Empirical coefficient method of bending moment empirical calculation method at the moment when numerical calculation is developed, the empirical coefficient method still has strong vitality.
In principle, the size of column cap needs to be calculated and determined to meet the punching shear resistance of slab (including punching shear at variable order) without excessive reinforcement.
There are mainly five types of column caps for beamless floor: a) column caps are generally used in the case of small span and small load.
The analysis of beamless floor below is also mainly based on this form of column cap.
2 / / bending calculation theory of beamless floor.
At present, in Shanghai, this structural system is adopted for Wujiaochang chuangzhihui (Fig.
For the calculation theory of beamless floor, the internal force calculation is divided into bending calculation and punching calculation.
In addition to properly improving the punching shear capacity of the plate, it mainly improves the bending capacity of the plate and reduces the amount of negative bending moment reinforcement of the plate; d) Broken line column cap, with small span but large load, which needs to greatly improve the punching shear capacity of the plate; e) The span and load of composite column cap and heavy column cap are large.
After World War II, the beamless floor structure system began to be widely used.
Figure 1 1933 laochangfang in Hongkou District (slaughtering yard of the former Ministry of Industry Bureau) Figure 2 Wujiaochang chuangzhihui in Yangpu District Figure 3 underground parking garage of Tongji University Figure 4 underground parking garage of CapitaLand xinfengyuan in view of the fact that there are many teaching materials and reference materials for the design and calculation method of beamless floor, the author will give a brief introduction in serial 1, mainly focusing on the easy missing calculation Miscalculation will be discussed and shared.
3), CapitaLand xinfengyuan two-story underground garage (Fig.
For the extremely irregular part, it is suggested to supplement the computer calculation or use the large span for envelope design..
For intermediate load, the economic and reasonable size is 0.35L.
1.
2), Tongji University underground garage (Fig.
The main function of column caps of beamless floor is to strengthen the junction of columns and plates with large stress, improve their punching shear (shear) resistance, and also improve the calculation height H0 and bending resistance.
Click on “Star”, the public official account will appear yellow five pointed star (Android and iOS user operation same) beam floor design and construction points (1) node form and bending calculation theory / Ceng Zhaojie, Du Xu, Bian Haitao about 1925 before the large number of no Liang Lougai structural system appeared in Guangdong, Shanghai and other coastal areas.
The beamless floor of underground garage is mainly composed of roof beamless floor and floor beamless floor.
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Considering the uneven shear stress around punching, punching is considered as an adverse working condition in practice and specifications, so the one-way shear resistance is not used as a control working condition in practice and calculation.) 1.
The moment coefficient method can generally be used to design directly or check the reliability of the calculation results.
From the late 1960s to the early 1970s, scholars conducted in-depth experimental research on the punching shear resistance of slabs.
4), etc.
In particular, there are a large number of warehouses and offices in Hongkou area of Shanghai, which adopt this structural system, such as the old building complex of shuimen of the World Expo, and the slaughtering yard of the former Shanghai Ministry of Industry Bureau of Hongkou (Figure 1), which was built in 1933.
Punching calculation of column edge and variable order is often carried out in beamless floor and used as the control condition.
Scholars had done a lot of experimental research on this floor in the late 1960s.
At present, it has become the old workshop of the creative park.
2.
The form of column cap of beamless floor a) no column cap b) conical column cap C) supporting plate column cap d) broken line column cap E) composite column cap.
Figure 6 schematic diagram of punching of beamless floor the size of column cap is mainly determined by punching.
Figure 5 for the classification of column caps of beamless floor, please refer to the classification of column caps of beamless floor.
Generally, it is based on the standard span.
For the underground garage of high-rise buildings, considering the size of load and convenient construction, the form of composite heavy-duty column cap is commonly used, that is, the conical column cap with supporting plate.
Even if not, the punching at the variable step of the supporting plate plays a main control role.
The heavy column cap C is the calculated width of the column cap (effective width), that is, the width of the rigid body of the column cap, which is generally 0.2L ~ 0.3L, and the reasonable value is 0.22l (L is the column grid size in the corresponding direction); H is the thickness of beamless floor slab; H1 is the thickness of the supporting plate, generally taken as half of the thickness of H; H2 is the thickness of conical column cap; B is the width of the supporting plate, ≥ 0.35L.
All these results are finally reflected in the specifications of aci 77 of the American Concrete society.
(Note: the one-way shear resistance is called shear resistance, and the shear resistance with closed surrounding area is called punching.
Generally, when the plate thickness of the beamless floor and the size of the supporting plate and the cone part of the abutment meet the above structural requirements, the punching checking calculation requirements will be met in most cases.
Empirical formula can fundamentally reveal the basic relationship of structural stress, and plays a great role in the grasp of structural design.
1 / / column cap form and punching shear resistance calculation of beamless floor.
As shown in Figure 6, punching checking calculation includes two aspects: 1) punching checking calculation of abutment cone part, that is, punching checking calculation of abutment cone pair (supporting plate + top plate); 2) Punching and cutting checking calculation of the supporting plate, that is, punching and cutting checking calculation of the supporting plate at the variable order of the roof.
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It is necessary to greatly improve the punching shear energy, strengthen the bending capacity of the slab and reduce the amount of negative moment reinforcement.
The specific structure is usually divided into column cap structure and reinforcement structure.
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The bending and punching resistance is easy to meet, beautiful, but the economy is poor; b) Conical column cap is mainly suitable for small span and small load, so it is necessary to properly improve the punching capacity of the plate; c) The supporting plate column cap is mainly suitable for small load and certain span.
Because the shear capacity of general floor is relatively strong, it can be met in most cases.
