Experimental study of the torsion of reinforced concrete members

Chalioris, Constantin E. Techno-Press 2006 Structural Engineering and Mechanics, An Int'l Jou Vol.23 No.6

This paper presents the results of an experimental investigation on the behaviour of 56 reinforced concrete beams subjected to pure torsion. The reported results include the behaviour curves, the failure modes and the values of the pre-cracking torsional stiffness, the cracking and ultimate torsional moments and the corresponding twists. The influence of the volume of stirrups, the height to width ratios and the arrangement of longitudinal bars on the torsional behaviour is discussed. In order to describe the entire torsional behaviour of the tested beams, the combination of two different analytical models is used. The prediction of the elastic till the first cracking part is achieved using a smeared crack analysis for plain concrete in torsion, whereas for the description of the post-cracking response the softened truss model is used. A simple modification to the softened truss model to include the effect of confinement is also attempted. Calculated torsional behaviour of the tested beams and 21 beams available in the literature are compared with the experimental ones and a very good agreement is observed.

Flexural analysis of steel fibre-reinforced concrete members

Constantin E. Chalioris,Thomas A. Panagiotopoulos 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.1

A numerical approach for the evaluation of the flexural response of Steel Fibrous Concrete (SFC) cross-sections with arbitrary geometry, with or without conventional steel longitudinal reinforcing bars is proposed. Resisting bending moment versus curvature curves are calculated using verified non-linear constitutive stress-strain relationships for the SFC under compression and tension which include post-peak and post-cracking softening parts. A new compressive stress-strain model for SFC is employed that has been derived from test data of 125 stress-strain curves and 257 strength values providing the overall compressive behaviour of various SFC mixtures. The proposed sectional analysis is verified using existing experimental data of 42 SFC beams, and it predicts the flexural capacity and the curvature ductility of SFC members reasonably well. The developed approach also provides rational and more accurate compressive and tensile stress-strain curves along with bending moment versus curvature curves with regards to the predictions of relevant existing models.

Strength of prestressed concrete beams in torsion

Karayannis, Chris G.,Chalioris, Constantin E. Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.10 No.2

An analytical model with tension softening for the prediction of the capacity of prestressed concrete beams under pure torsion and under torsion combined with shear and flexure is introduced. The proposed approach employs bilinear stress-strain relationship with post cracking tension softening branch for the concrete in tension and special failure criteria for biaxial stress states. Further, for the solution of the governing equations a special numerical scheme is adopted which can be applied to elements with practically any cross-section since it utilizes a numerical mapping. The proposed method is mainly applied to plain prestressed concrete elements, but is also applicable to prestressed concrete beams with light transverse reinforcement. The aim of the present work is twofold; first, the validation of the approach by comparison between experimental results and analytical predictions and second, a parametrical study of the influence of concentric and eccentric prestressing on the torsional capacity of concrete elements and the interaction between torsion and shear for various levels of prestressing. The results of this investigation presented in the form of interaction curves, are compared to experimental results and code provisions.

Flexural/shear strength of RC beams with longitudinal FRP bars An analytical approach

Parthena-Maria K. Kosmidou,Constantin E. Chalioris,Chris G. Karayannis 사단법인 한국계산역학회 2018 Computers and Concrete, An International Journal Vol.22 No.6

An analytical methodology for the calculation of the flexural and the shear capacity of concrete members with Fibre-Reinforced-Polymer (FRP) bars as tensional reinforcement is proposed. The flexural analysis is initially based on the design provisions of ACI 440.1R-15 which have properly been modified to develop general charts that simplify computations and provide hand calculations. The specially developed charts include non-dimensional variables and can easily be applied in sections with various geometrical properties, concrete grade and FRP properties. The proposed shear model combines three theoretical considerations to facilitate calculations. A unified flexural/shear approach is developed in flow chart which can be used to estimate the ultimate strength and the expected failure mode of a concrete beam reinforced with longitudinal FRP bars, with or without transverse reinforcement. The proposed methodology is verified using existing experimental data of 138 beams from the literature, and it predicts the load-bearing capacity and the failure mode with satisfactory accuracy.

Detection of flexural damage stages for RC beams using Piezoelectric sensors (PZT)

Karayannis, Chris G.,Voutetaki, Maristella E.,Chalioris, Constantin E.,Providakis, Costas P.,Angeli, Georgia M. Techno-Press 2015 Smart Structures and Systems, An International Jou Vol.15 No.4

Structural health monitoring along with damage detection and assessment of its severity level in non-accessible reinforced concrete members using piezoelectric materials becomes essential since engineers often face the problem of detecting hidden damage. In this study, the potential of the detection of flexural damage state in the lower part of the mid-span area of a simply supported reinforced concrete beam using piezoelectric sensors is analytically investigated. Two common severity levels of flexural damage are examined: (i) cracking of concrete that extends from the external lower fiber of concrete up to the steel reinforcement and (ii) yielding of reinforcing bars that occurs for higher levels of bending moment and after the flexural cracking. The purpose of this investigation is to apply finite element modeling using admittance based signature data to analyze its accuracy and to check the potential use of this technique to monitor structural damage in real-time. It has been indicated that damage detection capability greatly depends on the frequency selection rather than on the level of the harmonic excitation loading. This way, the excitation loading sequence can have a level low enough that the technique may be considered as applicable and effective for real structures. Further, it is concluded that the closest applied piezoelectric sensor to the flexural damage demonstrates higher overall sensitivity to structural damage in the entire frequency band for both damage states with respect to the other used sensors. However, the observed sensitivity of the other sensors becomes comparatively high in the peak values of the root mean square deviation index.

Detection of flexural damage stages for RC beams using Piezoelectric sensors (PZT)

Chris G. Karayannis,Maristella E. Voutetaki,Constantin E. Chalioris,Costas P. Providakis,Georgia M. Angeli 국제구조공학회 2015 Smart Structures and Systems, An International Jou Vol.15 No.4

Structural health monitoring along with damage detection and assessment of its severity level innon-accessible reinforced concrete members using piezoelectric materials becomes essential since engineersoften face the problem of detecting hidden damage. In this study, the potential of the detection of flexuraldamage state in the lower part of the mid-span area of a simply supported reinforced concrete beam usingpiezoelectric sensors is analytically investigated. Two common severity levels of flexural damage areexamined: (i) cracking of concrete that extends from the external lower fiber of concrete up to the steelreinforcement and (ii) yielding of reinforcing bars that occurs for higher levels of bending moment and afterthe flexural cracking. The purpose of this investigation is to apply finite element modeling using admittancebased signature data to analyze its accuracy and to check the potential use of this technique to monitorstructural damage in real-time. It has been indicated that damage detection capability greatly depends on thefrequency selection rather than on the level of the harmonic excitation loading. This way, the excitationloading sequence can have a level low enough that the technique may be considered as applicable andeffective for real structures. Further, it is concluded that the closest applied piezoelectric sensor to theflexural damage demonstrates higher overall sensitivity to structural damage in the entire frequency band forboth damage states with respect to the other used sensors. However, the observed sensitivity of the othersensors becomes comparatively high in the peak values of the root mean square deviation index.

On the mechanical characteristics of fiber reinforced polymer concrete

Asteris, Panagiotis G.,Naseri, Hamid,Hajihassani, Mohsen,Kharghani, Mehdi,Chalioris, Constantin E. Techno-Press 2021 Advances in concrete construction Vol.12 No.4

Polymer Concrete (PC) is a composite material made by fully replacing the cement hydrate binders of conventional cement concrete with polymer binders or liquid resins. As expected, the physico-mechanical properties of PC concrete are governed by the composition of the PC mixture. The present study aims to examine the effect of the aggregate type and of the addition of steel fibers on the mechanical properties of PC. In particular, two PC concrete mixtures, using granite or silica aggregates, have been developed and the effect of the addition of steel fibers has been investigated. The PC mixtures are characterized by mechanical tests such as the compression test, the flexural test, the splitting tensile test and the estimation of the energy absorption. The results of this study demonstrate a relative superiority, in terms of mechanical properties, of the PC made with granite aggregates as compared to that of the silica aggregate mixture. Moreover, the addition of steel fibers on PC mixtures showed a significant increase of the compressive toughness, of the splitting tensile and of the flexural strength, whereas the Young's modulus and compressive strength showed a slight increase.

Green-blue intracytoplasmic inclusions in the bone marrow in severe COVID-19

Elpiniki Kritikou-Griva,Ioulia Chaliori,Nikolaos J. Tsagarakis,Georgios Androutsos,Sofia Chaniotaki,Georgios Paterakis 대한혈액학회 2021 Blood Research Vol.56 No.3

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