Diagrid Core-tube Structure Seismic Performance Based on Equivalent Stiffness Ratio of Inner and Outer Tubes

Chengqing Liu,Dibing Xu 대한토목학회 2023 KSCE Journal of Civil Engineering Vol.27 No.4

To study the relationship between the stiffness ratio of the inner and outer tube of the diagrid core-tube structure of high-rise buildings and the redistribution of the storey shear force, the structural ductility, overstrength factor and the seismic performance, a total of 12 kinds of diagrid core-tube structures of equivalent stiffness ratios were established at 71°, 77° and 80° diagonal angles. Based on the static pushover analysis method, combined with the principle of capacity spectrum and demand spectrum, the characteristics and laws of the position change of the weak layer, the redistribution of the storey shear force, the shear lag effect of the bottom compression flange and the overall ductility of the structure are analyzed under the action of the frequent earthquake (70 gal), fortification earthquake (200 gal), rare earthquake (400 gal), extremely rare earthquake (510 gal) and huge earthquake (620 gal). The results show that under different earthquake actions, there is an obvious redistribution of floor shear force in the diagrid core-tube structure, and the storey shear coefficient decreases with the increase of earthquake level and equivalent stiffness ratio. The diagonal angle is the main factor affecting the location of the weak floor and the shear lag effect. The shear lag effect of the structure increases with the increase of the seismic fortification level. The structural ductility with a diagonal angle of 77° is generally optimal. When the equivalent stiffness ratio is 0.64, the structural ductility reaches the optimal value of 1.46, which is 1.1 times that of 71° and 80° diagonal angles. In the structure with the same diagonal angle, the overstrength factor increases with the increase of the equivalent stiffness ratio.

Different distribution patterns of microorganisms between aquaculture pond sediment and water

Dai Lili,Liu Chengqing,Peng Liang,Song Chaofeng,Li Xiaoli,Tao Ling,Li Gu 한국미생물학회 2021 The journal of microbiology Vol.59 No.4

Aquatic microorganisms in the sediment and water column are closely related; however, their distribution patterns between these two habitats still remain largely unknown. In this study, we compared sediment and water microeukaryotic and bacterial microorganisms in aquaculture ponds from different areas in China, and analyzed the influencing environmental factors as well as the inter-taxa relationships. We found that bacteria were significantly more abundant than fungi in both sediment and water, and the bacterial richness and diversity in sediment were higher than in water in all the sampling areas, but no significant differences were found between the two habitats for microeukaryotes. Bacterial taxa could be clearly separated through cluster analysis between the sediment and water, while eukaryotic taxa at all classification levels could not. Spirochaetea, Deltaproteobacteria, Nitrospirae, Ignavibacteriae, Firmicutes, Chloroflexi, and Lentimicrobiaceae were more abundantly distributed in sediment, while Betaproteobacteria, Alphaproteobacter, Cyanobacteria, Roseiflexaceae, Dinghuibacter, Cryomorphaceae, and Actinobacteria were more abundant in water samples. For eukaryotes, only Cryptomonadales were found to be distributed differently between the two habitats. Microorganisms in sediment were mainly correlated with enzymes related to organic matter decomposition, while water temperature, pH, dissolved oxygen, and nutrient levels all showed significant correlation with the microbial communities in pond water. Intensive interspecific relationships were also found among eukaryotes and bacteria. Together, our results indicated that eukaryotic microorganisms are distributed less differently between sediment and water in aquaculture ponds compared to bacteria. This study provides valuable data for evaluating microbial distributions in aquatic environments, which may also be of practical use in aquaculture pond management.

Capacity Difference of Circular Hollow Section X-joints Under Brace Axial Compression and Tension

Bida Zhao,Chengqing Liu,Zeyang Yao,Yangzheng Cai 한국강구조학회 2020 International Journal of Steel Structures Vol.20 No.5

In the current regulations, there are two methods to describe the relationship between the two capacities of circular hollow section (CHS) X-joints under brace compression ( N uc ) and brace tension ( N ut ): N ut = N uc and N ut = fN uc ( f is a coeffi cient larger than 1.0). In order to study the diff erence between N uc and N ut of the X-joints, two experimental tests (monotonic compression load and cyclic axial load) and fi nite element (FE) analysis are performed to study the diff erence between N uc and N ut . Test results show that the ultimate capacity is close to the resistance load corresponding to the connection deformation of 3% of chord diameter (limit deformation criterion). Both two specimens showed good deformability and ductility. The fi nal failure modes are chord wall buckling and chord wall tearing for the specimens under monotonic compression load and cyclic axial load, respectively. Test and FE results indicate that N ut is signifi cantly larger than the corresponding N uc , and the ratio N ut / N uc increases as the chord radius-to-thickness ratio γ increases. It is also found that the ratio N ut / N uc increases as the brace-to-chord diameter ratio β increases, especially β larger than 0.8. Based on test and FE data, a new equation for the ratio N ut / N uc is proposed to overcome the defect of the current specifi cations that cannot consider the infl uence of β . The equation is proved to be reasonable by tests and FE results.

Semi-rigidity Connection Model for Unstiff ened CHS X-type Joints Subjected Out-of-plane Bending

Bida Zhao,Chengqing Liu,Zhengxi Yan,Xin Chen,Yangzheng Cai 한국강구조학회 2019 International Journal of Steel Structures Vol.19 No.3

Mechanical performance of unstiff ened circular hollow section (CHS) multi-planar X-joints subjected two diff erent directions (sagging and hogging) of out-of-plane bending moment (OPBM) was analyzed. A seven-parameter exponential function model, which describing semi-rigidity behavior (moment-rotation curves) of the X-joints subjected sagging and hogging OPBM, was proposed, and then the method to obtain the values of each parameters in the seven- parameter model was also proposed. Based on the results of FE parametric analysis, formulas for parameters in the seven-parameter model were established combined with multiple nonlinear regression analysis. FE and test results were used to verifi ed the seven-parameter model. The results indicated that: the seven-parameter model can well refl ect the semi-rigidity behavior of CHS multi-planar X-joints subjected to OPBM.

Impact response of ultra-high performance fiber-reinforced concrete filled square double-skin steel tubular columns

Jie Li,Weiqiang Wang,Chengqing Wu,Zhongxian Liu,Pengtao Wu 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.42 No.3

This paper studies the lateral impact behavior of ultra-high performance fiber-reinforced concrete (UHPFRC) filled double-skin steel tubular (UHPFRCFDST) columns. The impact force, midspan deflection, and strain histories were recorded. Based on the test results, the influences of drop height, axial load, concrete type, and steel tube wall thickness on the impact resistance of UHPFRCFDST members were analyzed. LS-DYNA software was used to establish a finite element (FE) model of UHPFRC filled steel tubular members. The failure modes and histories of impact force and midspan deflection of specimens were obtained. The simulation results were compared to the test results, which demonstrated the accuracy of the finite element analysis (FEA) model. Finally, the effects of the steel tube thickness, impact energy, type of concrete and impact indenter shape, and void ratio on the lateral impact performances of the UHPFRCFDST columns were analyzed.