Inter-story pounding between multistory reinforced concrete structures

Karayannis, Chris G.,Favvata, Maria J. Techno-Press 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.5

The influence of the inter-story structural pounding on the seismic behaviour of adjacent multistory reinforced concrete structures with unequal total heights and different story heights is investigated. Although inter-story pounding is a common case in practice, it has not been studied before in the literature as far as the authors are aware. Fifty two pounding cases, each one for two different seismic excitations, are examined. From the results it can be deduced that: (i) The most important issue in the inter-story pounding is the local effect on the external column of the tall building that suffers the impact from the upper floor slab of the adjacent shorter structure. (ii) The ductility demands for this column are increased comparing with the ones without the pounding effect. In the cases that the two buildings are in contact these demands appear to be critical since they are higher than the available ductility values. In the cases that there is a small distance between the interacting buildings the ductility demands of this column are also higher than the ones of the same column without the pounding effect but they appear to be lower than the available ductility values. (iii) It has to be stressed that in all the examined cases the developed shear forces of this column exceeded the shear strength. Thus, it can be concluded that in inter-story pounding cases the column that suffers the impact is always in a critical condition due to shear action and, furthermore, in the cases that the two structures are in contact from the beginning this column appears to be critical due to high ductility demands as well. The consequences of the impact can be very severe for the integrity of the column and may be a primary cause for the initiation of the collapse of the structure. This means that special measures have to be taken in the design process first for the critically increased shear demands and secondly for the high ductility demands.

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.

Nonlinear analysis and tests of steel-fiber concrete beams in torsion

Karayannis, Chris G. Techno-Press 2000 Structural Engineering and Mechanics, An Int'l Jou Vol.9 No.4

An analytical approach for the prediction of the behaviour of steel-fiber reinforced concrete beams subjected to torsion is described. The analysis method employs a special stress-strain model with a non-linear post cracking branch for the material behaviour in tension. Predictions of this model for the behaviour of steel-fiber concrete in direct tension are also presented and compared with results from tests conducted for this reason. Further in this work, the validation of the proposed torsional analysis by providing comparisons between experimental curves and analytical predictions, is attempted. For this purpose a series of 10 steel-fiber concrete beams with various cross-sections and steel-fiber volume fractions tested in pure torsion, are reported here. Furthermore, experimental information compiled from works around the world are also used in an attempt to establish the validity of the described approach based on test results of a broad range of studies. From these comparisons it is demonstrated that the proposed analysis describes well the behaviour of steel-fiber concrete in pure torsion even in the case of elements with non-rectangular cross-sections.

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.

Inter-story pounding between multistory reinforced concrete structures

Chris G. Karayannis,Maria J. Favvata 국제구조공학회 2005 Structural Engineering and Mechanics, An Int'l Jou Vol.20 No.5

The influence of the inter-story structural pounding on the seismic behaviour of adjacentmultistory reinforced concrete structures with unequal total heights and different story heights isinvestigated. Although inter-story pounding is a common case in practice, it has not been studied beforein the literature as far as the authors are aware. Fifty two pounding cases, each one for two diferentthe inter-story pounding is the local effect on the external column of the tall building that sufers theimpact from the upper floor slab of the adjacent shorter structure. (ii) The ductility demands for thiscolumn are increased comparing with the ones without the pounding effect. In the cases that the twobuildings are in contact these demands appear to be critical since they are higher than the availabledemands of this column are also higher than the ones of the same column without the pounding effect butthey appear to be lower than the available ductility values. (i) It has to be stresed that in all theexamined cases the developed shear forces of this column exceeded the shear strength. Thus, it can beconcluded that in inter-story pounding cases the column that suffers the impact is always in a criticalbegining this column appears to be critical due to high ductility demands as well. The consequences ofthe impact can be very severe for the integrity of the column and may be a primary cause for theinitiation of the collapse of the structure. This means that special measures have to be taken in the designprocess first for the critically increased shear demands and secondly for the high ductility demands.

Synthesis of microwave-sintered ceramics from lignite fly and bottom ashes

Vayos G. Karayannis 한양대학교 세라믹연구소 2013 Journal of Ceramic Processing Research Vol.14 No.1

The fracture toughness of glass ceramics produced from the fly ash of the Seyitömer power plant of Turkey has been investigated using an indentation fracture technique. In this process, fly ash was melted and cast as a glass. The glass materials produced were heat treated at 1073 K, 1123 K and 1173 K for 30-240 minutes in order to obtain glass-ceramics. X-ray diffraction analysis (XRD) showed that the phases formed in the glass ceramics were diopsite and augite. Atomic force microscope (AFM) images were used for the examination of the surface structure of the glass ceramics. The fracture toughness of the glass ceramics ranged from 1.80 ± 0.15 MPa.m1/2 to 2.92 ± 0.65 MPa.m1/2 depending on the treatment temperature and time. The higher the crystallization temperature and the longer the treatment time, the higher the fracture toughness became.

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.

Experimental investigation of infilled r/c frames with eccentric openings

Kakaletsis, D.,Karayannis, C. Techno-Press 2007 Structural Engineering and Mechanics, An Int'l Jou Vol.26 No.3

The influence of masonry infills with eccentric openings on the seismic performance of reinforced concrete (r/c) frames that were designed in accordance with current code provisions are investigated. Eight 1/3-scale, single-story, single-bay frame specimens were tested under cyclic horizontal loading up to a drift level of 4%. In all examined cases the shear strength of columns was higher than the cracking shear strength of solid infill. The parameters investigated include the shape and the location of the opening. Assessment of the behavior of the frames is also attempted, based on the observed failure modes, strength, stiffness, ductility, energy dissipation capacity and degradation from cycling loading. Based on these results there can be deduced that masonry infills with eccentrically located openings has been proven to be beneficial to the seismic capacity of the bare r/c frames in terms of strength, stiffness, ductility and energy dissipation. The location of the opening must be as near to the edge of the infill as possible in order to provide an improvement in the performance of the infilled frame.

Influence of exterior joint effect on the inter-story pounding interaction of structures

Favvata, Maria J.,Karayannis, Chris G.,Liolios, Asterios A. Techno-Press 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.33 No.2

The seismic induced interaction between multistory structures with unequal story heights (inter-story pounding) is studied taking into account the local response of the exterior beam-column joints. Although several parameters that influence the structural pounding have been studied sofar, the role of the joints local inelastic behaviour has not been yet investigated in the literature as key parameter for the pounding problem. Moreover, the influence of the infill panels as an additional parameter for the local damage effect of the joints on the inter-story pounding phenomenon is examined. Thirty six interaction cases between a multistory frame structure and an adjacent shorter and stiffer structure are studied for two different seismic excitations. The results are focused: (a) on the local response of the critical external column of the multistory structure that suffers the hit from the slab of the adjacent shorter structure, and (b) on the local response of the exterior beam-column joints of the multistory structure. Results of this investigation demonstrate that the possible local inelastic response of the exterior joints may be in some cases beneficial for the seismic behaviour of the critical column that suffers the impact. However, in all the examined cases the developing demands for deformation of the exterior joints are substantially increased and severe damages can be observed due to the pounding effect. The presence of the masonry infill panels has also been proved as an important parameter for the response of the exterior beam-column joints and thus for the safety of the building. Nevertheless, in all the examined inter-story pounding cases the presence of the infills was not enough for the total amelioration of the excessive demands for shear and ductility of the column that suffers the impact.

Influence of exterior joint effect on the inter-story pounding interaction of structures

Maria J. Favvata,Chris G. Karayannis,Asterios A. Liolios 국제구조공학회 2009 Structural Engineering and Mechanics, An Int'l Jou Vol.33 No.2

The seismic induced interaction between multistory structures with unequal story heights (inter-story pounding) is studied taking into account the local response of the exterior beam-column joints. Although several parameters that influence the structural pounding have been studied sofar, the role of the joints local inelastic behaviour has not been yet investigated in the literature as key parameter for the pounding problem. Moreover, the influence of the infill panels as an additional parameter for the local damage effect of the joints on the inter-story pounding phenomenon is examined. Thirty six interaction cases between a multistory frame structure and an adjacent shorter and stiffer structure are studied for two different seismic excitations. The results are focused: (a) on the local response of the critical external column of the multistory structure that suffers the hit from the slab of the adjacent shorter structure, and (b) on the local response of the exterior beam-column joints of the multistory structure. Results of this investigation demonstrate that the possible local inelastic response of the exterior joints may be in some cases beneficial for the seismic behaviour of the critical column that suffers the impact. However, in all the examined cases the developing demands for deformation of the exterior joints are substantially increased and severe damages can be observed due to the pounding effect. The presence of the masonry infill panels has also been proved as an important parameter for the response of the exterior beam-column joints and thus for the safety of the building. Nevertheless, in all the examined inter-story pounding cases the presence of the infills was not enough for the total amelioration of the excessive demands for shear and ductility of the column that suffers the impact.