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CONTENTS
Volume 38, Number 4, May25 2011
 

Abstract
Continuous deep girders which transmit the gravity load from the upper wall to the lower columns have frequently long end shear spans between the boundary of the upper wall and the face of the lower column. This paper presents the results of tests and analyses performed on three 1:2.5 scale specimens with long end shear spans, (the ratios of shear-span/total depth: 1.8 < a/h < 2.5): one designed by the conventional approach using the beam theory and two by the strut-and-tie approach. The conclusions are as follows: (1) the yielding strength of the continuous RC deep girders is controlled by the tensile yielding of the bottom longitudinal reinforcements, being much larger than the nominal strength predicted by using the section analysis of the girder section only or using the strut-and-tie model based on elastic-analysis stress distribution. (2) The ultimate strengths are 22% to 26% larger than the yielding strength. This additional strength derives from the strain hardening of yielded reinforcements and the shear resistance due to continuity with the adjacent span. (3) The pattern of shear force flow and failure mode in shear zone varies depending on the amount of vertical shear reinforcement. And (4) it is necessary to take into account the existence of the upper wall in the analysis and design of the deep continuous transfer girders that support the upper wall with a long end shear span.

Key Words
reinforced concrete; continuous deep girder; strut-and-tie model; DIANA; shear capacity.

Address
Han-Seon Lee: School of Civil, Environmental, and Architectural Engineering, Korea University, Korea
Dong-Woo Ko: Department of Architectural Engineering, Jeju National University, Korea
Sung-Min Sun: Hyundai Engineering Co. Ltd, Korea

Abstract
An efficient two-level domain decomposition parallel algorithm is suggested to solve large-DOF structural problems with nonlinear material models generating unsymmetric tangent matrices, such as a group of plastic-damage material models. The parallel version of the stabilized bi-conjugate gradient method is developed to solve unsymmetric coarse problems iteratively. In the present approach the coarse DOF system is solved parallelly on each processor rather than the whole system equation to minimize the data communication between processors, which is appropriate to maintain the computing performance on a non-supercomputer level cluster system. The performance test results show that the suggested algorithm provides scalability on computing performance and an efficient approach to solve large-DOF nonlinear structural problems on a cluster system.

Key Words
parallel algorithm; domain decomposition; material nonlinearity; plastic-damage model.

Address
Jeeho Lee and Min Seok Kim: Department of Civil and Environmental Engineering, Dongguk University-Seoul, Seoul 100-715, Korea

Abstract
This paper presents recovering of missing vibration data of a bridge transmitted from wireless sensors. Kalman filter algorithm is adopted to reconstruct the missing data analytically. Validity of the analytical approach is examined through a field experiment of a bridge. Observations demonstrate that, even a part of recovered acceleration responses is underestimated in comparison with those responses taken from cabled sensors, dominant frequencies taken from the reconstructed data are comparable with those from cabled sensors.

Key Words
AR process; bridge health monitoring; Kalman filter; missing data recovery; wireless sensor node.

Address
C.W. Kim: Department of Civil & Earth Resources Engineering, Graduate School of Engineering, Kyoto University, Kyoto 615-8540, Kyoto, Japan
M. Kawatani, R. Ozaki: Department of Civil Engineering, Graduate School of Engineering, Kobe University, Kobe 657-8501, Japan
N. Makihata: JIP Techno Science Corporation, Osaka 532-0011, Japan

Abstract
In large-scale problem, a huge size of computational resources is needed for a reliable solution which represents the detailed description of dynamic behavior. Recently, eigenvalue reduction schemes have been considered as important technique to resolve computational resource problems. In addition, the efforts to advance an efficiency of reduction scheme leads to the development of the multilevel system condensation (MLSC) which is initially based on the two-level condensation scheme (TLCS). This scheme was proposed for approximating the lower eigenmodes which represent the global behavior of the structures through the element-level energy estimation. The MLSC combines the multi-level substructuring scheme with the previous TLCS for enhancement of efficiency which is related to computer memory and computing time. The present study focuses on the implementation of the MLSC on the direct time response analysis and the frequency response analysis of structural dynamic problems. For the transient time response analysis, the MLSC is combined with the Newmark

Key Words
structural dynamic system; system condensation; reduced system method; transient time integration; sub-structuring scheme; two-level condensation scheme.

Address
Sungmin Baek and Maenghyo Cho: WCU Multiscale Mechanical Design Division, School of Mechanical and Aerospace Engineering, Seoul National University, Seoul, Korea

Abstract
The loss of strength in a structure as a result of cyclic loads over a period of life time is an important phenomenon for the life-cycle analysis. Service loads are accentuated at the areas of stress concentration, mainly at the connection of components. Structural components unavoidably are affected by defects such as surface scratches, surface roughness and weld defects of random sizes, which usually occur during the manufacturing and handling process. These defects are shown to have an important effect on the fatigue life of the structural components by promoting crack initiation sites. The value of equivalent initial flaw size (EIFS) is calculated by using the back extrapolation technique and the Paris law of fatigue crack growth from results of fatigue tests. We try to analyze the effect of EIFS distribution in a multiple site damage (MSD) specimen by using the extended finite element method (XFEM). For the analysis, fatigue tests were conducted on the centrally-cracked specimens and MSD specimens.

Key Words
fatigue life prediction; equivalent initial flaw size; multiple site damage; back extrapolation; extended finite element method.

Address
JungHoon Kim, Goangseup Zi, Son-Nguyen Van, MinChul Jeong,
JungSik Kong: Department of Civil, Environmental and Architectural Engineering, Korea University, Seoul 136-701, Korea
Minsung Kim: Aerospace Technology Department (7-2), Agency for Defense Development, Daejeon 305-600, Korea

Abstract
Due to the low elastic modulus of FRP, concrete members reinforced with FRP rebars show greater deflections than members reinforced with steel rebars. Deflection is one of the important factors to consider the serviceability of horizontal members. In this study flexural test of AFRP reinforced concrete beams was performed considering reinforcement ratio and compressive strength as parameters. The test results indicated that flexural capacity and stiffness increase in proportion to the reinforcement ratio. The test results were compared with existing proposed equations for the effective moment of inertia including ACI 440. The most of the proposed equations were found to over-estimate the effective moment of inertia while the equation proposed by Bischoff and Scanlon (2007) most accurately predicted the values obtained through actual testing.

Key Words
AFRP rebar; beam; reinforcement ratio; concrete compressive strength; deflection; effective moment of inertia; serviceability.

Address
Min Sook Kim, Young Hak Lee, Heecheul Kim, Junbok Lee: Department of Architectural Engineering, Kyung Hee University, Yongin, Korea
Andrew Scanlon: Department of Civil Engineering, The Pennsylvania State University, University Park, USA

Abstract
Even though fiber reinforced polymer (FRP) has been widely used as a retrofitting material, the FRP behavior and effect in FRP retrofitted structure under blast loading, impulsive loading with instantaneous time duration, has not been accurately examined. The past studies have focused on the performance of FRP retrofitted structures by making simplifications in modeling, without incorporating accurate failure mechanisms of FRP. Therefore, it is critical to establish an analytical model that can properly consider the specific features of FRP material in evaluating the response of retrofitted concrete structures under blast loading. In this study, debonding failure analysis technique for FRP retrofitted concrete structure under blast loading is suggested by considering FRP material characteristics and debonding failure mechanisms as well as rate dependent failure mechanism based on a blast resisting design concept. In addition, blast simulation of FRP retrofitted RC panel is performed to validate the proposed model and analysis method. For validation of the proposed model and analysis method, the reported experimental results are compared with the debonding failure analysis results. From the comparative verification, it is confirmed that the proposed analytical model considering debonding failure of FRP is able to reasonably predict the behavior of FRP retrofitted concrete panel under blast loading.

Key Words
fiber reinforced polymer; KFRP; AFRP; GFRP; CFRP; retrofitting material; blast load; failure mechanism; rate dependent; debonding failure.

Address
Ho Jin Kim: Civil Engineering Research Institute, ATMACS Co. Ltd., Sungnam 463-760, Korea
Na Hyun Yi: School of Civil and Environmental Engineering, Yonsei University, Concrete Structural Engineering Laboratory, Seoul 120-794, Korea
Sung Bae Kim: School of Civil and Environmental Engineering, Yonsei University, Concrete Structural Engineering Laboratory, Seoul 120-794, Korea
Jin Won Nam: Department of Civil & Environmental Engineering, Southern University, Suite 321, Pinchback Building, Baton Rouge, LA, 70813, USA
Ju Hyung Ha: Material Division, Hyundai Institute of Construction Technology, Yongin-si, Gyunggi-do 446-716, Korea
Jang-Ho Jay Kim: 2School of Civil and Environmental Engineering, Yonsei University, Concrete Structural Engineering Laboratory, Seoul 120-794, Korea

Abstract
Uncertainty in concrete properties, including concrete modulus of elasticity and modulus of rupture, are predicted by developing a microstructural homogenization model. The homogenization model is developed by analyzing a concrete representative volume element (RVE) using the finite element (FE) method. The concrete RVE considers concrete as a three phase composite material including: cement paste, aggregate and interfacial transition zone (ITZ). The homogenization model allows for considering two sources of variability in concrete, randomly dispersed aggregates in the concrete matrix and uncertain mechanical properties of composite phases of concrete. Using the proposed homogenization technique, the uncertainty in concrete modulus of elasticity and modulus of rupture (described by numerical cumulative probability density function) are determined. Deflection uncertainty of reinforced concrete (RC) beams, propagated from uncertainties in concrete properties, is quantified using Monte Carlo (MC) simulation. Cracked plane frame analysis is used to account for tension stiffening in concrete. Concrete homogenization enables a unique opportunity to bridge the gap between concrete materials and structural modeling, which is necessary for realistic serviceability prediction.

Key Words
uncertainty; concrete; deflection; homogenization; RVE; Monte Carlo method.

Address
Jung J. Kim, Tai Fana and Mahmoud M. Reda Taha: Department of Civil Engineering, University of New Mexico, Albuquerque, NM, USA

Abstract
A topology optimization and shape optimization method are widely used in the design area of engineering field. In this paper, a unified procedure to combine both topology and shape optimization method is used. A material distribution method is used first to extract necessary design parameters of the structure and a shape optimization scheme using genetic algorithm and satisfying all the condition follows. As an example, a GFRP bridge deck is designed and compared with other commercial products. The performance of the designed deck shows that the used design procedure is very efficient and safe. This procedure can be generalized for using in other areas of engineering.

Key Words
topology optimization; shape optimization; genetic algorithm; minimum compliance design; GFRP deck.

Address
Eun-Hyung Lee and Jaegyun Park: Department of Civil & Environmental Engineering, Dankook University, Yong-In, Korea

Abstract
This paper presents the global-local finite cover method (GL-FCM) that is capable of analyzing structures involving local heterogeneities and propagating cracks. The suggested method is composed of two techniques. One of them is the FCM, which is one of the PU-based generalized finite element methods, for the analysis of local cohesive crack growth. The mechanical behavior evaluated in local heterogeneous structures by the FCM is transferred to the overall (global) structure by the so-called mortar method. The other is a method of mesh superposition for hierarchical modeling, which enables us to evaluate the average stiffness by the analysis of local heterogeneous structures not subjected to crack propagation. Several numerical experiments are conducted to validate the accuracy of the proposed method. The capability and applicability of the proposed method is demonstrated in an illustrative numerical example, in which we predict the mechanical deterioration of a reinforced concrete (RC) structure, whose local regions are subjected to propagating cracks induced by reinforcement corrosion.

Key Words
global-local analysis; finite cover method; hierarchical analysis method; multiple cohesive crack growth; reinforcement corrosion.

Address
Mao Kurumatani: Department of Urban and Civil Engineering, Ibaraki University, 4-12-1, Nakanarusawa, Hitachi, Ibaraki 316-8511, Japan
Kenjiro Terada: Department of Civil and Environmental Engineering, Tohoku University, 6-6-06, Aramaki Aza-Aoba,
Aoba-ku, Sendai, Miyagi 980-8579, Japan


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