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Abstract
Even though blast events in inhabited areas are characterized by a low probability of occurrence, they can present a high risk for buildings and their occupants. The means to reduce the vulnerability and prevent the progressive collapse of buildings includes large stand-offs, enhanced local strength of structural elements, and increased redistribution capacity after a local damage. Blasts are extremely complex events, especially when the charge is detonated at a small distance from the building. In such cases, the application of analytical methods may give inaccurate results. The paper presents the results of a combined experimental/numerical program, which focused on the response of steel frames to close-in detonations. Two identical specimens were tested inside a specialized bunker for different charge sizes and stand-off distances. Very similar behaviors and failure modes were observed for the two specimens. The numerical model, calibrated against test data, was able to accurately predict the deformations and failure mode of the specimens. The results of the parametric numerical study indicated that the local failure mechanism and resistance to progressive collapse of steel building frames depend very much on the blast load parameters but also on the level of gravity loads in columns.
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... In recent years, relevant research on the progressive collapse of structures has provided many insights. Various researchers have conducted a series of studies on the collapse resistance of the structure [4][5][6][7][8][9]. Among them, the beam-column substructures are the most common experimental object due to their clear force, simple structural form, and ease of testing. ...
In actual situations, it is not possible to determine the exact location where the column will fail (in a member or building structure). Based on the location of the failure, the lateral constraint stiffness of the directly affected area of the structure will change, affecting the structure's anti-collapse performance. This study aims to explore how the location of the failure column affects the collapse resistance of composite beam–column substructures; the double-sided restraint substructure (DSRS) and the single-sided restraint substructure (SSRS) were chosen as research objects, and the two test structures were subjected to static loading tests to compare their collapse resistance. The results showed that the two specimens had similar failure modes and deformation patterns. In addition, the development trend of the internal force of the two specimens was comparable, but the axial force of the SSRS was smaller. The contribution of the catenary mechanism of DSRS was approximately 24%, while the catenary effect of SSRS was not fully exerted, leading to only 15% of the total resistance. Two specimens were modeled in ABAQUS, and the finite element method was verified by comparing the simulation results with the test results. A full-scale model was established to analyze the effects of the lateral restraint stiffness of DSRS and SSRS and the side column size on the collapse resistance of the substructure. The finite element analysis results are as follows: (1) lateral restraint stiffness had less influence on the small deformation stage of the substructure; (2) the beam end tension force played a significant role in the collapse resistance of the substructure; (3) increasing the horizontal lateral restraint stiffness can effectively improve the anti-collapse performance of composite beam–column substructure; (4) the side column can provide effective axial and rotational restraint for the beam end. Having too large or too small a side column can have an adverse effect on the structure. Moreover, the larger the side column size, the better the continuous collapse resistance of the substructure when the beam–column linear stiffness ratio is between 0.6 and 1.1.
... In such a case, the use of numerical analysis can lead to more accurate results, in particular when the results are validated using relevant experimental data. Relatively few experimental studies on the resistance of steel structure buildings to near field explosions have been carried out worldwide, so the interest in such investigations is high [1], [2], [3]. As an alternative to the explicit design to explosions, the structure can be designed to withstand local damage (e.g. ...
... Many scientific research papers on the successful use of AEM over the FEM to model the collapse of full structural systems were published as discussed previously and in (Dinu et al., 2017), (Zerin et al., 2017), (Cismasiu et al., 2017), (Elshaer et al., 2017), (Garofano & Lestuzzi, 2016), (H. Salem et al., 2016), (H. ...
Progressive collapse is defined as either partial or overall failure of the structure due to losing one of the main structural elements. In order to control this chain reaction, it is important to study the main structural elements behavior under column removal. Precast concrete structures become widely used recently due to the quality control assurance, economical aspects, and time-saving construction. Due to this many researchers studied the precast concrete structures behavior under earthquake loading, observing the failure patterns, weak points, and how to overcome all those parameters, however, regarding progressive collapse , Precast concrete structures need intensive researches to cover all the parameters that will affect the structure's behavior due to accidental loading. One of the main parameters that still ambiguous is the Precast beam span lengths and its behavior on the overall structure When subjected to progressive collapse. In this paper, the influence of different span lengths of precast beams is studied under different column removal scenarios. A precast concrete structure case study is adopted and designed according to Precast/Prestressed Concrete Institute and ACI 318-14 and a multiple 3D models, for different span lengths, are modeled in Extreme Loading of Structures software based on the Applied Element Method. Non-linear dynamic time-dependent analysis is conducted on two case studies; bare frame structure without any slab contribution (Case1), and full structure with slab contribution (Case2). Column removal scenarios are applied according to the UFC regulations, partial collapse took place in case1 while case 2 showed high resistance to progressive collapse. Observations are reported in terms of failure cause for case 1 and the resisting mechanism that took place in case 2. Rotational ductility redistributed applied loads for beams and columns are obtained for case 2. A comparison took place between the rotations obtained in the case study and the rotation limits specified by the UFC and found that the system is satisfying the UFC limits, and no additional consideration needs to be done in resisting progressive collapse.
... Olmati et al. (2013) presented a robustness method for assessing structural safety under different local damage levels after explosion. In summary, the damage assessment of components subjected to the local explosion loading could be carried out by the local model experiment (Dinu et al., 2017) or local refined finite element simulation, and then, the further analysis could be executed by substituting damaged components into the global structural model. For the external detonation in far range of the large structure, or the internal detonation of the large span space structure, it is necessary to calculate the explosive responses of the global structure because the shock waves would cover the whole structure. ...
In order to analyse the mechanical behaviour of a reticulated shell structure under explosive load, a novel method was proposed to calculate the dynamic displacement response of the cylindrical reticulated shell structure by using the influence surface in this article. First, the theory of the dynamic influence line was developed and the consistency between the dynamic influence lines and the static ones was verified. Then, based on the theory of the dynamic influence line and for the simplified calculation of dynamic responses, the dynamic influence lines of a simply supported beam were simplified as the static ones multiplied by the dynamic amplification factor β. And then the explosion dynamic responses of the beam could be fast calculated using the influence lines. The extended application of the above method to single-layer cylindrical reticulated shell was the influence surface method. The results of numerical examples showed that the nodal displacements of the structure obtained by using the influence surface method agreed well with those obtained by using ANSYS/LS-DYNA. The research results also indicated that the influence surface method was applicable to the node displacement calculation of the structure under three different conditions, including the centre node of the symmetrical structure, the arbitrary nodes (excluding those near the supports) of symmetrical structure under symmetrical loads and the arbitrary nodes of arbitrary structures in which the load holding time is much longer than the natural vibration period of structure. The proposed approach could reduce the computation cost for analysing the explosion dynamic response of the reticulated shell structure, thereby providing a more effective method for the anti-explosion design of reticulated shell structures.
The execution of the blasting works involves the management of the problem of storage of explosive materials. This aspect is easier to solve in the case of mines activities with long exploitation time and where storage capacities are arranged, according to the legislation that provides constructive and safety criteria depending on the type and quantity of explosive materials stored. In the case of isolated blasting works, those for road construction, building demolition, underwater or forestry, etc., storage facilities must be arranged for shorter periods of time and smaller capacity, but which must comply with security, environmental and risk requirements, such as high-capacity deposits with long duration of activity. Considering that for the execution of such blasting works, the national legislation provides the possibility of arranging temporary explosive depots, of small capacity, but without specifying the constructive details and the necessary safety requirements to be observed, mentioning only that they must be executed based on a specialized project. This paper presents a series of tests conducted by INSEMEX, to establish recommendations regarding the constructive and safety requirements that must be observed when designing and building mobile explosive depots.
Steel frames subjected to a column removal typically exhibit a complex load resisting mechanism characterised by three contributions: i) beam yielding mechanism, ii) compressive arch, and iii) catenary action. The development of compressive arch actions in the beams bridging over the lost column has not been yet thoroughly investigated in steel frames, although such effects proved to significantly contribute to the collapse‐resistance of reinforced concrete frames.
This paper aims at shedding light on the compressive arch actions of steel beams in case of column removals accounting for various boundary conditions. Numerical and analytical methods were employed for quantifying the contribution of these effects to the structural robustness of steel frames. A simplified analytical model that allows estimating the magnitude of arching effects in steel beams with various types of end‐connections and horizontal restraints provided by the surrounding structure was introduced. The agreement between numerical and analytical results suggests that the proposed analytical model allows for accurate predictions. This validates the model's use for practical applications and gives promising prospects for its inclusion in consistent analytical methods for predicting the activated alternative load path in steel frames subjected to a column loss scenario.
Today, due to the diversity of the conditions in which the blasting works are executed, they often require a special organization regarding the transportation and storage of the explosive goods near the blasting field. If for explosive storage arranged for long-term use such as those of the producers, there are detailed regulations regarding the constructive and security requirements that they must meet, for the temporary storage facilities, there are not enough details regarding the constructive requirements that they must comply with. One of the most important aspects taken into account when designing and arranging a mobile explosive depot is the limitation to the maximum of the dynamic action and the throw effect of pieces of material under the pression of an accidental detonation. The paper describes the results obtained after testing a container prototype designed for the storage of explosives. Following the tests performed and the evaluation of the dynamic effects of explosions inside and outside the container as well as the analysis of the measurement regarding the pressure generated by the detonation of explosive charges, it turned out that the construction and detonation behavior of the tested container complies with the purpose and safety requirements for setting up a mobile explosive depot.
Present paper summarises a case study aiming to evaluate the robustness performance of a multi-story steel frame building designed for persistent and seismic design requirements. On this purpose, a reference 6-story steel building with dual inverted V bracing and moment frames was first designed. Then, the robustness performance of the structure was assessed considering extreme events that are deemed credible after an earthquake, i.e., internal gas explosion and localized fire. The structural performances were evaluated using nonlinear static and dynamic analyses. Numerical model was calibrated against experimental test data.KeywordsDual frameSeismic resistant systemMulti-hazardRobustness assessmentColumn removal
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.
In this study, 13 typical wide-flange steel columns, each carrying an axial load equal to 25% of its axial capacity, are field tested using live explosives, involving charge size of 50 to 250 kg of ammonium nitrate/fuel oil (ANFO) and ground stand-off distance of 7.0 to 10.3 m. The reflected pressure time histories, time-dependent displacements, accelerations, and strains of the columns are measured, and their postblast damages and failure modes are reported. Maximum deformations, vibration periods, strain-rate, and contributing modes in the dynamic response of the columns are compared to those of companion steel beams (without axial load) tested in the same setup. Results show that columns that exhibit elastic response, due to the elongation of the column vibration period caused by the axial load, the lateral deformation caused by blast load is reduced rather than magnified by the axial load. The axial-bending interaction, or P-delta effect, may be neglected for steel columns with axial load up to 25% of their axial capacity, provided the column response remains within the elastic range-but if it crosses into the plastic range, the interaction cannot be ignored. (C) 2014 American Society of Civil Engineers.
A new method, Applied Element Method (AEM) for analysis of structures is introduced. The structure is modeled as an assembly of distinct elements made by dividing the structural elements virtually. These elements are connected by distributed springs in both normal and tangential directions. We introduce a new method by which the total behavior of structures can be accurately simulated with reasonable CPU time. This paper deals with the formulations used for linear elastic structures in small deformation range and for consideration of the effects of Poisson's ratio. Comparing with theoretical results, it is proved that the new method is an efficient tool to follow mechanical behavior of structures in elastic conditions.
The beam-to-column connections of moment-resisting steel frames should exhibit capacities that allow them to transfer the forces that develop under normally expected loading conditions. However, when a column is lost owing to accidental loading, these conditions change, and the forces are redistributed to the adjacent beams and columns. In such cases, the connections must be capable of resisting the combined axial and flexural loads and allow for the redistribution of the loads, so that progressive collapse development is prevented. In this study, we investigated the performances of four types of beam-to-column connections, namely, the welded cover plate flange connection (CWP), the haunch end plate bolted connection (EPH), the reduced beam section welded connection (RBS), and the unstiffened extended end plate bolted connection (EP), against progressive collapse. Two span frames were constructed and tested under a central column removal scenario until failure. The results from the experimental tests were used to validate finite element models. The CWP, EPH, and RBS specimens showed good ductility, with the catenary action making a significant contribution to the ultimate load resistance. Further, the ultimate rotations of the beams were greater than the deformation limit given in the latest Unified Facilities Criteria guidelines for design of buildings to resist progressive collapse. Specimen EP showed the lowest ductility and ultimate load resistance, with the bolts in the rows under tension fracturing before the catenary action could develop. Further, the failure mode for specimen EP indicated that bolt strengthening is necessary for improving its progressive collapse resistance.
The different nature and intensity of accidental loads make difficult the development of design requirements for such situations. Therefore, a better strategy is to limit the ex-tent of damage so that the progressive collapse is not initiated. Features like ductility and continuity provide more deformation capacity and redistribution of loads, so that the structure can bridge over damaged/lost elements. Interaction between the steel beams and the concrete slab is also expected to enhance the resistance after the loss of a column. This paper presents the results of an experimental study that aimed at investigating the contribution of the floor system and beam-floor interaction to the load redistribution capacity in case of a column loss. For this purpose, a 3D steel frame structure, with composite beams and extended end-plate bolted beam-to-column connections, was considered. The specimen was tested under mono-tonic loading applied to the top of the central column until complete failure. The results showed the system was capable of developing larger capacity to resist the loss of a column but lower deformation capacity when compared to a bare steel frame tested under similar conditions.
During last decades, there was an increased interest from research and design professionals to provide effective strategies in protecting buildings and other assets from the direct effects of blasts or other incidents. Experimental tests, conducted over a large range of distances and charge weights, helped at developing analytical approaches and charts which can be used to calculate blast parameters. Due to the lack of test data and inapplicability of common scaling rules, in the last years special attention was devoted to close-in blasts, located in the proximity of the structural elements. Such explosive charges may cause extreme lo-cal damage of the elements or even complete loss of load bearing capacity. In the study presented in the paper, two types of beam-column assemblies have been tested under explosive charges detonated close to the specimens. Numerical models, developed using Extreme Loading for Structures software, were validated using the test data collected in the experimental program.
Multistory steel frames are expected to provide resistance to progressive collapse following local damage or failure caused by extreme loading events. Features like ductility and continuity provide more deformation capacity and redistribution of loads so that the structure can bridge over damaged elements. Special measures should be taken to ensure that the connections can withstand the extreme loading and deformation demands arising from the occurrence of local failure. In addition, two-way frames will enhance the progressive collapse resistance over planar systems as the loading demand on each element reduces.
In this study, we investigated the response of two-way steel frame systems under the removal of a central column. Extended end-plate bolted connections were used to join the beams to the columns. First, an experimental test was carried out, and then, a numerical model was validated using the advanced nonlinear dynamic analysis software Extreme Loading for Structures. The system was capable of developing large deformations associated with catenary response in the beams without failure of the connections. The beam ultimate rotation is larger than the deformation limit given in the codes.
A new extension for the Applied Element Method (AEM) is introduced. Using this method, the structure is modeled as an assembly of distinct elements made by dividing the structural elements virtually. These elements are connected by distributed springs in both normal and tangential directions. This paper describes the applicability of the AEM for different fields of analysis and structure types and it deals with the formulations used for RC structures under monotonic loading. It is proved in this paper that the structural failure behavior including crack initiation and propagation can be simulated accurately with reasonable CPU time and without any use of complicated material models.
Structural identification continues to develop an expanding role within performance-based civil engineering by offering a means to construct high-fidelity analytical models of in-service structures calibrated to experimental field measurements. Although continued advances and case studies are needed to foster the transition of this technique from exploration to practice, potential applications are diverse and range from design validation, construction quality control, assessment of retrofit effectiveness, damage detection, and lifecycle assessment for long-term performance evaluation and structural health monitoring systems. Existing case studies have been primarily focused on large civil structures, specifically bridges, large buildings, and towers, and the limited studies exploring application to damaged structures have been primarily associated with seismic events or other conventional hazards. The current paper produces the first experimental application of structural identification to a component of a full-scale building structure with structural deterioration resulting from an internal blast load. Experimental modal analysis, nondestructive testing, and visual documentation of the structure was performed both prior to and after the internal blast, while a suite of blast overpressure transducers and shock accelerometers captured applied loads and structural response during the blast event. This paper presents an overview of the field testing and observed structural response followed by extensive treatment of the experimental characterization of structural damage in a masonry infill wall. Combined stochastic-deterministic system identification is applied to the acquired input-output data from the vibration testing to estimate the modal parameters of the infill wall for both the in-service state and in the postblast condition with damage characterized by interfacial cracking and permanent set deformation. Structural identification by global optimization of a modal parameter-based objective function using genetic algorithm is employed over two stages to produce calibrated finite-element models of the wall in the preblast and postblast conditions. Damage characterization is explored through changes in the structural properties of the calibrated models. Plausibility of the results are supported by observed cracking and spall documented in the experimental program and further reinforced through nonlinear applied element simulation of the response of the wall. (C) 2014 American Society of Civil Engineers.
Much of past research in the civilian area on the response of civil structures to explosive loading has focused on large detonations in the far field that result in relatively uniform pressure distribution over the structure and specific structural elements. A paucity of research has been conducted that investigates the effect of explosive loading in close proximity to key structural elements. The studies that have been conducted focused primarily on loading perpendicular to the strong axis of bending that result in global deformation, but no rupture or loss of material. Through experimental testing and finite-element simulation, the present study investigates the effect of blast loading on wide flange columns loaded perpendicular to the weak axis of bending. This loading scenario is critical for such columns because the near field shock wave can rupture the web, and in some cases, lead to material loss; both conditions can potentially jeopardize the axial load carrying capacity of the column as a result of increased demands on flanges and possible local buckling of the unrestrained flanges. Therefore, this critical scenario needs to be considered for developing blast resistant measures or assessing the remaining axial and bending capacity of the column. Finite-element simulation can be used for this purpose; the analyses conducted as part of this study replicate, with reasonable accuracy, the experimentally obtained localized deformation, ruptures, and loss of material as a result of blast load, although the finite-element simulation is less successful at replicating the global deformation of the column. (C) 2013 American Society of Civil Engineers.
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