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Torsional behavior and analysis of steel fiber reinforced concrete (SFRC) beams is investigated in this paper. The purpose of this study is twofold; to examine the torsion strength models for SFRC beams available in the literature and to address properly verified design formulations for SFRC beams under torsion. A total of 210 SFRC beams tested under torsion from 16 different experimental investigations around the world are compiled. The few strength models available from the literature are adapted herein and used to calculate the torsional strength of the beams. The predicted strength is compared with the experimental values measured by the performed torsional tests and these comparisons showed a room for improvement. First, a proposed model is based on optimizing the constants of the existing formulations using multi-linear regression. Further, a second model is proposed, which is based on modifying the American Concrete Institute (ACI) design code for reinforced concrete (RC) members to include the effect of steel fibers on the torsional capacity of SFRC beams. Applications of the proposed models showed better compliance and consistency with the experimental results compared to the available design models providing safe and verified predictions. Further, the second model implements the ACI code for RC using a simple and easy-to-apply formulation.
Ahmed Deifalla; Adamantis Zapris; Constantin Chalioris. Multivariable Regression Strength Model for Steel Fiber-Reinforced Concrete Beams under Torsion. Materials 2021, 14, 3889 .
AMA StyleAhmed Deifalla, Adamantis Zapris, Constantin Chalioris. Multivariable Regression Strength Model for Steel Fiber-Reinforced Concrete Beams under Torsion. Materials. 2021; 14 (14):3889.
Chicago/Turabian StyleAhmed Deifalla; Adamantis Zapris; Constantin Chalioris. 2021. "Multivariable Regression Strength Model for Steel Fiber-Reinforced Concrete Beams under Torsion." Materials 14, no. 14: 3889.
The effectiveness of externally applied fiber-reinforced polymer (FRP) ropes made of carbon fibers in X-shape formation and in both sides of the joint area of reinforced concrete (RC) beam–column connections is experimentally investigated. Six full-scale exterior RC beam–column joint specimens are tested under reverse cyclic deformation. Three of them have been strengthened using carbon FRP (CFRP) ropes that have been placed diagonally in the joint as additional, near surface-mounted reinforcements against shear. Full hysteretic curves, maximum applied load capacity, damage modes, stiffness and energy dissipation values per each loading step are presented and compared. Test results indicated that joint sub assemblages with X-shaped CFRP ropes exhibited improved hysteretic behavior and ameliorated performance with respect to the reference specimens. The effectiveness and the easy-to-apply character of the presented strengthening technique is also discussed.
Emmanouil Golias; Adamantis Zapris; Violetta Kytinou; Mourhat Osman; Michail Koumtzis; Danai Siapera; Constantin Chalioris; Chris Karayannis. Application of X-Shaped CFRP Ropes for Structural Upgrading of Reinforced Concrete Beam–Column Joints under Cyclic Loading–Experimental Study. Fibers 2021, 9, 42 .
AMA StyleEmmanouil Golias, Adamantis Zapris, Violetta Kytinou, Mourhat Osman, Michail Koumtzis, Danai Siapera, Constantin Chalioris, Chris Karayannis. Application of X-Shaped CFRP Ropes for Structural Upgrading of Reinforced Concrete Beam–Column Joints under Cyclic Loading–Experimental Study. Fibers. 2021; 9 (7):42.
Chicago/Turabian StyleEmmanouil Golias; Adamantis Zapris; Violetta Kytinou; Mourhat Osman; Michail Koumtzis; Danai Siapera; Constantin Chalioris; Chris Karayannis. 2021. "Application of X-Shaped CFRP Ropes for Structural Upgrading of Reinforced Concrete Beam–Column Joints under Cyclic Loading–Experimental Study." Fibers 9, no. 7: 42.
The necessity of ensuring the long-term sustainability of existing structures is rising. An important issue concerning existing reinforced concrete (RC) structures in seismically active regions is that a significant number of them lack the required earthquake-resistant capacities to meet the increased design earthquake demands. Inexpensive, fast and long-term strengthening strategies for repairing/strengthening RC structures are urgently required, not only after destructive earthquakes, but even before they occur. Retrofitting existing buildings extending their service life rather than demolishing and rebuilding new ones is the best option in terms of economic gain and environmental protection. This paper experimentally investigates the effectiveness of externally applied (i) carbon fiber-reinforced polymer (C-FRP) ropes in X-type form and (b) C-FRP sheets that are bonded on both sides of the joint area of RC beam-column joint connections. Six comparative full-scale exterior RC beam-column joint specimens were tested under reverse cyclic deformation. Two of them were control specimens, two were strengthened using C-FRP ropes (novel technique) and two were retrofitted using C-FRP sheets (widely used technique). Extensive comparisons and discussion of the test results derive new quantitative and qualitative results concerning the seismic capacity and the service life extension of the strengthened RC members using the proposed retrofitting scheme.
Emmanouil Golias; Adamantis Zapris; Violetta Kytinou; George Kalogeropoulos; Constantin Chalioris; Chris Karayannis. Effectiveness of the Novel Rehabilitation Method of Seismically Damaged RC Joints Using C-FRP Ropes and Comparison with Widely Applied Method Using C-FRP Sheets—Experimental Investigation. Sustainability 2021, 13, 6454 .
AMA StyleEmmanouil Golias, Adamantis Zapris, Violetta Kytinou, George Kalogeropoulos, Constantin Chalioris, Chris Karayannis. Effectiveness of the Novel Rehabilitation Method of Seismically Damaged RC Joints Using C-FRP Ropes and Comparison with Widely Applied Method Using C-FRP Sheets—Experimental Investigation. Sustainability. 2021; 13 (11):6454.
Chicago/Turabian StyleEmmanouil Golias; Adamantis Zapris; Violetta Kytinou; George Kalogeropoulos; Constantin Chalioris; Chris Karayannis. 2021. "Effectiveness of the Novel Rehabilitation Method of Seismically Damaged RC Joints Using C-FRP Ropes and Comparison with Widely Applied Method Using C-FRP Sheets—Experimental Investigation." Sustainability 13, no. 11: 6454.
The utilization and effectiveness of a custom-made, portable and low-cost structural health monitoring (SHM) system that implements the PZT-based electro-mechanical admittance (EMA) methodology for the detection and evaluation of the damage of flexural reinforced concrete (RC) beams is presented. Tests of large-scale beams under monotonic and cyclic reversal-imposed deformations have been carried out using an integrated wireless impedance/admittance monitoring system (WiAMS) that employs the voltage measurements of PZT transducers. Small-sized PZT patches that have been epoxy-bonded on the steel bars surface and on the external concrete face of the beams are utilized to diagnose damages caused by steel yielding and concrete cracking. Excitations and simultaneous measurements of the voltage signal responses of the PZT transducers have been carried out at different levels of the applied load during the tests using the developed SHM devices, which are remotely controlled by a terminal emulator. Each PZT output voltage versus frequency response is transferred wireless and in real-time. Statistical index values are calculated based on the signals of the PZT transducers to represent the differences between their baseline response at the healthy state of the beam and their response at each loading/damage level. Finite Element Modeling (FEM) simulation of the tested beams has also been performed to acquire numerical results concerning the internal cracks, the steel strains and the energy dissipation and instability parameters. FEM analyses are used to verify the experimental results and to support the visual observations for a more precise damage evaluation. Findings of this study indicate that the proposed SHM system with the implementation of two different PZT transducer settings can be effectively utilized for the assessment of structural damage caused by concrete cracking and steel yielding in flexural beams under monotonic and cyclic loading.
Constantin Chalioris; Violetta Kytinou; Maristella Voutetaki; Chris Karayannis. Flexural Damage Diagnosis in Reinforced Concrete Beams Using a Wireless Admittance Monitoring System—Tests and Finite Element Analysis. Sensors 2021, 21, 679 .
AMA StyleConstantin Chalioris, Violetta Kytinou, Maristella Voutetaki, Chris Karayannis. Flexural Damage Diagnosis in Reinforced Concrete Beams Using a Wireless Admittance Monitoring System—Tests and Finite Element Analysis. Sensors. 2021; 21 (3):679.
Chicago/Turabian StyleConstantin Chalioris; Violetta Kytinou; Maristella Voutetaki; Chris Karayannis. 2021. "Flexural Damage Diagnosis in Reinforced Concrete Beams Using a Wireless Admittance Monitoring System—Tests and Finite Element Analysis." Sensors 21, no. 3: 679.
The use of fibers as mass reinforcement to delay cracking and to improve the strength and the post-cracking performance of reinforced concrete (RC) beams has been well documented. However, issues of common engineering practice about the beneficial effect of steel fibers to the seismic resistance of RC structural members in active earthquake zones have not yet been fully clarified. This study presents an experimental and a numerical approach to the aforementioned question. The hysteretic response of slender and deep steel fiber-reinforced concrete (SFRC) beams reinforced with steel reinforcement is investigated through tests of eleven beams subjected to reversal cyclic loading and numerical analysis using 3D finite element (FE) modeling. The experimental program includes flexural and shear-critical SFRC beams with different ratios of steel reinforcing bars (0.55% and 1.0%), closed stirrups (from 0 to 0.5%), and fibers with content from 0.5 to 3% per volume. The developed nonlinear FE numerical simulation considers well-established relationships for the compression and tensional behavior of SFRC that are based on test results. Specifically, a smeared crack model is proposed for the post-cracking behavior of SFRC under tension, which employs the fracture characteristics of the composite material using stress versus crack width curves with tension softening. Axial tension tests of prismatic SFRC specimens are also included in this study to support the experimental project and to verify the proposed model. Comparing the numerical results with the experimental ones it is revealed that the proposed model is efficient and accurately captures the crucial aspects of the response, such as the SFRC tension softening effect, the load versus deformation cyclic envelope and the influence of the fibers on the overall hysteretic performance. The findings of this study also reveal that SFRC beams showed enhanced cyclic behavior in terms of residual stiffness, load-bearing capacity, deformation, energy dissipation ability and cracking performance, maintaining their integrity through the imposed reversal cyclic tests.
Violetta K. Kytinou; Constantin E. Chalioris; Chris G. G. Karayannis; Anaxagoras Elenas. Effect of Steel Fibers on the Hysteretic Performance of Concrete Beams with Steel Reinforcement—Tests and Analysis. Materials 2020, 13, 2923 .
AMA StyleVioletta K. Kytinou, Constantin E. Chalioris, Chris G. G. Karayannis, Anaxagoras Elenas. Effect of Steel Fibers on the Hysteretic Performance of Concrete Beams with Steel Reinforcement—Tests and Analysis. Materials. 2020; 13 (13):2923.
Chicago/Turabian StyleVioletta K. Kytinou; Constantin E. Chalioris; Chris G. G. Karayannis; Anaxagoras Elenas. 2020. "Effect of Steel Fibers on the Hysteretic Performance of Concrete Beams with Steel Reinforcement—Tests and Analysis." Materials 13, no. 13: 2923.
This paper investigates the ability of steel fibers to enhance the short-term behavior and flexural performance of realistic steel fiber-reinforced concrete (SFRC) structural members with steel reinforcing bars and stirrups using nonlinear 3D finite element (FE) analysis. Test results of 17 large-scale beam specimens tested under monotonic flexural four-point loading from the literature are used as an experimental database to validate the developed nonlinear 3D FE analysis and to study the contributions of steel fibers on the initial stiffness, strength, deformation capacity, cracking behavior, and residual stress. The examined SFRC beams include various ratios of longitudinal reinforcement (0.3%, 0.6%, and 1.0%) and steel fiber volume fractions (from 0.3% to 1.5%). The proposed FE analysis employs the nonlinearities of the materials with new and established constitutive relationships for the SFRC under compression and tension based on experimental data. Especially for the tensional response of SFRC, an efficient smeared crack approach is proposed that utilizes the fracture properties of the material utilizing special stress versus crack width relations with tension softening for the post-cracking SFRC tensile response instead of stress–strain laws. The post-cracking tensile behavior of the SFRC near the reinforcing bars is modeled by a tension stiffening model that considers the SFRC fracture properties, the steel fiber interaction in cracked concrete, and the bond behavior of steel bars. The model validation is carried out comparing the computed key overall and local responses and responses measured in the tests. Extensive comparisons between numerical and experimental results reveal that a reliable and computationally-efficient model captures well the key aspects of the response, such as the SFRC tension softening, the tension stiffening effect, the bending moment–curvature envelope, and the favorable contribution of the steel fibers on the residual response. The results of this study reveal the favorable influence of steel fibers on the flexural behavior, the cracking performance, and the post-cracking residual stress.
Violetta K. Kytinou; Constantin E. Chalioris; Chris G. Karayannis. Analysis of Residual Flexural Stiffness of Steel Fiber-Reinforced Concrete Beams with Steel Reinforcement. Materials 2020, 13, 2698 .
AMA StyleVioletta K. Kytinou, Constantin E. Chalioris, Chris G. Karayannis. Analysis of Residual Flexural Stiffness of Steel Fiber-Reinforced Concrete Beams with Steel Reinforcement. Materials. 2020; 13 (12):2698.
Chicago/Turabian StyleVioletta K. Kytinou; Constantin E. Chalioris; Chris G. Karayannis. 2020. "Analysis of Residual Flexural Stiffness of Steel Fiber-Reinforced Concrete Beams with Steel Reinforcement." Materials 13, no. 12: 2698.
The application of externally bonded fiber-reinforced polymer (EB-FRP) as shear transverse reinforcement applied in vulnerable reinforced concrete (RC) beams has been proved to be a promising strengthening technique. However, past studies revealed that the effectiveness of this method depends on how well the reinforcement is bonded to the concrete surface. Thus, although the application of EB-FRP wrapping around the perimeter of rectangular cross-sections leads to outstanding results, U-jacketing in shear-critical T-beams seems to undergo premature debonding failures resulting in significant reductions of the predictable strength. In this work, five shear-critical RC beams with T-shaped cross-section were constructed, strengthened and tested in four-point bending. Epoxy bonded carbon FRP (C-FRP) sheets were applied on the three sides and along the entire length of the shear-strengthened T-beams as external transverse reinforcement. Furthermore, the potential enhancement of the C-FRP sheets anchorage using bolted steel laminates has been examined. Test results indicated that although the C-FRP strengthened beams exhibited increased shear capacity, the brittle failure mode was not prevented due to the debonding of the FRP from the concrete surface. Nevertheless, the applied mechanical anchor of the C-FRP sheets delayed the debonding. Moreover, the design provisions of three different code standards (Greek Code of Interventions, Eurocode 8 and ACI Committee 440) concerning the shear capacity of T-shaped RC beams retrofitted with EB-FRP jackets or strips in U-jacketing configuration are investigated. The ability of these code standards to predict safe design estimations is checked against 165 test data from the current experimental project and data available in the literature.
Constantin E. Chalioris; Adamantis G. Zapris; Chris G. Karayannis. U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design. Fibers 2020, 8, 13 .
AMA StyleConstantin E. Chalioris, Adamantis G. Zapris, Chris G. Karayannis. U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design. Fibers. 2020; 8 (2):13.
Chicago/Turabian StyleConstantin E. Chalioris; Adamantis G. Zapris; Chris G. Karayannis. 2020. "U-Jacketing Applications of Fiber-Reinforced Polymers in Reinforced Concrete T-Beams against Shear—Tests and Design." Fibers 8, no. 2: 13.
The effectiveness of slightly reinforced thin U-shaped cementitious mortar jacketing for the repair of damaged shear-critical reinforced concrete beams is experimentally investigated. The test project includes two parts. In the first one, five concrete beams over-reinforced against flexure and under-reinforced against shear with different ratio of closed stirrups were initially subjected to monotonic loading until failure. The initially tested beams have been designed to fail in shear after wide diagonal cracking and to exhibit various strength and deformation capacities along with different levels of damages. In the second experimental part, the heavily damaged beams were jacketed with mild steel small diameter U-shaped transverse stirrups and longitudinal reinforcing bars. The retrofitted specimens using the proposed jacketing technique were tested again following the same four-point-bending load scheme. Based on the overall performance of the beams, it is deduced that the shear strength and deformation capability of the jacketed beams were substantially increased compared to the corresponding capacities of the initial beams. Further, although all beams failed in a shear abrupt manner, the retrofitted ones exhibited reduced brittleness and higher deflections at failure up to six times with respect to the initially tested specimens. The level of the initial damage influences the efficiency of the jacketing. Additional test data derived from relative shear-damaged beam specimens and retrofitted with similar thin jackets is also presented herein in order to establish the effectiveness of this repair system and to clarify the parameters affecting its structural reliability. Comparisons indicated that jacketed beams can alter the failure mode from brittle shear to ductile flexural under certain circumstances.
Constantin E. Chalioris; Violetta K. Kytinou; Maristella E. Voutetaki; Nikos A. Papadopoulos. Repair of Heavily Damaged RC Beams Failing in Shear Using U-Shaped Mortar Jackets. Buildings 2019, 9, 146 .
AMA StyleConstantin E. Chalioris, Violetta K. Kytinou, Maristella E. Voutetaki, Nikos A. Papadopoulos. Repair of Heavily Damaged RC Beams Failing in Shear Using U-Shaped Mortar Jackets. Buildings. 2019; 9 (6):146.
Chicago/Turabian StyleConstantin E. Chalioris; Violetta K. Kytinou; Maristella E. Voutetaki; Nikos A. Papadopoulos. 2019. "Repair of Heavily Damaged RC Beams Failing in Shear Using U-Shaped Mortar Jackets." Buildings 9, no. 6: 146.
Reinforced concrete (RC) beams under cyclic loading usually suffer from reduced aggregate interlock and eventually weakened concrete compression zone due to severe cracking and the brittle nature of compressive failure. On the other hand, the addition of steel fibers can reduce and delay cracking and increase the flexural/shear capacity and the ductility of RC beams. The influence of steel fibers on the response of RC beams with conventional steel reinforcements subjected to reversal loading by a four-point bending scheme was experimentally investigated. Three slender beams, each 2.5 m long with a rectangular cross-section, were constructed and tested for the purposes of this investigation; two beams using steel fibrous reinforced concrete and one with plain reinforced concrete as the reference specimen. Hook-ended steel fibers, each with a length-to-diameter ratio equal to 44 and two different volumetric proportions (1% and 3%), were added to the steel fiber reinforced concrete (SFRC) beams. Accompanying, compression, and splitting tests were also carried out to evaluate the compressive and tensile splitting strength of the used fibrous concrete mixtures. Test results concerning the hysteretic response based on the energy dissipation capabilities (also in terms of equivalent viscous damping), the damage indices, the cracking performance, and the failure of the examined beams were presented and discussed. Test results indicated that the SFRC beam demonstrated improved overall hysteretic response, increased absorbed energy capacities, enhanced cracking patterns, and altered failure character from concrete crushing to a ductile flexural one compared to the RC beam. The non-fibrous reference specimen demonstrated shear diagonal cracking failing in a brittle manner, whereas the SFRC beam with 1% steel fibers failed after concrete spalling with satisfactory ductility. The SFRC beam with 3% steel fibers exhibited an improved cyclic response, achieving a pronounced flexural behavior with significant ductility due to the ability of the fibers to transfer the developed tensile stresses across crack surfaces, preventing inclined shear cracks or concrete spalling. A report of an experimental database consisting of 39 beam specimens tested under cyclic loading was also presented in order to establish the effectiveness of steel fibers, examine the fiber content efficiency and clarify their role on the hysteretic response and the failure mode of RC structural members.
Constantin E. Chalioris; Parthena-Maria K. Kosmidou; Chris G. Karayannis. Cyclic Response of Steel Fiber Reinforced Concrete Slender Beams; an Experimental Study. Materials 2019, 12, 1398 .
AMA StyleConstantin E. Chalioris, Parthena-Maria K. Kosmidou, Chris G. Karayannis. Cyclic Response of Steel Fiber Reinforced Concrete Slender Beams; an Experimental Study. Materials. 2019; 12 (9):1398.
Chicago/Turabian StyleConstantin E. Chalioris; Parthena-Maria K. Kosmidou; Chris G. Karayannis. 2019. "Cyclic Response of Steel Fiber Reinforced Concrete Slender Beams; an Experimental Study." Materials 12, no. 9: 1398.
Innovative reinforcement as fiber-reinforced polymer (FRP) bars has been proposed as alternative for the substitution of the traditional steel bars in reinforced concrete (RC) structures. Although the advantages of this polymer reinforcement have long been recognised, the predominantly elastic response, the reduced bond capacity under repeated load and the low ductility of RC members with FRP bars restricted its wide application in construction so far. In this work, the behavior of seven slender concrete beams reinforced with carbon-FRP bars under increasing static loading is experimentally investigated. Load capacities, deflections, pre-cracking and after-cracking stiffness, sudden local drops of strength, failure modes, and cracking propagation have been presented and commented. Special attention has been given in the bond conditions of the anchorage lengths of the tensile carbon-FRP bars. The application of local confinement conditions along the anchorage lengths of the carbon-FRP bars in some specimens seems to influence their cracking behavior. Nevertheless, more research is required in this direction. Comparisons of experimental results for carbon-FRP beams with beams reinforced with glass-FRP bars extracted from recent literature are also presented and commented. Comparisons of the experimental results with the predictions according to ACI 440.1R-15 and to CSA S806-12 are also included herein.
Chris G. Karayannis; Parthena-Maria K. Kosmidou; Constantin E. Chalioris. Reinforced Concrete Beams with Carbon-Fiber-Reinforced Polymer Bars—Experimental Study. Fibers 2018, 6, 99 .
AMA StyleChris G. Karayannis, Parthena-Maria K. Kosmidou, Constantin E. Chalioris. Reinforced Concrete Beams with Carbon-Fiber-Reinforced Polymer Bars—Experimental Study. Fibers. 2018; 6 (4):99.
Chicago/Turabian StyleChris G. Karayannis; Parthena-Maria K. Kosmidou; Constantin E. Chalioris. 2018. "Reinforced Concrete Beams with Carbon-Fiber-Reinforced Polymer Bars—Experimental Study." Fibers 6, no. 4: 99.
The effectiveness of a new retrofitting technique to upgrade the structural behaviour of reinforced concrete (RC) deep beams without steel stirrups using carbon fibre-reinforced polymer (CFRP) ropes as the only transverse shear reinforcement is experimentally investigated. Five shear-critical beams with rectangular and T-shaped cross-section are tested under monotonic loading. The strengthening schemes include (a) one vertical and one diagonal single-link CFRP rope that are internally applied through the web of the rectangular beam using an embedded through-section (ETS) system and (b) two vertical U-shaped double-link ropes that are applied around the perimeter of the web of the flanged beam using a near-surface-mounted (NSM) system. In both cases, the free lengths of the CFRP ropes have been properly anchored using epoxy bonded lap splices of the rope as NSM at (a) the top and the bottom of the web of the rectangular beam and (b) the top of the slab of the T-beam. Promising results have been derived, since the proposed strengthening technique enhanced the strength and altered the brittle shear failure to a ductile flexural one. The experimental results of this study were also used to check the validity of an analytical approach to predict the strength of shear strengthened deep beams using FRP ropes as transverse link reinforcement.
Constantin E. Chalioris; Parthena-Maria K. Kosmidou; Nikos A. Papadopoulos. Investigation of a New Strengthening Technique for RC Deep Beams Using Carbon FRP Ropes as Transverse Reinforcements. Fibers 2018, 6, 52 .
AMA StyleConstantin E. Chalioris, Parthena-Maria K. Kosmidou, Nikos A. Papadopoulos. Investigation of a New Strengthening Technique for RC Deep Beams Using Carbon FRP Ropes as Transverse Reinforcements. Fibers. 2018; 6 (3):52.
Chicago/Turabian StyleConstantin E. Chalioris; Parthena-Maria K. Kosmidou; Nikos A. Papadopoulos. 2018. "Investigation of a New Strengthening Technique for RC Deep Beams Using Carbon FRP Ropes as Transverse Reinforcements." Fibers 6, no. 3: 52.
Constantin E. Chalioris; Kosmas Bantilas. Shear strength of reinforced concrete beam-column joints with crossed inclined bars. Engineering Structures 2017, 140, 241 -255.
AMA StyleConstantin E. Chalioris, Kosmas Bantilas. Shear strength of reinforced concrete beam-column joints with crossed inclined bars. Engineering Structures. 2017; 140 ():241-255.
Chicago/Turabian StyleConstantin E. Chalioris; Kosmas Bantilas. 2017. "Shear strength of reinforced concrete beam-column joints with crossed inclined bars." Engineering Structures 140, no. : 241-255.
The application of an innovative real-time structural health monitoring system is studied through tests performed on flexural and shear-critical reinforced concrete elements subjected to monotonic and cyclic loading. The test set-up involves a Wireless impedance/Admittance Monitoring System (WiAMS) that comprises specially manufactured small-sized portable devices to collect the voltage frequency responses of an array of smart piezoelectric transducers mounted on structural members of reinforced concrete constructions. Damage detection and evaluation is achieved using the in-situ measurements of the integrated piezoelectric sensors/actuators signals at the healthy state of the member and at various levels of damage during testing. Three different installations of Piezoelectric lead Zirconate Titanate (PZT) transducers are examined: (a) epoxy bonded PZTs on the surface of the steel reinforcing bars of the flexural elements, (b) PZTs embedded inside the concrete mass of the shear-critical beams and (c) externally epoxy bonded PZTs attached to the concrete surface of the tested elements. The smart piezoelectric materials have been pre-installed before testing based on the potential flexural and shear cracking of the elements. Quantitative assessment of the examined damage levels using values for the statistical damage index is also presented and discussed. Voltage signals and index values acquired from the PZTs’ measurements using the proposed wireless monitoring technique demonstrated obvious discrepancies between the frequency response of the healthy and the examined damage levels for every tested element. These differences clearly indicate the presence of damage, whereas their gradation reveals the magnitude of the occurred damage. Promising results concerning the prediction of the forthcoming fatal failures at early damage stages have also been derived.
Constantin E. Chalioris; Chris G. Karayannis; Georgia M. Angeli; Nikos A. Papadopoulos; Maria J. Favvata; Costas P. Providakis. Applications of smart piezoelectric materials in a wireless admittance monitoring system (WiAMS) to Structures—Tests in RC elements. Case Studies in Construction Materials 2016, 5, 1 -18.
AMA StyleConstantin E. Chalioris, Chris G. Karayannis, Georgia M. Angeli, Nikos A. Papadopoulos, Maria J. Favvata, Costas P. Providakis. Applications of smart piezoelectric materials in a wireless admittance monitoring system (WiAMS) to Structures—Tests in RC elements. Case Studies in Construction Materials. 2016; 5 ():1-18.
Chicago/Turabian StyleConstantin E. Chalioris; Chris G. Karayannis; Georgia M. Angeli; Nikos A. Papadopoulos; Maria J. Favvata; Costas P. Providakis. 2016. "Applications of smart piezoelectric materials in a wireless admittance monitoring system (WiAMS) to Structures—Tests in RC elements." Case Studies in Construction Materials 5, no. : 1-18.
This study presents an experimental effort for the damage assessment of concrete reinforcing bars using bonded piezoelectric transducers and the implementation of an integration analytical approach based on the electromechanical admittance method. Tests are performed in (i) single steel reinforcing bars with predefined and artificially induced damages corresponding to two different damage states and (ii) steel reinforcing bars embedded in typical large scale reinforced concrete beams subjected to flexural load at two different loading levels (before and after yielding) that inevitably cause two different damage levels. The damage of the embedded steel bars in the concrete beams after yielding is the result of excessive elongation of the bars due to yielding caused by flexural deformation of the beams. Test measurements of healthy and damaged steel bars and reinforced concrete beams have been conducted using the developed monitoring system. The experimental program comprises data acquisition of current intensity curves for healthy and damaged bars as detected by the test instrumentation and implementation of the adopted admittance-based procedure to evaluate damages at different levels. It can be concluded that the sensitivity of the piezoelectric transducers greatly depends on the selection of the excitation frequencies. Admittance signatures showed a clear gradation of the examined damage levels. The experimental results provide cogent evidence that piezoelectric lead zirconate titanate transducers are sensitive to damage detection in concrete and in steel reinforcing bars from an early stage of the performed tests. Thus, the use of these sensors for monitoring and detecting concrete cracking and steel yielding by employing the electromechanical admittance approach can be considered as a highly promising non-destructive structural health monitoring method.
Chris G. Karayannis; Constantin E. Chalioris; Georgia M. Angeli; Nikos A. Papadopoulos; Maria J. Favvata; Costas P. Providakis. Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors. Construction and Building Materials 2016, 105, 227 -244.
AMA StyleChris G. Karayannis, Constantin E. Chalioris, Georgia M. Angeli, Nikos A. Papadopoulos, Maria J. Favvata, Costas P. Providakis. Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors. Construction and Building Materials. 2016; 105 ():227-244.
Chicago/Turabian StyleChris G. Karayannis; Constantin E. Chalioris; Georgia M. Angeli; Nikos A. Papadopoulos; Maria J. Favvata; Costas P. Providakis. 2016. "Experimental damage evaluation of reinforced concrete steel bars using piezoelectric sensors." Construction and Building Materials 105, no. : 227-244.
Chris G. Karayannis; Maristella E. Voutetaki; Constantin E. Chalioris; Costas P. Providakis; Georgia M. Angeli. Detection of flexural damage stages for RC beams using Piezoelectric sensors (PZT). Smart Structures and Systems 2015, 15, 997 -1018.
AMA StyleChris G. Karayannis, Maristella E. Voutetaki, Constantin E. Chalioris, Costas P. Providakis, Georgia M. Angeli. Detection of flexural damage stages for RC beams using Piezoelectric sensors (PZT). Smart Structures and Systems. 2015; 15 (4):997-1018.
Chicago/Turabian StyleChris G. Karayannis; Maristella E. Voutetaki; Constantin E. Chalioris; Costas P. Providakis; Georgia M. Angeli. 2015. "Detection of flexural damage stages for RC beams using Piezoelectric sensors (PZT)." Smart Structures and Systems 15, no. 4: 997-1018.
The use of photogrammetric surveys for the recording of the structural system status for historic masonry buildings is a new and sound tool for in-depth pathology understanding and rehabilitation decision-making. In this study, the structural system of two historic masonry buildings is investigated based on the recording data obtained via photogrammetry. The first one is a four-storey traditional tobacco warehouse of the late 19th century in Alexandroupolis, Northern Greece, which has been partially collapsed in 2005 and constituted an extremely dangerous working environment. Therefore, the photogrammetric recording was the only really accurate and safe in situ measurement procedure of the existing damaged structural system of the building. The second one is an old customs house located in the old historic town of Nafplio, Southern Greece, and specifically in front of the central part of the port. It was built around the middle of the 19th century by the well-known Architect S. Kleanthis. Its architectural, structural and morphological characteristics along with its artistic details have been excellently brought out through the advanced method of photogrammetry. Simultaneously, this detailed display of the structural system pointed out its pathology. This way, all the necessary information for the presented structures have been acquired with an appropriate accuracy in order to assist the Engineer to choose the proper repairing and strengthening techniques for the renovation and the re-use of these historic buildings; finally proposed rehabilitation techniques are also presented. The recording procedure used, combines the conventional topographic surveys and the photogrammetric image processing for the formation of all the façades’ orthoimages. The orthoimages were used as background information to digitize details of the buildings façades in a CAD environment. The Photomodeler software and the freeware application Hugin has been used to create respectively a detailed 3D model and an interactive panorama file of the buildings. A proper intervention plan is presented and commented for each building.
Constantin E. Chalioris; Vassilios E. Tsioukas; Chris G. Karayannis. Recording and Rehabilitation Procedures for Historic Masonry Buildings. Computational Methods in Applied Sciences 2015, 341 -364.
AMA StyleConstantin E. Chalioris, Vassilios E. Tsioukas, Chris G. Karayannis. Recording and Rehabilitation Procedures for Historic Masonry Buildings. Computational Methods in Applied Sciences. 2015; ():341-364.
Chicago/Turabian StyleConstantin E. Chalioris; Vassilios E. Tsioukas; Chris G. Karayannis. 2015. "Recording and Rehabilitation Procedures for Historic Masonry Buildings." Computational Methods in Applied Sciences , no. : 341-364.
Damage detection at early cracking stages in shear-critical reinforced concrete beams, before further deterioration and their inevitable brittle shear failure is crucial for structural safety and integrity. The effectiveness of a structural health monitoring technique using the admittance measurements of piezoelectric transducers mounted on a reinforced concrete beam without shear reinforcement is experimentally investigated. Embedded “smart aggregate” transducers and externally bonded piezoelectric patches have been placed in arrays at both shear spans of the beam. Beam were tested till total shear failure and monitored at three different states; healthy, flexural cracking and diagonal cracking. Test results showed that transducers close to the critical diagonal crack provided sound and graduated discrepancies between the admittance responses at the healthy state and thedamage levels.Damage assessment using statistical indices calculated from the measurements of all transducers was also attempted. Rational changes of the index values were obtained with respect to the increase of the damage. Admittance responses and index values of the transducers located on the shear span where the critical diagonal crack formed provided cogent evidence of damage. On the contrary, negligible indication of damage was yielded by the responses of the transducers located on the other shear span, where no diagonal cracking occurred.
Constantin E. Chalioris; Nikos A. Papadopoulos; Georgia M. Angeli; Chris G. Karayannis; Asterios A. Liolios; Costas P. Providakis. Damage Evaluation in Shear-Critical Reinforced Concrete Beam using Piezoelectric Transducers as Smart Aggregates. Open Engineering 2015, 5, 1 .
AMA StyleConstantin E. Chalioris, Nikos A. Papadopoulos, Georgia M. Angeli, Chris G. Karayannis, Asterios A. Liolios, Costas P. Providakis. Damage Evaluation in Shear-Critical Reinforced Concrete Beam using Piezoelectric Transducers as Smart Aggregates. Open Engineering. 2015; 5 (1):1.
Chicago/Turabian StyleConstantin E. Chalioris; Nikos A. Papadopoulos; Georgia M. Angeli; Chris G. Karayannis; Asterios A. Liolios; Costas P. Providakis. 2015. "Damage Evaluation in Shear-Critical Reinforced Concrete Beam using Piezoelectric Transducers as Smart Aggregates." Open Engineering 5, no. 1: 1.
Constantin E. Chalioris; Georgia E. Thermou; Stavroula J. Pantazopoulou. Behaviour of rehabilitated RC beams with self-compacting concrete jacketing – Analytical model and test results. Construction and Building Materials 2014, 55, 257 -273.
AMA StyleConstantin E. Chalioris, Georgia E. Thermou, Stavroula J. Pantazopoulou. Behaviour of rehabilitated RC beams with self-compacting concrete jacketing – Analytical model and test results. Construction and Building Materials. 2014; 55 ():257-273.
Chicago/Turabian StyleConstantin E. Chalioris; Georgia E. Thermou; Stavroula J. Pantazopoulou. 2014. "Behaviour of rehabilitated RC beams with self-compacting concrete jacketing – Analytical model and test results." Construction and Building Materials 55, no. : 257-273.
Constantin Chalioris; Chris G. Karayannis. Experimental investigation of RC beams with rectangular spiral reinforcement in torsion. Engineering Structures 2013, 56, 286 -297.
AMA StyleConstantin Chalioris, Chris G. Karayannis. Experimental investigation of RC beams with rectangular spiral reinforcement in torsion. Engineering Structures. 2013; 56 ():286-297.
Chicago/Turabian StyleConstantin Chalioris; Chris G. Karayannis. 2013. "Experimental investigation of RC beams with rectangular spiral reinforcement in torsion." Engineering Structures 56, no. : 286-297.
The behaviour of reinforced concrete shear-critical beams with rectangular cross-section and continuous rectangular spiral reinforcement as transverse reinforcement under monotonous loading is experimentally investigated. Further, an advanced rectangular spiral reinforcement that has shear-favourably inclined vertical links is also presented and tested as shear reinforcement. The experimental program includes eight (8) beams. Test results clearly indicate that the use of rectangular spiral reinforcement provided enhanced bearing capacity and improved shear performance in the examined beams. Beams with spiral reinforcement spacing at 120 mm and 80 mm exhibited 14.9% and 14.7% increased shear capacity with respect to the corresponding beams with stirrups, respectively. Furthermore beams with advanced spirals spacing at 120 mm and 80 mm exhibited 17.2% and 21.7% increased shear capacity with respect to the corresponding beams with stirrups, respectively. Moreover, the beams with advanced spirals exhibited deformation ductility values 2.10 and 2.60, respectively, demonstrating this way improved post-peak deformation ductility compared to the beams with equal quantity of commonly used stirrups.
Chris G. Karayannis; Constantin E. Chalioris. Shear tests of reinforced concrete beams with continuous rectangular spiral reinforcement. Construction and Building Materials 2013, 46, 86 -97.
AMA StyleChris G. Karayannis, Constantin E. Chalioris. Shear tests of reinforced concrete beams with continuous rectangular spiral reinforcement. Construction and Building Materials. 2013; 46 ():86-97.
Chicago/Turabian StyleChris G. Karayannis; Constantin E. Chalioris. 2013. "Shear tests of reinforced concrete beams with continuous rectangular spiral reinforcement." Construction and Building Materials 46, no. : 86-97.