Column Failure Research Articles

A Quantitative Method for Seismic Robustness of RC Frame Considering Resistance Vulnerability of Column and Storey Drift Ratios

The concept of seismic robustness is proposed by combining the concept of seismic performance and structural robustness. The existing qualitative, quantitative and evaluation methods of seismic robustness are all direct researched on the whole structure, and the influence mechanism of its internal components on the overall seismic robustness is still unclear. It is very important to establish a clear relationship between component design and structural seismic robustness for the structural design, reinforcement design and final evaluation of structural seismic robustness. Based on this, taking the column as the starting point, a quantitative method for the seismic robustness of RC frame by the seismic robustness index is proposed, which takes into account the resistance vulnerability of column and influence of column on the storey drift ratios (SDRs). In which, the resistance vulnerability is represented by the defined control vulnerability coefficient Pimax, and the influence on the SDRs are represented by the storey drift ratio importance coefficients (SDRCs) λ. The method not only reflects the essential mechanical properties of the column, but also reflects the effects brought about by different SALs. The feasibility of the method is demonstrated by numerical examples of two types of failures (assuming single column and two columns failure), and four optimization design proposals are proposed for it. The analysis shows that λ of the target columns to the floor where the target columns located are obviously greater than those on the remaining floors of the target frame. The seismic robustness index R decreases sharply with the increase of the seismic action level (SAL). R is different compare single column failure with two columns failure under 4 SALs. The most effective way to improve the R of the frame under a certain SAL is to retrofit its control column.

Mechanical response of masonry structure strengthened with ultra-high performance concrete (UHPC): a comparative analysis for different strengthening tactics

Rehabilitation and strengthening of existing masonry structures can improve their safety, prolong life and save economic costs. In this study, a total of eighteen masonry column specimens strengthened by ultra-high performance concrete (UHPC) were fabricated and tested in compression. The effects of strengthening method, strengthening thickness and loading eccentricity were investigated. The failure mode, bearing capacity, strain, ductility, and energy dissipation were discussed in before and after strengthening to evaluate the UHPC strengthening effectiveness. A three-dimensional numerical model established using finite element analysis (FEA) was validated with the experimental results. Results indicated that the brittle failure of masonry columns in compression could be significantly avoided using UHPC strengthening. Among three methods of strengthening, hoop strengthening was the most effective in increasing the ultimate load, ductility, and dissipated energy of masonry columns by 185.81%, 49.09%, and 297.12%, respectively. With the strengthening thickness increased from 0 to 20 and 30 mm, the ultimate bearing capacity of masonry columns was respectively increased by 29.17% and 117.26%, while the corresponding lateral displacement was decreased by 32.44% and 37.24%, respectively. The horizontal buckling of masonry columns can be relieved by UHPC, and the increase in eccentricity did not weaken the contribution of UHPC in strengthened masonry columns. The numerical results were in good agreement with the test results, with errors below 7.6%.

Seismic behaviour of precast concrete beam-column connections with bolted end plates

This paper presents the seismic behaviour of a dry beam-column connection with bolted end plates for precast concrete structures. Experimental tests were carried out on one cast-in-situ connection and three precast concrete connections with bolted end plates to study the behaviour under reversed cyclic loading. The load resistance, failure mode, ductility and energy dissipation capacity were determined from experimental results. Comparisons were made among different connections to show the influence of end plates and stiffeners on the connection behaviour. Test results showed that precast concrete connections with bolted end plates mainly dissipated energy through bending of the end plate and deformation of steel bolts. The final failure of connection resulted from the yielding of the end plate or crushing of concrete in the compression zone of beams, depending on the thickness of the end plate and the presence of stiffeners. The connection with bolted end plates could achieve good ductility and energy dissipation. Moreover, failure of columns and the joint core was prevented through the use of end plates. An analytical method was also proposed to evaluate the moment-rotation relationship of connections. The contributions of joint core, steel bolts and the end plate to rotational stiffness and moment resistance were quantified in the analytical method. Comparisons with test results showed that the analytical method can estimate the moment-rotation curve of connections with bolted end plates with good accuracy when failure of connection was dominated by steel bolts or the end plate. Design recommendations were also proposed for connections with bolted end plates.

Seismic behavior of irregular shaped beam-column connections

This paper reports test results and numerical analysis of special-shaped beam-column connections based on a frame-shear wall structure. Four connections of 1/5 scale ratio were tested under constant axial force and reversed lateral load on the top of column. The experiment investigated the effect of steel reinforced concrete (SRC) beam, in-plane and out of-plane reinforced concrete (RC) wall on the connections’ seismic behavior. The failure modes, hysteresis curves, ductility, strength degradation and energy-dissipating capacity of test specimens are reported. The results indicated that test joints were susceptible to suffer more brittle failure caused by formation of plastic hinge on column, which is considered unfavorable compared to conventional joint with regular shape in earthquake resisting. Adding in-plane shear walls to the connection switched column failure to beam failure mode, and significantly improved the connection’s strength, stiffness and ductility. Finite element models were detailed established and validated through experiment data. Influence of parameters including axial load ratio, concrete strength grade, section area and steel ratio of upper column, transverse hoops volumetric, RC wall of two orthogonal directions on connection’s seismic behavior were studied through modeling results.

Behaviour of FRP-ECC-HSC composite stub columns under axial compression: Experimental and mathematical approach

The composite stub column composed of fiber-reinforced polymer (FRP), Eco engineered cementitious composite (ECC), and high-strength concrete (HSC) core is experimentally investigated in this study. The ductile performance of HSC-FRP is enhanced by proving an ECC ring of 30 mm thickness as sandwich layer between HSC and FRP. During experimentation the premature failure of the FRP-HSC column is observed at the initial phase, which exhibits brittle nature of the column. The material properties of FRP, ECC, and HSC were characterized. The performance of composite columns was observed with four FEH (FRP-ECC-HSC) columns, four HE (HSC-ECC) columns, and two FH (FRP-HSC) columns. The parameters such as uniform hoop strain distribution, ultimate load-carrying capacity, axial and hoop strain, and confining efficiency of the FRP were investigated to understand the behaviour of composite columns. From results, the ultimate load-carrying capacity of FH columns was 15.56 % higher than the FEH columns. The FEH columns showed the enhanced confining efficiency of FRP and 21% increase in uniform hoop strain distribution than the FH columns. The hoop strain capacity of FEH columns were increased twice the times of FH columns, which indicates the increased ductile behaviour of the FEH columns. In addition, experimental results of composite columns were highly correlated with the existing theoretical equation from literatures

Ultimate Compressive Strength of H-Section Stub Columns Subject to Random Pitting Corrosion Damage

H-section columns with random pitting corrosion exhibit localized damage, making it imperative to conduct a thorough assessment in order to guarantee their long-term structural safety and integrity. This paper presents a method for constructing finite element models of randomly pitted H-section stub columns. The accuracy of the models was first validated against existing experiments. Various scenarios, accounting for different levels of pitting intensities and locations of corrosion occurrence, were considered, to elucidate the mechanisms of the reduction in ultimate strength and stiffness, as well as the failure of columns. Additionally, the influence of the width-to-thickness ratio of the plate on the ultimate strength of stub columns was also taken into account. A method to address the thickness loss resulting from random pitting corrosion was proposed for the ultimate strength assessment of randomly pitted stub columns, and its accuracy was verified based on the Chinese and European Standards. An empirical formula was proposed and verified upon the results of numerous stochastic simulations of randomly pitted H-section columns. The results demonstrated that for axially loaded H-section stub columns, both ultimate strength and stiffness decrease significantly and nonlinearly with the increase in the degree of pitting damage. Corrosion can change the failure mode of a stub column by inducing local buckling in a plate that initially satisfies the buckling criterion before the overall column failure.

Experimental and Numerical Study on Progressive Collapse of the Midcolumn in a Glulam Timber Frame Exposed to Fire

This paper presents experimental and numerical investigations on the progressive collapse behavior of a two-story glulam frame when the middle column is exposed to ISO834 standard fire. The stress characteristics, temperature distributions, and deformation relationship curves of the bottom middle column after a fire are obtained. The collapse resistance performance and the mechanism of the glulam structure under local fire are studied in combination with the failure mode of the frame. The experimental results show that the failure time of the middle column in fire is 16.8 min, and the time to determine the progressive collapse of the structure is 17.17 min when the rotation angle exceeds the limit. The structure can remain stable for some time after the failure of the fire column, but as the fire continues to spread, the structure will collapse further. In addition, a temperature-field analysis model with the grid element type of DC3D8 and a structural field analysis model with the grid element type of C3D8R was established by using ABAQUS software under the experimental conditions. The numerical simulation is carried out by means of thermal–mechanical sequential coupling. The numerical simulation results show that the temperature of the beam end rose to more than 300 °C in about 15 min although it was not directly exposed to fire. The temperature of the whole connector at the pillar foot in the bottom column reached more than 700 °C when the fire time reached 60 min. The numerical simulation results agree well with the experimental results. The analysis results show that, in the failure process of the fire column, the junction of beam ends begins to produce stretching force to form a catenary effect. As the fire time increases, the catenary effect eventually fails. The stretching force at the beam end rapidly decreases and withdraws from the work, causing the progressive collapse of the frame.

Development of reinforced concrete column with embedded concrete hinge and lateral restraints for Anti-Catastrophe oriented design

In Japan, since the 2011 Tohoku Earthquake, there has been a growing interest in addressing earthquakes that exceed design assumptions. Consequently, the concept of “anti-catastrophe” has been proposed as a new approach to the seismic design of infrastructures. This approach necessitates considering the conditions after significant structural damage, a concept not explicitly addressed in current seismic design codes. This study proposes two types of reinforced concrete (RC) columns: Embedded Concrete Hinge RC column (ECH-RC) and Embedded Concrete Hinge unbonded bar RC column (ECH-UBRC) to minimize the uncertainty of failure behaviors of RC columns during Beyond Design-Basis Events (BDBE) while ensuring high ductility during Design-Basis Events (DBE). ECH-RC features a Mesnager hinge embedded at its base, while ECH-UBRC incorporates unbonded high-strength bars in addition to a Mesnager hinge. ECH-RC and ECH-UBRC are designed for bridge columns subjected to low axial loads. To ensure the stability of the entire bridge structure during BDBE, providing lateral restraints at large displacements is essential. Results from cyclic loading tests revealed that embedded Mesnager hinges effectively prevented the uncontrollable failure of RC columns during BDBE by limiting axial and shear deformation at the plastic hinge, while the unbonded bars enhanced the stability of RC columns.

Shaking table test on irregular and complex connected structure

Affected by the external environment, it is easy to cause complex and irregular problems in the building structure, bringing new safety hazards to the seismic resistance of the structure. Based on the background of the east building of the railway station with cross ground crack, the seismic performance of irregular and complex connected structures under different seismic intensities was analysed.The research results indicate that under the action of a 7-degree seismic fortification, the structure is basically in an elastic state, with a stiffness degradation of 12.9%, meeting the performance requirements of being undamaged during small earthquakes; Under seismic fortification, the structure is mainly characterized by cracking at the bottom beam end, with a small crack width and a stiffness degradation of 41.7%, meeting the requirements for moderate earthquake repairability; Under the rare earthquake of 8degree , plastic hinges begin to form at the beam and column ends of the structure and gradually develop, with stiffness degradation reaching 81.9%. All seismic responses of the structure comply with the limit requirements of the code (GB 50011-2010); Under the rare earthquake of 8 degree , there is a serious torsion phenomenon in the small triangle area, which leads to the disharmony of forces on the inner and outer beams and columns. In earthquakes, it is easy to cause structural collapse due to the first failure of the outer columns. Suggesting to increasethe stiffness of the small triangular column to solve the above problem. Under extremely rare earthquakes, the plastic hinge mechanism of the structure has developed completely, with stiffness degradation approaching 90% and no collapse phenomenon, indicating that complex connected structures have excellent seismic performance.

Innovative scheme for RC building progressive collapse prevention

Progressive collapse of reinforced concrete (RC) building due to column failure can cause human casualties and severe irreparable damage or total collapse of the building. Different methods have been presented to mitigated progressive collapse of RC buildings; however, most of them are installed externally after construction and are costly, demanding, and require manufacturing mitigating elements such as steel cables, steel devices, or composites. This study presents an innovative mitigating scheme to improve the progressive collapse resistance of such buildings. The proposed scheme applies during construction and comprises of adding short wasted leftover steel bars from the construction site with special configuration in the slab around potential failed interior column. To examine the effectiveness of the proposed scheme, three-dimensional nonlinear fiber element-based model was developed, validated, and utilized for the analysis of such buildings. The findings of the study show that the proposed scheme improved progressive collapse behavior of the building with a percentage increase in total dissipated energy up to 241.8%. The scheme is eco-efficient and cost effective as it requires minimum amount of material, saves energy required to produce new steel bars, and can serve as an effective solution to mitigate progressive collapse of RC buildings subjected to column failure.

Mechanism of Cement Deep Mixing and Design Method Improving Soft Ground in Mekong Delta

Soil improvement technique for embankment fill is often needed to rapidly improve the strength of the soft ground. In recent years, the cement deep mixing (CDM) method has been commonly used as an alternative to improve the soft soil foundation of embankment. This method is a reasonable solution used for several applications as to treat the soft soil behind the bridge abutment, to minimize settlement and enhance the bearing capacity of soil foundation for a storage tank, to support segmental retaining walls, and to prevent differential settlement between a new embankment over soft soil and existing embankment where the settlement has ceased. The stability of cement column stabilized embankments can be analyzed either by a numerical calculation method such as the finite element method (FEM) or by a limit equilibrium method. The numerical calculation methods require reliable material parameters as determined by field and laboratory tests or in-situ on excavated columns and on the unstabilized soil. Another method considering simplified method is limit equilibrium method. In analysis of this method, the stability of cement column is analyzed by assuming that failure of the cement columns and the soil.

Compressive behavior of brick masonry columns confined with composites embedded in the horizontal mortar joint

The application of composite materials embedded in the horizontal mortar joints to strengthen masonry structures with insufficient load-bearing capacity has shown beneficial effects in terms of improving mechanical behavior and preserving the aesthetics of the building. To investigate the effectiveness of this strengthening technique, concentric axial compressive tests were performed on eight masonry columns, including two unconfined columns, five specimens confined by carbon fiber reinforced polymer (CFRP) plates, and one specimen confined by engineered cementitious composite (ECC). The failure mode, strength, deformability, and energy dissipation capacity of the specimens were investigated. The effective tensile strain of the CFRP plates was also discussed. The results showed that the CFRP-confined masonry columns exhibited brittle failure, which was characterized by the debonding failure of the CFRP caused by the sudden fracture of the epoxy resin, while the failure of the ECC-confined masonry column exhibited significant ductility, the reason for which was that the propagation of vertical cracks was delayed due to the strain-hardening characteristics of the ECC. The reinforcement technique was effective for masonry columns in obtaining better compressive performance. The peak strength and energy dissipation of the confined columns were increased by a maximum of 86.31% and 115.71%, respectively. A non-uniform distribution of the effective tensile strain of the CFRP plates along the perimeter was observed. In addition, a simple strength model for masonry columns confined by embedded material in the horizontal mortar joints was developed based on the best-fit analysis of a database assembled from the existing literature and the current study. The predictive capabilities of the proposed model and an existing model for the compressive strength of confined masonry columns were analyzed.

Fragility curves for reinforced concrete frames with retrofitted masonry infills

Seismic retrofit of existing reinforced concrete framed buildings often involves both structural members and infill walls. The strengthening of infill walls is mainly aimed at preventing out-of-plane mechanisms and, in some cases, also increases in-plane capacity. On the other hand, the enhancement of the infill's strength might modify the failure mode of the frame, as stated by recent studies. In the case of gravity load-designed buildings, the presence of strong infill walls can lead to brittle failure of columns due to local interaction. This study investigates the effects of the in-plane shear retrofit of infills on the seismic behaviour of reinforced concrete buildings through non-linear dynamic analyses on a three-dimensional infilled frame. The seismic response of the structure is analysed in case of un-reinforced masonry wall and retrofitted wall, considering two types of retrofit. The analysis results are used to calibrate a simplified model aimed at computing fragility curves of reinforced concrete infilled frames and updating existing formulations, in order to account for the properties and the type of the infill. The proposed parameter can be applied in vulnerability assessment studies and for the design of new buildings.

Synchrotron X-ray diffraction and radiography - Lattice strain characterization in thin-walled carbon fibre channel structures subjected to buckling

Carbon fibre composites are widely used in low specific stiffness and high strength structures such as airframes. Compressive loading of these assemblies can lead to buckling and localised deformation around defects and imperfections that can hinder performance and lead to overengineering via excessive safety factors. Synchrotron X-Ray Diffraction (SXRD) has recently been shown to be capable of performing lattice strain mapping within carbon fibre composites at the microscale, a previously unprecedented resolution. In this study SXRD and radiography was performed on carbon fibre composite columns produced via two different methods (standard lamination and half square) at a range of different load states: unbuckled, one-third of the buckling load and post buckling. The results provide quantitative insights into the impact of these different production methods on lattice strain and fibre orientation, as well as the influence these factors have on reducing buckling load (by up to 22%). As well as being the first use of SXRD on industrially representative full-size carbon fibre samples, these insights provide invaluable detail into the factors which limit performance and the origins of column failure; crucial factors required to optimise structural design, production and loading capability.

Progressive Collapse Analysis of Intermediate Moment-Resisting Steel Frame under Fire-Induced Column Failure

This paper evaluated the progressive collapse robustness of steel intermediate moment-resisting frames (MRFs) under different fire-induced column failure scenarios. For this purpose, 3-, 7-, and 12-story intermediate MRFs were modeled numerically and analyzed under different gravity and fire loads. The effects of the seismic design requirements, number of stories, gravity load ratio (utilization ratio), and redundancy and position of the heated column were discussed. Because the investigations included models with different number of stories and different seismic to gravity load ratios, the results can be applied for a wide range of IMFs. The results show that none of the studied frames in the high seismic zone with a low gravity loads ratio experienced progressive collapse under any of the considered fire scenarios. However, by increasing the ratio of gravity loads in frames, the vulnerability to progressive collapse was increased. This suggests that in areas with a lower risk of environmental lateral loads, where MRFs generally are designed for gravity loads and smaller lateral forces, the progressive collapse robustness of MRFs under fire-induced column failure should be given serious consideration. In addition, the results show that the possibility of progressive collapse under the fire-induced column failure scenarios in the first story of low-rise frames is more than that in the first story of high-rise frames, and generally low-rise frames are more vulnerable to progressive collapse than high-rise frames. Furthermore, the possibility of progressive collapse under fire scenarios in the upper stories is more than that in the lower stories, especially for the top story. In this study, a new combined failure mechanism for global collapse of MRFs was identified.

Development of a novel fire following earthquake probabilistic framework applied to a steel braced frame

This paper describes a novel probabilistic fire following earthquake (FFE) framework to develop FFE fragility functions for steel braced frames. In particular, an 8-storey steel braced frame, located in a high seismic area, was used to demonstrate the framework. An algorithm was formulated to generate fire scenarios based on seismic damage. Damage caused by the earthquake was expressed in terms of inter-storey drift ratio (IDR) and peak floor acceleration (PFA). Damage was captured in structural and non-structural components, such as glazing and partition walls. In particular, floors with IDR and PFA that exceeded pre-defined thresholds were considered to experience ignition after an earthquake. More than 1100 nonlinear FFE analyses were performed by randomly generating values of window widths, fire load densities, earthquake intensities, and yield strength of steel at ambient and at high temperatures. Historic ground motions and natural fire curves were employed to characterize the hazards. Thermomechanical analyses were completed and failure criteria based on displacement and displacement rate were applied to the girders (primary beams) and columns. The results of simulations were processed to generate FFE fragility curves and surfaces for girder and column failures with respect to the time to failure in the FFE scenario and grouped based on spectral acceleration intervals. The results showed that the girder always failed first given the low structural redundancy due to the end conditions. Moreover, the higher the spectral acceleration, the more uniform the damage across the structure with a lower time to reach failure. It was finally found that the fire load density did not have a significant effect on the probability of failure for the case study under consideration.

Parameters Affect Flexural Mechanism to Prevent Progressive Collapse of RC Buildings

This study investigates the effect of spans length, reinforcement ratio and continuity of flexural reinforcement on the progressive collapse performance of double span beams over failed columns. The investigations focus on initial flexural resisting mechanism to prevent the progressive collapse. Detailed nonlinear finite element simulation of double span beam-column sub-assemblages subjected to residual gravity loads that initially carried by the failed column is adopted for the investigations. Nonlinear static pushover analysis is conducted in which capacity curves are derived and compared with demanded capacities. The effect of spans length, reinforcement ratio and number of continuous bottom flexural reinforcement on progressive collapse are considered in the investigations. Analysis results show that the strength to resist progressive collapse has decreased by 25.4 % and the ductility increased by 103 % following the increasing in span length from 5 m to 7 m. On the other hand, increasing reinforcement ratio of top flexural reinforcement from 0.447 to 1.089 leads to 26.27 % increasing in strength accompanied with a decrease in ductility equal to 16.42 %. In addition, extending all bottom bars rather than the minimum specified two bars resulted in 12 % increasing in strength and 40.28 % decreasing in ductility.

Progressive collapse behaviour of advanced precast reinforced concrete joints with headed bars and plastic hinge relocation

This study proposed three types of precast concrete (PC) wet joints, viz., using Headed bars (Type H) to replace hooked bars, placing an Additional bottom bar layer (Type A), or implementing plastic hinge relocation method with X-bent bars (Type X) in the beam-joint region. These detailing features could compensate for negative effects caused by geometric discontinuity at the joint interface and prevent pull-out failure, as observed in conventional PC joints with hooked bars. An experimental investigation based on four interior joints showed that based on the steel content in Type H joint, by increasing respective steel contents of 7% and 8% in Type A and Type X joints, structural resistance to collapse could be enhanced by 34% and 47%, respectively. A fourth specimen of Type A joint incorporated the slab. It was found that although the slab could slightly enhance flexural resistance, it also reduced the joint rotational capacity. Subsequently, component-based joint models (CBM) with a bond-slip model of headed bars were proposed for the three types of PC joints and validated against the test results with satisfactory accuracy. Based on the validated CBMs, parametric studies were conducted for different cases, such as exterior and penultimate joints, under a penultimate column removal scenario. It was found that if the exterior column was too weak, compressive arch action and catenary action could not be effectively triggered, and column failure governed joint behaviour. Hence, to mitigate progressive collapse, the exterior columns and joints must be required to possess a sufficient level of horizontal resistance and stiffness.

How inadequate heat treatment or complete lack thereof can cause component failures

Abstract This paper is a compilation of failure analysis case studies exploring the subject of inadequate heat treatment. As with other papers in this series, the presented failure cases are rather simple and may appear trivial to the experienced failure analyst. The authors can guarantee however, that minor heat treatment errors are committed easily and have a considerable damage potential which may entail heavy financial losses. Therefore, cases of inadequate heat treatment or a complete lack of necessary heat treatment belong by all means in the column Failure Analysis. The metallurgical subject of these failure cases are low-alloy hardenable steels without exception. Common heat treatment processes such as induction hardening, case hardening, nitriding as well as through-hardening and tempering will be touched upon.

Feasibility of two-storey substructures to equivalently investigate behaviour of multi-storey steel frames

Disproportionate collapse of steel frame is often an indicator of the overall behaviour of multi-storey building. The corner column failure is followed by deformation of all beams and columns above removed columns and redistribution of the load carried by the corner columns. Although several experimental studies of disproportionate collapse have been carried out after corner column loss, most of them only focused on the single-storey substructure, while inevitably ignoring the interaction between the storeys in the multi-storey frames (Vierendeel action). In this study, the performance of a two-storey substructure after corner column loss was experimentally studied and a corresponding numerical model was established utilizing LS-DYNA. FE model was validated and used to further study the effects of the proposed boundary assumptions, load redistribution of multi-bay steel frames, and number of bays and storeys on load resisting mechanisms. The results indicated that Vierendeel action is essential in resisting disproportionate collapse, with a contribution of 43% to the peak load. For a multi-storey frame with more than two storeys, the normalized load resistance of each storey is approximate. However, due to Vierendeel action, further internal force analysis indicates that the load resisting mechanisms are different in each storey. The two-storey substructures for understanding the disproportionate collapse behaviour of multi-storey steel frames under corner column loss are highly recommended by the parametric analysis.