Comparison of Three Dimensional Translational and Rotational Mechanisms in
Seismic Slope Stability Analyses by Upper Bound Limit Analysis
Behzad
Amirloo
School of Civil Engineering, University of Tehran, Tehran, Iran
author
Orang
Farzaneh
School of Civil Engineering, University of Tehran, Tehran, Iran
author
Faradjolla
Askari
Geotechnical Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
text
article
2019
per
In this paper, seismic stability of slopes in three dimensional cases is investigated, using rotational and translational failure mechanisms and compared based on the upper bound limit analysis method. Definition of lateral surfaces of three dimensional failure mechanisms in upper bound method requires considering the associated flow rule, which makes it necessary that particular equations be satisfied. To develop further studies on three dimensional stability of slopes using translational and rotational mechanisms, the present work compares the results of a translational mechanism with a rotational one.
In order to compare the factor of safety in slopes stability problems between translational and rotational mechanisms under body forces due to the weight of the soil mass and horizontal acceleration of the earthquake, the parameter λφc is used, where γ is the unit weight of the soil, H is the height of slope and c and ϕ are the soil shear strength parameters.
This comparison is carried out for different slope inclination angles (30◦, 60◦, 90◦), two ratios of the width of the failure mechanism (L) to the slope height (H), i.e. 1 and 8, and for cohesive (λφc = 0) and non-cohesive soils (λφc ≠ 0). L/H = 1 and L/H = 8 are used to model the three dimensional and two dimensional mechanisms, respectively. By an increase in the parameter of λφc, the soil behaves more frictional.
Some of the most important results of this research are as follows:
- Generally, the importance of three dimensional analyses is more in seismic states.
- The trend of variations of the safety factor of slopes is almost the same by increase in the coefficient of horizontal earthquake acceleration for both rotational and transitional mechanisms.
- The results of this study show that in rotational mechanisms, in most cases, especially in vertical slopes, the safety factors are smaller than translational mechanisms.
- Translational mechanisms results (safety factors) are usually lower in cohesive soils.
- The difference between the results of two translational and rotational mechanisms is less in cohesive soils and more in frictional soils.
- By an increase in inclination angle of the slope, the difference between the results of the two mechanisms becomes more.
Regardless of the kind of the mechanism, in assessing the effect of different parameters on the factor of safety of slopes stability, the following general points can be noted:
- The increase in the coefficient of horizontal earthquake acceleration (from 0 to 0.3) contributes to the decrease in the factor of safety. The reductions for cohesive soils and inclination angle equal to 30 degrees are about 69 and 40 percent, respectively for two dimensional and three dimensional mechanisms. The mentioned reductions for frictional soils in vertical slopes, are about 35 and 20 percent. These results indicate that the effect of earthquake is more in lower slopes with cohesive soil.
- As the failure mechanism widens, the safety factor decreases, and at higher kh values, this decrease becomes more pronounced. This indicates the greater impact of earthquakes on reducing the stability of two-dimensional mechanisms.
- The difference between the results of two dimensional and three dimensional mechanisms in cohesive soils is more than frictional soils.
- The factors of safety of slopes in three dimensional mechanisms are more than two dimensional. This is due to the fact that the contribution of lateral surfaces in 3D mechanisms is more outstanding than the bottom logarithmic spiral surface. It contributes to the increase in the rate of dissipated work and consequently the factor of safety of the slope increases.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
1
10
http://www.bese.ir/article_240404_02bf7a29ee010258c64f712b0f855d18.pdf
Determination of the Dynamic Behavior of Soil Nailed Walls Based
on Displacement
Iraj
Rahmani
Department of Geotechnical Engineering, Road, Housing and Urban Development Research Center (BHRC), Tehran, Iran
author
Amir
Nejati
Faculty of Engineering, Islamic Azad University Central Tehran Branch, Tehran, Iran
author
text
article
2019
per
Demand for high-rise buildings and shopping malls has increased in recent years. For this reason, these buildings have a variety of basements. Due to insufficient land, some parts of these structures are being built underground. Stabilizing vertical cuts by emerging methods provides a new way for the construction industry. In addition, the demand for stabilizing vertical cuts on highways and railways against dynamic forces has been raised. There are various methods for stabilizing underground cuts. Soil nailing is one of the most common methods for stabilizing cut slopes in building industry. In this method, the soil is strengthened by placing the steel rods into the drilled holes on the wall and the ground. It is worth mentioning that, this method could be used for underground construction. Whereas soil nailing wall system needs less space in comparison with other retaining wall systems, in urban areas especially where walls cuts are surrounded by structures is more applicable. Observations of the performance of soil nails walls in recent earthquakes indicate that their destruction by deep excavations rarely occurs. Literature review on the soil nail walls shows that the mechanism of reinforcement and design of the soil nail walls is without considering of seismic loading. However, few studies have been performed on the seismic behavior of these walls. In this paper, the dynamic behavior of the steel soil nail walls has been investigated numerically. In order to validate two-dimensional, nonlinear finite difference model created by FLAC software, obtained results from the instrumental excavation wall (Hotel Narges No.2) were used. In this study, a numerical parametric study was performed to investigate the factors affecting the behavior of the soil nail wall system. This parametric study has the effect of wall height (3, 6 and 9 m), nail angle (10 and 15 degrees), soil properties (type 1 to 3 based on Iranian code of practice for seismic resistant design of building (2800)) and seismic loading characteristics such as magnitude, frequency of the maximum acceleration of the earth's surface were examined. In addition, four equivalent harmonic loads instead of 15 time history are used. After analyzing 72 different models, it was concluded that by decreasing the soil shear strength (types 1 to 3), the displacement of the upper edge of the wall would increase sharply, with the decrease of the nail angle (from 15 to 10) horizontal displacement of the upper edge wall reduced. By decreasing the angle of the nails (from 15 to 10), the force of the nails is increased. Increasing the height of the wall increases the horizontal displacement of the upper edge of the wall. Also by changing the type of harmonic loading type 1 to type 4, the behavior of the soil nail wall varies with soil type changes, which can be attributed to the effect of soil damping and soil type on the different seismic behavior of the nailed structures. The calculated dynamic analysis results show that the data are scattered under four different harmonic loads. Therefore, the seismic performance of the soil nail structures depends on the geometry parameters and the selection of the main mapping parameters including mold period, acceleration, and mapping duration is very important and requires sufficient accuracy. The dominant mode of deformation of the soil nail wall for four harmonic loads, and for all heights is around the intersection point of the wall and cavity.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
11
21
http://www.bese.ir/article_240406_695dd79c01e4024d3d57356d96844530.pdf
Evaluation of Dynamic Properties of Building by Comparison of Numerical Analysis and H/V Spectral Ratio of Microtremor Method
Mehdi
Mokhberi
Department of Civil Engineering, Estahban Branch, Islamic Azad University, Estahban, Iran
author
text
article
2019
per
Dynamic soil characteristics such as natural frequency, damping ratio, and shear wave velocity have important effects on seismological structures response. Earthquake codes have been used to determine frequency or damping ratio that are suggested by analytical methods and empirical amount, while due to the influence of several factors such as designing style, type of structure, construction materials and site conditions, the existing structures have different response to earthquake. Therefore, the proposed dynamic properties are not sufficiently reliable yet. In order to recognise the natural frequency and damping ratio, experimental approach can be used to evaluate the natural frequency of buildings by using the seismic records of existing buildings. The soil layer specifications are recognized by different methods, including geotechnical and geophysical as well as spectral ratio. A method that can be used to determine the structural response, and estimate the natural frequency from ambient records, is the horizontal-to-vertical spectral ratio of microtremor (H/V). This technic has been revealed by Nakamura (1989), a practical method in site characterization studies due to its low cost and its functionality.This paper has presented a method to estimate the variation of structure’s natural frequency with stories that changes, using the spectral ratio of microtremor H/V. The study was carried out to investigate the influence of building’s age and performance on frequency changes. Accordingly, the natural frequency values obtained from the two methods of numerical analysis of structures and microtremor analysis have been compared. As a matter of fact, 12 buildings including 6 new constructed and 6 old ones in Shiraz were selected. The buildings included from 1- and 2-story masonry buildings up to 12-story framed structures. The new buildings are designed or retrofitted by new standards such as 3rd or 4th edition of Iranian Code of Practice for Resistant Design of Buildings (Standard No 2800). The old buildings have been designed and constructed by oldest earthquake codes and have more than 30 years of age. In order to evaluate the dynamic characteristics of the buildings, two methods were used. First, the analytical results obtained from ETABS software analysis, to find the dynamic properties of structures. Therefore, the architectural and structural map of these buildings was prepared and the structures were numerically analyzed again. Secondly, the empirical data resulted from H/V spectral ratio of microtremor records. Microtremor measurement were performed on the floors and roofs of the building. Microtremor H/V spectral ratios were obtained according to the SESAME H/V user guidelines. Finally, the relationship formula resulting from these two techniques were compared in terms of fundamental frequency, amplitude, exhibiting agreements and disagreements. In both methods, the correlation formula between the resonant frequency and the number of stories of buildings were compared and the effect of age, construction methods, materials and standards codes on natural frequency were evaluated. The results show that the spectral ratio method of microtremor H/V can be a useful approach for real analysis of seismic response of buildings. In addition, the numerical analysis is conservative compared to the field measurement methods. Also, the frequency variation of the building follows the power functions as the stories increased. The age of structure and changes in the earthquake standards code cause about 10% difference in the frequencies value. In addition, comparison of the formula correlation obtained from numerical analyzes with the values resulted from microtremor H/V spectral ratio show that the proposed relationships of the analytic methods are more unreliable from the values of ambient vibrations data. Finally, the results show that the properties of the soil layers, the material of the building, the regular and irregular effect of the building and the site effect have a significant influence on the frequency variations.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
23
36
http://www.bese.ir/article_240411_9d15eb708b10ada8e339d6e3cdba2e92.pdf
Evaluation of Mathematical Relationships of Shear Wave Velocity and Standard Penetration Test Results with Bayesian Statistics Approach
Solmaz
Charoosaei
Department of Civil Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
author
Navid
Khayat
Department of Civil Engineering, Ahvaz Branch, Islamic Azad University, Ahvaz, Iran
author
Mehdi
Mahdavi Adeli
Department of Civil Engineering, Shoushtar Branch, Islamic Azad University, Shoushtar, Iran
author
text
article
2019
per
Shear wave velocity is one of the most important geophysical parameters in which the seismic response of the sites is expressed. This seismic parameter gives valuable information about the project site, but since geophysical tests are usually expensive and time consuming, the use of indirect methods to reduce costs is increasing. Much research has been done in different regions of the world, in most of them have used both simple power equations and multiple power equations to derive equations. However, in this paper, a comprehensive study is conducted to evaluate the effects of standard penetration number and depth on shear wave velocity estimation as one of the most important soil dynamic parameters with Bayesian statistics approach. In summary, data from 28 boreholes drilled in three cities of Hormozgan province were collected. The collected data were subdivided into four main categories of all soils: clay soils, silty soils, sandy and gravel soils. In this way, the researchers identified 8 variables and 13 functions with the help of Bayesian statistics to determine the mathematical functions with greater reliability, taking into account standard penetration number, depths or a combination of both. The results of this analysis showed that the standard penetration number parameter alone for all soils and classifications as well as simple and multiple power equations are not the best parameter and equations in predicting shear wave velocity, respectively. Other results can be pointed out that soil clustering is not always the most effective factor in estimating shear wave velocity. Finally, it is suggested that if the correlation equation is defined on the basis of standard penetration number with higher confidence percentage, the equation will be extracted by intervals from standard penetration number. In addition, despite the results, it should be noted that these equations have been developed for a specific site and these results should be used with regard to site specific arrangements with other geotechnical conditions.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
37
51
http://www.bese.ir/article_240412_92c7d8f474f7594b772349f04e78ab71.pdf
Adaptation of the NGA-WEST2 Ground Motion Prediction Equations by Implementing the Resampling Analysis Algorithm
Alireza
Azarbakht
Department of Civil Engineering, Faculty of Engineering, Arak University, Iran, and
Department of Civil and Environmental Engineering, University of Strathclyde, Glasgow, UK
author
Hamed
Zeinali
Department of Civil Engineering, Faculty of Engineering, Arak University, Iran
author
Zinat
Rajabi
Department of Civil Engineering, Faculty of Engineering, Arak University, Iran
author
text
article
2019
per
The realistic estimation of Peak Ground Acceleration (PGA) is crucial for the purpose of seismic design in high seismic prone regions. The common practice is using Seismic Hazard Analysis (SHA) to estimate the design spectra in order to be used in the design and rehabilitation of structures. The most influential part of any SHA is the use of Ground Motion Prediction Equation (GMPE), which usually has the highest level of epistemic uncertainty.The Pacific Earthquake Research Centre (PEER) have released two sets of GMPEs, which are known as NGA-WEST1 and NGA-WEST2, and they are introduced as global GMPEs for all regions around the globe. However, the reliability of GMPEs needs to be assessed properly. Therefore, a recent methodology by Azarbakht et al. (2014) has been implemented in this study in order to enhance the given GMPEs only in the case of PGA. The better model in this approach is the one which has less sensitivity due to the small changes in the input catalogue. This effect cannot be captured by the common statistical tests that are widely using in the development of GMPEs. Therefore, three NGA GMPEs are taken into consideration, and the coefficients are optimized by aiming at maximizing the reliability, i.e. Campbell and Bozorgnia, Abrahamson and Silva, and Boore and Atkinson GMPEs. The ground motion database of the Campbell and Bozorgnia (2014) was used throughout this study, which consists of 15493 records of 319 earthquake events.A multi-objective Genetic algorithm was used to optimize four fitness functions, three of them related to resampling of the data and the forth is taken as the LLH. The results show that the employed resampling analysis show better performance when compared to other statistical approaches such as Var-test, Lillifors, and Z-test. However, the optimized coefficients show better GMPE performance with those statistical tests. Error estimation approaches were also considered, i.e. RMSE, MAE, R-square and E methods. In the end, the hazard curves for a hypothetical site are calculated based on the original and optimized GMPEs. The comparison between the obtained hazard curves shows that the hazard curves obtained from the optimized coefficients result in conservative when compared to the hazard curves from the original GMPEs. In conclusion, the optimized GMPEs show better performance when compared to the original GMPEs by means of the common statistical approaches as well as the new resampling algorithm. This proves that the sensitivity of GMPEs to the input catalogue is a key criterion when developing a new GMPE, otherwise the estimated parameters such as PGA will not be accurate enough.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
53
74
http://www.bese.ir/article_240413_ffcd1b3b3953dff665db8135238d39f7.pdf
Improvement of Steel Shear Wall Behavior Based on Link Beam Approach
Hadis
Mohammad Moradi
International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Behrokh
Hosseini Hashemi
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Mohammad Ali
Jafari
Niroo Research Institute (NRI), Tehran, Iran
author
text
article
2019
per
In seismic-prone countries like Japan, structures are designed against earthquakes and reinforced concrete shear walls, steel shear walls or steel bracing are usually used as seismic resistant elements. However, their hysteretic characteristics in plastic region, ductility and capacity of energy absorption are not always good. The use of steel plate shear wall systems (SPSW) is more advantageous than many lateral load resistant systems considering performance and economy. The steel plates are so strong and ductile, and their weight is so light that they are suitable as a material of shear wall. Despite the many advantages of steel shear walls, this system is not widely used. Some of the underlying reasons include a lack of understanding of the behavior of the system and the significant size of the columns around the wall compared to the concrete shear wall. Over the last two decades, the semi-supported steel shear wall at the edges (SSSW) has been introduced as an alternative to the traditional shape of the steel plate shear wall system. In this system, the infill steel plate is not attached to the main frame columns and instead is attached to the secondary columns. Removing the connection of the steel plate to the main columns will reduce the demand for the peripheral columns, thereby reducing their size of cross section. However, due to buckling of the steel plate, the phenomenon of pinching still exists in hysteresis curves. This reduces the area under the hysteresis curves and consequently, reduces the energy dissipation in the system.The aim of this study is to improve the behavior of the above defined system by utilizing shear behavior of the plate and secondary columns around it and utilizing the maximum system capacity. In this research, plate and secondary columns are considered as shear link beam in eccentrically bracing frame (EBF) systems, with plate and secondary columns playing the role of web and flanges of shear link beam, respectively. In this system, a shear panel consisting of infill steel plate, perpendicular stiffeners and secondary columns is positioned in the midspan of the steel frame with simple connections. Unlike the conventional steel plate shear wall system and the semi-supported steel shear wall system at the edges, the buckling of the steel plate is prevented and the energy dissipation is due to the shear failure mechanism.In this study, the effect of infill steel plate thickness, distance of perpendicular stiffeners and ratio of shear panel width to height on system behavior is investigated. For this purpose, different samples are modeled in the nonlinear finite element software and their cyclic behaviors have been studied. The results showed that the increase of steel plate thickness and ratio of shear panel width to its height has been lead to an increase in the ultimate capacity of system and area under the hysteresis curves. Adding stiffeners can increase the shear strength of the system up to 35%. In addition, increasing the distance of the stiffeners by up to 2 times the value specified for short-link beams has no effect on the system hysteresis behavior. The results also showed that the use of this system in steel frames compared to conventional steel plate shear walls increases the energy dissipation and area under hysteresis curves and reduces the pinching phenomenon in hysteresis curves. Other benefits of the system include a significant reduction in column demand, adaptability to architecture, stable cyclic curves, and no impact of the proposed system on the behavior of beam-to-column connections and thus no need for rigid connections, usability in High-rise buildings as well as usability in the seismic rehabilitation and retrofit of existing buildings.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
75
85
http://www.bese.ir/article_240414_4923538469826b46dca3563b739be390.pdf
Performance Assessment of Special and Intermediate Steel Moment Resisting Frames Under Post-Earthquake Fire
Mohsen
Gerami
Civil Engineering Department, Semnan University, Semnan, Iran
author
Pouria
Mirzaei
Civil Engineering Department, Semnan University, Semnan, Iran
author
text
article
2019
per
Severe earthquakes may cause extensive fires in the structures. In the aftermath of earthquake, factors such as the occurrence of residual displacement in the structural stories (geometrical damage), increased fire intensity, and damage to the fireproofing (local damage) reduce structural resistance rating to fire. The methods and requirements of seismic design of structures can have a great impact on their fire resistance rating. In this paper, the performance of intermediate and special moment frames in post-earthquake fire is compared.For this purpose, two 5 and 10 story frames are designed with two special and intermediate moment frame systems assuming they are in a high risk seismic zone. It is supposed that the beams and columns of the frames were protected by cement vermiculite spray fireproof material and accordingly the required thickness of the fireproofing is designed for two hours of fire resistance time. The 2D-frames model in Abaqus software for pushover- heat transfer- and thermal-mechanical analyses. The compartment fire scenario is assumed to start from the second floor and extend to two-fifths the height of the frames. For seismic loading, two hazard levels including the Design Base Earthquake (DBE) and the Maximum Credible Earthquake (MCE) are considered. The results of seismic and thermal-mechanical analyses are combined to accurately consider the behavior of seismically-loaded structures under fire loads. The fire resistance time of two sample steel moment frames for pre- and post-earthquake situations is compared to specify the reduction of fire resistance time due to the seismic effects. Two types of temperature-time curves for natural fire in pre- and post-earthquake conditions are considered in relation to Eurocode 3 and fire extinguishing coefficients in post-earthquake conditions. To determine the seismic damage (geometric and local damages) in the frames, the pushover method is employed in which the frames were first pushed by the first mode loading pattern to reach the target displacement of each hazard levels and then unloaded to return their elastic displacements and stay plastic displacements in the frame’s stories as the permanent displacements. The location of the plastic hinges in frame’s members at the target roof displacement is determined for each hazard levels. It is assumed that the fireproofing delaminate at these points as long as the depth of the beam cross section and directly exposed to the fire. The collapse of the structural systems under fire loads mainly occurs in three different modes: (i) yield of beam members, (ii) buckling of columns, and (iii) side-way collapse. The occurrence of the mentioned collapse mechanisms depends on the factors such as structural characteristics, fireproofing and geometric damage. The resistance time of the frames is the time at which any of the abovementioned collapse modes are detected.The results show that the failure mode of the undamaged and damaged special moment frames (SMF) under fire scenarios is yield of beam members. The fire resistant rating for undamaged SMF is about 21% less than damaged one. The reason for the low resistance time reduction is due to the redistribution forces in the damaged beam at high temperatures so that by eliminating the fireproofing at the two ends of the beam, the temperature at these points increases more rapidly than the beam center. By reducing the stiffness of the two ends of the beam, due to the redistribution of forces, the moment at these points will be reduced and added to the mid-beam moment. Therefore, some of the lower two end resistance of the beam is compensated by its middle. The fire resistance time of Intermediate Moment Frames (IMF) after Design Base Earthquakes (DBE) is estimated to be 19% less than undamaged one. However, Maximum Credible Earthquakes (MCE) reduce the resistance time of these frames by 75% since at this hazard level the plastic hinges occurrence in some columns of such frames that results in damage to the column’s fireproofing. Also, the results of natural fire analyses show that after MCE earthquakes, the intermediate moment frames may collapse under natural fire, while special moment frames are able to withstand against the natural fire in post-earthquake conditions.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
87
106
http://www.bese.ir/article_240415_a76c45d6a6954633904b3b610177e693.pdf
Modification Factor of Solid and Perforated Infill Panels Based
on Experimental Results
Majid
Mohammadi
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Alireza
Sarmayekhah
Ayandegan College, Tonekabon, Iran
author
text
article
2019
per
The infills are walls which are in full contact with surrounding frame elements. They considerably increase the stiffness and strength. It is recommended in many rehabilitation codes and guidelines to model each infill by an equivalent compression-only strut element. However, before modeling infills in the structures, adequacy of the surrounding elements and connections should be checked for the infill forces. The same procedure is proposed for perforated infill panels, the infill with large opening such as door or window. Therefore, in rehabilitation projects, the capacity of infills, both solid and perforated, can be applied against seismic loads. However, a modification factor, shown by m in many codes or guidelines such as ASCE-41 or FEMA-356, is required. The m-factors of solid infill panels have already been calculated through experimental test results and listed in the guidelines. Despite, m-factors of perforated infills have not been determined yet.The main subject of this paper is to calculate m-factors of perforated infill panels, based on the experimental test results of the literature and comparing them with those of similar solid infills. It is shown that m-factor of a perforated infill can be assumed almost the same value of similar solid infill panel. Regarding the importance of solid infills’ m-factors, they are focused. For this, many experimental test results of solid infills are reported herein and their m-factors are calculated. It has been shown that this factor depends only on infill material and, despite FEMA-356 or ASCE-41 suggestions; it is independent of infill aspect ratio or the ratio of the frame to the infill strengths. Eventually, m-factors of some infills with different materials are suggested; the m-factors of infills with clay bricks, clay hollow bricks and hollow tiles are 2, 3.5 and 3, respectively. For infills made of concrete blocks, the m-factor is 3 for hollow blocks and 4 for solid blocks.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
107
119
http://www.bese.ir/article_240405_174038f77ffbe859e5d8249ccc4dfd45.pdf
Comparison of Viscous and Hysteresis Dampers in Reducing the Seismic Vulnerability of Resistant Steel Buildings Based on the Division of the Building’s Structure into Inner and Outer Parts Having Dynamic Interaction
Abbas
Taheri
Department of Civil Engineering, Arak Branch, Islamic Azad University, Arak, Iran
author
Mahmoud
Hosseini
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Abdolreza
S. Moghadam
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
text
article
2019
per
In order to avoid the adverse consequences of building design based on the conventional regulations, such as the necessity of evacuation of thousands of heavily-damaged buildings and their demolishment and reconstruction, the design of the structure in such a way to be repairable even after a major earthquake is a desired alternative design method. In this regard, the authors of the paper recently proposed dividing the building’s structure into two parts, inner and outer, with different periods, and using hysteresis dampers with suitable properties between them for energy dissipation. In the present study, the use of viscous dampers between the two parts of the structure for energy dissipation has been studied and the optimal locations and damping coefficient of the dampers have been determined. For this purpose, first, by dividing a 5-storey building into two sections and by using viscous dampers at the roof level, formulating the equations of motion and coding them in MATLAB platform, the appropriate damping coefficient of the viscous dampers was obtained. The results showed that by choosing the proper damping values, the system could absorb high amount of energy and significantly reduce the drift of the building stories. Then, three 5-, 8- and 11-story steel braced-frames buildings were designed using ETABS software and were divided into inner and outer parts, and modeled for seismic response analyses in PERFORM-3D software. Based on these analyses, performances of viscous dampers with appropriate damping coefficient and hysteresis dampers with appropriate stiffness and strength were compared. Results show that when viscous dampers with appropriate damping coefficient are used, the maximum story drift will be reduced by approximately 35% in the outer structure and approximately 50% in the inner structure relative to the integrated original structure. However, if the hysteresis dampers are used with the proper stiffness and strength, the maximum story drift relative to the integrated original structure will be reduced by approximately 20% in the outer structure and 65% in the inner structure.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
121
134
http://www.bese.ir/article_240407_9b7e5ba93dfd6ec4136c7f337787d15a.pdf
Evaluating Seismic Performance of Steel Structures Equipped with MADAS Dampers in Comparison with Moment-Resisting Frames
Mohammad Ghasem
Vetr
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Abbas
Shafizadeh
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Abolfazl
Riahi Nouri
Department of Arts and Architecture, West Tehran Branch, Islamic Azad University, Tehran, Iran
author
text
article
2019
per
One of the effective methods to improve dynamic response of steel structures is using adjunct elements among which metal yielding dampers are the most common. The working mechanism of these dampers in the lateral load-resisting structural system is related to the fact that development of inelastic strains in metallic dampers as the fuse elements results in dissipating the earthquake input energy imparted to the structure in a major seismic event. On the other hand, the aim of implementation of such damping devices is to substantially reduce the seismic demand in main structural systems, such as beams and columns, and hence, these members remains essentially elastic. One of the types of metallic yielding dampers is Added Damping and Stiffness (ADAS) metal damper that is a series of X-shaped steel sheets, which can be efficient in dissipating seismic energy but have shown apparent weakness due to the buckling resulted from development of axial forces in the dampers.The objective of the present paper is to investigate the characteristics of a Modified Added Damping and Stiffness (MADAS) damper to be used as a supplementary device to improve seismic performance of low- and mid-rise steel structures. In MADAS damper, X-shape plates are configured in a way that their displacement along vertical axis is quite free, and hence, no axial force is developed in such metallic dampers. In this paper, a numerical Finite Element (FE) model of MADAS damper was simulated in ABAQUS and used to compare the predicted numerical results to those of experimental results of the MADAS damper subjected to cyclic displacements. It should be noted that, the experimental cyclic tests have been conducted by previous researchers for MADAS dampers, and, have shown superior cyclic performance compared to conventional metallic dampers such as Triangular Added Damping and Stiffness (TADAS) dampers.In addition, three 4-, 5-, and 6-story buildings with steel moment-resisting frames have been studied, as the representative of the low- and mid-rise structures. For each building, two design alternatives, one for the case of conventional Steel Moment-Resisting Frame (MRF) and the other alternative is the one equipped with MADAS dampers, have been designed to be studied using numerical models. The structural members of the adopted buildings equipped with metallic MADAS dampers are designed according to ASCE/SEI 7-10 design code. The behavior of the numerical models has been investigated regarding seismic parameters including the Response Modification Factor, R, and Overstrength Factor, (Ω). The application of metallic dampers have shown to provide an increase of about (50%-80%) in the Response Modification Factor, R, and about (10%-20%) in the Overstrength Factor, (Ω). Pushover analyses for the numerical models have been conducted to obtain Base shear-Displacement curves. Based on the obtained pushover results, a maximum decrease of about 20% was noticed in the inter-story drifts of the numerical models in the Collapse Prevention (CP) performance level.In addition, to investigate the seismic performance of analysis cases, time-history analyses of the numerical models subjected to 1940 El-Centro, 1994 Northridge, and 1978 Tabas earthquakes have been conducted. The earthquake records have been scaled to Maximum Credible Earthquake (MCE) and Design Based Earthquake (DBE) intensity levels. Based on the obtained time-history results, a decrease of about (40%-50%) has been observed in the peak inter-story drift values due to the application of metallic MADAS dampers compared to that of moment-resisting steel frames. In addition, regarding the results of time-history analyses, the values of equivalent damping has been observed to be in the range of about (15%-20%) for the analysis cases. The obtained results indicate significant improvement in the seismic response of the structures equipped with MADAS dampers compared to the same buildings utilizing Steel Moment-Resisting Frames (MRFs) as their lateral-resistant structural system.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
135
152
http://www.bese.ir/article_240408_298a94083175a74f338ab99a9c48b680.pdf
Performance Evaluation of Rocking Wall Moment Frame Using Incremental Dynamic Analysis (IDA)
Nader
Khaje Ahmad Attari
Road Housing and Urban Research Center, Tehran, Iran
author
Zahra
Rahimi Sojasi
Road Housing and Urban Research Center, Tehran, Iran
author
text
article
2019
per
Conventional seismic lateral force resisting systems dissipate seismic energy through distributed damage to primary structural elements and residual drifts, which can result in significant socio-economic losses due to repair costs and business downtime after an earthquake event. Although these systems have low primary cost in the construction process, the recent recommendation of seismic design guidelines, which was minimizing the horrible seismic consequences of an earthquake led to the wide range of analytical and experimental research on the new generation of seismic structure system called low-damaged system. One of these low-damaged systems is Rocking wall.Like a traditional structural wall, a base-rocking system acts as a vertical cantilever to transfer lateral building loads to the foundation through shear and bending moments in the wall. The system is not capable of transmitting tension to the foundation; however, it is not rigidly tied to it as a traditional wall. Base bending moments are resisted by the restoring moment available due to the gravity loads acting on the wall, and once that effect is exceeded, a gap opens at the base of the wall. Because no elements yield during this process, the nonlinear behavior of the structure is not associated with permanent deformations. Reports of retrofitting projects indicate that there are significant economic costs in the foundation of the shear walls due to the large reaction forces at the base of the wall. Therefore, it is expected to economize the cost of construction by extending the details of the design of the rocking systems.On the other word, rocking walls can rock on the foundation during the earthquake by releasing the rotational constraint at the base, and they reduce residual drift by returning the attached structure to the original position.In this research, the behavior of the Reinforce Concrete frame with rocking wall is investigated using nonlinear Incremental Dynamical Analysis in two 2D models with 5-storey and 10-storey.Far field record set of the FEMA-p695 were used for IDA analysis and the structure response was compared with the corresponding frame response with conventional shear wall. There are 11 samples in total, four samples were designed for the 5-story model and seven samples for the 10-storey model, and 56 non-linear time histories analysis was performed on the each sample. Seven pairs of far field records, which are horizontal components were selected in proportion of record selection criteria of FEMA-p695. One of each pair of the records with larger peak ground acceleration was selected and they were scaled first to the gravity acceleration and second to the weight coefficient of intensity. Analysis and design of models are performed using SAP2000-v14 software.Rocking walls are modeled such as pre-stress reinforce concrete wall with unbounded post-tensioned cables. Rocking movement is modeled using gap element and hinge constraint at the bottom of the wall. Rigid beams are used to connect the frame to the wall.The results show that the rocking wall in both 5 and 10 storey models has a significant reduction in residual drift, and by equipping them with post-tensioned cables and dampers in 10-story model, can insure of the behavior of non-structural components during the earthquake. The connection of the frame to the wall was also investigated in different models, and hinge connection of the frame to the wall was evaluated well for the proper behavior of the rocking system.Although the design and construction of such systems is still not common in the worldwide due to the high uncertainties, further study and research in this field can lead to applied design and evolution in the current constructions. The purpose of this study is first to become more familiar with rocking walls and then to survey the behavior and performance of these walls in combination with concrete moment frame. However, simplification has been done in the software for simulation of this system, which will definitely affect the results. The general view obtained by these results will be effective in the study process on these systems.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
153
168
http://www.bese.ir/article_240409_baf5c3bcef4fc038ad8ce6eebbdbf3d4.pdf
Developing Building and Population Inventories Using Dasymetry and Remote Sensing Techniques for Urban Loss Estimation – Case Study: City of Sari
Babak
Mansouri
Earthquake Risk Management Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Parham
Jalilvand
International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
Mohsen
Ghafory-Ashtiany
Structural Engineering Research Center, International Institute of Earthquake Engineering and Seismology (IIEES), Tehran, Iran
author
text
article
2019
per
Residential buildings and associated population distribution modeling, is an integral part for assessing and estimating the direct and indirect risks/losses related to natural disasters, including earthquakes in the built environments such as in urban and rural settings. In this study, the geospatial database for the buildings were derived by compiling existing census data sets and the geospatial map that was derived by the comprehensive urban planning and development of the study area (Sari metropolitan area in Mazandaran, north of Iran) as obtained by the related consultant engineering firm. Combining the information from different data sets with different scales or spatial resolution involves some techniques that are mainly based on statistical inferencing methods and/or utilizing some spatial distribution patterns that exhibit the built environment topology. Once the distribution of the buildings or the residential units are derived and finalized, the population distribution pattern can be extracted based on similar aforementioned concepts. The second step in this research involved the development of the population inventory.In this study, as mentioned earlier, the statistical datasets from different sources (related to urban zones and city blocks) were combined first. For the purpose of comparison and overall verifications, some digital imageries such as aerial and satellite images were collected in order to extract urban features such as buildings. In this fashion, detailed geometric information concerning each individual building footprint are extracted that can be summarized according to their related city block polygons. This scheme was applied for some selected parts of the city that can be evenly utilized and extended for any desired geographic extents. In conducting the present research, a simplified method for building height (or city parcel height) assignment was also delivered that indicates the average number of stories within each city block.After the urban database has been developed (building and population inventories), the earthquake damage to the elements at risks (i.e. building destruction and human casualty) can be assessed in the study area. As a case study, the metropolitan area of Sari was focused, and some probable hypothetical scenario earthquakes were considered. For each scenario earthquake, damages to the building stock and the associated human losses were estimated according to some predefined domestic vulnerability functions and a global human casualty model as reported. For example, as a result, considering the Khazar Fault earthquake scenario, more than 5000 housing units are expected to experience very heavy damage to destruction.This study has presented a comprehensive model according to the existing data sets and the local conditions for the study area that can be modified, upgraded and updated with newer and more accurate data whenever accessible. Also the same method can be applied for other parts of the country. Moreover, the results indicate that the expected damages, losses and human casualties are high and alarming suggesting more detailed study on the region and also devising and implementing suitable disaster management measures for the region.
Bulletin of Earthquake Science and Engineering
International Institute of Earthquake Engineering and Seismology
2476-6097
6
v.
4
no.
2019
169
179
http://www.bese.ir/article_240410_3471511fbff3c327bac434c69abcfc56.pdf