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CONTENTS
Volume 14, Number 4, April 2018
 

Abstract
In this study, the effect of local site conditions (site class and site amplifications) and structural variability are investigated on fragility functions of typical building structures. The study area is chosen as Eastern Turkey. The fragility functions are developed using site-specific uniform hazard spectrum (UHS). The site-specific UHS is obtained based on simulated ground motions. The implementation of ground motion simulation into seismic hazard assessment has the advantage of investigating detailed local site effects. The typical residential buildings in Erzincan are represented by equivalent single degree of freedom systems (ESDOFs). Predictive equations are accomplished for structural seismic demands of ESDOFs to derive fragility functions in a straightforward manner. To study the sensitivity of fragility curves to site class, two sites on soft and stiff soil are taken into account. Two alternative site amplification functions known as generic and theoretical site amplifications are examined for these two sites. The reinforced concrete frames located on soft soil display larger fragilities than those on stiff soil. Theoretical site amplification mostly leads to larger fragilities than generic site amplification more evidently for reinforced concrete buildings. Additionally, structural variability of ESDOFs is generally observed to increase the fragility especially for rigid structural models.

Key Words
fragility functions; ground motion simulation; site effects

Address
Aida Azari Sisi: Federal Institute for Geoscience and Natural Resources (BGR), Hannover, Germany
Murat A. Erberik and Ayşegül Askan: Department of Civil Engineering, Middle East Technical University, Ankara, Turkey

Abstract
Seismic behavior of Osmanli and Senyuva stone bridges was addressed in this study. A combination of FEM and DEM was employed for getting closer to the real behavior of the bridge. One of the unique features of this combinational method is simulation close to reality. Modal numerical analysis was also used to verify the modeling. At the end of earthquake, a part of two lateral walls of Osmanli bridge was broken. The growth of arch cracks also increased during the earthquake. A part of right-hand wall of Senyuva Bridge was destructed during the earthquake. The left-hand side of the bridge wall was damaged during the earthquake but was not destructed.

Key Words
FEM; earthquake; bridges; simulation; seismic

Address
Melika Naderi: Dipartimento di Architettura Urbanistica Ingegneria delle Costruzioni, Politecnico di Milano,Piazza Leonardo da Vinci 32 , 20133 Milano, Italy
Mehdi Zekavati: Civil Engineering Department, Qazvin Branch, Islamic Azad University, Nokhbegan Boulevard, Qazvin, Iran

Abstract
Significant research efforts were undertaken to evaluate seismic performance of vertically irregular buildings on flat ground. However, there is scarcity of study on seismic performance of buildings on hill slopes. The present study attempts to investigate seismic behaviour of reinforced concrete irregular stepback building frames with different configurations on sloping ground. Based on extensive regression study of free vibration results of four hundred seventeen frames with varying ground slope, number of story and span number, a modification is proposed to the code based empirical fundamental time period estimation formula. The modification to the fundamental time period estimation formula is a simplified function of ground slope and a newly introduced equivalent height parameter to reflect the effect of stiffness and mass irregularity. The derived empirical formula is successfully validated with various combinations of slope and framing configurations of buildings. The correlation between the predicted and the actual time period obtained from the free vibration analysis results are in good agreement. The various statistical parameters e.g., the root mean square error, coefficient of determination, standard average error generally used for validation of such regression equations also ensure the prediction capability of the proposed empirical relation with reasonable accuracy.

Key Words
reinforced concrete frame; sloping ground; fundamental time period; free vibration

Address
Mithu De: Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India
Piyali Sengupta: Department of Civil Engineering, Indian Institute of Technology (ISM), Dhanbad, Dhanbad 826004, India
Subrata Chakraborty: Department of Civil Engineering, Indian Institute of Engineering Science and Technology, Shibpur, Howrah 711103, India

Abstract
The present study is dedicated to investigate the SH body-as well as Love-waves propagation effects in porous media with uncertain porosity and permeability. A unified formulation of the governing equations for one-dimensional (1-D) wave propagation in anisotropic porous layered media is presented deterministically. The uncertainties around the above two cited parameters are taken into account by random fields with the help of Monte Carlo Simulations (MCS). Random samples of the porosity and the permeability are generated according to the normal and lognormal distribution functions, respectively, with a mean value and a coefficient of variation for each one of the two parameters. After performing several thousands of samples, the mathematical expectation (mean) of the solution of the wave propagation equations in terms of amplification functions for SH waves and in terms of dispersion equation for Love-waves are obtained. The limits of the Love wave velocity in a porous soil layer overlaying a homogeneous half-space are obtained where it is found that random variations of porosity change the zeros of the wave equation. Also, the increase of uncertainties in the porosity (high coefficient of variation) decreases the mean amplification function amplitudes and shifts the fundamental frequencies. However, no effects are observed on both Love wave dispersion and amplification function for random variations of permeability. Lastly, the present approach is applied to a case study in the Adapazari town basin so that to estimate ground motion accelerations lacked in the fast-growing during the main shock of the damaging 1999 Kocaeli earthquake.

Key Words
SH wave; Love wave; dispersion; Monte Carlo simulations; amplification; acceleration

Address
Amina Sadouki, Zamila Harichane: Geomaterials Laboratory, Hassiba Benbouali University of Chlef, Algeria
Sidi Mohammed Elachachi: University of Bordeaux, I2M, GCE Department, France
Ayfer Erken: Civil Engineering Faculty, Istanbul Technical University, Turkey

Abstract
Machine foundations with impact loads are common powerful sources of industrial vibrations. These foundations are generally transferring vertical dynamic loads to the soil and generate ground vibrations which may harmfully affect the surrounding structures or buildings. Dynamic effects range from severe trouble of working conditions for some sensitive instruments or devices to visible structural damage. This work includes an experimental study on the behavior of dry dense sand under the action of a single impulsive load. The objective of this research is to predict the dry sand response under impact loads. Emphasis will be made on attenuation of waves induced by impact loads through the soil. The research also includes studying the effect of footing embedment, and footing area on the soil behavior and its dynamic response. Different falling masses from different heights were conducted using the falling weight deflectometer (FWD) to provide the single pulse energy. The responses of different soils were evaluated at different locations (vertically below the impact plate and horizontally away from it). These responses include; displacements, velocities, and accelerations that are developed due to the impact acting at top and different depths within the soil using the falling weight deflectometer (FWD) and accelerometers (ARH-500A Waterproof, and Low capacity Acceleration Transducer) that are embedded in the soil in addition to soil pressure gauges. It was concluded that increasing the footing embedment depth results in increase in the amplitude of the force-time history by about 10-30% due to increase in the degree of confinement. This is accompanied by a decrease in the displacement response of the soil by about 40- 50% due to increase in the overburden pressure when the embedment depth increased which leads to increasing the stiffness of sandy soil. There is also increase in the natural frequency of the soil-foundation system by about 20-45%. For surface foundation, the foundation is free to oscillate in vertical, horizontal and rocking modes. But, when embedding a footing, the surrounding soil restricts oscillation due to confinement which leads to increasing the natural frequency. Moreover, the soil density increases with depth because of compaction, which makes the soil behave as a solid medium. Increasing the footing embedment depth results in an increase in the damping ratio by about 50-150% due to the increase of soil density as D/B increases, hence the soil tends to behave as a solid medium which activates both viscous and strain damping.

Key Words
circular footing; dry sand; embedment depth; displacement; impact

Address
Adnan F. Ali: Civil Engineering Department, University of Baghdad, Baghdad, Iraq
Mohammed Y. Fattah: Building and Construction Engineering Department, University of Technology, Baghdad, Iraq
Balqees A. Ahmed: Civil Engineering Department, University of Baghdad, Baghdad, Iraq

Abstract
This paper presents some shaking table tests conducted on a 1/4-scaled model with 5-story steel reinforced concrete (SRC) spatial frame with irregular section columns under a series of base excitations with gradually increasing acceleration peaks. The test frame was subjected to a sequence of seismic simulation tests including 10 white noise vibrations and 51 seismic simulations. Each seismic simulation was associated with a different level of seismic disaster. Dynamic characteristic, strain response, acceleration response, displacement response, base shear and hysteretic behavior were analyzed. The test results demonstrate that at the end of the loading process, the failure mechanism of SRC frame with irregular section columns is the beam-hinged failure mechanism, which satisfies the seismic code of \"strong column-weak beam\". With the increase of acceleration peaks, accumulated damage of the frame increases gradually, which induces that the intrinsic frequency decreases whereas the damping ratio increases, and the peaks of acceleration and displacement occur later. During the loading process, torsion deformation appears and the base shear grows fast firstly and then slowly. The hysteretic curves are symmetric and plump, which shows a good capacity of energy dissipation. In summary, SRC frame with irregular section columns can satisfy the seismic requirements of \"no collapse under seldom earthquake\", which indicates that this structural system is suitable for the construction in the high seismic intensity zone.

Key Words
steel reinforced concrete (SRC); spatial frame; irregular section column; shaking table test; seismic response

Address
Jianyang Xue, Chaofeng Zhou, Zuqiang Liu and Liangjie Qi: College of Civil Engineering, Xi

Abstract
Reinforced concrete (RC) moment frames supported on two ground levels have been widely constructed in mountainous areas with medium to high seismicity in China. In order to investigate the seismic collapse behavior and risk, a scaled frame model was tested under constant axial load and reversed cyclic lateral load. Test results show that the failure can be induced by the development of story yielding at the first story above the upper ground. The strong column and weak beam mechanism can be well realized at stories below the upper ground. Numerical analysis model was developed and calibrated with the test results. Three pairs of six case study buildings considering various structural configurations were designed and analyzed, showing similar dynamic characteristics between frames on two ground levels and flat ground of each pair. Incremental dynamic analyses (IDA) were then conducted to obtain the seismic collapse fragility curves and collapse margin ratios of nine analysis cases designated based on the case study buildings, considering amplification of earthquake effect and strengthening measures. Analysis results indicate that the seismic collapse safety is mainly determined by the stories above the upper ground. The most probable collapse mechanism may be induced by the story yielding of the bottom story on the upper ground level. The use of tie beam and column strengthening can effectively enhance the seismic collapse safety of frames on two ground levels.

Key Words
moment frame; incremental dynamic analysis; collapse; fragility; earthquake; irregularity

Address
Yun-Tian Wu: Key Laboratory of New Technology for Construction of Cities in Mountain Area, Ministry of Education; School of Civil Engineering, Chongqing University, Chongqing 400045, China
Qing Zhou, Bin Wang, Yeong-Bin Yang and Tian-Qing Lan: School of Civil Engineering, Chongqing University, Chongqing 400045, China

Abstract
In this paper, an alternative reliability-based methodology is developed and implemented on the safety evaluation of structures subjected to seismic loading. To effectively elaborate the approach, structures are represented by finite elements and seismic loading is applied in time domain. The accuracy of the proposed reliability-based methodology is verified using Monte Carlo Simulation. It is confirmed that the presented approach provides adequate accuracy in calculating structural reliability. The efficiency and robustness in problems related to performance-based seismic design are verified. A structure designed by experts satisfying all post-Northridge seismic design requirements is studied. Rigidities related to beam-to-column connections are incorporated. The structure is excited by three suites of ground motions representing three performance levels: immediate occupancy, life safety, and collapse prevention. Using this methodology, it is demonstrated that only hundreds of deterministic finite element analyses are required for extracting reliability information. Several advantages are documented with respect to Monte Carlo Simulation. To showcase an applicability extension of the proposed reliability-based methodology, structural risk is calculated using simulated ground motions generated via the broadband platform developed by the Southern California Earthquake Center. It is validated the accuracy of the broadband platform in terms of structural reliability. Based on the results documented in this paper, a very solid, sound, and precise reliability-based methodology is proved to be acceptable for safety evaluation of structures excited by seismic loading.

Key Words
reliability analysis; performance-based seismic design; limit state functions; Monte Carlo Simulation; artificial ground motions

Address
J. Ramon Gaxiola-Camacho: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa, México
Achintya Haldar: Department of Civil Engineering and Engineering Mechanics, University of Arizona, Tucson, Arizona, USA
Alfredo Reyes-Salazar: Facultad de Ingeniería, Universidad Autónoma de Sinaloa, Culiacán, Sinaloa, México
Federico Valenzuela-Beltran: Instituto de Ingeniería, Universidad Nacional Autónoma de México, Coyoacán, Ciudad de México, México
G. Esteban Vazquez-Becerra: Instituto de Ingeniería, Universidad Nacional Autónoma de México, Coyoacán, Ciudad de México, México
A. Omar Vazquez-Hernandez: Department de Exploración de Aguas Profundas, Instituto Mexicano del Petróleo, G. A. Madero, Ciudad de México, México


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