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 of such 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.

SUMMARYThis paper presents evidence that the extension of conclusions based on the widely used simplified, one story, eccentric systems of the shear-beam type, to actual, nonsymmetric buildings and consequent assessments of the pertinent code provisions, can be quite erroneous, unless special care is taken to match the basic properties of the simplified models to those of the real buildings. The evidence comes from comparisons of results obtained using three variants of simplified models, with results from the inelastic dynamic response of three-and five-story eccentric buildings computed with detailed MDOF systems, where the members are idealized with the well-known plastic hinge model. In addition, a convincing answer is provided on a pertinent hanging controversy: For frame-type buildings, designed in accordance with the dynamic provisions of modern codes (such as EC8 or IBC2000), which allow reduced shears at the stiff edge due to torsion, the frames at the flexible sides are the critical elements in terms of ductility demands.

SUMMARYThe inelastic earthquake response of eccentric, multistorey, frame-type, reinforced concrete buildings is investigated using three-and ÿve-storey models, subjected to a set of 10, two-component, semi-artiÿcial motions, generated to match the design spectrum. Buildings designed according to the EC8 as well as the UBC-97 code were included in the investigation. It is found that contrary to what the simpliÿed onestorey, typical, shear-beam models predict, the so-called ' exible' side frames exhibit higher ductility demands than the 'sti ' side frames. The substantial di erences in such demands between the two sides suggest a need for reassessment of the pertinent code provisions. This investigation constitutes one of the ÿrst attempts to study the problem of inelastic torsion by means of realistic, multistorey inelastic building models. Additional studies with similar or even more reÿned idealizations will certainly be required to arrive at deÿnite results and recommendations for possible code revisions.

SUMMARYThe inelastic seismic torsional response of simple structures is examined by means of shear-beam type models as well as with plastic hinge idealization of one-story buildings. Using mean values of ductility factors, obtained for groups of ten earthquake motions, as the basic index of post-elastic response, the following topics are examined with the shear-beam type model: mass eccentric versus sti ness eccentric systems, e ects of di erent types of motions and e ects of double eccentricities. Subsequently, comparisons are made with results obtained using a more realistic, plastic hinge type model of singlestory reinforced concrete frame buildings designed according to a modern Code. The consequences of designing for di erent levels of accidental eccentricity are also examined for the aforementioned frame buildings.

No abstract