after first online publication: Majd Armaly's surname has been corrected from 'Majd Armali' to 'Majd Armaly'] The increase in population especially in third world countries demands taller, more flexible, and lighter buildings. Most of these countries are subjected to a high risk of earthquakes, which requires more control of building seismic response. However, several techniques exist to minimize the vibrations induced by an earthquake shock. This paper will discuss the effectiveness of using friction dampers as a passive dissipative device and proposes some design optimization of the number and position of dampers in the building. Friction dampers offer a supplemental damping in conjunction with appropriate stiffness, offering an innovative and attractive solution for the seismic response control of tall structures in risky areas. The originality of this work is in the detailed seismic study of an asymmetric reinforced concrete (RC) building, located in a risky seismic zone and using real earthquake seismic waves. The seismic response of this dissipative structural method is compared with the response of the conventional method (shear wall system) for the high rise building. To accomplish this objective, a nonlinear modal time history analysis using the El Centro earthquake record for a 40-storey RC high rise building, is performed with four different damper type formats using ETABS software. To illustrate the response improvement by dampers, storey accelerations, storey displacements, base shear forces, and storey drifts are compared with a conventional fixed base system (shear wall system) for the same building. Results show that using an optimum position and number of dampers, a tall building can remain operational during a seism.

Roots provide basic functions to plants such as water/nutrient uptake and anchoring in soil. The growth and development of root systems contribute to colonizing the surrounding soil and optimizing the access to resources. It is usually admitted that the variability of plant root architecture results from the combination of genetic, physiological and environmental factors, in particular soil mechanical impedance. However this last factor has never been investigated at the soil grain scale. In this paper, we are interested in the effect of the disordered texture of granular soils on the evolution of external forces experienced by root cap. We introduce a numerical model in which the root is modeled as a flexible self-elongating tube that probes a soil composed of solid particles. By means of extensive simulations, we show that the forces exerted on the root cap during its growth reflect interparticle force chains. Our extensive simulations also show that the mean force declines exponentially with root flexibility, the highest force corresponding to the soil hardness. Furthermore, we find that this functional dependence is characterized by a single parameter that combines the granular structure and root bending stiffness. This finding will be useful to further address the biological issues of mechanosensing and thigmomorphogenesis in plant roots.

Abstract. We use molecular dynamics simulations to investigate the effects of root bending stiffness and packing fraction on the path followed by a growing root in 2D packings of grains representing a soil. The root is modeled as a chain of elements that can grow in length and change their direction depending on the forces exerted by soil grains. We show that the root shape is mainly controlled by the bending stiffness of its apex. At low stiffness, the root randomly explores the pore space whereas at sufficiently high stiffness, of the order of soil hardness multiplied by mean grain size, the root follows a straight path across the soil. Between these two limits, the root shape can be characterized by the standard deviation of its re-directions at the scale of soil grains. We find that this shape parameter varies as a power-law function of the normalized bending stiffness.