Transcript Eurocode 1: Actions on structures

Eurocode 1: Actions
on structures –
Part 1–2: General actions –
Actions on structures exposed to fire
Annex A (informative)
→ Parametric temp-time curves
Part of the One Stop Shop program
Introduction
• Method of determining a more realistic
temperature-time curve
• Valid for compartments
– Up to 500m2 of floor area
– Without openings in roof
– Up to 4m in height
Basic fundamental equation
• Temperature-time curves in heating phase
are given by:

 g  20  1325  1  0.324 e
0.2 t *
 0.204 e
1.7 t *
 0.472 e
19 t *
where  g is the gas temperature in the
fire compartment
• The “time” t * is not strictly the time, but an
adjusted time based on other factors

Breaking down the equation
t  t 
*
b
O / b
c 
2


c

Av
heq
At
0.04 / 1160
2
O
Av heq
(“Opening factor”)
At
Density of enclosure boundary
Specific heat of enclosure boundary
This outlines the basis of
the equation used
Thermal conductivity of enclosure boundary
Total area of vertical openings on walls
Weighted average of window heights on all walls
Total area of enclosure (incl. openings)
Further details of
limitations and further
provisos are also
necessary…..
Different materials in surface layer
b
Layer 2
c 
Layer 1
Fire side
Boundary
layers of
enclosure
For layer 1, the subscript 1 is used and
similarly for layer 2……
Different materials in surface layer
b  c 
• If b1 < b2 , then b  b1
• If, however, b1 > b2 then a limit thickness is
calculated for the exposed material:
slim
If
3600 t max  1

c1 1
s1 > s lim, then b  b1
(We will find an
expression for t max
in a few slides
time….)

s1
s1 
b2
b1  1 
If s1 < s lim, then b 
slim
 slim 
Different materials in surface layer
b  c 
• To account for the different b factors in the
walls, the above equation should be
introduced as
b A 

b
j
j
At  Av
Where
A j is the area of the surface enclosure and
b j is the b factor derived from the previous slide
Maximum temperature limit
• The maximum temperature in the heating
*
phase occurs when *
t  t max
at which point t
with t max
*
max
 t max  
 2  104  qt ,d
 max

O



; t lim 



Where………
Maximum temperature limit
•
qt ,d
is the design value of the fire load
density related to the area of the enclosure
qt , d  q f , d 
Af
At
Design value of fire
load density related to
surface area of the
floor – from Annex E
•
Surface area of the floor
tlim is described later…..
Total surface area of
compartment
Maximum temperature limit
• When t max  t lim the t in the main
*
equation is replaced by t  t  lim
*
Olim / b
2
with lim 
0.04 / 1160
where Olim 
2
1 104  qt ,d
t lim
t limis 25min for slow fire growth, 20min for medium fire
growth and 15min for fast fire growth.
This is expanded upon in Annex E
Further numerical limit
• A further limit is imposed on the operation
under the following criteria:
If O > 0.04
Then lim must be
multiplied by a factor
and qt ,d < 75
and b < 1160
given below….
 O  0.04  qt ,d  75  1160 b 

k  1 


 0.04  75  1160 
Curves in the cooling phase
*
• For t max
 0.5
 g  max  625(t  t
*
Where
t  t 
t
*
max
 x)
For t max  t lim
*
 2  104  qt ,d


O

*
max
x 1




For t max  t lim
t lim  
x *
t max
Curves in the cooling phase
• For 0.5  t
*
max
2

 g  max  250 3  t
Where
 2  10  qt ,d


O

4
t
*
max




t  t 
*
*
max
 t
*
t
*
max
x

For t max  t lim
x 1
For t max  t lim
t lim  
x *
t max
Curves in the cooling phase
• For t
*
max
2
 g  max  250(t  t
*
Where
t  t 
t
*
max
 x)
For t max  t lim
*
 2  104  qt ,d


O

*
max
x 1




For t max  t lim
t lim  
x *
t max