MEP-Technical Manual CDN 0408.qxd - Hambro

DESIGN PRINCIPLES AND CALCULATIONS
4. DESIGN PRINCIPLES AND CALCULATIONS
4.1 SLAB DESIGN
4.1.1 THE HAMBRO SLAB
The slab component of the Hambro Composite Floor System
behaves as a continuous one-way slab carrying loads
transversely to the joists, and often is required to also act
as a diaphragm carrying lateral loads to shear walls or
other lateral load resisting elements.
The slab design is based on CSA Standard A23.3-04, Design
of Concrete Structures which stipulates that in order to
provide adequate safety level, the factored effects shall be
less than the factored resistance.
� S ≤ ø R
Where � = load factor, taking into account the probability
of exceeding the specified load
S = load effect (dead or live)
ø = performance factor
R = member resistance
4.1.2. EFFECTS OF LOADING
The Canadian concrete code (CSA Standard A23.3-04)
cl. 9.2.3.1. requires that we consider dead load to act simultaneously
with the live load applied on:
i) Adjacent spans (maximum negative moment at support)
or
ii) Alternate spans (maximum positive moment at mid-span).
However, if criteria (a) thru (c) of cl. 9.3.3. are satisfied, the
following approximate value may be used in the design of
one-way slabs. Refer to fig. 4 for location of the design
moments.
4.1.2.1 POSITIVE MOMENT
Extra mesh at 1 & 2
when required
1
Spacing S1
S2 /3
Spacing S2
Fig. 4
Exterior span:
M f = W f L 1 2 / 11 ... Location �
Interior span:
M f = W f L i 2 / 16 ... Location �
4.1.2.2 NEGATIVE MOMENT
First interior support:
Mf = Wf L2 / 10 ... Location �
At other interior supports:
M f = W f L 2 / 11 ... Location �
4.1.2.3 SHEAR
At face of first interior support:
Vf = 1.15 Wf L1 / 2 ... Location �
At other interior supports:
V f = W f L i / 2 ... Location �
Where W f = Total factored design load
= 1.25 x dead + 1.5 x live
L1 = First interior span
Li = Interior spans
L = Average of two adjacent spans
Note: L is clear span (mm)
S is joist spacing (mm)
L = (S) - 45
2 4
4 Location
indexing
numbers
3 3
Spacing Si
1