5 - UTM

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53




CHAPTER V





RESULTS AND DISCUSSION






The failure modes of the experimental model were evaluated by stress
contour diagram and load versus displacement graph. The failure of the reinforced
concrete can either in compression or tension.
The structur
al element were failed by
cracking when reaches the tensile strength of 0.1
f
cu
.
The crushing condition is
defined when the ultimate strain reaches 0.0022 or the ultimate compressive strength
is exceeding the 0.8
f
cu
.





5.1

Result of Tension Stiffening Curve

Parameter




The tension stiffening curve parameters searched begin at 0.0002 until
achieved the convergence. Each of the analysis result is shown in Figures 5.1, 5.12

and 5.3. Based on the stress output data during the solution process terminated, the
t
ension stiffening curve parameter could managed into 4 conditions as shown in
Table 5.1.





54

Graph of Load Vs. Displacement
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0
0.05
0.1
0.15
Displacement ( m )
Load Parameter
0.0002
0.0004
0.0006
0.0008
Table 5.1: Condition of the concrete during the solution analysis stop

The behavior of the concrete during the
solution analysis stop

Tension stiffening curve
pa
rameter

Concrete intact (no crack and crush)

0.0002
-

0.0004

Concrete begin to crack without crush

0.0006
-

0.0015

Concrete crushing

0.0017
-

0.0025

Convergence with crushing

0.0027
















Figure 5.1

Tension stiffening parameter a range of 0
.0002
-
0.0008












Load coefficient = 22164 KN


55

Graph of Load Vs. Displacement
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0.00
0.05
0.10
0.15
0.20
Displacement ( m )
Load Parameter
0.001
0.0013
0.0015
0.0017
Graph of Load Vs. Displacement
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5
0.00
0.05
0.10
0.15
0.20
0.25
Displacement ( m )
Load Parameter
0.0020
0.0022
0.0025
0.0027













Figure 5.2

Tension stiffening parameter a range of 0.001
-
0.0017
















Figure 5.3

Tension stiffening parameter a range of 0.002
-
0.0027




Load coefficient = 22164 KN

Load coefficient = 22164 KN


56


5.2

Influence of Tension Stiffening Curve Parameter



As shown in Figures

5.1, 5.2 and 5.3, each tension stiffening parameter were
not representing the large variation of deflection profile results. Anywhere, the
greater of tension stiffening curve value were found effortless to achieve the
convergence in the analysis.


Resul
ts in Table 5.1, the tension stiffening curve with value of 0.0006
unsuccessful obtained the convergences after concrete cracking, while the values
0.0027 was completing the solution analysis process with condition of concrete
crushing with convergence. T
he tension stiffening value of 0.0006 could not
continue the solution process may be due to the concrete incapability to sustain the
incoming stress. Thus, the value 0.0027 successfully achieved the convergence
possibly due to numerical problem.





5.3

Res
ult of Failure













Figure 5.4

Load displacement curve

Concrete cracking at
shearwall bas
e

( 2.9122 x 10
6

N/m
2

)

Concrete crushing

( 2.8268 x 10
7

N/m
2

)

Load coefficient = 22164 KN


57

The tension stiffening value of 0.0027 is use to present the load
-
displacement
curves shown in Figure 5.4. The graph indicated that concrete cracking at load of
48827 KN and the displace
ment of 0.10485m, while the concrete crushing at load of
69404 KN and the displacement of 0.15681m.



The concrete cracking started occur near the shear wall base (element 1146,
node 2819) when the principle stress; P1 exceed 0.1

cu =2.8 x 10
6

N/ m
2

at st
ep 20
(Figure 5.5). The concrete crushing was occurring at the same element that crack’s
but at node 2830 at arc step 31. The principles stress were recorded at 2.8268 x 10
7

N/mm
2
(Figure 5.6), which is exceeding the allowable principle stress; P3 at va
lue of
0.8

cu (2.8 x 10
7

N/ m
2
). Since, the analysis achieved the convergence when
entering step 39. The c
racks pattern of element structure could observe from the
Figure 5.5 and 5.6 with clearly stated crushing pattern. The represented stress
contour d
iagram of the reinforcement concrete element either cracking area or
crushing area is
denoting the failure is prominent.


















Figure 5.5

The stress contour diagram at the shear wall base during the


concrete cracking occur at step 20

Concrete
cracking
area

Element 1146

Node 2819


58

















Figure 5.6

The stress contour diagram at the shear wall base during the


concrete cracking occur at step 31





5.4


Discussion of Failure and Behaviour of the Building




The presented failure modes of tube in tube building we
re significantly
display the experimental model is definitely controls by the compression failure
rather that tension. The shear wall is failed in compression under lateral load due to
bending action (Figure 5.7). The areas in tension under lateral load w
ere occurring
along the perimeter tube, while the compression areas were initiated along the shear
wall. As in Figure 5.7, the area of a connection between shear wall and slab were
found slightly in compression. Hence, the function of slab a transfer la
teral load to
the primary structure is found to be significant on this study of tube in tube type of
tall building.

Concrete
crushing
area

Element 1146

Node 2830


59
































Figure 5.7

The stress contour diagram of the quarter building at step 31



The location of
the failure in
compression

The area in
compression

The area in tension
located at perimeter
tube


The slight compression of the
shear w
all cause of slab at step
21



60

Shearwall

Coupling beam

Shearwall

Coupling beam


From the stress
-
strain investi
gations (Figure 5.8), it is found that the coupling
beam could not perform properly the function of flexible beams as in experimental
model. The restraints parameter has significant affected on the stress diagram of the
shear wall especially at the area b
etween the wall and beam. This kind of behavior
extremely displayed on stress contour diagram of step 20, 31 or 39 as shown in
below. The behavior of coupling beam still displays some stress without any
crushing at convergence. These behaviors occur beca
use of the coupling beam could
not distribute the stress between the two walls. This may be influence of the
restraints parameter along the missing section could not behave as the real condition
of full 3D structures.




















Figure 5.8

The stress contour diagram of the shear wall from the base up to

few Storey