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CONTENTS
Volume 22, Number 3, March 2022
 

Abstract
Knowing that the variability of soil properties is an important source of uncertainty in geotechnical analyses, we will study in this paper the effect of this variability on the seismic response of a structure within the framework of Soil Structure Interaction (SSI). We use the proposed and developed model (N2-ISS, Mekki et al. 2014). This approach is based on an extension of the N2 method by determining the capacity curve of the fixed base system oscillating mainly in the first mode, then modified to obtain the capacity curve of the system on a flexible basis using the concept of the equivalent nonlinear oscillator. The properties of the soil that we are interested in this paper will be the shear wave velocity and the soil damping. These parameters will be modeled at first, as independent random fields, then, the two parameters will be correlated. The results obtained showed the importance of the use of random field in the study of SSI systems. The variability of soil damping and shear wave velocity introduces significant uncertainty not only in the evaluation of the damping of the soil-structure system but also in the estimation of the displacement of the structure and the base-shear force.

Key Words
damping; seismic performance; shear wave velocity; soil structure interaction; uncertainty; variability

Address
Mohammed Mekki:LM2SC Laboratory, Department of Civil Engineering, Faculty of Architecture and Civil Engineering, University of Sciences and Technology
Mohamed Boudiaf, BP 1505 El Mnaouer, 31.000, Oran, Algeria

Miloud Hemsas: LSTE Laboratory, Department of Civil Engineering, Faculty for Sciences and Technology, University of Mascara, BP 763, Route de
Mamounia, 29000, Mascara, Algeria

Meriem Zoutat:LM2SC Laboratory, Department of Civil Engineering, Faculty of Architecture and Civil Engineering, University of Sciences and Technology
Mohamed Boudiaf, BP 1505 El Mnaouer, 31.000, Oran, Algeria

Sidi M. Elachachi:I2M Laboratory, GCE Department, University of Bordeaux, UMR 5295, bat. B18, Av des Facultés, 33405, Talence, France

Abstract
Beam-column joints (BCJs) are recognized among the most crucial zones in reinforced concrete structures, as they are the critical elements subjected to a complex state of forces during a severe earthquake. Under such conditions, BCJs exhibit behaviors with impacts that extend to the whole structure and significantly influence its ductility and capability of dissipating energy. The focus of this paper is to investigate the effect of undamaged transverse beam (secondary beams) on the ductility of concrete BCJs reinforced with conventional steel and shape memory alloys bars using pushover analysis at tip of beam under different axial load levels at the column using a nonlinear finite element model in ABAQUS environment. A numerical model of a BCJ was constructed and the analysis outcomes were verified by comparing them to those obtained from previous experiments found in the literature. The comparison evidenced the capability of the calibrated model to predict the load capacity response of the joint. Results proved the ability of undamaged secondary beams to provide a noticeable improvement to the ductility of reinforced concrete joints, with a very negligible loss in load capacity. However, the effect of secondary beams can become less significant if the beams are damaged due to seismic effects. In addition, the axial load was found to significantly enhance the performance of BCJs, where the increase in axial load magnified the capacity of the joint. However, higher values of axial load resulted in greater initial stiffness of the BCJ.

Key Words
axial load; ductility; finite element analysis; reinforced concrete joints; secondary beam; Shape Memory Alloy (SMA)

Address
Abdulsamee M. Halahla:Department of Civil Engineering, Palestine Polytechnic University, Hebron, Palestine

Yazan B. Abu Tahnat:Department of Civil and Water Engineering, Laval University, Québec, Canada

and Monther B. Dwaikat:Department of Building Engineering, An-Najah National University, Nablus, Palestine

Abstract
Key questions to researchers interested in nonlinear analysis of skeletal structures are whether the distributed plasticity approach – albeit computationally demanding – is more reliable than the concentrated plasticity to adequately capture the extent and severity of the inelastic response, and whether force-based formulation is more efficient than displacement-based formulation without compromising accuracy. The present research focusing on performance-based seismic response of mid-span concrete bridges provides a pilot holistic investigation opting for some hands-on answers. OpenSees software is considered adopting different modeling techniques, viz. distributed plasticity (through either displacement-based or force-based elements) and concentrated plasticity via beam-with-hinges elements. The pros and cons of each are discussed based on nonlinear pushover analysis results, and fragility curves generated for various performance levels relying on incremental dynamic analyses under real earthquake records. Among prime conclusions, distributed plasticity modeling albeit inherently not relying on prior knowledge of plastic hinge length still somewhat depends on such information to ensure accurate results. For instance, displacement-based and force-based approaches secure optimal accuracy when dividing, for the former, the member into sub-elements, and satisfying, for the latter, a distance between any two consecutive integration points, close to the expected plastic hinge length. On the other hand, using beam-with-hinges elements is computationally more efficient relative to the distributed plasticity, yet with acceptable accuracy provided the user has prior reasonable estimate of the anticipated plastic hinge length. Furthermore, when intrusive performance levels (viz. life safety or collapse) are of concern, concentrated plasticity via beam-withhinges ensures conservative predicted capacity of investigated bridge systems.

Key Words
sumptions; bridges; fragility assessment; non-linear analysis; OpenSees; performance-based analysis

Address
B.N. Morkos:Civil Engineering Department, Faculty of Engineering, The British University in Egypt, Suez Road, El-Sherouk City, Egypt

M.M.N. Farag:Structural Engineering Department, Faculty of Engineering, Cairo University, 1Gamaa St., Giza, Egypt

S. Salem:Civil Engineering Department, Faculty of Engineering, The British University in Egypt, Suez Road, El-Sherouk City, Egypt

S.S.F. Mehanny:Structural Engineering Department, Faculty of Engineering, Cairo University, 1Gamaa St., Giza, Egypt/ Dar Al-Handasah (Shair and Partners) – Smart Village, Cairo, Egypt

M.M. Bakhoum:Structural Engineering Department, Faculty of Engineering, Cairo University, 1Gamaa St., Giza, Egypt


Abstract
Structural collapses can occur as a result of a dynamic amplification of either, the building's seismic response or the ground shaking by local site effects; one of the reasons is a resonance effect due to the proximity of the structural elastic fundamental period TE and the soil fundamental period TS. We evaluate the vulnerability to resonance effects in Guadalajara, México, in a three-step schema: 1) we define structural systems in the building environment of western Guadalajara, in terms of their construction materials and structural components; 2) we estimate TE with different equations, to obtain a representative value in elastic conditions for each structural system; and, 3) we evaluate the resonance vulnerability by the analysis of the ratio between TE and TS. We observe that the larger the soil fundamental period, the higher the resonance vulnerability for buildings with height between 17 and 39 m. For the sites with a low TS, the most vulnerable buildings will be those with a height between 2 and 9 m. These results can be a helpful tool for disaster prevention, by avoiding the construction of buildings with certain heights and structural characteristics that would result in a dangerous proximity between TE and TS.

Key Words
framed structures; fundamental period; infill panels; masonry; reinforced concrete; resonance; shear walls; steel

Address
Alejandro Ramírez-Gaytán:Departamento de Ciencias Computacionales CUCEI, UdeG, Marcelino García Barragán 1421, 44430, Guadalajara, México

Adolfo Preciado:Departamento del Hábitat y Desarrollo Urbano, Instituto Tecnológico y de Estudios Superiores de Occidente (ITESO),
Periférico Sur Manuel Gómez Morín 8585, 45604 Tlaquepaque, México

Hortencia Flores-Estrella:Department of Applied Geophysics, Institute of Applied Geosciences, TU Berlin, Ernst-Reuter-Platz 1, 10587 Berlin, Germany

Juan Carlos Santos:Departamento del Hábitat y Desarrollo Urbano, Instituto Tecnológico y de Estudios Superiores de Occidente (ITESO),
Periférico Sur Manuel Gómez Morín 8585, 45604 Tlaquepaque, México

Leonardo Alcántara:Instituto de Ingeniería, Universidad Nacional Autónoma de México, Circuito Interior, Ciudad Universitaria,
Coyoacán, 04510 México City, México


Abstract
The ancient underground cities are a collection of self-supporting spaces that have been manually excavated in the soil or rock in the past. Because these structures have a very high cultural value due to their age, the study of their stability under the influence of natural hazards, such as earthquakes, is very important. In this research, while introducing the underground city of Ouyi Nushabad located in the center of Iran as one of the largest man-made underground cities of the old world, the analysis of dynamic stability is performed. For this purpose, the dynamic stress-displacement analysis has been performed through numerical modeling using the finite element software PLAXIS. At this stage, by simulating the Khorgo earthquake as one of the large-scale earthquakes that occurred in Iran, with a magnitude of 6.9 on the Richter scale, dynamic analysis by time history method has been performed on three selected sections of underground spaces. This study shows that the maximum amount of horizontal and vertical dynamic displacement is 12.9 cm and 17.7 cm, respectively, which was obtained in section 2. The comparison of the results shows that by increasing the cross-sectional area of the excavation, especially the distance between the roof and the floor, in addition to increasing the amount of horizontal and vertical dynamic displacement, the obtained maximum acceleration is intensified compared to the mapping acceleration applied to the model floor. Therefore, preventive actions should be taken to stabilize the excavations in order to prevent damage caused by a possible earthquake.

Key Words
deformability; dynamic analysis; earthquake; finite element method; man-made underground city

Address
Hooman Rezaee:Department of Mining Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran

Majid Noorian-Bidgoli:Department of Mining Engineering, Faculty of Engineering, University of Kashan, Kashan, Iran

Abstract
During strong ground motions, adjacent structures with insufficient separation distances collide with each other causing considerable architectural and structural damage or collapse of the whole structure. Generally, existing design procedures for determining the separation distance between adjacent buildings subjected to structural pounding are based on approximations of the buildings' peak relative displacement. These procedures are based on unknown safety levels. This paper attempts to evaluate the influence of foundation flexibility on the structural seismic response by considering the variability in the system and uncertainties in the ground motion characteristics through comprehensive numerical simulations. Actually, the aim of this study is to evaluate the influence of foundation flexibility on probabilistic evaluation of structural pounding. A Hertz-damp pounding force model has been considered in order to effectively capture impact forces during collisions. In total, 5.25 million time-history analyses were performed over the adopted models using an ensemble of 25 ground motions as seismic input within OpenSees software. The results of the study indicate that the soil-structure interaction significantly influences the poundinginvolved responses of adjacent structures during earthquakes and generally increases the pounding probability.

Key Words
probabilistic analysis; separation distance; soil-structure interaction; structural pounding; time-history analyses

Address
Mojtaba Naeej:Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Javad Vaseghi Amiri:Department of Civil Engineering, Babol Noshirvani University of Technology, Babol, Iran

Abstract
This paper presents a comparative study of the damage potentials for the 2016 Gyeongju and 2017 Pohang earthquakes in Korea. Plausible technical explanations are provided for the more severe damage observed in the 2017 Pohang earthquake in spite of its relatively weaker magnitude and intensity measures based on the response analysis of elastic and inelastic single-degree-of-freedom systems for the recorded ground motions. In addition, a detailed case study was conducted for a fatally damaged piloti building with an eccentric shear wall core based on nonlinear dynamic analysis using the input ground motions modified for the building site.

Key Words
earthquake damage potential; irregularity; nonlinear dynamic analysis; piloti building; seismic design

Address
Cheol-Ho Lee:Department of Architecture and Architectural Engineering, Seoul National University, Seoul 08826, Korea

Ji-Hun Park:Division of Architecture and Urban Design, Incheon National University, Incheon 22012, Korea

Sung-Yong Kim:School of Architecture, Changwon National University, Changwon 51140, Korea

Dong-Kwan Kim:Department of Architecture Engineering, Cheongju University, Cheongju 28503, Korea

Su-Chan Jun:Department of Architecture and Architectural Engineering, Seoul National University, Seoul 08826, Korea

Abstract
Retrofit of soft-story buildings due to seismic loads using Gap-Inclined-Brace (GIB) system is considered a new retrofit technique that aims to maintain both strength and stiffness of structure. In addition, it provides more ductility and less Pdelta effect, and subsequently better performance is observed. In this paper, the effect of the eccentricity between GIB and the retrofitted column due to installation on the efficiency of the retrofitting system is studied. In addition, a modification in the determination method of GIB properties is introduced to reduce the eccentricity effect. Also, the effect of GIB system on the seismic response of mid-rise buildings with different heights considering soft-story at various heights has been studied. A numerical model is developed to study the impact of such system on the response of retrofitted soft-story buildings under the action of seismic loads. To achieve that goal, this model is used to perform a numerical investigation, by considering five case study scenarios represent several locations of soft-story of two mid-rise reinforced concrete buildings. At first, Non-linear static pushover analysis was carried out to develop the capacity curves for case studies. Then, Non-linear time history analyses using ten earthquake records with five peak ground accelerations is performed for each case study scenario before and after retrofitting with GIB. The results show that large GIB eccentricity reduce the ultimate lateral resistance and deformation capacity of the retrofitting system. Moreover, the higher the retrofitted building, the more deformation capacity is observed but without significant increase in ultimate lateral resistance.

Key Words
gapped inclined brace; GIB; retrofit; seismic analysis; soft-story; time history analysis

Address
Mohamed. A. Tohamy:Structural Engineering Department, Cairo University, Giza, 12613, Egypt

Mostafa. M. Elsayed:Structural Engineering Department, Cairo University, Giza, 12613, Egypt

Adel. Y. Akl:Structural Engineering Department, Cairo University, Giza, 12613, Egypt

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