Dynamic Progressive Collapse Research Articles

Refined dynamic progressive collapse analysis of RC structures

Post-earthquake field investigation has revealed that if reinforced concrete (RC) structures in seismic regions were not designed to the level required by modern seismic design codes, they are vulnerable to severe damage or even progressive collapse when subjected to strong earthquakes. To gain insight into the mechanism and prevention of progressive collapse, it is imperative to develop an effective and efficient approach to capture the physical collapse of RC structures by numerical simulation. Finite element method (FEM)-based numerical simulation is one of the most widely used approaches for progressive collapse analysis, but some uncertainties still exist in its element removal algorithms. This paper refines FEM-based dynamic progressive collapse simulation for RC structures by introducing the concept of degree-of-freedom (DOF) release. With the concept, a RC beam-column element removal is a natural consequence of release of all DOFs of the element. This concept is implemented in an open-source finite element code of OpenSees. The test results of a RC beam with two ends fixed under a static load and a RC column with light transverse reinforcement under lateral pseudo-static load are first used to assess and demonstrate the advantages of the DOF release over the beam element removal. The refined progressive analysis method is then applied to a RC frame structure to demonstrate its dynamic progressive collapse with catenary effect included. Finally, a two-span continuous RC bridge with a two-column pier is taken as an example to demonstrate its flexure-shear-axial failure predicted by the proposed method.

Experimental Study of Dynamic Progressive Collapse in Flat-Plate Buildings Subjected to Exterior Column Removal

AbstractThe experimental results of dynamically removing an interior column in a single-story, 2-bay-by-2-bay reinforced concrete flat-plate substructure are presented. The test specimen represente...

Experimental study on progressive collapse-resistant behavior of planar trusses

This paper presents an experimental study on the dynamic progressive collapse behavior of planar trusses. A specially designed member-breaking device has been invented to ‘break’ a predefined structural member suddenly, particularly a diagonal member in the experiments. Videogrammetric technique was adopted to obtain the full field 3D displacement of the remaining structure, and strain instrumentation was carefully used to monitor the internal forces of all members. In association with the experiments, finite-element simulations of the test trusses have also been performed, with extended analysis on the effect of removal of members at different locations. Experimental results in conjunction with the numerical analysis have shown that: (1) the truss with directly welded joints (specimen truss-WJ) was able to quickly regain balance upon member loss, and the load-redistributing capacity was provided mainly through catenary action developed in the bottom chord; (2) the truss with pinned joints (truss-PJ) behaved almost identically to truss-WJ, suggesting that when computational models of truss structures need to be developed to obtain structural responses under a collapse scenario, pinned-joints with continuous chord could be assumed; (3) the truss with rigid joints (truss-RJ) experienced progressive buckling of three diagonal members and was damaged severely, indicating a detrimental influence of excessive joint stiffness on the collapse resistance of trusses.

Numerical simulation of the dynamic progressive collapse of a plastic film greenhouse under typhoon

Artificial cutting of 13 cable-stayed steel wire ropes that fixed pillars on the periphery of a plastic film greenhouse resulted in a lawsuit. The results of calculation show that the surrounding soil foundation was disturbed and the constraint ability of soil foundation to the pillars was weakened by the weights of greenhouse and grapes after the wire ropes were cut. It directly caused, and accelerated, the progressive collapse of the greenhouse under typhoon loading. The results also indicate that the greenhouse would not collapse under the typhoon loading if none of the steel wire ropes were cut. In other words cutting the wires was the main factor which induced the progressive collapse of greenhouse. The results of this paper were adopted by court and the farmer's damage was finally compensated. The similar collapse configurations of pillars from simulation and site photos after typhoon can prove the validity of the simulations.

Component-based steel beam–column connections modelling for dynamic progressive collapse analysis

A component-based model is developed to predict the dynamic response of bolted-angle connections, such as web cleat connections and top and seat with web angle (TSWA) connections subjected to sudden column removal scenario. This model considers the behaviour of bolted-angles under large tension forces. A failure criterion determined from the test results is introduced into the model for the bolted-angle component to predict the connection resistance. The hysterical behaviour of each component under cyclic loads is also included for ensuring dynamic analysis. The proposed component-based connection models with detailed springs as well as their constitutive laws are implemented within a self-developed finite element programme FEMDYA to validate the model against both static and dynamic test results. A comparison study showed the capabilities of the component-based model in predicting the connection performance. Based on the failure criterion of the connection component, an accurate simulation of the fracture of the connections is conducted. Subsequently, the component model is incorporated directly into two types of 4-storey steel frames to simulate catenary action developed due to the loss of support to a middle column. The analysis results indicate that a value of up to 2.9 should be used as the dynamic increase factor for structures with web cleat connections when incorporating the dynamic effects into the nonlinear static load resistances. It is also shown that the ultimate load capacity of unbraced structure is much smaller than the one in the braced frame due to horizontal movements of adjacent columns under catenary action.

A modified member stiffness procedure for dynamic progressive collapse analysis of planar frames

A modified member stiffness procedure for dynamic progressive collapse analysis of planar frames

A modified member stiffness procedure for dynamic progressive collapse analysis of planar frames

A computer program for progressive collapse analysis of planar frames is under development. The software has a capability to analyze structures after failures of members in which failure can occur at one or both ends of a member. When an end of a member fails, the failed end separates from the main structure and becomes discontinuous. In this paper, a modified member stiffness procedure with releases of end forces to track the response of a failed end is discussed. The procedure utilizes a condensation process of the element stiffness matrix of the failed member. An example in applying the modified member stiffness procedure is given to show that the assembly process for the stiffness matrix and the applied force vector of the main structure does not change. In addition, the Equation solver still determines the same number of unknown degrees of freedom. Accordingly, this approach provides a convenient, simple, yet efficient means of keeping track of all failed members for progressive collapse analysis of frame structures.

Progressive Collapse Resistance Demand of RC Frames under Catenary Mechanism

Progressive collapses are resisted by the catenary mechanism in reinforced concrete (RC) frame structures undergoing large deformations. Research to date has mainly focused on the nonlinear dynamic progressive collapse resistance demand of this type of structures under the beam mechanism (that is, for small deformations), and that the catenary mechanism is lacking. As a first attempt, this study establishes a dynamic amplification factor for evaluating the resistance demands of RC frames under the catenary mechanism. To achieve this, an energy-based, theoretical framework is proposed for calculating the aforementioned demands. Based on this framework, the analytical solution for the collapse resistance demands of regular RC frames under the catenary mechanism is readily obtained. Numerical validation indicates that the proposed equations can accurately describe the progressive collapse demand of RC frames undergoing large deformations.

Dynamic Progressive Collapse of an RC Assemblage Induced by Contact Detonation

The nature of progressive collapse is a dynamic event caused by accidental or intentional extraordinary loading. Most published experimental programs are conducted statically, without any consideration of the accidental loading and treating progressive collapse as threat independent. This paper demonstrates the more realistic process of progressive collapse in an experimental program on reinforced concrete subassemblages collapsed by a combination of dead weight loading and contact detonation. The dynamic results are represented systematically at different aspects and compared with previous published quasi-static experiments in terms of structural mechanisms, crack patterns and local failure modes. Moreover, the dynamic increase factor (DIF) of reinforcing bars and the dynamic load amplification factor (DLAF) are investigated and discussed. Following the above comparisons and the findings in the dynamic tests, previous quasi-static test results can be linked to actual progressive collapse behavior more convincingly. Finally, the dynamic tests also highlight the effect of contact detonation on structures, which are often not considered in quasi-static tests and design guidelines. The test results indicate that contact detonation causes uplift and out-of-plane actions to the subassemblage before their downward movement under gravity load, in which the strain rate of reinforcement is between 10⁻² and 10⁻¹/s. Moreover, the structural mechanisms are similar in both quasi-static and dynamic tests.

A New Measure to Reduce the Potential for Progressive Collapse of Steel Frame Structure

In order to improve the capacity of resistance to progressive collapse for steel frame structures, a new measure, which uses bracing systems to help damaged frame to bridge across the local damage caused by abnormal loads, is presented in this study. The dynamic progressive collapse analysis is carried out to investigate the effect of resistance to progressive collapse in two different cases of column removal. Analytical results show that bracing systems on the top of steel frame structure have obvious effects on collapse prevention. Comparison with the unbraced steel frame structure, fixing bracing system could decrease the vertical displacement of the node corresponding to the top of the removed columns, and reduce the moment peak value at the end section of beams. And after column removal, plastic hinges come into being in the unbraced steel frame, on the other hand, there are no plastic hinges formed in the steel frame with bracing system.

An efficient compound-element for potential progressive collapse analysis of steel frames with semi-rigid connections

In this paper, the formulation of a novel 1D frame compound-element for the materially and geometrically non-linear analysis of steel frames with flexible connections is outlined. The element is formulated based on the force interpolation concept and the total secant stiffness approach, and implemented in a FORTRAN computer code. The accuracy and efficiency of the formulation are verified through some numerical examples. For steel frames with bolted flush end-plate and extended end-plate connections, a static and dynamic progressive collapse assessment based on the alternate load path (ALP) method is undertaken by employing the developed analytical tool and dynamic load factor (DLF) is estimated. Furthermore, the implications of analyzing semi-rigid steel frames based on the assumption of fixed connections and the effects of the connection details on the global response of a frame during different progressive collapse scenarios are investigated.

Strain rate dependent component based connection modelling for use in non-linear dynamic progressive collapse analysis

This paper introduces the use of rate dependent springs to component-based joint models. This allows strain rate hardening as well as strain rate induced reductions in ductility to be included in component spring models for inclusion in non-linear dynamic analysis. Experimental tests of fin-plate connections are carried out under static and dynamic conditions with loading time as low as 32ms to failure. The joints were tested under the combined effects of tensile load and rotation in order to simulate the complex conditions experienced by joints during catenary action. The strain rate modifications to the component models of the joint were observed to be able to accurately model strain rate induced hardening, as well as reductions in failure rotation which occur in joints under dynamic conditions.The rate dependent component models were subsequently incorporated directly into sub-frame models to simulate catenary action developed due to the loss of support to a column. The individual failure criteria of the joint components provide for an accurate simulation of the progressive fracture of joints during collapse. The results are compared with the conventional approach in which joints are modelled using axial and rotational springs. The comparison reveals that, for the scenario investigated, the conventional method leads to a 20% overestimation of load capacity, due to the lack of inclusion of dynamic material property effects and moment capacity reductions resulting from prying action and catenary action axial forces. Thus the approach goes some way to developing a more realistic approximation of moment–tension–rotation response through to fracture of joints in whole frame progressive collapse computer simulations.

Enhanced Modeling of Steel Structures for Progressive Collapse Analysis Using the Applied Element Method

AbstractThis paper studies performing progressive collapse analysis for steel structures using the requirements of recent codes released by the U.S. Department of Defense and the General Services Administration. Based on a review of the code requirements, the nonlinear dynamic progressive collapse analysis resulted in a more uniform factor of safety than the linear static analysis. The applied element method in the structural analysis is proposed as an efficient alternative for performing progressive collapse analysis. A case study is undertaken where the results of the progressive collapse analysis using traditional finite-element-method simplifications are compared with the results from the applied element method in the analysis of a moment-resisting steel frame. The case study shows that simplifications that are usually done in finite-element analysis when studying traditional load cases can be overconservative when performing progressive collapse analysis. The results show that the use of the nonlinea...

Investigation of the influence of design and material parameters in the progressive collapse analysis of RC structures

This contribution deals with the modelling of reinforced concrete (RC) structures in the context of progressive collapse simulations. One-dimensional nonlinear constitutive laws are used to model the material response of concrete and steel. These constitutive equations are introduced in a layered beam approach, in order to derive physically motivated relationships between generalised stresses and strains at the sectional level. This formulation is used in dynamic progressive collapse simulations to study the structural response of a multi-storey planar frame subjected to a sudden column loss (in the impulsive loading range). Thanks to the versatility of the proposed methodology, various analyses are conducted for varying structural design options and material parameters, as well as progressive collapse modelling options. In particular, the effect of the reinforcement ratio on the structural behaviour is investigated. Regarding the material modelling aspects, the influence of distinct behavioural parameters can be evaluated, such as the ultimate strain in steel and concrete or the potential material strain rate effects on the structural response. Finally, the influence of the column removal time in the sudden column loss approach can also be assessed. Significant differences are observed in terms of progressive failure patterns for the considered parametric variations.

Nonlinear analysis of 3D reinforced concrete frames: effect of section torsion on the global response

In this paper the formulation of an efficient frame element applicable for nonlinear analysis of 3D reinforced concrete (RC) frames is outlined. Interaction between axial force and bending moment is considered by using the fibre element approach. Further, section warping, effect of normal and tangential forces on the torsional stiffness of section and second order geometrical nonlinearities are included in the model. The developed computer code is employed for nonlinear static analysis of RC sub-assemblages and a simple approach for extending the formulation to dynamic cases is presented. Dynamic progressive collapse assessment of RC space frames based on the alternate path method is undertaken and dynamic load factor (DLF) is estimated. Further, it is concluded that the torsional behaviour of reinforced concrete elements satisfying minimum standard requirements is not significant for the framed structures studied.

3-D nonlinear dynamic progressive collapse analysis of multi-storey steel composite frame buildings — Parametric study

A 3-dimensional finite element model built by the author was used in this paper to analyze the progressive collapse of a multi-storey steel composite frame building. The proposed model can represent the global 3-D behavior of the multi-storey building under the sudden column removal scenarios. Based on this model, parametric studies were carried out to investigate the structural behavior with variations in: strength of structural steel, strength of concrete and reinforcement mesh size. Through the parametric study, the measures to mitigate progressive collapse in the future design were recommended.

Progressive Collapse Analysis of Planar Reinforced Concrete Frames Using a 1D Element with Distributed Non-Linearity

SummaryIn this paper, a highly efficient 1D discrete element is developed for progressive collapse analysis of reinforced concrete planar frames. The element takes advantage of the force- interpolation and total secant stiffness approach, as well as a non-local averaging technique adopted to maintain the objectivity of displacement and force responses. Dynamic load distribution, softening of concrete under compression, effect of mass type (consistent or lump) and catenary action of the beams are addressed. Concerning geometrical non-linearities, the strains are assumed to be small; however, the effect of transverse displacement on the axial strain is large and it is taken into account. The accuracy and efficiency of the element for static and dynamic progressive collapse assessment of the reinforced concrete frames is demonstrated through some numerical examples.

Krylov Subspace Accelerated Newton Algorithm: Application to Dynamic Progressive Collapse Simulation of Frames

An accelerated Newton algorithm based on Krylov subspaces is applied to solving nonlinear equations of structural equilib- rium. The algorithm uses a low-rank least-squares analysis to advance the search for equilibrium at the degrees of freedom DOFs where the largest changes in structural state occur; then it corrects for smaller changes at the remaining DOFs using a modified Newton computation. The algorithm is suited to simulating the dynamic progressive collapse analysis of frames where yielding and local collapse mechanisms form at a small number of DOFs while the state of the remaining structural components is relatively linear. In addition, the algorithm is able to resolve erroneous search directions that arise from approximation errors in the tangent stiffness matrix. Numerical examples indicate that the Krylov subspace algorithm has a larger radius of convergence and requires fewer matrix factorizations than Newton-Raphson in the dynamic progressive collapse simulation of reinforced concrete and steel frames. DOI: 10.1061/ASCEST.1943-541X.0000143 CE Database subject headings: Algorithms; Failures; Nonlinear analysis; Progressive collapse; Steel frames. Author keywords: Algorithms; Collapse; Nonlinear analysis; Progressive failure.

Parallel Axial-Flexural Hinge Model for Nonlinear Dynamic Progressive Collapse Analysis of Welded Steel Moment Frames

In this study, a parallel axial-flexural hinge model capable of representing postyield flexural behavior and considering interaction effects of axial force and moment is proposed for a simplified nonlinear progressive collapse analysis of welded steel moment frames. To this end, the load-resisting mechanism of the column-removed double-span beams was investigated based on the material and geometric nonlinear parametric finite-element analysis. A multilinear parallel point hinge model which captures the moment-axial tension interaction was then proposed. The emphasis was to develop a reliable and computationally efficient macromodel for practical progressive collapse analysis. The application of the proposed hinge model to nonlinear dynamic progressive collapse analysis was illustrated by using OpenSEES program. The accuracy as well as the efficiency of the proposed model was verified based on inelastic dynamic finite-element analysis results. The importance of including catenary action effects for proper progressive collapse resistant analysis and design was also emphasized.

Explosive loading of multi storey RC buildings: Dynamic response and progressive collapse

The resilience of a city confronted with a terrorist bomb attack is the background of the paper. The resilience strongly depends on vital infrastructure and the physical protection of people. The protection buildings provide in case of an external explosion is one of the important elements in safety assessment. Besides the aspect of protection, buildings facilitate and enable many functions, e.g., offices, data storage, -handling and -transfer, energy supply, banks, shopping malls etc. When a building is damaged, the loss of functions is directly related to the location, amount of damage and the damage level. At TNO Defence, Security and Safety methods are developed to quantify the resilience of city infrastructure systems (Weerheijm et al. 2007b). In this framework, the dynamic response, damage levels and residual bearing capacity of multi-storey RC buildings is studied. The current paper addresses the aspects of dynamic response and progressive collapse, as well as the proposed method to relate the structural damage to a volume-damage parameter, which can be linked to the loss of functionality. After a general introduction to the research programme and progressive collapse, the study of the dynamic response and damage due to blast loading for a single RC element is described. Shock tube experiments on plates are used as a reference to study the possibilities of engineering methods and an explicit finite element code to quantify the response and residual bearing capacity. Next the dynamic response and progressive collapse of a multi storey RC building is studied numerically, using a number of models. Conclusions are drawn on the ability to predict initial blast damage and progressive collapse. Finally the link between the structural damage of a building and its loss of functionality is described, which is essential input for the envisaged method to quantify the resilience of city infrastructure.