This document discusses the reliability assessment of existing bridge structures. It provides background on structural reliability and limit states for building structures. It then discusses engineering methods for reliability assessment, specifically the probabilistic method. It provides statistical data on road and railway bridges in Slovakia, noting that 22% of road bridges and 14% of railway bridges do not meet required loading capacity. Causes of reduced reliability are also outlined. The document emphasizes that reliability assessment of existing bridges must consider differences from new designs, such as actual condition, remaining lifetime, and adjusted reliability levels. Loading capacity is identified as a basic parameter for existing bridge evaluation.

1. Reliability of Existing Bridge
Structures
SUBMITTED TO SUBMITTED BY
Mr.Bhupendra Gahlot sir Dharmendra
singh
Career Point University UID-K11541
Branch-civil
sem-4th

2. 1. General formulation of the reliability
assessment of building structures
1.11.1 Reliability of building structuresReliability of building structures
Structural reliability is an ability of a structure to meet required
functions from the viewpoint of preserving real service indicators
in actual conditions and limits over the required time period.
Partial reliability components are:
• safety – do not endanger human health and environment,
• serviceability – utilization of a structure for intended purpose,
• durability – time period of reliable service.

3. The structure occurs in certain states during its lifetime:
• from the viewpoint of activity: - service
- downtime
• from the viewpoint of failure: - failure-free state
- state of failure.
Specific structural state - limit state
• state when performing required functions is stopped
• state when the structure does not meet the proposed requirements
anymore
• the state of failure downtime
In the case of building structures, we can distinguish:
• ultimate limit states – related to the safety and durability of
structures
• serviceability limit states – related to the serviceability of
structures

4. Ultimate Limit State
Exceeding them leads to structural failure – structural collapse
• failures due to exceeding the material strength or due to
excessive
deformation,
• lost of member or structural stability,
• fatigue or brittle failure,
• lost of structural equilibrium.

5. Serviceability Limit States
Due to their exceeding, service requirements of structures will not be
fulfilled.
• excessive deformations affecting features or utilization of structure,
• unacceptable vibrations influencing psychics and convenience of people
as well as structural behaviour
• local failures (cracks) reducing structural durability.
To prevent attaining individual limit states, the reliability conditions shall
be fulfilled. These reliability condition are defined in corresponding codes
for structural design.

6. 1.31.3 Engineering methods for reliability assessment ofEngineering methods for reliability assessment of
building structuresbuilding structures
The engineering probabilistic method (Ržanicyn,
Cornell)
It is the most simple probabilistic method of structural reliability
verification based on probabilistic evaluation of reliability margin G
defined in the form:
R is the structural resistance as a function random variable
enter
parameters,
E are action effects as a function of random variable enter
G R E 0 (1a)
G R / E 1 (1b)
= − ≥
= ≥

7. 2. Reliability of existing bridge structures
2.12.1 Relationship between structural design and
evaluation of existing structures
Reliability of existing bridge structure is the ability to meet required
functions within bridge remaining lifetime respecting usual traffic
condition and bridge maintenance.
Required functions:
• to carry all actions especially traffic action on bridges
• to preserve required operating efficiency of transport communications
• to preserve required comfort and convenience for passengers

8. Number of bridges: 7423 persistent bridges
29 temporary bridges
Material: concrete - 93 %
steel - 3 %
others - 4 %
Global length of bridges: 106,521 km
from this: 96,6 % massive bridges
3,4 % steel bridges
Evaluation : 22 % bridges do not meet required
loading capacity
2.1 % is in accidental condition
Statistical data about road bridges in SlovakiaStatistical data about road bridges in Slovakia

9. Number of bridges: 2281 bridges
Material: 78 % massive bridges
22 % steel bridges
Global length of bridges: 78,030 km
from this: 52,5 % massive bridges
47,5 % steel bridges
Evaluation: 23 % is more than 77 years
14 % is more than 100 years
2.4 % bridges do not meet required loading
capacity
Statistical data about railway bridges in SlovakiaStatistical data about railway bridges in Slovakia

10. Causes
• Bad concept and technology of the bridge erection
• Increasing of transport intensity
• Material degradation due to retrogressive environment
• Insufficient and unqualified bridge maintenance
• Shortage of financial resources for bridge maintenance
• Development of Slovak motorway network and modernisation of
European railway corridors

11. The main differences between existing bridges and
newly designed ones:
• effect of the regular inspection as well as the results of the
technical diagnostics, which reduce the uncertainties of input
parameters of reliability verification,
• lengths of the bridge remaining lifetime; it means time,for
which the results of evaluation are reliable,
• effect of the reliability level differentiation in dependence on
function of the element in the whole system,
• actual bridge condition found by diagnostic investigation.
Therefore, the adjusted reliability level for existing
bridge evaluation should be considered.
In assessing reliability of existing structures include bridges,it is
necessary to consider differences they may have in comparison with
newly designed structures.

12. 2.3 Loading capacity as the basic parameter of
existing bridge evaluation
Process of reliability verification of existing bridge structures is a
crucial part of their overall evaluation, which is understood as a
complex assessment based on processing all available information to
reach the optimum most economic decision concerning the bridge
rehabilitation strategy.
Two approaches to existing bridge evaluation :
• classification approaches
• reliability – based approaches