Applied Element Method (AEM)

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  • Structural Identification and Damage Characterization of a Masonry Infill Wall in a Full-Scale Building Subjected to Internal Blast Load

    Abstract: 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.

    Keywords: Structural identification, Blast loading, Vibration-based damage detection, Finite-element model updating, Applied element method.

    Timothy P. Kernicky; Matthew J. Whelan; David C. Weggel, P.E.; and Corey D. Rice. Structural Identification and Damage Characterization of a Masonry Infill Wall in a Full-Scale Building Subjected to Internal Blast Load. J. Struct. Eng. , 10.1061/(ASCE)ST.1943-541X.0001158 , D4014013.

  • Collapse Analysis of Utatsu Ohashi Bridge Damaged by Tohuku Tsunami using Applied Element Method

    Abstract: The 2011 Tohuku tsunami on the east coast of Japan resulted in killing more than 15,000 people and missing more than 2,500 people, washing away of more than 250 coastal bridges and loss of US$235 billion. Collapse of coastal bridges due to tsunami impact represents a huge obstacle for rescue works. Therefore, in the current study, the collapse of Utatsu Ohashi bridge is numerically studied. The analysis is carried out using the Applied element Method due to its advan-tages of simulating structural progressive collapse. The AEM is a discrete crack approach, in which elements can be separated, fall and collide to other elements in a fully nonlinear dynamic scheme of computations. The Utatsu Ohashi bridge collapse was successfully simulated using AEM. It was numerically found that the amount of trapped air between deck girders during tsunami had a significant effect on the behavior of the bridge. This is attributed to the buoyant force accompanied with the trapped air. A simplified method for estimating trapped air was assumed and proved to give reasonable results compared to reality. Three different solution examples for mitigating collapse of similar existing bridges were introduced and applied to Utatsu Ohashi bridge case and found to be efficient for preventing collapse.

    Keywords: Tsunami, Impact, Bridge, Progressive Collapse, Applied Element Method.

    Hamed Salem, Suzan Mohssen, Kenji Kosa, Akira Hosoda. Collapse Analysis of Utatsu Ohashi Bridge Damaged by Tohuku Tsunami using Applied Element Method. Journal of Advanced Concrete Technology Vol. 12(2014) No. 10. p.388-402. Released: October 11, 2014.

  • Performance-Based Seismic Vulnerability Evaluation of Masonry Buildings Using Applied Element Method in a Nonlinear Dynamic-Based Analytical Procedure

    Abstract: A thorough four-step performance-based seismic evaluation for a six-story unreinforced masonry building is conducted. Incremental dynamic analysis is carried out using the applied element method to take advantage of its ability to simulate progressive collapse of the masonry structure including out-of-plane failure of the walls. The distribution of the structural responses and inters-tory drifts from the incremental dynamic analysis curves are used to develop both spectral-based (Sa) and displacement-based (interstory drift) fragility curves at three structural performance levels. The curves resulting from three-dimensional (3-D) analyses using unidirectional ground motions are combined using the weakest link theory to propose combined fragility curves. Finally, the mean annual frequencies of exceeding the three performance levels are calculated using the spectral acceleration values at four probability levels 2%, 5%, 10%, and 40% in 50 years. The method is shown to be useful for seismic vulnerability evaluations in regions where little observed damage data exists.

    Keywords: Progressive Collapse, Seismic, Vulnerability Assessment, Masonry.

    Karbassi A., Nollet M. Performance-Based Seismic Vulnerability Evaluation of Masonry Buildings Using Applied Element Method in a Nonlinear Dynamic-Based Analytical Procedure: Earthquake Spectra: May 2013, Vol. 29, No. 2, pp. 399-426. Keywords: Progressive Collapse, Seismic, Vulnerability Assessment, Masonry.

  • Progressive Collapse Assessment of Framed Reinforced Concrete Structures According to UFC Guidelines for Alternative Path Method

    Abstract: A structure is subjected to progressive collapse when a primary vertical structural element fails, resulting in failure of adjoining structural elements which, in their turn, cause further structural failure leading eventually to partial or total collapse. The failure of a primary vertical support might occur due to extreme loadings such as bomb explosion in a terrorist attack, gas explosion and huge impact of a car in the parking area. Different guidelines such as the General Services Administration (GSA) and the Unified Facilities Criteria (UFC) addressed the structural progressive collapse due to the sudden loss of a main vertical support. In the current study, a progressive collapse assessment according to the UFC guideline is carried out for a typical 10-story reinforced concrete framed structure designed according to (ACI 318-08). Fully nonlinear dynamic analysis for the structure was carried out using Applied Element Method. The investigated cases included the removal of a corner column, an edge column, an edge shear wall, internal columns and internal shear wall. The numerical analysis showed that for economic design, the slabs should be taken into consideration due to their significant effect on structural integrity after support removal. The simplification of the problem into 3D bare frames would lead to uneconomic design. It was found for the studied case that, reinforced concrete structures designed according to ACI code does not meet the UFC limits and that they a have a high potential for progressive collapse for cases of loss of either the corner column or edge shear wall. A modification for the ACI code was proposed to meet the UFC limits.

    Keywords: Progressive collapse; UFC; ELS; AEM; Slabs; Catenry action; Collapsed area and rotation limits

    Helmy H., Salem H. , and Mourad S. Progressive Collapse Assessment of Framed Reinforced Concrete Structures According to UFC Guidelines for Alternative Path Method, Engineering Structures 42 (2012) pp 127–141.

  • Computer-Aided Design of Framed Reinforced Concrete Structures Subjected to Flood Scouring

    Abstract: In the beginning of 2010, several reinforced concrete structures collapsed due to floods in Sinai and Aswan, Egypt. Scour of soil beneath foundations lead to excessive differential settlements, failure of main structural members and finally complete structural collapse. A three-dimensional nonlinear dynamic analysis of a multi-storey reinforced concrete framed structure with induced soil scour under its foundation is carried out using the Applied Element Method. The analysis of the structure is followed until its complete collapse. The numerical analysis is then used to propose a safe design against collapse. Three different alternatives proposed for preventing progressive collapse are independently investigated; floor beams, tie beams connecting footings, and diagonal bracings.

    Increasing the size of the floor beams was found not to have significant effect on mitigating progressive collapse, while the use of diagonal bracings in the ground floor or rigid tie beams connecting the structure’ footings was found to efficiently prevent progressive collapse. With diagonal bracings or rigid tie beams, the excessive differential settlements of the footings can be eliminated and the gravity loads can follow a safe alternative path preventing the structural collapse. The tie beam reinforcement was found to have a significant effect on the structural behavior during such an extreme loading case. Section analysis of the tie beam suggests that its ultimate strength should be based on rupture of main reinforcement, which is more economical and appropriate for such loading case.

    Keywords: Flood scouring, progressive collapse, Applied Element Method, tie beams

    Hamed, S. Computer-Aided Design of Framed Reinforced Concrete Structures Subjected to Flood Scouring. Journal of American Science 2011;7(10):191-200]. (ISSN: 1545-1003). http://www.americanscience.org.

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

    Abstract: This paper studies performing progressive collapse analysis for steel structures using the requirements of recent codes released by the United States Department of Defense and the General Services Administration. Based on review of the code requirements, nonlinear dynamic progressive collapse analysis results in a more uniform factor of safety than linear static analysis. The Applied Element Method in structural analysis is proposed as an efficient alternative for performing progressive collapse analysis. A case study is undertaken where the results of progressive collapse analysis using traditional finite-element-method simplifications are compared to 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 over-conservative when performing progressive collapse analysis. The results show that the use of the nonlinear dynamic Applied Element Method while taking into account the effect of secondary members such as slabs and secondary beams can lead to considerable savings in the total weight of the steel frame.


    Keywords: Progressive, disproportionate, collapse, steel, deck, applied element, AEM, Unified Facilities Criteria, alternate path, column removal.

    A. Khalil, Enhanced Modeling of Steel Structures for Progressive Collapse Analysis Using Applied Element Method, Journal of Performance of Constructed Facilities, ASCE, Available online 3 August 2011, ISSN: 0887-3828 (print) 1943-5509 (online).

     

  • Toward an Economic Design of Reinforced Concrete Structures Against Progressive Collapse

    Abstract: A three-dimensional discrete crack model based on the Applied Element Method is used to perform economic design for reinforced concrete structures against progressive collapse. The model adopts fully nonlinear path-dependent constitutive models for concrete and reinforcing bars. The model applies a dynamic solver in which post-failure behavior, element separation, falling and collision are predicted.  First, the model is used to study the behavior of multi-story reinforced concrete buildings designed in a traditional manner according to the ACI 318-08 and subjected to accidental removal of one or two central columns at the ground level. In an iterative way, the model is then used to investigate a safe design against progressive collapse for such extreme loading case. Based on the analytical results of the AEM, it can be concluded that the collapse of only one column would not lead to any progressive collapse of the studied reinforced concrete structure. However, the collapse of more than one column may lead to a progressive collapse of a considerable part of it. It is concluded also that theAEMcould be successfully used as an analytical tool to suggest economical designs that are safe against progressive collapse of reinforced concrete structures.

    Keywords: Applied Element Method; Numerical analysis; Progressive collapse; GSA; UFC; ASCE

    H.M. Salem, A.K. El-Fouly, H.S. Tagel-Din, Toward an economic design of reinforced concrete structures against progressive collapse, Engineering Structures, In Press, Corrected Proof, Available online 28 July 2011, ISSN 0141-0296, DOI: 10.1016/j.engstruct.2011.06.020. 
  • Effect of Retrofit Strategies on Mitigating Progressive Collapse of Steel Frame Structures

    Abstract: In this study, the effect of three retrofit strategies on enhancing the response of existing steel moment resisting frames designed for gravity loads is investigated using Alternate Path Methods (APM) recommended in the General Services Administration (GSA) and the Department of Defense (DoD) guidelines for resisting progressive collapse. The response is evaluated using 3-D nonlinear dynamic analysis. The studied models represent 6-bay by 3-bay 18-storey steel frames that are damaged by being subjected to six scenarios of sudden removal of one column in the ground floor. Four buildings with bay spans of 5.0 m, 6.0 m, 7.5 m, and 9.0 m were studied. The response of the damaged frames is evaluated when retrofitted using three approaches, namely, increasing the strength of the beams, increasing the stiffness of the beams, and increasing both strength and stiffness of the beams.

    The objective of this paper is to assess effectiveness of the studied retrofit strategies by evaluating the enhancement in three performance indicators which are chord rotation, tie forces, and displacement ductility demand for the beams of the studied building after being retrofitted.

    Keywords: Progressive collapse; Steel frame; Retrofit; Strengthening; Chord rotation; Tie forces; Displacement ductility demand

    Khaled Galal and Tamer El-Sawy: Effect of Retrofit Strategies on Mitigating Progressive Collapse of Steel Frame Structures, Journal of Constructional Steel Research, Volume 66, Issue 4, pp 520-531, April 2010.

  • Applied Element Method Analysis of Porous GFRP Barrier Subjected to Blast

    Abstract: Numerical analysis of highly dynamic phenomena represents a critical field of study and application for structural engineering as it addresses extreme loading conditions on buildings and the civil infrastructure. In fact, large deformations and material characteristics of elements and structures different from those exhibited under static loading conditions are important phenomena to be accounted for in numerical analysis. The present paper describes the results of detailed numerical analyses simulating blast tests conducted on a porous (i.e. discontinuous) glass fiber reinforced polymer (GFRP) barrier aimed at the conception, validation and deployment of a protection system for airport infrastructures against malicious disruptions. The numerical analyses herein presented were conducted employing the Applied Element Method (AEM). This method adopts a discrete crack approach that allows auto cracking, separation and collision of different elements in a dynamic scheme, where fully nonlinear path-dependant constitutive material models are adopted. A comparison with experimental results is presented and the prediction capabilities of the software are demonstrated.D. Asprone,

    A. Nanni, H. Salem, and H. Tagel-Din: Applied Element Method Analysis of Porous GFRP Barrier Subjected to Blast, Advances in Structural Engineering, Volume 13, Number 1, pp 152-170, February 2010.

  • Collapse Modeling of Model RC Structure using the Applied Element Method

    Abstract: In order to analyze collapse behavior of structure containing irregular and large displacement, many numerical analyses have been conducted. In this study, using a new method, Applied Element Method (AEM) for collapse analysis of structures, collapse behavior of model RC structures is simulated. From these simulations results, displacement of X-direction (or horizontal) and displacement of Y-direction (or vertical) is similar to that of model RC structures. It is confirmed that collapse behavior of structures using AEM is reliable accurately simulated with that of model RC structures.

    Hoon Park, Chul-Gi-Suk, Seung-Kon Kim: Collapse Modeling of Model RC Structure using the Applied Element Method, Journal of Korean Society for Rock Mechanics, TUNNEL & UNDERGROUND SPACE, Vol. 19, No. 1, 2009, pp. 43-51.

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