Failure Modes Of Columns Research Articles

Research on column overdesign factor of reinforced concrete frame structures in the 2022 Ms 6.8 Luding earthquake

The strong column-weak beam failure mode of reinforced concrete (RC) frame structures is one of the most important targets of structural seismic design and is primarily realized by a reasonable column overdesign factor (COF). However, most RC frame structures in previous earthquakes were often subjected to strong beam-weak column failure modes. To address this issue, the RC frame with a strong column-weak beam failure mode and a typical strong beam-weak column RC frame in the 2022 Ms 6.8 Luding earthquake were intensively studied in this study. The differences between the two failure modes of the RC frame structure were comparatively analyzed at both the overall structure and member levels. A numerical simulation was conducted to obtain the structural response under actual ground motion. Finally, a probabilistic analysis method was adopted to process the COF data of the RC frame joints. The results indicate that the structural safety redundancy of the RC frame with the undesired failure mode cannot be fully utilized, whereas the RC frame with the strong column-weak beam failure mode allows more structural members to participate in the energy dissipation through a complex redistribution mechanism of internal forces. Damage to the infill wall further mitigates the degree of damage to the main structure and reduces the risk of soft-story failure. The COF of the actual RC frame structure shows a non-uniform distribution, and it is recommended that the COF be higher than 1.5 for the seismic design of the structure following the Chinese code.

Axial compressive behavior of reinforced hollow circular high strength concrete filled steel tubular short columns

This study aims to investigate the mechanical behavior of reinforced hollow circular high-strength concrete-filled steel tubular (RHCFST) short columns under axial compression. The axial compression test of 6 RHCFST short columns was carried out, and the bearing capacity, ductility and failure modes of the columns were analyzed. The results revealed that the failure modes of RHCFST short columns primarily included mixed failure, shear failure, and crushing failure. Comparatively, the failure modes of specimens with ordinary reinforcement exhibited a shift towards mixed failure, significant improvement in ductility, and a decrease in the increase trend of ultimate bearing capacity with the growth of steel tube thickness. Based on the test results, finite element models were developed using ABAQUS software for parameter analysis. The results demonstrated a positive correlation between the short column’s bearing capacity and parameters such as steel strength, sandwich concrete strength, steel tube thickness, and ordinary reinforcement diameter. Additionally, the initial stiffness of the short column increased with the increase of steel tube thickness. Considering the mechanical properties and engineering applicability of the member, the recommended design of steel tube yield strength, sandwich concrete strength, steel tube thickness and ordinary reinforcement diameter were given. Furthermore, the axial bearing capacity calculation formulae for RHCFST short columns were proposed. The calculated values were found to closely match both experimental and simulated values, with errors falling within 10 %. Consequently, the formulae can offer a reliable prediction of the member’s axial bearing capacity.

Study on Seismic Performance of RC Frame Structures Considering the Effect of Infilled Walls

This paper studies the impact of half-height infilled walls on the failure modes of frame columns through quasi-static tests of both frame models and half-height infilled wall frame models. Based on the experimental results, a seismic analysis model of reinforced concrete (RC) frame structures is established, and parametric studies are carried out to analyze the effects of masonry materials and masonry heights on the seismic performance of structures. The results show that the load-bearing capacity and stiffness of the structure are improved, while the ductility of the structure is reduced because of the existence of infilled walls. As the height of infilled walls increases, there is a notable decrease in the free height of frame columns. At a wall-to-column height ratio of 0.2, the masonry walls exert a negligible effect on the frame structure’s seismic performance. In contrast, at a ratio of 0.6, there is a transition in column failure modes from bending to shearing. When evaluated at consistent masonry heights, aerated concrete block-infilled walls demonstrate the least impact on the seismic performance of RC frame structures. Thus, in the absence of additional structural enhancements, the use of aerated concrete blocks is recommended to mitigate the negative implications of infilled walls on the seismic integrity of RC frames.

Axial compressive behavior of low-alkalinity seawater sea-sand concrete column reinforced with hydrophobic longitudinal SFCBs and FRP hoops

To address corrosion problem of steel bars and shortage of freshwater and river sand in marine and offshore structures, a novel hydrophobic-modified longitudinal steel-FRP composite bars (SFCB) and FRP hoops reinforced low-alkalinity seawater sea-sand concrete (SWSSC) is developed. However, axial compressive behavior of hybrid SFCB and FRP reinforced columns is not clear and the applicability of existing design methods is low. Here, nine hybrid reinforced columns have been designed and tested. Typical failure modes of columns and axial compressive behavior of constituent materials (i.e., hydrophobic reinforcements and low-alkalinity SWSSC) are investigated. It is found that the synergistic confining effect formed by hybrid reinforcement are significant. The mesh confinement formed by densely distributed FRP hoops and longitudinal SFCBs improves the local buckling behavior, and effectively constrains the lateral expansion of concrete core, resulting in improved compressive strength and ductility of column. The compressive contribution of single longitudinal SFCB to ultimate load capacity of column can be enhanced effectively, up to 36.3 %, by increasing steel content of SFCB. Based on this, a prediction model of hybrid reinforced columns is proposed, which can accurately evaluate the ultimate load capacity. This work provides valuable experimental observations and load capacity model for hybrid reinforced column, which promote its design and application in marine engineering.

Exterior weak-axis beam-to-column bolted connections between GFRP I-shaped pultruded profiles using stainless steel cleats

This paper presents an experimental investigation on the mechanical behaviour of bolted GFRP pultruded profiles beam-to-column connections, using I-shaped profiles and stainless-steel cleats, rotating around the weak-axis of the column. Using metallic cleats increases resistance, by comparison with composite cleats, using straightforward connection systems, unlike cuff connections, that can be readily used in construction. The campaign included web-cleated and flange-cleated connections, using different cleat thicknesses (4 mm, 6 mm and 8 mm), investigating the influence of the edge end distance (w.r.t. the beam end). The specimens were tested under monotonic and cyclic loads. The results show that the thickness of the cleats influences the behaviour of the flange-cleated configuration, but not that of the web-cleated connections. Additionally, while the former configuration can be considered as semi-rigid, for design, web-cleated connections should be considered as pinned. Both configurations presented significant resistance and rotation capacity, unlike connections using GFRP cleats, reported in previous research. On the other hand, the cyclic tests indicate that these connections present limited energy dissipation capacity, therefore they are not expected to contribute to dissipate energy under seismic actions. Overall, the results show that these weak-axis connections can support load bearing beams, although global structural design must avoid their (brittle) column failure modes.

Dynamic behaviors of eccentrically loaded RC column under lateral low-velocity impact

This study aims to examine the influence of eccentric axial loads on the lateral low-velocity impact behaviors of RC columns. Firstly, the numerical simulation approach is validated by accurately reproducing the impact force, as well as the deflection, axial load and failure mode of columns in pendulum impact and eccentrically loading tests. Secondly, the effects of the axial load ratios and eccentric distances on the dynamic behaviors of RC columns are analyzed as follows: (i) Increasing the axial load ratio and the eccentric distance at the impact direction can reduce the deflection of RC columns when the axial load ratio is relatively low; (ii) the instability failure could occur on columns with large enough axial load and impact energy; (iii) the eccentric distance of axial loads on the fixed-supported RC column can be neglected since the induced boundary rotation is constrained by fixed supports; (iv) for RC columns with pinned-fixed or pinned-pinned supports, the eccentric distance at the impact direction should be considered, while the eccentric distance at the vertical impact direction can be neglected. Furthermore, the dynamic coupled flexural and shear resistance function of eccentrically loaded RC columns are established and validated. A 2DOF model is presented to predict low-velocity impact behaviors of RC columns with varying axial load ratios and eccentric distances. The failure modes transition mechanism induced by the axial load is further revealed. Increasing axial loads can enhance columns’ flexural resistance and tendency of failure mode from flexural to shear/flexure-shear. The P-δ effect is amplified by larger axial loads and deflections, causing the instability failure of columns. Finally, a theoretical impact energy of the critical instability of eccentrically loaded RC columns is proposed to assist the structural impact-resistant design.

A Machine-Learning-Based Failure Mode Classification Model for Reinforced Concrete Columns Using Simple Structural Information

The seismically deficient column details in existing reinforced concrete buildings affect the overall behavior of the building depending on the failure type of the column. The purpose of this study is to develop and validate a machine-learning-based prediction model for the column failure modes (shear, flexure–shear, and flexure failure modes). For this purpose, artificial neural network (ANN), K-nearest neighbor (KNN), decision tree (DT), and random forest (RF) models were used considering previously collected experimental data. Using four machine learning methodologies, we developed a classification learning model that can predict the column failure modes in terms of the input variables using the concrete compressive strength, steel yield strength, axial load ratio, height-to-dept aspect ratio, longitudinal reinforcement ratio, and transverse reinforcement ratio. The performance of each machine learning model was compared and verified by calculating the accuracy, precision, recall, F1-Score, and ROC. Based on the performance measurements of the classification model, the RF model has the highest average value for the classification model performance measurements among the considered learning methods and can conservatively predict the shear failure mode. Thus, the RF model can rapidly predict the column failure modes with the simple column details. Additionally, it was demonstrated that the predicted failure modes from the selected model were exactly same as the failure mode determined from a code-defined equation (traditional method).

Self-centering capacity of RC columns reinforced by martensitic NiTi SMA bars in plastic hinge region

This study aimed to assess self-centering in reinforced concrete (RC) columns incorporating martensitic shape memory alloy (SMA) bars within the plastic hinge region. Three RC columns were prepared: one conventional, the others with SMA bars in the hinge zone. Columns, 400 mm in diameter and 1400 mm in height, with an aspect ratio of 3.5, were used. SMA bars, 400 mm long, were connected to steel rebars with specialized couplers. Through cyclic lateral loading, lateral displacements and corresponding forces were measured. Strain in the SMA bars was also recorded. The RC column with SMA bars displayed a plastic hinge near the couplers, concentrating concrete damage at this location, a departure from the conventional column failure mode. SMA bars remained elastic, while steel rebars yielded within the couplers. The RC column with SMA bars demonstrated exceptional self-centering, recovering about 95% at a 5% drift. However, its energy dissipation capacity was lower than the conventional RC column. The equivalent damping ratio for the RC column with SMA bars stabilized at approximately 3% after a 1.75% drift. This suggests that the remarkable self-centering capacity in the RC column with SMA bars was primarily due to the elastic behavior of the martensitic SMA bars.

Performance of eccentrically loaded ultra-high-strength concrete-filled Q770 steel tubular columns with varying slenderness ratios: Experimental and numerical investigations

This study conducts experimental and numerical investigations into the response of ultra-high-strength (UHS) concrete-filled ultra-high-strength steel tubular (UHSCFST) columns under eccentric loading, varying the slenderness ratio, to develop effective design guidelines for engineering applications. A series of eccentric compression tests were conducted on twelve UHSCFST columns with varying slenderness ratios to identify failure mechanisms and load-bearing characteristics. In the experimental program, critical influencing factors, including load eccentricity ratio, slenderness ratio, and UHS steel strength, were considered. Finite element models of eccentrically loaded UHSCFST columns were developed using ABAQUS and validated through a comparison of tested and simulated results to analyze load-sharing ratios and stress distribution for each column component. The findings indicated that UHSCFST column failure modes were characterized by compression-controlled and flexure-dominated damage under the combined effects of slenderness ratio and load eccentricity ratio. UHS concrete played a dominant role in bearing the eccentric load, and a judicious selection of UHS steel yield strength can improve column capacity and resistance. Additionally, these validated models were employed to conduct parametric studies that evaluated the effects of design and load parameters on the eccentric load capacity of UHSCFST columns. Design equations were developed based on tested and simulated results to predict the ultimate load capacity of UHSCFST column with varying slenderness ratios under eccentric loading conditions.

Hysteretic behaviors of square hollow column-truss beam-diagonal brace connections in steel buildings

This paper presents a novel square hollow column-truss beam connections incorporating diagonal braces, aimed at enabling accurate and efficient onsite assembly of modular, multi-story, and high-rise prefabricated steel structures. The hysteretic behavior of these connections was assessed through experimental study of ten cross-shaped specimens. Based on the experimental study, the load-displacement curve, ultimate bearing capacity, ductility and energy dissipation capacity were carefully examined. The test results show that with different combinations of critical components, three distinct failure modes including beam, column, and diagonal brace failure were demonstrated. For specimens without diagonal braces, the dominating failures were concentrated either on the beam or the column regions, and the hysteretic behavior of specimens with beam failure mode was superior than that of specimens with column failure mode. With incorporation of the diagonal braces in the connections, the failure region of specimens was shifted from the truss beam or the column to the braces, and the stiffness and load capacity of the connection were significantly improved. In addition, finite element model was established, and the accuracy of the numerical simulation results was verified by test results. Finally, based on the experimental and finite element analysis (FEA) results, the strategy for controlling the occurrence location and sequence of critical damage of such connections were proposed.

Axial Compressive Behavior of Cross-Shaped CFST Stub Columns with Steel Bar Truss Stiffening.

Concrete-filled steel tube (CFST) columns have been widely used in residential buildings due to their high bearing capacity, good ductility, and reliable seismic performance. However, conventional circular, square, or rectangular CFST columns may protrude from the adjacent walls, resulting in inconvenience in terms of the arrangement of furniture in a room. In order to solve the problem, special-shaped CFST columns, such as cross-shaped, L-shaped, and T-shaped columns, have been suggested and adopted in engineering practice. These special-shaped CFST columns have limbs with the same width as the adjacent walls. However, compared with conventional CFST columns, the special-shaped steel tube provides weaker confinement to the infilled concrete under axial compressive load, especially at concave corners. The parting at concave corners is the key factor affecting the bearing capacity and ductility of the members. Therefore, a cross-shaped CFST column with steel bar truss stiffening is suggested. In this paper, 12 cross-shaped CFST stub columns were designed and tested under axial compression loading. The effects of steel bar truss node spacing and column-steel ratio on the failure mode, bearing capacity, and ductility were discussed in detail. The results indicate that the columns with steel bar truss stiffening can change the final deformation mode of the steel plate from single-wave buckling to multiple-wave buckling, and the failure modes of columns also subsequently change from single-section concrete crushing failure to multiple-section concrete crushing failure. The steel bar truss stiffening shows no obvious effect on the axial bearing capacity of the member but significantly improves the ductility. The columns with a steel bar truss node spacing of 140 mm can only increase the bearing capacity by 6.8% while nearly doubling the ductility coefficient from 2.31 to 4.40. The experimental results are compared with those of six design codes worldwide. The results show that the Eurocode 4 (2004) and the Chinese code CECS159-2018 can be safely used to predict the axial bearing capacity of cross-shaped CFST stub columns with steel bar truss stiffening.

Fire-resistance behavior of concrete columns produced with recycled ceramic and silica aggregates: An experimental and numerical approach

This article aims to fully assess the fire-resistance behavior of fiber-reinforced concrete (FRC) columns made with recycled ceramic aggregates when subjected to severe thermal loading. In addition, the effects of fiber reinforcements and ceramic recycled aggregates (RAs) on the thermal behavior of concrete columns were addressed and compared with that of the conventional silica-made concrete columns. In this regard, twelve small-scale FRC columns containing recycled ceramic and silica aggregates are prepared and placed in a heating chamber for 90 min. Next, the columns were axially loaded until failure, and variations in compressive stress and axial strain of the specimens were measured, aiming to capture the thermal effects on the load-carrying capacity, axial strain, and failure modes of the concrete columns. The specimens were exposed to high temperatures of 20 °C, 600 °C, and 1000 °C according to ISO 834 Fire Standard, and were tested in humid and dry environmental conditions. Moreover, the failure modes of the columns (e.g., concrete spalling, crack pattern, etc.) are presented in terms of macroscopic imaging. In addition, in-depth analyses of the effects of fibers (steel and polypropylene) and moisture content on the thermal behavior of concrete columns is addresses utilizing scanning electronic microscope (SEM) technique. The results indicate that below the temperature of 600 °C, the axial behavior of the FRC columns with silica and ceramic aggregate are similar. However, as the temperature rises, the reduction in axial load-bearing capacity of the columns with silica aggregates is higher than that of the columns with ceramic aggregates. Also, it was observed that the environmental humidity negatively affects the overall fire-resisting behavior of the columns. Furthermore, a numerical procedure is presented in ABAQUS to estimate the behavior of FRC columns subjected to thermal loading and validated using the experimental results.

Prediction of column failure modes based on artificial neural network

Prediction of column failure modes based on artificial neural network

Experimental study on the effects of whole heating cycle on post-fire behavior of restrained high strength structural steel columns

This paper presents the results of an experimental study of post-fire behavior and residual strength of restrained high strength structural steel (HSSS) columns, including loading tests of columns at ambient temperature to failure, restrained columns under sustained loading going through heating and cooling cycle in fire and then followed by post-fire loading tests to failure. All the columns were axially restrained in fire. The investigated parameters include with and without rotational restraint, load eccentricity, load ratio and maximum experienced temperature. It was found that if the column failure mode was predominantly overall buckling (columns without rotational restraint in this study), the heating and cooling process would result in a large residual lateral deflection in the column, and the post-fire load carrying capacity of the column would be much lower than without fire exposure. On the other hand, if the column slenderness was low and its failure mode was mainly cross-section yielding (columns with rotational restraint in this study), the post-fire residual lateral deflection was low and the post-fire column would be able to retain a very high proportion of its load carrying capacity without fire exposure, and sometimes even exceeded this value due to strain hardening, which indicated complete reusability of such columns.

Experimental and numerical studies on seismic behavior of new cross square hollow column-truss beam connections

Five cyclic tests on the specimens were conducted to investigate seismic behavior of new cross square hollow column-truss beam connections. The variables are beam, column section size and axial force ratio. The paper reports on the failure modes, hysteretic curves, ultimate load carrying capacity, ductility, energy dissipation capacity, and stiffness degradation of the specimens. Two types of failure modes, i.e., column failure and beam failure mode, were found from the tests. The specimens experiencing the column failure mode exhibit poor seismic performance due to the overall instability induced by the occurrence of the plastic hinge of the column. While, the specimens displaying the beam failure mode exhibit well seismic behavior owing to the redistribution of the plastic stresses among the members of the truss beam. Noteworthy, the failure mode will change from column failure to beam failure when the column thickness increases and the axial force ratio decreases. Additionally, in the beam failure mode, the increase of the column thickness can improve the connection’s bearing and energy dissipation capacity, while the impact of the axial force ratio can be ignored. Based on the test results, the limit value of axial force ratio corresponding to the boundary failure mode under different column thicknesses is determined by using the nonlinear numerical model.

Numerical Analysis on Dynamic Response of CFRP-Wrapped RC Columns under Lateral Impact Loading

This paper presents a numerical study examining the dynamic response and resistance mechanism of reinforced concrete (RC) columns strengthened with or without carbon-fiber-reinforced polymer (CFRP) wraps under lateral impact loading by using the software LS-DYNA. First, the information of eight column models was briefly introduced as part of the laboratory experimental program from the literature. Secondly, finite element (FE) models were established in terms of the geometries of impact tests. Then, a detailed comparison between numerical results and experimental results was made, and FE models showed a relatively high simulation accuracy. Subsequently, a series of parametric analyses were carried out with a focus on the effects of axial compression ratio, the boundary condition at the column top, the layer number of CFRP wraps, and the impact velocity and impact height on the dynamic responses of plain and strengthened columns. The results demonstrated that the CFRP retrofit mechanism was not activated during the initial Stage-I when the impact force rapidly increased to the first peak and then decreased to zero. CFRP strengthening came into play in the second stage, Stage-II, and affected the response of the shear force and moment along the column height, as well as had a great influence on the control of shear damage. The dynamic response of RC columns was more sensitive to the impact velocity than to other parameters, regardless of whether CFRP wrapping was applied. The axial compression ratio would have a different influence on the column failure mode if the impact velocity was varied. The variation in impact height and boundary condition at the column top had little influence on the damage mode of strengthened columns.

The Efficiency of Steel Brace Strengthening of School Buildings according to the Failure Mode of Columns

The Efficiency of Steel Brace Strengthening of School Buildings according to the Failure Mode of Columns

Global buckling behaviour of bamboo scrimber box columns under axial compression: Experimental tests and numerical modelling

With the advancement of manufacturing technologies, bamboo scrimber members made of hot-pressed plates have been increasingly used in building structures in the form of thin-walled members. However, limited investigations have been conducted on global buckling behaviour of bamboo scrimber members. This paper presents experimental tests and numerical simulations of the global buckling behaviour of bamboo scrimber columns. Six groups of box columns with different slendernesses were tested under axial compression. The buckling resistance and failure mode of columns were obtained. Test results showed that due to the inelastic stress-strain relationship of bamboo scrimber, most of the box columns exhibited inelastic global buckling, with significant lateral deflections at failure. Comparisons were made between experimental results and design equations in existing codes for glulam structures to evaluate the applicability of the design equations to bamboo scrimber columns. Besides, numerical simulations were also performed for bamboo scrimber columns under axial compression, in which the nonlinear stress-strain relationship and geometric imperfections were incorporated. Numerical results showed that the model could predict the global buckling resistance of columns with reasonably good accuracy. Based on the numerical model, parametric studies were conducted on the effect of column slenderness on the buckling resistance. Finally, design recommendations were proposed for bamboo scrimber columns against global buckling.

Experimental analysis of embankment on soft soil improved with bottom ash columns

Bottom ash is a byproduct formed during the combustion of coal and can be used as an alternative to aggregate and sand as a green material in columns to achieve sustainability in ground improvement. In this study, the bearing capacity performance of highway embankment models constructed on bottom ash columns reinforced soil was investigated. Model tests were carried out with various area replacement ratios (Ar) of 10.91 %, 16.37 % and 21.83 % and column length to diameter ratios (L/D) of 6 and 8. Load cell and three miniature pressure transducers were used for the measurement of vertical stress on the embankment surface, top and base of the column and adjacent soil surrounding the columns. A Pore pressure transducer was employed to record the excess-pore water pressure during the loading test. The stress concentration ratio and column failure modes were investigated for the stress transfer mechanism. The tests results revealed that bottom ash columns, whether floating or end bearing, was most effective in enhancing the ultimate bearing capacity (qult) of improved soil at almost 1.24, 1.39 and 1.63 times and 1.27, 1.42 and 1.83 times that of unreinforced soil for Ar of 10.91 %, 16.37 % and 21.83 % with L/D of 6 and 8, respectively. The stress concentration ratio (SCR) increased with higher Ar and L/D values. The highest improvement ratio was obtained for the model improved with bottom ash columns at Ar = 21.83 % and L/D = 8. The end-bearing bottom ash columns fail by bulging and floating bottom ash columns fail by bulging along with punching at the base. Furthermore, a mathematical expression with R2 = 0.9913 was developed for calculating the approximate qult. The approximate qult are in good agreement with actual qult. The findings of this study resulted in the utilization of bottom ash as a sustainable granular material in the column for the ground improvement underneath embankments.

Seismic fragility assessment of bridges with as-built and retrofitted splice-deficient columns

A significant proportion of existing bridges in high seismic regions were constructed prior to the 1970s. As a result of poor reinforcement detailing, pre-1970s bridge columns are susceptible to lap-splice or shear failure in the plastic region. Given the high economic impact of retrofitting all pre-1970s reinforced concrete (RC) bridges, it is essential to identify the most vulnerable bridges for retrofit prioritisation. Analytical fragility functions are useful for quantifying the seismic vulnerability of existing bridge stock. However, the accuracy of these fragility functions relies on the adequacy of the adopted modelling approach. This paper presents a hinge-type modelling approach for capturing the seismic response of as-built splice-deficient and retrofitted RC bridge columns. Fragility analysis is carried out for typical seat and diaphragm abutment two-span bridges using the proposed hinge-type modelling approach. The results showed that the vulnerability of the bridges depends on the column failure mode and the limit state under consideration. Also, the common notion that the column is the most vulnerable component may not necessarily be true. The study underscored that retrofitting columns without retrofitting other components may not effectively mitigate the damage and associated risk.