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CONTENTS
Volume 48, Number 2, October25 2013
 

Abstract
The current paper presents the numerical blind prediction of nonlinear seismic response of two full-scale, three dimensional, one-story reinforced concrete structures subjected to bidirectional earthquake simulations on shaking table. Simulations were carried out at the laboratories of LNEC (Laboratorio Nacional de Engenharia Civil) in Lisbon, Portugal. The study was motivated by participation in the blind prediction contest of shaking table tests, organized by the challenge committee of the 15th World Conference on Earthquake Engineering. The test specimens, geometrically identical, designed for low and high ductility levels, were subjected to subsequent earthquake motions of increasing intensity. Three dimensional nonlinear analytical models were implemented and subjected to the input base motions. Reasonably accurate reproduction of the measured displacement response was obtained through appropriate modeling. The goodness of fit between analytical and measured results depended on the details of the analytical models.

Key Words
reinforced concrete structures; shaking table test; blind prediction; nonlinear modeling; numerical simulation; Opensees

Address
Beyhan Bayhan : Department of Civil Engineering, Bursa Technical University, 16330, Bursa, Turkey

Abstract
In this paper, influence of geometric configurations of multi-story bracing on shear lag behaviour of braced tube structures is investigated. The shear lag of 24-, 36- and 72-story braced tube structures are assessed considering all possible configurations of overall X and Chevron bracing types. Based on the analytical results, empirical equations, useful for the preliminary design phase, are proposed to provide the optimum number of stories that braced, in order to exert minimum shear lag on structures. Studying the interaction behaviour of a tube and different bracing types along with paying attention to the shear lag behaviour, a better explanation about the reasons behind the efficiency of a specific bracing module in decreasing the shear lag is developed. The analytical results show that there are distinct differences between the anatomy of braced tube structures with X and Chevron bracing regarding the shear lag behaviour.

Key Words
tall buildings; framed tube; braced tube; shear lag; multi-story bracing

Address
Rouzbeh Zahiri-Hashemi, Ali Kheyroddin : Department of Civil Engineering, Semnan University, Semnan, Iran
Basir Farhadi : Department of Civil Engineering, Islamic Azad University, Roudehen Branch, Roudehen, Tehran, Iran

Abstract
The buckling problem of linearly tapered micro-columns is investigated on the basis of modified strain gradient elasticity theory. Bernoulli-Euler beam theory is used to model the non-uniform micro column. Rayleigh-Ritz solution method is utilized to obtain the critical buckling loads of the tapered cantilever micro-columns for different taper ratios. Some comparative results for the cases of rectangular and circular cross-sections are presented in graphical and tabular form to show the differences between the results obtained by modified strain gradient elasticity theory and those achieved by modified couple stress and classical theories. From the results, it is observed that the differences between critical buckling loads achieved by classical and those predicted by non-classical theories are considerable for smaller values of the ratio of the micro-column thickness (or diameter) at its bottom end to the additional material length scale parameters and the differences also increase due to increasing of the taper ratio.

Key Words
buckling; strain gradient theory; size effect; Rayleigh-Ritz method; non-uniform micro-column

Address
Bekir Akgoz and Omer Civalek : Civil Engineering Department, Division of Mechanics, Akdeniz University, Antalya, Turkey

Abstract
In this study, the vulnerability of two existing asymmetric steel building frames to Progressive Collapse (PC) is assessed. The buildings have different frame systems, steel sections and number of stories (nine and six). An alternate path method (APM) with a linear static analysis (LS) is carried out according to General Services Administration (GSA) 2003 guidelines. The Demand Capacity Ratio (DCR) of each primary element (beams and columns) is given with its specific details for all frames. The results show that the nine-story building with a dual frame system (moment frame with bracing system) has a lower susceptibility and greater resistance to PC than the six-story building with a simple building frame system (gravity system with bracing system). Implementing built-up box-shaped sections for columns is a better choice than using built-up I-shaped sections because there is no weak axis for the box section.

Key Words
Alternate Path Method (APM); deflection; Demand Capacity Ratio (DCR); Linear Static Analysis (LS); Progressive Collapse (PC)

Address
Reza JalaliLarijani, Murude Celikag and Mahdi Kazemi : Deptartment of Civil Engineering, Eastern Mediterranean University, Famagusta, Mersin 10, Turkey
Iman Aghayan : Deptartment of Civil Engineering, Shahrood University of Technology, Shahrood, Iran

Abstract
This paper focuses on a development of strut-and-tie model (STM) to predict the capacity of an improved longitudinal joint for decked bulb-tee bridge systems. Nine reinforced concrete beam/slab specimens anchored by spliced headed bars with different details were tested. Test results were evaluated and compared with an anticipation of the validated STM. The proposed STM provides a lower bound of the ultimate capacity of the joint zone. It shows that the lap length of headed bars has a significant effect on structural behaviors of the improved joint. To develop a full strength joint, the range of the lap length can be determined by the strength and compatibility requirement. Design recommendations to spliced headed bars, concrete strength, as well as lacer bars in the joint zone are proposed for developing a full strength joint.

Key Words
lap length; headed reinforcement; joint zone; strut-and-tie model; accelerated construction

Address
Lungui Li, Lingkan Yao : School of Civil Engineering, Southwest Jiaotong University, 111 Erhuan Rd. North 1 Section, Chengdu, 610031, China
Zhiqi He : School of Civil Engineering, Southeast University, 2 Sipailou, Nanjing, 210096, China
Zhongguo John Ma : Department of Civil and Environmental Engineering, University of Tennessee Knoxville, 223 Perkins Hall, Knoxville, 37996-2010, USA

Abstract
The receding contact problem for two elastic layers whose elastic constants and heights are different supported by two elastic quarter planes is considered. The lower layer is supported by two elastic quarter planes and the upper elastic layer is subjected to symmetrical distributed load whose heights are 2a on its top surface. It is assumed that the contact between all surfaces is frictionless and the effect of gravity force is neglected. The problem is formulated and solved by using Theory of Elasticity and Integral Transform Technique. The problem is reduced to a system of singular integral equations in which contact pressures are the unknown functions by using integral transform technique and boundary conditions of the problem. Stresses and displacements are expressed depending on the contact pressures using Fourier and Mellin formula technique. The singular integral equation is solved numerically by using Gauss-Jacobi integration formulation. Numerical results are obtained for various dimensionless quantities for the contact pressures and the contact areas are presented in graphics and tables.

Key Words
contact mechanics; theory of elasticity; quarter plane; integral transform technique; elastic layer

Address
Murat Yaylac: Naval Architecture and Marine Engineering Department, Karadeniz Technical University, 61530, Trabzon, Turkey
Ahmet Birinci: Civil Engineering Department, Karadeniz Technical University, 61080, Trabzon, Turkey

Abstract
In this study, seismic performance of one story hinged precast buildings, which represents the majority of existing lightweight industrial building stock of Turkey, was assessed. A lot of precast buildings, constructed in one of the important seismic zones of western Turkey, were investigated and building inventories were prepared. By this method, structural properties of inventory buildings and damaged precast buildings in recent earthquakes were compared. Damage estimations based on nonlinear analysis methods have shown that estimated damage levels of inventory buildings and observed damage levels in recent earthquakes are similar. Accuracy of damage estimation study and the simplicity of the one story precast building models implied that rapid seismic performance assessment method for these buildings can be developed. In this assessment method, capacity curves and vibration periods of precast buildings were calculated by using structural properties of precast buildings. The proposed assessment method was applied to inventory buildings by using two different seismic demand scenarios which reflect moderate and soft soil conditions. Comparison of detailed analysis and rapid assessment methods have indicated that reliable seismic performance estimations can be performed by using proposed method. It is also observed that distribution of damage estimations is compatible in both scenarios.

Key Words
precast industrial buildings; nonlinear analysis; seismic performance; damage estimation; rapid evaluation

Address
Mehmet Palanci : Institute of Natural Sciences, Pamukkale University, Kinikli Campus, Denizli, Turkey
Sevket Murat Senel : Civil Engineering Department, Pamukkale University, Kinikli Campus, Denizli, Turkey

Abstract
The cross sections of multi-span beams are sometimes suddenly increased at the interior support of continuous beams to resist high negative moment. An earlier study on elastic lateral torsional buckling of stepped beams was conducted to propose new design equations. This research aims to continue the earlier study by considering the effect of inelastic buckling of stepped beams subjected to pure bending and general loading condition. A three-dimensional finite element-program ABAQUS and a statistical program MINITAB were used in the development of new design equations. The inelastic lateral torsional buckling strengths of 36 and 27 models for singly and doubly stepped beams, respectively, were investigated. The general loading condition consists of 15 loading cases based on the number of inflection point within the unbraced length of the stepped beams. The combined effects of residual stresses and geometrical imperfection were also considered to evaluate the inelastic buckling strengths. The proposed equations in this study will definitely improve current design methods for the inelastic lateral-torsional buckling of stepped beams and will increase efficiency in building and bridge design.

Key Words
inelastic buckling; buckling strength; stepped beam; moment gradient factor; beam design

Address
Jong Sup Park and Yi Seul Park : Department of Civil Engineering, Sangmyung University, 300 Anseo-dong Seobuk-gu, Cheonan, Chungnam, 330-720, Republic of Korea


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