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2nd example


Materials
To be continued >
Introduction

2nd example

project < Β_422-2>

The structure of this example derives from 1st example by removing the two middle beams. The aspect ratio for both slabs is ε=Ly/Lx=12.0/4.0=3.0> 2.0, therefore they can be treated and analysed as two continuous one-way slabs.

 

 

Slab analysis using hand methods

For 1.00 m wide slab strip:

Self-weight: go=0.15m×1.00m×25.00 kN/m3= 3.75 kN/m, Covering load: ge=1.00 kN/m (given),

Total dead load: g=4.75 kN/m, Live load: q=5.00 kN/m (given).

Thus, the total load is p=γg×g+γq×q=1.35×4.75+1.50×5.00=13.9 kN/m. The bending moment at the support is calculated using table b3, line 1.

 

M1=-p×L2/8=-13.9×4.02/8=-27.8 kNm,

 

V01=p×L/2+M1/L=13.9×4.0/2-27.8/4.0= =20.8 kN

V10= p×L/2-M1/L=13.9×4.0/2+27.8/4.0= =34.8 kN

 

maxM01=V012/(2×p)=20.82/(2×13.9)= =15.6 kNm

 

According to §4.5.2, from expression (3)

C1=(-13.9×4.03/24+20.8×4.02/6)m2= =18.4 kN×m2

Expression (4)

(13.9/6)z3-(20.8/2)z2-0+18.4=0

2.317z3-10.4z2+18.4=0 zmax=1.68 m

(2) y(z)=1/9.225×[(13.9/24)×1.684-(20.8/6)×1.683+0×1.682+18.4×1,68)] y(1.68)=2.07 mm

 

Slab analysis using software: The actual structure in 3D

Before analysing, set these parameters, as in 1st example: Tab Meshing: “Overall size” = 0.10 m, “Perimeter size” = 0.05 m, Tab Modules: “SLABS” = ON, Tab Loads: “Adverse Slabs” = ΟΝ.

The deformation of slabs in 3D

For most of the region towards direction y, the slab is curved only along direction x.

Shear forces from ‘Slab Results’

to the respective values of the one-way slabs, calculated previously.

Also, shears [Vy] extend in an area near the supports with maximum value of 15.0 kN.


 

The 3D distribution of shear forces [Vx]

In the largest part, it matches the corresponding distribution of one-way slabs.

The 3D distribution of shear forces [Vy]

Shear forces [Vy] extended only to the regions of end supports.

 

The bending moments from ‘Slabs Results’

Notice that in the middle cross-section, the moments [Mx] 15.5 and -27.4 kNm, are equal to the values of the one-way slabs calculated previously.

On the other hand, moments [My] do exist, 3.6 kNm, but they are insignificant.


The 3D distribution of bending moments [Mx]

Along most of the region, it resembles the corresponding distribution of one-way slabs.

The 3D distribution of bending moments [My]

Bending moments [My] are small and extended only in the regions of end supports.

 

Deflection from ‘Slab Results’

Notice that in the middle cross-section, the deflection is 2.10 mm, that is equal to the respective deflection of the one-way slabs calculated previously.