Experimental and numerical studies on interface debonding visualization for a rectangular CFST column with surface stress wave measurement and a threshold-based probability imaging algorithm

Strength and ductility of spirally reinforced rectangular concrete columns

Experimental study of rectangular CFST columns subjected to eccentric loading

The current paper provides a comprehensive review of experimental studies on corrosion damaged reinforced concrete (RC) components, and the ability of current state-of-the-art numerical models to predict the residual capacity of these corroded RC components. The experimental studies on corroded RC components are classified into five different categories including: (i) beams in flexure, (ii) beams in shear, (iii) columns under pure axial compression, (iv) circular columns in flexure, and (v) rectangular columns in flexure. For each group, a summary of all the previous research are provided. Through the regression analyses, the experimental results of each abovementioned groups are used to examine the adverse effect of corrosion on ductility and, flexural, shear, and axial capacity loss of the corroded RC components. Finally, the observed results of the previous experimental studies are compared with the predicted values using the state-of-the-art numerical models currently available in the literature. The summarised experimental results show that corrosion has much more adverse impact on ductility of the RC columns than strength. However, the effect of corrosion on ductility and strength reduction of RC beams is the same. Moreover, results of cross-sectional moment-curvature analyses using the state-of-the-art corrosion damage models show a good correlation between the predicted residual flexural capacity and observed experimental results. Finally, the existing shortcomings in the literature and open issues to be addressed in the future research are discussed, and some recommendations are provided.

A systematic experimental study and dimensionless analysis of bubble plume oscillations in rectangular bubble columns

Interface bonding conditions between concrete and steel materials play key roles in ensuring the composite effect and load-carrying capacity of concrete-steel composite structures such as concrete-filled steel tube (CFST) members in practice. A method using both surface wave and electromechanical impedance (EMI) measurement for detecting the existence and the location of inaccessible interface debonding defects between the concrete core and steel tube in CFST members using piezoelectric lead zirconate titanate (PZT) patches as actuators and sensors is proposed. A rectangular CFST specimen with two artificially mimicked interface debonding defects was experimentally verified using PZT patches as the actuator and sensor. By comparing the surface wave measurement of PZT sensors at different surface wave travelling paths under both a continuous sinusoidal signal and a 10-period sinusoidal windowed signal, three potential interface debonding defects are quickly identified. Furthermore, the accurate locations of the three detected potential interface debonding defects are determined with the help of EMI measurements from a number of additional PZT sensors around the three potential interface debonding defects. Finally, the accuracy of the proposed interface debonding detection method is verified with a destructive observation by removing the local steel tube at the three detected interface debonding locations. The observation results show that the three detected interface debonding defects are two mimicked interface debonding defects, and an unexpected debonding defect occurred spontaneously due to concrete shrinkage in the past one and a half years before conducting the test. Results in this study indicate that the proposed method can be an efficient and accurate approach for the detection of unknown interface debonding defects in existing CFST members.

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

Reliability analysis of normal strength CFST rectangular columns through multiple approaches

3 extended-end-plate joints of T-shaped concrete-filled rectangular composite tubular column with H-shaped beam were designed. The experimental research and ANSYS nonlinear finite element analysis on the earthquake resistance behaviors of the joints were conducted under low cyclic loading. The results indicate that the shapes of hysteresis curve of each specimen is full and presents spindle, all the specimens possess good energy dissipation capacity. The end-plate thickness and high-strength bolt diameter have a great influence on the bearing capacity of the joints. Increasing the thickness of end-plate and the diameter of high-strength bolt, the displacement ductility factors of the joints decrease slightly, but their ultimate bearing capacities obviously enhance. The stress distributions and the finite element failure characteristics of the joints are basically consistent with the test phenomena, yield bearing capacity and ultimate bearing capacity of the finite element calculations can agree well with the experimental results.

Liquid flow patterns in rectangular air-water bubble column investigated with Radioactive Particle Tracking

Experimental and theoretical studies have been carried out to predict the fire resistance of rectangular hollow steel columns filled with bar-reinforced concrete. A mathematical model to calculate the temperatures, deformations, and fire resistance of the columns is presented in this paper. Calculated results are compared with those measured. The results indicate that the model is capable of predicting the fire resistance of square hollow steel columns, filled with bar-reinforced concrete, with an accuracy that is adequate for practical purposes. The model enables the expansion of data on the fire resistance of square concrete-filled steel columns, which at present consists predominantly of data for columns filled with plain concrete with data for columns filled with bar-reinforced concrete. Using the model, the fire resistance of square concrete-filled steel columns can be evaluated for any value of the significant parameters such as load, column-section dimensions, column length, and the percentage of r...

This paper presents behaviour of normal concrete, ultrahigh-strength concrete, engineered cementitious composite, lightweight concrete, self-consolidating concrete and crumb rubber concrete under confinement. Forty-six circular, square and rectangular concrete-filled steel tube columns with varying slenderness are tested under axial compression. Failure modes, axial load–displacement responses and stress–strain characteristics are analysed as well as concrete confined strengths are determined based on experimental results and existing models. The performance of existing confined strength models is evaluated and modified to accommodate different types of high-performance concretes and column shapes. The modified model improves the prediction of confined concrete strength with a mean predicted-to-experimental ratio of 1.05 as shape and concrete type factors are introduced.

In concrete structures, damage is identified by the appearance of cracks on the surface. Monitoring the level of tensile stress in the material provides an indication of microcrack localization, which leads to the formation of a crack in the medium. In this study, the stress in the substrate leading to the localized cracking in a concrete substrate is evaluated using surface-mounted PZT patches. The PZT patches are used in a local electrical impedance (EI) measurement mode and for distributed stress wave measurements. The EI measurements from PZT patches sensitively detect the tensile stress in the substrate. The localization of damage resulting in the formation of a crack in the concrete medium is detected sensitively by stress wave measurements. A frequency-dependent attenuation factor, which is independent of the intervening material effects is presented for quantifying the changes in the stress waves. The localization of microcracks leading to the formation of a crack is detected by the attenuation factor measurements of stress waves significantly before visual detection of a surface crack. The combined use of the EI measurement with the distributed stress wave attenuation allows for detecting stress and microcracking in the concrete leading up to the formation of a localized crack. The attenuation factor gives an indication of the crack opening once the crack is formed.

Bars of 1 in (25 mm) square section and frames made up of such bars are impacted at various points and the development of ensuing vibrations is studied by means of strain gauges. Experimental methods and recording equipment normally used for relatively slow impact tests are described.

To investigate the seismic performance of hollow reinforced concrete (RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges (JTG/T B02-01-2008). The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.

This paper presents a comprehensive experimental study on the behaviour of FRP-confined concrete in square and rectangular columns and focuses on some issues that might be addressed with a view to improving the predictive models. For this purpose, 31 prismatic concrete specimens with a height of 600 mm and low- and medium-strength concrete (20–35 MPa) were tested under centred compression. The parameters studied were the aspect ratio between the sides of the section (1, 1.5 and 2), the radius of curvature of the corners (20, 25 and 30 mm) and the number of carbon FRP layers applied. The experimental results included stress–strain curves of specimens and detailed information about the confined concrete strength and the axial and lateral strain achieved on the FRP jacket during the tests. The stress–strain response and ultimate condition are analysed, showing that FRP jacketing is an efficient technique for increasing the strength and strain capacity, but that confinement efficiency decreases as the aspect ratio of the section increases. In spite of such decrease, significant strength improvement was achieved for low-strength concrete in rectangular sections with aspect ratios of 1.5 (strength gain up to 81%), and even 2 (up to 36%). The axial strength of the tests was compared with the design criteria of four international guidelines, resulting in predictions that did not properly fit for rectangular sections. A predictive equation is proposed to assess the axial compressive strength of the FRP-confined concrete, which includes a better adjustment for the strain efficiency factor and the shape factor for rectangular columns.