6. Load
combinations
The load conditions described above were
combined in the following load combinations:
|
1
2
3
4
5
6
7
8 |
1.0 a + 1.0 b
1.0 a + 1.0 c
1.35 a + 1.35 b
1.35 a + 1.35 c
1.35 a + 0.54 b + 1.5 d
1.35 a + 0.54 b + 1.5 e
1.35 a + 0.40 b + 0.5 d + 1.0 f
1.00 a + 0.5 d + 1.5 g |
|
load conditions
|
- dead and permanent loads
- live load uniformly distributed
over the whole bridge
- live load uniformly distributed
over half the bridge
- uniform thermal load +15 °C
- uniform thermal load -15 °C
- flood load
- earthquake load
|
7. Soil characteristics at the
abutments
The geotechnical characteristics of the soil beyond the
abutments were obtained from the Conex report, and particularly from the
drawings showing the vertical sections of the abutments.
The three-dimensional finite element model was extended
on each side, starting from the arch springers, for a depth of about 6 m.
On both banks it is possible to identify the following
stratigraphy: upperly there is a clayey sand material with fragments of
stone, then there is a layer of masonry of about 7 m, and finally hard
conglomerate is encountered.
From the samples which were driven out from the
vertical and horizontal boreholes in the abutments, the following values
of the materials of the abutments were obtained.
|
Hard
conglomerate Edyn (Mpa) |
Masonry
Qu (MPa) |
|
43200 |
1.70 |
|
14800 |
2.60 |
|
12000 ¸ 28700 |
- |
|
22650 |
- |
|
7100 ¸ 13500 |
- |
|
1400 ¸ 2300 |
- |
|
17500 |
- |
|
Boreholes |
| |
|
|
Fc MPa |
E MPa |
|
BH3 |
Tenelja |
0.0 ¸ 0.8 |
22.57 |
17000 / 20000 |
|
BH4 |
Conglomerate |
2.5 ¸ 3.0 |
|
24000 |
|
BH5 |
Conglomerate |
2.0 ¸ 2.5 |
7.40 |
10435 |
|
BH6 |
Conglomerate |
2.0 ¸ 2.5 |
8.80 |
22642 |
|
BH7 |
Conglomerate |
1.0 ¸ 1.3 |
10.95 |
5634 |
|
Masonry
Strength fc |
|
Mean MPa |
Min MPa |
Max MPa |
|
9 |
7.4 |
10.95 |
|
Masonry
Modulus E |
|
Mean MPa |
Min MPa |
Max MPa |
|
19000 |
10000 |
24000 |
8. Values of the material parameters assumed in
the design
On the basis of the values listed above, the following
values of the masonry strength and elasticity modulus were adopted.
Strength of the masonry
| |
fc
min MPa |
fc
max MPa |
fc
mean MPa |
ft
MPa |
|
Arch |
6 |
10 |
8 |
0.05 |
|
Wedge |
3 |
5 |
5 |
0.05 |
|
Middle spandrel |
3 |
5 |
5 |
0.05 |
|
Lateral spandrels |
5 |
8 |
6 |
0.05 |
|
Slab |
5 |
8 |
6 |
0.05 |
|
Abutments
Upper part |
- |
- |
4 |
0.05 |
|
Abutments lower part |
- |
- |
4 |
0.05 |
9. Elasticity modulus of the masonry
The Conex data show a large variation of
the values of the elasticity modulus, so that three different values were
defined for each material (minimum, mean and maximum).
| |
E
min MPa |
E
max MPa |
E
mean MPa |
|
Arch |
6000 |
10000 |
8000 |
|
Wedge |
3000 |
5000 |
5000 |
|
Middle spandrel |
3000 |
5000 |
5000 |
|
Lateral spandrels |
5000 |
8000 |
6000 |
|
Slab |
5000 |
8000 |
6000 |
|
Abutments
Upper part |
- |
- |
4000 |
|
Abutments lower part |
- |
- |
15000 |
The analyses were performed adopting
three different combinations of the elasticity modulus of the structural
elements:
| A |
the mean
values of the elasticity modulus for all the structural elements |
| B |
the
maximum value of the elasticity modulus for the arch and the minimum
values for the other structural elements |
| C |
the
maximum values of E for all the structural elements. |
The following table lists all the
analyses performed. The number indicates the load combination, while the
capital letter (A, B or C) indicates the combination of the elasticity
moduli.
|
Symbol |
Combination of
load conditions |
Values of the elasticity
modulus adopted |
|
1 A |
1.0 a + 1.0 b |
mean values of the elasticity modulus for the
whole structure |
|
1 B1 |
1.0 a + 1.0 b |
maximum value of E for the arch and minimum
value of E for the other parts |
|
2 A1 |
1.0 a + 1.0 c |
mean values of the elasticity modulus for the
whole structure |
|
2 B1 |
1.0 a + 1.0 c |
maximum value of E for the arch and minimum
value of E for the other parts |
|
3 A |
1.35 a + 1.35 b |
mean values of the elasticity modulus for the
whole structure |
|
3 B |
1.35 a + 1.35 b |
maximum value of E for the arch and minimum
value of E for the other parts |
|
4 A |
1.35 a + 1.35 c |
mean values of the elasticity modulus for the
whole structure |
|
4 B |
1.35 a + 1.35 c |
maximum value of E for the arch and minimum
value of E for the other parts |
|
5 A |
1.35 a + 0.54 b + 1.5
d |
mean values of the elasticity modulus for the
whole structure |
|
5 C |
1.35 a + 0.54 b + 1.5
d |
maximum values of the elasticity modulus for
the whole structure |
|
6 A |
1.35 a + 0.54 b + 1.5
e |
mean values of the elasticity modulus for the
whole structure |
|
6 C |
1.35 a + 0.54 b + 1.5
e |
maximum values of the elasticity modulus for
the whole structure |
|
7 A |
1.35 a + 0.40 b + 0.5
d + 1.0
f |
mean values of the elasticity modulus for the
whole structure |
|
8 A |
1.00 a + 0.5
d +
1.5 g |
mean values of the elasticity modulus for the
whole structure |
(1) The first four load
combinations were used in the phase A of the research, where the
"allowable stresses" method was used. In the phase B the
"limit state" method was used according to Eurocode, anyway the
combinations of the phase A were maintained.
- dead and permanent loads
- live load uniformly distributed
over the whole bridge
- live load uniformly distributed
over half the bridge
- uniform thermal
load +15 °C
- uniform thermal
load -15 °C
- flood load
- earthquake load
|
|
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