MINISTRY OF SCIENCE & TECHNOLOGY

earthwhistleΠολεοδομικά Έργα

25 Νοε 2013 (πριν από 3 χρόνια και 7 μήνες)

50 εμφανίσεις

MINISTRY OF SCIENCE & TECHNOLOGY

DEPARTMENT OF TECHMCAL AI
\
ID VOCATIONAL EDUCATION

FINAL EXAMINATION FOR B. Tech Year 2 ( Architecture) 2006

QUESTION

Arch 04013 Building Science II

1. What are the various types of water proofing basement used in building?
Explain the
m
astic

asphalt tanking construction techniques.

2. Describe the f
o
llowing popular shell roof constructions.

(a) Hyperbolic
Parabolic

shell structures.

(b) Ba
rr
el vault shell roof structur
es.

3. Describe construction techniques for on
e
of the fo
llowing.

(a) Reinforced concrete suspended floors.

(b) Pre
-
cast concrete floors.

4. Write about the concrete floor screed construction methods for the followings;

(a) Separate screeds

(b) Laying floor screeds

(c) Un
-
bonded screeds.

(d) Floating screeds.



(OR)

Write short notes on the followings.

(a) Spira
l
land Helical stairs.

(b) Ribbed floors.










SAMPLE ANSWER (2006)

Arch 04013 Building Science II


1.

Waterproofing Basements

-

basements can be waterproofed by one of three ba
s
ic

rnethods namely
-

1. Use of dense monolithic concrete w
alls and

floor

2.

Tanking techniques


3.

Drained cavity sy
stem

M
astic Asph
alt Tanking

-

the objective of ranking is to provide a cont
inuous waterproof
membrane
which is
applied

to the
basic

slab and

walls with complete continuity between
the

two

applications.

The tanking can be
applied

externally or internally according t
o the
circums
tance
s

pre
vailing on site. Al
ternatives to mastic asphalt are polythe
ne

sheeting;
bituminous compounds ep
oxy resin com
pounds
and bitumen laminates.

External Mastic Asphalt T
anking

-

this is
the

preferred me
tho
d since it not only
prevents the ingress of water it also protects the main st
r
ucture of the base
ment from
aggressive sulphates

w
hich may be present in t
h
e su
rroun
di
ng soil or ground wat
e
r.



Internal Mastic Asphalt Tanking

-
this method should only be adopted if external
tanking is nor possible since it will not give protection to the main structure and unless
adequate loaded may be forced a
way form the walls and floor by hydrostatic pressure. To
be effective the horizontal and vertical coats of mastic asphalt must be continuous.




2.(a)
H
yper
b
o
l
i
c

Paraboloids

-
the true hyperbolic paraboloid shell roof shape is
generated by
the moving
vert
i
cal parabola
(
the generator) over
a
nother vertical parabola
(the directrix) set at

rig
ht
angles

to the moving parabola. l
-
his forms a saddle shape where
horizontal sections taken

through

the

roof arc hyperbolic in f
or
mat and ertical section
s
arc parabolic. The resultant" shape is very suitable for

roofing purposes
therefore only
part of the saddle shape is used and this is

forme
d

by joining the center points thus.



To obtain a more practical shape than th
e true saddle a straight line limited hyperbolic is
used
. This is formed by raising or lowering one or more corners of a square forming
swarped parallelogram thus
-




(b)
Other Forms of barrel Vault
-
by cutting intersecting and

placing at different levels
the basic barrel vault roof can be formed into a groin or north light barrel vault roof
-




3. (a)
Reinforced Concrete Suspended floors


A simple reinforce concrete flat slab cast to act as a susp
ended floor is not usually
economical for spans over 5000.To overcome this problem beams can be incorporated
into the design to span in one or two directions. Such beams usually span between
columns which transfers their loads to the foundation. The disadv
antages of introducing
beams are the greater overall depth of the floor construction and the increased complexity
of the formwork
and reinforcement
.


To
reduce

the overall depth of the floor construction

flat slabs can be used where
the beam is incorporate
d with the depth of the slab. This method usually results in a
deeper slab with complex reinforcement especially at the column positions.




3.(
b) Precast Concrete Floors

These are

available

in
several

basic
formers
and provide an alternative
form of
floor c
onstruction to suspended ti
m
ber floors and insitu

reinforced concrete suspended
floors
. The main advantages of precast concrete floor are:

l.
E
limination

of the need f
o
r
form w
ork except for nominal propping, which is


required with some s
ystems.

2. Curing time of
concrete

is eliminated theref
ore

t
he floor is available
for

use as

a

working platform at an earlier stag
e.

3
.Sup
er quality
control of product is possible
wi
th factory
pro
d
uced

components
.

The

main disadvantages of

precast concrete floor when compared with insitu reinforced
concrete floors are:


1. Less flexible in design terms.

2. Formation of large openings in the floor for ducts, shafts and stairwells usually
have to be formed by casting an insitu reinforced floo
r strip around the opening
position.

3. Higher degree of site accuracy is required to ensure that the precast concrete
floor
uits can be accommodated without any alternations or making good.






4.
Concrete Floor Screeds

Concret
e Floor Screeds


these

are used to give a concrete floor a finish suitable
to receive the floor
finish or covering specified.

It should be noted that it is not always
necessary or desirable to
apply a floor screed to receive a

floor covering, techniques a
re
available to enable the concrete fl
oor surface to be
prepare
d

at the

time of casting
to
receive the coverings at a later stage.

(a)

Separate Screeds
_ screed is laid onto the concrete floor slab after it has cured.
The floor surface must be cleaned and rough

enough to ensure an adequate bond
unless the floor surface is prepared by applying a suitable bonding a gent or by
brushing with a cement/water grout of a thick crean like consistency just before
laying the screed.





(b)

Laying Floor Screeds

_floor screed should not be laid in bays since this can
cause curling at the edges, screeds can however be laid in 3,000 wide strips to
receive thin coverings. Leveling of screeds is achieved by working to leveled
timber screeding b
atten or alternatively a 75 mm wide band of leveled screed
with square edges can be laid to the perimeter of the floor prior to the general
screed laying operation.



(c)

U
nbonded Screeds

-

screed is laid
directly

over a

damp
-
proof membrane or
over

a da
m
p

m
embrane

and insulation. A rigid form of floor insulation is required
where the concrete floor slab is in contact with the ground. Care must be taken
during this operation to ensure that the dump
-
proof membrane is not da
maged.



(
d

)
Floating

Screeds

-

a resilient quilt of 25mnr thickness is
laid

with

but
t

joints

and
turned up at the edge against the abutment walls the screed being laid directly over the
resilient quilt. Th
e main objectives of this form of floor screed is to improve
the sound
insulation properties of the floor.



4.(a)

Spiral and
Helical

Stairs

These
stairs

constructed in insit
u reinforced
concrete

are considered to be
aest
hetically

pleasing

but are expensive to construct.

They

are therefore mainly confined
t
o prestige buildings

u
sually as accommodation stairs l
inking floors
within

the same
compartment. Like all other

form of
stair they must
conform

to the requirements of Pa
rt

K of the Building Regulations and if

used as a mean
s of

escape in case of

fire with the
requirements of part B.
Spiral

stairs can be

defined as those describing a helix around a
central column whereas a helical stair has an open

well. T
he open
well of a

helical st
air is
usuall
y

circular

or elliptical in plan and
t
he formwork is

b
uilt up around a vertical timber
core.






(b)

Ribbed Floors


T
o reduce the overall depth of a traditional cast insitu reinforced
concrete be
a
m

and

sla
b suspended

flo
or a ribbed floor could be used
. The basic concept is to re
place

the

w
ide

spaced

deep

beam
s

with narrow

spaced shallow bea
m
s or ribs, which

will carry
only a sma
ll a
mount

of

slab
loading. These floors
can be designed as one or two way
sp
anning fl
oors.
One

way spanning

r
ibbed floors are sometime
s called thronged floors
whereas the two way spanning ribbed floors are

call
ed cofferd or waf
fle floors.
Ribbed

floors are usually
cast

agai
nst metal or reinforced pl
astic
formers

in
the

form of
pre
f
ormed moulds

which can
be

left

in
place

to pro
vide

the soffit finish
.