a) To bind both the coarse and fine aggregates

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29 Νοε 2013 (πριν από 3 χρόνια και 6 μήνες)

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QUESTION ONE

a)

Cement

-


To bind both the coarse and fine aggregates

together by setting and hardening such
particles



(2)


Fire aggregates

-

Fill all
the ope
n

space between the
courses


particles




(2)


Coarse aggregates
-

These are the main load
beami
ng

component
s

of
concrete


(
2)

Water
-


Determines the quality of the concrete
pro
duced



(2)

b)

Hardness

-

Resistance

to abrasion

(1)


Tougher

-

Resistance of concrete to crushing






(1)

Creep

-

Long
term behavior

of concrete

that
is




u
nder contin
ou
s

lo
ading


(1)


Reactivity

-

The
reaction of concrete

with chemicals






found in the

soil or air


(1)

c)

Poorly cured con
crete

-

W
ill not achieve the desi
red

s
trength and

hardness

(3)

Poorly designed concrete mix



W
ill have incorrect strength that could le
ad to
building collapse (3)

d)

A
dvantages of poor stressed concreted



High comprehensive strength



Low risk of developing tension cracks



High shea
r resistance



Can use light weight



Reinforcement bars

(5
marks for
4 points)

e)

D
ifferent types of concrete



Ordina
ry concrete. Concrete

mix is
1: 2

:4
.

U
sed for
construction of residential buildings.



Aerated concrete
. R
esistant to scaling and abrasion



Light weight concrete.
Has density

less than 1920
kg/m
3
.


Used in b
ri
dge construction



High density concrete. Has densi
ty of over 3000 kg/m
3
.

Used in construction of nuclear reactors



Reinforced cement concrete (RCC)
.
High strength
concrete
. U
sed in constructing high
rise b
uildings



Pre
-
cast

concrete. Factory made



Pre
-

Stressed concrete
.Factory pre
-

t
ensioned concrete

(5 mar
ks for 5 point
s

well explained)


QUESTION TWO

a)

Safe soil bearing capacity

=
Load bearing capacity


Safety factor



(2)


Damp proof membrane



This is

polythene

lining used to

prevent the entry of groundwater
into
the building

(2)


Floor
scree
d
ing




T
his is a thin concrete floor
covering. The purposes of
screeding is to make it easy to
wash and maintain the floor (2)



Elastic foundation settlement
-
This is the immediate
settlement of subsoil as the building is being constructed (2)



Foundation settlement



This is

the long term
se
ttlement of concrete due to creep
.






A B C D E



A

-

A

Gauging

rod to placed
vertically

at point A

B

-

A level is placed at

point
B

C

-

The level provides a dead
ho
rizontal line

of sight. The

level is
swung
backwards

and a reading taken on both
rods A and C

D

-

With rod C

still in place the level is moved to D

and a




reading is
taken on
both rods

C and E


The level of the line of sight rises and falls as on
e

move
s

from
one point to another.




Station

Back
-
sight

Inter
-
sight

Fore
-
sight

Reduced
levels

A

8.00



100.00

B



6.00

102.00

C

9.00




D



5.00

106.00

E

7.00




F


6.00


107.00

G



5.00

108.00

H

4.00




I



6.00

106.00

Checks

28.00


100.00



22.00


-
__________



6.00


6.00



(2)










QUESTION THREE

a)

Beam

-

Steel bars are placed on the periphery to
take up both
static and

dynamic

tensile and she
a
r stresses
(2)



Columns


Steel bars are placed on the

periphery to take up
both static

and dyn
amic and she
a
r stresses (2)

b)

S
tructural steel
s
-

These are the steels that are used in
construction. These indicate



Concrete reinforcement steel

Reinforcement steels are mild steels (low carbon)



Pre

Stressed steels. These must

be tensioned before
reinforce
ment



Bridge steels. These are used in construction of
suspension budges. Very high strength.



Cladding steel. These steels are used in the
manufacture of wall and floor coverings



Railway steel. These are used in the

construction of

railway lines

(4 marks
for
4 points)


c)

Benefits of heat treatment



Reduces amount of internal
cracks

due to fatigue



Causes

more elongation then cold rolled

steels



Refines the internal structure of the steel. The internal


structure
is homogenous.



Easy to work the steel


(4 marks for 4 points)

d)

Cold rolling methods



Forging



Pressing



Drawing



Extrusion



Powder
metallurgy


(2 marks for 4 points)

e)

Annealing

-
Heating steel upto the critical

te
mperature

(550
-
650
0
c)
.

H
old it there

for an

adequate

time and then
cool it gradual
ly in air or
furnace.

This
increas
es the
ductility

of
steel (
2)


Normalizing

-

Heat

steel
above the
critical

temperature (> 650
0
C).

Hold

it there

for

sufficient time and allow in
cooling

gradually in air or
furnace
.
Done to

make steel
suitable for

t
empering

(2)


Tempering


-


The reheating
of normalized
or
quenched steel

to temperature
s

below
the
critical

temperature (400
-
600
0
c
)
.

Removes



brittleness

but
retains
strength (
2)


f)

Quenched steel

-


Heat steel above the critical

T
emperature
.

H
old it
there for
sufficient t
ime

and then cools

it
suddenly in w
ater

or oil.

Increases
hardness

by

a

big amount,
but

the resulting

steel is very b
rittle
.
Must be tempered before use (2)


Case hardening

-

Make the surface hard by hea
t
ing steel

for 1
-
8 hours

in the presence of
carbon

(

charcoal
/ coal) or ammonia at a
temperature of 500
-
600
0
c (1)

QUESTION FOUR

(a)

Functions of a building




To provide thermal comfort and safety



To provide
visual

comfort and safety



To provide acoustic
comfort

and safety



To provide

hygrometric comfort and safety



To provide ergonometric comfort and safety

(
5 Marks

for 5 points)


(b)

Thermal function of a wall




To ensure the surface indoor temperature does

not fall
below the de
w point



To cause large temperature differenti
als

between t
he
indoor and outdoor temperature.



To respond slowly to sudden changes in
both outdoor
and

indoor temperature.



To act as a heat sink and source (2)

(c)

Plastering

and rendering



The placement of thin mortar layer on the indoor side of
a wall is called plasterin
g. The placement of the m
or
t
a
r
on the outdoor
-

side of the wall is called rendering (3)

Aging and
fatigue



Aging

is

the change of a loaded or unloaded material
properties

with time (3)



Fatigue is the cumulative

c
racking of a material due to
dynamic loads

(d)

Dynamic

and static loads



Static loads are the stresses imposed on a material
that do
not change

in position,
magnitude

or
with
time
.



Dynamic

loads are the stresses that are
continually

changing in direction, m
agnitude
,

location

or

with
time (3)

Yield a
nd proof
stress



Yield stress
occurs

at the point at which a material
behavior

changes
from being

elastic

and becomes
plastic
.



Ultimate

stress is the maximum
stress

a material can
withstand before it breaks.





Ductility

and malleability



Ductility

is the
ability of a material to turn into a wire
upon being stretched.



Malleability is the ability of a material to
spread

into a
plate

upon being pressed. (2)



(e)

Role of the external window




Acts as a building ventilator



Acts as an acoustic insulator



Acts as a
thermal insulator



Acts as a source of daylight



Acts beauty to the building



Determines the
ergonometric comfort
.

(3 marks for 3 points)

QUESTION FIVE

a)

P
urpose of ventilation




Supply oxygen to the building



Removal

of
carbon dioxide from the building



Control

humidity in the building



Control the velocity of the air through the buildings



Removal of odo
ur
s



Removal of micro
-
organisms from the building



Removal of excess heat from the building



Removal of
particulate

m
a
t
t
er such as dust and




smoke




( 8 m
arks for 8 points)

b)

dB

+

10 log (p/po)
2



(1)

Po

=

thresholds

pressure


= 20 x 10
-
6

pa

72 =

10log (

P
/
20X10
-
6
)
2



(1)

P

=0.0796 pa


(1)


c)

Noise insulation measures




Source reduction. Use legal regulations to prevent noise



Separation distance. Keep your
distance away from the
noise source



Use of air
-

tight windows and doors



Use of high density building materials

(3 marks on 3 points)



d)

dB

= 10 lo
g I/I
O

Doubling of noise power

dB

= 10 log
2 I





I
O


= 10 log

1



+
10 lo
g 2


1
0


= 10
log 1/1
0

+ 3




(3)


Dewpoint is the temperature at which air of given moisture c
ontent
would become saturated at

this temperature
.

Condensation

would
start to form on the walls of

the
building

(3)

Effect of distance doubling on the noise dB


I

=

P




4

R
2


I
1


=

P




4


(2R)
2



= P



4

R
2



(4)


I
1


=

1


I



4




dB

=

10 log
(1/4 I)






I
0



=

10 log I/1
o

-

10 log 4



=

10 log 1/1
0

-
11


(3)