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CONTENTS
Volume 59, Number 5, September10 2016
 

Abstract
Gas pipelines are types of structures that are highly susceptible to corrosion. Sometimes, the pipes are subjected to a thinning of the wall thickness at the inside or outside wall due to erosion/corrosion. Therefore, it is important to evaluate the strength of the pipes undergoing corrosion to maintain the integrity of the piping systems. The main purpose of this study is to understand failure aspects caused by degradation of metal due to corrosion through. The ASME standard offers a relationship for the yielding pressure of the corroded pipes which was compared with the finite element results. The results demonstrate to obtain accurate results, the ASME relationship is unreliable. Moreover, pitting corrosion must be considered critical more than of other types.

Key Words
gas pipeline; limit failure pressure; geometric pattern corrosion; ASME code

Address
Nemat Hassani, S. Mohammad S. Kolbadi, Mahmud Reza Shiravand and Jafar H. Golafshani: Department of Civil Engineering, Shahid Beheshti University, Tehran, Iran

Abstract
In this study a direct displacement-based design (DDBD) procedure for a continuous deck bridge isolated with triple friction pendulum bearings (TFPB) has been proposed and the seismic demands of the bridge such as isolator\'s displacement and drift of piers obtained from this procedure evaluated under two-directional near-field ground motions. The structural model used here are continuous, three-span, castin-place concrete box girder bridge with a 30-degree skew which are isolated with 9 different TFPBs. By comparing the results of DDBD method with those of nonlinear time history analysis (NTHA), it can be concluded that the proposed procedure is able to predict seismic demands of similar isolated bridges with acceptable accuracy. Results of NTHA shows that dispersion of peak resultant responses for a group of ground motions increases by increasing their average value of responses. It needs to be noted that the demands parameters calculated by the DDBD procedure are almost overestimated for stiffer soil condition, but there is some underestimation in results of this method for softer soil condition.

Key Words
direct displacement-based design; triple friction pendulum bearing; seismic isolation; bridge; near field ground motion

Address
Gholamreza Ghodrati Amiri: Center of Excellence for Fundamental Studies in Structural Engineering, School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran
Mahdi Mohammadian Shalmaee: Department of Civil Engineering, Faculty of Engineering, University of Guilan, Rasht, Iran
Pejman Namiranian: School of Civil Engineering, Iran University of Science and Technology, Tehran, Iran

Abstract
A simple design process is proposed for supplemental viscous dampers based on structural safety redundancy. In this process, the safety redundancy of the primary structure without a damper is assessed by the capacity and response spectra. The required damping ratio that should be provided by the supplemental dampers is estimated by taking the structural safety redundancy as a design target. The arrangement of dampers is determined according to the drift distribution obtained by performing pushover analysis. A benchmark model is used to illustrate and verify the validity of this design process. The results show that the structural safety redundancy of the structure provided by the viscous dampers increases to approximately twice that of the structure without a damper and is close to the design target. Compared with the existing design methods, the proposed process can estimate the elastic-plastic response of a structure more easily by using static calculation, and determine the required damping ratio more directly without iterative calculation or graphical process. It can be concluded that the proposed process is simple and effective.

Key Words
structural safety redundancy; viscous damper; elastic-plastic design; seismic spectrum

Address
Linfei Hao: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, Shanghai 200092, China; Department of Architecture, Tohoku University, Sendai 980-8579, Japan
Ruifu Zhang: Research Institute of Structural Engineering and Disaster Reduction, Tongji University, Shanghai 200092, China

Abstract
The present paper is concerned with the investigation of propagation of thermoelastic media, the finite difference technique is used to obtain the solution for the uncoupled dynamic thermoelastic stress problem in a non-homogeneous orthrotropc thick cylindrical shell. In implementing the method, the linear dynamic thermoelasticity equations are used with the appropriate boundary and initial conditions. Thermal shock stress becomes of significant magnitude due to stress wave propagation which is initiated at the boundaries by sudden thermal loading. Numerical results have been given and illustrated graphically in each case considered. The presented results indicate that the effect of inhomogeneity is very pronounced.

Key Words
thermal stress; thermal shock; orthotropic material; thermoelastic medium; wave propagation

Address
E. Edfawy: Mathematics Department, Faculty of Science, Taif University, K.S.A.; Mathematics Department, Faculty of Science, Assuit University, Egypt

Abstract
This paper examines a methodology for computing the probability of structural failure of reinforced concrete beams subjected to fire. The significant load variables considered are dead load, sustained live load and fire temperature. Resistance is expressed in terms of moment capacity with random variables taken as yield strength of steel, concrete class (or grade of concrete), beam width and depth. The flexural capacity is determined based on the design equations recommended in Indian standard IS456:2000. Simplified method named 500oC isotherm method detailed in Eurocode 2 is incorporated for fire design. A transient thermal analysis is conducted using finite element software ANSYS(R) Release15. Reliability is evaluated from the initial state to 4h of fire exposure based on the first order reliability method (FORM). A procedure is coded in MATLAB for finding the reliability index. This procedure is validated with available literature. The effect of various parameters like effective cover, yield strength of steel, grade of concrete, distribution of reinforcement bars and aggregate type on reliability indices are studied. Parameters like effective cover of concrete, yield strength of steel has a significant effect on reliability of beams. Different failure modes like limit state of flexure and limit state of shear are checked.

Key Words
reinforced concrete; fire exposure; reliability index; failure modes; IS456:2000

Address
Aneesha Balaji, M.S. Aathira, T.M. Madhavan Pillai and Praveen Nagarajan: Department of Civil Engineering, National Institute of Technology, Calicut, India

Abstract
In this paper, the effects of steel-fiber and rebar reinforcements on the ultimate bearing strength of the local anchorage zone were investigated based on experiments and comparisons between test results and design-equation predictions (AASHTO 2012, NCHRP 1994). Eighteen specimens were fabricated using the same anchorage device, which is one of the conventional anchorage devices, and two transverse ribs were used to secure an additional bearing area for a compact anchorage-zone design. Eight of the specimens were reinforced with only steel fiber and are of two concrete strengths, while six were reinforced with only rebars for two concrete strengths. The other four specimens were reinforced with both rebars and steel fiber for one concrete strength. The test and the comparisons between the design-equation predictions and the test results showed that the ultimate bearing strength and the section efficiency are highly affected by the reinforcement details and the concrete strength; moreover, the NCHRP equation can be conservatively applied to various local anchorage zones for the prediction of the ultimate bearing strength, whereby conditions such as the consideration of the rib area and the calibration factor are changed.

Key Words
post-tension; anchorage; bearing strength; steel fiber; local anchorage zone

Address
Jin-Kook Kim, Jun-Mo Yang: Steel Structure Research Group, POSCO, 100, Songdogwahak-ro, Yeonsu-gu, Incheon, 21985, Republic of Korea
Yangsu Kwon: Site & Structural Engineering Group, KHNP Central Research Institute, 70, 1312-gil, Yuseong-daero, Yuseong-gu, Daejeon, 34101, Republic of Korea

Abstract
The energy-based approach to predict the fatigue crack growth behavior under constant and variable amplitude loading (VAL) of the aluminum alloy 2024 T351 has been investigated and detailed analyses discussed. Firstly, the plastic strain energy was determined per cycle for different block load tests. The relationship between the crack advance and hysteretic energy dissipated per block can be represented by a power law. Then, an analytical model to estimate the lifetime for each spectrum is proposed. The results obtained are compared with the experimentally measured results and the models proposed by Klingbeil\'s model and Tracey\'s model. The evolution of the hysteretic energy dissipated per block is shown similar with that observed under constant amplitude loading.

Key Words
fatigue crack growth; variable amplitude; hysteretic energy; energy approach; aluminum alloy

Address
Sofiane Maachou, Abdelkader Boulenouar, Mohamed Benguediab, Mohamed Mazari: Materials and Reactive Systems Laboratory, Mechanical Engineering Department, University of Sidi-Bel-Abbes, BP. 89, City Larbi Ben Mhidi, Sidi Bel Abbes 22000, Algeria
Narayanaswami Ranganathan: School Polytechnic University of Tours, 7 Avenue Marcel Dassault 37004 Tours, France

Abstract
MeshFree methods have become popular owing to the ease with which high stress gradients can be identified and node density distribution can be reformulated to accomplish faster convergence. This paper presents a strategy for nodal density refinement with strain energy as basis in Element-Free Galerkin MeshFree technique. Two popular flat plate problems are considered for the demonstration of the proposed strategies. Issue of integration errors introduced during nodal density refinement have been addressed by suggesting integration cell refinement. High stress effects around two symmetrical semi-circular notches under in-plane axial load have been addressed in the first problem. The second considers crack propagation under mode I and mode II fracture loading by the way of introducing high stress intensity through line crack. The computational efficacy of the adaptive refinement strategies proposed has been highlighted.

Key Words
adaptive refinement; element-free Galerkin; crack propagation; stress intensity; stress concentration

Address
Bhavana S.S. Patel: National Institute of Technology Karnataka, India; RV College of Engineering, India
Babu K.S. Narayan and Katta Venkataramana: National Institute of Technology Karnataka, India

Abstract
This paper presents a theoretical analysis for determining the transverse deflection of simply supported battened beams subjected to a uniformly distributed transverse quasi-static load. The analysis considers not only the shear effect but also the discrete effect of battens on the transverse deflection of the battened beam. The analytical solution is obtained using the principle of minimum potential energy. Numerical validation of the present analytical solution is accomplished using finite element methods. The present analytical solution shows that the shear effect on the transverse deflection of battened beams increases with the cross-section area of the main member but decreases with the cross-section area of the batten. The longer the battened beam is, or the larger the moment of inertia of the main member is, the smaller the shear effect will be.

Key Words
analytical method; computational mechanics; finite element method (FEM); frames; quasistatic; steel structures

Address
Ji-liang Li and Jian-kang Chen: The Faculty of Mechanical Engineering and Mechanics, Ningbo University, 315211 Ningbo, China

Abstract
Decks, interior beams, edge beams and girders are the parts of a steel floor system. If the deck is optimized without considering beam optimization, finding best result is simple. However, a deck with higher cost may increase the composite action of the beams and decrease the beam cost reducing the total cost. Also different number of floor divisions can improve the total floor cost. Increasing beam capacity by using castellated beams is other efficient method to save the costs. In this study, floor optimization is performed and these three issues are discussed. Floor division number and deck sections are some of the variables. Also for each beam, profile section of the beam, beam cutting depth, cutting angle, spacing between holes and number of filled holes at the ends of castellated beams are other variables. Constraints include the application of stress, stability, deflection and vibration limitations according to the load and resistance factor (LRFD) design. Objective function is the total cost of the floor consisting of the steel profile cost, cutting and welding cost, concrete cost, steel deck cost, shear stud cost and construction costs. Optimization is performed by enhanced colliding body optimization (ECBO), Results show that using castellated beams, selecting a deck with higher price and considering different number of floor divisions can decrease the total cost of the floor.

Key Words
structural optimization; steel floor optimization; composite castellated beams; enhanced colliding bodies optimization; floor division number

Address
A. Kaveh and M.H. Ghafari: Centre of Excellence for Fundamental Studies in Structural Engineering, Iran University of Science and Technology, Narmak, Tehran, P.O. Box 16846-13114, Iran


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