Theoretical and experimental study on empty and foam-filled columns with square and rectangular cross section under axial compression

Core confinement and cover spalling in square and rectangular SCC and SFRC columns

Strength and ductility of spirally reinforced rectangular concrete columns

This paper presents the experimental results on the strength and axial behavior of rectangular steel tube columns filled with cellular lightweight concrete (CLC) under axial compression. A total of 24 specimens, including 6 reinforced cellular lightweight concrete (RCLC) columns and 18 cellular lightweight concrete-filled steel tube (CLCFT) columns are investigated. The nominal dimension of the rectangular columns are 150×75 mm in cross-section and 750 mm in height. The parameter used in all tests are the ultimate compressive strengths of the CLC, which are 15 MPa, 20 MPa and 25 MPa, and the wall thicknesses of steel tubes, which are 3.0 mm, 4.5 mm and 6.0 mm. All specimens are prepared and loaded concentrically in axial compression to failure. The results of these tests demonstrated that the CLCFT columns have a linear behavior up to the approximately 80-90% of their maximum compressive load. Then, the behavior of the columns is nonlinear. The nonlinear behaviors are due to the crushing of the concrete core and local wall buckling of the steel hollow tube. In addition, it is found that the CLCFT columns have high axial deformability at the failure when compared to the reference RCLC columns. Finally, by comparing the maximum compressive load of the test results with those obtained from the ACI composite design equation, the comparison results show that calculation formula in ACI code can be applied to compute the axial capacity of CLCFT columns under axial compression.

Tests on tubular columns made of the aluminium alloy 6060-T4 under axial and oblique, quasi-static loading have been performed. The columns were fixed at one extremity, while a concentrated force was applied at the other through a rigid collar. Empty and foam-filled columns were tested for load angles equal to 0, 5, 15 and 30 degrees with respect to the longitudinal direction of the column. The column's outer diameter was 80 mm and the thickness was 1.5 mm, while the distance from the point of load application to the fixed support was 245 mm. The aluminium foam density was about 0.3 g/cm3. The response parameters were the peak force, the absorbed energy and the mean crush force, in addition to visual observations of the deformation mode and fracture. Furthermore, LS-DYNA simulations of the experiments were performed. The columns were modelled with shell elements, while brick elements were used to model the aluminium foam core. The aluminium alloy was modelled using an isotropic elastoplastic model with isotropic strain hardening. Fracture in the aluminium column was not considered in the simulations. The aluminium foam was modelled using the Deshpande-Fleck model. In selected simulations, fracture was assumed to occur at a critical value of the plastic volumetric strain. The agreement between the experimental and predicted results was in general good.

A close form solution of the maximum deflection for cracked columns with rectangular cross-sections was developed and thus the elastic buckling behavior and ultimate bearing capacity were studied analytically. First, taking into account the effect of the crack in the potential energy of elastic systems, a trigonometric series solution for the elastic deflection equation of an arbitrary crack position was derived by use of the Rayleigh-Ritz energy method and an analytical expression of the maximum deflection was obtained. By comparison with the rotational spring model (Okamura et al. 1969) and the equivalent stiffness method (Sinha et al. 2002), the advantages of the present solution are that there are few assumed conditions and the effect of axial compression on crack closure was considered. Second, based on the above solutions, the equilibrium paths of the elastic buckling were analytically described for cracked columns subjected to both axial and eccentric compressive load. Finally, as examples, the influence of crack depth, load eccentricity and column slenderness on the elastic buckling behavior was investigated in the case of a rectangular column with a single-edge crack. The relationship of the load capacity of the column with respect to crack depth and eccentricity or slenderness was also illustrated. The analytical and numerical results from the examples show that there are three kinds of collapse mechanisms for the various states of cracking, eccentricity and slenderness. These are the bifurcation for axial compression, the limit point instability for the condition of the deeper crack and lighter eccentricity and the fracture for higher eccentricity. As a result, the conception of critical transition eccentricity (e/ h)c , from limit-point buckling to fracture failure, was proposed and the critical values of (e/h)c were numerically determined for various eccentricities, crack depths and slenderness.

Kinetic properties of open rectangular columns (based on Poppe data).

Elliptical concrete-filled steel tubes (CFST) are structural elements where concrete is embedded in an elliptical steel tube, offering significant advantages such as effective axial compression resistance. These structures are widely applied in civil engineering and critical infrastructure like airport terminals and bridges. While most CFST research focuses on circular and rectangular cross-sections, there is limited study on elliptical CFST. The emergence of neural networks offers a novel approach to calculate the compressive capacity of elliptical CFST. Neural networks can learn from sample data without predefined assumptions, uncovering nonlinear relationships between the data and results. Furthermore, they can predict new variables, overcoming the constraints of traditional experimental and finite element methods. This paper proposes an advanced calculation method to quickly and accurately assess the axial compressive bearing capacity of elliptical CFST short columns. The model integrates neural network capabilities with unified strength theory, simulating the bearing capacity of elliptical CFST stub columns. Through simulation training, the method is validated for calculating the compressive performance of elliptical CFST. The findings demonstrate that this approach not only enhances computational efficiency but also provides a reliable and optimized tool for structural evaluation. The calculation efficiency of the compressive capacity of elliptical CFST based on a neural network is increased by about 23.7%.

While there is abundant research on fibre reinforced polymer (FRP)-confined circular concrete columns, information on FRP-confined rectangular concrete columns is much more limited. This paper thus presents the axial compression test results of carbon fibre reinforced polymer (CFRP)-confined concrete short columns with rectangular cross-sections. The parameters considered in this study were (a) the concrete strength; (b) the cross-sectional aspect ratio; (d) the number of CFRP layers; and (d) the corner radius. Five existing design-oriented models were used to predict the stress–strain curves of the test specimens with an aim to verify their accuracy. Considerable deviations were found between various model predictions.

This paper presents the effect of the high-strength concrete on the behavior and strength of concrete-filled steel tube (CFST) columns. To evaluate the structural performance, load-axial shortening responses, failure modes and axial load capacity are performed for ten high-strength concrete-filled steel tube (HSCFT) columns. All of the columns are 750 mm in height, and have compressive strength of 66 MPa. Test parameters included the wall thicknesses of the rectangular tube (3.0 mm, 4.5 mm and 6.0 mm) and three different of rectangular cross-sections (150×50 mm, 150×75 mm and 150×100 mm). From the experimental results, it is indicate that the load-axial shortening response of the columns have a linear behavior up to approximately 80-90% of their axial load capacity. Then, the behavior of the HSCFT columns is nonlinear with a very large deformation before failure. It is also shown that the axial load capacity and ductility of the HSCFT columns are increased significantly compared to the RC columns (reference columns), depending mainly on the wall thickness and cross-section of the hollow steel tube. Finally, by comparing the axial load capacity of the test results with those obtained from the AISC/LRFD design equation, the comparison results show that calculation formula in AISC/LRFD specification can be applied to compute the axial load capacity of HSCFT columns under axial compression.

Methods for calculating deflections (at service loads) prescribed in codes such as EC2 and ACI 318 are largely based on semi‐empirical methods validated for beams with rectangular cross sections. The applicability of these methods to beams with circular cross section is validated in this paper using experimental studies on eight circular beams with different grades of concrete and different percentages of reinforcing steel. Similar beams with square cross section have also been studied for comparison and it is found that the code estimates have more‐or‐less the same degree of conservatism for square and circular beams. The complete load‐deflection behavior generated by the test specimens could also be simulated numerically using a layered approach, considering material nonlinearity in concrete and steel rebar. Using the proposed procedure, the influences of percentage of reinforcing steel and axial compression on the load‐deflection behavior have also been studied. This study shows that the postcracking stiffness increases and ductility decreases with increase percentage of reinforcing steel. The circular beams are found to have less strength and ductility when compared to square beams (with the same area of cross section) owing to differences in distribution of steel rebar.

Experimental investigation on the fire behaviour of rectangular and elliptical slender concrete-filled tubular columns

Classical, local buckling of tubes having rectangular cross-sections

The paper presents the specification of research methods commonly encountered in the studies of heat transfer processes in minichannels. In particular the following methods have been emphasized: electrochemical limiting current method as well as the thermal balance method. In thermal balance method the mean heat transfer coefficient is determined by the set of experimental thermal measurements of the investigated heat exchanger. In turn, limiting current method is based on heat and mass transfer analogy. The discussed research methods have been implemented on two specially designed and constructed test facilities with compact minichannel heat exchangers, which have been presented and described in details. In order to validate the designed setup, the preliminary experimental measurements of two minichannel heat exchangers with hydraulic diameter of 2 mm and rectangular cross sections during single-phase liquid flows have been carried out. In further perspective it is planned to extend the experimental studies of minichannel heat exchangers and to compare the results obtained by both methods described.

Due to high bearing capacity and excellent seismic performance, the section steel reinforced concrete-filled rectangular steel tube has been widely applied in engineering. The application of stainless steel for outer steel tube can improve the durability performance of members. In this study, ABAQUS software was used to perform nonlinear seismic analysis on section steel reinforced concrete-filled rectangular stainless steel tubular columns, and the numerical model was validated against experimental data. The mechanism and parametric study of the hysteresis performance were conducted. These parameters mainly include: concrete strength, strength of stainless steel, strength of section steel, steel ratio of stainless steel tube, steel ratio of section steel, axial compression ratio, and slenderness ratio. The analysis results showed that: increasing the strength of stainless steel tube and concrete can significantly improve the bearing capacity of members, but the strength of section steel has little effect; the bearing capacity decreases with the increasing slenderness ratio; when the axial compression ratio is smaller than 0.4, increasing axial compression can improve the bearing capacity. The strength of each material shows little influence on the shape of load–displacement skeleton; the axial compression ratio presents high effect on the shape of descending stage of curve, and the larger the axial compression ratio, the steeper the descending stage; the slenderness shows high influence on curve shape, and the larger the slenderness, the less the elastic stiffness, and the more gentle the descending stage of curve. Finally, a simplified load–displacement hysteretic model was proposed, which exhibits good agreement with finite element numerical analysis.

A theory of concentric, kink and sinusoidal folding and of monoclinal flexuring of compressible, elastic multilayers: IV. Development of sinusoidal and kink folds in multilayers confined by rigid boundaries