Due to the transformation of structural members caused by differences in service functions and structural systems between the upper and lower parts of rail transit upper cover structure, discontinuity of vertical members, uneven mass distribution and abrupt change in lateral stiffness between the upper and lower parts are inevitable, making it difficult to meet the limit requirements for lateral stiffness ratio specified in codes. The calculation methods and regulation for the lateral stiffness ratio of upper cover structure in national codes and various upper cover structure design standards were summarized. Taking a typical seismic-resisting unit of an electric multiple units depot as the research object, the influences of the second-floor column section below the cover on the lateral stiffness ratio of the stories above and below the transfer story were analyzed. The effects of second-floor height, first-floor column section size and steel ratio of first-floor column section on the lateral stiffness ratio between the first and second floors were investigated, and a comparison was made between the lateral stiffness ratios of the first and second floors below the cover calculated by lateral stiffness ratio γ1 and equivalent shear stiffness ratio γe1. Furthermore, discussions were carried out on the limit values of the lateral stiffness ratio between the first and second floors below the cover and the rational design of upper cover structure. The results show that the calculation methods of lateral stiffness ratio γe1 and equivalent shear stiffness ratio γe2 for the stories above and below the transfer story should consider both the story number and height where the transfer story is located. Appropriate calculation formulas should be adopted for the lateral stiffness ratio of upper cover structure. When the lateral stiffness ratio γ1 is less than 0.5, stricter limit requirements than those specified in codes should be imposed on interlayer displacement angle and axial compression ratio. Regardless of the stiffness ratio calculation method adopted, the structure should have a reasonable yield mechanism, and its seismic performance should be evaluated through elasto-plastic analysis under rarely occurred earthquakes.
Beijing CBD Sunshine Insurance Financial Center tower adopts a concrete filled steel tube collum-H shaped steel beam frame-concrete core tube structural system, the building height is 205 meters. As the tower′s exterior profile gradually tapers upward, the square plan at the ground floor transitions to an oval plan at the top. The tower′s core tube plan is oriented at a 45° oblique angle relative to the building′s orthogonal main axes. The ground-floor lobby spans four stories in height, and the sky lobby spans three stories. There were multiple irregular items such as height exceeding limit, discontinuous floor slabs, irregular torsion, and sudden changes in local floor lateral stiffness, cross-story columns, inclined columns, transition beams, etc. , making it an ultra-limit high-rise building with both height and regularity exceeding limit. By setting reasonable seismic performance targets for the structure and components, comprehensive calculation and analysis were performed, and corresponding strengthening measures shall be adopted, the structure was ensured to have good seismic resistance performance and safety. Combining with the refuge floor of the building, two outrigger trusses were set along the short side direction of the core tube on the 15th and 30th floors, and ring trusses were set along the periphery of the frame to improve the lateral stiffness of the structure. In response to the layout requirements of the ground floor lobby and the aerial lobby crossing stories, the local floor above was supported by hanging columns and columns on the beam, and the calculation length coefficient of the crossing story columns was determined through overall structural buckling analysis. A narrow inner ring plate + tension reinforced steel column-beam joints of large diameter concrete filled steel tubular was proposed, which directly transmits force, and saves steel. Reinforced concrete beams were connected to concrete-filled steel tube columns through steel cow legs, using a combination of welding and steel bar connectors, which can effectively reduce the eccentric stress caused by single-sided connection of cow leg flanges.
In low-headroom foundation pit support engineering, traditional reinforced concrete bored piles are associated with issues such as low construction efficiency and difficulties in ensuring welding precision. To address these challenges, steel strand concrete (SSC) support piles which leverage the toughness and flexural properties of steel strands were proposed. To investigate the flexural behavior of SSC support piles, four-point bending tests, finite element simulations and theoretical analyses were conducted on both SSC support piles and connector-type SSC support piles. The results indicate that during the flexural failure of SSC support piles, crushing occurs in the concrete within the compression zone, while the steel strands below the neutral axis reach their yield strength. For connector-type SSC support piles, the compressive capacity of the concrete and the tensile capacity of the steel strands are not fully utilized, resulting in a bending capacity slightly lower than that of SSC support piles. The steel strand reinforcement ratio, steel strand strength and concrete strength all significantly influence the flexural behavior of the pile, with the steel strand reinforcement ratio exerting the most substantial impact. Theoretical analysis based on layered model can accurately determine the flexural bearing capacity of SSC support piles.
A novel steel grid-concrete composite shell structure integrating the advantages of thin concrete shells and steel grid shells was adopted for the roof of Bajiaowan International Sports Center swimming pool. A novel steel-concrete connection configuration combining cast-in-place concrete construction and shotcrete construction with the concrete shell segment embedded inside the lower chord grids of truss steel grids was proposed for the aforementioned novel composite shell structure. Refined finite element solid models were established, and investigations on the compressive performance of lower chord-concrete connections as well as the influence laws of relevant parameters were implemented. Analyses on the compressive performance of lower chords considering the influence of full-length welding of horizontal support plates were further conducted. The results show that the transmission path of the lower chord-concrete connections is clear, and reliable stiffness and axial bearing capacity are exhibited by such connections. Welding deformations of lower chords of truss steel grids are controllable, and the influence of welding on the axial compressive performance of chords can be neglected. The proposed steel-concrete connection technology enables the anticipated architectural effects and structural performance of composite shell roofs to be achieved while construction convenience is simultaneously guaranteed.
To meet the construction quality control requirements for large-format polymethyl methacrylate unit panels and their supporting structural systems in Shenzhen Bay Mixc-The Wave, research on fabrication and on-site installation accuracy monitoring was conducted based on three-dimensional scanning technology. High-precision three-dimensional scanning and large-scene laser scanning were employed to acquire measured point cloud models of the components. Combined with control-point constraints, point-cloud registration, feature extraction and deviation quantification, the fabrication accuracy of the acrylic glass unit panels and their associated supporting components was evaluated at the factory stage, while the planar positional and orientation deviations of the unit panels were analyzed at the on-site installation stage. The results indicate that the overall geometry of unit panels at the fabrication stage is generally consistent with the design model, and deviations in width and thickness satisfy fabrication quality requirements, while localized length deviations exit only in certain end regions. At the on-site installation stage, the centers of the overall circular arcs of the unit panels substantially coincides with the designed waterscape center. The average torsional angle deviations of the upper-layer and lower-layer unit panels are 0.261° and 0.452°, respectively, among which the lower-layer No. 1 panel exhibits a torsional angle deviation of approximately 1.707°. The average circumferential deviation of the lower-layer unit panels is approximately 22mm, which should be prioritized for subsequent installation verification and adjustment. The research demonstrates that three-dimensional scanning technology, integrated with point cloud processing and deviation quantification methods, can be effectively applied to construction process monitoring and quality control of complex polymethyl methacrylate waterscape projects, and provides technical reference for production inspection, installation accuracy evaluation, and on-site adjustment of similar transparent special-shaped components.
