In order to alleviate the mechanics defects of PEC columns fabricated with thin-walled built-up sections as the biaxial unequal flexural stiffness and concentration of local buckling in flanges, new PEC columns fabricated with crimping thin-walled built-up sections were put forward. The transverse steel sheet links-spacing was taken as a primary design parameter, 4 specimens were designed and fabricated by full-scale. The tests of specimens were conducted with constant axial compression and low-cycle lateral reversed loading in the column strong axis, the local buckling in the flange of a crimping thin-walled built-up section and the crack forming and crushing of concrete were investigated, the load-displacement hysteretic curves were obtained. Base on the test results, the specimens’ relative performance were analyzed, including the load-carrying capacity, lateral stiffness, the seismic ductility and energy-dissipation capacity, the deformation pattern and failure mode. The conclusion showed that all specimens exhibited soundly deformation and energy-dissipation capacity resulted from the post-buckling performance of crimping flanges were utilized fully; the failure mode is primarily induced by the local buckling region growing in flanges of crimping thin-walled built-up sections with large-area crushing and spalling of concrete at the corner region of a column.
The smeared crack and plasticity damage models in general finite element program ABAQUS were detailed introduced, including the uniaxial stress-strain relationship, crack model, yield criterion, flow rules and hysteretic rules. Then comparison and analysis were made on the key factors of concrete constitutive models that have effect on the static mechanical behavior of structural members. The mechanical behavior of reinforced concrete members and steel-concrete composite members under monotonic and cyclic loadings were simulated using various concrete constitutive models, thusly the suitable model could be chosen when analyzing structural members according to the comparison results.
A steel-concrete composite fiber beam model is developed in this paper, which can divide the composite sections into fibers and the user-defined uniaxial hysteretic material constitutive model can be incorporated in subprogram UMAT provided by ABAQUS. The steel-concrete composite fiber beam model can be used to perform global elasto-plastic analysis of composite frames with full connections subjected to the combined action of gravity and cyclic lateral loads. The model is verified through a number of experiments showing that the composite fiber beam model developed by authors possesses good accuracy and wide applicability compared with the traditional finite element model. Although the fiber beam model neglects the slip between steel beam and concrete slab, the accuracy of global predictions of steel-concrete composite frames is not affected. So the developed steel-concrete fiber beam model possesses modelling simplicity and calculation efficiency, and is suitable for the seismic analysis of steel-concrete composite frames.
Shaking table tests were conducted for two three-story spacial slab-column structure models with weak stories. The El-Centro (NS) earthquake record was used to produce the excitation and its peak acceleration increased gradually until the pancake collapse of the weak story occurred. Horizontal accelerations were recorded for all stories before and after the occurring of pancake collapse. The vertical accelerations induced by the pancake collapse were also recorded for the floor slabs of the weak story and the story just below. Model M-2 had more weight than Model M-1. Test results show that: 1) with the increasing of the seismic damage degree, the models’ torsional responses increased; 2) the fundamental frequencies of Models M-1 and M-2 prior to the occurring of pancake collapse were only 8.9% and 4.7% lower than their initial values respectively, indicating that it may be impractical to use the change of frequency to predict structural collapses; 3) intensive fluctuation occurred in a very short time period for the horizontal acceleration of each story due to the pancake collapse; and the maximum absolute accelerations of Models M-1 and M-2 during the fluctuating period were in a range of 5g~10g, 5~20 times larger of M-1’s and 10~50 times larger of M-2’s maximum absolute accelerations respectively; 4) the vertical accelerations of the weak story floor slab and the floor slab just below the weak story induced by the pancake collapse were in a range of 30g～40g.
The failure of an underground rock structure is a synthetic process of energy dissipation and energy release. The releasable strain energy stored in rock structure and dissipated energy mainly depend on the unloading elastic modulus and Poisson’s ration of rocks in-situ and are related to the loading rate and load level. In this paper, static cyclic loading-unloading uniaxial compression tests under different loading rates are carried out. The variation laws of unloading elastic modulus and Poisson’s ratio, as well as the releasable strain energy and dissipated energy are obtained. The SHPB impact tests are also conducted and the total absorbed energy is measured. The testing analysis results can be used for the calculation of releasable strain energy, dissipated energy in a rock structure and for the prediction of rock structure failure.
The vibration-based damage identification method has been rapidly developed in the past few decades. The basic idea behind this technology is that the vibration characteristics (such as frequency, mode shape, modal damping, etc.) are functions of the physical properties of the structure (such as mass, damping and stiffness). Therefore, changes in the physical properties will cause detectable changes in the vibration characteristics. In this paper, the meaning, application status and classification of vibration-based damage identification methods in structural health monitoring are described. The structural damage detection methods based on dynamic characteristics and recognition algorithms are presented, and their advantages and shortcomings are analyzed. Finally, some topics which are worth studying further and the future trends for damage detection of civil engineering structures are proposed.