Maura Imbimbo

Simple Model for Bond Behavior of Masonry Elements Strengthened with FRP

The aim of the present paper is the development of a simple procedure for the analysis of the bond behavior of fiber-reinforced polymer (FRP) sheets or plates externally applied to masonry supports for the strengthening or repair of masonry constructions. The procedure allows evaluation of the bond strength and the fracture energy developed during the debonding process through simple formulas based on a few parameters, evaluated either by standard tests performed on the materials making up the support and the strengthening system or by theoretical considerations. A brief discussion on the main experimental evidence and the theoretical models provided by the literature is also reported in this paper. The comparison between the theoretical results obtained by applying the proposed procedure and the experimental data deduced from literature is carried out.

F.E. stress analysis of rubber bearings under axial loads

Abstract In this paper the influence of the shape factor on the stress distributions and stress concentrations of a laminated elastomeric bearing subjected to vertical loads is discussed. The investigation is performed by adopting the finite element approach. The numerical results are compared with an analytical approximate solution. The analyses show a beneficial effect of the shape factor; in particular the edge effects decrease by increasing the shape factor and, moreover, the agreement between the numerical solution and the analytical one improves.

Bond Behavior of Historical Clay Bricks Strengthened with Steel Reinforced Polymers (SRP)

In the strengthening interventions of past and historical masonry constructions, the non-standardized manufacture processes, the ageing and the damage of masonry units, could significantly affect the properties of the surfaces where strengthening materials are applied. This aspect requires particular care in evaluating the performance of externally bonded strengthening layers, especially with reference to the detachment mechanism. The bond response of old masonries could be very different from that occurring in new masonry units which are the ones generally considered in most of the bond tests available in technical literature. The aim of the present paper is the study of the bond behavior of historical clay bricks strengthened with steel reinforced polymers (SRP) materials. In particular, the results of an experimental study concerning new manufactured clay bricks and old bricks extracted from different historical masonry buildings are presented. The obtained results, particularly in terms of bond resistance, detachment mechanism and strain distributions, are discussed for the purpose of analyzing the peculiarities of the historical bricks in comparison with new manufactured ones. Some considerations on the efficacy of the theoretical formulations of the recent Italian code are also carried out.

Stability Aspects of Elastomeric Isolators

The theoretical analysis for the buckling of isolators is well known and has generally been verified by experimental work, but there are some aspects of the analysis that have not been addressed in detail. This paper will study two examples, first the effect of end plate rotation on the buckling load and, secondly, the buckling of an isolator that is made up of two bearings, one on the top of the others. The effect of end plate rotation on the buckling load arises in situations where the stiffness of the superstructure is not high enough to ensure that the isolator is constrained against rotation at the top; this is often the case when retrofitting existing structures. The influence of the flexibility of the superstructure on the horizontal stiffness of the isolator and the reduction of the critical load due to this flexibility is evaluated in the paper. The results show a significant reduction of the critical load. The second analysis presented in the paper models the buckling of a composite isolator that is made up of two bearings, one on top of the other. Two approaches for evaluating the critical load of this composite isolator are discussed, and an approximate method is developed that provides results close to the complete solution.

Identification of Linear Structural Systems With a Limited Set of Input-Output Measurements

In this paper, a methodology is presented for the identification of the complete mass, damping, and stiffness matrices of a dynamical system using a limited number of time histories of the input excitation and of the response output. Usually, in this type of inverse problems, the common assumption is that the excitation and the response are recorded at a sufficiently large number of locations so that the full-order mass, damping, and stiffness matrices can be estimated. However, in most applications, an incomplete set of recorded time histories is available and this impairs the possibility of a complete identification of a second-order model. In this proposed approach, all the complex eigenvectors are correctly identified at the instrumented locations (either at a sensor or at an actuator location). The remaining eigenvector components are instead obtained through a nonlinear least-squares optimization process that minimizes the output error between the measured and predicted responses at the instrumented locations. The effectiveness of this approach is shown through numerical examples and issues related to its robustness to noise polluted measurements and to uniqueness of the solution are addressed.

The role of the adhesive on the bond behavior of SRPs applied on masonry supports: experimental and numerical study

Steel Reinforced Polymers (SRP) have been recently introduced and adopted as strengthening systems for existing constructions. Although the interest for this kind of strengthening materials is increasing also for masonry structures, in particular for historic constructions, only few studies specifically pertained to masonry elements strengthened with SRPs are available in the literature. In this context, a twofold purpose is at the basis of the present paper. The first one consists of experimentally investigating the bond behavior of masonry elements strengthened with SRPs using different types of adhesives and strips density. The second purpose aims at developing simple formulations for evaluating the bond resistance of masonry elements strengthened with SRPs applied with different types of adhesive systems.

FRP-strengthening of masonry structures: Effect of debonding phenomenon

The present paper shows and discusses some aspects concerning the delamination phenomenon of Fibre Reinforced Plastic (FRP) materials fixed on masonry support. With this aim, in the first part of the paper the results of an experimental campaign conducted by the authors concerning the effect of the bond length on the delamination phenomenon of CFRP glued on clay bricks are discussed. Moreover, in order to underline further aspects concerning the decohesion mechanism of FRP-reinforcements, in the second part some numerical analyses are also presented.

Experimental Response of RC Beams Strengthened in Shear by FRP Sheets

The paper discusses the results of an experimental investigation carried out on reinforced concrete (RC) beams strengthened in shear by externally bonded fiber reinforced plastic (FRP) sheets. The study is devoted to analyze the role that the transverse steel reinforcement and the beam slenderness ratio could play on the resistant mechanism of RC beams strengthened in shear by FRP composites. The results are summarized and analyzed in detail in the paper in terms of shear capacity, cracking pattern and shear resisting contribution of FRP.

Identification of structural damage using dynamic input-output measurements

This paper presents a variety of methodologies that are used to detect the location and amount of structural damage using dynamic measurements of the input and of the structural response. One approach (and its variations) starts from an identified first order model of a structural system and obtain estimation of the structures mass, damping and stiffness matrices. For these approaches, both the full instrumentation option and the partial instrumentation option are presented. An alternative approach for the identification of the dynamic characteristics of the structure is based on Evolution Strategies. Once these dynamic characteristics have been determined, structural damage is assessed by comparing the undamaged and damaged estimation of such parameters. Both these methodologies are tested on simulated numerical results and their effectiveness in determining structural damage is evaluated.

Stability of Isolators at Large Horizontal Displacements

Elastomeric bearings used as seismic isolators are susceptible to a buckling type of instability similar to that of structural columns. The buckling load and buckling behaviour can be determined from an elastic analysis of the isolator modelled as a continuous composite column with bending and shear flexibility; this analysis cannot be used, however, to assess the post-buckling behaviour or the stability of the isolator at large horizontal displacements. By using a two-spring rigid link model that considers large angles without using linear approximations, it is possible to predict the post-buckling behaviour of an isolator. Using the simple closed form expression, this paper will model three aspects of post-buckled isolator behaviour: the dependence of horizontal stiffness on vertical load, the stability at large horizontal displacements, and the increase of horizontal displacement with respect to axial load and vertical displacement.