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CONTENTS
Volume 26, Number 3, June20 2007
 

Abstract
The influence of masonry infills with eccentric openings on the seismic performance of reinforced concrete (r/c) frames that were designed in accordance with current code provisions are investigated. Eight 1/3-scale, single-story, single-bay frame specimens were tested under cyclic horizontal loading up to a drift level of 4%. In all examined cases the shear strength of columns was higher than the cracking shear strength of solid infill. The parameters investigated include the shape and the location of the opening. Assessment of the behavior of the frames is also attempted, based on the observed failure modes, strength, stiffness, ductility, energy dissipation capacity and degradation from cycling loading. Based on these results there can be deduced that masonry infills with eccentrically located openings has been proven to be beneficial to the seismic capacity of the bare r/c frames in terms of strength, stiffness, ductility and energy dissipation. The location of the opening must be as near to the edge of the infill as possible in order to provide an improvement in the performance of the infilled frame.

Key Words
infilled r/c frames; masonry infills; openings; cycling loading; experiments

Address
D. Kakaletsis; Technological Educational Institution of Serres, Terma Magnesias, Serres 62124, Greece
C. Karayannis; Laboratory of Reinforced Concrete, Dept. of Civil Engineering, Democritus University of Thrace, Xanthi 67100, Greece

Abstract
This paper examines the application of artificial neural networks (ANN) to the response prediction of geometrically nonlinear truss structures. Two types of analysis (deterministic and probabilistic analyses) are considered. A three-layer feed-forward backpropagation network with three input nodes, five hidden layer nodes and two output nodes is firstly developed for the deterministic response analysis. Then a back propagation training algorithm with Bayesian regularization is used to train the network. The trained network is then successfully combined with a direct Monte Carlo Simulation (MCS) to perform a probabilistic response analysis of geometrically nonlinear truss structures. Finally, the proposed ANN is applied to predict the response of a geometrically nonlinear truss structure. It is found that the proposed ANN is very efficient and reasonable in predicting the response of geometrically nonlinear truss structures.

Key Words
artificial neural networks; geometrically nonlinear analysis; truss structures; uncertainties; response.

Address
Jin Cheng; Dept. of Bridge Engineering, Tongji University, Shanghai, 200092, China
C. S. Cai; Dept. of Civil and Environmental Engineering, 3418H CEBA, Louisiana State University,
Baton Rouge, LA 70803, USA
Ru-Cheng Xiao; Dept. of Bridge Engineering, Tongji University, Shanghai, 200092, China

Abstract
Steel frame structures have been widely used in multi-storey and high-rise buildings and the connections in these structures are critical. In the Northridge and Kobe Earthquake, beam-column connections suffered damage due to brittle fracture. According to seismic design codes, ductility of the beam to column connection is also necessary. A study on the behavior of a beam to column connection with the aim of improving ductility as well as preventing brittle failure was carried out. In order to control the position of a plastic hinge on the beam, a connection with a hole in the beam web was developed. Five specimens with different parameters under cyclic load were assessed. The results are presented in terms of the stress distribution of the beam, hysteretic behavior, and ultimate capacity. Furthermore, the finite element method was also used to analyze the model, and the results were compared with those obtained from the experiment. It is shown from the analysis and experimental results that this type of connection is effective in terms of improving ductility for a beam to column connection in low-rise buildings.

Key Words
steel frame; beam to column connections; position of plastic hinge; experiments study; finite element analysis.

Address
Xiuli Wang; School of Civil Engineering, Lanzhou, University of Technology, Lanzhou, 730050, China
School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China
Zhanzhong Yin and Qingfu Li; School of Civil Engineering, Lanzhou, University of Technology, Lanzhou, 730050, China
Shizhao Shen; School of Civil Engineering, Harbin Institute of Technology, Harbin 150090, China

Abstract
3-D wall panels are used in construction of exterior and interior bearing and non-load bearing walls and floors of building of all types of construction. Fast construction, thermal insulation, reduced labor expense and weight saving are the most well pronounced advantage of such precast system. When the structural performance is concerned, the main disadvantage of 3D panel, when used as floor slab, is their brittleness in flexure. The current study focuses on upgrading ductility and load carrying capacity of 3D slabs in two different ways; using additional tension reinforcement, and inserting a longitudinal concentrated beam. The research is carried on both experimentally and numerically. The structural performance in terms of load carrying capacity and flexural ductility are discussed in details. The obtained results could give better understanding and design consideration of such prefabricated system

Key Words
3D panel; flexural performance; experiments; finite element

Address
Department of Civil and Environmental Engineering, Amirkabir University, Tehran, Iran
Prefabricated SAP Company, Tehran, Iran

Abstract
A preliminary performance-based seismic design methodology is proposed. The top yield displacement of the system is computed from these of the components, which are assumed constant. Besides, a simple procedure to evaluate the top yield displacement of frames is developed. Seismic demands are represented in the form of yield point spectra. The methodology is general, conceptually transparent, uses simple calculations based on first principles and is applicable to asymmetric systems. To consider a specific situation two earthquake levels, occasional and rare are considered. The advantage of an arbitrary assignment of strength to the different components to reduce eccentricities and improved the torsional response of the system is addressed. The methodology is applied to an asymmetric five story building, and the results are verified by push-over analysis and non linear dynamic analysis.

Key Words
design; system; earthquake-resistant; displacement; yield.

Address
Marcelo Rubinstein and Oscar Moller: Instituto de Mecanica Aplicada y Estructuras (IMAE), Facultad de Ciencias Exactas, Ingenieria y Agrimensura, Universidad Nacional de Rosario, Riobamba y Berutti, 2000 Rosario, Santa Fe, Argentina
Alejandro Giuliano: Instituto Nacional de Prevencion Sismica, Roger Balet 47 N, 5400 San Juan, Argentina

Abstract
A sudden change of stiffness in a structure, associated with the events such as weld fracture and brace breakage, will cause a discontinuity in acceleration response time histories recorded in the vicinity of damage location at damage time instant. A new damage index is proposed and implemented in this paper to detect the damage time instant, location, and severity of a structure due to a sudden change of structural stiffness. The proposed damage index is suitable for online structural health monitoring applications. It can also be used in conjunction with the empirical mode decomposition (EMD) for damage detection without using the intermittency check. Numerical simulation using a five-story shear building under different types of excitation is executed to assess the effectiveness and reliability of the proposed damage index and damage detection approach for the building at different damage levels. The sensitivity of the damage index to the intensity and frequency range of measurement noise is also examined. The results from this study demonstrate that the damage index and damage detection approach proposed can accurately identify the damage time instant and location in the building due to a sudden loss of stiffness if measurement noise is below a certain level. The relation between the damage severity and the proposed damage index is linear. The wavelet-transform (WT) and the EMD with intermittency check are also applied to the same building for the comparison of detection efficiency between the proposed approach, the WT and the EMD.

Key Words
sudden damage; acceleration response; signal discontinuity; damage index; empirical mode decomposion; wavalet transform; damage detection.

Address
B. Chen and Y. L. Xu: Dept. of Civil and Structural Eng., The Hong Kong Polytechnic University, Kowloon, Hong Kong

Abstract
This article presents a numerical tool for dimensioning two-threaded fasteners connecting prismatic parts subjected to fatigue tension loads that are coplanar with the screw axis. A simplified numerical model is developed from unidirectional finite elements, modeling the connected parts and screws with bent elements and the elastic contact layer between the parts with springs. An algorithm updating the contact stiffness matrix, calculating forces and displacements at each node of the structure and thus normal stresses in the screws in both static and fatigue is further developed using C language. An experimental study is also conducted in parallel with the numerical approach to validate the developed model assumptions, the numerical model and the 3D finite element results. Since stiffness values for the compressive zones in the parts are analytically difficult to determine, a statistical software method is used, from which a tuning factor is derived for identifying these stiffness values. The method is also applied to set out the influence of each parameter on the fatigue behaviour of each screw. Finally, the developed model will be used to establish a new, sophisticated, fast and accurate tool for dimensioning bolted mechanical structures.

Key Words
bolted connections; numerical modeling; finite elements; structures.

Address
Alain Daidie: Toulouse Mechanical Engineering Laboratory, INSA Toulouse, France
Jamel Chakhari: Toulouse Mechanical Engineering Laboratory, INSA Toulouse, France
Solid Mechanics, Structures and Technological Developments Laboratory, HSST Tunis, Tunisia
Ali Zghal: Solid Mechanics, Structures and Technological Developments Laboratory, HSST Tunis, Tunisia


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