A PARAMETRIC SURVEY OF THE INFLUENCE OF THE SEMI-RIGID CONNECTIONS ON THE SHAKEDOWN OF ELASTO-PLASTIC FRAMES

In the past it was generally assumed that the connection of the beams and columns of the steel-framed multistorey structures are either rigid or pinned. In the reality, however, they are semi-rigid. This circumstance influences significantly the behaviour of the entire structure, therefore, it has to be taken into consideration in the analysis and design. In this paper a parametric study is presented to analyse the influence of the semi-rigid connections on the shakedown of elasto-plastic steel framed structures under multi-parameter static loading. To control the plastic behaviour of the structure bound on the complementary strain energy of the residual forces is also applied. The semi-rigid behaviour is modelled by appropriate internal springs at the beam column-connections. The formulation of the problem yields to nonlinear mathematical programming which is solved by the use of an iterative procedure. The parametric study is illustrated by the solution of an example

Nonlinear Time-Dependent Behavior of Composite Steel-Concrete Beams

International audienceThis paper presents a mixed finite element (FE) model for the nonlinear time-dependent analysis of composite beams with partial shear connection. The key idea is to consider, as a first approach, a viscoelastic/plastic model for the concrete slab in order to simulate the interaction between the time effects of concrete, such as creep and shrinkage, and the concrete cracking. Creep is taken into account via linear aging viscoelasticity, while cracking is modeled using an elastoplastic model with softening. A nonlinear isotropic/kinematic hardening model is adopted for steel behavior and an appropriate nonlinear constitutive relationship is utilized for the shear stud. A consistent time integration is performed by adopting the Euler backward scheme. Finally, comparisons between the numerical results and experimental data available in the literature are undertaken to validate the accuracy of the model. It is shown that the interaction between cracking and time effects (creep and shrinkage) significantly increases the deflection

Existence of renormalized solutions for some degenerate and non-coercive elliptic equations

summary:This paper is devoted to the study of some nonlinear degenerated elliptic equations, whose prototype is given by \begin{aligned}t 2&-{\rm div}( b(|u|)|\nabla u|^{p-2}\nabla u) + d(|u|)|\nabla u|^{p} = f - {\rm div}(c(x)|u|^{\alpha }) &\quad &\mbox {in}\ \Omega ,\\ & u = 0 &\quad &\mbox {on}\ \partial \Omega , \end{aligned}t where $\Omega$ is a bounded open set of $\mathbb {R}^N$ ($N\geq 2$) with $1<p<N$ and $f \in L^{1}(\Omega ),$ under some growth conditions on the function $b(\cdot )$ and $d(\cdot ),$ where $c(\cdot )$ is assumed to be in $L^{\frac {N}{(p-1)}}(\Omega ).$ We show the existence of renormalized solutions for this non-coercive elliptic equation, also, some regularity results will be concluded

Experimental study on in-plane capacities of composite steel-concrete floor

[EN] In steel frame structures, composite floor is an important element that plays a significant role in contributing to lateral stability. Its working role in the in-plane action is to transfer lateral loads, such as wind loads and seismic loads, to vertical load-resisting members. Such load transferring process depends on the in-plane capacities of the floor, which can be reduced after being subjected to explosion. However, the remaining capacities have not been previously studied yet in the literature. This paper presents an experimental investigation on the initial and residual in-plane capacities of the composite steel-concrete floor after being subjected to explosion, which was made within the RFCS research project BASIS:“Blast Action on Structures In Steel”. Large-scale experimental tests on four composite floor specimens, consisting of a reinforced concrete panel casted on a profile steel sheet Comflor, are performed to determine the in-plane capacities. The initial damaging of the composite floor caused by the explosion is reproduced by a flexural test using a quasi-static loading. In the in-plane shear tests, special connections between the rigid frames of the shear rig and the embedded bolts in the concrete are used to ensure a good transferring of the applied load. The results from this experimental study are the first insights on the behavior of the composite floor with and without initial pre-damaging. They can also be useful for a preliminary recommendation to estimate residual in-plane capacities (stiffness and resistance) of the composite floor after being subjected explosion.Heng, P.; Somja, H.; Hjiaj, M. (2018). Experimental study on in-plane capacities of composite steel-concrete floor. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 881-887. https://doi.org/10.4995/ASCCS2018.2018.6987OCS88188

Effect of the steel material variability on the seismic capacity design of steel-concrete composite structures : a parametric study

International audienceModern seismic codes recommend the design of ductile structures able to absorb seismic energy through high plastic deformation. Since seismic ductile design relies on an accurate control of plastic hinges formation, which mainly depends on the distribution of plastic resistances of structural elements, efficiency of the design method strongly depends on the actual mechanical properties of materials. The objective of the present contribution is therefore to assess the impact of material variability on the performance of capacity-designed steel-concrete composite moment resisting frames

The SMARTCOCO design guide for hybrid concrete-steel structures

[EN] Standard buildings in steel and in reinforced concrete are constructed by two different industrial sectors with little interaction. Even steel-concrete composite buildings remain designed as steel structures, with a limited benefit of the presence of concrete slabs. For some years however, a more integrated design between both materials is used, merely in high rise and heavy loaded structures. This new trend is not supported by actual standards that give little guidance for the specific arrangements that come from this new practice. The RFCS SMARTCOCO research project is intended to fill these gaps in knowledge and provide design guidance for some composite elements covered neither by Eurocode 2 nor by Eurocode 4 : composite columns or walls reinforced by several fully encased steel sections, reinforced concrete columns reinforced by one steel section over the height of one storey and concrete flat slabs or beams connected to columns or walls by means of steel shear keys. Gaps in knowledge are mostly related to force transmission between concrete and embedded steel profiles. A generic design approach has been developed and then used to design test specimens. The results have been used to calibrate the design proposals. The output is a design guide which complements Eurocode 2 and 4.This paper was developed in the frame of the SMARTCOCO project funded by RFCS, the Research Fund for Coal and Steel of the European Commission, Research grant agreement RFSR-CT-2012-00031 Smartcoco. The companies BESIX and ArcelorMittal are also acknowledged for their involvement in the project.Somja, H.; Hjiaj, M.; Nguyen, QH.; Plumier, A.; Degee, H. (2018). The SMARTCOCO design guide for hybrid concrete-steel structures. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 749-755. https://doi.org/10.4995/ASCCS2018.2018.7023OCS74975

Geometrically exact beam dynamics, with and without rotational degree of freedom

Abstract Non-linear rod dynamics is the focus of research in many engineering areas such as structural, aerospace and petroleum engineering as well as multibody dynamics. Also in non-classical areas such as biomechanics, micro-and nano-mechanics, geometrically exact formulations for rod dynamics are of importance. Rod formulations can be distinguished in regard to the basic kinematic assumption underlying the formulation. In the so-called Timoshenko-type beams, shear effects are taken into account and so rotational degrees of freedom describing the rotation of the cross section are considered. These are highly non-linear in nature. In contrast the Euler-Bernoulli assumption of zero shear deformation can be carried over into the non-linear regime resulting in displacementonly formulation but with highly non-linear expressions for the strain tensor incorporating higher gradients. In either formulation, the integration of the time dependent equations is challenging. It has been recognised that energy conservation is key for stable integration in long term dynamics. The so-called energy-momentum methods is a class of integrators, which, by design, conserve the momentum, angular momentum and the energy in the discrete case, if the same conservation properties are present in the continuous case. While for the Timoshenko beam some progress has been made and specific energy-momentum methods are known in the literature, the same is not true far the higher-gradient beam formulation of the Bernoulli beam. In this paper, we are going to develop a unified formulation of an energy-momentum integration scheme for both geometrically exact Bernoulli and Timoshenko beams. We will show that the stable integration in either case is achievable with excellent results. Further important novel aspect of the models are the full incorporation of the rotational inertia. A range of applications from structural dynamics to flexible multibody dynamics will show the excellent performance of the new energy-momentum integration scheme

Comportement hystérétique du frottement anisotrope

Ce papier présente des simulations numériques de problèmes de contact 3D avec une loi de frottement orthotrope et une loi de glissement non associée. L'algorithme de résolution est basé sur la méthode du bi-potentiel appliquée à un système d'équations non linéaires et non différentiables. Une attention particulière est portée aux chargements cycliques car le taux d'usure est fortement couplé à la dissipation par frottement. Cette première étude semble indiquer une grande influence de l'anisotropie du frottement sur l'usure des pièces

Identification d'un modèle de charge pour les activités rythmiques de groupe sur la base de mesures en accélération réalisées sur un plancher de bâtiment

peer reviewedThe floors of modern buildings are prone to excessive vibrations induced by human actions, especially when a group of people perform rhythmic activities in a coordinated manner. A reliable model for this load case, taking into account the experimentally observed group effect, is thus essential for the serviceability assessment of such structures. In this paper, a frequency-domain load model for either a single person or multiple individuals was established for two rhythmic activities. The model parameters were determined by an indirect identification method from acceleration responses. An extensive experimental test campaign was conducted on a steel–concrete composite floor in order to provide input data for identification, including experimental modal analysis and human-induced vibration tests for up to 32 individuals. The load parameters were first determined for the single-person load model. Root Mean Square (RMS) forces were then calculated from the identified load models, and corresponding coordination factors as a function of crowd size are suggested. A decreasing exponential was obtained for up to 8 persons for skipping and 12 persons for jumping, followed by a constant plateau for larger groups. The proposed models involve a global coordination factor to be used in conjunction with the identified model corresponding to skipping and jumping activities. A comparison of the proposed model and three existing coordination factor models against experimentally identified forces was performed. The comparison revealed the accuracy of the suggested models with respect to experimentally identified forces, whereas differences to existing factors were found especially for jumping

Influence of variability of material mechanical properties on seismic performance of steel and steel-concrete composite structures

Modern standards for constructions in seismic zones allow the construction of buildings able to dissipate the energy of the seismic input through an appropriate location of cyclic plastic deformations involving the largest possible number of structural elements, forming thus a global collapse mechanisms without failure and instability phenomena both at local and global level. The key instrument for this purpose is the capacity design approach, which requires an appropriate selection of the design forces and an accurate definition of structural details within the plastic hinges zones, prescribing at the same time the oversizing of non-dissipative elements that shall remain in the elastic field during the earthquake. However, the localization of plastic hinges and the development of the global collapse mechanism is strongly influenced by the mechanical properties of materials, which are characterized by an inherent randomness. This variability can alter the final structural behaviour not matching the expected performance. In the present paper, the influence of the variability of material mechanical properties on the structural behaviour of steel and steel/concrete composite buildings is analyzed, evaluating the efficiency of the capacity design approach as proposed by Eurocode 8 and the possibility of introducing an upper limitation to the nominal yielding strength adopted in the design