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CONTENTS
Volume 41, Number 3, February10 2012
 

Abstract
A three-dimensional formulation is proposed to analyze the lateral loading distribution of external actions in high-rise buildings. The method is extended to encompass any combination of bracings, including bracings with open thin-walled cross-sections, which are analyzed in the framework of Timoshenko-Vlasov\'s theory of sectorial areas. More in detail, the proposed unified approach is a tool for the preliminary stages of structural design. It considers infinitely rigid floors in their own planes, and allows to better understand stress and strain distributions in the different bearing elements if compared to a finite element analysis. Numerical examples, describing the structural response of tall buildings characterized by bracings with different cross-section and height, show the effectiveness and flexibility of the proposed method. The accuracy of the results is investigated by a comparison with finite element solutions, in which the bracings are modelled as three-dimensional structures by means of shell elements.

Key Words
structural behaviour; modelling methods; tall buildings; lateral loading distribution; thinwalled cross-section; Timoshenko-Vlasov\'s theory; finite element method

Address
Alberto Carpinteri, Mauro Corrado, Giuseppe Lacidogna and Sandro Cammarano: Department of Structural and Geotechnical Engineering, Politecnico di Torino, Torino, Italy

Abstract
The slope stability analysis is usually done using the methods of calculation to rupture. The problem lies in determining the critical failure surface and the corresponding factor of safety (FOS). To evaluate the slope stability by a method of limit equilibrium, there are linear and nonlinear methods. The linear methods are direct methods of calculation of FOS but nonlinear methods require an iterative process. The nonlinear simplified Bishop method\'s is popular because it can quickly calculate FOS for different slopes. This paper concerns the use of inverse analysis by genetic algorithm (GA) to find out the factor of safety for the slopes using the Bishop simplified method. The analysis is formulated to solve the nonlinear equilibrium equation and find the critical failure surface and the corresponding safety factor. The results obtained by this approach compared with those available in literature illustrate the effectiveness of this inverse method.

Key Words
stability; inverse analysis; genetic algorithm; safety factor

Address
D. Mendjel and S. Messast: Department of Civil Engineering, LMGHU Laboratory, University of Skikda, Algeria

Abstract
Fuzzy logic based control has recently been proposed for regulating the properties of magnetorheological (MR) dampers in an effort to reduce vibrations of structures subjected to seismic excitations. So far, most studies showing the effectiveness of these algorithms have focused on the use of a single MR damper. Because multiple dampers would be needed in practical applications, this study aims to evaluate the effects of multiple individually tuned fuzzy-controlled MR dampers in reducing responses of a multi-degree-of-freedom structure subjected to seismic motions. Two different fuzzy-control algorithms are considered, a traditional controller where all parameters are kept constant, and a gainscheduling control strategy. Different damper placement configurations are also considered, as are different numbers of MR dampers. To determine the robustness of the fuzzy controllers developed to changes in ground excitation, the structure selected is subjected to different earthquake records. Responses analyzed include peak and root mean square displacements, accelerations, and interstory drifts. Results obtained with the fuzzy-based control schemes are compared to passive control strategies.

Key Words
MR damper; semi-active control; fuzzy logic; fuzzy control; structural control

Address
Claudia Mara Dias Wilson: New Mexico Institute of Mining and Technology, Socorro, NM, USA

Abstract
In this study, strength reduction factors are investigated for SDOF systems with period range of 0.1-3.0 s with elastoplastic behavior considering soil structure interaction for 64 different earthquake motions recorded on different site conditions such as rock, stiff soil, soft soil and very soft soil. Soil structure interacting systems are modeled and analyzed with effective period, effective damping and effective ductility values differing from fixed-base case. For inelastic time history analyses, Newmark method for step by step time integration was adapted in an in-house computer program. Results are compared with those calculated for fixed-base case. A new equation is proposed for strength reduction factor of interacting system as a function of structural period of system (T), ductility ratio (u) and period lengthening ratio (T/T). It is concluded that soil structure interaction reduces the strength reduction factors for soft soils, therefore, using the fixed-base strength reduction factors for interacting systems lead to nonconservative design forces.

Key Words
soil-structure interaction; strength reduction factors; ductility demand; structural analysis

Address
Muberra Eser, Cem Aydemir and Ibrahim Ekiz: Department of Civil Engineering, Y ld z Technical University, Istanbul, Turkey

Abstract
Of the various methods of splicing reinforcing bar in reinforced concrete structure, mortarfilled sleeve reinforcement splice offers diverse benefits, not only in terms of structural performance but also for the construction process. Consequently, after the mortar-filled sleeve splices have been developed in recent years, research and development on these splices has been actively carried out, in order to evaluate its macro structural performance, such as its strength and stiffness, with the aim of enabling this system to be applied to construction in the field as early as possible. However, to make a proper evaluation on the overall structural performance of the mortar-filled sleeve reinforcing bar splice, it is of critical importance to understand the lateral confining action of the sleeve, which is known to affect the bond strength between the embedded bar and mortar in the sleeve. Accordingly, in this study, an experiment of monotonic loading and cyclic loading was conducted with a full-sized mortar-filled sleeve splice attaching strain gauges on the sleeve surface with experimental variables such as development length of bar, etc. Based on the test results, the effect of the lateral confining action of the sleeve was analyzed and considered in terms of the bond strength between the bar and mortar in this splice.

Key Words
lateral confining action; mortar-filled sleeve reinforcing bar splice; bond strength; confining pressure; development length

Address
Hyong-Kee Kim: Department of Architectural Engineering, Kangwon National University, 346 Joongang-ro, Samcheok, Gangwon-do, Korea
Sang-Ho Lee: Department of Architectural Engineering, Hanzhong University, 200 Jiyang-gil, Donghae, Gangwon-do, Korea

Abstract
Basic problem of pile foundation is three dimensional in nature. Three dimensional finite element formulation is employed for the analysis of pile groups. Pile, pile-cap and soil are modeled using 20 node element, whereas interface between pile or pile cap and soil is modeled using 16 node surface element. A parametric study is carried out to consider the effect of pile spacing, number of piles, arrangement of pile and soil modulus on the response of pile group. Results indicate that the response of pile group is dependent on these parameters.

Key Words
pile; pile-cap; spacing; series arrangement; parallel arrangement

Address
V.A. Sawant and K.B. Ladhane: Department of Civil Engineering, Indian Institute of Technology (IIT), Roorkee, Uttarakhand 247 667, India

Abstract
This study investigated possible ways to replace conventional stirrups used on high-strength concrete members with improved reinforcing materials. Headed bar and high-strength steel were chosen to substitute for conventional stirrups, and an experimental comparison between the shear behavior of highstrength concrete large beams reinforced with conventional stirrups and the chosen stirrup substitutes was made. Test results indicated that the headed bar and the high-strength steel led to a significant reserve of shear strength and a good redistribution of shear between stirrups after shear cracking. This is due to the headed bar providing excellent end anchorage and the high-strength steel successfully resisting higher and sudden shear transmission from the concrete to the shear reinforcement. Experimental results presented in this paper were also compared with various prediction models for shear strength of concrete members.

Key Words
shear; high-strength concrete; headed bar; high-strength steel; anchorage

Address
Jun-Mo Yang: Steel Structure Research Division, Research Institute of Industrial Science & Technology, Incheon, Korea
Kyung-Hwan Min and Young-Soo Yoon: School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, Korea

Abstract
In this analytical study numerous prior experimental studies on reinforced concrete beam-tocolumn connections subjected to cyclic loading are investigated and a database of geometric properties, material strengths, configuration details and test results of subassemblies is established. Considering previous experimental research and employing statistical correlation method, parameters affecting joint shear capacity are determined. Afterwards, an equation to predict the joint shear strength is formed based on the most influential parameters. The developed equation includes parameters that take into account the effect of eccentricity, column axial load, wide beams and transverse beams on the seismic behavior of the beam-to-column connections, besides the key parameters such as concrete compressive strength, reinforcement yield strength, effective joint width and joint transverse reinforcement ratio.

Key Words
reinforced concrete; beam-to-column connections; joint shear strength; cyclic loading

Address
Mehmet Unal and Burcu Burak: Department of Civil Engineering, Middle East Technical University, Ankara, Turkey


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