Barbara Ferracuti

Strengthening of Masonry Elements by FRP: Influence of Brick Mechanical and Microstructural Properties

In this paper, the effect of several brick and mortar mechanical and microstructural parameters on the maximum debonding force of the same glass fiber reinforced polymer (GFRP), applied on different bricks and on corresponding masonry panels, was investigated. GFRP sheets were bonded by epoxy resin to four different types of solid fired-clay brick and four types of masonry panels, manufactured using the same bricks and a natural hydraulic lime mortar. The reinforced specimens were subjected to bond tests to evaluate the maximum debonding force. Bricks and mortar were characterized in terms of compressive strength (in the case of bricks, along two different orthogonal directions), surface roughness and pore size distribution. Based on the results of the study, alongside brick mechanical properties in different directions, also brick microstructural parameters seem to play a very important role, which should be taken into account for fully explaining the experimental results.

Fuzzy sets based interpretation of the safety factor

Abstract Safety factor is a universally utilized concept in several branches of engineering. On one hand, most engineers, as it were, neglect uncertainty, but on the other hand, the allowable stress level was introduced long time ago as a ratio of the yield stress to the so-called safety factor to provide the region for the safe utilization of the structure. Thus the uncertainty is introduced into practice by the “back door”. This observation led to a considerable literature dedicated to the probabilistic interpretation of the safety factor. The present paper deals with the novel aspect of elucidation of the concept of safety factor through the theory of fuzzy sets, apparently for the first time in the literature. The aim of the paper is to present the safety factor that is uniformly employed by engineers, but in the new light. The safety factor in the fuzzy setting is introduced. The ideas are illustrated on two strength of material problems; simple examples are chosen so as to allow for clearer illustration of ideas.

Experimental Study on Masonry Panels Strengthened by GFRP: The Role of Inclination between Mortar Joints and GFRP Sheets

For the shear strengthening of masonry walls, different configurations for FRP sheets are currently used in real application, such as vertical, horizontal or diagonal strips. In the last configuration the FRP sheet is inclined with respect to the direction of mortar joints. In the experimental campaign presented in this paper, it is investigated whether the FRP-masonry bond could be affected by this inclination. In order to analyze this issue, three different typologies of masonry panels (with different textures) retrofitted by FRP sheets, inclined of 45 degrees with respect to the vertical axis of the specimen, are subjected to single-lap shear tests. Results of shear tests are presented in terms of maximum debonding forces, force-elongation curves, failure modes and strain profiles along the specimens. The use of Digital Image Correlation (DIC) technique allowed to obtain complete strain maps on the surface of the specimens tested, with the purpose of investigating possible variations in the strain field within the bonded area.

Inverse Analysis for the Calibration of FRP—Concrete Interface Law

The inverse analysis technique is used to derive a non linear mode II interface law for Fiber Reinforced Polymer (FRP) – concrete bonding starting from experimental data. The proposed interface law is based on a fractional formula and includes the non linear compliance contributions of adhesive and concrete cover at high shear stresses. It depends on three parameters (the maximum shear stress, the corresponding slip and an exponent), which are calibrated from experimental results on debonding tests. The values of maximum loads and strain profiles along the FRP plates for different bonding lengths are used. The parameter identification is performed by the inverse analysis using a Direct Search algorithm. Some considerations on the well-posedness of the inverse problem adopting different cost functions to minimize the error between experimental and numerical data are given. After the parameter identification, the numerical results obtained with the proposed interface law are in very good agreement with the experimental results.

A New Set-Up for FRP-Concrete Stable Delamination Test

Synopsis: Results of an experimental campaign on FRP – concrete delamination are presented. Two specimens have been tested by using a particular experimental set-up where a CFRP plate has been bonded to concrete and its back side fixed to an external restraining system. The adopted set-up allows a stable delamination process and transition between two limit states (perfect bonding and fully delaminated plate) to be observed. Both strain gages along the FRP plate and LVDT transducers have been used. Starting from experimental data, shear stress – slips data have been computed. A non linear interface law has been calibrated and compared with analogous results obtained by a more conventional experimental set-up. A numerical bond – slip model has been used, adopting the above mentioned law for the FRP – concrete interface to simulate experimental tests. Numerical results are found to be in good agreement with experimental results.

FRCM Strengthened Masonry Panels: The Role of Mechanical Anchorages and Symmetric Layouts

The use of fiber reinforced composite materials for the retrofitting of existing masonry buildings is investigated in this paper. Indeed, they represent a great alternative to traditional strengthening techniques for the improvement of the seismic performance of masonry walls. Focusing on the in-plane behavior of masonry, an experimental campaign is here presented with the objective of studying the efficiency of different strengthening solutions. Diagonal compression tests were conducted on single-leaf masonry panels reinforced with Fiber Reinforced Cementitious Matrix (FRCM) using different fibers typologies and layouts. Glass or carbon fiber grids embedded in a lime-based mortar matrix were applied on one or both sides of masonry panels, with or without mechanical anchorages. The comparison of the different strengthening techniques is analyzed in terms of failure mode, strength and ductility. The results are then discussed considering the provisions and design formula proposed for FRP strengthening by the Italian CNR Guidelines.

Post-Seismic Damage Assessment of a Historical Masonry Building: The Case Study of a School in Teramo

The historical masonry buildings are characterised by a great vulnerability regard the seismic action, as the recent events occurred in Central Italy have highlighted. During the seismic emergency the authors, in collaboration with the Civil Protection Department as part of the ReLUIS activities, have carried out usability inspections, analysing also the case study described in this paper. The structure, a school in Teramo, was already affected by previously seismic damages and it has been highly involved by the seismic events abovementioned. In this work the results of first inspection, reported in the AeDES form, and a more accurate visual inspection are presented in terms of detection of the crack patterns and evaluation of the seismic damages index. Moreover the vulnerability index has been calculated according to the GNDT 2° level method. The vulnerability index is finally used to calculate the damage index expected for the seismic intensity registered during the seismic event of October 30, 2016, and compared with the observed post-seismic damage level.

Seismic vulnerability assessment of a historical masonry building: Pandone Castle

The knowledge of a historical masonry building is a prerequisite both for the purposes of a reliable evaluation of the actual seismic safety and for the choice of an effective intervention for the preservation of the monumental building. It is therefore a need to refine the investigations and techniques of analysis by different degree of reliability, as well as in relation to their impact. Knowledge can be achieved with different levels of detail, depending on the accuracy of geometric survey operations, historical research, and experimental investigations. The aim of the study is the analysis of the seismic vulnerability of the historical building “Pandone Castle”. The knowledge procedure has led to the assessment of security level against seismic actions.