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CONTENTS
Volume 4, Number 6, June 2013
 

Abstract
The given paper presents a new approach in design of seismic isolation systems of base isolated buildings. The idea is to install not one big size rubber bearing under the columns and/or shear walls, or one by one with certain spacing under the load-bearing walls, but to install a group/cluster of small size bearings, in order to increase the overall effectiveness of the isolation system. The advantages of this approach are listed and illustrated by the examples. Also the results of analyses of some buildings where the approach on installation of clusters of rubber bearings was used in their isolation systems are given for two cases: i) when the analyses are carried out based on the provisions of the Armenian Seismic Code, and ii) when the time history analyses are carried out. Obtained results are compared and discussed. Paper also presents, as an example, detailed analysis and design of the 18-story unique building in one of the residential complexes in Yerevan. Earthquake response analyses of this building were carried out in two versions, i.e. when the building is base isolated and when it is fixed base. Several time histories were used in the analyses. Comparison of the obtained results indicates the high effectiveness of the proposed structural concepts of isolation systems and the need for further improvement of the Seismic Code provisions regarding the values of the reduction factors. A separate section in the paper dedicated to the design of high damping laminated rubber-steel bearings and to results of their tests.

Key Words
seismic isolation; new approach; cluster of small size bearings; base isolated buildings; analysis and design; seismic code; time history; fixed base building; comparison of results; design and tests of bearings

Address
Mikayel G. Melkumyan : Armenian Association for Earthquake Engineering

Abstract
The application of shape memory alloys (SMAs) to the seismic response reduction of civil engineering structures has attracted growing interest due to their self-centering feature and excellent fatigue performance. The loading rate dependence of SMAs raises a concern in the seismic analysis of SMA-based devices. However, the implementation of micromechanics-based strain-rate-dependent constitutive models in structural analysis software is rather complicated and computationally demanding. This paper investigates the feasibility of replacing complex rate-dependent models with rate-independent constitutive models for superelastic SMA elements in seismic time-history analysis. Three uniaxial constitutive models for superelastic SMAs, including one rate-dependent thermomechanical model and two rate-independent phenomenological models, are considered in this comparative study. The pros and cons of the three nonlinear constitutive models are also discussed. A parametric study of single-degree-of-freedom systems with different initial periods and strength reduction factors is conducted to examine the effect of the three constitutive models on seismic simulations. Additionally, nonlinear time-history analyses of a three-story prototype steel frame building with special SMA-based damping braces are performed. Two suites of seismic records that correspond to frequent and design basis earthquakes are used as base excitations in the seismic analyses of steel-braced frames. The results of this study show that the rate-independent constitutive models, with their parameters properly tuned to dynamic test data, are able to predict the seismic responses of structures with SMA-based seismic response modification devices.

Key Words
shape memory alloy; superelasticity; loading rate effect; damper; constitutive model

Address
Songye Zhu : The Hong Kong Polytechnic University Shenzhen Research Institute, Shenzhen 518057, China; Department of Civil and Environmental Engineering, The Hong Kong Polytechnic University, Hong Kong,
Yunfeng Zhang : Department of Civil and Environmental Engineering, University of Maryland, College Park, MD 20742, USA

Abstract
Loading protocols have been developed for quasi-static cyclic testing of structures and components. However, it is uncertain if protocols developed for conditions of intense ground shaking in regions of high seismicity would also be applicable to regions of low-moderate seismicity that are remote from the tectonic plate boundaries. This study presents a methodology for developing a quasi-static cyclic displacement loading protocol for experimental bracing evaluation of cold-formed steel stud shear walls. Simulations presented in the paper were based on conditions of moderate ground shaking (in Australia). The methodologies presented are generic in nature and can be applied to other regions of similar seismicity conditions (which include many parts of China, Korea, India and Malaysia). Numerous response time histories including both linear and nonlinear analyses have been generated for selected earthquake scenarios and site classes. Rain-flow cycle counting method has been used for determining the number of cycles at various ranges of normalized displacement amplitude. It is found that the number of displacement cycles of the loading protocol increases with increasing intensity of ground shaking (associated with a longer return period).

Key Words
loading protocols; low-moderate seismicity; cold-formed steel stud shear walls; number of cycles; normalized displacement amplitude

Address
Rojit Shahi, Nelson Lam : Department of Infrastructure Engineering, The University of Melbourne, Parkville, VIC 3010, Australia
Emad Gad, John Wilson : Faculty of Engineering and Industrial Sciences, Swinburne University of Technology, Hawthorn, VIC 3122, Australia

Abstract
It is known that a base-isolated building exhibits a large response to a long-duration, long-period wave and an inter-connected system without base-isolation shows a large response to a pulse-type wave. To compensate for each deficiency, a new hybrid passive control system is investigated in which a base-isolated building is connected to another building (free wall) with oil dampers. It is demonstrated that the present hybrid passive control system is effective both for pulse-type ground motions and long-duration and long-period ground motions and has high redundancy and robustness for a broad range of disturbances.

Key Words
base-isolation; building connection; hybrid system; passive damper; structural control; robustness; redundancy

Address
Mitsuru Murase, Masaaki Tsuji and Izuru Takewaki : Department of Architecture and Architectural Engineering, Kyoto University, Kyotodaigaku-Katsura, Nishikyo-ku, Kyoto 615-8540, Japan

Abstract
The May 19, 2011 an earthquake hit Simav (Kütahya) province in Turkey. Simav is a district of Kütahya located 255 km southwest from capital city of Turkey. According to Turkish General Directorate of Disaster Affairs (DAD), the magnitude of this moderate earthquake was 5.7. The major percent of the housing stock in the affected region was built in masonry. Many masonry dwellings, mosques and also minarets were heavily damaged due to this seismic activity. The Halil Aga Mosque and its minaret were also heavily damaged as a masonry structure around the earthquake region. In this paper, a site survey of masonry damages is presented and Response Spectrum Analysis of the Halil Aga Mosque is performed using the finite element method.

Key Words
structural damages; simav (Kütahya) earthquake; masonry buildings; strong ground motions

Address
Ali Ural : Engineering Faculty, Department on Civil Engineering, Aksaray University, 68400, Aksaray, Turkey

Abstract
Static torsional provisions employing equivalent lateral force method (ELF) require that the earthquake-induced lateral force at each story be applied at a distance equal to design eccentricity (ed) from a reference resistance centre of the corresponding story. Such code torsional provisions, albeit not explicitly stated, are generally believed to be applicable to the regularly asymmetric buildings. Examined herein is the applicability of such code-torsional provisions to buildings with set-back using rigid as well as flexible diaphragm model. Response of a number of set-back systems computed through ELF with static torsional provisions is compared to that by response spectrum based procedure. Influence of infill wall with a range of opening is also investigated. Results of comprehensive parametric studies suggest that the ELF may, with rational engineering judgment, be used for practical purposes taking some care of the surroundings of the setback for stiff systems in particular.

Key Words
irregular; torsion; seismic; code-provisions; elastic

Address
Rana Roy : Department of Applied Mechanics, Bengal Engineering and Science University, Shibpur, India
Somen Mahato : Department of Civil Engineering, Bengal Engineering and Science University, Shibpur, India


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