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  • 1. Alhasawi, Anas
    et al.
    Heng, Piseth
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges. Université Européenne de Bretagne, France.
    Hjiaj, Mohammed
    Guezouli, Samy
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Co-rotational planar beam element with generalized elasto-plastic hinges2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 151, p. 188-205Article in journal (Refereed)
    Abstract [en]

    Slender elements in framed structures may undergo large displacement and experience highly nonlinear behavior. This paper presents a two-node co-rotational flexible beam with generalized elasto-plastic hinges at the beam ends. A Condensation procedure is used to remove the internal degrees of freedom so that the formulation is easily incorporated with the standard co-rotational approach. A family of asymmetric and convex yield surfaces of super-elliptic shape is considered for the plastic behavior of the hinges. By varying the roundness factor, an infinite number of yield surfaces are obtained making it possible to select the yield function that best fit experimental data of any type of cross-section and material. The nonlinear response of bolted connections subjected to both bending and axial forces are conveniently modeled with such a yield surface. Discrete constitutive equations for the hinge plastic deformations are derived using the implicit scheme for both smooth and non-smooth cases. Numerical examples demonstrate the accuracy of the model in predicting the large displacement inelastic response of framed structures. Effect of the roundness factor on the ultimate load strongly depends on the structure typology. It was observed that cyclic loading produces pinching effect, cyclic softening and ductile behavior. Those effects are more pronounced with anisotropic yield criteria.

  • 2.
    Heng, Piseth
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Simplified mechanical models for the nonlinear dynamic analysis of elasto-plastic steel structures impacted by a rigid body2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Buildings subjected to impact and explosion are usually studied using large scale and highly nonlinear finite element model which are time-consuming. The first part of the thesis deals with the development of simple and accurate models for evaluating the nonlinear inelastic behaviour of steel frame structures subjected to impact. The research work in this part has produced four simplified models. The first model concerns with a 4DOF model that reproduces the behaviour of the impacted column. The restraining effect from the rest of the structure is modelled by an elastic spring, a head mass and a static load applied at the top of the column. In the second model, the impacted column is then further simplified using a SDOF model. The behaviour of the SDOF model is governed by an analytical force-displacement expressions of the column loaded by a located force. The maximum displacement of the impacted column can also be determined explicitly by adopting an energy-equivalent approach. Afterwards, in an effort to model the whole structure, two finite element models are developed. For these models, a co-rotational super-element that consists of a beam element and two generalized elasto-plastic hinges is obtained by performing a static condensation. An elastic flexible beam element is used in the first finite element model, whereas a rigid beam element is considered in the second one.

    In these models, inelasticity is concentrated at generalized elasto-plastic hinges which are modelled by combined axial-rotational springs. The behaviour of the hinges is uncoupled in the elastic range while an axial-bending interaction is considered in the plastic range making it possible to reproduce a wide range of cross-sections and joints. In addition, unilateral contact between rigid point masses is considered and the energy loss during impact is accounted by means of a restitution coefficient following Newton’s impact law. Energy-momentum scheme is used to solve the equations of motion produced by these models.

    The second part of the thesis concerns with the performance of the connectors in composite steel-concrete slabs under explosion. The purpose is to determine residual capacities of the shear connectors after being damaged by explosion using large-scale pull-out and push-out experimental tests and finite element simulations.

  • 3.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Alhasawi, Anas
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Hjiaj, Mohammed
    Co-rotating rigid beam with generalized plastic hinges for the nonlinear dynamic analysis of planar framed structures subjected to impact loading2017In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925Article in journal (Refereed)
  • 4.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France.
    Alhasawi, Anas
    Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France..
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Hjiaj, Mohammed
    Univ Europeenne Bretagne, INSA Rennes, LGCGM Struct Engn Res Grp, 20 Ave Buttes de Coesmes,CS 70839, F-35708 Rennes 7, France..
    Co-rotating rigid beam with generalized plastic hinges for the nonlinear dynamic analysis of planar framed structures subjected to impact loading2019In: Finite elements in analysis and design (Print), ISSN 0168-874X, E-ISSN 1872-6925, Vol. 157, p. 38-49Article in journal (Refereed)
    Abstract [en]

    The purpose of this paper is to model the nonlinear dynamical response of steel frame structures subjected to impact loading. A 2D co-rotational rigid beam element with generalized elasto-plastic hinges is presented. The main idea is to integrate the concept of the generalized elasto-plastic hinge into the standard co-rotational framework by performing a static condensation procedure in order to remove extra internal nodes and their corresponding degrees of freedom. In addition, impact loading is applied through a contact model that is described in the rigorous framework of non-smooth dynamics. In this framework, equations of motion are derived using a set of differential measures and convex analysis tools, whereas Newton's impact law is imposed by means of a restitution coefficient in order to accommodate energy losses. An energy and momentum conserving scheme is adopted to solve the dynamical equations. The main interest of the current model is the ability to evaluate the geometrically nonlinear inelastic behaviour of steel structures with semi-rigid connections subjected to impact in a simple and efficient way, using only a few number of elements. The accuracy of the proposed formulation is assessed in three numerical applications.

  • 5.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Université Européenne de Bretagne, France.
    Bud, M.
    Somja, H.
    Hjiaj, M.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Building Technology and Design.
    Residual stiffness and strength of shear connectors in steel-concrete composite beams after being subjected to a pull-out pre-damaging: An experimental investigation2017In: Structures, ISSN 2352-0124, Vol. 11, p. 189-205Article in journal (Refereed)
    Abstract [en]

    Horizontal stability of the medium rise steel frame structures is usually ensured by vertical bracings and diaphragm action of composite floors. Load transfer within the composite floor system is made through shear connectors, e.g. headed studs. In an event of explosion, such connectors must reserve sufficient residual stiffness and strength in order to avoid a sudden or delayed collapse of the building. These remaining capacities have not been experimentally studied yet in the literature. This paper presents large scale horizontal push out tests to determine the residual stiffness of the shear connectors after being initially damaged by explosion. The initial damaging is reproduced by a pull-out test using a quasi-static loading. Two types of numerical simulation have also been developed using ABAQUS/CAE software to provide a better understanding of the experimental results.

  • 6.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering. Univ Europeenne Bretagne, France.
    Hjiaj, M.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering.
    Limam, A.
    A simplified model for nonlinear dynamic analysis of steel column subjected to impact2016In: International Journal of Non-Linear Mechanics, ISSN 0020-7462, E-ISSN 1878-5638, Vol. 86, p. 37-54Article in journal (Refereed)
    Abstract [en]

    This paper presents a new simplified model of the nonlinear dynamic behavior of a steel column subjected to impact loading. In this model, the impacted column, which undergoes large displacement, consists of two rigid bars connected by generalized elastic–plastic hinges where the deformation of the entire steel column as well as the connections is concentrated. The effect of the rest of the structure on the column is modeled by an elastic spring and a point masse both attached to the top end of the column which is also loaded by a compressive force. The plastification of the hinges follows the normality rule with a yield surface that accounts for the interaction between M and N. The latter is described by a super-elliptic yield surface that allows ones to consider a wide range of convex yield criterion by simply varying the roundness factor that affects the shape of the limit surface. By including these features, the model captures both geometry and material nonlinearities. Both the flow rule and the equations of motion are integrated using the midpoint scheme that conserves energy. The non-smooth nature of impact is considered by writing the equations of motion of colliding masses using differential measures. Contact conditions are written in terms of velocity and combined with Newton's law to provide the constitutive law describing interactions between masses during impact. Numerical applications show that the model is able to capture the behavior of a column subjected to impact.

  • 7.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Hjiaj, Mohammed
    INSA de Rennes, France.
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    A simplified model of a steel column subjected to impact2016Conference paper (Refereed)
  • 8.
    Heng, Piseth
    et al.
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Hjiaj, Mohammed
    Battini, Jean-Marc
    KTH, School of Architecture and the Built Environment (ABE), Civil and Architectural Engineering, Structural Engineering and Bridges.
    Limam, Ali
    An enhanced SDOF model to predit the behaviour of a steel column impacted by a rigid body2017In: Engineering structures, ISSN 0141-0296, E-ISSN 1873-7323, Vol. 152, p. 771-789Article in journal (Refereed)
    Abstract [en]

    The transient dynamic response of a steel beam-column subjected to impact loading is a complex phenomenon involving large localized plastic deformations and non-smooth contact interactions. Exposed to high intensity of the contact force generated from impact, the beam-column may undergo large displacement and inelastic deformation. Previous research has shown that a calibrated elasto-plastic single degree of freedom system is able to reproduce both the displacement and the force time-history of a steel beam subjected to non-impulsive loading or low-velocity impact. In these models, the static force-displacement curve is derived from either experiments or detailed 3D nonlinear analysis. Tri-linear resistance function has been extensively used to reproduce the different stages of the response including catenary effects. A rigorous treatment of such a complex problem calls for the use of non-smooth analysis tools to handle the impulsive nature of the impact force, the unilateral constraint, the impenetrability condition and the discontinuity of the velocity in a rigorous manner. In this paper, we present a non-smooth elasto-plastic single degree of freedom model under impact loading that permits the use of arbitrary resistance function. Adopting the non-smooth framework offers tools such as differential measures and convex analysis concepts to deal with unilateral contact incorporating Newton’s impact law. The mid-point scheme is adopted to avoid numerical unrealistic energy decay or blowup. Furthermore, the non-penetration condition is numerically satisfied by imposing the constraint at only the velocity level to guarantee energy-momentum conservation [1]. The explicit expression of resistance functions of the beam that are used in the SDOF model are obtained from a simplified nonlinear static analysis of two beam-column models. In the analysis, a linear relation between normal force and bending moment is assumed for the plastification of the hinges. Two proposals to simplify the explicit expressions of the model’s response behavior are given. Performing an energy-based analysis, we predict maximum displacement that is needed to absorb the kinetic energy arising from the impact for different coefficient of restitution. The numerical examples underline the validity of the model by showing good agreement with the predictions of reference models.

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