Techno Press


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CONTENTS
Volume 39, Number 2, July25 2011
 

Abstract
This paper is devoted to the development of the equations which describe the elastic response of a curved laminate subjected to in-plane loads and bending moments. Similar to the classic 6 x 6 ABD matrix constitutive relation of a flat laminate, a new 6 x 6 matrix constitutive relation between force resultants, moment resultants, mid-plane strains and deformed curvatures for a curved laminate is formulated. This curved lamination theory will provide the fundamental basis for the analyses of curved laminated structures. The stress predictions by the present curved lamination theory are compared to those by the curved laminate analysis that neglected the nonlinear terms in the derivation of the constitutive relation. The results show that the curved laminate analysis that neglected the nonlinear terms cannot reflect the effect of curvature and can no longer predict the stresses accurately as the curvature becomes noticeable. In this paper, a curved lamination theory that retains the nonlinear terms and, therefore, accounts for the effect of the non-flat geometry of the structure will be developed.

Key Words
curved laminate; constitutive relation; nonlinear

Address
Yih-Cherng Chiang: Department of Mechanical Engineering, Chinese Culture University, No. 55, Hua-Kang Rd., Taipei, Taiwan

Abstract
This paper uses dynamic computer simulation techniques to develop and apply a multicriteria procedure using non-destructive vibration-based parameters for damage assessment in truss bridges. In addition to changes in natural frequencies, this procedure incorporates two parameters, namely the modal flexibility and the modal strain energy. Using the numerically simulated modal data obtained through finite element analysis of the healthy and damaged bridge models, algorithms based on modal flexibility and modal strain energy changes before and after damage are obtained and used as the indices for the assessment of structural health state. The application of the two proposed parameters to truss-type structures is limited in the literature. The proposed multi-criteria based damage assessment procedure is therefore developed and applied to truss bridges. The application of the approach is demonstrated through numerical simulation studies of a single-span simply supported truss bridge with eight damage scenarios corresponding to different types of deck and truss damage. Results show that the proposed multi-criteria method is effective in damage assessment in this type of bridge superstructure.

Key Words
truss bridges; damage assessment; finite element method; vibration; flexibility; strain energy

Address
H.W. Shih, D.P. Thambiratnam and T.H.T. Chan: School of Urban Development, Faculty of Built Environment and Engineering, Queensland University of Technology, Brisbane, Australia

Abstract
This paper aims to study the behavior of short reinforced concrete columns confined with external glass Fiber Reinforced Polymers (GFRP) sheets under eccentric loads. The experimental part of the study was achieved by testing 9 specimens under eccentric compression. Three eccentricity ratios corresponding to e/t = 0, 0.10, 0.50 in one direction of the column were used. Specimens were divided into three groups. The first group was the control one without confinement. The second group was fully wrapped with GFRP laminates before loading. The third group was wrapped under loading after reaching 75% of failure loads of the control specimens. The third group was investigated in order to represent the practical case of strengthening a loaded column with FRP laminates. All specimens were loaded until failure. The results show that GFRP laminates enhances both failure load and ductility response of eccentrically loaded column. Moreover, the study also illustrates the effect of confinement on the first crack load, lateral deformation, strain in reinforcement and failure pattern. Based on the analysis of the experimental results, a simple model has been proposed to predict the improvement of load carrying capacity under different eccentricity ratios. The predicted equation takes into consideration the eccentricity to cross section depth ratio, the ultimate strength of GFRP, the thickness of wrapping laminate, and the time of wrapping (before loading and under loading). A good correlation was obtained between experimental and analytical results.

Key Words
confinement; columns; eccentricity; glass fiber reinforced polymer (GFRP); wrap; strengthening

Address
S.K. Elwan and A.S. Rashed: Department of Civil Engineering, The Higher Institute of Engineering, El Sherouk City, Cairo, Egypt

Abstract
This paper presents a methodology to detect and locate damages and faults in orthotropic plate structures. A specific damage index based on dynamic mode shapes of the damaged and undamaged structures has been introduced. The governing differential equation on transverse deformation, the transverse shear force equations and the invariant expression for the sum of transverse loading of an orthotropic plate are employed to obtain the aforementioned damage indices. The validity of the proposed methodology for isotropic and orthotropic damage states is demonstrated using a numerical example. It is shown that the algorithm is able to detect damages for both isotropic and orthotropic damage states acceptably.

Key Words
damage detection; orthotropic plates; modal parameters; damage indices

Address
Amir Hossein Gandomi, Mohammad G. Sahab: Department of Civil Engineering, Tafresh University, Tafresh, Iran
Alireza Rahai: Department of Civil and Environmental Engineering, Amirkabir University of Technology, Tehran, Iran

Abstract
The Self Compacting Concrete, SCC is the new generation type of concrete which is not needed to be compacted by vibrator and it will be compacted by its own weight. Since SCC is a new innovation and also the high strength self compacting concrete, HSSCC behavior is like a brittle material, therefore, understanding the strength effect on the serviceability performance of reinforced self compacting concretes is critical. For this aim, first the normal and high strength self compacting concrete, NSSCC and HSSCC was designed. Then, the serviceability performance of reinforced connections consisting of NSSCC and HSSCC were investigated. Twelve reinforced concrete connections (L = 3 m, b = 0.15 m, h = 0.3 m) were simulated, by this concretes, the maximum and minimum reinforcement ratios p and p\' (percentage of tensile and compressive steel reinforcement) are in accordance with the provision of the ACI-05 for conventional RC structures. This study was limited to the case of bending without axial load, utilizing simple connections loaded at mid span through a stub (b = 0.15 m, h = 0.3 m, L = 0.3 m) to simulate a beam-column connection. During the test, concrete and steel strains, deflections and crack widths were measured at different locations along each member. Based on the experimental readings and observations, the cracked moment of inertia (Icr) of members was determined and the results were compared with some selective theoretical methods. Also, the flexural crack widths of the members were measured and the applicability for conventional vibrated concrete, as for ACI, BS and CSA code, was verified for SCCs members tested. A comparison between two Codes (ACI and CSA) for the theoretical values cracking moment is indicate that, irrespective of the concrete strength, for the specimens reported, the prediction values of two codes are almost equale. The experimental cracked moment of inertia (Icr)exp is lower than its theoretical (Icr)th values, and therefore theoretically it is overestimated. Also, a general conclusion is that, by increasing the percentage of p, the value of Icr is increased.

Key Words
SCCs; connection; neutral axis; crack width; cracked moment of inertia; serviceability

Address
Ali Akbar Maghsoudi: Department of Civil Engineering, University of Kerman & International Center for Science,
High Technology & Environmental Sciences, Kerman, Iran

Abstract
There can be a significant amount of moment redistribution in composite frames consisting of steel columns and composite beams, due to cracking, creep and shrinkage of concrete. Considerable amount of computational effort is required for taking into account these effects for large composite frames. A methodology has been presented in this paper for taking into account these effects. In the methodology that has been demonstrated for moderately high frames, neural network models are developed for rapid prediction of the inelastic moments (typically for 20 years, considering instantaneous cracking, and time effects, i.e., creep and shrinkage, in concrete) at a joint in a frame from the elastic moments (neglecting instantaneous cracking and time effects). The proposed models predict the inelastic moment ratios (ratio of elastic moment to inelastic moment) using eleven input parameters for interior joints and seven input parameters for exterior joints. The training and testing data sets are generated using a hybrid procedure developed by the authors. The neural network models have been validated for frames of different number of spans and storeys. The models drastically reduce the computational effort and predict the inelastic moments, with reasonable accuracy for practical purposes, from the elastic moments, that can be obtained from any of the readily available software.

Key Words
composite frames; cracking; creep; shrinkage; neural networks

Address
Umesh Pendharkar: Civil Engineering, Ujjain Engineering College, Ujjain, India
Sandeep Chaudharyb: Structural Engineering, Malaviya National Institute of Technology, Jaipur, India
A.K. Nagpal: Civil Engineering, Indian Institute of Technology Delhi, New Delhi, India

Abstract
This paper is focused on the residual capacity of steel columns, as a damage criterion. Load-Impulse (P-I) diagrams are frequently used for analysis, design, or assessment of blast resistant structures. The residual load carrying capacity of a simply supported steel column was derived as a damage criterion based on a SDOF computational approach. Dimensionless P-I diagrams were generated numerically with this quantitative damage criterion. These numerical P-I diagrams were used to show that traditional constant ductility ratios adopted as damage criteria are not appropriate for either the design or damage assessment of blast resistant steel columns, and that the current approach could be a much more appropriate alternative.

Key Words
residual load carrying capacity; blast; steel column; P-I diagram

Address
Jong Yil Park: Agency for Defense Development, Joint Modeling and Simulation Center, PO Box 35-5 Yuseong,
Daejon 305-600, Korea
Theodor Krauthammer: Center for Infrastructure Protection and Physical Security (CIPPS), University of Florida,
365 Weil Hall, PO Box 116580, Gainesville, FL 32611-6580, USA


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