Abstract: Time history dynamic analysis of structures is considered as an exact method while being computationally intensive. Filtration of earthquake strong ground motions applying wavelet transform is an approach towards reduction of computational efforts, particularly in optimization of structures against seismic effects. Wavelet transforms are categorized into continuum and discrete transforms. Since earthquake strong ground motion is a discrete function, the discrete wavelet transform is applied in the present paper. Wavelet transform reduces analysis time by filtration of non-effective frequencies of strong ground motion. Filtration process may be repeated several times while the approximation induces more errors. In this paper, strong ground motion of earthquake has been filtered once applying each wavelet. Strong ground motion of Northridge earthquake is filtered applying various wavelets and dynamic analysis of sampled shear and moment frames is implemented. The error, regarding application of each wavelet, is computed based on comparison of dynamic response of sampled structures with exact responses. Exact responses are computed by dynamic analysis of structures applying non-filtered strong ground motion.
Abstract: Regional variations in strong ground motions for the Iranian Plateau have been investigated by using a simple statistical method called Analysis of Variance (ANOVA). In this respect, a large database consisting of 1157 records occurring within the Iranian Plateau with moment magnitudes of greater than or equal to 5 and Joyner-Boore distances up to 200 km has been considered. Geometric averages of horizontal peak ground accelerations (PGA) as well as 5% damped linear elastic response spectral accelerations (SA) at periods of 0.2, 0.5, 1.0, and 2.0 sec are used as strong motion parameters. The initial database is divided into two different datasets, for Northern Iran (NI) and Central and Southern Iran (CSI). The comparison between strong ground motions of these two regions reveals that there is no evidence for significant differences; therefore, data from these two regions may be combined to estimate the unknown coefficients of attenuation relationships.
Abstract: Since the evolution of computational tools and simulation software, there has been considerable increase in research on Soil Structure Interaction (SSI) to decrease the computational time and increase accuracy in the results. To aid the designer with a proper understanding of the response of structure in different soil types, the presented paper compares the deformation, shear stress, acceleration and other parameters of multi-storey building for a specific input ground motion using Response-spectrum Analysis (RSA) method. The response of all the models of different heights have been compared in different soil types. Finite Element Simulation software, ANSYS, has been used for all the computational purposes. Overall, higher response is observed with SSI, while it increases with decreasing stiffness of soil.
Abstract: This study presents the seismic safety evaluation of weir structure subjected to strong earthquake ground motions, as a flood defense structure in civil engineering structures. The seismic safety analysis procedure was illustrated through development of Finite Element (FE) and InFinite Element (IFE) method in ABAQUS platform. The IFE model was generated by CINPS4, 4-node linear one-way infinite model as a sold continuum infinite element in foundation areas of the weir structure and then nonlinear FE model using friction model for soil-structure interactions was applied in this study. In order to understand the complex behavior of weir structures, nonlinear time history analysis was carried out. Consequently, it was interesting to note that the compressive stress gave more vulnerability to the weir structure, in comparison to the tensile stress, during an earthquake. The stress concentration of the weir structure was shown at the connection area between the weir body and stilling basin area. The stress both tension and compression was reduced in IFE model rather than FE model of weir structures.
Abstract: This study described the seismic performance evaluation of bridge structures, located near Daegu metropolitan city in Korea. The structural design code or regulatory guidelines is focusing on the protection of brittle failure or collapse in bridges’ lifetime during an earthquake. This paper illustrated the procedure in terms of the safety evaluation of bridges using simple linear elastic 3D Finite Element (FE) model in ABAQUS platform. The design response spectra based on KBC 2009 were then developed, in order to understand the seismic behavior of bridge structures. Besides, the multiple directional earthquakes were applied and it revealed that the most dominated earthquake direction was transverse direction of the bridge. Also, the bridge structure under the compressive stress was more fragile than the tensile stress and the vertical direction of seismic ground motions was not significantly affected to the structural system.
Abstract: Fragility analysis is an effective tool for the seismic vulnerability assessment of civil structures in the last several years. The design of the expansion joints according to various bridge design codes is almost inconsistent, and only a few studies have focused on this problem so far. In this study, the influence of the expansion joint clearances between the girder ends and the abutment backwalls on the seismic fragility assessment of continuous integral bridge frames is investigated. The gaps (ranging from 60 mm, 150 mm, 250 mm and 350 mm) are designed by following two different bridge design code specifications, namely, Caltrans and Eurocode 8-2. Five bridge models are analyzed and compared. The first bridge model serves as a reference. This model uses three-dimensional reinforced concrete fiber beam-column elements with simplified supports at both ends of the girder. The other four models also employ reinforced concrete fiber beam-column elements but include the abutment backfill stiffness and four different gap values. The nonlinear time history analysis is performed. The artificial ground motion sets, which have the peak ground accelerations (PGAs) ranging from 0.1 g to 1.0 g with an increment of 0.05 g, are taken as input. The soil-structure interaction and the P-Δ effects are also included in the analysis. The component fragility curves in terms of the curvature ductility demand to the capacity ratio of the piers and the displacement demand to the capacity ratio of the abutment sliding bearings are established and compared. The system fragility curves are then obtained by combining the component fragility curves. Our results show that in the component fragility analysis, the reference bridge model exhibits a severe vulnerability compared to that of other sophisticated bridge models for all damage states. In the system fragility analysis, the reference curves illustrate a smaller damage probability in the earlier PGA ranges for the first three damage states, they then show a higher fragility compared to other curves in the larger PGA levels. In the fourth damage state, the reference curve has the smallest vulnerability. In both the component and the system fragility analysis, the same trend is found that the bridge models with smaller clearances exhibit a smaller fragility compared to that with larger openings. However, the bridge model with a maximum clearance still induces a minimum pounding force effect.
Abstract: Geological and tectonic framework indicates that
Bangladesh is one of the most seismically active regions in the world.
The Bengal Basin is at the junction of three major interacting plates:
the Indian, Eurasian, and Burma Plates. Besides there are many
active faults within the region, e.g. the large Dauki fault in the north.
The country has experienced a number of destructive earthquakes due
to the movement of these active faults. Current seismic provisions of
Bangladesh are mostly based on earthquake data prior to the 1990.
Given the record of earthquakes post 1990, there is a need to revisit
the design provisions of the code. This paper compares the base shear
demand of three major cities in Bangladesh: Dhaka (the capital city),
Sylhet, and Chittagong for earthquake scenarios of magnitudes
7.0MW, 7.5MW, 8.0MW, and 8.5MW using a stochastic model. In
particular, the stochastic model allows the flexibility to input region
specific parameters such as shear wave velocity profile (that were
developed from Global Crustal Model CRUST2.0) and include the
effects of attenuation as individual components. Effects of soil
amplification were analysed using the Extended Component
Attenuation Model (ECAM). Results show that the estimated base
shear demand is higher in comparison with code provisions leading to
the suggestion of additional seismic design consideration in the study
regions.
Abstract: Non-linear dynamic time history analysis is
considered as the most advanced and comprehensive analytical
method for evaluating the seismic response and performance of
multi-degree-of-freedom building structures under the influence of
earthquake ground motions. However, effective and accurate
application of the method requires the implementation of advanced
hysteretic constitutive models of the various structural components
including masonry infill panels. Sophisticated computational research
tools that incorporate realistic hysteresis models for non-linear
dynamic time-history analysis are not popular among the professional
engineers as they are not only difficult to access but also complex and
time-consuming to use. In addition, commercial computer programs
for structural analysis and design that are acceptable to practicing
engineers do not generally integrate advanced hysteretic models
which can accurately simulate the hysteresis behavior of structural
elements with a realistic representation of strength degradation,
stiffness deterioration, energy dissipation and ‘pinching’ under cyclic
load reversals in the inelastic range of behavior. In this scenario,
push-over or non-linear static analysis methods have gained
significant popularity, as they can be employed to assess the seismic
performance of building structures while avoiding the complexities
and difficulties associated with non-linear dynamic time-history
analysis. “Push-over” or non-linear static analysis offers a practical
and efficient alternative to non-linear dynamic time-history analysis
for rationally evaluating the seismic demands. The present paper is
based on the analytical investigation of the effect of distribution of
masonry infill panels over the elevation of planar masonry infilled
reinforced concrete [R/C] frames on the seismic demands using the
capacity spectrum procedures implementing nonlinear static analysis
[pushover analysis] in conjunction with the response spectrum
concept. An important objective of the present study is to numerically
evaluate the adequacy of the capacity spectrum method using
pushover analysis for performance based design of masonry infilled
R/C frames for near-field earthquake ground motions.
Abstract: This paper presents the influence of the vertical
seismic component on the non-linear dynamics analysis of three
different structures. The subject structures were analyzed and
designed according to recent codes. This paper considers three types
of buildings: 5-, 10-, and 15-story buildings. The non-linear
dynamics analysis of the structures with assuming elastic-perfectlyplastic
behavior was performed using RAM PERFORM-3D software;
the horizontal component was taken into consideration with and
without the incorporation of the corresponding vertical component.
Dynamic responses obtained for the horizontal component acting
alone were compared with those obtained from the simultaneous
application of both seismic components. The results show that the
effect of the vertical component of ground motion may increase the
axial load significantly in the interior columns and, consequently, the
stories. The plastic mechanisms would be changed. The P-Delta
effect is expected to increase. The punching base plate shear of the
columns should be considered. Moreover, the vertical component
increases the input energy when the structures exhibit inelastic
behavior and are taller.
Abstract: This paper presents the influence of the vertical
seismic component on the non-linear dynamics analysis of three
different structures. The subject structures were analyzed and
designed according to recent codes. This paper considers three types
of buildings: 5-, 10-, and 15-story buildings. The non-linear dynamics
analysis of the structures with assuming elastic-perfectly-plastic
behavior was performed using RAM PERFORM-3D software; the
horizontal component was taken into consideration with and without
the incorporation of the corresponding vertical component. Dynamic
responses obtained for the horizontal component acting alone were
compared with those obtained from the simultaneous application of
both seismic components. The results show that the effect of the
vertical component of ground motion may increase the axial load
significantly in the interior columns and, consequently, the stories.
The plastic mechanisms would be changed. The P-Delta effect is
expected to increase. The punching base plate shear of the columns
should be considered. Moreover, the vertical component increases the
input energy when the structures exhibit inelastic behavior and are
taller.
Abstract: Investigating the dynamic responses of high rise
structures under the effect of siesmic ground motion is extremely
important for the proper analysis and design of multitoried structures.
Since the presence of infilled walls strongly influences the behaviour
of frame systems in multistoried buildings, there is an increased need
for developing guidelines for the analysis and design of infilled
frames under the effect of dynamic loads for safe and proper design
of buildings. In this manuscript, we evaluate the natural frequencies
and natural periods of single bay single storey frames considering the
effect of infill walls by using the Eigen value analysis and validating
with SAP 2000 (free vibration analysis). Various parameters obtained
from the diagonal strut model followed for the free vibration analysis
is then compared with the Finite Element model, where infill is
modeled as shell elements (four noded). We also evaluated the effect
of various parameters on the natural periods of vibration obtained by
free vibration analysis in SAP 2000 comparing them with those
obtained by the empirical expressions presented in I.S. 1893(Part I)-
2002.
Abstract: Damage status of RC buildings is greatly influenced
by the characteristics of the imposed ground motion. Peak Ground
Acceleration and frequency contents are considered the main two
factors that affect ground motion characteristics; hence, affecting the
seismic response of RC structures and consequently their damage
state. A detailed investigation on the combined effects of these two
factors on damage assessment of RC buildings is carried out. Twenty
one earthquake records are analyzed and arranged into three groups,
according to their frequency contents. These records are used in an
investigation to define the expected damage state that would be
attained by RC buildings, if subjected to varying ground motion
characteristics. The damage assessment is conducted through
examining drift ratios and damage indices of the overall structure and
the significant structural components of RC building. Base and story
shear of RC building model, are also investigated, for cases when the
model is subjected to the chosen twenty one earthquake records.
Nonlinear dynamic analyses are performed on a 2-dimensional model
of a 12-story RC building.
Abstract: This study presented to reduce earthquake damage and
emergency rehabilitation of critical structures such as schools, hightech
factories, and hospitals due to strong ground motions associated
with climate changes. Regarding recent trend, a strong earthquake
causes serious damage to critical structures and then the critical
structure might be influenced by sequence aftershocks (or tsunami)
due to fault plane adjustments. Therefore, in order to improve seismic
performance of critical structures, retrofitted or strengthening study
of the structures under aftershocks sequence after emergency
rehabilitation of the structures subjected to strong earthquakes is
widely carried out. Consequently, this study used composite material
for emergency rehabilitation of the structure rather than concrete and
steel materials because of high strength and stiffness, lightweight,
rapid manufacturing, and dynamic performance. Also, this study was
to develop or improve the seismic performance or seismic retrofit of
critical structures subjected to strong ground motions and earthquake
aftershocks, by utilizing GFRP-Corrugated Infill Panels (GCIP).
Abstract: A reliability-based methodology which uses structural demand hazard curves to consider the increment of the ductility demands of structures with tilting is proposed. The approach considers the effect of two orthogonal components of the ground motions as well as the influence of soil-structure interaction. The approach involves the calculation of ductility demand hazard curves for symmetric systems and, alternatively, for systems with different degrees of asymmetry. To get this objective, demand hazard curves corresponding to different global ductility demands of the systems are calculated. Next, Uniform Exceedance Rate Spectra (UERS) are developed for a specific mean annual rate of exceedance value. Ratios between UERS corresponding to asymmetric and to symmetric systems located in soft soil of the valley of Mexico are obtained. Results indicate that the ductility demands corresponding to tilted structures may be several times higher than those corresponding to symmetric structures, depending on several factors such as tilting angle and vibration period of structure and soil.
Abstract: Predicting the collapse potential of a structure during
earthquakes is an important issue in earthquake engineering. Many
researchers proposed different methods to assess the collapse
potential of structures under the effect of strong ground motions.
However most of them did not consider degradation and softening
effect in hysteretic behavior. In this study, collapse potential of
SDOF systems caused by dynamic instability with stiffness and
strength degradation has been investigated. An equation was
proposed for the estimation of collapse period of SDOF system which
is a limit value of period for dynamic instability. If period of the
considered SDOF system is shorter than the collapse period then the
relevant system exhibits dynamic instability and collapse occurs.
Abstract: The number of Ground Motion Prediction Equations
(GMPEs) used for predicting peak ground acceleration (PGA) and
the number of earthquake recordings that have been used for fitting
these equations has increased in the past decades. The current PF-L
database contains 3550 recordings. Since the GMPEs frequently
model the peak ground acceleration the goal of the present study was
to refit a selection of 44 of the existing equation models for PGA in
light of the latest data. The algorithm Levenberg-Marquardt was used
for fitting the coefficients of the equations and the results are
evaluated both quantitatively by presenting the root mean squared
error (RMSE) and qualitatively by drawing graphs of the five best
fitted equations. The RMSE was found to be as low as 0.08 for the
best equation models. The newly estimated coefficients vary from the
values published in the original works.
Abstract: A key issue in seismic risk analysis within the context
of Performance-Based Earthquake Engineering is the evaluation of
the expected seismic damage of structures under a specific
earthquake ground motion. The assessment of the seismic
performance strongly depends on the choice of the seismic Intensity
Measure (IM), which quantifies the characteristics of a ground
motion that are important to the nonlinear structural response. Several
conventional IMs of ground motion have been used to estimate their
damage potential to structures. Yet, none of them has been proved to
be able to predict adequately the seismic damage. Therefore,
alternative, scalar intensity measures, which take into account not
only ground motion characteristics but also structural information
have been proposed. Some of these IMs are based on integration of
spectral values over a range of periods, in an attempt to account for
the information that the shape of the acceleration, velocity or
displacement spectrum provides. The adequacy of a number of these
IMs in predicting the structural damage of 3D R/C buildings is
investigated in the present paper. The investigated IMs, some of
which are structure specific and some are non structure-specific, are
defined via integration of spectral values. To achieve this purpose
three symmetric in plan R/C buildings are studied. The buildings are
subjected to 59 bidirectional earthquake ground motions. The two
horizontal accelerograms of each ground motion are applied along
the structural axes. The response is determined by nonlinear time
history analysis. The structural damage is expressed in terms of the
maximum interstory drift as well as the overall structural damage
index. The values of the aforementioned seismic damage measures
are correlated with seven scalar ground motion IMs. The comparative
assessment of the results revealed that the structure-specific IMs
present higher correlation with the seismic damage of the three
buildings. However, the adequacy of the IMs for estimation of the
structural damage depends on the response parameter adopted.
Furthermore, it was confirmed that the widely used spectral
acceleration at the fundamental period of the structure is a good
indicator of the expected earthquake damage level.
Abstract: Currently, seismic probabilistic risk assessments
(SPRA) for nuclear facilities use In-Structure Response Spectra
(ISRS) in the calculation of fragilities for systems and components.
ISRS are calculated via dynamic analyses of the host building
subjected to two orthogonal components of horizontal ground
motion. Each component is defined as the median motion in any
horizontal direction. Structural engineers applied the components
along selected X and Y Cartesian axes. The ISRS at different
locations in the building are also calculated in the X and Y directions.
The choice of the directions of X and Y are not specified by the
ground motion model with respect to geographic coordinates, and are
rather arbitrarily selected by the structural engineer. Normally, X and
Y coincide with the “principal” axes of the building, in the
understanding that this practice is generally conservative. For SPRA
purposes, however, it is desirable to remove any conservatism in the
estimates of median ISRS. This paper examines the effects of the
direction of horizontal seismic motion on the ISRS on typical nuclear
structure. We also evaluate the variability of ISRS calculated along
different horizontal directions. Our results indicate that some central
measures of the ISRS provide robust estimates that are practically
independent of the selection of the directions of the horizontal
Cartesian axes.
Abstract: Performance based design (PBD) is an iterative exercise in which a preliminary trial design of the building structure is selected and if the selected trial design of the building structure does not conform to the desired performance objective, the trial design is revised. In this context, development of a fundamental approach for performance based seismic design of masonry infilled frames with minimum number of trials is an important objective. The paper presents a plastic design procedure based on the energy balance concept for PBD of multi-story multi-bay masonry infilled reinforced concrete (R/C) frames subjected to near-field earthquakes. The proposed energy based plastic design procedure was implemented for trial performance based seismic design of representative masonry infilled reinforced concrete frames with various practically relevant distributions of masonry infill panels over the frame elevation. Non-linear dynamic analyses of the trial PBD of masonry infilled R/C frames was performed under the action of near-field earthquake ground motions. The results of non-linear dynamic analyses demonstrate that the proposed energy method is effective for performance based design of masonry infilled R/C frames under near-field as well as far-field earthquakes.
Abstract: In this study, we estimated the seismic ground motion parameters based on microtremor measurements atPalu City. Several earthquakes have struck along the Palu-Koro Fault during recent years. The USGS epicenter, magnitude Mw 6.3 event that occurred on January 23, 2005 caused several casualties. We conducted a microtremor survey to estimate the strong ground motion distribution during the earthquake. From this surveywe produced a map of the peak ground acceleration, velocity, seismic vulnerability index and ground shear strain maps in Palu City. We performed single observations of microtremor at 151 sites in Palu City. We also conducted8-site microtremors array investigation to gain a representative determination of the soil condition of subsurface structures in Palu City.From the array observations, Palu City corresponds to relatively soil condition with Vs ≤ 300m/s, the predominant periods due to horizontal vertical ratios (HVSRs) are in the range of 0.4 to 1.8 s and the frequency are in the range of 0.7 to 3.3 Hz. Strong ground motions of the Palu area were predicted based on the empirical stochastic green’s function method. Peak ground acceleration and velocity becomes more than 400 gal and 30 kine in some areas, which causes severe damage for buildings in high probability. Microtremor survey results showed that in hilly areas had low seismic vulnerability index and ground shear strain, whereas in coastal alluvium was composed of material having a high seismic vulnerability and ground shear strain indication.