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CONTENTS
Volume 13, Number 5, May 2014
 

Abstract
A sophisticated finite element modeling approach is proposed to simulate unbonded post-tensioned concrete slabs. Particularly, finite element contact formulation was employed to simulate the sliding behavior of unbonded tendons. The contact formulation along with other discretizing schemes was selected to assemble the post-tensioned concrete system. Three previously tested unbonded post-tensioned two-way and one-way slabs with different reinforcement configurations and boundary conditions were modeled. Numerical results were compared against experimental data in terms of global pressure-deflection relationship, stiffness degradation, cracking pattern, and stress variation in unbonded tendons. All comparisons indicate a very good agreement between the simulations and experiments. The exercise of model validation showcased the robustness and reliability of the proposed modeling approach applied to numerical simulation of post-tensioned concrete slabs.

Key Words
post-tensioning; prestressed concrete; two-way slabs; finite element; numerical model

Address
Uksun Kim and Pinaki R. Chakrabarti: Department of Civil Engineering, California State University at Fullerton, 800 N. State College Blvd., Fullerton, CA 92834, U.S.A.

Yu Huang: School of Civil Engineering and Environmental Science, The University of Oklahoma, 202 W. Boyd St. Rm 334, Norman, OK 73019, U.S.A.

Thomas H.-K. Kang: Department of Architecture & Architectural Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul151-744, Republic of Korea




Abstract
Soft storey buildings are characterised by having a storey that has a large amount of open space. This soft storey creates a major weak point during an earthquake. As the soft stories are typically associated with retail spaces and parking garages, they are often on the lower levels of tall building structures. Thus, when these stories collapse, the entire building can also collapse, causing serious structural damage that may render the structure completely unusable. The use of special soft storey is predominant in the tall building structures constructed by several local developers, making the issue important for local building structures. In this study, the effect of the incorporation of an isolator on the seismic behaviour of tall building structures is examined. The structures are subjected to earthquakes typical of the local city, and the isolator is incorporated with the appropriate isolator time period and damping ratio. A FEM-based computational relationship is proposed to increase the storey height so as to incorporate the isolator with the same time period and damping ratio for both a lead rubber bearing (LRB) and high-damping rubber bearing (HDRB). The study demonstrates that the values of the FEM-based structural design parameters are greatly reduced when the isolator is used. It is more beneficial to incorporate a LRB than a HDRB.

Key Words
rubber-steel bearing, nonlinear model; soft storey structure; Floor acceleration; Masonry infill; Inter-storey drift, Seismic isolation

Address
A.B.M. Saiful Islam, Mohammed Zamin Jumaat and Kh Mahfuz ud Darain: Department of Civil Engineering, Faculty of Engineering, University of Malaya, Kuala Lumpur, Malaysia

Raja Rizwan Hussain: Associate Professor, Department of Civil Engineering, College of Engineering, King Saud University, Riyadh, Saudi Arabia

Kh Mahfuz ud Darain: Architecture Discipline, Khulna University, Khulna, Bangladesh


Abstract
This paper is aimed at adapting Artificial Neural Networks (ANN) to predict the compressive strength of High Performance Concrete (HPC) containing binary and quaternary blends. The investigations were done on 23 HPC mixes, and specimens were cast and tested after 7, 28 and 56 days curing. The obtained experimental datas of 7, 28 and 56 days are trained using ANN which consists of eight input parameters like cement, metakaolin, blast furnace slag and fly ash, fine aggregate, coarse aggregate, superplasticizer and water binder ratio. The corresponding output parameters are 7, 28 and 56 days compressive strengths. The predicted values obtained using ANN show a good correlation between the Experimental data. The performance of the 8-9-3-3 architecture was better than other architectures. It concluded that ANN tool is convenient and time saving for predicting compressive strength at different ages.

Key Words
HPC; metakaolin; slag; fly ash; modeling; prediction; artificial neural networks

Address
Allam Lingama and J.Karthikeyan: Department of Civil Engineering, National Institute of Technology, Tiruchirappalli - 620015, Tamilnadu, India

Abstract
The seismic safety of concrete dams is one of the important problems in the engineering due to the vast socio-economic disasters which may be caused by collapse of these infrastructures. The accuracy of the risk evaluation associated with these existing dams as well as the efficient design of future dams is highly dependent on a proper understanding of their behaviour due to earthquakes. This paper develops an anisotropic damage model for arch dam under strong earthquakes. The modified Drucker-Prager criterion is adopted as the failure criteria of the dynamic damage evolution of concrete. Some process fields and other necessary information for the safety evaluation are obtained. The numerical results show that the seismic behaviour of concrete dams can be satisfactorily predicted.

Key Words
damage analysis; high-arch dam; seismic response; safety evaluation

Address
Xinhua Xue and Xingguo Yang: State Key Laboratory of Hydraulics and Mountain River Engineering, College of Water Resource and Hydropower, Sichuan University, No.24 South Section 1, Yihuan Road, Chengdu, Sichuan, 610065, P.R.China

Abstract
In this paper, effects of magnetic water on different properties of cement paste including fluidity, compressive strength, time of setting and etc, has been studied in concrete laboratory of Sahand University of Technology. For production of magnetic water, three devices including an AFM called device(made in UAE) ,a device marked AC(made in Germany) and finally a device was designed and made in Concrete Laboratory of Sahand University of Technology) have been used. The results show that, intensity and direction of magnetic field, velocity and time of water passing through magnetic device, and amount and type of Colloidal particles have direct effects on properties of magnetic water and using such a water in making cement paste, increases its fluidity and compressive strength up to 10%.

Key Words
concrete; cement paste; magnetic water; fluidity; compressive strength; time of setting

Address
N. Khorshidi: Department of Civil and Environmental Engineering, Sahand University, Tabriz, Iran

M. Ansari: Department of Civil and Environmental Engineering, Tarbiat Modares University of, Tehran, Iran

M. Bayat: Department of Civil Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran

Abstract
A Bayesian response surface updating procedure is applied in order to update the parameters of the covariance function of a random field for concrete properties based on a limited number of available measurements. Formulas as well as a numerical algorithm are presented in order to update the parameters of response surfaces using Markov Chain Monte Carlo simulations. The parameters of the covariance function are often based on some kind of expert judgment due the lack of sufficient measurement data. However, a Bayesian updating technique enables to estimate the parameters of the covariance function more rigorously and with less ambiguity. Prior information can be incorporated in the form of vague or informative priors. The proposed estimation procedure is evaluated through numerical simulations and compared to the commonly used least square method.

Key Words
bayesian updating techniques; random fields; concrete properties; covariance function; variogram; Markov chain Monte Carlo simulations

Address
Pieterjan Criel, Robby Caspeele and Luc Taerwe: Ghent University, Department of Structural Engineering, Magnel Laboratory for Concrete Research, Ghent, Belgium

Abstract
The selected carrier systems of reinforced concrete frame buildings are quite important on structural damages. In this study are examined comparatively nonlinear behaviours of reinforced concrete frames which having different stiffening members under a horizontal load. In that respect, the study consists of six parametric models. With this purpose, nonlinear structural analyses of reinforced concrete frames which having different stiffening members were carried out with LUSAS which uses the finite element method. Thus, some conclusions and recommendations to mitigate the damage of reinforced concrete buildings in the future designs are aimed to present. The obtained results revealed that in terms of performance, the x-shaped diagonal elements can be used as an option to shear walls. In addition, it was found that frame-2, frame-3 and frame-4 showed a better performance than traditional frame system (frame-1).

Key Words
different stiffening members; finite element method; nonlinear analysis

Address
Şenol Gürsoy: Department of Civil Engineering, Karabük University, 78050 Karabük, Turkey


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