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CONTENTS
Volume 27, Number 2, September30 2007
 

Abstract
The force (load) reduction factor, R, which is one of the most important parameters in earthquake load calculation, is independent of the dimensions of the structure but is defined on the basis of the load bearing system of the structure as defined in earthquake codes. Significant damages and failures were experienced on prefabricated reinforced concrete structures during the last three major earthquakes in Turkey (Adana 1998, Kocaeli 1999, Duzce 1999) and the experts are still discussing the main reasons of those failures. Most of them agreed that they resulted mainly from the earthquake force reduction factor, R that is incorrectly selected during design processes, in addition to all other detailing errors. Thus this wide spread damages caused by the earthquake to prefabricated structures aroused suspicion about the correctness of the R coefficient recommended in the current Turkish Earthquake Codes (TEC - 98). In this study, an attempt was made for an approximate determination of R coefficient for widely utilized prefabricated structure types (single-floor single-span) with variable dimensions. According to the selecting variable dimensions, 140 sample frames were computed using pushover analysis. The force reduction factor R was calculated by load-displacement curves obtained pushover analysis for each frame. Then, formulated artificial neural network method was trained by using 107 of the 140 sample frames. For the training various algorithms were used. The method was applied and used for the prediction of the R rest 33 frames with about 92% accuracy. The paper also aims at proposing the authorities to change the R coefficient values predicted in TEC - 98 for prefabricated concrete structures.

Key Words
neural network; force reduction factor; prefabricated industrial buildings.

Address
M. Hakan Arslan, Murat Ceylan, M. Yasar Kaltakci and Yuksel Ozbay: Selcuk University 42075, Konya, Turkey
Fatma Gulten Gulay: Dept. of Civil Engineering, Istanbul Technical University, Istanbul, Turkey

Abstract
A new finite shear wall element model and a method for calculation of 3D multi-storied only shear walled or shear walled-framed structures using finite shear wall elements assumed ideal elasto-plastic material are developed. The collapse load of the system subjected to factored constant gravity loads and proportionally increasing lateral loads is calculated with a method of load increments. The shape functions over the element are determined as a cubic variation along the story height and a linear variation in horizontal direction because of the rigid behavior of the floor slab. In case shear walls are chosen as only one element in every floor, correct solutions are obtained by using this developed element. Because of the rigid behavior of the floor slabs, the number of unknowns are reduced substantially. While in framed structures, classical plastic hinge hypothesis is used, in nodes of shear wall elements when vertical deformation parameter is exceeded ?e, this node is accepted as a plastic node. While the system is calculated with matrix displacement method, for determination of collapse safety, plastic displacements and plastic deformations are taken as additional unknowns. Rows and columns are added to the system stiffness matrix for additional unknowns.

Key Words
finite shear wall element; elasto-plastic behaviour; lateral load parameter; plastic hinge hypothesis; matrix displacement method; a method of load increments.

Address
Emel Yukselis Cengiz: Directorate of Construction Analysis and Development, Istanbul Metropolitan Municipality, Sarachane-Eminonu, 34478,Istanbul, Turkey
Ahmet Isin Saygun: Dept. of Civil Engineering, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey

Abstract
An experimental study of five full-scale coupling beam specimens has been conducted to investigate the seismic behavior of strengthened RC coupling beams by bolted side steel plates using a reversed cyclic loading procedure. The strengthened coupling beams are fabricated with different plate thicknesses and shear connector arrangements to study their respective effects on load-carrying capacity, strength retention, stiffness degradation, deformation capacity, and energy dissipation ability. The study revealed that putting shear connectors along the span of coupling beams produces no significant improvement to the structural performance of the strengthened beams. Translational and rotational partial interactions of the shear connectors that would weaken the load-carrying capacity of the steel plates were observed and measured. The hierarchy of failure of concrete, steel plates, and shear connectors was identified. Furthermore, detailed effects of plate buckling and various arrangements of shear connectors on the post-peak behavior of the strengthened beams are discussed.

Key Words
coupling beam; strengthening; seismic behavior; steel plate; bolt connection.

Address
Y. Zhu: Earthquake Engineering Research Test Centre, The Univ. of Guang Zhou, China
R. K. L. Su: Dept. of Civil Engineering, The University of Hong Kong, Hong Kong, China
F. L. Zhou: Earthquake Engineering Research Test Centre, The University of Guang Zhou, China

Abstract
A wavelet-based procedure to generate artificial accelerograms compatible with a prescribed seismic design spectrum is described. A procedure to perform a baseline correction of the compatible accelerograms is also described. To examine how the frequency content of the modified records evolves with time, they are analyzed in the time and frequency using the wavelet transform. The changes in the strong motion duration and input energy spectrum are also investigated. An alternative way to match the design spectrum, termed the ?two-band matching procedure?, is proposed with the objective of preserving the non-stationary characteristics of the original record in the modified accelerogram.

Key Words
spectrum compatible accelerograms; wavelet transform; baseline correction; input energy spectrum; strong motion duration.

Address
Luis E. Suarez: Dept. of Civil Engineering and Surveying, University of Puerto Rico, Mayaguez, Puerto Rico 00681-9041, U.S.A.
Luis A. Montejo: Dept. of Civil Construction and Environmental Engineering, North Carolina State University, Raleigh, North Carolina 27695-7908, U.S.A.

Abstract
Composite laminated structures supported on elastic foundations are being increasingly used in a great variety of engineering applications. Composites exhibit larger dispersion in their material properties compared to the conventional materials due to large number of parameters associated with their manufacturing and fabrication processes. And also the dispersion in elastic foundation stiffness parameter is inherent due to inaccurate modeling and determination of elastic foundation properties in practice. For a better modeling of the material properties and foundation, these are treated as random variables. This paper deals with effects of randomness in material properties and foundation stiffness parameters on the free vibration response of laminated composite plate resting on an elastic foundation. A C0 finite element method has been used for arriving at an eigen value problem. Higher order shear deformation theory has been used to model the displacement field. A mean centered first order perturbation technique has been employed to handle randomness in system properties for obtaining the stochastic characteristic of frequency response. It is observed that small amount of variations in random material properties and foundation stiffness parameters significantly affect the free vibration response of the laminated composite plate. The results have been compared with those available in the literature and an independent Monte Carlo simulation.

Key Words
Composite plates; uncertain system properties; elastic foundation; free vibration; second order statistics; C0 finite element.

Address
Achchhe Lal: Dept. of Applied Mechanics, MNNIT Allahabad-211004, India
B. N. Singh: Dept. of Aerospace Engineering, IIT Kharagpur-721302, India
Rakesh Kumar: Dept. of Applied Mechanics, MNNIT Allahabad-211004, India

Abstract
Seven full-scale exterior beam-column joints were produced and tested under reversible cyclic loads to determine. Two of these seven specimens were produced using ordinary reinforced concrete (RC). Steel Fiber Reinforced Concrete (SFRC) was placed in three different regions of the beams of the rest five specimens to determine the extent of the region where SFRC is the most effective. The extent of the region of SFRC was kept constant at the columns of all five specimens. Three of these five specimens which had one stirrup in the joint, were tested to evaluate the effect of the stirrup on the behavior of the beam-column joint together with SFRC. In production of the specimens with SFRC, all special requirements of the Turkish Earthquake Code related to the spacing of hoops were disregarded. Previous researches reported in the literature indicate that the fiber type, the volume content, and the aspect ratio of steel fibers affect the behavior of beam-column joints produced with SFRC. The results of the present investigation show that the behavior of exterior beam-column joints depends on the extent of the region where SFRC is used and the usage of stirrup in the joint, in addition to the parameters listed in the literature.

Key Words
beam-column joint; reversible cyclic loading; steel fiber; concrete, energy capacity; ductility; earthquake.

Address
Mustafa Gencoglu: Istanbul Technical University, Faculty of Civil Engineering, Division of Structural Engineering, 34469 Maslak, Istanbul, Turkey

Abstract
A numerically efficient superelement is proposed as a low degree of freedom model for dynamic analysis of rotating tapered beams. The element uses a combination of polynomials and trigonometric functions as shape functions in what is also called the Fourier-p approach. Only a single element is needed to obtain good modal frequency prediction with the analysis and assembly time being considerably less than for conventional elements. The superelement also allows an easy incorporation of polynomial variations of mass and stiffness properties typically used to model helicopter and wind turbine blades. Comparable results are obtained using one superelement with only 14 degrees of freedom compared to 50 conventional finite elements with cubic shape functions with a total of 100 degrees of freedom for a rotating cantilever beam. Excellent agreement is also shown with results from the published literature for uniform and tapered beams with cantilever and hinged boundary conditions. The element developed in this work can be used to model rotating beam substructures as a part of complete finite element model of helicopters and wind turbines.

Key Words
rotating beams; superelement; free vibration; finite element method; helicopter blades; wind turbine blades.

Address
Jagadish Babu Gunda, Anuj Pratap Singh, Parampal Singh Chhabra and Ranjan Ganguli: Dept. of Aerospace Engineering, Indian Institute of Science, Bangalore 560012, India

Abstract
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Key Words
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Address
H. Gokda and O. Kopmaz: Dept. of Mechanical Engineering, College of Engineering and Architecture, Uluda University, Gorukle, Bursa 16059, Turkey


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