Reinforced concrete ribbed floors can be with beam slabs and slabs supported along the contour. Beam plates have the ratio of the long side to the short, and plates supported by the contour,.
In this course work discusses the principles of design of ribbed slabs with beam slabs.
In single-span buildings (up to 5-7 m wide) beams usually rest directly on the longitudinal walls. In multi-span buildings, ribbed slabs with beam plates are a structure consisting of main and secondary beams arranged in mutually perpendicular directions, and a plate monolithically connected to the beams as a whole. The secondary beams serve as supports plates, the main supports of secondary beams and walls and columns: - supports to the main beams.
When a uniformly distributed load and the absence of holes in the ceiling, it is recommended to assign an equal span of slab and beam. If the overlap has a significant concentrated load, the beam should be placed directly under this load.
Approximate distances in meters between secondary beams (or spans of a plate) and the minimum thickness of beam plates corresponding to them depending on loading are accepted on table. I. I. methodical instructions.
When choosing the distance between the secondary beams should strive to ensure that the thickness of the plate was minimal (for industrial buildings - at least 60 mm).
Recommended spans of overlapping elements and the sizes of their cross sections are given in table No. 1.
The installation of a few extra secondary beams has less impact on the total consumption of concrete on the floor than the increase in the thickness of the plate. Based on these considerations, the span of the plate is chosen, as a rule, within 1.7-2.7 m.
Currently, for multi-storey industrial buildings, standardized distances between columns (multiples of 3000 mm and equal to 6.9 and 12 m) and unified floor heights (multiples of 600 mm and equal to 3.6: 4.2; 4.8; 6.0 and 7.2 m) are accepted.
For methodological reasons, the length of the course design dimensions in the plan and the height of the floors are set, as a rule, non-standardized. Despite this. all dimensions should be subject to a single modular system based on the module 100 mm. to be able to more quickly static calculation using ready-made formulas and tables, overlap elements - it is recommended to assign equal spans or spans that do not differ by more than 20% for plates and more than 10% for beams. Usually extreme spans of a plate, minor and main beams I carry out less average. In this case, the bending moments and shear forces in the extreme spans are close in magnitude to the calculated forces in the middle spans.
The location of the main beams in the longitudinal or transverse directions are taken depending on the architectural, structural and technological requirements. At course design we are limited to the choice of the constructive scheme of overlapping on the basis of comparison of several options of overlapping on the expense of concrete.
Extreme center axis in industrial buildings are located along inner faces of the walls (zero binding) or with an offset inside the wall at a distance that is a multiple of 100 mm. In the present work adopted a zero reference.
In order to unify the height of the beams takes a multiple of 50 mm with dimensions up to.600 mi and a multiple of 100 mm for larger sizes.
Width of section of beams appoint 100.120, 150, 200, 220, 250 and further multiple of 50 mm.
Thus, the implementation of the project begins with the selection of a grid of columns, binding the outer walls to the extreme center axes and layout of structural schemes of the floor.
On the basis of all requirements and recommendations we apply:
- flight plate Lпл = 1700mm
- span of secondary beam LVB = 5800 mm
- span of the main balcony LGB = 6800 mm
- height and width of the main beam respectively HGB = 600 mm BGB = 300 mm
- height and width of the secondary beam respectively HBB = 400 mm BVB = 200 mm
- The thickness of a plate at standard loading of 9500 N / m2 is accepted equal HPL = 70 mm.
Source data:
- the building has dimensions in terms of 20, 4x40 m;
- floor height-4,8 m
- number of floors-8
- external walls-brick bearing
- normative payload on the overlap of 4kpa.
- In the present work we accept a binding of 200 mm.
While the outer mills are of brick the length of opiranie plate to the wall accept 120 mm, the secondary beam is 250 mm and the main beam - 380 mm