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CONTENTS
Volume 17, Number 1, July 2019
 

Abstract
In the structures with high level of ductility, the earthquake energy dissipation in structural components is an important factor that describes their seismic behavior. Since the connection details play a major role in the ductile behavior of structure, in this paper, the seismic response of 3-, 5- and 8-story steel special moment frames (SMFs) is investigated by considering the effects of panel zone modeling and the influence of forward-directivity near-field ground motions. To provide a reasonable comparison, selected records of both near and far-field are used in the nonlinear time-history analysis of models. The results of the comparison of the median maximum inter-story drift under excitation by near-field (NF) records and the far-field (FF) ground motions show that the inter-story drift demands can be obtained 3.47, 4.86 and 5.92 times in 3-, 5- and 8-story structures, respectively, undergoing near-field earthquakes.

Key Words
special steel moment frame; forward directivity; inter-story drift; panel-zone, near-field

Address
Iman Mansouri: Department of Civil Engineering, Birjand University of Technology, Birjand, Iran
Shahrokh Shahbazi: TAAT Investment Group, Tehran, Iran
Jong Wan Hu: Department of Civil and Environmental Engineering, Incheon National University, Incheon 22012, South Korea; Incheon Disaster Prevention Research Center, Incheon National University, Incheon 22012, South Korea
Salar Arian Moghaddam: International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran

Abstract
The present study aims to present a comprehensive understanding of the performance of neighboring multi-story buildings with different dynamic characteristics under blast loads. Two different scenarios are simulated in terms of explosion locations with respect to both buildings. To investigate the effect of interaction between the neighboring buildings in terms of the induced responses, the separation gap is set to be sufficiently small to ensure collisions between stories. An adequately large separation gap is set between the buildings to explore responses without collisions under the applied blast loads. Several blast loads with different peak pressure intensities are employed to perform the dynamic analysis. The finite-element toolbox Computer Aided Learning of the Finite-Element Method (CALFEM) is used to develop a MATLAB code to perform the simulation analysis. The dynamic responses obtained in the scenarios considered herein are presented comparatively. It is found that the obtained stories\' responses are governed mainly by the location and intensity of the applied blast loads, separation distances, and flexibility of the attacked structures. Moreover, explosions near a light and flexible building may lead to a significant decrease in blast resistance because explosions severely influence the dynamic responses of the building\'s stories.

Key Words
explosive loads; adjacent structures; separation gaps; pounding forces

Address
Sayed Mahmoud: Department of Civil and Construction Engineering, College of Engineering, Imam Abdulrahman Bin Faisal University, Dammam, Saudi Arabia

Abstract
This work presents a free vibration analysis of functionally graded beams by employing an original high order shear deformation theory (HSDBT). This theory use only three unknowns, but it satisfies the stress free boundary conditions on the top and bottom surfaces of the beam without requiring any shear correction factors. The mechanical properties of the beam are assumed to vary continuously in the thickness direction by a simple power-law distribution in terms of the volume fractions of the constituents. In order to investigate the free vibration response, the equations of motion for the dynamic analysis are determined via the Hamilton

Key Words
free vibration; functionally graded materials; Hamilton

Address
Abdelkader Sahouane: 1Department of Civil Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret, 14000, Algeria;
Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes,
Sidi Bel Abbes, Algeria
Lazreg Hadji: Department of Mechanical Engineering, Ibn Khaldoun University, BP 78 Zaaroura, Tiaret, 14000, Algeria; Laboratory of Geomatics and Sustainable Development, Ibn Khaldoun University of Tiaret, Algeria
Mohamed Bourada: Material and Hydrology Laboratory, Faculty of Technology, Civil Engineering Department, University of Sidi Bel Abbes, Sidi Bel Abbes, Algeria

Abstract
This paper presents an experimental study on a 1/2 scale steel frame with archaized-style under the pseudo-dynamic loading. Four seismic waves, including El Centro wave, Taft wave, Lanzhou wave and Wenchuan wave, were input during the test. The hysteresis characteristic, energy dissipation acceleration response, displacement response, strength, stiffness and strain were analyzed. Based on the experiment, the elastoplastic dynamic time-history analysis was carried out with the software ABAQUS. The stress distribution and failure mode were obtained. The results indicate that the steel frame with archaized-style was in elastic stage when the peak acceleration of input wave was no more than 400 gal. Under Wenchuan wave with peak acceleration of 620 gal, the steel frame enters into the elastoplastic stage, the maximum inter-story drift was 1/203 and the bearing capacity still tended to increase. During the loading process, Dou-Gong yielded first and played the role of the first seismic fortification line, and then beam ends and column bottom ends yielded in turn. The steel frame with archaized-style has good seismic performance and meets the seismic design requirement of Chinese code.

Key Words
archaized building; steel frame; pseudo-dynamic test; seismic performance; elastoplastic time-history analysis; dynamic response

Address
Zuqiang Liu, Chaofeng Zhou and Jianyang Xue: School of Civil Engineering, Xi\'an University of Architecture and Technology, Xi\'an 710055, China

Abstract
A novel asymmetrical resistance friction damper (ARFD) was proposed in this study to be applied on a rocking column base. The damper comprises multiple steel plates and was fastened using high-strength bolts. The sliding surfaces can be switched into one another and can cause strength to be higher in the loading direction than in the unloading direction. By combining the asymmetrical resistance with the restoring resistance that is generated due to an axial load on the column, the rocking column base can develop a self-centering behavior and achieve high connection strength. Cyclic tests on the ARFD proved that the damper performs a stable asymmetrical hysteretic loop. The desired hysteretic behavior was achieved by tuning the bolt pretension force and the diameter of the round bolt hole. In this study, full-scale, flexural tests were conducted to evaluate the performance of the column base and to verify the analytical model. The results indicated that the column base exhibits a stable self-centering behavior up to a drift angle of 4%. The decompression moment and maximum strength reached 42% and 88% of the full plastic moment of the section, respectively, under a column axial force ratio of approximately 0.2. The strengths and self-centering capacity can be obtained by determining the bolt pretension force. The analytical model results revealed good agreement with the experimental results.

Key Words
asymmetrical resistance; friction damper; self-centering; column base

Address
Yu-Lin Chung: Department of Architecture, National Cheng Kung University, 701 No.1, University Road, Tainan City, Taiwan
Li-Jyun Du and Huang-Hsing Pan: Department of Civil Engineering, National Kaohsiung University of Science and Technology, 80778 No. 415, Jiangong Rd., Kaohsiung City, Taiwan

Abstract
This paper studies damage detection as an optimization problem. A new objective function based on changes in natural frequencies, and Natural Frequency Vector Assurance Criterion (NFVAC) was developed. Due to their easy and fast acquisition, natural frequencies were utilized to detect structural damages. Moreover, they are sensitive to stiffness reduction. The method presented here consists of two stages. Firstly, Finite Element Model (FEM) is updated. Secondly, damage severities and locations are determined. To minimize the proposed objective function, a new bio-inspired optimization algorithm called salp swarm was employed. Efficiency of the method presented here is validated by three experimental examples. The first example relates to three-story shear frame with two single damage cases in the first story. The second relates to a five-story shear frame with single and multiple damage cases in the first and third stories. The last one relates to a large-scale eight-story shear frame with minor damage case in the first and third stories. Moreover, the performance of Salp Swarm Algorithm (SSA) was compared with Particle Swarm Optimization (PSO). The results show that better accuracy is obtained using SSA than using PSO. The obtained results clearly indicate that the proposed method can be used to determine accurately and efficiently both damage location and severity in multi-story shear frames.

Key Words
changes in natural frequencies; natural frequency vector assurance criterion; salp swarm; optimization; finite element model updating; damage detection

Address
Parsa Ghannadi and Seyed Sina Kourehli: Department of Civil Engineering, Ahar Branch, Islamic Azad University, Ahar, Iran

Abstract
The paper presents experimental and numerical studies carried out on low-rise RC frames, typically found in developing countries. Shake table tests were conducted on 1:3 reduced scaled two-story RC frames that included a code conforming SMRF model and another non-compliant model. The later was similar to the code conforming model, except, it was prepared in concrete having strength 33% lower than the design specified, which is commonly found in the region. The models were tested on shake table, through multiple excitations, using acceleration time history of 1994 Northridge earthquake, which was linearly scaled for multi-levels excitations in order to study the structures\' damage mechanism and measure the structural response. A representative numerical model was prepared in finite element based program SeismoStruct, simulating the observed local damage mechanisms (bar-slip and joint shear hinging), for seismic analysis of RC frames having weaker beamcolumn joints. A suite of spectrum compatible acceleration records was obtained from PEER for incremental dynamic analysis of considered RC frames. The seismic performance of considered RC frames was quantified in terms of seismic response parameters (seismic response modification, overstrength and displacement amplification factors), for critical comparison.

Key Words
SMRF; response modification factor; nonlinear modelling; over strength; displacement amplification factor

Address
Muhammad Rizwan, Naveed Ahmad and Akhtar Naeem Khan: Earthquake Engineering Center, Department of Civil Engineering, UET Peshawar, 25120 Khyber Pakhtunkhwa, Pakistan

Abstract
Fragility analysis is an effective tool that is frequently used for seismic risk assessment of bridges. There are three different approaches to derive a fragility curve: experimental, empirical and analytical. Both experimental and empirical methods to derive fragility curve are based on past earthquake reports and expert opinions which are not suitable for all bridges. Therefore, analytical fragility analysis becomes important. Nonlinear time history analysis is commonly used which is the most reliable method for determining probabilistic demand models. In this study, to determine the probabilistic demand models of bridges, time history analyses were performed considering both material and geometrical nonlinearities. Serviceability limit states for three different service velocities were considered as a performance goal. Also, support displacements, component yielding and collapse limits were taken into account. Both serviceability and component fragility were derived by using maximum likely hood methods. Finally, the seismic performance and critical members of the bridge were probabilistically determined and clearly presented.

Key Words
railway bridge; fragility curve; nonlinear time history analysis; probabilistic seismic assessment

Address
Mehmet F. Yilmaz: Department of Civil Engineering, Ondokuz Mayis University, Kurupelit 55139, Samsun, Turkey
Barlas O. Caglayan and Kadir Ozakgul: Department of Civil Engineering, Istanbul Technical University, Maslak 34469, Istanbul, Turkey

Abstract
Earthquake-induced pounding is one of the major reasons for structural failure in earthquake prone cities. An accurate description of the pounding phenomenon of two buildings requires the consideration of systems with a large number of degrees of freedom including adequate contact impact formulations. In this paper, firstly, a node to surface formulation for the realization of state-of-the-art pounding models for structural beam elements is presented. Secondly, a hierarchical substructure technique is introduced, which is adapted to the structural pounding problem. The numerical accuracy and efficiency of the method, especially for the contact forces, are verified on an academic example, applying four different impact elements. Error estimations are carried out and compared with the classical modal truncation method. It is demonstrated that the hierarchical substructure method is indeed able to significantly speed up the numeric integration procedure by preserving a required level of accuracy.

Key Words
pounding problem; substructure technique; model order reduction; Craig-Bampton method

Address
Jianye Shi, Franz Bamer and Bernd Markert: Institute of General Mechanics, RWTH Aachen University, Templergraben 64, 52064 Aachen, Germany

Abstract
The effectiveness of an innovative method for the earthquake-resistant rehabilitation of existing poorly detailed reinforced concrete (RC) structures is experimentally investigated herein. Eight column subassemblages were subjected to earthquake-type loading and their hysteretic behaviour was evaluated. Four of the specimens were identical and representative of columns found in RC structures designed in the 1950s-70s period for gravity load only. These original specimens were subjected to cyclic lateral deformations and developed brittle failure mechanisms. Three of the damaged specimens were subsequently retrofitted with innovative high-strength steel fiber-reinforced concrete (HSSFC) jackets. The main variables examined were the jacket width and the contribution of mesh steel reinforcement in the seismic performance of the enhanced columns. The influence of steel fiber volume fraction was also examined using test results of a previous work of Tsonos et al. (2017). The fourth earthquake damaged subassemblage was strengthened with a conventional RC jacket and was subjected to the same lateral displacement history as the other three retrofitted columns. The seismic behaviour of the subassemblages strengthened according to the proposed retrofit scheme was evaluated with respect to that of the original specimens and that of the column strengthened with the conventional RC jacket. Test results clearly demonstrated that the HSSFC jackets effectively prevented the development of shear failure mechanisms, while ensuring a ductile seismic response similar to that of the subassemblage retrofitted with the conventional RC jacket. Ultimately, an indisputable superiority in the overall seismic performance of the strengthened columns was achieved with respect to the original specimens.

Key Words
columns; high-strength steel fiber-reinforced concrete; retrofit; RC jacket

Address
George I. Kalogeropoulos, Alexander-Dimitrios G. Tsonos, Pantelis E. Iakovidis: Department of Civil Engineering, Aristotle University of Thessaloniki, GR-54-124 Thessaloniki, Greece
Dimitrios Konstantinidis: Department of Civil Engineering T.E., Alexander Technological Educational Institute of Thessaloniki, GR-57-400, Greece

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