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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
> Journal Vol & Issue
Earthquakes and Structures
Journal Basic Information
Journal DOI :
Editor in Chief :
Izuru Takewaki / Stavros A. / Anagnostopoulos / Jerome P. Lynch
Volume & Issues
Volume 9, Issue 6 - Dec 2015
Volume 9, Issue 5 - Nov 2015
Volume 9, Issue 4 - Oct 2015
Volume 9, Issue 3 - Sep 2015
Volume 9, Issue 2 - Aug 2015
Volume 9, Issue 1 - Jul 2015
Volume 8, Issue 6 - Jun 2015
Volume 8, Issue 5 - May 2015
Volume 8, Issue 4 - Apr 2015
Volume 8, Issue 3 - Mar 2015
Volume 8, Issue 2 - Feb 2015
Volume 8, Issue 1 - Jan 2015
Selecting the target year
Earthquake induced torsion in buildings: critical review and state of the art
Anagnostopoulos, S.A. ; Kyrkos, M.T. ; Stathopoulos, K.G. ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 305~377
DOI : 10.12989/eas.2015.8.2.305
The problem of earthquake induced torsion in buildings is quite old and although it has received a lot of attention in the past several decades, it is still open. This is evident not only from the variability of the pertinent provisions in various modern codes but also from conflicting results debated in the literature. Most of the conducted research on this problem has been based on very simplified, highly idealized models of eccentric one-story systems, with single or double eccentricity and with load bearing elements of the shear beam type, sized only for earthquake action. Initially, elastic models were used but were gradually replaced by inelastic models, since building response under design level earthquakes is expected to be inelastic. Code provisions till today have been based mostly on results from one-story inelastic models or on results from elastic multistory idealizations. In the past decade, however, more accurate multi story inelastic building response has been studied using the well-known and far more accurate plastic hinge model for flexural members. On the basis of such research some interesting conclusions have been drawn, revising older views about the inelastic response of buildings based on one-story simplified model results. The present paper traces these developments and presents new findings that can explain long lasting controversies in this area and at the same time may raise questions about the adequacy of code provisions based on results from questionable models. To organize this review better it was necessary to group the various publications into a number of subtopics and within each subtopic to separate them into smaller groups according to the basic assumptions and/or limitations used. Capacity assessment of irregular buildings and new technologies to control torsional motion have also been included.
Torsional effects due to concrete strength variability in existing buildings
De Stefano, M. ; Tanganelli, M. ; Viti, S. ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 379~399
DOI : 10.12989/eas.2015.8.2.379
Existing building structures can easily present material mechanical properties which can largely vary even within a single structure. The current European Technical Code, Eurocode 8, does not provide specific instructions to account for high variability in mechanical properties. As a consequence of the high strength variability, at the occurrence of seismic events, the structure may evidence unexpected phenomena, like torsional effects, with larger experienced deformations and, in turn, with reduced seismic performance. This work is focused on the torsional effects related to the irregular stiffness and strength distribution due to the concrete strength variability. The analysis has been performed on a case-study, i.e., a 3D RC framed 4 storey building. A Normal distribution, compatible to a large available database, has been taken to represent the concrete strength domain. Different plan layouts, representative of realistic stiffness distributions, have been considered, and a statistical analysis has been performed on the induced torsional effects. The obtained results have been compared to the standard analysis as provided by Eurocode 8 for existing buildings, showing that the Eurocode 8 provisions, despite not allowing explicitly for material strength variability, are conservative as regards the estimation of structural demand.
Seismic assessment of existing r.c. framed structures with in-plan irregularity by nonlinear static methods
Bosco, Melina ; Ferrara, Giovanna A.F. ; Ghersi, Aurelio ; Marinoc, Edoardo M. ; Rossi, Pier Paolo ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 401~422
DOI : 10.12989/eas.2015.8.2.401
This paper evaluates the effectiveness of three nonlinear static methods for the prediction of the dynamic response of in-plan irregular buildings. The methods considered are the method suggested in Eurocode 8, a method previously proposed by some of the authors and based on corrective eccentricities and a new method in which two pushover analyses are considered, one with lateral forces applied to the centres of mass of the floors and the other with only translational response. The numerical analyses are carried out on a set of refined models of reinforced concrete framed buildings. The response predicted by the nonlinear static analyses is compared to that provided by nonlinear dynamic analyses. The effectiveness of the nonlinear static methods is evaluated in terms of absolute and interstorey displacements.
Torsional effects in symmetrical steel buckling restrained braced frames: evaluation of seismic design provisions
Roy, Jonathan ; Tremblay, Robert ; Leger, Pierre ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 423~442
DOI : 10.12989/eas.2015.8.2.423
The effects of accidental eccentricity on the seismic response of four-storey steel buildings laterally stabilized by buckling restrained braced frames are studied. The structures have a square, symmetrical footprint, without inherent eccentricity between the center of lateral resistance (CR) and the center of mass (CM). The position of the bracing bents in the buildings was varied to obtain three different levels of torsional sensitivity: low, intermediate and high. The structures were designed in accordance with the seismic design provisions of the 2010 National Building Code of Canada (NBCC). Three different analysis methods were used to account for accidental eccentricity in design: (1) Equivalent Static Procedure with static in-plane torsional moments assuming a mass eccentricity of 10% of the building dimension (ESP); (2) Response Spectrum Analysis with static torsional moments based on 10% of the building dimension (RSA-10); and (3) Response Spectrum Analysis with the CM being displaced by 5% of the building dimension (RSA-5). Time history analyses were performed under a set of eleven two-component historical records. The analyses showed that the ESP and RSA-10 methods can give appropriate results for all three levels of torsional sensitivity. When using the RSA-5 method, adequate performance was also achieved for the low and intermediate torsional sensitivity cases, but the method led to excessive displacements (5-10% storey drifts), near collapse state, for the highly torsionally sensitive structures. These results support the current provisions of NBCC 2010.
Evaluating the reliability of using the deflection amplification factor to estimate design displacements with accidental torsion effects
Lin, Jui-Liang ; Wang, Wei-Chun ; Tsai, Keh-Chyuan ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 443~462
DOI : 10.12989/eas.2015.8.2.443
Some model building codes stipulate that the design displacement of a building can be computed using the elastic static analysis results multiplied by the deflection amplification factor,
. This approach for estimating the design displacement is essential and appealing in structural engineering practice when nonlinear response history analysis (NRHA) is not required. Furthermore, building codes stipulate the consideration of accidental torsion effects using accidental eccentricity, whether the buildings are symmetric-plan, or asymmetric-plan. In some model building codes, the accidental eccentricity is further amplified by the torsional amplification factor
in order to minimize the discrepancy between statically and dynamically estimated responses. Therefore, this warrants exploration of the reliability of statically estimated design displacements in accordance with the building code requirements. This study uses the discrepancy curves as a way of assessing the reliability of the design displacement estimates resulting from the factors
. The discrepancy curves show the exceedance probabilities of the differences between the statically estimated design displacements and NRHA results. The discrepancy curves of 3-story, 9-story, and 20-story example buildings are investigated in this study. The example buildings are steel special moment frames with frequency ratios equal to 0.7, 1.0, 1.3, and 1.6, as well as existing eccentricity ratios ranging from 0% to 30%.
Should accidental eccentricity be eliminated from Eurocode 8?
Anagnostopoulos, S.A. ; Kyrkos, M.T. ; Papalymperi, A. ; Plevri, E. ;
Earthquakes and Structures, volume 8, issue 2, 2015, Pages 463~484
DOI : 10.12989/eas.2015.8.2.463
Modern codes for earthquake resistant building design require consideration of the so-called accidental design eccentricity, to account for torsional response caused by several factors not explicitly considered in design. This provision requires that the mass centres in the building floor be moved a certain percentage of the building's dimension (usually 5%) along both the x and y axes and in both positive and negative directions. If one considers also the spatial combinations of the two component motion in a dynamic analysis of the building, the number of required analyses and combinations increases substantially, causing a corresponding work load increase for practicing structural engineers. Another shortcoming of this code provision is that its introduction has been based primarily on elastic results from investigations of oversimplified, hence questionable, one story building models. This problem is addressed in the present paper using four groups of eccentric braced steel buildings, designed in accordance with Eurocodes 3 (steel) and 8 (earthquake design), with and without accidental eccentricities considered. The results indicate that although accidental design eccentricities can lead to somewhat reduced inelastic response demands, the benefit is not significant from a practical point of view. This leads to suggestions that accidental design eccentricities should probably be abolished or perhaps replaced by a simpler and more effective design provision, at least for torsionally stiff buildings that constitute the vast majority of buildings encountered in practice.