Papehttp://ascelibrary.org/doi/abs/10.1061/%28ASrs by Triantafyllos K . Makarios, Ph.D. Professor
The Open Construction & Building Technology Journal, 2023
In this paper, a new method for damage detection in reinforced concrete multi-storey frames is pr... more In this paper, a new method for damage detection in reinforced concrete multi-storey frames is presented. Methods: The proposed new methodology is a hybrid technique consisting of two parts. The first step involves determining the seismic pushover capacity curve of the structure, and the second step includes formulating the diagram of the instantaneous eigenfequencies of the structure in the nonlinear regime. With reference to this diagram, more details are given in the text. To estimate the equivalent target displacement defined at the top of the structure, which corresponds to the instantaneous eigenfrequencies of a structure with damage, the diagram of these eigenfrequencies is combined with the seismic pushover capacity curve of the structure. Thus, the target displacement at the top of the frame is calculated.
The application of the equivalent static method (or simplified spectral method) for the seismic d... more The application of the equivalent static method (or simplified spectral method) for the seismic design of the spatial asymmetric buildings presupposes the existence of the elastic axis (center of stiffness) -geometrical locus of the elastic centers of the floors- so as to identify the eccentricity of the static seismic loads. But, while in single-storey buildings the elastic center is always defined and has determined static properties, in multi-storey buildings the above properties are not, in general, identified and the definition of the vertical elastic axis is, in general, impossible. In the present doctoral thesis we will first proceed to the analysis of the cases of existence and non-existence of the elastic axis and of a building’s principal bending planes, according to research data. Following this stage, and based on the buildings’ “optimum torsion” criterion, the fictitious elastic axis is defined for every case of frame-wall multistorey building that is regular in elevati...
This paper deals with the earthquake response of the historic traditional buildings of Lefkas Isl... more This paper deals with the earthquake response of the historic traditional buildings of Lefkas Island, Greece. These structures have up to four storeys and are located in the central area of the Lefkas town. The main characteristic of these buildings is their dual bearing system, which consists of a spatial timber multi-storey system and a single-storey masonry wall system, respectively. The multi-storey wooden system possesses in elevation various diagonal trusses infilled by bricks with lime mortar. The top of the building is spatially connected by means of a tiled wooden truss roof. During the strong earthquake at Lefkas Island (August 14, 2003) the earthquake behavior of the above-mentioned buildings was very good. Only damages that could be repaired (without total collapse) were observed, e.g. partial collapse of masonry walls at ground floor, various cracks in the vicinity of masonry<br> openings. In the timber multi-storey frames many bricks cracked and fell out of plane...
Στην εργασία αυτή παρουσιάζεται ένα αριθμητικό παράδειγμα ενός στρεπτικά ευαίσθητου, διπλά ασύμμε... more Στην εργασία αυτή παρουσιάζεται ένα αριθμητικό παράδειγμα ενός στρεπτικά ευαίσθητου, διπλά ασύμμετρου μονώροφου κτιρίου από οπλισμένο σκυρόδεμα (Ο/Σ), ώστε να αναδειχθεί η βήμα προς βήμα εφαρμογή μιας νέας τεκμηριωμένης διαδικασίας μη-γραμμικής στατικής (pushover) ανάλυσης που προτάθηκε πρόσφατα από τους συγγραφείς. Κατά την εφαρμογή της προτεινόμενης διαδικασίας, και λαμβάνοντας υπόψη πλήρως το φαινόμενο της στρέψης του κτιρίου στην μη-γραμμική περιοχή, το πλευρικό στατικό φορτίο του ορόφου προτείνεται να εφαρμόζεται πάντοτε έκκεντρα σε σχέση με το Κέντρο Μάζας του διαφράγματος, κατά μήκος των πραγματικών ή πλασματικών κύριων (κατάλληλων) διευθύνσεων του κτιρίου, χρησιμοποιώντας τις ανελαστικές εκκεντρότητες σχεδιασμού, οι οποίες προέρχονται από τη σύνθεση κατάλληλων ανελαστικών δυναμικών εκκεντροτήτων με τις αντίστοιχες τυχηματικές. Οι τιμές των ανελαστικών δυναμικών εκκεντροτήτων για τη δύσκαμπτη και εύκαμπτη πλευρά του κτιρίου έχουν προκύψει από εκτεταμένη παραμετρική ανάλυση μο...
For the estimation of the dynamic properties of structures, forced vibration tests are often used... more For the estimation of the dynamic properties of structures, forced vibration tests are often used. Various methodologies for the predetermination of the force level and the position of the shaker have been developed. In the present work the methodologies of field-testing and analytical evaluations of the structural response are defined through an interactive procedure. During field-testing, a group of parameters may vary, such as the position and the direction of the excitation force, and the amount, eccentricity and frequency of the rotating mass. These parameters should be defined and estimated before the actual testing, in order to perform an effective test plan. For this purpose, the structure under investigation is analytically modeled and its dynamic properties (mode shapes and frequencies) are estimated. Parametric analyses follow, by considering a vibrating mass on the analytical model for the simulation of the vibrator action. These analyses are performed for various positi...
Engineering Structures, 2021
Abstract This paper proposes a new direct Displacement-based procedure of nonlinear static (pusho... more Abstract This paper proposes a new direct Displacement-based procedure of nonlinear static (pushover) analysis on multi-storey reinforced concrete (R/C) buildings designed to exclude floor plastic mechanism formation. The proposed procedure can be easily applied with safety on all asymmetric multi-storey R/C buildings with the necessary regularity in elevation required by the seismic codes, irrespective of torsional sensitivity or high asymmetry. The proposed methodology places under full control by the designer of both the seismic inelastic angular deformation demands of the building floors in elevation and the actual seismic floor inelastic displacement demands that develop at the Near Collapse state of the building. The proposed procedure takes full account of the following: (a) the coupling between translational and rotational degrees of freedom at the floor-diaphragms, (b) the contributions resulting from the action of higher modes in the linear area of response, and (c) the P- Delta effects. According to the proposed procedure, a vector of enforced-displacements is applied on the floor-diaphragms and a set of sixteen final nonlinear static analysis cases coming from all possible sign combinations is performed having as action the previous floor enforced-displacements, without the use of any other floor force or moment information. Suitable drift-based values for floor enforced-displacements are proposed, following an extensive parametric analysis. These floor enforced-displacements are combined in such a way that the spatial action of the two seismic horizontal components of the ground motion is fully considered, avoiding at the same time the various superposition techniques recommended by the seismic codes within the nonlinear area. The envelope of the abovementioned sixteen final nonlinear static analyses can adequately approximate the seismic demand resulting from nonlinear response history analyses.
Journal of Constructional Steel Research, 2015
Abstract Conventional buckling restrained braces used in concentrically braced frames are expecte... more Abstract Conventional buckling restrained braces used in concentrically braced frames are expected to yield in both tension and compression without significant degradation of capacity under severe seismic ground motions. On the other hand, a new short core buckling restrained brace system could be introduced as an alternative for a conventional full core BRB. In a short core BRB (SCBRB), the core element is built shorter than usual. Therefore, for a given story drift, the core accepts bigger axial strains compared to a conventional (full core) BRB. A short core BRB seems to be easily fabricated, inspected, and replaced after a severe earthquake. The purpose of this study is to show how this type of buckling restrained braces is feasible. Reducing the core length in a buckling restrained brace may result in a shorter encasing member, decrease in frictional forces acting at the core and buckling restraining mechanism interface, and, as a consequence, reduction of the compression strength adjustment factor in the brace. This paper numerically investigates the seismic behavior of short core buckling restrained braced frames. The minimum core length of BRB is determined by considering the low cycle fatigue life of the core plate and the maximum anticipated strain demand under standard loading protocol. Nonlinear time history analyses were also performed on four and ten story prototype buildings equipped with full core (conventional BRBs) and short core BRBs and the story drifts were compared. The results showed that the SCBRB system is partially able to reduce the story and residual story drifts in the braced frames. In addition, SCBRBs sustain large plastic deformations without crossing the low cycle fatigue life borders or instability of the encasing system. However, the economic and practical aspects of using SCBRB seem to be more distinct in comparison to its mechanical characteristics.
ABSTRACT In the present work, the measurements that resulted from the tests of eleven wall specim... more ABSTRACT In the present work, the measurements that resulted from the tests of eleven wall specimens with aspect ratio of 1.0 and 1.5 are used, in order to set up analytical models for the calculation of the displacements due to the deformation of each considered strength resisting mechanism. For this reason the flexural, web shear and sliding shear mechanisms are distinguished. The novel subjects of the present study are the calculation methodologies of the sliding shear strength and of the top displacement due to the deformation of the sliding shear mechanism. The quantity and arrangement of the specimen reinforcement were chosen so as to ensure a flexural type of failure. It was found that web shear deformation increased, until maximum strength was achieved. After the point of maximum strength, web shear deformations decreased, while sliding shear deformations along the base main flexural crack increased. Relationships proposed to describe these phenomena are derived from appropriately modified existing models along with new, semi-empirical, ones. The analytical calculated quantities are compared with the experimental measurements and a good match is noted. It is concluded that in shear walls with low aspect ratio, sliding shear deformations appeared at the base plastic hinge, even in the case that flexural response initially dominates. Neglecting such shear deformations results in underestimating shear forces at the base of other vertical structural elements. According to this methodology, strength and deformation quantities are calculated permitting thus the use of the proposed methodology in both cases of force and displacement based design methods.
A few hours after the earthquake and during the subsequent three weeks, teams of experts (seismol... more A few hours after the earthquake and during the subsequent three weeks, teams of experts (seismologists and civil engineers of the research staff of ITSAK) visited the meizoseismal area. ITSAK teams consisted of engineering seismologists B.
The Structural Design of Tall and Special Buildings, 2008
ABSTRACT The present paper refers to the definition of the torsional stiffness radii of multistor... more ABSTRACT The present paper refers to the definition of the torsional stiffness radii of multistorey tall buildings using both the continuous and the discrete model of the structure. The magnitude of the torsional stiffness radius of a building is the most important structural characteristic in order to explain the torsional behaviour of a building during an earthquake as it directly affects the building&#39;s torsional flexibility. The importance of the torsional flexibility of buildings is recognized by contemporary Seismic Codes that propose a grid of torsional provisions in order to avoid soft-storey operation due to floor torsional vibrations around a vertical axis. However, contrary to single-storey buildings, the torsional stiffness radius of multistorey buildings is not defined directly because both the translational and torsional stiffness of these buildings are expressed in matrix form. In the present paper, this weakness has been overcome using the continuous model of the structure, from which the torsional stiffness radius of a general monosymmetric multistorey tall system arises via a closed mathematical equation. The discrete model of the structure has numerically verified this closed mathematical equation. Copyright © 2007 John Wiley &amp; Sons, Ltd.
Journal of Vibration and Control, 2012
In the present paper the continuous model method is applied to the prototype of a wind turbine to... more In the present paper the continuous model method is applied to the prototype of a wind turbine tower in order to perform its modal structural analysis. This mathematical analysis is used as an alternative approach to the modal analysis method that uses discrete models. It is well known that in discrete models with high-level discretization and a large number of finite elements, several open questions on the accuracy, the convergence and the stability of the solution arise during the modal or response history analysis. In this sense, the results of the analysis by means of discrete modeling are in several cases doubtful and, therefore, a modal analysis by applying a continuous model as an effective alternative is recommended. To this end, the present paper proposes a continuous model approach to calculate the eigen-frequencies, periods and mode shapes to a wind turbine tower prototype. Starting from the equilibrium of forces on a differential element of the structure, the equation of...
Journal of Earthquake Engineering, 2012
In order to design a structure according to Eurocode EN 1990, a uniform "reliability index" must ... more In order to design a structure according to Eurocode EN 1990, a uniform "reliability index" must be defined for all design parameters (strengths, loadings, etc.) that present an "uncertainty." However, Design Earthquakes constitute exception of the above parameters; thus, the present article covers this gap. For various values of reliability index and using an ideal, fictitious, Standard Normal Probability Density Function, new Peak Ground Acceleration functions of the mean return period of the design earthquakes are proposed. As a pilot scheme, we chose the 82 most important seismic records of the last 40 years for the seismic area of Greece.
Earthquake Spectra, 1998
The equivalent static eccentricities of seismic forces are usually defined by codes with simple e... more The equivalent static eccentricities of seismic forces are usually defined by codes with simple expressions of the static eccentricity. This paper presents certain formulae for the exact calculation of these eccentricities on the basis of the dynamic response of a simplified model. From the parametric analysis of such formulae the determinative role of the torsional and lateral stiffness of the system becomes obvious for the correct evaluation of the equivalent static eccentricities. Finally, a proposal is made for the improvement of the static torsional provisions of the current codes.
Seismic Behaviour and Design of Irregular and Complex Civil Structures III, 2020
Α new version about a method of documented application of pushover analysis on asymmetric single-... more Α new version about a method of documented application of pushover analysis on asymmetric single-storey buildings has been presented, recently. The main target of this new method was to rationally consider the coupling between torsional (about vertical axis) and translational vibrations of asymmetric singlestorey building diaphragm under translational seismic excitation of its base. For this reason, the equivalent lateral static floor force according to the new method is applied using suitable dynamic eccentricities, eccentric to building Mass Centre, which are added with the accidental eccentricities, in such a way that the final design eccentricities move the application point of floor, external, lateral, static force away from the diaphragm Mass Centre. The origin point for measuring the dynamic eccentricities is called "Capable Near Collapse Centre of Stiffness ". Also, the floor lateral static force must be oriented along the building principal axes which are called "Capable Near Collapse Principal Axes" and , respectively. The appropriate dynamic eccentricities for the stiff-side and the flexible-one of the floor plan derive from extensive parametric analysis and are calculated by graphs and suitable equations. In the present work, a numerical example of an asymmetric single-storey building is presented to illustrate clearly and in detail the step by step application of the proposed pushover analysis method. It is a torsional sensitive reinforced concrete building designed in accordance with Eurocodes EN 1992-1 and 1998-1 for ductility class high (DCH). The proposed method is evaluated relative to the results of non-linear response history analysis (ΤΗ). The final results show that the proposed method of pushover analysis predicts with safety the displacement of the stiff side of the building as well as that of the flexible side.
Seismic Behaviour and Design of Irregular and Complex Civil Structures IV
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Papehttp://ascelibrary.org/doi/abs/10.1061/%28ASrs by Triantafyllos K . Makarios, Ph.D. Professor
perform its modal structural analysis. This mathematical analysis is used as an alternative approach to the modal analysis
method that uses discrete models. It is well known that in discrete models with high-level discretization and a large
number of finite elements, several open questions on the accuracy, the convergence and the stability of the solution arise
during the modal or response history analysis. In this sense, the results of the analysis by means of discrete modeling are
in several cases doubtful and, therefore, a modal analysis by applying a continuous model as an effective alternative is
recommended. To this end, the present paper proposes a continuous model approach to calculate the eigen-frequencies,
periods and mode shapes to a wind turbine tower prototype. Starting from the equilibrium of forces on a differential
element of the structure, the equation of motion of the tower is formulated and using in turn the known boundary
conditions at the two ends of the wind tower, the tower eigen-problem is numerically treated and solved. The action of
the higher mode-shapes is very important and may become critical in the case that the tower is subjected to strong
dynamic loading (cf. e.g. wind) and simultaneously is excited by a strong seismic motion.