Lin Zhu Sun

Stress-Strain Model for Confined Concrete in Cross-Shaped Columns

To establish complete stress-strain curve equations for confined concrete in cross-shaped columns, we designed 7 test specimens corresponding to the usable eigenvalue range of stirrup of the cross-shaped columns. We obtained the test results of the reinforced concrete cross-shaped columns through axial compression test, got the system parameters of a stress-strain model through statistical analysis of the test data, and then established stress-strain curves for confined concrete in the cross-shaped columns. This model reflects the variation rule of the stress-strain curve of confined concrete in cross-shaped columns. Compared with the stress-strain model for confined concrete in square columns, the confined concrete in cross-shaped columns has smaller peak stress, larger peak strain, and relatively steeper descending part of curve. The research results provide theorotical basis for nonlinear analysis of cross-shaped columns.

Orthogonal Experimental Study on Thermal Insulation Mortar Containing Mixed Ceramic Sand and Vitrified Micro Bead Aggregates

Mixed light aggregates can effectively reduce the coefficient of thermal conductivity of composite materials. Through orthogonal experiments of thermal insulation mortar containing mixed ceramic sand and vitrified micro bead aggregates, we analyzed the law of influence of relevant factors on the dry bulk density, coefficient of thermal conductivity and compressive strength of mortar containing mixed ceramic sand and vitrified micro bead aggregates and provided basic data for further improvement of such thermal insulation mortar so as to promote the development and application of high performance thermal insulation materials.

Theoretical Study on Optimal Design of Thermal Performance of Aerated Concrete-Based Composite Thermal Insulation Wall

A wall of aerated concrete only can hardly meet the requirements for energy-saving architectural design. If both sides of the wall are provided with thermal insulation mortar to form a composite wall, the heat transfer performance of the wall will be significantly improved. In this Paper, we established an optimization model for the thermal economy of a thermal insulation composite wall according to heat transfer theory and in consideration of the depreciation and maintenance costs of the wall during use, and took the average heat transfer coefficient and index of thermal inertia of the wall as restricted conditions to calculate and analyze the economical thickness of the thermal insulation layer. We expect the optimization model be valuable reference in promoting the application of aerated concrete-based composite thermal insulation walls.

Intelligent Optimization of Material Mixing Ratio and Process Parameters for Aerated Concrete

To determine the optimal material mixing ratio of and process parameters for aerated concrete products, we adopted various combinations of material mixing ratio and process parameters to test aerated concrete according to the characteristics of local material and process equipment in this study, and obtained the strength and density of the aerated concrete. Using artificial neural network, we built a three-layer neural network model, which was trained based on the data of test samples to obtain a neural network based model system. Sample test showed that the predicted values of the model system fit the test values well; we utilized this system to analyze the material mixing ratio of and process parameters for aerated concrete products, and obtained their optimization results. The strength and density of the aerated concrete manufactured with the optimized parameters reached the desired targets. This method has some reference value for instructing the production of aerated concrete.

Study on the Strength and Deformation of Stirrup Confined Concrete in Cruciform Columns

In order to determine the strength and deformation characteristics of confined concrete under axial compression of cruciform columns, the test results have been obtained for reinforced concrete cruciform columns through axial compression experiment in the study. After analysis and research, the stress-strain curves of confined concrete have been established, the relational expression between the relatively increased value of the peak strain value of confined concrete in cruciform columns and the stirrup characteristic value was proposed, the descending section of the stress-strain curves of confined concrete was studied, and the variation relationship between the strain ductility coefficient of the confined concrete and the stirrup characteristic value was established. The study results will be provided as reference for the structural design and deformation calculation of cruciform columns.

Direct Displacement Based Seismic Design of High Rise Structures with Strengthened Stories (I) - Theory

High rise structures with strengthened stories are widely used nowadays. A rational seismic design procedure for this kind of structure is thus necessary. Based on mode theory and direct displacement based seismic design of multi-story buildings, this paper proposed a new direct displacement based seismic design procedure. In the proposed method, each mode of the high rise structure is equivalent to a single degree of freedom (SDOF) system. Seismic response of each mode is calculated and adds up to consider the contributions of higher modes. Considering the characteristic of strengthened stories, two stories above the strengthened stories are taken as the “key stories”, whose performance indicates the performance of the building. The proposed procedure is logical, simple and can serve for reference of actual design.

Microstructure and Microhardness of Copper Subjected to High Pressure Torsion

Experiments were conducted on copper subjected to High Pressure Torsion to investigate the evolution of microstructure and microhardness with shear strain, γ. Observations have been carried out in the longitudinal section for a proper demonstration of the structure morphology. An elongated dislocation cell/subgrain structure was observed at relatively low strain level. With increasing strain, the elongated subgrains transformed into elongated grains and finally into equiaxed grains with high angle grain boundaries. Measurements showed the hardness increases with increasing γ then tends to saturations when γ >5. The variation tendency of microhardness with γ can be simulated by Voce-type equation.

Study on Load-Bearing Characteristics of Double Layer Stirrup Confined Concrete Square Columns

Double layer stirrup confined concrete columns use two layers of stirrup, inside and outside, to constrain the core concrete. In this paper, in order to analyze the effect of double layer stirrups on the axial compression characteristics of concrete square columns, to determine the strength and deformation characteristics of double layer stirrup confined concrete square columns, and to establish the bearing capacity calculation equation for double layer stirrup confined concrete square columns, we designed 16 specimens to conduct axial compression test, from which a series of test data were obtained for double layer stirrup confined concrete square columns. We built the bearing capacity calculation equation for double layer stirrup confined concrete components on the basis of analysis and study and compared the calculated values with the test ones, and these data fit well; therefore, the study can provide reference for design and application of double layer stirrup confined concrete square columns.

Direct Displacement Based Seismic Design of High Rise Structures with Strengthened Stories (II) - Application

Based on mechanical characteristics of high rise structures with strengthened stories, the author performed direct displacement based seismic design on a high rise structure with 2 strengthened stories according to the direct displacement based seismic design principle. The performance levels are set to be “serviceability” under medium earthquake and “life safety” under major earthquake, respectively. The design procedures are with the following features: (1) Definition and selection of “key” stories are based on mechanical characteristics of high rise structures with strengthened stories; (2) Determination of mode number and calculation of horizontal earthquake action verified the availability of the design procedure; (3) some new ideas are proposed to improve the earthquake action calculation and structural performance control. The design procedure verified the effectiveness, feasibility and availability of the proposed direct displacement based seismic design method.

Influence of Grey System Parameter Identification Method on Prediction of Bearing Capacity of Piles

An unequal interval grey model GM (1,1) was established according to the variation characteristics of sequence data about the bearing capacity of overlength piles, and a difference equations was usually adopted to replace the grey differential equation for determining the system parameters of the model; however, great errors would occur when the model thus established was used to predict the bearing capacity of overlength piles, that is, the prediction results would be overestimated or underestimated. In order to improve the prediction accuracy of the model, we established an error objective function based on optimization theory in this study, employed the method of nonlinear least squares to identify the system parameters in the grey differential equation for the bearing capacity of overlength piles, and built an optimization-based grey optimization model. The model system built with optimization method was used to predict the bearing capacity of overlength piles, and the predicted values fit the test values well. In addition, the model system had a higher accuracy, compared with the grey difference model built with difference method; therefore, the model system built with optimization method could provide reference for prediction of the bearing capacity of overlength piles.