BUILDING STRCTURES I
S.2. Load transfer
Mgr inż. arch. Joanna Wojtas
Gdansk University of Technology
Faculty of Architecture
Structural slab systems (one-way slabs)
A. Beamless floor (One-way slab)
• Slab supported alond two opposite sides, on walls.
• Limited span of slab: Lmax=5m.
• Thickness depends on span.
B. Rib-and-slab floor
A.
B.
• Slab supported on ribs. Ribs supported on walls.
• Limited span of floor: Lmax=7,5m.
• Thickness of slab depends on spacing between ribs
(max 6cm).
• Max. Spacing between ribs 1,20m.
C. Ribbed slab
• Slab supported on ribs. Ribs supported on walls.
• Limited span of floor: Lmax=7,5m.
• Span of slab 1,50÷3,50m = spacing between ribs.
C.
D.
D. Floor: slab-rib-girder
• Slab supported on ribs, ribs on girders, girders on
walls (or columns).
• Limited span of floor: Lmax=7,5m.
• Span of slab 1,50÷3,50m = spacing between ribs.
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
Beam- slab floor: cross-sectional dimensions
h
hż
bp
B. Rib (secondary beam)
1 - slab
2 i 3 – inter and extrenal rib
4 i 5 – inter and extrenal girder
6 i 7 – inter and extrenal column
A. Slab
Leff = A
1
1
÷ ) Leff
35 25
• The thickness of two-way spanning slab:
h=
1
( Lx + Ly )
90 ÷ 75
Leff = B
• Span of rib limited: 4- 7,5m;
• The thickness of one-way spanning slab:
h=(
hp
1 1
• Height of cross-section: hż = ( ÷ ) L (min 25cm)
18 15
1
• Wight of cross-section: bż = ( ÷ 1 )hż (15, 18, 20cm)
2 2,5
C. Girder (major beam)
Leff = C
• Span of girder limited: 5- 7,5m;
1 1
• Height of cross-section: hp = ( ÷ ) L (min 25cm)
12 10
• Widht of cross-section: bp = ( 1 ÷ 1 )hp (15, 18, 20cm)
2 2,5
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
Elementy stropu – wymiary przekrojów
Example 1.
Adjust the initial dimentions of cross-section the
reinforced concrete elements of the floors shown below.
A. Beamless floor
• Slab (Leff=500cm): h= 500/35÷500/25=14,3÷20cm
assumed: h = 20 cm (simple beam → significant deflection)
B i C. Ribbed slab
• Slab (Leff = 120cm):
h= 120/35÷120/25=3,4÷4,8cm
assumed: h =4cm (thickness of concrete overlay or as a
prefabricated slab )
• Slab (Leff = 250cm):
h= 250/35÷250/25=7,1÷10cm
assumed: h =8cm (multi-span slab)
A.
B.
• Rib (Leff = 750cm):
h= 750/18÷750/15=41,7÷50cm
b=(0,35÷0,5)·h=17,5÷25cm
assumed : h = 50 cm, b = 25 cm
D. Floor: slab-rib-girder
• Slab (Leff = 150cm):
h= 150/35÷150/25=4,3÷6,0cm
assumed: h =6cm (min. thickness of slab made in building place)
• Rib (Leff = 500cm):
h= 500/18÷500/15=27,8÷33,3cm
b=(0,35÷0,5)·h=10,5÷15cm
assumed: h = 30 cm, b = 18 cm
C.
D.
• Girder (Leff = 750cm): h=750/12÷750/10=62,5÷75,0cm
b=(0,35÷0,5)·h=26,2÷37,5cm
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
assumed: h = 70 cm, b = 35 cm
Building process
Floor performed on formwork on building place
deskowaniu tradycyjnym
Floor with prefabricated slabs
Composite floor, Filigran type
Prefabricated structure of building
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
Floor elements – load schemes
A. Beamless slab
Example 2.
Determine the load on the support elements of floor (walls),
assuming all structure elements in the schema in simple-span
beam . Dead load of claddind floor g1=5 kN/m2, changing load
p=7,5 kN/m2. Should take into account the weight of own
structural elements of the floor.
Slab band, width b=1m
• Dead weight of slab with thickness h = 20 cm
g2 = 0,20x25x1,1 = 5,5 kN/m2
• Dead load:
g = g1+ g2 = 5,5+5,0 =
10,5 kN/m2
• Changing load:
p = 7,5 kN/m2
• Total load:
q = 18,0 kN/m2
Slab band:
It’s a band of slab with width b=1,0m. The loadings are:
A.
• Dead load:
g = 10,5 x 1,0 = 10,5 kN/m
• Changing load:
p = 7,5 x 1,0 = 7,5 kN/m
• Total load :
q = 18,0 x 1,0 = 18,0 kN/m
Statics scheme of slab (slab band):
ANSWER
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
Floor elements – load schemes
C. Ribben slab
• Dead weight of slab with thickness h = 8 cm
g2 = 0,08x25x1,1 = 2,2 kN/m2
• Dead load:
7,2 kN/m2
g = g1+ g2 = 2,2+5,0 =
• Changing load:
p = 7,5 kN/m2
• Total load:
q = 14,7 kN/m2
Statics scheme of slab (slab band):
C.
Slab band , width b=1m
• Dead weight of rib: bxh = 25x50 cm
g3 = 0,25x(0,50-0,08)x25x1,1 = 2,9 kN/m
• Total load: q = 2x18,4+2,9 = 39,7 kN/m
Statics scheme of rib:
ANSWER
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
x2
+CW
Floor elements – load schemes
D. Floor: slab-rib-girder
• Dead weight of slab with thickness h = 6 cm
g2 = 0,06x25x1,1 = 1,65 kN/m2
• Dead load:
6,7 kN/m2
g = g1+ g2 = 1,65+5,0 =
• Changing load:
p = 7,5 kN/m2
• Total load:
q = 14,2 kN/m2
Statics scheme of slab (slab band):
D.
Statics scheme of major beam:
• Dead weight of ribŁ bxh = 18x30 cm
• Dead weight of major beamŁ bxh = 35x70 cm
g3 = 0,18x(0,30-0,06)x25x1,1 = 1,2 kN/m
g4 = 0,35x(0,70-0,06)x25x1,1 = 6,2 kN/m
• Total load: q = 2x10,65+1,2 = 22,5 kN/m
• Reaction from rib: Q = 2x56,25 = 112,5 kN
x2
Statics scheme of rib:
Mgr inż. arch. Joanna Wojtas Gdansk University of Technology Faculty of Architecture
x2
+CW