How To Calculate U-Boot Slab

 

 

U-Boot slab calculation system

 Advantages of using U-boot slab (comparing (comparing U-boot slab to a trad traditional itional flat slab without drop beams or drop panels):

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concrete saving

reduced own weight reinforcement saving high bending stiffness

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high torsion stiffnes

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low inertia losing low deflections

 

 

 How to calculate a U-boot two-ways voided flat slab

1- Having project details (span between columns, co lumns, overloads and fireproofing requirement), determine thickness of U-boot slab and geometrical characteristics of the section, as the related table in U-boot brochure. For example:

Upper Reinforcement Lightening u-boo tbeto n

Lattice

       6

       4        2

       7

14

52

14

Lower Reinfor Reinforcement cement

2- For instance, let s consider the section: ’

t=14 cm 6 cm

H-beam section h

U-boot

h=37 cm

=24 cm

7 cm b=66 cm

Using Autocad software, draw the section and convert it to a region. Then click instruments and  properties mass-region. The principal moment moment (I) referred to the mass centre will be used to calculate the virtual height of U-boot slab. It could be also calculated in a different way: I=(b*h^3)/12-(hU-boot*(b-t)^3)/12 where: 52 is the U-boot lenght 24 is the U-boot height

 

 

3- To calculate virtual height of U-Boot slab, s lab, use the formula reported below: I=b*hvirtual^3/12 So, to evaluate hvirtual: hvirtual=((I*12)/b)^(1/3)

h

virtual

b=66 cm

4- Using a software like SAP 2000 or STRAUSS, or any other F.E.M. software, realize a slab sla b with shell elements. The shell elements thickness t hickness has to be the virtual or real section sect ion thickness reduced according to real U-boot section inertia. inert ia. Own weight of slab has to be reduced according acco rding to the real weight of slab (including air volume of U-boots). 5- The software analyzes the structure str ucture and shows as output the stresses, visualized through t hrough a coloured values scale.

6- Verify that reinforcement supports output stresses in the real I-beam section.