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CONTENTS
Volume 51, Number 3, August10 2014
 

Abstract
The main aim of this paper is to investigate the relationship between thickness and height of the axially symmetric cylindrical reinforced concrete (RC) walls by the help of a meta-heuristic optimization procedure. The material cost of the wall which includes concrete, reinforcement and formwork, was chosen as objective function of the optimization problem. The wall thickness, compressive strength of concrete and diameter of reinforcement bars were defined as design variables and tank volume, radius and height of the wall, loading condition and unit cost of material were defined as design constants. Numerical analyses of the wall were conducted by using superposition method (SPM) considering ACI 318-Building code requirements for structural concrete. The optimum wall thickness-height relationship was investigated under three main cases related with compressive strength of concrete and density of the stored liquid. According to the results, the proposed method is effective on finding the optimum design with minimum cost.

Key Words
aially symmetric cylindrical reinforced concrete walls; optimization; harmony search; optimum cost; optimum design

Address
Gebrail Bekdaş : Department of Civil Engineering, Istanbul University, 34320 Avcilar, Istanbul, Turkey

Abstract
In this study, optimal distribution of springs which supports a cantilever beam is investigated to minimize two objective functions defined. The optimal size and location of the springs are ascertained to minimize the tip deflection of the cantilever beam. Afterwards, the optimization problem of springs is set up to minimize the tip absolute acceleration of the beam. The Fourier Transform is applied on the equation of motion and the response of the structure is defined in terms of transfer functions. By using any structural mode, the proposed method is applied to find optimal stiffness and location of springs which supports a cantilever beam. The stiffness coefficients of springs are chosen as the design variables. There is an active constraint on the sum of the stiffness coefficients and there are passive constraints on the upper and lower bounds of the stiffness coefficients. Optimality criteria are derived by using the Lagrange Multipliers. Gradient information required for solution of the optimization problem is analytically derived. Optimal designs obtained are compared with the uniform design in terms of frequency responses and time response. Numerical results show that the proposed method is considerably effective to determine optimal stiffness coefficients and locations of the springs.

Key Words
optimal stiffness; beam vibrations; transfer functions; optimal support location; support stiffness

Address
Ersin Aydin : Faculty of Engineering, Department of Civil Engineering, Nigde University, Nigde, Turkey

Abstract
In this paper, enhancement of corrosion and chloride resistance of high performance self compacting concrete (SCC) through incorporating nanosilica into the binder has been investigated. For this purpose, different mixtures were designed with different amounts of silica fume and nano silica admixtures. Different binder contents were also investigated to observe the binder content effect on the concrete properties. Corrosion behavior was evaluated by chloride penetration and resitivity tests. Water absorption and capillary absorption were also measured as other durability-related properties. The results showed that water absorption, capillary absorption and Cl ion percentage decreased rather significantly in the mixtures containing admixtures especially blend of silica fume and nano silica. By addition of the admixtures, resistivity of the SCC mixtures increased which can lead to reduction of corrosion probability.

Key Words
concrete; nano silica; corrosion; durability; chloride penetration; resistivity

Address
Mostafa Jalal : Young Researchers Club and Elites, Science and Research Branch, Islamic Azad University, Tehran, Iran

Abstract
By carrying out the experiment of eight pieces of brick masonry walls with pilaster strengthened by Glass fiber reinforced polymer (GFRP) and one piece of normal masonry wall with pilaster under low reversed cyclic loading, the failure characteristic of every wall is explained; Seismic performances such as hysteresis, stiffness and its degeneration, deformation, energy consumption and influence of some measures including strengthening means, reinforcement area proportion between GFRP and wall surface, \"through-wall\" anchor on reinforcement effects are studied. The test results showed that strengthening modes have little influence on stiffness, stiffness degeneration and deformation of the wall, but it is another thing for energy consumption of the wall; The ultimate load, deformation and energy consumption of the walls reinforced by glass fiber sheets was increased remarkably, rigidity and its degeneration was slower; Seismic performance of the wall which considers strengthening means, reinforcement area proportion between GFRP and wall surface, \"through –wall\" anchor at the same time is better than under the other conditions.

Key Words
cycle tests; glass fiber reinforced polymer (GFRP); reinforcement; brick masonry wall with pilaster;

Address
Quanfeng Wang : Xiamen Institute of Technology, Huaqiao University, Xiamen 361021, China
Quanfeng Wang, Zhenling Chai : College of Civil Engineering, Huaqiao University, Xiamen 361021, China
Lingyun Wang : College of Urban Construction and Safety Engineering, Shanghai Institute of Technology, Shanghai 201418, China

Abstract
The purpose of the research presented in this paper was to investigate the effectiveness of several conventional, multi-modal and adaptive pushover procedures. In particular, an extensive numerical study was performed considering eight RC frames characterized by a variable number of storeys and different properties in terms of regularity in elevation. The results of pushover analyses were compared with those of nonlinear dynamic analyses, which were carried out considering different earthquake records and increasing values of earthquake intensity. The study was performed with reference to base shear-top displacement curves and to different storey response parameters. The obtained results allowed a direct comparison between the pushover procedures, which in general were able to give a fairly good estimate of seismic demand with a tendency to better results for lower frames. The advanced procedures, in particular the multi-modal pushover, provided an improvement of the results, more evident for the irregular frames.

Key Words
RC frames; pushover analysis; irregular structures; modal pushover; adaptive pushover; nonlinear dynamic analysis; incremental dynamic analysis

Address
Luca Landi, Bernardino Pollio and Pier Paolo Diotallevi : Department of Civil, Chemical, Environmental and Materials Engineering, University of Bologna, Viale Risorgimento 2, 40136 Bologna, Italy

Abstract
Numerical simulation of the non-linear behavior of (RC) structural walls subjected to severe earthquake ground motions requires a reliable modeling approach that includes important material characteristics and behavioral response features. The objective of this paper is to optimize a simplified method for the assessment of the seismic response and damage development analyses of an RC structural wall building using macro-element model. The first stage of this study investigates effectiveness and ability of the macro-element model in predicting the flexural nonlinear response of the specimen based on previous experimental test results conducted in UCLA. The sensitivity of the predicted wall responses to changes in model parameters is also assessed. The macro-element model is next used to examine the dynamic behavior of the structural wall building−all the way from elastic behavior to global instability, by applying an approximate Incremental Dynamic Analysis (IDA), based on Uncoupled Modal Response History Analysis (UMRHA), setting up nonlinear single degree of freedom systems. Finally, the identification of the global stiffness decrease as a function of a damage variable is carried out by means of this simplified methodology. Responses are compared at various locations on the structural wall by conducting static and dynamic pushover analyses for accurate estimation of seismic performance of the structure using macro-element model. Results obtained with the numerical model for rectangular wall cross sections compare favorably with experimental responses for flexural capacity, stiffness, and deformability. Overall, the model is qualified for safety assessment and design of earthquake resistant structures with structural walls.

Key Words
RC structural walls; macro-element; pushover analysis; incremental dynamic analysis; equivalent SDOF system; damage index; seismic performance

Address
Miloud Hemsas : LSTE, Department of Sciences and Techniques (Civil Engineering), University of Mascara, BP 763, Route de Mamounia, 29000, Mascara, Algerie
Sidi-Mohammed Elachachi and Denys Breysse : I2M-GCE, CNRS, UMR5295, Department of Civil and Environmental Engineering, University of Bordeaux 1, Bat. B 18, Av des Facultes, 33405 Talence, France

Abstract
Until now, the finite corner stiffness of the right-angle frames used as horizontal girders in a bonnet, have not been considered during the design process to result in not a precise result. This paper presents a design equation set for right-angle frames used as horizontal girders in a bonnet assuming rigid corner stiffness. By comparing the center stresses of the right-angle frame according to the design equation set with the results of the finite element method, the master curves for the empirical corner stiffness can be determined as a function of slenderness ratio. A second design equation set for a right-angle frame assuming finite corner stiffness was derived and compared with the first equation set. The master curves for the corner stiffness and the second design equation set can be used to determine the design moments at the centers of the girder so that the bending stresses can be analyzed more precisely.

Key Words
frame; bonnet; slide gate; wide flange beam; slenderness ratio; corner stiffness; master curves

Address
Young-Doo Kwon, Soon-Bum Kwon : School of Mechanical Engineering & IEDT, Kyungpook National University, Daegu, Korea
Hyuck-Moon Gil : Department of Offshore Structure Design & Engineering, Hyundai Heavy Industry, Ulsan, Korea
Hui-Jeong Cho : Graduate School, Kyungpook National University, Daegu, Korea

Abstract
In buildings structures, the flexural stiffness reduction of beams and columns due to concrete cracking plays an important role in the nonlinear load-deformation response of reinforced concrete structures under service loads. Most Seismic Design Codes do not precise effective stiffness to be used in seismic analysis for structures of reinforced concrete elements, therefore uncracked section properties are usually considered in computing structural stiffness. But, uncracked stiffness will never be fully recovered during or after seismic response. In the present study, the effect of concrete cracking on the lateral response of structure has been taken into account. Totally 120 cases of 3 Dimensional Dynamic Analysis which considers the real and accidental torsional effects are performed using ETABS to determine the effective structural system across the height, which ensures the performance and the economic dimensions that achieve the saving in concrete and steel amounts thus achieve lower cost. The result findings exhibits that the dual system was the most efficient lateral load resisting system based on deflection criterion, as they yielded the least values of lateral displacements and inter-storey drifts. The shear wall system was the most economical lateral load resisting compared to moment resisting frame and dual system but they yielded the large values of lateral displacements in top storeys. Wall systems executes tremendous stiffness at the lower levels of the building, while moment frames typically restrain considerable deformations and provide significant energy dissipation under inelastic deformations at the upper levels. Cracking found to be more impact over moment resisting frames compared to the Shear wall systems. The behavior of various lateral load resisting systems with respect to time period, mode shapes, storey drift etc. are discussed in detail.

Key Words
3 dimensional seismic analysis; effective structural system; response spectrum analysis; stiffness degradation; time period and mode shapes

Address
K. Subramanian : Department of Civil Engineering, Coimbatore Institute of Technology,Tamil Nadu, Coimbatore, 641 014, India
M. Velayutham : Anna University, Chennai, 600 025, India

Abstract
On October 23, 2011, an earthquake of magnitude 7.0 struck Van, Turkey. This powerful earthquake caused the deaths of 604 people, more than 2,000 injuries, and a considerable loss of property. After this devastating earthquake, on November 9, 2011, another earthquake of magnitude 5.7 occurred. This moderate earthquake caused the deaths of 40 people. Partial and total collapse of the masonry and adobe buildings occurred in the rural areas of Van. In this paper, the acceleration records and response spectrums of the earthquakes were given and the structural deficiencies and reasons of the failures of the rural buildings were evaluated according to the Turkish Seismic Code. The observed failures showed that low quality of structural materials, poor workmanship, lack of engineering services and insufficient detailing of the structural elements are the main reasons of damages.

Key Words
masonry and adobe buildings; 2011 Van earthquakes; earthquake damage; structural deficiencies

Address
Erkut Sayin, Burak Yon, Yusuf Calayir and Mesut Gor : Civil Engineering Department, Firat University, 23119, Elaziğ, Turkey

Abstract
This paper attempts to investigate the nonlinear dynamic analysis of strong nonlinear problems by proposing a new analytical method called Hamiltonian Approach (HA). Two different cases are studied to show the accuracy and efficiency of the method. This approach prepares us to obtain the nonlinear frequency of the nonlinear systems with the first order of the solution with a high accuracy. Finally, to verify the results we present some comparisons between the results of Hamiltonian approach and numerical solutions using Runge-Kutta\'s [RK] algorithm. This approach has a powerful concept and the high accuracy, so it can be apply to any conservative nonlinear problems without any limitations.

Key Words
approximate frequency; Hamiltonian approach; analytical investigations

Address
Mahdi Bayat, Mahmoud Bayat : Department of Civil Engineering, College of Engineering, Mashhad Branch, Islamic Azad University, Mashhad, Iran
Iman Pakar : Young Researchers and Elites Club, Mashhad Branch, Islamic Azad University, Mashhad, Iran


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