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STRUCTURAL DESIGN - PART 05

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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

 

  1. dead and permanent loads
  2. live load uniformly distributed over the whole bridge
  3. live load uniformly distributed over half the bridge
  4. uniform thermal load +15 C
  5. uniform thermal load -15 C
  6. flood load
  7. 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.

 
  1. dead and permanent loads
  2. live load uniformly distributed over the whole bridge
  3. live load uniformly distributed over half the bridge
  4. uniform thermal load +15 C
  5. uniform thermal load -15 C
  6. flood load
  7. earthquake load

 


CREDITS:

Intellectual property of this report and of the design drawings is owned by the University of Florence - Department of Civil Engineering

author of the text: Prof.Eng. Andrea Vignoli other contributes have been mentioned in related paragraphs

- General Engineering Workgroup -

SOURCE:

Final Design Report

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