Andrea Vignoli

Strengthening techniques tested on masonry structures struck by the Umbria-Marche earthquake of 1997-1998

The results of experiments carried out on structures damaged in the Umbria–Marche earthquake of 1997–1998 are presented. These tests were carried out in situ on masonry panels of various dimensions, which had been strengthened with either traditional or innovative materials and techniques. Concerning traditional methods, panels injected with new limed-based mixes were tested. Other tests were realized by gluing to the wallettes sheets of monodirectional carbon fiber (CFRP) or fiber glass (GFRP) with epoxy resins. In both cases the purpose of the tests was to analyze the effectiveness of the intervention, above all as a technique of seismic-upgrading against in-plane mechanisms of collapse. The results show a significant increase in strength. The experiments carried out allowed to obtain interesting indications for their practical utilization of the studied technique. The injection technique is substantially more efficient when used as a method of repair damaged panels, confirming that a preliminary evaluation of dimension and distribution of voids is necessary before adopting this technique. The experimental work showed that the use of composite materials on double-leaf roughly cut stone masonry is more effective when conducted with other stabilization schemes. The failure of the double leaf roughly cut stone panels strengthened with composite materials resulted from the separation of the two masonry leaves. In both cases the strengthening showed remarkable benefits in terms of increase in strength, providing the masonry with greater shear strength. The increase in stiffness following the intervention, as well as its effect, was also analyzed.

Experimental study on the determination of strength of masonry walls

The results of a research project carried out on masonry panels obtained from structures struck by the Umbria-Marchigiano earthquake of 1997–1998 are presented. The project consists of two parts: tests were performed in the laboratory, and in situ in order to determine the correct parameters describing masonry behavior. With regard to the laboratory tests, several compression tests were performed on cylindrical stone samples. Stone samples were obtained from the panels on which in situ tests had been previously carried out. Depending on the three types of in situ tests carried out (compression test, diagonal compression test, shear–compression test), different dimensions of panels were used using an appropriate cutting technique in order to leave the panels undisturbed. The shear strength and the Young and shear elastic modulus were measured. These results were compared with the values suggested by different standards. The experimental research allowed to characterize the mechanical properties of some typical masonry walls in old buildings of Umbria. These results are reported, together with an analysis of the masonry textures and sections.

Seismic Behavior of Short Coupling Beams with Different Reinforcement Layouts

This paper presents an experimental investigation on the seismic behavior of reinforced concrete coupling beams. The reinforcement layout and the loading history were the main variables of the tests. Fifteen short coupling beams with four different reinforcement arrangements were tested. They were subjected to monotonic and cyclic loading by a suitable experimental setup. All specimens were characterized by a shear span-depth ratio of 0.75. The reinforcement layouts consisted of a classical scheme, diagonal scheme without confining ties, diagonal scheme with confining ties, and inclined bars to form a rhombic configuration. Concrete compressive strengths of the specimens varied from 40 MPa to 54 MPa. Test results showed that the beams with diagonal or rhombic reinforcement layouts behaved better than beams with longitudinal arrangement of the steel bars. These results were produced by the different resisting truss mechanisms that were developed in the coupling beams after the first cracking. The differences in energy dissipation were negligible between the diagonal and rhombic layouts. The rhombic arrangement, however, was more advantageous in terms of rotational ductility capacity and decay in strength and stiffness of the beams. Moreover, cyclic tests demonstrated that the behavior of the rhombic layout was less affected by the different loading histories.

Assessment of seismic resistance of a basilica-type church under earthquake loading: Modelling and analysis

In this paper a finite element methodology for the static and dynamic non-linear analysis of historical masonry structures is described and applied to a case study. A basilica-type masonry church is analysed in order to assess its structural behaviour and its seismic vulnerability with respect to the actual state of conservation. Moreover the actual efficiency of current techniques for repairing and strengthening are analyzed in order to evaluated their benefits. A quasi-static approach (the seismic coefficient method) for the evaluation of the seismic loads have been used (as indeed common in many analyses of the seismic behaviour of masonry structures). This paper addresses the concern of seismic analysis and vulnerability of a basilica-type church with a specific case study: the Farneta abbey. The comparison demand vs. capacity confirms the susceptibility of this type of buildings to extensive damage and possibly to collapse, as frequently observed. The analysis of repairing and strengthening techniques show the effectiveness of the usual structural reinforcement in term of increased seismic capacity. It is believed that the conclusions obtained with respect to the seismic assessment of masonry church can be extrapolated for the wide variety of historical basilica-type church.

A numerical study on seismic risk assessment of historic masonry towers: a case study in San Gimignano

After a brief introduction on the research project RiSEM (Seismic Risk of Monumental Buildings), the paper discusses on the seismic assessment of historic masonry towers according to the Italian “Guidelines for the assessment and mitigation of the seismic risk of the cultural heritage” that identifies an analysis methodology based on three different levels of evaluation, according to an increased knowledge of the structure. The RiSEM project aimed at developing and testing innovative and expeditious methodologies (i.e. either without or with a minimal direct contact with the masonry building) to evaluate all the main structural features of the monumental buildings required for the assessment of their seismic safety. As a relevant case study the “Town of Fine Towers”, San Gimignano (Italy), listed under the UNESCO World Cultural Heritage Sites, was selected. The paper summarizes the analyses performed on one of the San Gimignano towers: the Coppi-Campatelli one. The seismic vulnerability of the tower was evaluated with reference to the above guidelines, and the paper reports and critically compares the results obtained for the three levels of evaluation there defined: LV1 (analysis at territorial level), LV2 (local analysis) and LV3 (global analysis).

Strength and Ductility of HSC and SCC Slender Columns Subjected to Short-Term Eccentric Load

Although several methods to predict the ultimate strength of slender columns under eccentric loads are available, the reliability of these approaches has been extensively investigated only for columns made of conventional concrete. This paper seeks to expand available experimental data for slender columns of high strength concrete (HSC) and self-consolidating concrete (SCC). Tests were conducted on 60 eccentrically-loaded slender columns constructed of HSC, SCC, and traditional vibrated concrete. All columns have cross sections of 100 x 100 mm (3.94 x 3.94 in.) and lengths of 2000 mm (78.8 in.). The main variables considered in the tests were the concrete strength, the longitudinal steel reinforcement ratio, and the load eccentricity. Attention is focused on the overall performance of columns: type of failure, cracking pattern, peak strength, and ductility. Findings from the tests carried out with small eccentricity indicate that the ultimate normalized strengths of SCC slender columns are lower than the strengths obtained for the traditional vibrated concrete columns. The tests carried out with medium and high eccentricities showed comparable strengths. The tests on SCC columns made of normal-strength concrete showed very soft and ductile failures. In these columns, cracking patterns are located along the whole length of the specimens with a high number of cracks. More concentrated damage was observed in the medium-strength concrete and HSC columns. The ductility of slender columns was higher for the SCC columns made of normal-strength concrete. For medium-strength concrete and HSC, no notable differences were observed between SCC and vibrated columns.

In Situ Shear and Compression Tests in Ancient Stone Masonry Walls of Tuscany, Italy

The present paper reports methods and results of an extensive experimental project performed to assess the mechanical characteristics of ancient stone masonry walls of Tuscany (Italy). Some relevant considerations concerning the determination of common design shear strength parameters via experimental test results are also presented. Results from 22 in situ tests performed on nine large-scale stone masonry panels are reported. Test panels were selected as part of shear walls in six different old masonry buildings in the northern part of Tuscany so as to represent a reliable sample of the most common masonry types in this region. In situ tests were carried out according to experimental schemes for vertical compression, shear compression, and diagonal compression. After the first test, several panels were repaired and reinforced by means of cement mortar injections (full cement grouting) or reinforced concrete (RC) jackets, and then tested again to determine the effectiveness of the intervention. Particular attention was then devoted to evaluate the referential shear strength τk of these masonry assemblages in the original state. To this purpose, a fitting process for experimental data was used, adopting two different schemes for interpretation of the shear strength of masonry (the Coulomb and the Tumsek-Cacovic equations). The results from this work have shown that the Turnsek-Cacovic equation gives a better fit to experimental data than the Coulomb equation, especially for medium- and poor-quality masonry walls. Finally, conclusions are presented noting the difference between shear strength values calculated from fitting the data from test results and the values suggested by European and Italian standards.

Seismic Response Of Masonry Plane Walls: A Numerical Study On Spandrel Strength

The paper reports the results of a numerical investigation on masonry walls subjected to in‐plane seismic loads. This research aims to verify the formulae of shear and flexural strength of masonry spandrels which are given in the recent Italian Standards [1]. Seismic pushover analyses have been carried out using finite element models of unreinforced walls and strengthened walls introducing reinforced concrete (RC) beams at the floor levels. Two typologies of walls have been considered distinguished for the height to length ratio h/l of the spandrels: a) short beams (h/l = 1.33) and b) slender beams (h/l = 0.5). Results obtained for the unreinforced and the strengthened walls are compared with equations for shear and flexural strength provided in Standards [1]. The numerical analyses show that the reliability of these equations is at least questionable especially for the prediction of the flexural strength. In the cases in which the axial force has not been determined by the structural analysis, Standards ...

Finite Element Modelling for Seismic Assessment of Historic Masonry Buildings

The chapter discusses on the use of the finite element modelling technique for the seismic assessment of historic masonry buildings, outlining that advanced numerical analyses can provide significant information to understand their actual structural behaviour. A finite element methodology for the static and dynamic nonlinear analysis of historic masonry structures is described and exemplified through the discussion of two representative case studies: a masonry church and an old residential building.

Diagonal cracking shear strength of unreinforced masonry panels: a correction proposal of the b shape factor

Abstract After summarising the failure criteria adopted by the new Italian Seismic Code (NTC 2008) for the seismic assessment of unreinforced masonry panels (URM), the paper presents a numerical study aimed at investigating the b shape factor. This factor is a coefficient, function of the panels’ slenderness, employed to evaluate the ultimate shear strength of URM for the failure mechanism with diagonal cracking. The results herein presented show that the actual values of the coefficient b are higher than those proposed by the NTC (2008); consequently, the shear strength obtained by applying the Italian Seismic Code is not conservative. An amendment is proposed for the b shape factor, and its effects are evaluated through the analysis of three plane-URM walls with regular openings and different slenderness of the masonry beams. Pushover analyses were performed to estimate their seismic capacity and their collapse modes. The walls were modelled by both the finite element method (FEM) and the equivalent frame approach (EFM). In the EFM approach the b shape factor was selected both according to the NTC (2008) and as proposed in the paper. The seismic capacity curves show that the EFM approach significantly overestimate the ultimate shear strength of the walls with respect to the results obtained by the FEM, and this effect is amplified when the b shape factor is evaluated as recommended by the NTC (2008).