Rectangular Members Research Articles

Flexural buckling performance of concrete-filled aluminium alloy tubular columns

The use of aluminium alloys as a structural material has recently increased because of their advantageous properties such as high strength-to-weight ratio and corrosion resistance. However, due to their low Modulus of Elasticity, instability is a major concern for aluminium alloy structural members subjected to compression. One of the ways to improve the performance of aluminium alloy hollow sections on this count is to have concrete infill within them. Past research studies have demonstrated the potential of concrete-filled aluminium tubular (CFAT) stub columns and beams to have improved structural performance, but there is still no reported research on CFAT slender columns. This paper presents an experimental and numerical investigation on the structural response of square and rectangular CFAT members under axial compression. A series of 18 tests were carried out, including 9 CFAT and 9 bare aluminium tubular (BAT) columns for reference purpose. The columns had pin-ended boundary conditions allowing rotation about the minor axis. The tubes were made of 6082-T6 heat-treated aluminium alloy and filled with concrete. The experimental failure modes, ultimate strengths and load versus mid-height lateral displacement curves are reported. Finite element models were developed and validated against the test results. A parametric study was subsequently conducted to study the buckling behaviour for a range of cross-sections and concrete strengths. The test and numerical results were utilised to assess Eurocode design equations for Class A aluminium alloy columns. It was shown that the current codified equations underestimate the actual strength of BAT slender columns and a new buckling curve improving the design accuracy is proposed. In absence of design provisions for CFAT columns, the design methodology of European standards for composite steel-concrete members with the material properties of steel replaced by those of aluminium is adopted. Finally, on the basis of the results of this study a design buckling curve suitable for CFAT columns is proposed.

Theoretical and Experimental Analysis of Thin-Walled Curved Rectangular Box Beam under In-Plane Bending.

Thin-walled curved box beam structures especially rectangular members are widely used in mechanical and architectural structures and other engineering fields because of their high strength-to-weight ratios. In this paper, we present experimental and theoretical analysis methods for the static analysis of thin-walled curved rectangular-box beams under in-plane bending based on 11 feature deformation modes. As to the numerical investigations, we explored the convergence and accuracy analysis by normal finite element analysis, higher-order assumed strain plane element, deep collocation method element, and inverse finite element method, respectively. The out-of-plane and in-plane characteristic deformation vector modes derived by the theoretical formula are superimposed by transforming the axial, tangential, and the normal deformation values into scalar tensile and compression amounts. A one-dimensional deformation experimental test theory is first proposed, formulating the specific contributions of various deformation modes. In this way, the magnitude and trend of the influence of each low-order deformation mode on the distortion and warping in the actual deformation are determined, and the significance of distortion and warping in the actual curved beams subjected to the in-plane loads is verified. This study strengthens the deformation theory of rectangular box-type thin-walled curved beams under in-plane bending, thus providing a reference for analyzing the mechanical properties of curved-beam structures.

AISC Provisions for Web Stability under Local Compression Applied to HSS

The relevant limit states for local compression loading on the webs of a rectangular HSS member are reviewed, and the 2016 AISC Specification Chapter J provisions are adapted from their normal application to the single web of a W-shape or I-section to this case. Two recent laboratory tests on matched-width, rectangular HSS-to-HSS cross-connections are described to illustrate the behavior of such connections under branch axial compression. The data from these tests are supplemented by experimental results from a further 76 cross-connection tests, with the branches being either welded plates or welded HSS. From this 78-test database, the existing provisions for local yielding of the chord sidewalls, local crippling of the chord sidewalls, and buckling of the chord sidewalls, are evaluated. Recommendations are made for handling transverse compression loading on HSS webs in the AISC Specification, and a design example is given to illustrate the approach.

Levitas

We received and we gladly publish this contribution by distinguished designer and theorist Ian Ritchie, as an example of that bridging research and practice which our journal intends to promote and disseminate. [MS] ABSTRACT - The design and engineering development of two apex connected square woven flat surfaces, each constrained at ground level by three anchors and lifted to form a 3D gridshell whose theoretical geometry is modified by the small sectional profile of the rectangular members made of wood. The warp and weft of the weave are of identical section and made from Italian red oak. The process of artistic investigation is explained and then taken into theoretical designs, computed, and is then tested iteratively through choice of wood, a 33% physical model which is laser surveyed and fed back into the computer model and FEM (Finite Element Method) analysis, and finally followed by a partial full scale mock up, before realising the sculpture at the Arte Sella environmental art park.

Bearing capacity of bolted ball-cylinder joint under uniaxial tensile force

The bolted ball-cylinder (BBC) joint is a new type of joint system for non-purlin grid structures. Since the BBC joints may subject to tensile force in the cantilevered parts of the structure, or under situations where the wind suction dominates, this paper investigates the bearing capacity of the BBC joints under uniaxial tensile force by means of numerical analysis. Firstly, the establishment and verification of the finite element (FE) model is introduced briefly. Then, the parametric studies, considering various dimensions of the hollow cylinder, rectangular tube member, ribbed stiffener, convex washer, and high strength bolts are carried out based on the verified FE model, and the influence of each parameter is analyzed in detail. Finally, the formulae to estimate the bearing capacity of the BBC joint under uniaxial tensile force are obtained by regression analysis. The comparison of the calculation results using the formulae, the numerical and the experimental results shows that the proposed formulae are with satisfactory accuracy and can be applied to practical engineering.

Ductility Behaviour of Rectangular Compression Members Retrofitted by Modified Technique of FRP Wrapping

This paper presents an experimental investigation on ductility behaviour of reinforced concrete compression members, rectangular in cross section, modified to elliptical shape in cross section by bonding precast segment covers followed by Carbon Fiber Reinforced Polymer wrapping (CFRP) under concentric and eccentric loading conditions. Eighteen reinforced concrete rectangular compression members of size 100mm×150mm in cross section and 300mm in height were prepared using normal-strength concrete. Reinforcement ratio was kept at minimum, to simulate compression members that need retrofitting. Out of eighteen specimens, nine specimens were converted to elliptical shape in cross section. From nine remaining rectangular specimens, three specimens retained as it is without wrapping FRP and designated as Group1, remaining six specimens were wrapped with one and two layers of CFRP and designated as Group2. Out of nine elliptical specimens, three specimens were retained as it is without wrapping FRP and designated as Group3, remaining six elliptical specimens were wrapped with one and two layers of CFRP and designated as Group4. Specimens were tested upto failure under monotonic axial compression with concentric and eccentric load conditions. From the experimental results, it is observed that rectangular compression members shape modified to ellipse in cross section and then wrapped with CFRP show outstanding increase in the ultimate load carrying capacity which may be due to increased cross sectional area and effective confinement of FRP wrapping. As the number of layers of CFRP increases the ultimate load carrying capacity increases. With increase in eccentricity, the ultimate loads of the compression members were found to be decreased. Elliptical specimens wrapped with one and two layers of CFRP reported exponential increase in deformation ductility under concentric load condition and considerable increase under eccentric load condition compared to rectangular specimens wrapped with CFRP.

Experimental investigation and FE modelling of the flexural performance of square and rectangular SRCFST members

In this study, experimental investigation and finite element (FE) modelling of the flexural performance of square and rectangular steel-reinforced concrete-filled steel tubular (SRCFST) members are carried out. Six square SRCFST specimens and four rectangular ones are fabricated and tested to obtain their failure modes, the strain data, the deformation and the moment capacity under four-point bending. The effects of profiled steel configuration, loading planes, shear-span ratios (a/D) and depth-to-width ratios (D/B) on the flexural performance of SRCFST members are evaluated. Moreover, the experimental data reported in this study are employed to verify the numerical model comprehensively. Thereafter, the verified FEA model is utilized to evaluate the stress distribution, the interaction between steel and concrete, the moment resisted by each component and the role of embedded profiled steel. Finally, the measured bending moment capacities are adopted to calibrate the accuracy of existing design method on SRCFST members stipulated in Eurocode 4 (EC4) (2004), while the results demonstrate that high accuracy for the prediction of bending moment capacity can be obtained.

Testing of aluminum alloyed bolted joints for connecting aluminum rectangular hollow sections in reticulated shells

A new joint system for connecting aluminum alloy rectangular hollow section (ARH) members is proposed to overcome the problem of connecting rectangular tubes using the traditional Temcor joint. The structural performance of the ARH joint system under an out-of-plane bending moment is studied experimentally. The moment-rotation (M-Φ) curves, stress variation, and failure modes of the ARH joint obtained from the tests are discussed. A bilinear model is proposed to summarize the M-Φ curves of the joint. The influence of the key parameters, gusset thickness and bolt quantity on the mechanical behavior of the ARH joint is analyzed. Subsequently, finite element analysis is conducted to investigate the moment rotational behavior of the ARH joint. The comparison between the experimental and numerical results proves that the proposed finite element model is accurate enough and can be used to study the moment resistance behavior of the ARH joint system. The results show that the proposed ARH joint, for connecting rectangular hollow section members, can be considered as a semi-rigid connection. This study provides a reference for the practical application of the ARH joint in reticulated structures made of aluminum rectangular members.

Structural performance of cold-formed high strength steel tubular X-Joints under brace axial compression

The experimental investigation presented in this study focused on the static strengths and load-deformation behaviour of cold-formed high strength steel tubular X-joints made up of S900 and S960 steel grades. The X-joints include brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The nominal yield strengths of square and rectangular tubular members were 900 and 960 MPa, while the nominal yield strength of circular tubular members was 900 MPa. Two configurations of tubular X-joints were fabricated, first, where both brace and chord members were made up of square and rectangular hollow sections, and second, where circular hollow section braces were welded to square and rectangular hollow section chord members. The welds were laid using semi-automatic gas metal arc welding process. A total of 34 tests was conducted where an axial compression was applied through the brace members without any chord preload. The ratio of brace-to-chord width (β) ranged from 0.34 to 1, brace-to-chord thickness (τ) from 0.53 to 1.28, chord width-to-thickness (2γ) from 20.2 to 38.9, and chord side wall slenderness (h0/t0) from 12.7 to 39.0. In order to assess the applicability of the existing design provisions, test strengths were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT. It is shown that the existing design provisions are not capable of providing accurate and reliable predictions for cold-formed high strength steel tubular X-joints made up of S900 and S960 steel grades.

Compression capacities of cold-formed high strength steel tubular T-joints

The paper presents a test programme on cold-formed high strength steel tubular T-joints with fully supported chord members. The T-joints consist of brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The T-joints were fabricated by both brace and chord members made up of square and rectangular hollow sections as well as circular hollow section braces were welded to square and rectangular hollow section chord members. The brace and chord members were welded by semi-automatic gas metal arc welding process. The steel grade of 900 MPa was used for the square, rectangular and circular tubular members, while the steel grade of 960 MPa was used for the square and rectangular tubular members only. A total of 22 tests was conducted where an axial compression was applied through the brace members, while the chord members were resting on a solid flat base. The ratio of brace-to-chord width (β) ranged from 0.33 to 1, brace-to-chord thickness (τ) from 0.53 to 1.27, chord width-to-thickness (2γ) from 20.6 to 38.7, and chord side wall slenderness (h0/t0) from 12.7 to 38.6. The test results were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT for the assessment of the existing design rules for tubular T-joints with fully supported chord members. It is found that the existing design rules are not applicable for the design of cold-formed high strength steel tubular T-joints with fully supported chord members.

Torsion of Rectangular Connection Elements

Traditionally, the torsional design of rectangular members has been based on elastic calculations. For member design, this approach is justified because beams subjected to torsion are usually controlled by torsional rotation serviceability limits. However, designs that are based on a first yield criterion underestimate the strength of connection elements. To evaluate the true torsional behavior of connection elements, various factors affecting the torsional strength of short rectangular members are investigated, showing that the torsional strength of connection elements can be predicted with rational analysis models using an ultimate strength approach. A method is proposed for calculating the strength of rectangular connection elements subjected to any possible combination of loads, including torsion. The design method results in a significant increase in torsional strength compared to traditional analysis methods. The method can be used to analyze extended single-plate connections subjected loads in any direction, including axial forces and combined vertical and horizontal shear forces. Three design examples show the proper application of the design method.

Tests of cold-formed high strength steel tubular T-joints

The paper presents an experimental investigation on cold-formed high strength steel tubular T-joints. The fabricated T-joints include brace members made up of square, rectangular and circular hollow sections, while chord members were made up of square and rectangular hollow sections. The nominal yield strengths of square and rectangular tubular members were 900 and 960 MPa, while the nominal yield strength of circular tubular members was 900 MPa. Two configurations of tubular joints were fabricated, first, where both brace and chord members were made up of square and rectangular hollow sections, and second, where circular hollow section braces were welded to square and rectangular hollow section chord members. The brace and chord members were joined together by automatic gas metal arc welding process. In total, 24 tubular T-joint tests were conducted where an axial compression was applied through the brace members of the T-joints, while the ends of the chord members were supported on rollers. The ratios of brace-to-chord width (β) ranged from 0.34 to 1, brace-to-chord thickness (τ) ranged from 0.52 to 1.27 and chord width-to-chord thickness (2γ) ranged from 20.63 to 38.55. The resistances and deformations of tubular T-joints were carefully examined. In order to evaluate the applicability of the existing design provisions for high strength steel tubular T-joints, test results were compared with the nominal strengths obtained from the Eurocode 3 (EC3) and CIDECT. It is shown that the existing design provisions are not capable of providing accurate and reliable predictions for the design of cold-formed high strength steel tubular T-joints made up of S900 and S960 steel grades.

The Service Life of Circular Section Member under Chlorine Ion Erosion

The concrete structure, when being eroded, suffers premature destruction due to poor durability. This is primarily attributed to overlooking the impact that the shape and diffusion of dimension exert on the chlorine ion diffusion while designing the durability of the concrete structure. The method that is used for calculation of the durability of circular section members under chlorine ion erosion was proposed herein with the service life ending when chloride concentration on the surface of rebar reaches the critical concentration of chloride concentration. Furthermore, efforts were made through giving examples in analysis of the distribution rule of chlorine ion contained in the circular section members when attacked by traditional single-dimension and two-dimension chlorine ions as well as the service life of concrete members with different sections. The examples demonstrate that if circular section members were adopted to design the durability of the concrete structure in resisting chlorine ion erosion, the durability the concrete mix-ratio scheme requires would be extended and achieved, beneficial to making it less difficult to prepare concrete and cutting construction cost. Therefore, it concludes the circular section member is more durable than rectangular section member.

Numerical Investigation of Load‐Carrying Capacity of GFRP‐Reinforced Rectangular Concrete Members Using CDP Model in ABAQUS

The present work demonstrates the nonlinear finite element analysis (NLFEA) of 13 concentrically and eccentrically loaded short rectangular concrete column specimens reinforced with GFRP and conventional steel bars. GFRP bars are lightweight having the high tensile strength and high corrosion resistance. An NLFEA model for the rectangular concrete specimens was developed using the commercial software ABAQUS Standard and calibrated for different materials and geometric parameters based on the previous experimental test results of the studied specimen. The behavior of reinforced concrete was modelled using the concrete damaged plasticity (CDP) model, the behavior of steel bars was simulated as a bilinear elastoplastic material, and the GFRP bars were considered as a linear elastic material. After the calibration of CDP parameters, the control sample was used for the further numerical parametric analysis to investigate the effect of critical parameters, i.e., the area of concrete (Ac), the compressive strength of concrete (), and the ratio of longitudinal reinforcement (ρl) and transverse reinforcement (ρt) on the load‐carrying capacity of columns. The results show that the selected NLFEA model can simulate the behavior of columns accurately and there was good agreement of numerical results obtained from ABAQUS Standard with the experimental results.

Optimization-Based Improved Softened-Membrane Model for Rectangular RC Members under Combined Shear and Torsion

AbstractRC elements are often subjected to combined actions including torsion under seismic events. Understanding the behavior of RC members under combined actions including torsion is essential fo...

Energy dissipation models for RC members and structures

SummaryThe unloading parameters of hysteretic models for RC members are given in terms of their shear‐span‐to‐depth ratio and the viscous damping used to model other energy dissipation sources. They reflect the energy dissipation in full post‐yield load cycles in 534 tests of rectangular or circular members. Pre‐yield hysteretic energy dissipation—ignored if the model is elastic till yielding—amounts in the tests to a mean viscous damping around 8.5% and can be considered in nonlinear response‐history analysis through a new model which combines constant elastic stiffness in virgin loading with hysteretic energy dissipation both before and after yielding. Models with linear behavior till yielding and hysteretic energy dissipation only after it come closer to the results of the new model if viscous damping is 5%.

A model to predict the torsional stiffness of ‘U-wrapped’ reinforced concrete beams

Wrapping is one of the effective ways of strengthening concrete elements. Several researchers have reported on the effectiveness of wrappings made from glass-fibre-reinforced polymers and carbon-fibre-reinforced polymers for improving the strength of concrete elements. Wrapping on three sides (‘U-wrapping’) is an effective method for enhancing the strength of beams supporting slabs, but scant literature is available on the strength enhancement of ‘U-wrapped’ concrete elements subjected to torsional loads. In the investigation reported in this paper, an attempt was made to quantify the improvement in the twist of U-wrapped rectangular concrete members subjected to torsional loads. Ferrocement was used as the wrapping material. Beams were cast with different amounts of reinforcement in the core and different wrapping portions, and the core concrete grade and wrapping mortar strength were also varied. The wrapped beams were analysed with the help of MARS software. An analytical model was subsequently developed to predict the secant stiffness at cracking torque (SSCT) using skew bending theory incorporating material properties. The model predictions for SSCT were found to be in good agreement with experimental test results.

Performance of segmental self-centering rubberized concrete columns under different loading directions

Segmental self-centering columns are an advantageous construction choice in earthquake prone areas due to their minimal or even zero residual deformation and their low repair/downtime costs. This research investigated the behavior of segmental rectangular column members with a high cross-sectional length to width ratio under different loading directions, with the aim of potentially extending the concept of segmental self-centering columns to wall members, such as shear walls and retaining walls. The main parameters of this study were the direction of loading: in-plane (strong-axis bending) and out-of-plane (weak-axis bending), provision (or absence) of reinforcement, and the type of concrete material (conventional concrete or rubberized concrete). Eight concrete columns with a cross-sectional length to width ratio of 2.5 and consisting of three concrete segments with dry joints in between, were tested under reversed-cyclic lateral loading. A pre-stressing force of 100 kN, corresponding to a stress of 2.8 MPa on the column, was applied using unbonded post-tensioning (PT) bars. The results indicated that although in-plane loaded columns had a higher load capacity, they exhibited a less ductile response, higher level of damage and higher loss in the PT force, compared with the out-of-plane loaded columns. The total equivalent viscous damping and its variation was very small in all tested specimens, and it increased slightly as the drift ratio increased. Empirical equations were developed to express the damping as a function of drift ratio. It was also concluded that in the out-of-plane loaded specimens, the effect of reinforcement on the load-displacement response was insignificant. In rectangular columns with high length-to-width ratio, under out-of-plane loading, if a minimum level of axial pre-stressing is applied (to prevent shear or sliding failure), no structural reinforcement is required. In addition, the strength reduction due to using rubber in concrete at the structural level was much lower than that at the material level. The results of this study can potentially be applied to segmental concrete walls due to the high length-to-width ratios of the tested columns.

High-Strength Rectangular CFT Members: Database, Modeling, and Design of Short Columns

AISC 360-16 (the current AISC Specification) does not endorse the use of high-strength materials (Fy≥525 MPa and fc′≥70 MPa) for concrete-filled steel tube (CFT) columns because of a lack of adequate research and comprehensive design equations. This paper makes a contribution toward addressing this gap and proposes effective stress-strain relationships and design equations for high-strength rectangular CFT members using a three-step method. The first step consists of compiling the experimental database of high-strength rectangular CFT column tests in the literature and evaluating the possibility of extending the current AISC 360-16 design equations to high-strength rectangular CFT short columns. The second step consists of developing and benchmarking detailed three-dimensional (3D) nonlinear finite-element models for predicting the behavior of high-strength CFT columns from the database. The benchmarked models are then used to perform comprehensive parametric studies to (1) address gaps in the database and (2) develop effective stress-strain relationships for modeling the steel tube and concrete infill of high-strength rectangular CFT members, while indirectly accounting for the effects of confinement, yielding, and local buckling. The third step consists of using these effective stress-strain relationships and the enhanced database to propose a new design approach (including equations) for high-strength rectangular CFT short columns. Finally, a reliability analysis is performed to establish a resistance (strength reduction) factor (ϕ) to be used with the proposed design equations.

Dominance of debonding defect of CFST on PZT sensor response considering the meso-scale structure of concrete with multi-scale simulation

Abstract Piezoelectric-lead-zirconate-titanate(PZT)-based interface debonding defects detection for concrete filled steel tubulars (CFSTs) has been proposed and validated through experiments, and numerical study on its mechanism has been carried out recently by assuming that concrete material is homogenous. However, concrete is composed of coarse and fine aggregates, mortar and interface transition zones (ITZs) and even initial defects and is a typical nonhomogeneous material and its mesoscale structure might affect the wave propagation in the concrete core of CFST members. Therefore, it is significantly important to further investigate the influence of mesoscale structure of concrete on the stress wave propagation and the response of embedded PZT sensor for the interface debonding detection. In this study, multi-physical numerical simulation on the wave propagation and embedded PZT sensor response of rectangular CFST members with numerical concrete core considering the randomness in circular aggregate distribution, and coupled with surface-mounted PZT actuator and embedded PZT sensor is carried out. The effect of randomness in the circular aggregates distribution and the existence of ITZs are discussed. Both a local stress wave propagation behavior including transmission, reflection, and diffraction at the interface between concrete core and steel tube under a pulse signal excitation and a global wave field in the cross-section of the rectangular CFST models without and with interface debonding defects under sweep frequency excitation are simulated. The sensitivity of an evaluation index based on wavelet packet analysis on the embedded PZT sensor response on the variation of mesoscale parameters of concrete core without and with different interface debonding defects under sweep frequency voltage signal is investigated in details. The results show that the effect of the interface debondings on the embedded PZT measurement is dominant when compared to the meso-scale structures of concrete core. This study verified the feasibility of the PZT based debonding detection for rectangular CFST members even the meso-scale structure of concrete core is considered.