1,721,027 research outputs found
Structural assessment and seismic analysis of a 14th century masonry tower
Full text linkThe masonry building Heritage embraces a large variety of structural typologies, including churches, bridges, arenas, theatres, portals, castles, temples, and towers. The structural behaviour of these constructions appears often complex to be understood due to the uncertainties related to the materials and internal geometry. In this paper, a complete study (i.e. from the data acquisition and elaboration to the vulnerability analysis and proposal for a non-invasive strengthening procedure) of a monumental bell tower building is reported. An extensive program of structural and geometrical surveys has been planned and performed. The main goal of the breakdown was to assess the stability and the seismic vulnerability of the bell tower. Moreover, an innovative use of the drone-based survey for the computation of the geometry of the structure is proposed, in order to significantly reduce the time-cost expenditure of the structural assessment, without any significant lack in the accuracy of the measurements. The resulting object, obtained from the drone-based digitalized survey, was inputted and set in a Finite Element Method (FEM) code for structural modelling. Moreover, a nonlinear kinematic analysis was performed to individuate the possible failure mechanisms. Finally, a non-invasive strengthening procedure, aiming to the improvement of the seismic capacity, is proposed
Durability of FRP Rods for Concrete Structures
No full textOver the last two decades fiber-reinforced polymer (FRP) rods have emerged as one of the most promising and affordable solutions to the corrosion problems of steel reinforcement in structural concrete. The application of FRP rods in new or damaged structures requires the development of design equations that must take into account the mechanical properties and the durability properties of FRP products.
Concerns still remain about the structural behavior of FRP materials under severe environmental and load conditions for long-time exposures. In the case of glass FRP rods, it is the high pH of the pore water solution created during the hydration of the concrete that may cause the chemical attack of the fibers.
In this study, an effort was made to develop an experimental protocol to study the effects of accelerated aging on FRP rods. The physico-mechanical properties of five types of carbon and glass FRP rods were investigated. FRP specimens were subjected to alkaline simulated concrete pore solution and environmental agents including freeze-thaw, high relative humidity, high temperature and ultraviolet (UV) radiations. 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 rod-specimens, GFRP rods are sensitive to alkaline attack when resin does not provide adequate protection to fibers
Seismic behavior of a masonry bell-tower with verticality defect
No full textThe seismic behaviour of slender structures, such as masonry towers, is dominated by bending which may lead to overturning. Since the geometrical survey of towers is hard to compute due to the prevalent longitudinal development of the structure, the shape inputted in the FEM-habitat (Finite Element Method) is commonly regularised (e.g. in cross-section, openings, global shape, etc.). This assumption may make the computation significantly more time-saving together with the increase of the model robustness. At the same time, it may compromise the accuracy of the theoretical prediction. The present study is aimed to report and discuss a seismic vulnerability analysis of a Heritage masonry bell-tower, dated back to the 14th century, placed in the south-east of Italy. The geometry of the structure was assessed by using a drone flying around the building and taking a series of photo afterwards computer-elaborated. The orientation of the photos, associated with the relative position of the drone in the 3D-space, allowed to assess a cloud of points belonging to the bell-tower, leading to an accurate geometrical survey. This process evidenced a verticality defect of the structure. After different investigations aimed to assess the mechanical properties of the masonry and the structural details, a FEM-analysis was achieved in order to compute the capacity under horizontal forces. Linear (modal) and non-linear (push-over) analyses were performed. Moreover, a nonlinear kinematic analysis was able to individuate the weakest rigid-body mechanism. The main results are presented and discussed in the paper, by evidencing that the lack of verticality produces an unsatisfactory seismic vulnerability index. In fact, the first failure mode consisted in the diagonal cracking at the middle height of the tower and the consequent overturning of the top-body, under the seismic acceleration at ultimate limit state (according to the Italian Technical Code)
A study on FRP-confined concrete in presence of different preload levels
No full textThe application of external confinement of concrete columns by using Fiber Reinforced Polymers (FRPs) composites has been widely studied and recognized as an effective technology. The most part of the experimental studies that were conducted are related to columns that were confined without a pre-loading condition, which is the most common situation that is met in the field. In order to increase the knowledge, this research illustrates and discusses the experimental results that were obtained by testing concrete cylinders that were confined with Carbon FRP (CFRP) unidirectional sheets at five different pre-loading levels. The concrete cylinders were prepared and poured at the same time in order to minimize difference in the starting properties of the concrete core. Five specimens were prepared for each pre-load level. Thus, 25 concrete specimens having a diameter of 100 mm diameter and height of 200 mm have been tested. In detail, 5 coupons were unconfined (“U”); 5 were CFRP-confined with null pre-load level (“P0”); and three sets of 5 specimens, named “P20”, “P50” and “P80”, were FRP-confined during the application of a pre-load level equal to 20%, 50% and 80% of the ultimate unconfined concrete compressive strength, respectively. The experimental results revealed the different mechanical response depending of the pre-damage state of the cylinders corresponding to different pre-load levels. Until a pre-load level of 20% the effects can be considered almost negligible, while for higher pre-load levels (50% and 80%) it is remarkable to consider the loss of mechanical properties respect to an ideal un-loaded configuration. The paper will discuss all the aspects related to the experimental results, also showing an analytical procedure to take into account the effects of the pre-loading conditions
Innovative FRP-Reinforced Self-Bearing Arches
No full textThe architectural beauty of curved structures is recognized worldwide. Owing to their balanced form, vaults, domes, and arches were largely adopted over the last centuries. Currently, the erection of new curved masonry structures is dramatically reduced. However, strengthening existing arches is often required to prevent their collapse under static or seismic force. Present limitations regarding such constructions include the antiquated and expensive erection technique employed for curved members. Moreover, the assembly of provisional supporting structures (scaffolding) is generally time- and cost-consuming. Accordingly, the following research provides an innovative construction method that focuses on overcoming the drawbacks of the scaffolding-based approach. A fast lift-up technique was developed to reduce the time and costs of traditional construction techniques. Specifically, the required number of blocks that constitute the arch in this study was aligned side by side on the floor and then connected using a bonded strip of composite material (i.e., FRP - fiber-reinforced polymer). The middle block was then lifted. Thus, each corresponding block could be rotated around the contact point with the adjacent block. When all blocks left the floor, an arch shape was achieved. To validate the proposed method in terms of mechanical performance, an experiment was conducted, as reported herein. A traditional masonry arch built using scaffolding was tested for comparison, and two types of reinforced arches were tested until failure. The first was traditionally built and then reinforced, whereas the second was built using the proposed innovative technique. The specimens were instrumented and tested under a centered or eccentric vertical point load. In all cases, the composite application prevented failure of the hinged joints, as is typical of unreinforced arches, resulting in significantly increased loadbearing capacity, which registered scatters of |11|% and |28|% for the centered and eccentric loads, respectively, when comparing the traditional reinforced arch with the innovative solution
Seismic capacity estimation of a masonry bell-tower with verticality imperfection detected by a drone-assisted survey
Full text linkMasonry towers are considered an important part of cultural heritage due to their architectural and historical value. From a structural perspective these kind of buildings are considered slender elements, the same as a cantilever beam. In real cases it is not easy to model with high accuracy these heritage constructions, since the geometry and mechanical properties of the constituent materials are not adequately known. On the other hand, a deep knowledge of the structural and seismic vulnerability of the masonry towers is needed in order to preserve and retrofit, when necessary, their architectural and cultural value. In the present research an exhaustive study is presented, as it regards the assessment of the seismic vulnerability of a heritage masonry bell-tower, built in the 14th century. An innovative protocol of structural survey followed, and it is proposed herein. The geometry of the tower was easily obtained by digital photogrammetry assisted by a drone. The geometrical model was easily converted into a digitalized input, that was introduced into a finite element method (FEM)-based code. The 3D model was used for linear static, linear dynamic and nonlinear static (pushover) structural analyses. The vulnerability of the masonry tower was assessed and at least one kinematic was found to be not verified
A removable use of FRP for the confinement of heritage masonry columns
Full text linkFor masonry structures in historical heritage with architecturally valuable features, such as frescoed surfaces, the application of structural reinforcement techniques appears to be very complex due to the requirements of removability and limited invasiveness. This is valid with reference to both traditional techniques and modern techniques, such as the external reinforcement with fibre-reinforced composite materials. In this scenario, the use of fibers reinforced polymers (FRPs) is drastically forbidden due to the use of epoxy-based matrix, which does not allow the removal of the intervention without damage of the substrate, even if the mechanical effectiveness of this system has been largely tested and proved. In fact, the reversibility is one of the most relevant aspects in the field of Heritage engineering. Thus, manyefforts need to be spent in order to meet possible solutions, able to mitigate the risk, especially against seismic forces and other natural risks, while ensuring the conservation of the built heritage. This experimental research, which follows a first study on a smaller scale, aims to answer the question: how could a masonry column with frescoes and valuable surfaces be strengthened or repaired in a completely reversible manner?. Two strengthening methods were studied and are proposed herein by assuring the removability of the FRP-confinement of masonry columns. The first technique consists of a liquid adhesion inhibitor applied by brush before the hand lay-up installation of the FRP. The second is set by the interposition of a MylarTM layer between the substrate and the FRP jacket. Uniaxial compression tests were performed in order to demonstrate the efficacy of the new strengthening techniques in increasing the axial strength (+39% and +27% on average for the tuffand limestone-based masonry, respectively) and displacement capacity (+32% and +171% on average for the tuff- and limestone-based masonry, respectively) with respect to un-confined columns. Masonry columns FRP-confined with traditional wet lay-up were also tested for direct comparison. At a later moment, the FRP-jacket was removed to observe the substrate, which has been found effectively preserved from the adhesive, without any discoloration. The experimental results are extensively shown and discussed in the paper
ANN-Based Model for the Prediction of the Bond Strength between FRP and Concrete
Full text linkIn the last decades, the uses of fiber reinforced polymer (FRP) composites in the structural strengthening of reinforced concrete (RC) structures have become the state of the art, providing a valid alternative to the traditional use of steel plates. These relatively new materials present, in fact, great advantages, including high corrosion resistance in aggressive environments, low specific weight, high strength-to-mass-density ratio, magnetic and electric neutrality, low axial coefficient of thermal expansion and sustainable costs of installation. In flexural and shear strengthening of RC members, the effectiveness of the epoxy bonded FRP strongly depends on the adhesion forces exchanged with the concrete substrate. When the flexural moment is present, the FRP strengthening is activated through the stress transfer on the tension side, which is guaranteed by the contact beam region to which the adhesive is bonded to the beam itself. Hence, the determination of the maximum forces that cause debonding of the FRP-plate becomes crucial for a proper design. Over the years, many different analytical models have been provided in the scientific literature. Most of them are based on the calibration of the narrow experimental database. Now, hundreds of experimental results are available. The main goal of the current study is to present and discuss an alternative theoretical formulation for predicting the debonding force in an FRP-plate, epoxy-bonded to the concrete substrate by using an artificial neural networks (ANNs) approach. For this purpose, an extensive study of the state of the art, reporting the results of single lap shear tests, is also reported and discussed. The robustness of the proposed analytical model was validated by performing a parametric analysis and a comparison with other existing models and international design codes, as shown herein
Pre-load effect on CFRP-confinement of concrete columns: Experimental and theoretical study
Full text linkThe axial compression strength of concrete columns has been proved to be significantly enhanced by external confinement. In this perspective, the use of Fiber-Reinforced Polymers (FRPs) has been extensively studied. In practical applications, the FRP-confinement is installed on loaded columns, which can already be significantly deformed, while theoretical models neglect this aspect. This paper concerns a new experimental investigation on the possibility that a pre-existing axial load affects the FRP-confinement of concrete. The research program also aimed at the development of a new analysis-oriented-model for the prediction of the compressive strength of FRP-jacketed concrete columns, depending on the level of the axial load, acting before the confinement. For this purpose, series of small-scale concrete cylinders were first loaded, then confined with Carbon FRP, and finally subjected to destructive pure axial compression tests. Four different levels of pre-existing loads were simulated, including the un-loaded condition
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