Progressive collapse analysis of high-rise building with 3-D finite element modeling method

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Abstract

Using the general purpose finite element package ABAQUS, a 3-D finite element model representing 20 storey buildings were first built in this paper to perform the progressive collapse analysis. Shell elements and beam elements were used to simulate the whole building incorporating non-linear material characteristics and non-linear geometric behavior. The modeling techniques were described in detail. Numerical results are compared with the experimental data and good agreement is obtained. Using this model, the structural behavior of the building under the sudden loss of columns for different structural systems and different scenarios of column removal were assessed in detail. The models accurately displayed the overall behavior of the 20 storey buildings under the sudden loss of columns, which provided important information for the additional design guidance on progressive collapse.

Introduction

Progressive collapse first attracted the attention of engineers from the structural failure of a 22-story apartment building at Ronan Point, London, UK, in 1968. The terminology of progressive collapse is defined as “the spread of an initial local failure from element to element, eventually resulting in the collapse of an entire structure or a disproportionately large part of it” [1]. After the event of 11 September 2001, more and more researchers have started to refocus on the causes of progressive collapse in building structures, seeking ultimately the establishment of rational methods for the assessment and enhancement of structural robustness under extreme accidental events. The UK Building Regulations [2] has led with requirements for the avoidance of disproportionate collapse. These requirements, which are refined in material-specific design codes (e.g. BS5950 [3] for structural steelwork), can be described as (i) prescriptive ‘tying force’ provisions which are deemed sufficient for the avoidance of disproportionate collapse (ii) ‘notional member removal’ provisions which need only be considered if the tying force requirements could not be satisfied, and (iii) ‘key element’ provisions applied to members whose notional removal causes damage exceeding prescribed limits. In the United States the Department of Defense (DoD) [4] and the General Services Administration (GSA) [5] provide detailed information and guidelines regarding methodologies to resist progressive collapse of building structures. Both employ the alternate path method (APM) to ensure that structural systems have adequate resistance to progressive collapse. APM is a threat independent methodology, meaning that it does not consider the type of triggering event, but rather, considers building system response after the triggering event has destroyed critical structural members. If one component fails, alternate paths are available for the load and a general collapse does not occur. The methodology is generally applied in the context of a ‘missing column’ scenario to assess the potential for progressive collapse and used to check if a building can successfully absorb loss of a critical member. The technique can be used for the design of new buildings or for checking the capacity of an existing structure.

Izzuddin et al. 6., 7., proposed a novel simplified framework for progressive collapse assessment of multi-storey buildings, considering sudden column loss as a design scenario. It analyzed the non-linear static response with dynamic effects evaluated in a simple method. It offers a practical method for assessing structural robustness at various levels of structural idealization, and importantly it takes the debate on the factors influencing robustness away from the generalities towards the quantifiable. Kim et al. [8] studied the progressive collapse-resisting capacity of steel moment resisting frames using alternate path methods recommended in the GSA and DoD guidelines. The linear static and non-linear dynamic analysis procedures were carried out for comparison. It was observed that the nonlinear dynamic analysis provided larger structural responses and the results varied more significantly. However the linear procedure provided a more conservative decision for progressive collapse potential of model structures. Khandelwal et al. [9] studied the progressive collapse resistance of seismically designed steel braced frames with validated two dimensional models. Two types of braced systems are considered: namely, special concentrically braced frames and eccentrically braced frames. The study is conducted on previously designed 10-story prototype buildings by applying the alternate path method. The simulation results show that while both systems benefit from placement of the seismically designed frames on the perimeter of the building, the eccentrically braced frame is less vulnerable to progressive collapse than the special concentrically braced frame. Paik et al. [10] investigated the possibility of progressive collapse of a cold-formed steel framed structure. Five different analysis cases were considered. The results showed that the removal of corner wall columns appeared to cause progressive collapse of a portion of the second and third floor of the end bay directly associated with the column removal, and not the entire building. Tsai et al. [11] conducted the progressive collapse analysis following the linear static analysis procedure recommended by the US General Service Administration (GSA). Using the commercial program SAP2000, the potential of an earthquake-resistant RC building for progressive collapse is evaluated. However, no validation of the accuracy of the SAP2000 model is presented.

Although there are some design guidances as shown above, some major shortcomings have been recognized by the researchers. As pointed out by Izzuddin et al. 6., 7., the prescriptive nature of the tying force requirements, deemed sufficient for the avoidance of disproportionate collapse yet unrelated to real structural performance, and the exclusion of ductility considerations at all levels of the provisions made the provisions unsafe. On the other hand, the alternative notional member removal provisions are more performance-based, but these are applied with conventional design checks, and hence they ignore the beneficial effects of such non-linear phenomena as compressive arching and catenary actions. This in turn can lead to the prediction of an unrealistically large damage area exceeding the prescribed limits, thus forcing the member to be designed as a key element when this may be unnecessary. Therefore, more detailed research toward the progressive collapse of multi-storey building is timely. However, as mentioned above, the research on the behavior of the progressive collapse of high rise building is quite limited due to the limited research tools. Full scale test of this type of problem is not possible due to its high cost. A 3-D Finite element model is definitely a best option. However, due to the geometric complexity of multi-storey building and poor preprocessing functions of current general purpose finite element packages, no full scale 3-D finite element model for investigating progressive collapse has been built so far there is also little research toward the modeling of the structural behavior of multi-story buildings under sudden column loss. Most of the modeling techniques mentioned in Section 1 are either the simplified models based on current design guidance or two dimensional models, which could not accurately monitor the overall structural behavior of the whole building.

In this paper, using the general purpose finite element package ABAQUS [12], a 3-D model is first developed by the author which enables the non-linear progressive collapse analysis of high rise building. Two 3-D finite element models representing 20 storey buildings with different structural forms were built to perform the progressive collapse analysis. The models accurately displayed the overall behavior of the 20 storey buildings under sudden loss of columns, which provided important information for additional design guidance on progressive collapse.

Section snippets

Preprocessing method

In order to accurately monitoring the structural behaviors of the high-rise building for progressive collapse, it is useful to build up a 3-D full scale finite element model. However, the preprocessing function of all the general purpose programs such as ABAQUS and ANSYS used in the current research is quite limited. Therefore, it is difficult to set up a multi-story building model due to the geometric complexity of the structures. The geometric shape of the model becomes a key issue of the

Validation of the model

In order to valid the proposed model, a two storey composite steel frame model was built up as shown in Fig. 5, Fig. 6. The model replicated the full scale testing of a steel–concrete composite frame by Wang et al. [17] as shown in Fig. 7. The model was set up based on the same modelling techniques discussed in part 2 of this paper. The frame size, slab thickness and boundary conditions are exactly the same as the full sale tests [17]. The section sizes are shown in Fig. 8 and the section

Column removal analysis

As stated in Section 1, the alternate path method (APM) which is proposed by DOD [4] and GSA [5] is applied here to perform the progressive collapse checking of the existing 20 storey buildings. As stated in DOD [4] and GSA [5], the methodology is generally applied in the context of a ‘missing column’ scenario to assess the potential for progressive collapse. Under extreme events, such as blast and impact, the dynamic influences are event-independent. Sudden column loss represents a more

Conclusions

In this paper, a 3-D finite element model was first built with the ABAQUS package to simulate the behaviour of multi-storey buildings under sudden column removal. The methodology for the modelling techniques is described in details. The model also incorporates non-linear material characteristics and non-linear geometric behaviour.

A two storey model was built for the validation of the proposed modelling method. The numerical results are presented and compared to experimental data and good

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