Collapse Of Frames Research Articles

Resistance to progressive collapse of monolithic frames of buildings at localized damage of nodes from push-through

Resistance to progressive collapse of monolithic frames of buildings at localized damage of nodes from push-through

Test on progressive collapse of steel moment-resisting frame with upper-and-lower flange angle steel connection

Both of test and numerical simulation methods are employed to study the vertical progressive collapse and collapse assessment methods of steel frame under accidental loads. Firstly, a steel frame collapse test model with a geometric similarity ratio of 1:1.5 is designed and manufactured. The ends of column of test model is fixed. The upper and lower flange angle steel connection is used. The far end of the beam is constrained by a controllable sliding hinge support. The various stages of vertical progressive collapse of structures are simulated by a large displacement loads applied at the far end of the beam. The main focus of the testing is to examine the stress and deformation of beam and joint at various stages, particularly the development of stress and deformation in the angle steel attached to the beam-column connection. The development law of collapse load-displacement curve, joint rotation, beam strain, and angle steel strain are analyzed. The structural resistance mechanism and the transformation relationship between resistance mechanisms during collapse are studied. Subsequently, the relationship between the structural dynamic increase factor curve and the structural collapse process is analyzed using finite element method. The results show that the strain of angle steels can better reflect the destruction and deformation process of substructure during the collapse, the collapse resistance mechanism of structure, and the transition between resistance mechanisms.With the help of the characteristic points on the structural dynamic increase factor curve, the collapse limit state of structure can be reliably determined.

Experimental study on progressive collapse of self-centering precast concrete frame with infill walls

The self-centering precast concrete (PC) frame has been proved to perform excellently under seismic load in many studies. However, its progressive collapse-resisting mechanism, especially in the presence of infill walls need to be investigated further. Three 1/2 scaled self-centering PC frame specimens, including one self-centering PC frame and two self-centering infilled PC frames were tested under quasi-static pushdown loading regime. The test results showed that the damage of self-centering bare frame was mainly concentrated at the beam ends under vertical load. The compressive arch action (CAA) and the tensile force in the prestressed strands undertook the vertical load together at the beginning of the test. The infill walls with lower strength could still obviously enhance the initial stiffness and progressive collapse resistance of self-centering frame, but did not change the failure location of the frame. The initial stiffness of self-centering infilled frame was 2.47 times of self-centering bare frame, and the peak load in the CAA stage was 1.33 times. The additional load path produced by the infill walls mitigated the concrete damage at the beam ends, thereby improving the ductility performance and repairability of the beams. As the beam span of self-centering infilled frame decreased by 1/4, the initial stiffness and peak load in the CAA stage increased by 1.65 times and 1.66 times respectively. Nevertheless, the concrete damage at the beam ends became severer and the ductility of the frame was reduced.

Probabilistic seismic performance assessment of steel moment‐resisting frames considering exposed column‐base plate connections with ductile anchor rods

AbstractThis paper presents a numerical study assessing the seismic performance of steel moment‐resisting frames (SMRFs) designed with ductile exposed column‐base plate (ECBP) connections employing yielding anchor rods. For their potential use as weak bases, the proposed ECBP detail is designed to accommodate plastic deformations in the anchors. The seismic performance of 2‐ and 4‐story archetype SMRFs with ECBPs is investigated to examine the effects of various base‐connection strengths on the frame collapse mechanisms and probabilities. To this aim, the ECBP connections of each frame are designed for a set of three strength levels, ranging from reduced seismic loads to capacity‐designed forces of the adjoining columns. These designs enable the base responses to vary from highly inelastic (i.e., weak‐base design) to elastic (i.e., strong‐base design) when subjected to earthquake‐induced ground shaking. Nonlinear time history analysis (NLTHA) is extensively performed, applying a suite of assembled ground‐motion sequences (i.e., two ground motions in series) to assess the ECBP connection response and the corresponding frame behavior. Fragility analyses accounting for only the first ground motions in each considered sequence (to derive fragility curves), and the entire ground‐motion sequences (to derive fragility surfaces) are also performed to evaluate the probabilities of frame collapse and base connection failure. Finally, key findings regarding the seismic performance of ductile ECBP connections and their effects on the frame collapse are discussed. The limitations of the study are also outlined.

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.

Collapse risk of steel framed buildings with deep columns under tri-directional excitation

Deep steel columns are widely used in steel buildings with perimeter moment frames (PMFs). Although their seismic behavior has been well examined at the member level, their influence on frame collapse response requires further exploration, especially their interaction with composite slabs, gravity frames, and ground motion components. To address this shortcoming, the collapse risk assessment of a set of steel buildings with PMFs and deep columns is performed via two modeling approaches: the conventional planar frame and the sophisticated space frame. The models are capable of capturing the instability, fracture, and collapse behavior in frame systems. The simulation results show that each additional ground motion component applied promotes the development of collapse mechanisms and significantly increases collapse probability, and that composite slabs combined with gravity frames greatly improve collapse capacity despite introducing additional local failures. Moreover, limiting slenderness ratios and controlling local buckling of deep columns is essential to prevent frames from vertical progressive collapse (VPC) and ensure sufficient collapse resistance. The available highly ductile limits (HDLs) are accordingly critiqued and revised. Due to the large discrepancies in the collapse risks determined by the two approaches, space frame modeling is suggested to accurately assess the collapse capacity of steel PMFs involving deep columns.

China's Mariculture Net Cages in Typhoon and sea Ice Disasters: Challenges and Prevention Strategy

In recent years, mariculture has been prominent in solving the problem of high-quality protein sources for human beings. As an essential mode of mariculture, cage culture has gradually entered a period of rapid development. However, extreme marine disasters such as typhoons and sea ice bring different degrees of damage to mariculture net cages and even jeopardize the lives and property safety of aquaculture practitioners. Strong winds and waves caused by typhoon disasters lead to cage overtopping, cage frame collapse, and structural damage. Sea ice disasters caused by net cage frozen and ice floes impingement lead to a decline in the structural stability of the net cage, deformation, shifting, and collapse. These problems cause the cultured fish to collide with each other, triggering fish injuries, fish diseases, and fish escapes. At the same time, drastic environmental changes have limited farmed fish growth, resulting in a significant decline in aquaculture production. In summary, typhoon and sea ice disasters have become essential factors restricting China's rapid development of mariculture net cages. This paper reviews the development of mariculture net cages in China, the damage of mariculture net cages in typhoons and sea ice disasters, and the hazards of typhoons and sea ice disasters on net cages. Moreover, put forward the routine maintenance of net cages and disaster prevention and mitigation strategies to provide references for the safety of mariculture net cages and the prevention and mitigation of marine disasters.

Experimental and Numerical Study on Progressive Collapse Analysis of a Glulam Frame Structure: I. Side Column Exposed to Fire

This paper presents experimental and numerical investigations on progressive collapse behavior of a two-story glulam frame when the side column is exposed to ISO834 standard fire. The collapse mechanism initiated by fire is identified. The experimental results show that the progressive collapse of a glulam frame could be described for three stages, namely bending effect stage, catenary effect stage and failure stage, respectively. These stages are discussed in detail to understand the structural behavior before and during collapse. It is demonstrated that the entire frame slopes towards the side of the heated column, and the “overturning” collapse occurs eventually. The catenary effect of beams is the main reason for the progressive collapse of the frame. In addition, a finite element model of a glulam frame is established to simulate the progressive collapse behavior. The effects of axial loads on the columns are summarized. The numerical simulation results agree well with the experimental results, which could verify the effectiveness and practicability of finite element simulation. Furthermore, the progressive collapse resistance of the frame in practical design were proposed.

The evaluation of collapse probability of low-rise buildings based on Monte Carlo simulation

Over recent years, wind-caused activities such as typhoons, hurricanes, and tornadoes have happened frequently in coastal areas, causing damage or even the collapse of many buildings. This study designs a three-story teaching building located in Dalian to discuss the influence of different wind speeds on the stability of this building and propose some measurements. This study firstly uses Monte Carlo simulation to analyze the probability of collapse of the beam. Results show that the probability of frame collapse on windy days is 0.399%. It indicates that the wind speed could affect the stability of the structure. Higher wind speed could cause a higher internal force and structure displacement, leading to structural disability. The study also provides some wind-resistant designs to increase structural stability. The first is to choose a wind-resistant location, making reasonable site selection. The second is to select a suitable roof to resist heavy wind, and to increase the safety factor of the roof wind load design. The third is to increase the cross-section reinforcement method to reduce the dynamic wind load effect of the structure effectively. The externally bonded steel from the reinforcement method should be checked to avoid shear damage to the members after the bending bearing capacity increase.

A simplified method for quantifying the progressive collapse fragility of multi-story RC frames in China

Multi-story reinforced concrete (RC) frames are one of the most widely-used structural systems in engineering practice. To prevent the progressive collapse of RC frames under disastrous events, it is desirable to systematically investigate the progressive collapse fragility of the structures under column loss scenarios. This study proposed a simplified procedure for quantifying the progressive collapse fragility of multi-story RC frames, taking into consideration the influences of dynamic effects and parameter uncertainties. Nine typical RC frames were designed according to the Chinese building codes and investigated by the proposed method. The effects of seismic design intensity and the number of stories on the progressive collapse fragility of the RC frames were investigated. The results indicate that the progressive collapse resistance of multi-story RC frames depends on the combining effects of the structural loads and the bearing capacity of the beams. The structural resistance generally improves when increasing the number of stories. In contrast, it improves with the increase of seismic design intensity only when the seismic load is involved in the controlled load combination. For the RC frames that have various componential dimensions along the height, the stories with a changed componential dimension tend to collapse more likely under column removal scenarios. The outcomes of this study can provide references for quantifying the progressive collapse resistance and recommending appropriate load increase factors for the engineering design of multi-story RC frames in China.

Strengthening strategies against the progressive collapse of steel frames with extended end-plate connections

In this paper, a new type of the strengthened strategy for the limited anti-collapse capacity of extended end-plate connections (EECs) is proposed. Bending stiffened steel plates (BSSPs) were placed in the joint region to form a new type of strengthened extended end-plate connection (SEEC). First, the geometric motion characteristics of the BSSPs on the tensile and compression sides of the joint are described through theoretical analyses, and the improvement mechanism of the anti-collapse performance of the SEEC is given. Subsequently, using the verified numerical model, nine groups of parameters affecting the ultimate rotation of the EEC were analyzed, and the calculation formula for the ultimate rotation of the EEC was given via nonlinear fitting based on its numerical results. The numerical analysis example shows that the process of resistance development in the SEEC comprises three stages: elastic, transition, and improvement. Among them, the BSSP works well with bolts and end plate, which makes the SEEC obtain a more significant improvement stage and proves that the BSSP design process is reasonable. Finally, the main parameters a1, b1, and the thickness of the SEEC, were analyzed and suggested using parametric analysis.

Evaluation of the Progressive Collapse of the Reinforced Concrete Frames Considering the Soil–Structure Interaction: Parametric Study Based on the Sensitivity Index

In this essay, to investigate the progressive collapse of the reinforced concrete (RC) frames, a nonlinear static pushdown analysis was performed with column removal scenarios from the first story. At first, a numerical model was simulated and verified with the experimental model in SeismoStruct software without soil–structure interaction (SSI). Afterward, the foundation, soil, and the RC frame were modeled simultaneously in FLAC software and verified with the numerical model of the SeismoStruct software. Furthermore, the effect of SSI was studied on the progressive collapse of RC frames based on the sensitivity index (SI). The sensitivity index is defined as the ratio of the residual capacity under gravity loading of the structure by removing the column to the value of the undamaged structure. The results showed that by considering SSI, the sensitivity index decreases. Then, a parametric study of the framed structures (thickness of the foundation) and substructures (soil density, soil types, soil layers, and the soil saturation conditions) was performed to evaluate the progressive collapse-resisting capacity based on the sensitivity index. The results showed that by considering SSI, with an increase in the soil density and decrease in the groundwater level, the conditions would be better for preventing progressive collapse. It was also shown that rock and silty sands (SM), compared to other studied soil types, and SM and silty sands—silty clay with low plasticity—silty sands (SM-CL/ML-SM), compared to other studied soil layers, are better for preventing progressive collapse.

Investigating the Progressive Collapse of Steel Frames Considering Vehicle Impact Dynamics

Investigating the Progressive Collapse of Steel Frames Considering Vehicle Impact Dynamics

Approach for early-warning collapse of double-span steel portal frames induced by fire

The unexpected collapse of burning buildings has posed a great threat to firefighters. Hence, early-warning methods for fire-induced collapse are urgently needed to avoid secondary casualties. This paper proposes an early-warning approach for predicting the collapse of double-span steel portal frames based on real-time measurement of displacements and displacement velocities of the burning frame. Firstly, numerical models are established to simulate the collapse behavior of double-span steel portal frames under fire, and six collapse modes of the frames are summarized through parametric analysis. The displacements and displacement velocities of the apex, eaves, and mid-span of rafters, defined as the key monitoring physical parameters (KMPPs), are found to have a close relationship with the collapse mode and time of the burning frames. Secondly, by exploring the rules of the KMPP-time curves, the characterized points that can be used for early warning of the collapse of the frame are extracted. Then, the early-warning approach applicable to six collapse modes is proposed based on the emergence of various characterized points. For universalizing the collapse prediction, early-warning time ratios are introduced and determined according to the reliability theory. Finally, the practicability and accuracy of the proposed approach are validated by an existing fire test.

Investigation of changes in steel frames stress state in fire and influence on its vitality

Modern studies of the multi-storey buildings load-bearing structures vitality are analyzed. The shortcomings of the previously studied measures to increase the steel multi-storey frames vitality are identified. The need to study more effective and cost-effective measures have been identified. The change of 2d steel frame various elements loading during a fire is investigated. The dependence of the frame load-bearing capacity on the location of the fire source on different floors and spans is analyzed. 4 scenarios of fire source location in 2d multi-storey frame are considered. The influence of the distribution of the internal forces in the heated beams on the frame stress state, in particular on the local buckling of the I-beam flange and the web is analyzed. It was found that due to temperature expansions due to fire, not only heated elements are can be the first to be damaged in the frame. It is established that during a fire the first destruction occurs faster in the outside span of the frame than in the middle. When comparing the fire scenarios on the lower and upper frame floors, it was determined that on the lower floor the columns are more prone to damage earlier than the beam on the upper floor. When comparing the fire scenarios in the middle and outside frame spans, it was determined that in the middle span the beams are more prone to collapse earlier than the column than in the outside. It has been confirmed that, depending on the fire source location on different floors and spans, both the beam and the column of the frame may be the first to collapse. It is established that depending on the fire source location there may be different mechanisms of multi-storey frame collapse. It is established that the frame structures' stress state is significantly influenced by the distribution of internal forces at temperature loads, and not only fire protection and steel structures fire resistance.

Seismic performance of moment frames under multiple fling-step pulse ground motions

The displacement fling-step pulse seldom signatures near-field earthquake in its ground motions. It is well recognized that the near-field ground motion with velocity pulse amplifies the building drift larger than the regular ground motion. Recent findings explain that the building experiences minor damage to collapse is not caused only by the single earthquakes, which in many cases are due to repeated ground motion. The seismic performance of moment frames under the displacement fling-step pulse motion is not studied, particularly when this type of motion applies. Thousands of nonlinear inelastic response history analyses are conducted in order to find out the inter-story drifts, as the engineering demand parameter throughout the incremental dynamic analysis, on the 5 to 20-story moment resisting frames under the influence of multiple ground motions with a fling-step pulse. The special, intermediate, and ordinary types of moment frames are considered, respectively. On average, the evaluation result explains that the intensity measure of multiple ground motions with a fling-step pulse needs 68.37% lower than the single ground motion in order to produce the near collapse inter-story drift. This means the multiple ground motion with fling step pulse increases the probability of near collapse of frames significantly.

Effectiveness of masonry infill walls on steel frames with different beam-column connections under progressive collapse

In this study, the effectiveness of masonry infill walls on steel frames with different beam-column connections under progressive collapse was investigated through a parametric study. A vertical force was applied to the center steelcolumn to represent the progressive collapse of steel frames. This study focused on the three most common types of steel beam-column connections found in steel structures: shear, bolted, and welded connections. Single-story (1/3 scale) steel-framed configurations with single shear and bolted beam-column connections and another infilled wall steel frame with welded connection from the literature were tested experimentally under a middle column loss event to validate the accuracy of 3D finite element models created with ABAQUS software. The verified finite element simulations were then used to study the performance of progressive collapse resistance for 12 various types of steel frames with masonry infill walls with three different types of beam-column connections. The effects of the full infilled frame, bare frame, and infilled frame with openings were explored. The size, location, and shape of the openings in the infilled frame, and the performance of these parameters with respect to the change in the type of beam-column connection were evaluated. In accordance with their mechanisms of failure and load–displacement behavior, masonry infill walls were compared in flexural and catenary action phases. The findings show that infill walls considerably improve the steel building’s structural strength and energy dissipation against progressive collapse.

Measurement, Characterization, and Modeling of Initial Geometric Imperfections in Wide-Flange Steel Members Subjected to Combined Axial and Cyclic Lateral Loading

Wide-flange (W-shape) steel members are known to have initial geometric imperfections. A three-dimensional noncontact laser-scanning technique is used to measure the imperfection fields in fourteen specimens. A spectral approach that models the imperfections in each plate of the W-shape member as a two-dimensional random field is employed to characterize the imperfections and capture the existence of periodicity in them. The proposed modeling approach along with the traditional modal approach are used to study the sensitivity of numerical models to initial geometric imperfections. The studies are conducted at both member and system levels using a set of column and frame models employing deep W-shape columns under combined axial and lateral cyclic loading. It is shown that although initial geometric imperfections can, in certain situations, influence column buckling behavior as well as frame collapse mode, their effect on nonlinear cyclic behavior is generally small and inconsistent. Based on this finding, it is recommended that initial geometric imperfections need not be incorporated in high-fidelity numerical models of W-shape members subjected to combined axial and cyclic lateral loads. However, this is conditioned upon the use of a computational platform with sufficient numerical precision to capture the early small deformations that promote geometric nonlinearity in the response.

Experimental and numerical study on collapse modes of single span steel portal frames under fire

This paper presents experimental and numerical investigations on the collapse modes of single span steel portal frames exposed to fire. A fire test on a scaled-down single span steel portal frame is conducted and measurements of deformation and collapse mode of the test frame are used to validate the numerical model for simulating the behavior of the single span steel portal frames subjected to fire. Four collapse modes of the portal frames, column lateral collapse, column buckling collapse, overall inward collapse and overall outward collapse, are revealed through parametric studies with the validated numerical model. The effects of heating conditions, stiffness of column base, temperature gradient, fire protection, load ratio, span-height ratio and column spacing on collapse modes of single span steel portal frames in fire are obtained. It is found that heating conditions, stiffness of column base and load ratio have a great impact on the portal frame collapse modes while temperature gradient and fire protection mainly affect the column collapse modes. The findings of this study lay the foundation for early-warning of fire-induced collapse of single span steel portal frames.

Progressive Collapse Behaviour Assessment of Steel Frame Structures – A Review

In building construction, steel structures are favoured as they have some advantageous properties, such as high strength, light weight and high construction performance. However, there are few disadvantages since steel structures are prone to incremental collapse caused by accidental scenarios in which structural components are weakened or eliminated, leading to structural failure. Many research studies have been carried out on steel frames are generally for single column removal scenario. Since more than single structural members may be affected during accidents, numerous column removal scenarios need to be investigated to assess the progressive collapse of steel frame. This reviews study on how the steel frame structures can be simulated numerically using various finite element software to determine progressive collapse resistance for steel frames for different Progressive Collapse scenarios. It is found that Demand Capacity Ratio (DCR), Dynamic Amplification Factor (DAF) and Robustness Index for the critical points are some of the parameters to check the stability of the steel structures due to Progressive collapse scenario.