Papers by Author: Liang Zhang

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: Structures may enter into nonlinear stage under strong earthquake, so precise prediction of nonlinear behavior for building structure in earthquake is important which can assess the earthquake resistance safety of structures accurately. The exact numerical analysis model is required in actual engineering. In this paper the concept of nonlinear dynamic damage is introduced in steel reinforced concrete (SRC) composite structure, based on the theory of continuous damage mechanics. The damage variable is defined and computed by effective plastic strain of material, furthermore, concrete dynamic constitutive model is derived which considered plastic strain of material. Finally, the damage dynamic balance equation is established. Via comparison with test results of a three-story, two-bay SRC frame model which is tested on a shaking table, it is shown that the results of numerical analysis agree well with test results, indicating that the nonlinear dynamic balance equation is capable of describing the dynamic response of SRC frame structure with satisfactory accuracy. The research supplies theoretical basis for the seismic behavior analysis of SRC high-rise buildings.

Abstract: The cumulative damage of the reinforced concrete (RC) crane girders occurred by overload, fatigue and other reasons in service may deteriorate the safety of RC crane girders seriously, so it is necessary to analyze the damage mechanism and rationally reinforce them in good time. In this paper, RC crane girder strengthened with CFRP strips is taken as a target, and the mechanical performance degradation under fatigue load is studied. According to the basic theory of continuum damage mechanics, a damage variable is defined by flexural rigidity, and fatigue- cumulative damage model, which describes the process of damage and fracture, is established. The variation law of cumulative damage of RC crane girders strengthened with FRP strips under crane load is discussed, and the failure patterns such as concrete cracking, debonding between CFRP strips and concrete, yield of steel bars etc., are studied. The criterion which can be used to estimate the cumulative damage degree of strengthened RC crane girders is proposed. Finally, the evolution of the fatigue damage in the RC crane girders strengthened with CFRP strips is numerically simulated, and the results show that the proposed model can correctly describe the damage and failure process of strengthened RC crane girders. The research will provide a reference for the damage analysis and reinforcement of RC crane girders strengthened with CFRP strips.

Abstract: The shear behaviors of steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns are studied through the test on a number of SRHSHPC specimens with grade of concrete strength varied from C80 to C120 subjected to constant axial compression and cyclically varying horizontal load. Four influencing factors, namely, shear span ratio, axial compression ratio, stirrup ratio and concrete strength, are taken into consideration in the test, and strain gauges are respectively placed on steel web, stirrups as well as reinforcement bars to study the shear mechanism of SRHSHPC composite columns. According to test results, the shear failure patterns and shear mechanism of the specimens are discussed. By analyzing the contribution of the steel web, concrete, stirrups and reinforcement bars to the shear capacity, the shear mechanism of the SRHSHPC composite columns is figured out. Therefore, the influence of shear span ratio, axial compression ratio, stirrup ratios and concrete strength on shear behaviors of the SRHSHPC frame columns is clear. Finally, concrete truss model and principle of accumulation are applied to discuss the shear capacity and a calculation model for shear strength of the SRHSHPC composite columns is established. It is indicated that the shear behaviors of the SRHSHPC frame composite columns are excellent, and the calculated results of shear strength have good conformity with test results.

Abstract: Based on experimental investigation under low cyclic reversed loading, the seismic behaviors and seismic damage model for steel reinforced high strength and high performance concrete (SRHSHPC) composite frame columns are studied. Several existing seismic damage models are firstly presented and their characteristics are comparatively analyzed. From the test results of low cyclic reversed loading, the variation history of cumulative dissipated hysteretic energy of the SRHSHPC composite frame columns under different loading cycle levels is figured out, and the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the cumulative dissipated hysteretic energy is also discussed. The damage index of the SRHSHPC composite frame columns is compared according to the existing seismic damage models, and the seismic damage model adapted for the SRHSHPC composite frame columns is established. According to the variation history of the damage index under different loading cycle levels, the rule of damage development for the SRHSHPC composite frame columns is proposed. The influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the damage development is also discussed. The results indicate that the seismic behaviors of the SRHSHPC composite frame column are outstanding, and the seismic damage model could give a quantitative description for damaging process of the samples, which is reference for establishing more rational damage criteria for the SRHSHPC earthquake-resistant composite structure.

Abstract: Based on tests under low cyclic reversed horizontal loading, damage behaviors of steel reinforced high strength and high performance concrete (SRHSHPC) frame columns are analyzed. The strength attenuation that considered as damage variable is figured out, and the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the strength attenuation is discussed. The accumulative damage model, which can reveal the effect of cyclic loading and maximum deformation, is established for the SRHSHPC frame columns. The different phases of damage growth and their features for the SRHSHPC frame columns are analyzed, and the relation of damage and displacement is ascertained. Furthermore, the influence of axial compression ratio, shear span ratio, stirrup ratio and concrete strength on the damage development is also discussed. The results show that the damage model could give a rational description for damaging process of the SRHSHPC frame columns.

Abstract: Steel reinforced high strength and high performance concrete (SRHSHPC) specimens were experimented to study the mechanical behaviors between steel and concrete interface. In experiment, interfacial bond softening process was observed, which can be explained in terms of damage along the interface, leading to progressive reduction of shear transfer capability between steel and high strength and high performance concrete (HSHPC). In this paper, bond softening process along the interface is considered in the analysis of crack-induced debonding. Interfacial bond-slip mechanism between steel and HSHPC is studied in detail based on fracture mechanics. With the help of acoustic emissions technology, the crack propagation in the interlayer was observed, thus the interfacial crack propagation and fracture model is set up. Under the assumption that the interlayer is weak concrete compared with concrete matrix, the stress field as well as displacement field around the crack tip is deduced. The characteristics of interfacial fracture process are discussed and a model for interfacial fracture process zone is built up. With this model, the size of fracture process zone can be derived. At last, the influence of the fracture process zone on interfacial fracture toughness is determined using critical fracture toughness. All these may contribute to improvement of theory for SRHSHPC composite structure.

Abstract: Based on damage mechanics and failure model, a seismic damage model applying to steel reinforced high strength and high performance concrete frame joints is put forward, which takes deformation and cumulative damage into account. The damage performance of five tentative frame joints is compared and analyzed according to deformation and dissipated hysteretic energy under different loading levels, and the main influence factors on damage performance are established. The damage indexes of tentative frame joints are calculated, and the influence of strength grade of concrete and axial compression ratio on damage performance is discussed. The results indicate that the general damage is controlled by the damage of concrete in the earlier stage of loading, and by the damage of shape steel and stirrup in the later stage of loading; joints with lower axial compression ratio and lower concrete strength grade possess better hysteretic energy performance. Damage analysis provides an available means for the research of steel reinforced high strength and high performance concrete frame joints under seismic load. The damage model presented can be a reference for seismic damage analysis of the structure, prediction of earthquake damage in future, estimation of economic loss and repair after earthquake.

Abstract: The damage constitutive relationship is a key problem to nonlinear analysis of structural members. It is much more necessary to study systematically related damage constitutive relationship of steel reinforced concrete (SRC) members because of their peculiarity. Based on the experimental phenomena analysis and damage theory, the mesoscopic failure mechanism of concrete as well as the interface of shaped steel and concrete is analyzed. At the same time, their mesoscopic damage models and corresponding assumptions of the models are established by considering material failure characteristics. Subsequently, the mechanism of the models is analyzed, which indicates that they fit to simulate failure process of the materials. According to the models, the related damage constitutive relationship for SRC members is deduced by principle of energy and force balance. Combined with corresponding experimental study, it is shown that the constitutive relationship presented is reasonable and practicable, so it facilitates SRC member nonlinear analysis.