Techno Press
Tp_Editing System.E (TES.E)
Login Search


sem
 
CONTENTS
Volume 45, Number 6, March25 2013
 

Abstract
This paper presents a parametric study of reinforced concrete bridge tall piers with hollow, rectangular sections. Such piers are typically used in railway construction of prestressed concrete viaducts. Twenty one different piers have been studied with seven column heights of 40, 50, 60, 70, 80, 90 and 100 m and three types of 10-span continuous viaducts, whose main span lengths are 40, 50 and 60 m. The piers studied are intermediate columns placed in the middle of the viaducts. The total number of optimization design variables varies from 139 for piers with column height of 40 m to 307 for piers with column height of 100 m. Further, the results presented are of much value for the preliminary design of the piers of prestressed concrete viaducts of high speed railway lines.

Key Words
ant colony optimization; concrete structures; economic optimization; structural design; tall piers

Address
Francisco J. Martinez-Martin: Department of Geotechnical Engineering, Universitat Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain
Fernando Gonzalez-Vidosa, Antonio Hospitaler and Victor Yepes: Department of Construction Engineering, Institute of Concrete Science and Technology (ICITECH), Universitat Politecnica de Valencia, Camino de Vera s/n, 46022 Valencia, Spain

Abstract
In this study, inelastic displacement ratios are investigated for existing systems with known lateral strength considering soil structure interaction. For this purpose, SDOF systems for period range of 0.1-3.0 s with different hysteretic behaviors are considered for a number of 18 earthquake motions recorded on soft soil. The effect of stiffness degradation on inelastic displacement ratios is investigated. The Modified Clough model is used to represent structures that exhibit significant stiffness degradation when subjected to reverse cyclic loading and the elastoplastic model is used to represent non-degrading structures. Soil structure interaction analyses are conducted by means of equivalent fixed base model 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. A new equation is proposed for inelastic displacement ratio of system with SSI with elastoplastic or degrading behavior as a function of structural period (T), strength reduction factor (R) and period lengthening ratio (T/T). The proposed equation for CR which takes the soil-structure interaction into account should be useful in estimating the inelastic deformation of existing structures with known lateral strength.

Key Words
soil-structure interaction; inelastic displacement ratio; strength reduction factor; lateral strength; stiffness degradation; seismic analysis

Address
Muberra Eser Aydemir: Department of Civil Engineering, Istanbul Aydin University, Istanbul, Turkey

Abstract
In this paper, a topology optimization method based on the element independent nodal density (EIND) is developed for continuum solids with multiple load cases and multiple constraints. The optimization problem is formulated as minimizing the volume subject to displacement constraints. Nodal densities of the finite element mesh are used as the design variables. The nodal densities are interpolated into any point in the design domain by the Shepard interpolation scheme and the Heaviside function. Without using additional constraints (such as the filtering technique), mesh-independent, checkerboard-free, distinct optimal topology can be obtained. Adopting the rational approximation for material properties (RAMP), the topology optimization procedure is implemented using a solid isotropic material with penalization (SIMP) method and a dual programming optimization algorithm. The computational efficiency is greatly improved by multithread parallel computing with OpenMP to run parallel programs for the shared-memory model of parallel computation. Finally, several examples are presented to demonstrate the effectiveness of the developed techniques.

Key Words
topology optimization; element independent nodal density; Shepard interpolation scheme; multiple load cases; multiple constraints; parallel computation

Address
Jijun Yi: School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China; School of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410004, China
Jianhua Rong: School of Automobile and Mechanical Engineering, Changsha University of Science and Technology, Changsha 410004, China
Tao Zeng: School of Mechanical and Electrical Engineering, Central South University, Changsha 410083, China
X. Huang: School of Civil, Environmental and Chemical Engineering, RMIT University, GPO Box 2476, Melbourne3001, Australia

Abstract
In this paper, adaptive neuro-fuzzy inference system (ANFIS) and artificial neural networks (ANNs) techniques are developed and applied to identify damage in a model steel girder bridge using dynamic parameters. The required data in the form of natural frequencies are obtained from experimental modal analysis. A comparative study is made using the ANNs and ANFIS techniques and results showed that both ANFIS and ANN present good predictions. However the proposed ANFIS architecture using hybrid learning algorithm was found to perform better than the multilayer feedforward ANN which learns using the backpropagation algorithm. This paper also highlights the concept of ANNs and ANFIS followed by the detail presentation of the experimental modal analysis for natural frequencies extraction.

Key Words
adaptive neuro fuzzy interface system (ANFIS); artificial neural networks (ANNs); backpropagation (BP); damage identification; experimental modal analysis

Address
S.J.S. Hakim and H. Abdul Razak: StrucHMRS Group, Department of Civil Engineering, University of Malaya, Kuala Lumpur 50603, Malaysia

Abstract
This paper addresses two main issues relevant to the structural assessment of buildings subjected to explosions. The first issue regards the robustness evaluation of steel frame structures: a procedure is provided for computing \"robustness curves\" and it is applied to a 20-storey steel frame building, describing the residual strength of the (blast) damaged structure under different local damage levels. The second issue regards the precise evaluation of blast pressures acting on structural elements using Computational Fluid Dynamic (CFD) techniques. This last aspect is treated with particular reference to gas explosions, focusing on some critical parameters (room congestion, failure of non-structural walls and ignition point location) which influence the development of the explosion. From the analyses, it can be deduced that, at least for the examined cases, the obtained robustness curves provide a suitable tool that can be used for risk management and assessment purposes. Moreover, the variation of relevant CFD analysis outcomes (e.g., pressure) due to the variation of the analysis parameters is found to be significant.

Key Words
blast engineering; robustness; progressive collapse; blast action; gas explosions; steel buildings

Address
Pierluigi Olmati, Francesco Petrini and Franco Bontempi: Department of Structural and Geotechnical Engineering, Sapienza University of Rome, Rome, Italy

Abstract
The acceleration that the electrical equipment experiences on a structure can be several times the ground acceleration. Currently, substation support structures are being designed according to ASCE (Substation Structure Design Guide 2008), without any consideration about effects of these structures on dynamic behavior of mounted equipment. In this paper, a parametric study is implemented in order to improve seismic design of candlestick substation structures based on this design guide. To do this, dynamic amplification factor (DAF) of different candlestick support-equipment combinations is evaluated and compared to the target DAF presented in IEEE STD 693 (2006). Based on this procedure, a new criterion is developed to restrict maximum acceleration at support-equipment intersection.

Key Words
seismic design; dynamic amplification factor; substations; support structures

Address
Reza Karami Mohammadi: Civil Engineering Department, K. N. Toosi University of Technology (KNTU), Tehran, Iran
Vahid Akrami: Civil Engineering Department, Amirkabir University of Technology, Tehran, Iran
Farzad Nikfarb: Civil Engineering Department, McMaster University, Hamilton, Canada

Abstract
In construction industry, strength is a primary criterion in selecting a concrete for a particular application. The concrete used for construction gains strength over a long period of time after pouring the concrete. The characteristic strength of concrete is defined as the compressive strength of a sample that has been aged for 28 days. Neither waiting for 28 days for such a test would serve the rapidity of construction, nor would neglecting it serve the quality control process on concrete in large construction sites. Therefore, rapid and reliable prediction of the strength of concrete would be of great significance. On this backdrop, the method is proposed to establish a predictive relationship between properties and proportions of ingredients of concrete, compaction factor, weight of concrete cubes and strength of concrete whereby the strength of concrete can be predicted at early age. Multiple regression analysis was carried out for predicting the compressive strength of concrete containing Portland Pozolana cement using statistical analysis for the concrete data obtained from the experimental work done in this study. The multiple linear regression models yielded fairly good correlation coefficient for the prediction of compressive strength for 7, 28 and 40 days curing. The results indicate that the proposed regression models are effectively capable of evaluating the compressive strength of the concrete containing Portaland Pozolana Cement. The derived formulas are very simple, straightforward and provide an effective analysis tool accessible to practicing engineers.

Key Words
concrete; compressive strength; admixture; regression analysis; predicted strength; predictive tools

Address
H.S. Chore and N.L. Shelke: Department of Civil Engineering, Datta Meghe College of Engineering, Sector-3, Airoli, Navi Mumbai- 400 708, India

Abstract
Inflatable panels made of modern and new textile materials can be inflated at high pressure to have a high mechanical strength. This paper is based on the finite element method as a general solution to determine the characteristics of deformed inflatable panels at high pressure in various end and loading conditions. Proposed method is based on the construction of weak form of formulation and application of Reduced Integration Element method (RIE) to solve the numerical problem of shear locking. The numerical results are validated as an outcome of comparison with other published results.

Key Words
inflatable panel, high pressure, deformable structures, textile material, finite element method

Address
S.R. Mohebpour: Department of Mechanical Engineering, Persian Gulf University, Bushehr, Iran


Techno-Press: Publishers of international journals and conference proceedings.       Copyright © 2017 Techno-Press
P.O. Box 33, Yuseong, Daejeon 34186 Korea, Tel: +82-42-828-7996, Fax : +82-42-828-7997, Email: info@techno-press.com