Alternate Load Path Method Research Articles

Analytical Investigation of Progressive Collapse Resistance Mechanism in Steel Moment Frame with Fiber Model

In order to investigate the resistance mechanism of steel frame structure in progressive collapse, an advanced finite element model(FEM) is presented based on fiber beam-column element. Using this FEM, non-linear static pushdown analysis of a ten-story structure was carried out by the alternate load path method, in the two cases that two different columns are removed respectively. Analytical results show that residual structure has the different resistance mechanism for the different column removal case. In the initial stage, bending resistance mechanism can provide dominate resistance capacity in the structural progressive collapse, after both middle and side columns are removed. However, when the bending resistance is out of work, the catenary action is induced in the case of the middle column removal only, which is not developed after the side column is removed. It can be seen that steel frame structure has higher collapse risk in the case of the side column removal than in the case of the middle column removal.

Reliability Assessment of Damaged RC Moment-Resisting Frame against Progressive Collapse under Static Loading Conditions

AbstractPrevention of structures against progressive collapse has become a concern of increasing significance and the alternative load path method (ALPM) is the extensively acknowledged approach in this area of research. With the basis of ALPM and by amalgamation of the Monte Carlo simulation method and an iterative algorithm, a new approach is developed in this paper to assess the reliability of ductile RC frame structures when subjected to one column failure. This paper focuses on the construction and solution of the performance function of the damaged structure under static service loadings. With this intention, three types of critical zones are identified and an optimum model is presented to determine the possible failure modes for each zone. By employing the virtual work principle and critical collapse mechanism criterion, the performance function is established in terms of minimum internal virtual work and external virtual work done by service loadings. Three equations containing the interaction bet...

Progressive Collapse Simulation of Underground Structure under Internal Blast Loading

Much research has been directed at the progressive collapse of the over-ground structures under free air burst loading in recent years, while less work has been stressed on the progressive collapse of the underground structures, which subjected to internal blast loading. A proposed method is presented in this paper to simulate the progressive collapse of one underground reinforced concrete frame under internal blast loading, which is using LS-DYNA. The numerical results indicate that the proposed method is more accurate and timesaving, compared with alternative load path method (ALPM) and direct simulation method (DSM).

Robustness of building structures – recent developments and adopted strategy

AbstractRecent events such as natural catastrophes or terrorism attacks have highlighted the necessity to ensure the structural integrity of buildings under an exceptional event. According to the Eurocodes and some different other national design codes, the structural integrity of civil engineering structures should be ensured through appropriate measures but, in most cases, no precise practical guidelines on how to achieve this goal are provided.At the University of Liège, the robustness of building frames is investigated following the so‐called “alternative load path method”, with the final objective to propose design requirements to mitigate the risk of progressive collapse considering the conventional scenario “loss of a column” further to an unspecified event. In particular, a complete analytical procedure has been developed for the verification of the robustness of steel or composite plane frames. For sake of simplicity, these first works have been based on the assumption that the dynamic effects linked to the column loss were limited and could therefore be neglected. More recently, complementary works have been carried out with the objective to address the dynamic effects. Besides, the extension of the static procedure to actual 3D frames is under investigation in Liège. The present paper gives a global overview of the ongoing researches in the field of robustness at the University of Liège and, in particular, the global strategy aiming at deriving design requirements is detailed.

Evaluation of progressive collapse alternate load path analyses in designing for blast resistance of steel columns

The alternate load path method is a convenient, “threat-independent” method used in progressive collapse analysis and design. Because no actual loadings are considered in this method, the resistance provided by the alternate load path method for specific extreme events is not well quantified. However, such quantification allows for an understanding of what real scenarios can be efficiently represented by alternate load path analyses. As blast loading is one of the abnormal loading events typically motivating an alternate path analysis, this load type is selected for evaluation in the present work. In order to find the blast threat that is representative of the alternate load path method in steel-framed buildings, finite element analyses of steel columns being subjected to blast loads were analyzed in the program LS-Dyna. Prior to this, sensitivity and validation studies were also completed, which are described herein. The results of the column analyses show that failure is governed by a stability-based deflection criterion. Conclusions regarding the charge sizes that the alternate load path method may be considered to be representative of, as well as the influence of column spacing, size, and end fixity on these results are given.

The Effect on The Overall Performance of Frame Structure of Local Column Destruction

How to ensure the whole stability of structure and avoid progressive collapse of structure caused by destruction of local structures under accidental loading have been paid close attention to extensively by researchers all over the world. According to GSA guidelines, FEM model of 3-D frame structure was established by ANSYS software. Failure of frame structure local column is simulated with the method of "killing" columns of long side, short side, corner side, and interior side, and two columns of long sides, in order to explore the regularity for change of series performance parameters when the frame structure suffering accidental loading. And the alternative load path method was used to analyse the collapse of reinforced concrete frame structure. The result indicates that the frame structure local column damage can make structure basic natural vibration period and maximum interlayer displacement angle larger, and make minimum ratio between shearing force and weight smaller, and if two columns of long side are destroyed, the progressive collapse of frame structure will occur.

정적 및 동적 해석을 통한 철근콘크리트 무량판 구조의 연쇄 붕괴 저항 성능 평가

현재 한국에서는 연쇄 붕괴에 대한 설계지침이 적용되고 있지 않으며, 특히 무량판 구조의 연쇄 붕괴 저항 성능에 대한 연구는 초기단계라고 할 수 있다. 따라서 이 연구에서는 철근콘크리트 무량판 구조의 연쇄 붕괴 저항 성능을 평가하기 위하여 3가지 해석법을 수행하였다. 선형 정적 해석을 통하여 GSA의 대체경로법에 의한 DCR 값의 차이를 비교하였고, 선형 동적 해석을 통하여 기둥 제거 이후의 수직 변위를 비교하였으며, 비선형 정적 해석을 통하여 최대 하중 계수를 판단하였다. 유효 보폭 모델과 판 유한 요소 해석 모델의 차이점을 분석하기 위하여 여러 변수들에 따라 유한 요소 해석이 수행되었다. 무량판 구조에서 실무에서 많이 사용되고 있는 유효 보폭으로 모델링하는 방법은 슬래브의 강성 기여도를 반영하고 있지 못해 연쇄 붕괴 성능 평가는 상세 유한 요소 해석이 적절할 것으로 판단된다.여러 변수들을 종합 모서리 기둥(CC)을 제거할 경우가 가장 불리한 조건이고, 내부 기둥(IC)이 제거될 경우가 가장 유리한 조건으로 나타났다. 이 연구에서 제시된 무량판 구조의 연쇄 붕괴 저항 성능 결과로부터 향후 무량판 구조의 성능을 합리적으로 평가하는데 유용하게 활용될 수 있을 것으로 사료된다.

Steel moment frames column loss analysis: The influence of time step size

This paper applies two well-known structural dynamics computational algorithms to the problem of disproportionate collapse of steel moment frames applying the alternate load path method. Any problem of structural dynamics strongly depends on the accuracy and the reliability of the analysis method since the parameters involved in the selection of the appropriate algorithm are affected by the nature of the problem. Disproportionate collapse is herein simulated via a time history analysis used to “turn off” the effectiveness of an element to the structure. For this kind of problem the time step size of the computational algorithm is of major importance for the accuracy of the method and thus, remains a variable throughout the present analyses. Two plane steel moment frames are used for the numerical examples, while all the analyses are performed independently. Firstly the β -Newmark method is applied and secondly the linear Hilbert–Hughes–Taylor a-method is applied and the respective results are compared and discussed in the last part of the paper.

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.

Collapse analysis of steel moment frames with various seismic connections

Seismic connections with high ductile capacity are generally considered to be effective for resisting seismic loads. However, additional studies are still needed to evaluate the performance of seismic connections during progressive collapse. In this study the progressive collapse resisting capacity of the Reduced Beam Section (RBS), Welded Cover Plated Flange (WCPF), and Welded Unreinforced Flange-Welded Web (WUF-W) connections, which are seismic connections recommended by the FEMA/SAC project, was investigated. For progressive collapse analysis, two types of steel moment frame buildings were considered; one designed for high-seismic load and the other designed for moderate-seismic load. The vertical displacement at the point of column removal and the plastic hinge rotation at beam ends were checked by using an alternative load path method proposed in the guidelines. The analysis results showed that the performance of the Cover Plate connection turned out to be the most effective in resisting progressive collapse, especially in structures located in moderate-seismic regions.