| Aiming at three complex tall buildings mentioned in "Technical specification forconcrete structures of tall building", tall buildings with transfer story, multi-towerand large podium structure, the staggered-floor structure, some key problems in thestructural design of these three kinds of complex tall buildings are analyzed in thispaper using engineering examples. Some conclusions are obtained as follow:1. Tall building with transfer story is systematically analyzed using engineeringexample. The conclusions are obtained as follow. (1) The forces of members indiagonal brace truss with vertical member are close and the sections are uniform andeconomical. The forces of members in diagonal brace truss without vertical memberare different and maximum difference can reach 40%. (2) In the separate forceanalysis of transfer truss, the difference between the result with one frame floor andthe result with more than three frame floors is 10%. The difference of the result withmore than three frame floors is about 2%. It can satisfy the demand of engineering. (3)The forces of transfer truss are remarkably influenced by the stiffness change ofbilateral columns. The forces of columns increase when the stiffness are increasedand the maximum amplitude of moment can reach 86%. The forces of chords anddiagonal braces decrease. The maximum decrease happens in lower chords and it canreach 22%. (4) In the outside transfer truss under difference in temperature resultedfrom day to night, the temperature stress of vertical members compared to the deadload stress can reach 8.3%. To some horizontal members, this proportion can be18.9%.2. A multi-tower and large podium structure is analyzed and the conclusions areobtained as follow. (1) It can be considered as normal tall buildings when the top slabof large podium can be used as position of fixity. The tower has little influence to thelarge podium which is far from it. The multi-tower and large podium structure mustbe analyzed by two kinds of 3D software using different mechanics models when thetop slab of large podium can't be used as position of fixity. The structure system program should be adjusted by the control index of complex tall buildings. The finiteanalysis should be applied to key positions of the structure. (2) The result of modalanalysis response spectrum(CQC) is as 2.0～3.07 times as the average result of severaltime history curves. The result is prone to safety.3. A staggered -floor structure is analyzed by ETABS and SATWE finite elementsoftware. The differences between mechanics models and dynamic properties areanalyzed. The conclusion shows that the stiffness of ETABS model is remarkablylarger than the stiffness of SATWE model.4. The Pushover analysis is applied to a staggered -floor frame structure and anormal frame structure. The results under 7, 8, 9 degree of small and rare earthquakeare compared. Comparing the force-displacement curves of two structures, the slopeof the staggered -floor frame structure is a little larger than the slope of the normalframe structure both in the elastic stage and in the elastic-plastic stage. In thedescendent stage of two curves, the curve of the staggered -floor frame structuredescends earlier than the curve of the normal frame structure. It indicates that thestaggered -floor frame structure damages earlier than the normal frame structure. |
