Fiber Grid Research Articles

Effectiveness of Using Carbon Fiber Grid Systems in Reinforced Two-Way Concrete Slab System

Effectiveness of Using Carbon Fiber Grid Systems in Reinforced Two-Way Concrete Slab System

Cyclic shear behavior of masonry walls strengthened with prestressed steel bars and glass fiber grids

The present study developed a new and original strengthening method to enhance the shear capacity and ductility of unreinforced masonry (URM) walls based on the unbonded prestressed units using steel bars and glass fiber (GF) grids. The strengthening efficiency was validated through the experimental analyses including the failure mode, the lateral load-displacement relationship, shear capacity, and work damage indicator measured from four specimens subjected to a constant axial load and cyclic lateral loads. In addition, new design equations for the shear capacity of masonry walls were derived based on the regression analysis of 172 datasets. In particular, the proposed equations considered the shear enhancement by the axial stresses created due to the prestressed strengthening materials. The test results showed that shear capacity of the masonry walls strengthened with diagonal steel bars and GF grids increased by 4.2 times when compared with that of the companion URM walls. The proposed design equations for shear capacity of masonry walls also exhibited superior accuracy to FEMA 306 and EC 6 models.

폴리프로필렌과 탄소섬유그리드를 보강한 친환경 콘크리트의 물리, 역학적 특성 연구

폴리프로필렌과 탄소섬유그리드를 보강한 친환경 콘크리트의 물리, 역학적 특성 연구

Evaluation on fatigue cracking resistance of fiber grid reinforced asphalt concrete with reflection cracking rate computation

Fiber grid reinforcement typically used in rehabilitated pavement has shown to mitigate reflective cracking. In this study, different fiber grid materials were evaluated based on fatigue cracking resistance using the Overlay Tester (OT) Machine. A comparison on the number of cycles to failure and a surrogate method was conducted. This observation led to further analysis on three sample configurations to evaluate its performance year based on reflection cracking rate. The test results indicated that using fiber grid reinforcement substantially increase the fatigue cracking resistance. Good correlation was observed between crack rate index and number of cycles to failure.

Probabilistic damage evolution in masonry strengthened with FRCM subjected to aggressive environment

This paper concerns the applications of advanced Fibre Reinforced Cementitious Matrix (FRCM) systems on existing masonry structures. At the state of the art, it shows that the FRCM-to-masonry bond is affected significantly by substrate properties and environmental conditions. For this purpose, an experimental campaign was realised recreating different experimental scenarios, and the results thereby achieved were critically and comparatively discussed. In particular, specimens constituted of two types of fired-clay bricks (either with a single brick or a running bond masonry) were reinforced with a carbon fibre grid, externally glued by means of a cementitious or a lime-based matrix, and then exposed to salt crystallisation induced by capillarity over several months. Visual observation combined with laser profilometer measurements revealed a progressive deterioration of the surface with material loss and signs of bulging between the composite - masonry interface. Pull-off tests on deteriorated samples confirmed the progressive weakening of the bond in terms of nominal strength. To interpret the amount of data, a novel probabilistic model was proposed, apt to predict possible damaging effects on the surface of reinforced masonry elements.

Theoretical model for the study of the tensile behavior of FRCM reinforcements

Fabric Reinforced Cementitious Matrix (FRCM) systems have been recently introduced for repairing or strengthening interventions of reinforced concrete and masonry structures. Thanks to the combination of a dry grid of fibers and a cement-based material (matrix), they present a good strength and numerous advantages with respect to traditional Fiber Reinforced Polymer (FRP) systems. The tensile and bond behavior of FRCM reinforcement systems is characterized by specific phenomena influencing their performance, which are generally not observed in the case of FRP, and that are still object of experimental and numerical studies. Aim of the present paper is the proposal of a theoretical model for numerically studying the tensile behavior of FRCM systems, able to consider the different phenomena characterizing the response of FRCM in tension. The model is carried out on the basis of equilibrium considerations by introducing both linear and nonlinear laws for schematizing the local behavior at the level of the matrix, reinforcement and reinforcement/matrix interface. The model is presented in detail in the first part of the paper and, in the second part, it is applied to an experimental case study derived from literature.

Influence of Matrix Properties on FRCM-CRM Strengthening Systems

During the last decades, widespread seismic events in the Southern European zone have significantly damaged the masonry built heritage. Designers and researchers studied different techniques to increase the performance of masonry panels subjected to horizontal actions due to seismic phenomena. In particular, two of the most common strengthening systems are Fiber Reinforced Cementitious Matrix (FRCM) and Composite Reinforced Mortar (CRM). These systems are usually applied on both surfaces of the load-bearing elements in order to increase their shear strength properties. This work aims at analyzing the effects of three different matrices, comparing FRCM and CRM systems applied on double-leaf masonry panels subjected to diagonal compression test in displacement control (ASTM E519). Compressive strength and thickness of the matrices applied on the masonry substrate were investigated in order to evaluate the relationship between the performance of matrices used within composite strengthening systems (FRCM or CRM) and the density of fiber grids adopted (basalt and glass). The mechanical characterization of the different strengthening systems was performed by means of tensile and bond tests on masonry prisms. Finally, the experimental results obtained were analyzed in terms of failure modes and maximum capacity attained by strengthened panels.

Comparison of Different FE Modeling for In-Plane Shear Strengthening of Brittle Masonry with FRCM

Few design oriented models on strengthening of unreinforced masonry (URM) panels under in-plane actions with composite systems are currently available (among them, the pioneers researches [1, 2] and the guidelines [3, 4] for FRPs). Usually, the in-plane shear capacity of a strengthened panel is evaluated as the sum of two terms: the contribution of URM masonry and that of the composite strengthening system (usually only the fibers are considered, also in the case of inorganic matrix, as illustrated in [5, 6, 7], neglecting the shear contribution of the matrix). Mostly, the models proposed to compute the strength increment of the URM can be seen as extensions of provisions for steel-reinforced masonry, where the reinforcement is modeled by the truss analogy [8] and an effective ultimate strain is introduced to account for premature failure of fibers in shear applications. However, the development of the ideal truss in a masonry wall is strongly conditioned by a proper anchorage of fibers and availability of a fiber grid, which is not always ensured. Several failure modes can be expected for strengthened masonry, like diagonal splitting cracking, sliding of a portion over the other, so that the contribution of the composite can be engaged in different ways. The aim of this study is to compare different modeling strategies in the numerical field accounting for matrix as a continuum or as a stiffening of individual fibers, and to provide novel FEM analyses revealing the different role of fiber orientations and matrix properties.

Shear crack pattern identification in concrete elements via distributed optical fibre grid

An experimental methodology to obtain the shear cracking pattern in concrete elements is presented. The method is based on the use of Distributed Optical Fibre Sensors (DOFS) connected to an Optical Backscattered Reflectometer (OBR). Using this OBR system and a 2D grid conformed by one or two DOFS, the crack patterns of three partially pre-stressed concrete (PPC) beams subjected experimentally to shear failure, were obtained for increasing level of load. The 2D distributed fibre optic sensoring mesh was formed by attaching the fibre to the shear span of each beam using an epoxy adhesive. The importance of a correct DOFS bonding procedure to the concrete surface to obtain accurate results is described, and the principal advantages of DOFS to complement the use of discrete sensors in concrete experimental shear tests are shown. The proposed technique is a powerful tool to be implemented in the structural health monitoring in shear of concrete structures, where the variable inclined cracks are difficult to monitor by other experimental techniques using discrete sensors.

The adult musculature of two pseudostomid species reveals unique patterns for flatworms (Platyhelminthes, Prolecithophora).

We analyzed the adult musculature of two prolecithophoran species, Cylindrostoma monotrochum (von Graff, 1882) and Monoophorum striatum (von Graff, 1878) using a phalloidin‐rhodamine technique. As in all rhabdithophoran flatworms, the body‐wall musculature consisted of three muscle layers: on the outer side was a layer of circular muscle fibers and on the inner side was a layer of longitudinal muscle fibers; between them were two different types of diagonally orientated fibers, which is unusual for flatworms. The musculature of the pharynx consisted of a basket‐shaped grid of thin longitudinal and circular fibers. Thick anchoring muscle fibers forming a petal‐like shape connected the proximal parts of the pharynx with the body‐wall musculature. Male genital organs consisted of paired seminal vesicles, a granular vesicle, and an invaginated penis. Peculiar ring‐shaped muscles were only found in M. striatum, predominantly in the anterior body part. In the same species, seminal vesicles and penis only had circular musculature, while in C. monotrochum also longitudinal musculature was found in these organs. Female genital organs were only present in M. striatum, where we characterized a vagina interna, and a bursa seminalis. Transverse, crossover, and dorsoventral muscle fibers were lacking in the middle of the body and greatly varied in number and position in both species.

Long-term performance of fiber-grid-reinforced asphalt overlay pavements: A case study of Korean national highways

Abstract The objective of this study was to verify the effect of fiber grid reinforcement on the long-term performance of asphalt overlay pavements by performing field investigation, laboratory test, and finite element analysis. Crack, rutting, roughness, and other miscellaneous distresses of fiber-grid-reinforced overlay sections and ordinary overlay sections were compared. Pavement conditions of fiber grid overlay sections before and after the overlay were also compared. Cores were obtained from the fiber-grid-reinforced and ordinary sections to measure bonding shear strength between the intermediate and overlay layers. Fracture energy, displacement after yield, and shear stiffness of the cores were also obtained by analyzing the test results. Finite element analysis was performed by using the test results to validate the effect of the fiber grid reinforcement on the long-term performance of asphalt overlay pavements. Rutting and fatigue cracking were predicted for three cases: 1) fiber grid was not used; 2) glass fiber grid was used; and 3) carbon fiber grid was used. The cracking ratio of fiber-grid-reinforced sections was much smaller than that of ordinary sections. The results of field investigation, laboratory test, and finite element analysis showed that the fiber grid reinforcement improved the long-term performance of asphalt overlay pavements.

Masonry columns strengthened with FRCM system: Numerical and experimental evaluation

The present paper deals with the structural behavior of masonry columns strengthened by a system made up of composite fiber grids embedded in cementitious matrix; in particular, the problem has been investigated both numerically and by performing experimental tests.Starting from the Spoelstra-Monti’s iterative approach for FRP-confined concrete columns, an analytical approach for FRCM-reinforced masonry columns has been proposed. In particular, critical equations have been improved or modified in order to properly taken into account masonry behaviour and its interaction with the composite reinforcement.A 3D numerical description of the problem has been also considered, by using the commercial code MIDAS FEA, based on a macro-model approach; masonry and the reinforcement system have been considered as homogeneous materials with non-linear constitutive behaviour. The two models have been compared in order to understand the capabilities and limitations of the 1D model.To calibrate the models, some tests on plain masonry columns and composite specimens have been carried out at the University of Bologna and described. Other tests on strengthened columns, coming from the same experimental campaign, have been used to validate the capability of the models. Different types of reinforcement have been considered. Further validation has been obtained by considering also experimental results coming from literature data.The comparison of the numerical models with the experimental outcomes shows a good matching both in terms of mode of failure and quantitative behavior.

The basic investigation of evaporation rate and burning temperature of various type of liquid fuels droplet

The investigation of spray combustion phenomenon in order to improve the combustion efficiency has been conducted through the experimentally or simulation. On the liquid spray combustion phenomenon the size of liquid fuel that was sprayed into the combustion chamber (droplet) is very small, ranging between 1-25 μm. Due to the very small size of liquid droplet, the gravitation effect of liquid droplet was negligible or near the microgravity condition. Therefore, this study was conducted to observe the behaviour of evaporation rate and the burning temperature of various types of liquid fuels droplet. The results of this research can be used as a basis in experiments or modelling of spray combustion. The liquid fuel that was used in this experiment are n-decane, pertamax, pertalite and pertamax turbo. Experiments were performed by injecting liquid fuel into droplets on SiC fiber grids with several variations of droplet size (0.5 mm, 0.75 mm, 1 mm, 1.25 mm and 1.5 mm).The results show that the droplet size of each fuel has a positive correlation to the evaporation rate and also the combustion temperature. This paper will discuss in detail the characteristics of the evaporation rate and the burning temperature of each type of liquid fuels droplet.

Quasi-static in-plane testing of FRCM strengthened non-ductile reinforced concrete frames with masonry infills

Performance of fibre reinforced cementitious matrix (FRCM) strengthened non-ductile reinforced concrete frames with hollow concrete masonry infill (RCFMI) subjected to cyclic in-plane loading was experimentally assessed herein. A set of nine two-third scaled one bay-single story RCFMI prototypes were constructed that represented one bay of a low to medium height RCFMI building. Of these specimens, one frame was tested as-built without infill, one frame was tested as-built with infill, and the remainder were retrofitted using different FRCM schemes. The as-built tested frames served as control specimens and represented the baseline collapse risk associated to RCFMI buildings. Three different types of fibre grids (i.e. basalt, carbon, and glass) and three different FRCM configurations were used for retrofitting (i.e. full surface, diagonal bands with varying width). FRCM strengthened test frames exhibited a controlled failure mode characterised by distributed cracking in the FRCM matrix, without any signs of fibre slippage/rupture or deboning noted during the testing. Separation at the un-strengthened infill-frame contact region in FRCM strengthened frames was noted at a lateral drift of 0.4–0.6% and an applied lateral force of 1.2–2.0 times the strength of as-built tested frame. In general, test frames strengthened using diagonal bands with width equal to 1/6 infill diagonal length performed very similar to other configuration and therefore was deemed the most effective configuration. Carbon fabric had the highest strength compared to other fabrics used, but resulted in the lowest strength increment for the RCFMI, whereas Basalt-FRCM strengthened RCFMI exhibited the largest in-plane strength.

Modeling of the interface between the concrete and the fibers grid in concrete slab

Abstract. Fiber grid reinforcements are widely used in construction, especially in the rehabilitation of structures; short fibers are also used in concrete. However, reinforcing mortars with textiles (fiber gratings) which offers an improved concrete, and a wide variety of new and exciting architectural forms, is still a relatively new application that shows a need for research. Tests on the use of Glass Fiber Grids (GFG) and Polypropylene Grids (PPG) in the concrete matrix which can be an interesting solution to improve the bearing capacity and change the failure mode of slabs subjected to a load of punching have been realized. The results showed a significant increase in the bearing capacity, a better distribution of the cracks, as well as an improvement of the deflexion before failure; compared to unreinforced reference slabs. In order to understand the behaviour of the concrete-GFG interface of the tested slabs, a modeling of this latter was carried out using a constitutive law expressing the shear stress between the two materials as a function of the relative sliding between the surfaces in contact, taking into account the mechanical characteristics of both materials. The analysis of the bond-slip curve obtained has shown that the use of the glass fiber grid inside the concrete matrix allows a better behaviour of the interface between constituent materials with respect to the glued fiber-reinforced polymer (FRP) plates on the surface of the slab.

Modeling of the interface between the concrete and the fibers grid in concrete slab

Fiber grid reinforcements are widely used in construction, especially in the rehabilitation of structures; short fibers are also used in concrete. However, reinforcing mortars with textiles (fiber gratings) which offers an improved concrete, and a wide variety of new and exciting architectural forms, is still a relatively new application that shows a need for research. Tests on the use of Glass Fiber Grids (GFG) and Polypropylene Grids (PPG) in the concrete matrix which can be an interesting solution to improve the bearing capacity and change the failure mode of slabs subjected to a load of punching have been realized. The results showed a significant increase in the bearing capacity, a better distribution of the cracks, as well as an improvement of the deflexion before failure; compared to unreinforced reference slabs.
 In order to understand the behaviour of the concrete-GFG interface of the tested slabs, a modeling of this latter was carried out using a constitutive law expressing the shear stress between the two materials as a function of the relative sliding between the surfaces in contact, taking into account the mechanical characteristics of both materials. The analysis of the bond-slip curve obtained has shown that the use of the glass fiber grid inside the concrete matrix allows a better behaviour of the interface between constituent materials with respect to the glued fiber-reinforced polymer (FRP) plates on the surface of the slab.

Effect of glass fibre grids on the bonding strength between two asphalt layers and its Contact Dynamics method modelling

This study evaluates the effect of glass fibre grids, used to reinforce asphalt structures, on the bonding strength between a wearing and a binder layer. For this purpose, a test surface consisting of a 6-cm thick binder (0/16 mm) and a 6-cm thick wearing layer (0/11 mm) was built. Four different grids coated with various quantities of bitumen emulsions C60B4-S and C40B5-S were used. Comparison sections were made without grid but also coated with different quantities of emulsions. Extracted cores with 150 mm diameter were tested at ambient laboratory temperature with a monotonic shear test (Leutner). Displacement, shear force and shear stress were measured. The influence of grid characteristics, the existence of a non-woven and the size of the strands as well as the effect of different emulsions on the shear bonding strength were observed, and a numerical model based on DEM simulations was developed. Also, the effect of temperatures on the shear strength with different reinforced and unreinforced specimens was studied. The numerical samples were created with the particles size distribution of the material, where a spherical shape was analysed. A viscoelastic model was implemented for the contact law. We show that the numerical model is able to reproduce the mechanical behaviour of asphalt mixture and reinforced asphalt mixture under the shear loading test. We find that the tests without a reinforcement grid reach more important values of stress at failure and that the decrease in shear stress levels at failure is more important for larger sections of the strands of the grid.

In-situ experimental tests on masonry panels strengthened with Textile Reinforced Mortar composites

Textile Reinforced Mortar (TRM) composites are a retrofitting techniques used for strengthening masonry structures. The system is composed of dry fibers grids embedded in two layers of inorganic matrix. The paper describes the results of an in-situ experimental campaign on ancient masonry panels reinforced with different TRM systems. The tests were performed in a building located in Finale Emilia (north of Italy) built at the beginning of the last century. Four diagonal compressive tests were performed on unreinforced and reinforced walls.The walls were strengthened with different configurations: two panels were reinforced with a TRM systems composed of a lime mortar and two different types of glass fiber grids and twist steel bars used as anchors; one panel was reinforced with a layer of TRM on one side and a Near Surface Mounted (NSM) system on the other one.The results of the tests are described and a complete mechanical characterization of the reinforcement systems and of the masonry was performed to analyze the experimental results and validate simple analytical models.

Directional scatter imaging for the stereoscopic tracking of fiducial markers in a single kV exposure.

To demonstrate, via Monte Carlo simulation, that an image obtained from the patient-generated scattered radiation forced to impinge on the detector from a known direction by means of parallel-focused grids, can be used to complement the information conveyed by the primary image, such that accurate stereoscopic three-dimensional localization of fiducial markers can be achieved in a single kV x-ray exposure. A voxelized Zubal phantom was used to model the process of fiducial marker localization. The markers were represented as made of gold and cylindrical in shape with dimensions of 5mm in length and 1mm in diameter. Three such markers were placed in the Zubal phantom at the prostate level. Two gantry-mounted image acquisition geometries were modeled: a single kV imaging system and a dual kV-MV imaging system. The detector was modeled as a 30cm×40cm Gd2 O2 S screen with a thickness of 0.2cm and a resolution of 768×1024 pixels. The PENELOPE Monte Carlo code was used to calculate the absorbed dose in this detector imparted by the transmitted primary and directional scatter radiation. A grayscale conversion was then applied to obtain an image from which the positions of the markers were determined. Two parallel-focused grid geometries were modeled, one based on the standard lead-carbon fiber grids and a proposed modification using tungsten as the shielding material. Absorbed dose in the patient model was also calculated. It is shown that the combination of primary and directional scatter images provides the means for an accurate stereoscopic fiducial marker 3D localization in a single x-ray exposure, provided the antiscatter grids are made thick enough to allow radiation traveling only in a particular direction to reach the detector. For the proposed tungsten grid and the x-ray spectrum used in this work, grid ratios of 20 and thickness of 0.2cm, provide the necessary shielding while for the standard lead grids, a ratio of at least 166 and a thickness of 2cm are needed to obtain discernible directional scatter images. We have shown that it is in principle possible to determine the 3D position of fiducial markers in a single exposure by making use of the radiation scattered by the patient to form an image that complements the information obtained with the primary beam. The method here proposed requires minimal modification of existing clinical hardware.

3D-FEM Analysis on Geogrid Reinforced Flexible Pavement Roads

Nowadays, the need to increase pavement service life, guarantee high performance, reduce service and maintenance costs has been turned a greater attention on the use of reinforcements. This paper presents findings of a numerical investigation on geogrid reinforced flexible pavement roads, under wheel traffic loads, using a three-dimensional Finite Element Method (FEM). The results obtained show the effectiveness of glass fibre grids as reinforcement which, with appropriate design and correct installation, by improving interface shear resistance, can be used to expand the performance of flexible pavements in different ways: by increasing the road service life providing a relevant contribution against superficial rutting or by decreasing the construction costs due to the reduction in the reinforced HMA layer thickness and thus of mineral aggregate required for its construction.