Bridge loading, the loads act on bridge and basic bridge design steps

1. 1
Bridge Loading

2. 2
Load Evaluation
• Infrastructure is funded from public funds and
large number of people use those => high level of
safety needed
• Well defined load paths ➔ effects of loads can be
evaluated accurately
• Loads may be determined to a greater precision
• Strength is often the governing condition
• Primary structure is a higher proportion of the
total investment

3. 3
Loading Standards
• BS 5400: Steel, concrete and composite bridges
Part 2 : Specification for loads
• British Department of Transport – Departmental
Standards
BD 37/88 : Loads for Highway bridges
• Eurocode 1 : Actions on structures
Part 2 : Traffic loads on bridges

4. 4
Eurocode 1: Actions on structures
- Part 2: Traffic loads on bridges

5. 5
Eurocode – Basis of structural design

6. 6
Bridge Design to Eurocodes
Worked examples

7. 7
Carriageway
Definition - the part of the road surface, supported by
a single structure (deck, pier, etc.), which includes all
physical traffic lanes (i.e. as may be marked on the
road surface), hard shoulders, hard strips and marker
strips
The width of the carriageway (w) has to be measured
between the inner limits of vehicle restraint systems.

8. 8
Carriageway Width

9. 9
Lanes
The width, taken as described in the previous slide,
should then be divided into notional lanes. The width
of the notional lanes and their number is defined
accordingly to the Code instructions.

10. 10
Notional Lane
Definition - strip of the carriageway, parallel to an
edge of the carriageway, which is deemed to carry a
line of cars and/or lorries
The first step when evaluating the loads on bridges
is the division of the carriageway into notional lanes.

11. 11
Division of the Carriageway into
Notional Lanes

12. 12
Number and Width of Notional Lanes
EN 1991-2:2003 (E) - Table 4.1

13. 13
Number of Notional Lanes
The number of notional lanes depends on the
width:
– w < 5.4 m => n1 = 1notional lane;
– 5.4 m ≤ w < 6 m => n1 = 2 notional lanes;
– w ≥ 6 m => n1 = Int (w/3) notional lanes.
Accordingly, their width is:
– w < 5.4 m => 3 m;
– 5.4 m ≤ w < 6 m => w/2;
– w ≥ 6 m => 3 m.

14. 14
Number of Notional Lanes
For example, for a carriageway width equal to 11 m:
– n1 = Int (11/3) = 3;
– wl = 3 m;
– remaining area = 11 – 3 x 3 = 2m.

15. 15
Classification of Actions
• Permanent action –
o Self weight of structure
o Superimposed dead load (e.g. road way)
Can be calculated when geometry and material types
are available
• Variable action
o Road traffic action
o Rail traffic action
o Footway / cycle track action
Presented in EN1991 – 2 : Eurocode 1-Part 2

16. 16
Load Models of EC 1-2 Specifications
• Do not describe actual loads
• Selected to represent the effects of the actual
traffic
• For ULS and particular SLS verification

17. 17
Load Models
For the evaluation of road traffic effects associated
with ULS verifications and with particular
serviceability verifications, four different load
models, LM1 to LM4, are considered in EN1991-2

18. 18
Load Models for Limit States
• Field of application: Loaded lengths less than 200m
• Four Load Models to represent vertical forces
• Load Model No. 1 (LM1) – Concentrated and distributed
loads (main model – general and local verifications)
• Load Model No. 2 (LM2) – Single axle load (semi local
and local verifications)
• Load Model No. 3 (LM3) – Set of special vehicles (general
and local verifications)
• Load Model No. 4 (LM4) – Crowd loading : 5 kN/m2
(general verifications)
• Horizontal forces : braking and acceleration, centrifugal,
transverse

19. 19
Load Model 1
Concentrated and uniformly distributed loads,
which cover most of the effects of the traffic of
lorries and cars. This model should be used for
general and local verifications.
Consists of two partial systems
• Tandem system
• UDL

20. 20
Load Model 1 (Page 35)
Load model LM1 generally reproduces traffic effects to be
taken into account for global and local verifications;
The Load Model 1 consists of two partial systems:
– Double axle concentrated loads, called Tandem System
(TS), with weight αQi x Qik per axle;
– Uniformly distributed loads (UDL), with weight αqi x qik
The adjustment factors αQi and αqi depend on the class of
the route and on the expected traffic type: in absence of
specific indications, they are assumed equal to 1.

21. 21
Load Model 1

22. 22
Load Model 1 (Page 37)

23. 23
Load Model 1 (Page 37)

24. 24
Division of the Carriageway into
Notional Lanes

25. 25
LM1 – Diagrammatic Representation
For the determination
of general effects, the
tandems travel
centrally along the
axes of notional lanes
Where two tandems on
adjacent notional lanes are
taken into account, they
may be brought closer, the
distance between the axles
being not less than 0.50m
For local verifications, a
tandem system should be
applied at the most
unfavourable location

26. 26
Load Model 1

27. 27
Load Model 1

28. 28
Load Model 1
• A

29. 29
Load Model 2 (Page 38)
Load model LM2 reproduces traffic effects on short
structural members. The local load model LM2
consists of a single axle load βQ×Qak on specific
rectangular tire contact areas, 0.35 x 0.6 m, being
Qak=400 kN, dynamic amplification included.
Unless otherwise specified βQ=aQ1. LM2, which is
intended only for local verifications, should be
considered alone on the bridge, travelling in the
direction of the longitudinal axis of the bridge, in
the most unfavourable position. When
unfavourable, only one wheel should be considered.

30. 30
Load Model 2

31. 31
Load Model 3
Load model LM3, special vehicles, should be
considered only when requested, in a transient
design situation. It represents abnormal vehicles
not complying with national regulations on weight
and dimension of vehicles. The geometry and the
axle loads of the special vehicles to be considered in
the bridge design should be assigned by the bridge
owner. Additional information can be found in
Annex A of EN 1991-2.

32. 32
Classes of Special Vehicles
Table A1

33. 33
Description of Special Vehicles – Table A2

34. 34
Arrangement of Special Vehicles –
Figure A1

35. 35
Application of the Special Vehicles on Notional Lanes
Figure A.2

36. 36
Load Model 4
Load model LM4, a crowd loading, is particularly
significant for bridges situated in urban areas. It
should be applied on all the relevant parts of the
length and width of the bridge deck, including the
central reservation, if necessary. Anyhow, it should
be considered only when expressly required. The
nominal value of the load, including dynamic
amplification, is equal to 5.0 kN/m2, while the
combination value is reduced to 3.0 kN/m2.

37. 37
Dispersal of Concentrated Loads

38. 38
Groups of Traffic Loads on Road Bridges (Page 43)
According to table 4.4.a of EN1991-2, the
characteristic values of the traffic actions acting
simultaneously with non-traffic actions can be
determined considering the five different, and
mutually exclusive groups, where the dominant
action is highlighted.
Each group of loads should be considered as
defining a characteristic action for combination with
non-traffic loads, but it can be also used to evaluate
infrequent and frequent values.

39. 39
Table 4.4.a of EN1991-2

40. 40
Classes of Special Vehicles
Table A1

41. 41
Description of Special Vehicles – Table A2

42. 42
Arrangement of Special Vehicles –
Figure A1

43. 43
Application of the Special Vehicles on Notional Lanes
Figure A.2