Papers by Author: Lei Li

Abstract: This paper investigates modeling approaches of circular concrete-filled steel tube (CFT) column under cyclic load based on flexibility and fiber model. The effects of model parameters on modeling results is discussed, including constitutive relationship of materials, division of the fiber section, and the number of integration points. The results show that the material constitutive relationships of concrete and steel are prime important to the accuracy of the computational results. Three to five integration points for one CFT column in the flexibility-based analysis can achieve the desired accuracy and computational efficiency. The computational result is not sensitive to the number of sectional fibers. However, the desired accuracy can not be obtained if the number of the sectional fiber is not enough.

Abstract: The optimization methodology of the steel-concrete composite beam was proposed in this paper. The objective function is the cost of the composite beams, and the design variables are the geometry parameters, including height and width of the concrete deck, as well as thickness of the steel flange and web. The constraint conditions are main requirements stated in Chinese code for the design of composite beam, reasonable calculating theories and indispensable constructions, as well as some mature and consistent conclusions confirmed by experimental studies. Stiffness reduction coefficient is used to consider the effect of bond-slip effect between concrete and steel when calculating the beam deformation. The optimization for composite beam under uniform loads is given as a demonstration example finally. The methodology proposed in this paper should be useful for obtaining the solution of this kind of optimization problem.

Abstract: Based on the experiments of 4 SRHSC (steel reinforced high strength concrete) column specimens, which were different in concrete strength, axial compression ratio and spacing of hoop reinforcement, this paper investigates the seismic behavior and flexural strength of SRHSC columns under cyclic lateral loading which is controlled by the displacement. According to the date and phenomenon of experiment, adopting existed theory and foreign codes for composite columns, the failure mode, lateral load-deflection relationship, strength and stiffness deterioration, ductility capacity and energy dissipation capacity of SRHSC columns is analyzed.

Abstract: According to the thought of engineering optimization and the theory of composite structure design, the minimum of the project cost and the maximum of the diagonal shear capacity are taken as the optimization objectives whose importance can be adjusted by weighting factors and the linear weighted method is used to establish evaluation function which changes multi-objective into single-objective in optimization. Taking the various constraints into consideration and choosing the sensitive design variables, the mathematical model of the multi-objective optimization design for steel reinforced high-strength concrete beams is provided. Based on the optimization thought of the Complex Method, the nonlinear optimization problems are solved by MATLAB program.

Abstract: The modeling methodology is investigated for steel reinforced high performance concrete (SRHPC) in this paper. According to the mechanical characteristics of the SRHPC members, the structural section can be divided into different zones, and the element suitable for each zone is determined. Some discussion is made for how to control finite element gridding as well as applied load. Hysteretic loops of the computation results and test results agree well with each other, indicating the accuracy and applicability of the methodology. This research may be helpful for the nonlinear finite analysis of the SRHPC frame structure.

Abstract: In this paper, the damage performance of 13 SRHSHPC frame columns are tested and analyzed under low cycle loading. The effect of concrete strength, axial compression ratio and shear span ratio on the damage of SRHSHPC frame columns is discussed, and then the experimental result is quantified with damage index. Based on existing seismic damage models, a new seismic damage model is put forward for SRHSHPC frame columns by a nonlinear combination of deformation and accumulative dissipation.

Abstract: According to experiment of four steel reinforced high strength and high performance concrete(SRHSHPC) columns with different eccentricity, this paper establishes four equally parameter numerical models by finite element program ANSYS. The failure mechanism, failure mode and mechanical behaviors of the SRHSHPC columns with large and small eccentricity can be revealed by comparing the numerical simulation results with the corresponding experimental results. And the approximate plane-section assumption in SRHSHPC eccentric columns is verified by the study of the relationship between load and strain. It is shown that when constitutive models and failure criteria of SRHSHPC and steel are in precise case, the calculation results agree well with the corresponding experimental results.

Abstract: The frame structure designed with the existing design code in zones of high earthquake intensity doesn’t satisfy with the expectation of strong column–weak beam. Therefore, a new optimal approach based on failure modes with the ability to limit the cost and the damage is proposed. In the process of optimization design, all the stories of a building with the same interstory drift is defined to obtiain the minor damage, while the damage values of beams and columns are difined to obtain the except failure modes. At last a six-story steel reinforced concrete frame structure is designed to verify the method developed inhere. It is concluded that the method can supply an effective way to reduce both the damage and the cost of steel reinforced concrete frame structure, and can obtain the except failure modes.

Abstract: The seismic performance and seismic damage model for steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns subjected to constant axial load and cyclically variety flexural loading was investigated experimentally. The main influencing parameters, including shear span ratio, axial compression ratio, stirrup ratio and concrete strength, on the seismic performance and seismic damage of the SRHSHPC frame columns is studied. From the test results, the failure mechanism is analyzed and damage quantization criterion is obtained. Several existing seismic damage models are comparatively analyzed. And then, the variation history of accumulated hysteretic energy of the specimens under different loading cycle indexes is figured out, and influence of different test parameters on it is also discussed. Finally, the damage index of the SRHSHPC columns is compared to the existing seismic damage models, and the double variables seismic damage model adapted for the SRHSHPC structure is established by statistical regression theory. The rule of damage evolvement for the specimens is proposed employing variation history of the damage index under different loading cycle indexes. The analytical results indicate that the seismic performance of the SRHSHPC composite column is good, and the double variables damage model could give a quantitative description for damaging process of the samples, which is a reference for seismic damage design of the SRHSHPC structure.

Abstract: A stochastic damage constitutive model is proposed based on Kelvin spring-damper model and Li Jie spring stochastic damage model. The model is made up by microscopic spring-slipper element. The slipper, parallel connected with spring, is introduced to consider the plasticity effect of concrete. Damage failure process of concrete subjected uniaxial tension is divided into spring broken state and slipper broken state to describe the elastic stage and plastic stage of damage respectively. In the light of energy conservation during the process of damage failure, stochastic damage constitutive equation of concrete material subjected to uniaxial tension stress is derived. Comparisons between test results and theoretical calculation results verify that the established constitutive damage equations are accord with the experimental situation, and the experimental data are observed undulated with theoretical curve in the range of variance. The research results can apply in the actual engineering.