Marco Corradi

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.

A method for the analysis and classification of historic masonry

It is known that the mechanical behavior of masonry material depends on many factors, such as compressive or shear strength of components (mortar and blocks), blocks shape, volumetric ratio between components and wall texture, that is the result of applying a series of construction devices which form the “rule of the art”. Taking into account the complexity of the problem due to the great number of variables, a fair assessment of the load carrying capacity of masonries can be made only with in situ test. Being in situ test a semi-destructive methods, not always viable, a numerical estimate of the mechanical parameters of the walls can be made on the basis of a qualitative criteria evaluation. The method here proposed, called Masonry Quality Index method, consists in evaluating the presence, the partial presence, or the absence of certain parameters that define the “rule of the art”, namely a set of construction devices that, if executed during the construction of a wall, provides a good behavior and ensure the compactness and the monolithicity.

An Assessment of Heat Transfer through Fins in a Fin-and-Tube Gas Cooler for Transcritical Carbon Dioxide Cycles

In CO2 transcritical refrigeration cycles, fin-and-tube coils are still considered possible gas cooling devices due to their lower cost when compared with recent aluminium minichannel heat exchangers. In spite of the very high working pressures, an off-the-shelf coil with four ranks of 3/8 in. (9.52 mm) copper tube and louvered fins was found suitable to work with high R-744 pressures and has been studied as a gas cooler in a test rig built for testing carbon dioxide (CO2) equipment operating with air as a secondary fluid. The test rig consists of two closed-loop air circuits acting as heat sink and heat source for the gas cooler and evaporator, respectively. The tested refrigerating circuit consists of two tube-and-fin heat exchangers as the gas cooler and the evaporator, a back-pressure valve as the throttling device, a double-stage compound compressor equipped with an oil separator, and an intercooler. A full set of thermocouples, pressure transducers, and flowmeters allows measurement and recording of all the main parameters of the CO2 cycle, enabling heat balance to be performed for both air side and refrigerant side. Tests focused on two different gas coolers, with continuous and cut fins, and on two different circuit arrangements. Tests on each heat exchanger were run at three different inlet conditions, for both CO2 and air. A simulation model was developed for this type of heat exchanger and three models (Dang and Hihara 2004; Gnielinski 1976; Pitla et al. 2002) proposed for the CO2 supercritical cooling heat transfer coefficients were implemented and compared in the code. The model results are compared with the experimental data for the finned coil; emphasis is given to the effect of heat conduction through fins between adjacent tube ranks on system efficiency. In the paper, the experimental results for transcritical CO2 entering the gas cooler at 87.0°C (7.911 MPa), 97.6°C (8.599 MPa), and 107.8°C (9.102 MPa) with air inlet temperatures of 20.3°C, 21.5°C, and 23.0°C, respectively, are presented. By using a coil with fins modified to reduce the heat conduction, a 3.7% to 5.6% heat flux improvement was gained. This improvement can be clearly translated in terms of coefficient of performance (COP), since a low value of the CO2 temperature at its outlet increases the cooling capacity. Considering a reference cycle with the same operating conditions, a 5.7% to 6.6% increase of COP can be obtained.

Optimisation of the throttling system in a CO2 refrigerating machine

This paper is an answer to the need of finding the optimal solution for the throttling system in refrigerating machines using CO2 as working fluid; such a solution must combine reliability, low installation cost and high energy efficiency. To this purpose, different expansion systems are compared by means of a simulation programme, including a new one, operating with a differential valve, a liquid receiver and a thermostatic valve. The typical compression refrigerating cycle performed by CO2 involves transcritical operations and therefore the upper pressure needs to be adjusted to the optimal value, that, unlike the traditional cycle, is not determined by heat transfer. The innovative system here proposed shows an intrinsic self-adjusting capability that leads to COP values quite close to the maximum ones when a fixed suitable value of the differential pressure is chosen, even if the temperature of the secondary fluid varies to a large extent.

Masonry Columns Confined by Steel Fiber Composite Wraps

The application of steel fiber reinforced polymer (SRP) as a means of increasing the capacity of masonry columns is investigated in this study. The behavior of 23 solid-brick specimens that are externally wrapped by SRP sheets in low volumetric ratios is presented. The specimens are subjected to axial monotonic load until failure occurs. Two widely used types of masonry columns of differing square cross-sections were tested in compression (square and octagonal cross-sections). It is concluded that SRP-confined masonry behaves very much like fiber reinforced polymers (FRP)-confined masonry. Confinement increases both the load-carrying capacity and the deformability of masonry almost linearly with average confining stress. A comparative analysis between experimental and theoretical values computed in compliance with the Italian Council of Research (CNR) was also developed.

Composite boat hulls with bamboo natural fibres

Bamboo laminates are made from bamboo strips milled out from bamboo wall core. In the present study, the overall mechanical characteristics of bamboo fibres reinforced composites and sandwich for general marine applications were analysed. An accurate analysis of processing possibilities and chemical-physical characterisation has been conducted, evaluating the relationship between composites performances, processing characteristics and environmental ageing. As applications, an hull panel and a spinnaker pole have been realised and respectively tested for impact and for axial compression load: successively a complete 6 meters boat hull has been realised in order to analyse critical lamination points and the effectiveness of vacuum bagging.

Determination of Shear Strength of Masonry Panels Through Different Tests

This study addresses the problem of evaluation of strength of masonry walls. In-plane behavior of masonry panels has been studied under monotonic diagonal-compression and shear-compression loading in quasi-static test facility. The results of 35 laboratory and in situ tests are analyzed to show that in the case of the diagonal compression test results are lower than the strength of masonry walls evaluated trough the shear-compression test, highlighting the problem of choosing the test which best simulates to the real behavior of the masonry when stressed by lateral loads. A presentation is also given of the results of a F.E. investigation for shear strength evaluation of masonry walls. F.E. modeling non-linear procedure was used for the representation of masonry panels. The numerical simulations are compared with experimental results and the reliability of the different finite element models is discussed, thus confirming the different shear strength values measured in the experimental campaign.

Durability analysis for FRP and SRG composites in civil applications

In this study, an effort was made to develop an experimental protocol to study the effects of accelerated ageing on composite materials based on bamboo and steel fibers. The physic-mechanical properties of different types of steel and bamboo fibers were investigated. Specimens were subjected to environmental agents. Mechanical and physical tests were used to measure the retained properties and to observe the causes of damage and strength reduction. The experimental data showed that resin properties may strongly influence the durability of FRP reinforcement, environmental combined cycles did not take to significant damage of conditioned specimens; steel fibers are sensitive to alkaline attack when resin does not provide adequate protection to fibers.

Bond Strength of Composite CFRP Reinforcing Bars in Timber

The use of near-surface mounted (NSM) fibre-reinforced polymer (FRP) bars is an interesting method for increasing the shear and flexural strength of existing timber members. This article examines the behaviour of carbon FRP (CFRP) bars in timber under direct pull-out conditions. The objective of this experimental program is to investigate the bond strength between composite bars and timber: bars were epoxied into small notches made into chestnut and fir wood members using a commercially-available epoxy system. Bonded lengths varied from 150 to 300 mm. Failure modes, stress and strain distributions and the bond strength of CFRP bars have been evaluated and discussed. The pull-out capacity in NSM CFRP bars at the onset of debonding increased with bonded length up to a length of 250 mm. While CFRP bar’s pull-out was achieved only for specimens with bonded lengths of 150 and 200 mm, bar tensile failure was mainly recorded for bonded lengths of 250 and 300 mm.