Progressive Collapse Analysis Method Research Articles

Progressive Collapse Analysis of Intact and Damaged Ships under Unsymmetrical Bending

This study examined the hull girder strength of intact and damaged ships by adopting the incremental-iterative method for progressive collapse analysis, which was extended to the general case of the unsymmetrical bending of beams with an arbitrary cross-section. The sources of an unsymmetrical loading, including rotation of the loading plane and section asymmetry caused by structural damage, are described. A fast and robust procedure is presented to determine the translation and rotation of the instantaneous neutral axis at each curvature increment when applying Smith’s progressive collapse analysis method. A series of analyses were conducted on a double hull VLCC and a bulk carrier, considering various loading plane angles and damage conditions. The decrease in ultimate strength and the influences of rotation of the instantaneous neutral axis and ship heeling are discussed. The proposed method can be used for a rapid and rational assessment of the hull girder strength under adverse conditions.

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads, Part 2: An extension of Smith's method

This paper is the second of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. The nonlinear finite element analysis in Part 1 has shown that local bending deformation of a double bottom due to bottom lateral loads significantly decreases the ultimate hogging strength of container ships. In this Part 2, extending Smith's method for pure bending collapse analysis of a ship's hull girder, a simplified method of progressive collapse analysis of ultimate hogging strength of container ships considering bottom local loads is developed. The double bottom is idealized as a plane grillage and the rest part of the cross section as a prismatic beam. An average stress-average strain relationship of plate/stiffened plate elements employed in Smith's method is transformed into an average stress-average plastic strain relationship, and implemented in the conventional beam finite element as a pseudo strain hardening/softening behaviors. The extended Smith's method is validated through a comparison with nonlinear finite element analysis.

Research progress on progressive collapse resistant analysis and design of building structures under blast loading

Progressive collapse is defined as the spread of an initial local failure from a key element to adjacent elements, eventually resulting in the collapse of the whole structure or a disproportionately large part of it. As an abnormal dynamic load, blast load has the characteristic of rapid propagation, high peak value and short duration. And it is also one of the main reasons that might cause the progressive collapse of building structures. Based on the existing research achievements on the progressive collapse of building structures, in this paper the classification method for structural progressive collapse analysis is put forward. Then the current methods for progressive collapse analysis are further divided into two categories, i.e., the method for evaluation of structural progressive collapse resistance and the method for whole process analysis of structural progressive collapse. Recent progress on the evaluation of structural progressive collapse resistance and the method for whole process analysis of structural progressive collapse are presented from literatures. Finally, the conceptual design method, structural detailing and the procedure for progressive collapse resistant design of building structures against blast loading are put forward.

Ultimate strength of container ships subjected to combined hogging moment and bottom local loads part 1: Nonlinear finite element analysis

This paper is the first of two companion papers concerning the ultimate hull girder strength of container ships subjected to combined hogging moment and bottom local loads. In the midship part of container ships, upward bottom local loads are usually larger than the downward ones. This leads to the increase of biaxial compression in the outer bottom plating and the reduction of the ultimate hull girder strength in the hogging condition. In this Part 1, the collapse behavior and ultimate strength of container ships under combined hogging moment and bottom local loads are analyzed using nonlinear finite element method. Buckling collapse behavior of bottom stiffened panels during the progressive collapse of a hull girder is closely investigated. It has been found that major factors of the reduction of ultimate hogging strength due to bottom local loads are (1) the increase of the longitudinal compression in the outer bottom and (2) the reduction of the effectiveness of the inner bottom, which is on the tension side of local bending of the double bottom. The obtained results will be utilized in the Part 2 paper to develop a simplified method of progressive collapse analysis of container ships under combined hogging moment and bottom local loads.

A new method for progressive collapse analysis of steel frames

As a massive explosion happens inside a building, a number of structural members (columns, beams, slabs and so on) are damaged or failed, along side with non-zero initial conditions (displacement, velocity, acceleration and so on), and the progressive collapse of the building structures is most likely to occur. However, limited research works about blast load effect of structural members inside a building can be found. In view of this, based on the substructure model, a new method for progressive collapse analysis of steel frames under blast load is proposed. First, the massive explosion scenario inside a building is introduced. Then, the substructure model within effective areas of blast influence is established. After that, the calculation method of non-zero initial conditions and initial damage for structural members is given, and finally the specific steps of the proposed method are described. By way of example of a steel frame with 5 stories in height, 4 bays in the longitudinal direction, 3 bays in the transverse direction, direct simulation method, alternative load path method and proposed method are all employed to simulate the progressive collapse process, respectively. Through the example analyses, it is shown that blast load effect of structural members cannot be ignored on the ground floor, and it can be ignored on the other floors by the effect of the reinforced concrete slab. The non-zero initial conditions and initial damage of structural members can be predicted well by the substructure model, and the proposed method is also reliable and accurate.

Tool for Predicting the Ultimate Bending Moment of Ship and Ship-Shaped Hull Girders

The present paper presents a historical review associated with the research works on hull girder strength of ship and ship-shaped structures. Then, a new program is developed to determine the ultimate vertical bending moment of hull girder by applying direct method, stress distribution method, and progressive collapse analysis method. Six ships and ship-shaped structures used in the benchmark study of International Ship and Offshore Structures Congress (ISSC) in 2012 are adopted as examples. The calculation results by applying the developed program are analyzed and compared with the existing results. Finally, the roles of the developed program and its further development are discussed.

A new method for progressive collapse analysis of RC frames

During the recent years, resistance mechanisms of reinforced concrete (RC) buildings against progressive collapse are investigated extensively. Although a general agreement is observed about their qualitative behavior in technical literature, there is not such a comprehensive point of view regarding the quantitative methods for predicting collapse resistance of RC members. Therefore, in the present study a simplified theoretical method is developed in order to predict general behavior of RC frames under the column removal scenario. In the introduced method, the robustness of the frame is extracted based on the capacity of the beams. The proposed method expresses ultimate arching and catenary capacities of the beams and also obtains the corresponding vertical displacements. Based on the calculated capacities, the introduced method also provides a quantitative assessment of structural robustness and determines whether or not the collapse occurs. The capability of the method is evaluated using experimental results in the literature. The evaluation study indicates that the proposed theoretical procedure can establish a reliable foundation for progressive collapse assessment of RC frame structures.

A new partial-distributed damage method for progressive collapse analysis of steel frames

The alternate load path method has so far dominated the field of progressive collapse of structures; in order to assess the resilience of structural systems, the concept of the removal of a key element is utilized as a means of damage introduction to the system. Recent studies have indicated that the complete column loss notion is unrealistic and unable to describe a real extreme loading event, e.g. a blast, that will introduce damage to more than one elements in its vicinity. This paper presents a new partial distributed damage method (PDDM) for steel moment frames, by utilizing powerful finite element computational tools that are able to capture loss of stability phenomena. Through the application of a damage index δj and the investigation of damage propagation, it is shown that the introduction of partial damage in the system can significantly modify the collapse mechanisms and overall affect the response of the structure.

Application of Progressive Collapse Analysis in a High-Rise Frame-Core Tube Structure

Frame-core tube structure system is commonly adopted in high-rise office buildings and landmarks, which will cause a large range of damage and serious loss of life and property once the progressive collapse occurs. To analysis the progressive collapse resistance of a high-rise frame-core tube practical project, numerical simulation analysis based on alternate path method and explicit dynamics theory was conducted to study the dynamic response of the remain structure after removing a key member. In addition, large-scaled tests for the frame-core tube structure under static and dynamic loads were carried out to study the behavior and damage situation of the structure. The numerical simulation and test results proved that progressive collapse would not occur when local damages occurred in the bottom corner column, and the structure still has a good seismic performance under dynamic actions. And the feasibility and reliability of the selected numerical simulation method of progressive collapse analysis is proved according to the test results.

Experimental Evaluation of the Ultimate Bending Moment of a Slender Thin-Walled Box Girder

The results of a four points bending test on a box girder are presented. The experiment is part of series of tests with similar configuration but with different thickness and span between frames. The present work refers to the slenderest plate box girder with a plate's thickness of 2 mm but with a short span between frames. The experiment includes initial loading cycles allowing for partial relief of residual stresses. The moment curvature relationship is established for a large range of curvature. The ultimate bending moment (UM) of the box is evaluated and compared with the first yield moment and the plastic moment allowing the evaluation of the efficiency of the structure. The postbuckling behavior and collapse mode are characterized. Comparison of the experiment with a progressive collapse analysis method is made taking into consideration the effect of residual stresses on envelop of the moment curvature curve of the structure.

Approximate approach to progressive collapse analysis of the monotonous thin-walled structures in vertical bending

Present article proposes improved assessment of the ultimate bending capacity (ultimate bending moment), i.e. enhancement of the ultimate limit state evaluation in the concept design of the monotonous thin-walled structures predominantly subjected to vertical bending loads during their exploitation. An alternative progressive collapse analysis method is proposed, which incorporates direct consideration of various relevant distributed load effects and consequently enables more sophisticated evaluation of the ultimate bending capacity and more accurate and reliable identification of the critical cross section and its collapse sequence. Relevant aspects of the employed approximate model for the cross sectional warping due to vertical bending are considered and determination of the (longitudinal) warping displacements and strains, shear strains and stresses, as well as the corrected longitudinal strains is described. Influence of the (ultimate) shear capacity on the (ultimate) bending capacity is discussed and detailed description and critical overview of the proposed method is given. Finally, various aspects of the considered problem and accuracy of the proposed approach are discussed and demonstrated on example of the thin-walled box-girder, whereby detailed comparison of the results obtained by the proposed approach and nonlinear finite element method analyses is given.

Numerical Study of Progressive Collapse in Intermediate Moment Resisting Reinforced Concrete Frame Due to Column Removal

Progressive collapse is a chain reaction of failures propagating throughout a portion of the structure disproportionate to the original local failure occurring when a sudden loss of a critical load‐bearing element initiates a structural element failure, eventually resulting in partial or full collapse of the structure. Both General Services Administration (GSA) and United States Department of Defense (DoD) guidelines incorporate a threat-independent approach to progressive collapse analysis. Therefore, there is an international trend for updating structural design requirements to explicitly design structures to resist progressive collapse. This paper presents simple analytical approach for evaluating progressive collapse potential of typical concrete buildings, comparing four methods for progressive collapse analysis by studying 5 and 10-story intermediate moment-resistant reinforced concrete frame buildings, employing increasingly more complex analytical procedures: linear-elastic static, nonlinear static, linear-elastic dynamic, and nonlinear dynamic methodologies. Each procedure is thoroughly investigated and its common shortcomings are identified. The evaluation uses current GSA progressive collapse guidelines and can be used in routine design by practicing engineers. These analyses for three column-removal conditions are performed to evaluate the behavior of RC buildings under progressive collapse. Based on obtained findings, dynamic analysis procedures -easy to perform for progressive collapse determination- yielded more accurate results.

Hull girder reliability using a Monte Carlo based simulation method

This paper presents a hull girder reliability assessment using a Monte Carlo based simulation method. The simulation method used was developed for component and system reliability problems and provides accurate estimates for the failure probability with reduced computational cost as compared to crude Monte Carlo simulation. The reliability assessment is performed considering as possible failure modes the ultimate collapse of the midship cross section in vertical bending or its local failure due to yielding of the material or buckling collapse of one of its structural elements. The local failure mode was formulated as a system reliability problem. The incremental-iterative method for progressive collapse analysis adopted in the IACS-CSR design rules for oil tankers and bulk carriers was adopted as strength assessment model. Due to the capabilities of the simulation method to deal with high-dimensional problems the geometric and material properties of the midship cross section elements were explicitly included in the simulation as basic random variables.

複合荷重下における船体梁の縦曲げ最終強度に関する研究

It is necessary to make clear the effect of torsional moment on the ultimate strength of the ships' hull girder for the accurate assessment of that of ultra large container ships with large deck openings. In the present study, the extension of the simplified method of progressive collapse analysis based on Smith’s method is attempted to the case of combined loading condition. Firstly, progressive collapse tests are carried out on 1/13-scale three-hold hull girder models referring to a Post-Panamax container ship. The models are fixed to the rigid wall at the aft end and a couple of forces are applied to the fore end so as to generate torsional and vertical bending moment simultaneously. The progressive collapse tests are conducted for the case of the various combinations of torsional and bending moment. The nonlinear finite element analyses by LS-DYNA are executed in accordance with the test conditions. From the test and calculation results, the progressive collapse behavior and the ultimate strength of hull girder models under combined loading are examined. The results will be a basis for the verification of a new simplified analysis method which will be presented in the forthcoming reports.

Evaluation of Dynamic Collapse Behavior of Steel Moment Frames Damaged by Blast

Blast effects on structures and blast mitigation strategies have been vigorously studied in the world. The alternate path method, or common progressive collapse analysis method, of structures assumes the threat-independent removal of vertical load-carrying elements. However, in reality, a blast-induced column-missing event will produce the damage on adjacent structural elements and the rapid dynamic response of the structures. In this study, the strain rate effects on the dynamic collapse behavior of steel moment frames are investigated by performing the blast-induced sequential progressive collapse analysis. Then, the improvement of the progressive collapse analysis method is discussed based on the numerical results.

A new method for progressive collapse analysis of RC frames under blast loading

The progressive collapse of structures under blast loading has attracted great attention all over the world. Some guidelines give specific procedures to analyse the progressive collapse of building structures. Numerical analysis and laboratory test results of the progressive collapse of structures have also been reported in the literature. Because the progressive collapse of a structure induced by blast loading occurs only after the blast-loading phase, most of these studies and guideline procedures perform progressive analysis by removing one or a few load-carrying structural members with static and zero initial conditions. The damage on adjacent structural members that might be induced by blast loads and the inevitable non-zero initial conditions when progressive collapse initiates are neglected. These simplifications may lead to inaccurate predictions of the structural collapse process. In this paper, a new method for progressive collapse analysis of reinforced concrete (RC) frame structures by considering non-zero initial conditions and initial damage to adjacent structural members under blast loading is proposed. A three-storey two-span RC frame is used as an example to demonstrate the proposed method. Numerical results are compared with those obtained using the alternative load path method, and with those from comprehensive numerical simulations by directly applying the blast loads on the frame. It is found that the proposed method with a minor and straightforward extension of the simplified ‘member-removal’ procedure is efficient and reliable in simulating the progressive collapse process of RC frame structures. It requires substantially less computational effort as compared to direct numerical simulations, and gives more accurate predictions of the structural progressive collapse process than the ‘member-removal’ approach.

Methods for progressive collapse analysis of building structures under blast and impact loads

Progressive collapse of building structures under blast and impact loads has attracted great attention all over the world. Progressive collapse analysis is essential for an economic and safe design of building structures against progressive collapse to blast and impact loads. Because of the catastrophic nature of progressive collapse and the potentially high cost of constructing or retrofitting buildings to resist it, it is imperative that the progressive collapse analysis methods be reliable. For engineers, their methodology to carry out progressive collapse evaluation need not only be accurate and concise, but also be easily used and works fast. Thus, many researchers have been spending lots of effort in developing reliable, efficient and straightforward progressive collapse analysis methods recently. In the present paper, current progressive collapse analysis methods available in the literature are reviewed. Their suitability, applicability and reliability are discussed. Our recent proposed new method for progressive collapse analysis of reinforced concrete frames under blast loads is also introduced.

Ultimate Longitudinal Strength of Ship Hulls of Composite Materials

A progressive collapse analysis method is proposed to predict the ultimate longitudinal strength of ship hulls of composite materials. The load-average strain curve derived from a progressive failure nonlinear finite element analysis is adopted for representing the behavior of each stiffened composite panel forming a hull cross section. The bending moment of the ship hull under a prescribed curvature is achieved by integrating the reaction force of each stiffened panel over a hull cross section based on the load-average strain curves. The ultimate longitudinal strength of a ship hull is obtained from the moment-curvature relationship of the ship hull, which is established by imposing progressively increasing curvatures of a hull cross section. An all-composite ship is analyzed as an application.

Comparison of Various Procedures for Progressive Collapse Analysis

We compare four methods for progressive collapse analysis by analyzing a nine-story steel moment-resistant frame building, employing increasingly complex analytical procedures: linear-elastic static, nonlinear static, linear-elastic dynamic, and nonlinear dynamic methodologies. Each procedure is thoroughly investigated and common shortcomings are identified, along with advantages and disadvantages, using side-by-side comparison, including approximate time spent on modeling and computation. The evaluation uses current General Services Administration progressive collapse guidelines. Our objective is to provide clear conceptual step-by-step descriptions of various procedures for progressive collapse analysis by performing example analyses using commercially available structural analysis software, such as SAP2000, with the aim that the explanations in this paper will be clear enough that they will be readily understandable and will be used by practicing engineers. We demonstrate that dynamic analysis procedures not only yield more accurate results, but are also easy to perform for progressive collapse determination. Additionally, we show that current GSA performance limits for linear analysis procedures are unconservative, meaning that a structure designed with acceptable linear evaluation criteria may exceed allowable ductility and rotation limits when nonlinear dynamic analysis is performed on the same structure. Finally, our recommendations for the analysis procedures take into account accuracy as well as ease of use.

Structural analysis for the design of VLFS

A review is presented here with respect to linear and nonlinear structural analyses for the design of very large floating structures (VLFS), with a particular focus on the pontoon-type VLFS, developed during the Mega-Float project in Japan. The role of structural analyses for the design of VLFS is first described through a structural design flow typical of VLFS and design limit states. Structural modeling techniques for hydroelastic global response analysis and a two-step approach for stress analysis of detailed structures, based on the results of global response analysis, are outlined. Regarding the assessment of structural safety for accidental loads, a simulation of airplane collision on VLFS is presented. Finally, a method of progressive collapse analysis of VLFS under abnormal wave loads, based on the idealized structural unit method (ISUM), is introduced.