Search

Understanding the evolutionary history of endangered species is crucial for identifying the main reasons for species endangerment in the past and predicting the changing trends and evolutionary directions of their future distribution. In order to study the impact of environmental changes caused by deep valley incision after the uplift of the Qinghai-Tibet Plateau on endangered species, we collected 23 samples belonging to four populations of Aleuritopteris grevilleoides, an endangered fern endemic to the dry-hot valleys (DHV) of Yunnan. Single-nucleotide variation sites (SNPs) were obtained by the genotyping-by-sequencing (GBS) method, and approximately 8085 SNP loci were identified. Through the reconstruction and analysis of genetic diversity, population structure, population dynamics, evolution time, and ancestral geographical distribution, combined with geological historical events such as the formation of dry-hot valleys, this study explores the formation history, current situation, reasons for endangerment and scientifically sound measures for the protection of A. grevilleoides. In our study, A. grevilleoides had low genetic diversity (Obs_Het = 0.16, Exp_Het = 0.32, Pi = 0.33) and a high inbreeding coefficient (Fis = 0.45). The differentiation events were 0.18 Mya, 0.16 Mya, and 0.11 Mya in the A. grevilleoides and may have been related to the formation of terraces within the dry-hot valleys. The history of population dynamics results shows that the diversion of the river resulted in a small amount of gene flow between the two clades, accompanied by a rapid increase in the population at 0.8 Mya. After that, the effective population sizes of A. grevilleoides began to contract continuously due to topographic changes resulting from the continuous expansion of dry-hot valleys. In conclusion, we found that the environmental changes caused by geological events might be the main reason for the changing population size of A. grevilleoides.

The ultimate load calculation formula for the solid multi barrel tube-confined concrete columns (CHS inner and SHS outer) was derived based on the Unified Strength Theory (UST) in this paper. The influence of intermediate principal stress and the double restriction effect and the decrease of longitudinal stress were considered in the formula. Based on the axial compression load and consider the eccentricity ratio and slenderness ratio, by introducing the reduction factor of concrete strength and the equivalent restriction reduction factor, based on unified strength theory solutions of thick tube, combined with concrete filled skin tube unified theory, deduce the calculation formula of eccentric compression bearing capacity of concrete filled steel tubular columns and analysis the influence complication.

Pressure-impulse diagrams have been extensively used for damage assessments of structural components subject to a specified blast loading. In this paper, a numerical method is used to generate pressure-impulse diagrams for unreinforced masonry walls subjected to blast loading. A previously developed plastic damage material model accounting for strain rate effects is used for brick and mortar. Three levels of damage criteria are defined based on maximum deflection of the wall and rotation of the supports. The obtained blast response for unreinforced masonry walls are validated against field test data. It is shown that the obtained pressure-impulse diagrams have an improved ability to evaluate the damage level of masonry walls.

In this paper, the dynamic response of concrete wall and steel fiber reinforced high strength concrete (SFRHSC) wall under blast load is simulated with the explicit dynamic finite element method. The J-H-C model is used for SFRHSC and the material parameters are determined based on the test results. The damage and strain rate effects are considered in above material model. The influences of scaled distance on the dynamic responses of walls are investigated and discussed.

This paper based on the unified strength theory, analyzed the ultimate bearing capacity of the reinforced concrete columns combined with FRP under axial loads. First, analyzed the mechanical property of the RC columns combined with FRP. Second, based on the unified strength theory, deduced the three-direction compressive stress of the core concrete and got the unified formula for calculating the ultimate bearing capacity of RC columns combined with FRP. Last, compared the analytical results obtained in this paper with the relevant experimental data, good agreement can be found and it proved the good applicability of the formula. Comparing with other methods in calculating the ultimate bearing capacity of RC columns combined with FRP，this method is well-founded, so it has a significant value in analysis of RC columns combined with FRP.

Recycling of waste concrete is beneficial and necessary from the viewpoint of environmental preservation and effective utilization of resources. The carbon fiber reinforced polymer tendon (CFRP tendon) has been widely used in concrete structures due to its high-strength, lightweight, good erosion-resistance, diamagnetism and anti-fatigue. The compressive behavior of recycled-concrete-segment/lump filled steel tubular columns with inner CFRP tendons are investigated in this paper. The formula of ultimate capacities of the columns under axial compression has been derived based on unified strength theory. Good agreement can be found from the comparison of the analytical results obtained in this paper and experimental data. Parametric studies are carried out to evaluate the effects of intermediate principal stress, mixture ratio of the recycled concrete and reinforcement ratio on the bearing capacities of the columns.

Based on the unified strength theory, the bearing capacity of the concrete filled square steel tube short columns with inner CFRP circular tube under eccentric compression was analyzed. The restriction effect of the inner CFRP circular tube upon the core concrete, strength reduction factor for eccentricity ratio and the equivalent reduction factor, which considered the ratio of thickness to side effect, were taken into account in the theoretical analysis. The axial bearing capacity formula of the square steel tube short columns filled with inner CFRP circular tube was deduced. By introducing the strength reduction factor for eccentricity ratio, the eccentric bearing capacity formula on the basis of the axial bearing capacity formula was obtained. Parametric studies were carried out to evaluate the effects of intermediate principal stress, different CFRP deployment ratios, eccentricity ratios and the tension-compression ratio on the eccentric bearing capacity of the column. The formula was verified by the comparison of the theoretical results with the experimental data. The results show that inner CFRP circular tube can effectively restrain the core concrete.

In this paper, the finite element program LS-DYNA was used to simulate the dynamic response of RC column with different constraints subjected to blast pressure. Through analyzing the five group columns with fixed end as well as one end fixed and one end simply supported, the maximum middle displacement and its relation with T/Tω were obtained. Thereby the dynamic factor of the column under blast pressure was acquired. Consequently the displacement response spectrum curve of the column was drawn. The results provide reference value to the design and protection of the RC column.

The failure of the reinforced concrete (RC) column on the ground floor may result in progressive collapse of the whole building. In the paper, the finite element program LS-DYNA is used to simulate the dynamic response of RC column with different constraints subjected to blast pressure. A three dimensional solid model is established for the RC column. A brittle damage model is applied to simulate the concrete. The lateral displacement and failure mode of RC column with different scaled distances are investigated and discussed. It can be found that the pressure nephogram and x-direction displacement of fixed end column under different scaled distance have the obvious symmetry. Moreover, both the maximum pressure and x-direction displacement of one end fixed and one end simply supported column are bigger than fixed end column with the same scaled distance.

Brick masonry is a traditional building material widely used loading-bearing or partition walls in various building structures. The detailed distinctive modelling of brick and mortar of a realistic masonry structure or a structure with masonry infilled walls are usually not possible due to the computational cost. In this paper, a homogenized dynamic material model which including the damage of brick and mortar and strain rate effect is developed based on dynamic test results of brick and mortar. The proposed homogenized material model was used in analysis of blast response of brick masonry wall.

The ultimate load-bearing capacities of axially-loaded steel tube composite column filled with steel reinforced concrete under three-dimensional stress based on the unified strength theory are analyzed in this paper. The influence of thickness-length ratio and scale effect are considered by introducing the reduction factor of equivalent constraints and concrete strength reduction factor, respectively. The nonlinear three-dimensional finite element analysis of the steel tube composite column filled with steel reinforced concrete is performed by the finite element software ANSYS. The numerical and the analytical results are compared with experimental results and good agreement can be observed. A series of numerical simulation technologies is studied and described in detail, such as selecting element type, defining material model of steel and concrete, establishing global finite element model with discrete reinforced bars elements, applying loads to the specimens, and setting solution controls option. The results indicate that ANSYS finite element software may well simulate the behavior of the steel tube composite column filled with steel reinforced concrete under axial compression through reasonably selecting parameters.

Unified solutions to the elastoplastic limit load of thick-walled cylindrical and spherical vessels under internal pressure are obtained in terms of the unified strength theory (UST) and the unified slip-line field theory (USLFT). The UST and the USLFT include or approximate an existing strength criterion or slip-line field theory by adopting a parameter b, which varies from 0 to 1. The theories can be used on pressure-sensitive materials, which have the strength difference (SD) effect. The solutions, based on the Tresca criterion, the von Mises criterion, the Mohr–Coulomb criterion, and the twin shear strength criterion, are special cases of the present unified solutions. The results based on the Mohr–Coulomb criterion (b=0) give the lower bound of the plastic limit load, while those according to the twin shear strength criterion (b=1) are the upper bound. The solution of the von Mises criterion is approximated by the linear function of the UST with a specific parameter (b≈0.5). Plastic limit solutions with respect to different yield criteria are illustrated and compared. The influences of the yield criterion as well as the ratio of the tensile strength to the compressive strength on the plastic limit loads are discussed.

A quantitative assessment of femur stress under compression and bending condition is essential for the understanding of failure mechanisms and providing guidance for the design and operation of femur replacement. The stress distribution of femur under bending moment and compressive load is simulated using finite element method (FEM) in this paper. A two-dimensional FEM model is established according to the dimension of a typical human femur. The bending moments are obtained by shifting the load action point to the outward lateral direction. Four excursion lengths 0mm, 5mm, 10mm and 15mm are tested. The deformation and stress distribution of femur, the stress in the cross section of femoral head, neck and femoral shift under bending moment and compressive load are obtained. It can be found from the numerical results that there is obvious stress concentration at femoral neck and tension stress occurs in the outside while the compressive stress occurs in inner side. In the cross section of femoral shaft, tension stress again occurs in the outside and compressive stress occurs in inner side. The femur stress increases significantly with the bending moment.