Georgios A. Drosopoulos

Modelling and strength evaluation of masonry bridges using terrestrial photogrammetry and finite elements

Several numerical models are presented in this article, for the study of the ultimate behaviour of a real stone arch bridge. For the exact representation of the geometry an integral and comprehensive survey involving Terrestrial Photogrammetry and Ground Penetrating Radar is in order to provide a realistic 3D geometric model for the subsequent mechanical analysis of the bridge. The accuracy of the photogrammetric method permitted detecting cracks in different areas and the GPR completed the geometric model with information of hidden parts such as backfill, arch ring thickness, etc. Finite element analysis models, incorporating damage, elastoplasticity and contact, are then developed. Comparison between these models is considered in a single arch of the structure. The classical four hinges mechanism appears in the arch. A model of the whole structure, where the arch and the fill are taken into account, is finally developed. Results show how damage is developed in the body of the arch, for loadings that include forces, or vertical and transverse displacements in the supports.

Unilateral Contact and Damage Analysis in Masonry Arches

Two unilateral models, the first with contact interfaces and the second with continuous damage material (Fremond’s model), are applied on the nonlinear analysis and collapse of masonry arches. The results are compared with the predictions of the classical Heyman theory.

Failure Behavior of a Top and Seat Angle Bolted Steel Connection with Double Web Angles

AbstractThe article presents a three-dimensional nonlinear finite-element model that was developed for the study of a top and seat angle bolted steel connection with double web angles. Unilateral contact and friction laws were used to simulate the interaction among the connected parts. Large displacements as well as the von Mises failure criterion were also considered for the steel parts and bolts. Numerical results were compared with the experimental research conducted on the same steel joint. This study finds yielding of the top angle as well as shear failure of the bolts connecting the beam bottom flange with the seat angle to be very important for the overall response of the structure. For this reason, a parametric investigation of the influence of the top angle on the behavior of the structure and the study of the prying forces developed at the top angle were conducted.

Investigation of the structural behaviour of a masonry castle by considering the actual damage

The structural behaviour of Frangokastello, a mediaeval masonry castle located in Crete, Greece is studied. The structure presents several damaged areas, consisting of cracks and local failure of masonry. The finite element method (FEM) is used to investigate how the existing failure of the structure affects its mechanical response. First, an eigenvalue analysis of the structure without the cracks and a dynamic modal analysis are done. Then, a non-linear constitutive model using a smear crack law is used to investigate the limit state of the structure under static and dynamic loading. Finally, unilateral contact interfaces are introduced, to simulate the cracks which appear in the structure. This model, which consists of several non-linearities, is tested under non-linear time history analysis. Comparison of the results demonstrates how the pathology of the structure affects its response. This procedure is necessary towards taking actions for the reinforcement of the structure.

Mechanical Behaviour of Auxetic Microstructures Using Contact Mechanics and Elastoplasticity

The design of novel mechanical microstructures having auxetic behaviour is proposed in this paper using techniques of topology optimization for compliant mechanisms. The resulting microstructure can be modified in order to cover additional needs, not included in the topology optimization formulation. Classical structural optimization, contact mechanics, homogenization and nonlinear finite element analysis are used for this step. Thus, the modified microstructure or composite is studied with numerical homogenization in order to verify that it still has the wished auxetic behaviour. Finally, nonlinear finite element analysis shows how the auxetic behaviour is influenced by unilateral contact between the constituent materials, large displacements and elastoplasticity.

OPTIMAL CONTROL TUNNING IN SMART STRUCTURES WITH DELAMINATIONS

Abstract. An efficient strategy for calculation of delaminations in composite beams and intelligent structures is used in order to quantify structural uncertainties within a finite element model of a piezocomposite (multilayered plate theory). Furthermore the dynamical system is connected with robust and neurofuzzy control. The problem of positioning of actuators and sensors has been investigated. Model based simulations of increasing complexity illustrate some of the attractive features of the strategy in terms of accuracy as well as computational cost. This shows the possibility of using such strategies for the development of smart structural and systems.

Influence of the frp strengthening, the shape and the movement of abutments on the collapse of arch stone bridges

The ultimate failure load of stone arch bridges is calculated in this paper by using finite element analysis. Contact interfaces simulating potential cracks are considered. Opening or sliding of a number of the potential interfaces indicates crack initiation [1]. Fiber Reinforced Plastic (FRP) strips are then applied to the stone bridge and the ultimate load is recalculated. The failure modes of the reinforced arch are compared well with the ones received from relevant experiments published in the literature. The analysis of the unreinforced arch shows that, under the most critical quarter span loading, a four - hinges collapse mechanism arises. The occurrence of this type of collapse is indicated in the classical work of Heyman [2] and has been observed in experiments. Three types of FRP reinforcement are applied in the arch. In particular, FRP is attached to the whole extrados, to the whole intrados and both to the extrados and the intrados of the arch. A cap model is used in order to model the failure of the masonry due to compression, while a v. Mises yield criterion is used for the FRP yielding. The possible failure modes of the reinforced structure are sliding of the masonry, crushing, debonding of the reinforcement and FRP rupture. Identical failure modes arise from the computer simulation and from experiments on reinforced arches published in the literature. A parametric investigation of the influence of the geometry of the unreinforced stone arch on the mechanical behavior of the structure is briefly described. Finally the effect of support settlement (vertical or horizontal movement) on the limit behavior is investigated. Common remarks with Heyman’s work arise. Further results and more details on the theory and the algorithms are given in the PhD Thesis of the first author [3].