Alberto Balsamo

Application-Oriented Chemical Optimization of a Metakaolin Based Geopolymer

In this study the development of a metakaolin based geopolymeric mortar to be used as bonding matrix for external strengthening of reinforced concrete beams is reported. Four geopolymer formulations have been obtained by varying the composition of the activating solution in terms of SiO2/Na2O ratio. The obtained samples have been characterized from a structural, microstructural and mechanical point of view. The differences in structure and microstructure have been correlated to the mechanical properties. A major issue of drying shrinkage has been encountered in the high Si/Al ratio samples. In the light of the characterization results, the optimal geopolymer composition was then applied to fasten steel fibers to reinforced concrete beams. The mechanical behavior of the strengthened reinforced beams was evaluated by four-points bending tests, which were performed also on reinforced concrete beams as they are for comparison. The preliminary results of the bending tests point out an excellent behavior of the geopolymeric mixture tested, with the failure load of the reinforced beams roughly twice that of the control beam.

Experimental Investigation of Exterior RC Beam-Column Joints Retrofitted with FRP Systems

Premature brittle failures because of seismic actions strongly affect the behavior of existing reinforced concrete (RC) structural systems. They commonly involve exterior beam-column joints of structures designed without transverse reinforcement. This paper investigates the behavior of unconfined joints that do not conform to current seismic codes and the effectiveness of externally bonded fiber-reinforced polymers (FRPs) as a strengthening technique. It presents an experimental program carried out on six full-scale RC corner joints under constant axial load and transverse cyclic loading in the as-built and FRP-strengthened configuration. After describing the specimen design strategy and test setup, seismic performance is compared. Particular attention is paid to comparing the experimental capacity of as-built joints and the capacity, which can be predicted on the basis of models available in the literature. Finally, a discussion on the effectiveness of different FRP-strengthening layouts is reported.

Seismic Strengthening of Masonry Vaults with Abutments Using Textile-Reinforced Mortar

AbstractInnovative materials and technologies have been developed to limit the effects of earthquakes on structures, and the use of composite materials has been shown to be effective in existing buildings. In view of this background, experimental tests can provide a contribution to the interpretation of available strengthening interventions. The results of experiments with an innovative strengthening system are presented herein. The strengthening technique used is based on a textile-reinforced mortar (TRM) system coupled with traditional strengthening approaches, and was applied to a type of full-scale masonry vault that is typically found in the roofs of religious buildings. The experiments consisted of several shaking table tests, both before and after the application of the strengthening system. The seismic behavior of the vault after strengthening was significantly improved. The instrumental response of the vault started to change before the initial visible damage, which only occurred when the peak gr...

Masonry Reinforcement with IMG Composites: Experimental Investigation

The interest in strengthening of historical masonry structures is significantly grown especially to techniques which combine properties like as reversibility, compatibility, and sustainability of the intervention. Among these, a promising technique is the use of inorganic matrix grid (IMG) composites. Several experimental tests have been carried out to prove the effectiveness of this system as a strengthening solution for different masonry types. The present paper presents the original results of five tests on uncoursed stone masonry panels under diagonal compression and collect the data of previous tests carried out by the authors on other masonry typologies. The tests results on several masonry types and strengthening layouts as well as Fiber reinforced Polymer (FRP) grid and mortar types are reported and discussed. The experimental programs clearly confirmed the effectiveness of the investigated strengthening technique to increase the panels shear capacity and ductility; however, a suitable theoretical expression to quantify the benefits provided by this strengthening solution, based on the reinforcement layout and on the masonry type, is still missing. The comparative analysis of the experimental data is presented in the paper in order to clarify the benefits provided by each strengthening system.

FRP Local Retrofit of Non-Conforming RC Beam-Column Joints

Recent seismic events have clearly confirmed the vulnerability of existing reinforced concrete (RC) structures. In particular, field observation of structures damaged by L’Aquila earthquake strongly confirmed that premature failure of partially confined (i.e. exterior) beam-column joints was one of the main causes limiting the global structural seismic capacity. Poor attention to details and a lack of adequate transverse reinforcement typically lead to premature brittle shear failure of joints. To provide support to practitioners involved in the L’Aquila reconstruction process, a proper guideline which illustrates the design of local retrofit interventions on structural and non structural elements has been edited by the Italian Civil Protection Department (DPC) and the Laboratories University Network of Seismic Engineering (ReLUIS). In particular, a viable FRP strengthening strategy to increase the seismic performances of partially confined joints (design procedure and installation steps) is widely discussed and presented in the document. To validate the strengthening system recommended in this guideline, an experimental program has been carried out on as-built and FRP strengthened full scale corner RC joints (T shaped joints). After presenting the main guideline recommendations for local strengthening of existing structures, the paper focuses on the experimental program activity; in particular, the specimen design strategy and test setup definition as well as the comparative analysis of the behavior of tested joints.

Confinement of Full-Scale Masonry Columns with FRCM Systems

The effectiveness of FRP systems as a confinement technique to strengthen masonry columns has been widely investigated in the last decades. Recently, a new technique, Fabric Reinforced Cementitious Matrix (FRCM), based on the use of fibrous nets embedded in inorganic matrix, has been developed and investigated as a strengthening solution in masonry buildings. Actually, the number of experimental tests on masonry columns confined by using FRCM systems is very limited, especially for real scale specimens. To fill such gap an experimental program aimed at investigating the behaviour of full scale columns made of limestone masonry blocks confined with different FRCM systems has been carried out. The results of four uniaxial compression tests are illustrated and discussed. The used FRCM systems are made with glass and basalt dry nets embedded in a lime-based mortar. The influence of transverse confinement by using internal reinforcement in forms of pultruded GFRP bars has been also investigated. The mechanical properties of the confined specimens resulted increased in terms of load-carrying capacity and ultimate axial strain.

Comparative Analysis of Existing RC Columns Jacketed with CFRP or FRCC

Reinforced concrete (RC) columns typical of existing structures often exhibit premature failures during seismic events (i.e., longitudinal bars buckling and shear interaction mechanisms) due to the poor quality concrete and the absence of proper seismic details in the potential plastic hinge region. The Fiber Reinforced Polymers (FRP) externally bonded reinforcement is known to be a valid technique to improve the shear capacity or the ductility of existing RC columns. However, few experimental tests have proven its effectiveness in the case of columns affected by shear interaction mechanisms. In this work, the behavior of existing RC columns with border line behavior between flexure and shear have been investigated in the case of poor quality concrete and light FRP strengthening with local jacketing and medium quality concrete and strong FRP strengthening with local jacketing, in order to highlight the effect of concrete strength on the effectiveness of the retrofit intervention. As an alternative to FRP jacketing; the effectiveness of the Fiber Reinforced Cementitious Composite (FRCC) jacketing for the seismic strengthening of columns with highly deteriorated concrete cover or columns already damaged by an earthquake is also evaluated. Six full-scale RC columns have been tested under cyclic loading: one was used as a control specimen; four were strengthened in the potential plastic hinge region with carbon FRP (CFRP); and one was fully jacketed with FRCC. The comparison between poor and medium quality concrete columns showed that the CFRP local jacketing is more effective in the case of poor quality concrete. The FRCC jacketing appears to be a sound repair strategy and a suitable alternative to the FRP jacketing in case of poor quality; however, more experimental research is needed for improving this retrofit technique.

BEHAVIOR OF CFRP CONFINED RC COLUMNS UNDER AXIAL LOAD AND UNIAXIAL CYCLIC LATERAL LOADING

In recent years, the use of FRP wrapping of reinforced concrete (RC) members has been recognized as a reliable method for seismic retrofit of existing structures. The external confinement of existing RC columns with FRPs is a sound technique for increasing the columns ductility, by preventing brittle mechanisms such as bars buckling or post-yielding shear failures and by improving the mechanical properties of concrete due to the lateral confining effect. Several models have been developed for predicting the ultimate displacement capacity and the ductility of FRP confined RC columns, however the accuracy of predictions has not been well established yet. In this study, the experimental behavior of a RC column confined at the plastic hinge region with one ply of carbon fibers (CFRP) is firstly analyzed and compared with the response of the unstrengthened control column. The specimens are cantilevers loaded with a low compressive axial load and subjected to uniaxial cyclic horizontal displacements. The responses of the columns have been analyzed and compared in terms of failure modes and strength and deformation capacity. Particular attention has been focused on the strain distribution recorded on the CFRP strips used to confine the RC column end; the strain profiles along the cross-section perimeter in case of axial load and bending moment interaction are presented and discussed at different load levels. In the second part of the study, the deformation capacity of FRP confined RC column is analytically obtained, by using models for FRP confined square columns available in literature. The comparison between analytical and experimental results showed that currently available models give conservative predictions of ultimate deformation capacity of confined columns. 2753 Available online at www.eccomasproceedia.org Eccomas Proceedia COMPDYN (2017) 2753-2764