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Earthquake Resistant Design and Strengthening of Reinforced Concrete Buildings
Abstract
It is already generally acceptable that a reinforced concrete building may securely resist the design earthquake if it may locally perform plastic deformations and avoid at the same time brittle failures. Main concern of the modern designer is metelastic behaviour, ductility, criteria of brittle fracture and design or redesign (strengthening) strategy. The above considerations are also valid for a new building that is designed in accordance with the current regulations for a reduced seismic action. This assumes elastoplastic response of the structure that remains unknown for the designer performing the a priori capacity design.
The first part covers the elastoplastic response of the single degree of freedom oscillator. The calculation of the maximum probable displacement of the oscillator is based either on the empirical method of the displacement coefficient or on the capacity spectrum method derived from the hysteretic damping of the system. The results are compared with those of the timehistory analysis of earthquake recordings of the last twenty years in Greece. For stiff, low strength structures, unfavorable soil conditions the results seem to be much higher than the theoretical values therefore improved solutions for practice are proposed. Application of pushover method in multi degree of freedom systems is analyzed followed by a presentation of evaluation strategies, design or redesign of the structure through the increase of stiffness, strength and ductility. Simple relations for the design of earthquake resistant walls are also proposed, suitable for preliminary studies.
The second part covers inelastic deformation and fracture mechanisms of concrete and the effect of confinement in the increase of ductility. The effect of brittle failure under compression and shear is examined as an result of concentration of inelastic deformations. Simple models for confinement, bending and shear are presented where various shear transfer mechanisms are analyzed. Examples for brittle failure of short columns are solved, plastic rotation is calculated and as a final point brittle failure of slabs under punching shear is modeled.
The third part covers examples of redesign and strengthening of buildings, designed using the pushover method and already constructed. Application of the new Greek regulations for interventions establishes the use of inelastic static analysis for such purposes.
... Diagrams relating the internal moment M with the chord rotation «θ» are used for checking the inelastic behaviour of the structural elements. The required verifications are: ductility in terms of deformations, resistance in terms of forces and deformations for functionality reasons [5]. ...
... • Ductile failure, e.g. due to bending or drift, in terms of deformation (chord plastic rotation) [5]. ...
The present thesis examines an existing building of year 1993, with piloti plus 4 typical floors, which was designed using triangular seismic distribution. The building was analysed using Pushover Nonlinear Static Analysis (D.C.M.). The structure was checked for SD and NC compliance criteria under the design earthquake and also for the DL criterion under an earthquake with a return period of 42 years. It was then strengthened with X steel braces.
... The concept of capacity design [Paulay, Bachmann, Moser, 1990] requires the designer to choose the relevant non-linear mechanism and must make sure that the structural system acts that way. This requires elastic behavior in all the structural components except where the non-linear action is to take place. ...
Three typical office buildings with hysteretic device systems (Hyde systems) were studied to show the effects of different types of distributions of Hyde forces. The safety of the buildings was calculated using the β-index concept of modern codes, taking the elastic story drift of the secondary horizontal stiffening system (SHS system) as limit criterion. The standard deviations of the story drifts were calculated from 500 non-linear time histories for this purpose. The study was performed for an excitation statistically equivalent to the 1995 Kobe earthquake. It showed the importance of the slenderness of the SHS system: The less slender the SHS, the less effective are the Hydes in the seismic links (SL) and with them, the whole Hyde system concept. The study also showed that with typical SHS designs, a SL in every 5 th story is preferable to a full distribution yielding a smaller total of Hyde forces. Again, it was shown that the Hyde system concept not only provides considerable performance advantages over conventional structural concepts but also yields very economical structures because of the slenderness requirement on the SHS that allows the use of simple connections and small x-sections through most of the structure.
In the earthquake resistant design of high-rise reinforced concrete(R/C) buildings, it is very important to clarify the inelastic behaviour of columns subjected to bending moment and axial force. Among the various analytical models for R/C column, the plasticity theorem model is considered to have a lot of advantage to 3-dimensional inelastic analysis. We have been developing an analytical method based on the plasticity theorem. In this paper, we performed static analyses of R/C columns under bending moment and varying axial force, and a dynamic analysis of shaking table test of a 3-story R/C space frame using this method. Through these analyses, the usefulness of this method based on the plasticity theorem to 3-dimensional inelastic analysis of R/C columns subjected to bending moment and axial force is shown.
An analytical modeling scheme is developed to assess the damageability of reinforced concrete buildings experiencing inelastic behavior under earthquake loads. The structural model used to discretize a building is capable of integrating ductile moment-resisting frames with shear-wall models and out-of-plane transverse elements to allow simulation of special interactions that are important in modeling overall structural behavior. The structural model is achieved using a combination of concentrated plasticity at member ends and a distributed flexibility rule that accounts for the spread of plasticity based on the variation of the contraflexure point during dynamic response. The inelastic behavior of components is monitored using a new hysteretic model that utilizes a nonsymmetric trilinear envelope and permits the modeling of stiffness degradation, strength deterioration, and pinching, respectively. The structural parameters, such as moment-curvature envelopes, etc., required for the inelastic seismic response analysis are computed in-core, using mechanical models and empirical equations that emerge from identification studies. The results of the response analysis are expressed as damage indices using a calibrated damage model based on energy and ductility. This enables the estimation of energy and strength reserves in the structure before collapse. Several examples are presented to illustrate the versatility of the proposed modeling schemes.
The states of the practice and art in seismic design of reinforced concrete dual frame-wall structural systems are reviewed. The review leads to the need to emphasize the use of conceptual seismic design principles to overcome the high level of uncertainties involved in present numerical analyses of such systems. Therefore, the main issues and decisions confronted by the designer in achieving a conceptual seismic design are reviewed and exemplified by the results obtained in analytical and experimental studies of seismic responses of a 15-story frame-coupled wall structure and of a 7-story frame-wall structure. Observed shortcomings of the state-of-the-practice, as represented by the seismic design building codes used in the U.S., are identified. Suggestions are offered to improve the states of the practice and art in the seismic design of this dual structural system.
Heutzutage darf sich der Bauingenieur im Hochbau nicht mehr ausschließlich auf das Tragwerk konzentrieren. Vielmehr muß er sich auch mit wesentlichen Aspekten der Bauphysik, der Gebäudehülle und des Ausbaus auseinandersetzen, da diese in ausgeprägter Wechselbeziehung mit dem Tragwerk stehen. Dieses Buch ist eine Einführung in das umfangreiche Gebiet des Hochbaus. Neben Studierenden sind Praktiker angesprochen, die sich mit den neuesten Begriffen und Verfahren vertraut machen wollen. Angestrebt wird eine ganzheitliche Betrachtung der Hochbauten. Zunächst werden die notwendigen Grundlagen der Bauphysik behandelt. Anschließend folgen eine Übersicht über die wichtigsten Elemente von Gebäudehülle und Ausbau und ein Kapitel über die ingenieurmäßige Berechnung und Bemessung von tragendem Mauerwerk. Der letzte Teil ist den Tragwerken von Skelettbauten gewidmet.
The results of an extensive series of tests of three types of concrete under biaxial loadings are used to develop stress-strain relations for concrete subjected to biaxial stress states. By means of a decomposition of the stresses and strains into their hydrostatic and deviatoric portions, it was possible to express the relations between octahedral normal stresses and strains, and octahedral shear stresses and strain through use of bulk and shear moduli.
Der Beitrag gibt einen Überblick über die Zulassungsverfahren für selbstverdichtenden Beton (SVB), technische Kennwerte und die gesammelten Erfahrungen auf den Baustellen, die die Problematik berücksichtigen, daß beim SVB die Kommunikation zwischen Betonhersteller und Baufirma oft unzureichend ist.
Introduction Constraints Seismic Design Alternatives Deep-Valley-Crossing Considerations Long-Span-Bridge Considerations
