The Limitations of Equivalent Linear Site Response Analysis Considering Soil Nonlinearity Properties

Seismic site effect has been a major issue in the field of earthquake engineering due to the large local amplification of the seismic motion. This paper presents the importance of an appropriate soil behavior model to simulate earthquake site response and gives a critical overview of the field of site response analysis. Some of the well known site response analysis methods are summarized and discussed. The objective of this paper is to investigate the influences of nonlinearity on the site response analysis by means of a more precise numerical model. In this respect, site responses of four different types of one layered soil deposit, based on various shear wave velocities, with the assumption of linear and rigid base bedrock, were analyzed by using the equivalent linear and fully nonlinear approaches. Nonlinear analyses’ results were compared with those of the linear method and the similarities and differences are discussed. As a result, it is concluded that, in the case of nonlinearity of soil under strong ground motions, 1-D equivalent linear modeling overestimates the amplification patterns in terms of absolute amplification level, and cannot correctly account for resonant frequencies and hysteric soil behavior. Hence more practical and appropriate numerical techniques for ground response analysis should be surveyed

The Prediction of Liquefaction Damages to a Large Span Bridge on Karoon River, Iran

Several damages have been imposed to bridges due to liquefaction of the soil layer in the position of their foundations. However, there is not a specific world - wide provisions for design of bridges in these conditions. In this paper the results of evaluating liquefaction potential and the consequence damages which is likely to happen for a large span bridge (Shirin-Shahr Bridge) to be constructed on the Karoon river (one of the main river in the south-western part of Iran) are presented. Since the liquefaction potential of a site depends not only on the geotechnical characteristics, but on the intensity of the ground motions as well, a comprehensive seismic hazard analysis was carried out to estimate the appropriate PGA in the area. At the end some geotechnical comments are suggested for the aseismic design of the bridge foundation accordingly

The Amplification of Seismic Waves in Tehran

Vibrations of the bedrock due to earthquakes are transferred to the ground level via different soil layers. The arrived waves in the ground surface which affect the superstructures are usually stronger than those induced in the bedrock, depending on the geological and geotechnical characteristics of the soil layers. In this paper the influence of different geotechnical parameters of a site on the amplification of earthquake waves are investigated using the mathematical equations of wave’s propagation in a visco-elastic half-space medium. A special computer software was used to analyze the geotechnical data of a site in the western part of Tehran. The obtained results are illustrated as the response spectra in the ground surface to evaluate the effect of each parameter on the earthquake amplification. Finally the amplification factor of the site was calculated by comparing the bedrock and the ground accelerations obtained from the analysis

Earth Pressure Variations under Cyclic Surcharges

There are a tremendous studies in literature about the earth pressure, most of them are concentrated on the static loading conditions. The problems of earth pressure under dynamic loadings are still the case of studies. In this paper the results of an experimental studies about variations of earth pressure at rest under different vertical cyclic loadings are presented. Cubical soil samples of 15 cm dimensions were subjected to vertical cyclic stresses and induced lateral pressure behind the rigid side walls of the soil were measured accurately. A dry and uniform sand was used and the samples were prepared by the raining technique. A kind of true triaxial apparatus was used and different samples in the quite dense and loose conditions were tested. The variations of lateral pressure versus vertical stress and number of load cycles are plotted and discussed. In the concluding section a recommendation is made for designing retaining walls under cyclic surcharges

The Crack Development Due to Liquefaction of Sand Lenses During Earthquake Loading

The failure of sand lenses during earthquake loadings has caused many damages to the ground and yet its mechanism has not been investigated extensively. In this paper the results of an analytical studies involving the mechanism of crack development of a sand lens due to liquefaction, are presented. A single loose and saturated sand lens embedded inside a stiff clay deposit, which will liquefy due to the earthquake loading, is modeled by finite element method. The principles of fracture mechanics were used and the soil behavior was considered as a non-linear elasto-plastic material. The computer package of NISA was used and the failure mechanism of the lens was analysed by this package. Finally, the crack development and the angle of developed crack from the tip of the lens to the horizontal was calculated and discussed

Investigating the Influence of Penetration Length of Cut-off Wall on its Dynamic Interaction with Core and Foundation of Earth Dam

Seepage and flow of water in the soil is one of the most important issue and effective elements in designing embankment dams. One of the methods to control seepage in alluvial foundation of earth dams is to use a plastic concrete cutoff-wall. For better seepage control, the cutoff-wall extends inside the clayey core as the one of common method of connection of cut-off wall and the core. Due to the stiffness difference of the core material and cutoff-wall, and also due to geological situation, physical and mechanical properties of rock and foundation, interaction of core and foundation with cut-off wall in different static and dynamic load cases is very considerable. Failure of cut-off wall occurs in cut-off wall and core joint.  So the study of their interaction, especially during an earthquake is very important. Karkheh dam cut-off wall with an area of about 150000 m2 is chosen for this study. FLAC software has been used to study the effect of cutoff-wall penetration length variation, inside the clay core of Karkheh earth dam under dynamic loading.  In numerical analysis of Karkheh earth dam model, all construction stages and seepage through dam are modelled. The model is first calibrated according to the results obtained from the dam instrumentations. After calibrating, according to available seismic studies of region, a suitable acceleration was selected and applied to the model. In this research, in order to find the optimum length, the effect of 0, 5, 10, 15 and 20 meters penetration length of cut-off wall in aforementioned conditions has been investigated. The results of the numerical study showed that the horizontal displacement and the maximum shear strain in the cutoff-wall is occurred adjacent to the clay core and the interface of core and foundation is a critical point for the cut-off wall, and also the stress in cut off wall joint increases with the elongation of penetration depth of the wall

Effect of Density on Critical Depth of Liquefaction in a Soil Deposit Containing Double Loose Sand Lenses

Large surface deformations due to liquefaction have been observed in many soil deposits which seem to feature good geotechnical characteristics. These deformations are often caused by the liquefaction of sand layers surrounded by clayey or silty soils called “sand lenses”. Liquefaction potential often decreases with increasing of depth. Hence, a specific depth of embedment of the lenses can be defined below which liquefaction would unlikely happen or the consequential surface deformation would be negligible. This depth is called critical depth. This research aims at studying the effects of the relative density of the sand within the lenses on the critical depth of liquefaction in a soil deposit containing double sand lenses. The soil deposit is simulated in plane strain condition using the computer code, FLAC (Version 4), which is based on finite difference method. Soil deformation, hysteresis loops, shear strain, shear stress, pore water pressure and effective stress in the sand lenses have been plotted during seismic loading. Results indicate that critical depth is strongly dependent on the relative density of the sand. The rate of change of the critical depth versus the standard penetration test number decreases with increasing relative density

The global burden of childhood and adolescent cancer in 2017: an analysis of the Global Burden of Disease Study 2017

© 2019 The Author(s). Published by Elsevier Ltd. This is an Open Access article under the CC BY 4.0 license Background: Accurate childhood cancer burden data are crucial for resource planning and health policy prioritisation. Model-based estimates are necessary because cancer surveillance data are scarce or non-existent in many countries. Although global incidence and mortality estimates are available, there are no previous analyses of the global burden of childhood cancer represented in disability-adjusted life-years (DALYs). Methods: Using the Global Burden of Diseases, Injuries, and Risk Factors Study (GBD) 2017 methodology, childhood (ages 0–19 years) cancer mortality was estimated by use of vital registration system data, verbal autopsy data, and population-based cancer registry incidence data, which were transformed to mortality estimates through modelled mortality-to-incidence ratios (MIRs). Childhood cancer incidence was estimated using the mortality estimates and corresponding MIRs. Prevalence estimates were calculated by using MIR to model survival and multiplied by disability weights to obtain years lived with disability (YLDs). Years of life lost (YLLs) were calculated by multiplying age-specific cancer deaths by the difference between the age of death and a reference life expectancy. DALYs were calculated as the sum of YLLs and YLDs. Final point estimates are reported with 95% uncertainty intervals. Findings: Globally, in 2017, there were 11·5 million (95% uncertainty interval 10·6–12·3) DALYs due to childhood cancer, 97·3% (97·3–97·3) of which were attributable to YLLs and 2·7% (2·7–2·7) of which were attributable to YLDs. Childhood cancer was the sixth leading cause of total cancer burden globally and the ninth leading cause of childhood disease burden globally. 82·2% (82·1–82·2) of global childhood cancer DALYs occurred in low, low-middle, or middle Socio-demographic Index locations, whereas 50·3% (50·3–50·3) of adult cancer DALYs occurred in these same locations. Cancers that are uncategorised in the current GBD framework comprised 26·5% (26·5–26·5) of global childhood cancer DALYs. Interpretation: The GBD 2017 results call attention to the substantial burden of childhood cancer globally, which disproportionately affects populations in resource-limited settings. The use of DALY-based estimates is crucial in demonstrating that childhood cancer burden represents an important global cancer and child health concern. Funding: Bill & Melinda Gates Foundation, American Lebanese Syrian Associated Charities (ALSAC), and St. Baldrick's Foundation

Anemia prevalence in women of reproductive age in low- and middle-income countries between 2000 and 2018

Anemia is a globally widespread condition in women and is associated with reduced economic productivity and increased mortality worldwide. Here we map annual 2000–2018 geospatial estimates of anemia prevalence in women of reproductive age (15–49 years) across 82 low- and middle-income countries (LMICs), stratify anemia by severity and aggregate results to policy-relevant administrative and national levels. Additionally, we provide subnational disparity analyses to provide a comprehensive overview of anemia prevalence inequalities within these countries and predict progress toward the World Health Organization’s Global Nutrition Target (WHO GNT) to reduce anemia by half by 2030. Our results demonstrate widespread moderate improvements in overall anemia prevalence but identify only three LMICs with a high probability of achieving the WHO GNT by 2030 at a national scale, and no LMIC is expected to achieve the target in all their subnational administrative units. Our maps show where large within-country disparities occur, as well as areas likely to fall short of the WHO GNT, offering precision public health tools so that adequate resource allocation and subsequent interventions can be targeted to the most vulnerable populations