Margherita Pauletta | Università degli Studi di Udine / University of Udine (original) (raw)

Papers by Margherita Pauletta

Research paper thumbnail of Experimental Investigation of a Device to Restrain the Horizontal Sliding of U-FREIs

Applied sciences, Apr 17, 2024

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Experimental Investigation of Basalt/Fibre Textile Reinforced Concrete Under Uniaxial Tensile Force

Lecture notes in civil engineering, 2023

Research paper thumbnail of Investigation of the Failure Modes of Textile-Reinforced Concrete and Fiber/Textile-Reinforced Concrete under Uniaxial Tensile Tests

Materials, Feb 28, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Shear strength formula for interior beam-column joints with plain bars in existing buildings

Research paper thumbnail of Indagine Sperimentale su Nodi Esterni Trave-Pilastro Armati con Barre Lisce

dist.unina.it

ABSTRACT: Un notevole numero di prove sperimentali riportate in letteratura evidenzia che le azio... more ABSTRACT: Un notevole numero di prove sperimentali riportate in letteratura evidenzia che le azioni sismiche possono produrre nei nodi trave-pilastro diffuse fessurazioni diagonali nelle due direzioni, e conseguente degrado della rigidezza del nodo e dell'aderenza armatura-...

Research paper thumbnail of Effectiveness of Tuned Mass Damper in Reducing Damage Caused by Strong Earthquake in a Medium-Rise Building

Applied Sciences

A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced ... more A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced concrete (RC) building is presented. The aim of the study was to investigate the effectiveness of the TMD in changing the structural behavior of medium-rise existing buildings from dissipative to non-dissipative in order to eliminate reparation or demolition costs resulting from damages caused by strong earthquakes. The TMD mass is made by a RC slab lying on flat surface sliders. Horizontal stiffness and damping of the TMD are both provided by lead rubber isolators in the first proposed solution and by low-damping rubber isolators and viscous linear dampers, respectively, in the second. The improvement in the building’s structural behavior attained with the installation of the TMD was assessed by considering the flexural demand over capacity ratios of structural elements and the energy dissipated by the TMD. These results are compared with those of the same building retrofitted with a ba...

Research paper thumbnail of Methods to Reproduce In-Plane Deformability of Orthotropic Floors in the Finite Element Models of Buildings

Applied Sciences

In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represe... more In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represent the in-plane behavior of floors was and still is very commonly adopted because of its simplicity and computational cheapness. However, since excessive floor in-plane deformability can cause a very different redistribution of lateral forces on vertical resisting elements, it may be necessary to consider floor deformability. This paper investigates the classical yet intriguing question of modeling orthotropic RC floor systems endowed with lightening elements by means of a uniform orthotropic slab in order to describe accurately the building response under seismic loads. The simplified method, commonly adopted by engineers and based on the equivalence between the transverse stiffness of the RC elements of the real floor and those of the orthotropic slab, is presented. A case study in which this simplified method is used is also provided. Then, an advanced finite element (FE)-based method...

Research paper thumbnail of Buckling strength of steel tube for lifting telescopic wind steel tower

Engineering Failure Analysis, 2021

Abstract A telescopic pole for wind energy production with low environmental impact and its lifti... more Abstract A telescopic pole for wind energy production with low environmental impact and its lifting system for a 60-250 kW turbine and a height of 30 m have been designed and manufactured. The tower, was raised and lowered by automation or by remote control, that allows one to differentiate the presence of the generator within the landscape over time. The jacking systems acting on the legs had a combination of holes (on the legs) and pegs actuated by hydraulic pistons. The aim of the paper was the experimental and the analytical verification of the stability condition of the steel piston as a lifting system of the prototype. An experimental investigation was carried out on small-scale specimens to examine the influence of lateral restraints constituted by external steel tubes and transverse devices to increase the buckling load and to ensure a stability condition during the elevation operation of the telescopic steel pole. Finally, the experimental results were numerically validated. The original contribution of the paper to research was the design of lifting system of telescopic wind tower though a steel piston with transverse stiffeners.

Research paper thumbnail of Failure analysis of three rigid block assemblies – A real collapse resulting in death

Engineering Failure Analysis

Research paper thumbnail of Destructive and non-destructive tests on columns and cube specimens made with the same concrete mix

Construction and Building Materials

Research paper thumbnail of Seismic Behavior of Exterior Beam-Column Connections with Plain Bars and Effects of Upgrade

ACI Structural Journal, 2012

Abstract: Cyclic load tests on six reinforced concrete (RC) exterior beam-column subassemblages s... more Abstract: Cyclic load tests on six reinforced concrete (RC) exterior beam-column subassemblages simulating joints of buildings constructed before the 1970s, with nonoptimal reinforcing details to resist earthquakes, are described. The exterior beam-...

Research paper thumbnail of Reinforced Concrete Deep Beams- Shear Strength Model and Design Formula

ACI Structural Journal, 2005

A new model for determining the shear strength of reinforced concrete deep beams is proposed in t... more A new model for determining the shear strength of reinforced concrete deep beams is proposed in this paper. An explicit formula that considers the shear strength contributions provided by the strut-and-tie mechanism due to the diagonal concrete strut and the longitudinal main ...

Research paper thumbnail of Reinforced Concrete Corbels - Shear Strength Model and Design Formula

ACI Structural Journal, 2006

A new model for determining the shear strength of reinforced concrete (RC) corbels, or brackets, ... more A new model for determining the shear strength of reinforced concrete (RC) corbels, or brackets, is proposed in this paper. The model is obtained by superimposing the shear strength contribution of the strut-and-tie mechanism due to the cracked concrete and principal ...

Research paper thumbnail of Shear and flexural strengthening of RC beams using BFRP fabrics

Engineering Structures, 2021

Abstract In a world in which the development of new technologies, materials and techniques plays ... more Abstract In a world in which the development of new technologies, materials and techniques plays a fundamental role, and the topic of sustainability is more relevant than ever, the application of eco-friendly Basalt Fiber Reinforced Polymers (BFRP) to structural engineering represents an important area of research. Research and innovation in the field of composite materials have provided a large variety of fiber reinforced polymers to be used for structural strengthening and rehabilitation. This paper presents an experimental research carried out to investigate the effectiveness of BFRP for the strengthening of reinforced concrete beams. Seven concrete beams used as specimens were tested utilizing a four-point bending load scheme. The properties of the unidirectional BFRP fabric used were exploited in different ways to produce shear and flexural strengthening systems. The BFRP fabric proved to be effective for increasing both the shear strength and the flexural capacity of the tested beams. Significant improvement of the ductility of the specimens was obtained as well. A comparison between the results of the shear strength calculations from different design standards and the experimental results is provided.

Research paper thumbnail of Roll-out instability of small size fiber-reinforced elastomeric isolators in unbonded applications

Engineering Structures, 2015

Abstract Unbonded fiber-reinforced elastomeric isolators, due to their light weight, low cost and... more Abstract Unbonded fiber-reinforced elastomeric isolators, due to their light weight, low cost and easy installation, are viable devices for seismic mitigation purposes, both for housing and building applications in highly seismic areas, even in the developing world. Important aspects of these isolators are that they do not have thick base plates, they are not bonded to the top and bottom structure, and their reinforcements are flexible. These features allow fiber-reinforced isolators to experience roll-over deformation under lateral loads. Roll-over deformation is stable, if the stabilizing moment due to vertical forces is higher than the overturning moment due to horizontal forces; however, if this condition is not verified, the isolator experiences a “roll-out instability.” This paper proposes a model for prediction of roll-out instability based on the applied forces equilibrium condition and on the assumption that a triangular distribution for the compressive stresses acts on the isolator. The model is developed considering that the isolator contact area varies with the applied displacement, and consequently the compressive stresses vary. An expression for the isolator instantaneous stiffness is proposed. Results are presented for roll-out tests performed on fiber-reinforced isolators that have varied aspect ratios and are subjected to different compression levels. A comparison is made between the measured displacement at roll-out and the results obtained from the aforementioned model. The comparison proves that the model accurately and reliably predicts roll-out displacement of elastomeric isolators subjected to horizontal and vertical forces.

Research paper thumbnail of A simple method for evaluating the maximum slip of anchorages

Materials and Structures, 2006

The analytical solutions to the bond problem for monotonically increasing loads are developed for... more The analytical solutions to the bond problem for monotonically increasing loads are developed for a monomial exponential local bond stress-slip relationship (law)-"exact solution"-, a linear local law-"proposed solution"-and a constant bond stress distribution, such as that recommended by the Eurocode. The three solutions are thoroughly developed for the pull-out of a bar embedded in a cylindrical element, with longitudinal concrete in tension. For short anchorages, which undergo a rigid motion and whose "exact solution" requires a complex iterative procedure, the "proposed solution" explicitly provides very accurate bond stress distributions. On the basis of this accuracy, an approximate expression for the slip distribution is derived. The proposed approximate solution is the first one providing a direct slip expression for short anchorages. Approximate explicit expressions for the maximum bond stress and the maximum slip are also given. The comparison between the maximum slip values measured during experimental tests and the corresponding values obtained from the proposed approximate expression demonstrates the accuracy of the latter.

Research paper thumbnail of Solution for bond distribution in asymmetric R.C. structural members

Engineering Structures, 2009

The bond problem regarding bottom reinforcing longitudinal continuous bars or anchorages or lappe... more The bond problem regarding bottom reinforcing longitudinal continuous bars or anchorages or lapped splices of RC beams is analyzed. This is an asymmetric problem both for the geometry and the mechanics. The geometrical asymmetry is due to the difference in the extension of the concrete areas surrounding the bars: the concrete area below the horizontal plane crossing the bars’ axes, and the concrete area over this plane up to the plane connecting the tips of the cracks. The mechanical asymmetry is due to the loading asymmetry with respect both to the above mentioned horizontal plane and to the vertical plane crossing the beam at the midspan of two consecutive cracks. Whenever a moment gradient exists, the equilibrium of the beam bottom portion bounded by two consecutive transversal cracks needs that the horizontal components of shear stress, acting on the plane connecting the tips of the cracks, balance the forces gradient acting along the bar. However, these components of shear stress have never been considered until now. The analytical solution to bond problems under asymmetrical conditions is worked out. Long and short anchorages are considered. Comparisons between 132 experimental results and values calculated by means of the proposed asymmetrical solution and an available symmetrical one are performed. The proposed solution provides more accurate and consistent predictions than the symmetrical unreliable one, and it is useful for studying serviceability behavior of reinforced concrete members.

Research paper thumbnail of Sliding instability of fiber-reinforced elastomeric isolators in unbonded applications

Engineering Structures, 2013

Fiber-reinforced isolators not anchored to the structure represent a new development in seismic i... more Fiber-reinforced isolators not anchored to the structure represent a new development in seismic isolation. Their light weight, low cost and great ease of installation, in comparison with conventional elastomeric isolators, could allow to extend the use of these valuable devices to seismic protection of housing and commercial buildings, particularly in developing countries. As demonstrated in studies available in the literature, fiber-reinforced isolators match the behavior of steel-reinforced ones. However the friction behavior between such new devices and the structure has not been investigated yet. This paper describes an experimental study on elastomeric isolators reinforced by bi-directional carbon fiber fabrics performed to investigate the static friction at contact surfaces. The isolators were placed in contact with concrete surfaces and subjected contemporaneously to compressive stress and shear strains. Friction behavior was analyzed in terms of isolator sliding with respect to the concrete sub-and superstructure. Influence on friction behavior of different parameters, such as level of compressive stress, rubber typology, concrete roughness, aging and loading rate, was investigated. The tests showed that, in relation to the value of the applied compressive stress, uncontrolled sliding of the isolator can occur by increasing the shear force. This unstable condition is called sliding instability herein. The experimental results are explained and the limit values of the compressive stress needed to avoid sliding instability is provided both for new and aged isolators, under quasi-static loading conditions. It is demonstrated that quasi-static tests are reasonably conservative with regard to safety. Patterns of stresses and relative displacements based on the experimental results are also proposed.

Research paper thumbnail of A weathering steel elastomer joint for the connection between new and existing bridges

Engineering Structures, 2015

Abstract Mechanical behavior and durability of a new bridge Weathering Steel Elastomer Joint (WSE... more Abstract Mechanical behavior and durability of a new bridge Weathering Steel Elastomer Joint (WSEJ) is investigated. The strength and deformation performances of the joint are determined through an experimental campaign, in order to verify if this element might comply with design requirements. A number of 30 specimens is considered, comprising samples with three different types of steel components, namely weathering (Cor-Ten), stainless (Inox) and carbon (S355) steel, two different shape types of the connecting rubber and two types of specimen geometry. Neutral Salt Spray and Cyclic Corrosion tests, simulating the environmental effects on steel component, are performed to control the joint capacity of maintaining resistance characteristics during its lifecycle. Moreover, temperature tests are carried out to simulate aging of rubber. Intact, corroded or aged specimens are all subjected to tensile tests to determine their strength and corresponding deformation capacity. Comparisons of test results are performed between groups of specimens differing only for one characteristic (deterioration state, corrosion test performed, rubber shape and geometry).

Research paper thumbnail of Experimental Behavior of Carbon Fiber Reinforced Isolators

AIP Conference Proceedings, 2008

This paper presents the results of an investigation on full-scale innovative low-cost unbounded p... more This paper presents the results of an investigation on full-scale innovative low-cost unbounded polyester-fiber reinforced high-damping elastomeric isolators (UPFREIs) to be used for seismic protection of residential buildings in Colombia, South America. In order to characterize the mechanical behavior of the UPFREIs, two full-scale prototypes were manufactured and tested at the Structures Laboratory of the Universidad del Valle. The experimental results were compared with results from the same test performed with two traditional connected steel reinforced isolators (SREIs). Both isolation systems were designed for a residential 5story building with a target period of 2,5s located in a medium-high seismicity region. A dedicated setup was designed and built specifically for the experimental tests. Results from shear tests up to 100% shear strain with sustained axial load exhibited very satisfactory behavior of the UPFREIs versus the SREIs with no residual deformation after unloading. An enhanced damping mechanism with damping ratio between 10 and 15 % was provided by the frictional fiber interface. Lower horizontal stiffness of the UPFREIs was obtained at higher deformation levels due to the typical rollover deformation. Despite the higher axial flexibility with respect to SREIs, UPFREIs also provided an adequate vertical to horizontal stiffness ratio. The results show that the developed UPFREIs have great potential to be implemented as a low-cost seismic isolation system of residential buildings.

Research paper thumbnail of Experimental Investigation of a Device to Restrain the Horizontal Sliding of U-FREIs

Applied sciences, Apr 17, 2024

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Experimental Investigation of Basalt/Fibre Textile Reinforced Concrete Under Uniaxial Tensile Force

Lecture notes in civil engineering, 2023

Research paper thumbnail of Investigation of the Failure Modes of Textile-Reinforced Concrete and Fiber/Textile-Reinforced Concrete under Uniaxial Tensile Tests

Materials, Feb 28, 2023

This article is an open access article distributed under the terms and conditions of the Creative... more This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY

Research paper thumbnail of Shear strength formula for interior beam-column joints with plain bars in existing buildings

Research paper thumbnail of Indagine Sperimentale su Nodi Esterni Trave-Pilastro Armati con Barre Lisce

dist.unina.it

ABSTRACT: Un notevole numero di prove sperimentali riportate in letteratura evidenzia che le azio... more ABSTRACT: Un notevole numero di prove sperimentali riportate in letteratura evidenzia che le azioni sismiche possono produrre nei nodi trave-pilastro diffuse fessurazioni diagonali nelle due direzioni, e conseguente degrado della rigidezza del nodo e dell'aderenza armatura-...

Research paper thumbnail of Effectiveness of Tuned Mass Damper in Reducing Damage Caused by Strong Earthquake in a Medium-Rise Building

Applied Sciences

A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced ... more A case study where a tuned mass damper (TMD) was installed at the top of a five-story reinforced concrete (RC) building is presented. The aim of the study was to investigate the effectiveness of the TMD in changing the structural behavior of medium-rise existing buildings from dissipative to non-dissipative in order to eliminate reparation or demolition costs resulting from damages caused by strong earthquakes. The TMD mass is made by a RC slab lying on flat surface sliders. Horizontal stiffness and damping of the TMD are both provided by lead rubber isolators in the first proposed solution and by low-damping rubber isolators and viscous linear dampers, respectively, in the second. The improvement in the building’s structural behavior attained with the installation of the TMD was assessed by considering the flexural demand over capacity ratios of structural elements and the energy dissipated by the TMD. These results are compared with those of the same building retrofitted with a ba...

Research paper thumbnail of Methods to Reproduce In-Plane Deformability of Orthotropic Floors in the Finite Element Models of Buildings

Applied Sciences

In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represe... more In the modelling of reinforced concrete (RC) buildings, the rigid diaphragm hypothesis to represent the in-plane behavior of floors was and still is very commonly adopted because of its simplicity and computational cheapness. However, since excessive floor in-plane deformability can cause a very different redistribution of lateral forces on vertical resisting elements, it may be necessary to consider floor deformability. This paper investigates the classical yet intriguing question of modeling orthotropic RC floor systems endowed with lightening elements by means of a uniform orthotropic slab in order to describe accurately the building response under seismic loads. The simplified method, commonly adopted by engineers and based on the equivalence between the transverse stiffness of the RC elements of the real floor and those of the orthotropic slab, is presented. A case study in which this simplified method is used is also provided. Then, an advanced finite element (FE)-based method...

Research paper thumbnail of Buckling strength of steel tube for lifting telescopic wind steel tower

Engineering Failure Analysis, 2021

Abstract A telescopic pole for wind energy production with low environmental impact and its lifti... more Abstract A telescopic pole for wind energy production with low environmental impact and its lifting system for a 60-250 kW turbine and a height of 30 m have been designed and manufactured. The tower, was raised and lowered by automation or by remote control, that allows one to differentiate the presence of the generator within the landscape over time. The jacking systems acting on the legs had a combination of holes (on the legs) and pegs actuated by hydraulic pistons. The aim of the paper was the experimental and the analytical verification of the stability condition of the steel piston as a lifting system of the prototype. An experimental investigation was carried out on small-scale specimens to examine the influence of lateral restraints constituted by external steel tubes and transverse devices to increase the buckling load and to ensure a stability condition during the elevation operation of the telescopic steel pole. Finally, the experimental results were numerically validated. The original contribution of the paper to research was the design of lifting system of telescopic wind tower though a steel piston with transverse stiffeners.

Research paper thumbnail of Failure analysis of three rigid block assemblies – A real collapse resulting in death

Engineering Failure Analysis

Research paper thumbnail of Destructive and non-destructive tests on columns and cube specimens made with the same concrete mix

Construction and Building Materials

Research paper thumbnail of Seismic Behavior of Exterior Beam-Column Connections with Plain Bars and Effects of Upgrade

ACI Structural Journal, 2012

Abstract: Cyclic load tests on six reinforced concrete (RC) exterior beam-column subassemblages s... more Abstract: Cyclic load tests on six reinforced concrete (RC) exterior beam-column subassemblages simulating joints of buildings constructed before the 1970s, with nonoptimal reinforcing details to resist earthquakes, are described. The exterior beam-...

Research paper thumbnail of Reinforced Concrete Deep Beams- Shear Strength Model and Design Formula

ACI Structural Journal, 2005

A new model for determining the shear strength of reinforced concrete deep beams is proposed in t... more A new model for determining the shear strength of reinforced concrete deep beams is proposed in this paper. An explicit formula that considers the shear strength contributions provided by the strut-and-tie mechanism due to the diagonal concrete strut and the longitudinal main ...

Research paper thumbnail of Reinforced Concrete Corbels - Shear Strength Model and Design Formula

ACI Structural Journal, 2006

A new model for determining the shear strength of reinforced concrete (RC) corbels, or brackets, ... more A new model for determining the shear strength of reinforced concrete (RC) corbels, or brackets, is proposed in this paper. The model is obtained by superimposing the shear strength contribution of the strut-and-tie mechanism due to the cracked concrete and principal ...

Research paper thumbnail of Shear and flexural strengthening of RC beams using BFRP fabrics

Engineering Structures, 2021

Abstract In a world in which the development of new technologies, materials and techniques plays ... more Abstract In a world in which the development of new technologies, materials and techniques plays a fundamental role, and the topic of sustainability is more relevant than ever, the application of eco-friendly Basalt Fiber Reinforced Polymers (BFRP) to structural engineering represents an important area of research. Research and innovation in the field of composite materials have provided a large variety of fiber reinforced polymers to be used for structural strengthening and rehabilitation. This paper presents an experimental research carried out to investigate the effectiveness of BFRP for the strengthening of reinforced concrete beams. Seven concrete beams used as specimens were tested utilizing a four-point bending load scheme. The properties of the unidirectional BFRP fabric used were exploited in different ways to produce shear and flexural strengthening systems. The BFRP fabric proved to be effective for increasing both the shear strength and the flexural capacity of the tested beams. Significant improvement of the ductility of the specimens was obtained as well. A comparison between the results of the shear strength calculations from different design standards and the experimental results is provided.

Research paper thumbnail of Roll-out instability of small size fiber-reinforced elastomeric isolators in unbonded applications

Engineering Structures, 2015

Abstract Unbonded fiber-reinforced elastomeric isolators, due to their light weight, low cost and... more Abstract Unbonded fiber-reinforced elastomeric isolators, due to their light weight, low cost and easy installation, are viable devices for seismic mitigation purposes, both for housing and building applications in highly seismic areas, even in the developing world. Important aspects of these isolators are that they do not have thick base plates, they are not bonded to the top and bottom structure, and their reinforcements are flexible. These features allow fiber-reinforced isolators to experience roll-over deformation under lateral loads. Roll-over deformation is stable, if the stabilizing moment due to vertical forces is higher than the overturning moment due to horizontal forces; however, if this condition is not verified, the isolator experiences a “roll-out instability.” This paper proposes a model for prediction of roll-out instability based on the applied forces equilibrium condition and on the assumption that a triangular distribution for the compressive stresses acts on the isolator. The model is developed considering that the isolator contact area varies with the applied displacement, and consequently the compressive stresses vary. An expression for the isolator instantaneous stiffness is proposed. Results are presented for roll-out tests performed on fiber-reinforced isolators that have varied aspect ratios and are subjected to different compression levels. A comparison is made between the measured displacement at roll-out and the results obtained from the aforementioned model. The comparison proves that the model accurately and reliably predicts roll-out displacement of elastomeric isolators subjected to horizontal and vertical forces.

Research paper thumbnail of A simple method for evaluating the maximum slip of anchorages

Materials and Structures, 2006

The analytical solutions to the bond problem for monotonically increasing loads are developed for... more The analytical solutions to the bond problem for monotonically increasing loads are developed for a monomial exponential local bond stress-slip relationship (law)-"exact solution"-, a linear local law-"proposed solution"-and a constant bond stress distribution, such as that recommended by the Eurocode. The three solutions are thoroughly developed for the pull-out of a bar embedded in a cylindrical element, with longitudinal concrete in tension. For short anchorages, which undergo a rigid motion and whose "exact solution" requires a complex iterative procedure, the "proposed solution" explicitly provides very accurate bond stress distributions. On the basis of this accuracy, an approximate expression for the slip distribution is derived. The proposed approximate solution is the first one providing a direct slip expression for short anchorages. Approximate explicit expressions for the maximum bond stress and the maximum slip are also given. The comparison between the maximum slip values measured during experimental tests and the corresponding values obtained from the proposed approximate expression demonstrates the accuracy of the latter.

Research paper thumbnail of Solution for bond distribution in asymmetric R.C. structural members

Engineering Structures, 2009

The bond problem regarding bottom reinforcing longitudinal continuous bars or anchorages or lappe... more The bond problem regarding bottom reinforcing longitudinal continuous bars or anchorages or lapped splices of RC beams is analyzed. This is an asymmetric problem both for the geometry and the mechanics. The geometrical asymmetry is due to the difference in the extension of the concrete areas surrounding the bars: the concrete area below the horizontal plane crossing the bars’ axes, and the concrete area over this plane up to the plane connecting the tips of the cracks. The mechanical asymmetry is due to the loading asymmetry with respect both to the above mentioned horizontal plane and to the vertical plane crossing the beam at the midspan of two consecutive cracks. Whenever a moment gradient exists, the equilibrium of the beam bottom portion bounded by two consecutive transversal cracks needs that the horizontal components of shear stress, acting on the plane connecting the tips of the cracks, balance the forces gradient acting along the bar. However, these components of shear stress have never been considered until now. The analytical solution to bond problems under asymmetrical conditions is worked out. Long and short anchorages are considered. Comparisons between 132 experimental results and values calculated by means of the proposed asymmetrical solution and an available symmetrical one are performed. The proposed solution provides more accurate and consistent predictions than the symmetrical unreliable one, and it is useful for studying serviceability behavior of reinforced concrete members.

Research paper thumbnail of Sliding instability of fiber-reinforced elastomeric isolators in unbonded applications

Engineering Structures, 2013

Fiber-reinforced isolators not anchored to the structure represent a new development in seismic i... more Fiber-reinforced isolators not anchored to the structure represent a new development in seismic isolation. Their light weight, low cost and great ease of installation, in comparison with conventional elastomeric isolators, could allow to extend the use of these valuable devices to seismic protection of housing and commercial buildings, particularly in developing countries. As demonstrated in studies available in the literature, fiber-reinforced isolators match the behavior of steel-reinforced ones. However the friction behavior between such new devices and the structure has not been investigated yet. This paper describes an experimental study on elastomeric isolators reinforced by bi-directional carbon fiber fabrics performed to investigate the static friction at contact surfaces. The isolators were placed in contact with concrete surfaces and subjected contemporaneously to compressive stress and shear strains. Friction behavior was analyzed in terms of isolator sliding with respect to the concrete sub-and superstructure. Influence on friction behavior of different parameters, such as level of compressive stress, rubber typology, concrete roughness, aging and loading rate, was investigated. The tests showed that, in relation to the value of the applied compressive stress, uncontrolled sliding of the isolator can occur by increasing the shear force. This unstable condition is called sliding instability herein. The experimental results are explained and the limit values of the compressive stress needed to avoid sliding instability is provided both for new and aged isolators, under quasi-static loading conditions. It is demonstrated that quasi-static tests are reasonably conservative with regard to safety. Patterns of stresses and relative displacements based on the experimental results are also proposed.

Research paper thumbnail of A weathering steel elastomer joint for the connection between new and existing bridges

Engineering Structures, 2015

Abstract Mechanical behavior and durability of a new bridge Weathering Steel Elastomer Joint (WSE... more Abstract Mechanical behavior and durability of a new bridge Weathering Steel Elastomer Joint (WSEJ) is investigated. The strength and deformation performances of the joint are determined through an experimental campaign, in order to verify if this element might comply with design requirements. A number of 30 specimens is considered, comprising samples with three different types of steel components, namely weathering (Cor-Ten), stainless (Inox) and carbon (S355) steel, two different shape types of the connecting rubber and two types of specimen geometry. Neutral Salt Spray and Cyclic Corrosion tests, simulating the environmental effects on steel component, are performed to control the joint capacity of maintaining resistance characteristics during its lifecycle. Moreover, temperature tests are carried out to simulate aging of rubber. Intact, corroded or aged specimens are all subjected to tensile tests to determine their strength and corresponding deformation capacity. Comparisons of test results are performed between groups of specimens differing only for one characteristic (deterioration state, corrosion test performed, rubber shape and geometry).

Research paper thumbnail of Experimental Behavior of Carbon Fiber Reinforced Isolators

AIP Conference Proceedings, 2008

This paper presents the results of an investigation on full-scale innovative low-cost unbounded p... more This paper presents the results of an investigation on full-scale innovative low-cost unbounded polyester-fiber reinforced high-damping elastomeric isolators (UPFREIs) to be used for seismic protection of residential buildings in Colombia, South America. In order to characterize the mechanical behavior of the UPFREIs, two full-scale prototypes were manufactured and tested at the Structures Laboratory of the Universidad del Valle. The experimental results were compared with results from the same test performed with two traditional connected steel reinforced isolators (SREIs). Both isolation systems were designed for a residential 5story building with a target period of 2,5s located in a medium-high seismicity region. A dedicated setup was designed and built specifically for the experimental tests. Results from shear tests up to 100% shear strain with sustained axial load exhibited very satisfactory behavior of the UPFREIs versus the SREIs with no residual deformation after unloading. An enhanced damping mechanism with damping ratio between 10 and 15 % was provided by the frictional fiber interface. Lower horizontal stiffness of the UPFREIs was obtained at higher deformation levels due to the typical rollover deformation. Despite the higher axial flexibility with respect to SREIs, UPFREIs also provided an adequate vertical to horizontal stiffness ratio. The results show that the developed UPFREIs have great potential to be implemented as a low-cost seismic isolation system of residential buildings.