) a native and fast growing species, is widely distributed in southern China. Yet our understanding of how TSC of Chinese fir plantations is affected by biotic (including size, competition, and age) and climatic variables in different sites is limited. A data set of 60 remeasured plots consisted of five spacing trials and distributed in in Fujian, Jiangxi, Guangxi, and Sichuan provinces in southern China were used to explore TSC of Chinese fir relating to biotic and climatic variables using nonlinear mixed effects model (NLME). Results showed that TSC values increased with increasing stand age (Age), stand basal area (BA), and mean annual temperature (MAT). In contrast, it decreased with increasing tree density index (TN), relative diameter (RD = DBH/quadratic mean diameter), mean warmest month temperature (MWMT), and annual heat-moisture index (AHM). The relative importance of RD influencing TSC was the most followed by Age, Spacing A, TN, Spacing D, MAT, BA, Spacing C, Spacing B, AHM, and MWMT through hierarchical partitioning analysis. MAT was the most important climate factor that contributed to TSC variations, followed by AHM, and MWMT, which indicated that temperature was a critical climate variable modulating TSC of Chinese fir in southern China. Additionally, trees grown in less dense stands of 1667, 3333, and 5000 trees ha−1 were more stable (lower TSC) than those grown in dense stands of 6667 and 10 000 trees ha−1. In a word, TSC variance explained by biotic variables was 59% much larger than climate variables 2.8%. Our results will help with further assessments of tree/stand stability of Chinese fir plantations under climate change.
The AISC Specification limits the use of steel and concrete materials in filled composite members to concrete strength (fc′) less than or equal to 69 MPa and steel yield strength (Fy) less than or ...equal to 517 MPa. This paper presents the results of comprehensive analytical investigations conducted using benchmarked numerical models to evaluate the behavior of rectangular filled composite members made from one or both materials exceeding the AISC Specification strength limits. The numerical models are developed and analyzed using the displacement-based formulation of the fiber-based finite element in OpenSees. Prior research has developed effective (phenomenological) stress–strain curves for steel and concrete materials that implicitly account for the effects of steel yielding, local buckling, concrete cracking, crushing and confinement, and the interaction between the two materials in the composite cross-section. This paper first benchmarks the modeling approach and then uses the benchmarked model to conduct analytical parametric studies covering a wide range of parameters, including: member slenderness, section slenderness, section aspect ratio, steel yield stress and concrete compressive strength. The results from the parametric studies are used to evaluate behavior and develop new design equations based on nominal stress distributions over the composite section. The nominal steel stress in compression (Fcr) is expressed as a continuous function of the section slenderness and yield strength, thus eliminating the current AISC Specification’s need for section classification (compact, noncompact and slender). The new design equations are recommended for relaxing the material strength limitations in the next version of the AISC Specification.
•Proposed design equations were recently adopted by the Specification for Structural Steel Buildings (AISC 360-22).•A novel procedure for designing high-strength concrete-filled steel tube members is presented.•Design equations based on an extensive parametric study conducted using OpenSees software.•Eliminating the current need for section classification with providing more accurate design equations.•Extend material strength limits to 15 ksi (104 MPa) for concrete and 100 ksi (690 MPa) for steel.
This paper presents laboratory tests, numerical simulations and web crippling design of high strength steel unlipped channel sections under interior-two-flange loading. An experimental programme ...comprising 10 test specimens (with six for grade S690 high strength steel and four for grade S960 high strength steel) was firstly implemented, and test results including failure modes, full load-deformation curves and ultimate loads were reported. Subsequently, finite element models were constructed and validated against the obtained test results, and then used to conduct supplementary parametric studies to widen the examined parameter ranges of high strength steel unlipped channel sections. Considering that relevant codified design rules are absent, the applicability of the design rules of EN 1993–1-3, EN 1993–1-5 and AISI S100 for normal strength steel unlipped channel sections to their high strength steel counterparts was evaluated against the obtained test and numerical results. It is shown that the resistance predictions from the codified design provisions were generally inaccurate and scattered. Hence, a modified AISI S100 design method and a slenderness-based design method were proposed and demonstrated to be accurate, consistent and reliable for the web crippling design of high strength steel unlipped channel sections under interior-two-flange loading.
•Web crippling of high strength steel unlipped channel sections under ITF loading is studied.•A total of 10 web crippling tests and 150 finite element simulations are carried out.•The codified European and American design methods are found to be inaccurate.•An improved AISI S100 design method and a slenderness-based design method are proposed.
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.
•Eccentric compression performance of partially CFRP wrapped SSC columns reinforced with ECR was investigated.•Effects of load eccentricities, thickness of CFRP strips, clear spacing ratios, and slenderness ratios were explored.•An eccentricity-dependent stress-strain model was developed for concrete under FRP strip-steel stirrup composite confinement.•The lateral deflection formula of columns was derived and a new formula of load and moment capacity was presented.
Glass fiber reinforced polymer (GFRP) stiffened composite plates with and without rectangular cutout are analysed under axial, lateral and combined axial and lateral loading using finite element ...software ABAQUS®. Ultimate load, maximum displacements and failure modes of GFRP stiffened composite plates with and without cutout obtained from finite element analyses are compared with experiments carried out at Department of Civil Engineering, IIT Madras. Validation of the finite element model is carried out by analysing a blade-stiffened composite panel and compared with the experimental results of Falzon and Hitchings (2003). Parametric studies are carried out for various plate slenderness ratios, column slenderness ratios, lateral pressure intensity and material type. Analysis of stiffened composite plates with reinforced cutout is carried out to determine the type and size of reinforcement required for restoring the lost strength and stiffness.
•Experimentally compare monotonic and low-cycle fatigue performance of HTRB600 and HRB400E steel bars.•Study the effects of yield strength, slenderness ratio, strain amplitude and rebar diameter on ...low-cycle fatigue properties of reinforcing bars.•Propose a low-cycle fatigue life prediction model considering the effect of inelastic buckling.•Calibrate buckling and low-cycle fatigue parameters for reinforcing steel bars by a valid FEM method.
Bar buckling and subsequently low-cycle fatigue fracture is one of the main failure modes of RC columns/piers under strong earthquakes. Due to the adoption of new metallurgical technology and possibly enduring higher stress, high-strength steel bars (HSSB) may be more prone to occur buckling and low-cycle fatigue failure, which will detrimentally affect the seismic performance of RC columns/piers. In view of this, this paper studies the buckling and low-cycle fatigue performance of high-strength steel bars (HSSB) HTRB600 and compares with normal steel bars (NSB) HRB400E. At first, the monotonic tensile and compressive tests of HTRB600 and HRB400E steel bars with different slenderness ratios (L/D = 6, 8, 10, 12, 15) were conducted to study their monotonic tensile and compressive properties. Then, the low-cycle fatigue tests of HTRB600 and HRB400E reinforcing steel with different strain amplitudes and slenderness ratios were conducted to evaluate their low-cycle fatigue performance. The fatigue life prediction formulas for HTRB600 and HRB400E steel bars taking into account the effects of inelastic buckling were proposed through the regression analysis of test results. Moreover, the fractured surfaces obtained by the scanning electron microscope (SEM) were used to compare the low-cycle fatigue failure features of HTRB600 and HRB400E steel bars. Finally, a finite element model (FEM) was developed to simulate the nonlinear mechanical behaviors of HTRB600 and HRB400E steel bars under monotonic and cyclic loading. Test results show that HTRB600 steel bars present lower tensile ductility, more severe post-buckling softening and pinching effect than HRB400E steel bars. The increase in yield strength, buckling length and strain amplitude will reduce the low-cycle fatigue life of steel bars. The range of striation marks observed from low-cycle fatigue fractured surfaces by SEM for HTRB600 steel bar is smaller than HRB400E steel. The calibrated buckling and low-cycle fatigue parameters by the validated finite element model (FEM) can be adopted to accurately simulate the inelastic seismic response of RC structures.
•Full-scale test on slender CFTST beam-columns under eccentric load.•Equivalent confinement factor to overall quantify the confinement effect in CFTSTs.•Fiber element model for CFTSTs.•Effects of ...cross-section dimensions, material properties, slenderness and loading angle on CFTST behavior.•Theoretical model predicting the interaction curves of CFTST beam-columns.
This paper presents an experimental and theoretical study on concrete-filled T-shape steel tubular (CFTST) beam-columns. Four full-scale slender beam-columns with slenderness ratio of 33.7–39.1 were tested under uniaxial eccentric compressive loads. In addition, three stub columns with the same cross-sections were axially compressed to investigate the confinement effect. Failure mode, axial displacement, lateral deflection, axial strain and hoop strain were obtained to understand the structural behavior of CFTST beam-columns. For beam-columns bended about the symmetric axis, torsion was not observed but a slight rotation of the neutral axis that was no longer parallel to the centroid axis was found by analyzing the experimental results. A fiber element model for CFTST beam-columns was developed and verified for parametrical analysis. The effects of key parameters, such as material properties, cross-section dimensions, loading angle and slenderness ratio, on the behavior of stub and slender beam-columns were investigated. Finally, theoretical models were proposed to estimate the interaction curve and the load-carrying capacity of CFTST beam-columns. The prediction matches well with the experimental results.
