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CONTENTS
Volume 62, Number 3, May10 2017
 

Abstract
In this study, recently developed swarm intelligence algorithm called Social Spider Optimization (SSO) approach and its enhanced version of SSO algorithm with spider jump techniques is used to develop a structural optimization technique for steel space structures. The improved version of SSO uses adaptive randomness probability in generating new solutions. The objective function of the design optimization problem is taken as the weight of a steel space structure. Constraints\' functions are implemented from American Institute of Steel Construction-Load Resistance factor design (AISC-LRFD) and Ad Hoc Committee report and practice which cover strength, serviceability and geometric requirements. Three steel space structures are optimized using both standard SSO and SSO with spider jump (SSO_SJ) algorithms and the results are compared with those available in the literature in order to investigate the performance of the proposed algorithms.

Key Words
optimization; swarm intelligence; metaheuristic; social spider optimization; space frame; space truss

Address
Ibrahim Aydogdu: Department of Civil Engineering, Akdeniz University, Dumlupinar Bvld., 07058, Antalya, Turkey
Perihan Efe, Metin Yetkin: Department of Civil Engineering, Balikesir University, Balikesir, Turkey
Alper Akin: Trinity Meyer Utility Structures, Memphis, TN, USA

Abstract
A meso-scale model is proposed to study filament-wound composites with fiber undulations and crossovers. First, the crossover and undulation region is classified as the circumferential undulation and the helical undulation. Next, the two undulations are separately regarded as a series of sub-models to describe the meso-structure of undulations by using mesoparameters such as fiber orientation, fiber inclination angle, resin rich area, fiber volume fraction and bundle cross section. With the meso-structure model and the classic laminate theory, a method for calculating the stiffness of filament wound composites is eventually established. The effects of the fiber inclination angle, the fiber and resin volume fraction and the resin rich area on the stiffness are studied. The numerical results show that the elastic moduli for the circumferential undulation region decrease to a great extent as compared with that of the helical undulation region. Moreover, significant decrease in the elastic and shear moduli and increase in the Poisson\'s ratio are also found for the resin rich area. In addition, thickness and bundle section have evident effect on the equivalent stiffness of the fiber crossover and the undulation region.

Key Words
filament wound composites; fiber crossover and undulation; meso-scale model; resin rich area; stiffness

Address
Chuangshi Shen: School of Mechanics, Civil and Architecture, Northwestern Polytechnical University, Xi\'an, 710072, China
Xiaoping Han: State Key Laboratory for Strength and Vibration of Mechanical Structures, Xi\'an Jiaotong University, Xi\'an,710049, China

Abstract
Damping value has considerable influence on the dynamic and seismic behaviors of bridges. However, currently the constant damping ratios that are prescribed by most bridge seismic design codes can\'t truly represent the complicated damping character of actual structures. In this paper, a cyclic loading experiment was conducted to study the effect of stress amplitude on material damping of concrete to present an analyzing model of the material damping of concrete. Furthermore, based on the fundamental damping of structure measured under ambient vibration, combined with the presented stress-dependent material damping concrete, the seismic response of a bridge pier was calculated. Comparison between the calculated and experiment results verified the validity of the presented damping model. Finally, a modified design and analysis method for bridge was proposed based on stress-dependent damping theory, and a continuous rigid frame bridge was selected as the example to calculate the actual damping values and the dynamic response of the bridge under different earthquake intensities. The calculation results indicated that using the constant damping given by the Chinese seismic design code of bridges would overestimate the energy dissipation capacity of the bridge.

Key Words
cyclic loading experiment; stress-dependent damping; seismic design of bridge; response spectrum

Address
Li Su, Yuanfeng Wang, Shengqi Mei and Kun Guo: Department of Civil Engineering, Beijing Jiaotong University, No.3 Shang Yuan Cun, Hai Dian District, Beijing, China
Pengfei Li: Bridge Technology Research Center, Research Institute of Highway, MOT, Beijing, China

Abstract
The behaviour of reinforced concrete beams strengthened with near surface mounted (NSM) CFRP prestressed prisms was experimentally investigated. Five RC beams were tested under four point bending. All beams were made with dimensions of 300 mm in width, 2000 mm in length and 150 in depth. The effects of presstress level of CFRP prestressed prisms and prism material type were studied. The failure mode, load capacity, deflection, CFRP strain, steel strain and ductility of the tested beams were all analyzed. The results showed that the behavior of the reinforced concrete beams strengthened with NSM CFRP prestressed prisms showed a significant increase in the load-carrying capacity and the deformation capacity. The NSM CFRP prestressed prisms strengthening technique could be considered as an effective method for repairing RC structures.

Key Words
flexural behaviour; near surface mounted; CFRP; strengthened; beam

Address
Jiong-Feng Liang: Jiangxi Engineering Research Center of Process and Equipment for New Energy, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R. China; Faculty of Civil and Architecture Engineering, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R. China
Shengjun Xie and Jianping Li: Faculty of Civil and Architecture Engineering, East China Institute of Technology, 418 Guanglan Road, Nanchang, P.R. China
Deng Yu: College of Civil and Architecture Engineering, Guangxi University of Science and Technology, 268 Donghuan Road, Liuzhou, P.R. China

Abstract
Structural reanalysis is frequently utilized to reduce the computational cost so that the process of design or optimization can be accelerated. The supports can be regarded as the design variables and may be modified in various types of structural optimization problems. The location, number, and type of supports can make a great impact on the performance of the structure. This paper presents a unified method for structural static reanalysis with imposition or relaxation of some support constraints. The information from the initial analysis has been fully utilized and the computational time can be significantly reduced. Numerical examples are used to validate the effectiveness of the proposed method.

Key Words
structural reanalysis; stiffness matrix; support constraints; Cholesky factorization; computational cost

Address
Haifeng Liu: School of Mathematics and Statistics, Xi\'an Jiaotong University, Xi\'an, 710049, P.R. China
Jihua Zhu: School of Software Engineering, Xi\'an Jiaotong University, Xi\'an, 710049, P.R. China
Mingming Li: Network Center, Jilin University, Changchun 130025, P.R. China

Abstract
The model updating problems, which are to find the optimal approximation to the discrete quadratic model obtained by the finite element method, are critically important to the vibration analysis. In this paper, the structured model updating problem is considered, where the coefficient matrices are required to be symmetric and positive semidefinite, represent the interconnectivity of elements in the physical configuration and minimize the dynamics equations, and furthermore, due to the physical feasibility, the physical parameters should be positive. To the best of our knowledge, the model updating problem involving all these constraints has not been proposed in the existed literature. In this paper, based on the semidefinite programming technique, we design a general-purpose numerical algorithm for solving the structured model updating problems with incomplete measured data and present some numerical results to demonstrate the effectiveness of our method.

Key Words
model updating problems; connectivity; positivity; positive semidefiniteness; semidefinite programming

Address
Yan Yu: School of Mathematical Sciences, Dalian University of Technology, Dalian, Liaoning 116024, China; College of Science, Shenyang Agricultural University, Shenyang, Liaoning, 110866, China
Bo Dong and Bo Yu: School of Mathematical Sciences, Dalian University of Technology, Dalian, Liaoning 116024, China

Abstract
In this paper a new eight-unknown higher order shear deformation theory is proposed for functionally graded (FG) material plates. The theory based on full twelve-unknown higher order shear deformation theory, simultaneously satisfy zeros transverse stresses at top and bottom surface of FG plates. Equations of motion are derived from principle of virtual displacement. Exact closed-form solutions are obtained for simply supported rectangular FG plates under uniform loading. The accuracy of present numerical results has been verified by comparing it with generalized shear deformation theory. The effect of power law index of functionally graded material, side-to-thickness ratio, and aspect ratio on static behavior of FG plates is investigated.

Key Words
bending analysis; functionally graded materials; higher order shear deformation theory; closed-form solution

Address
Tran Minh Tu, Tran Huu Quoc: National University of Civil Engineering, 55 Giai Phong Road, Hanoi, Vietnam
Nguyen Van Long: Construction Technical College No.1, Trung Van, Tu Liem, Hanoi, Vietnam

Abstract
The present paper investigates the propagation of Love-type wave in a composite structure comprised of imperfectly bonded piezoelectric layer with lower fiber-reinforced half-space with rectangular shaped irregularity at the common interface. Closed-form expression of phase velocity of Love-type wave propagating in the composite structure has been deduced analytically for electrically open and short conditions. Some special cases of the problem have also been studied. It has been found that the obtained results are in well-agreement to the Classical Love wave equation. Significant effects of various parameters viz. irregularity parameter, flexibility imperfectness parameter and viscoelastic imperfectness parameter associated with complex common interface, dielectric constant and piezoelectric coefficient on phase velocity of Love-type wave has been reported. Numerical computations and graphical illustrations have been carried out to demonstrate the deduced results for various cases. Moreover, comparative study has been performed to unravel the effects of the presence of reinforcement and piezoelectricity in the composite structure and also to analyze the existence of irregularity and imperfectness at the common interface of composite structure in context of the present problem which serves as a salient feature of the present study.

Key Words
Love-type wave; reinforced composite; piezoelectric; imperfectness; irregularity; electrically open and short

Address
Abhishek Kumar Singh, Mriganka Shekhar Chaki, Bristi Hazra and Shruti Mahto: Department of Applied Mathematics, Indian Institute of Technology (Indian School of Mines), Dhanbad, Jharkhand 826004, India

Abstract
The aim of the present study is to develop an elemental approach based on the differential quadrature method for free vibration analysis of cracked thin plate structures. For this purpose, the equations of motion are established using the classical plate theory. The well-known Generalized Differential Quadrature Method (GDQM) is utilized to discretize the governing equations on each computational subdomain or element. In this method, the differential terms of a quantity field at a specific computational point should be expressed in a series form of the related quantity at all other sampling points along the domain. However, the existence of any geometric discontinuity, such as a crack, in a computational domain causes some problems in the calculation of differential terms. In order to resolve this problem, the multi-block or elemental strategy is implemented to divide such geometry into several subdomains. By constructing the appropriate continuity conditions at each interface between adjacent elements and a crack tip, the whole discretized governing equations of the structure can be established. Therefore, the free vibration analysis of a cracked thin plate will be provided via the achieved eigenvalue problem. The obtained results show a good agreement in comparison with those found by finite element method.

Key Words
continuity condition; crack; differential quadrature method; element; thin plate

Address
Hossein Shahverdi and Mohammad M. Navardi: Department of Aerospace Engineering and Center of Excellence in Computational Aerospace, Amirkabir University of Technology,
424 Hafez Avenue, Tehran 15875-4413, Iran

Abstract
This paper presents the results of a study that investigated the improvement of the mechanical properties of coarse and fine recycled asphalt pavement (RAP) produced by adding silica fume (SF) with contents of 5%, 10%, and 15% by total weight of the cement. The coarse and fine natural aggregate (NA) were replaced by RAP with replacement ratio of 20%, 40% and 60% by the total weight of NA. In addition, SF was added to NA concrete mixes as a control for comparison. Twenty eight mixes were produced and tested for compressive, splitting tensile and flexural strength at the age of 28 days. The results show that the mechanical properties decrease with as the content of RAP increases. And the decrease in the compressive strength was more in the fine RAP mixes compared to the coarse RAP mixes, while the decrease in the splitting tensile and flexural strength was almost the same in both mixes. Furthermore, using SF enhances the mechanical properties of RAP mixes where the optimum content of SF was found to be 10%, and the mechanical properties enhancement of coarse RAP were better than fine RAP mixes. Accordingly, the RAP has the potential to be used in the concrete pavements or in other low strength construction applications in order to reduce the negative impact of RAP on the environment and human health.

Key Words
recycled asphalt pavement; silica fume; compressive strength; flexural strength; splitting tensile streng

Address
Hasan N. Katkhuda, Khaled H. Hyari: Civil Engineering Department, The Hashemite University, P.O. Box 330127, Zarqa, 13115, Jordan
Nasim K. Shatarat: Civil Engineering Department, The University of Jordan, Amman, 11942, Jordan

Abstract
Reliability analysis is a probabilistic approach to determine a safety level of a system. Reliability is defined as a probability of a system (or a structure, in structural engineering) to functionally perform under given conditions. In the 1960s, Basler defined the reliability index as a measure to elucidate the safety level of the system, which until today is a commonly used parameter. However, the reliability index has been formulated based on the pivotal assumption which assumed that the considered limit state function is normally distributed. Nevertheless, it is not guaranteed that the limit state function of systems follow as normal distributions; therefore, there is a need to define a new reliability index for no-normal distributions. The main contribution of this paper is to define a sophisticated reliability index for limit state functions which their distributions are nonnormal. To do so, the new definition of reliability index is introduced for non-normal limit state functions according to the probability functions which are calculated based on the convolution theory. Eventually, as the state of the art, this paper introduces a simplified method to calculate the reliability index for non-normal distributions. The simplified method is developed to generate non-normal limit state in terms of normal distributions using series of Gaussian functions.

Key Words
reliability; convolution theorem; non-normal distribution; probability of failure; limit state function

Address
Seyed Hooman Ghasemi: Department of Civil Engineering, Islamic Azad University, Qazvin Branch. Iran; Auburn University, Auburn, AL 36849, USA
Andrzej S. Nowak: Department of Civil Engineering, Auburn University, Auburn, USA

Abstract
Concrete structures are often subjected to long-term static and short-term dynamic loads. Due to a relatively low tensile strength and energy dissipating characteristics, the impact resistance of concrete is considered poor. This study investigates the feasibility of using polypropylene fibers to improve the impact resistance of reinforced concrete slabs. Fourteen polypropylene fiber reinforced concrete slabs were fabricated and tested using a drop weight test. The effects of slab thickness, fiber volume fractions, and impact energy on the dynamic behaviors were evaluated mainly in terms of impact resistant, crack patterns, and failure modes. The post impact induced strains versus time responses were obtained for all slabs. The results showed that adding the polypropylene fiber at a dosage of 0.90% by volume of concrete leads to significant improvement in the overall structural behavior of the slabs and their resistance to impact loading. Interestingly, the enhancement in the behavior of the slabs using a higher fiber dosage of 1.2% was not as good as achieved with 0.90%.

Key Words
impact resistance; polypropylene fibers; fiber-reinforced concrete; slabs; drop weight test; crack patterns

Address
Rajai Z. Al-Rousan, Mohammed A. Alhassan and Harith Al-Salman: Department of Civil Engineering, Jordan University of Science and Technology, Irbid, Jordan


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