BRIDGE BRIDGE REHABILITATIONREHABILITATION

Bambang SupriyadiBambang SupriyadiMPSP T.Sipil FT UGMMPSP T.Sipil FT UGM

Two main tasks for contemporary Two main tasks for contemporary bridge engineeringbridge engineering

• to construct new bridge structures according to the development of transportation needs,

• to maintain the existing bridge stock according to current and predicted traffic and safety requirements.

The Term of MaintenanceThe Term of Maintenance• is usually limited to the current works

performed systematically by maintenance services to ensure normal and safe utilization of bridge structures.

• These works consist mainly of inspection, maintenance, repair and replacement, if necessary, of expansion joints, bridge deck, drainage system, railings and barriers, pavement, bridge bearings, etc., as well as anti-corrosive protection of some elements, mostly by painting.

The term The term maintenancemaintenance

may also be considered, more widely, as: a multi-component process leading to the fulfillment of all conditions related to the safe utilization of existing bridges in the anticipated period of their future service.

Rapid deterioration of bridge Rapid deterioration of bridge structuresstructures

• In the recent two decades, rapid deterioration of bridge structures has become a serious technical and economical problem in many countries, including highly developed ones.

• It concerns also the concrete bridges, which for many years have been considered as durable and requiring minimum maintenance cost, while only the steel structures demand anti- corrosive protection being applied every few years

The reasons leading to deterioration of the The reasons leading to deterioration of the existing bridge stock (which have been in existing bridge stock (which have been in

service 20-30 years or more)service 20-30 years or more)

• increase in traffic flows and weight of vehicles, especially their axle loads, compared to the period when the bridges have been designed and constructed,

• harmful influence of environmental pollution, especially atmospheric ones, on the performance of structural materials,

• common use of de-icing agents in countries of moderate climate,

continue

• low quality structural materials as well as bridge equipment elements, such as expansion joints, waterproofing membranes, etc.,

• limited maintenance program or insufficient standard of maintenance,

• structural and material solutions particularly sensitive to damage produced by both traffic loads and environmental factors

Overloading or material fatigueOverloading or material fatigue

• deterioration of bridges, directly resulting from overloading or material fatigue, is relatively seldom observed till now, because of safety margins in load-carrying capacity and early remedial actions undertaken.

• The other above mentioned factors play predominant roles in affecting deterioration of bridges and leading to their structural deficiency

A A structurallystructurally deficientdeficient bridge bridge

• is one whose components may have deteriorated or been damaged, resulting in restrictions on its use.

• Apart from the technical condition problems, a great number of bridges built many years ago are functionally obsolete.

FunctionalFunctional obsolescenceobsolescence

Functional obsolescence refers to a bridge's load-carrying or geometrical characteristics; e.g.:

• a bridge, which was designed 40 years ago for lower load levels or traffic volumes or with inadequate under- or over-clearance and which now requires restrictions on its use, is functionally obsolete in spite of its good technical condition

The following remedial actions The following remedial actions can be undertakencan be undertaken

• repair,

• replacement,

• rehabilitation,

• strengthening,

• modernization

RepairRepair

• means to mend, to put into good shape or working order again, to recondition, to renovate, to restore and to correct. Repair concerns rather the local damages of structural members or bridge equipment elements than the overall structure.

ReplacementReplacement• means to substitute, to change and to

exchange. • Some elements of bridge structures, mostly

equipment elements, are usually replaced, e.g., expansion joints, bearings, barriers, etc.

• Sometimes, the structural members are also replaced, if necessary, e.g., deck elements, individual stringers, secondary or bracing elements, etc.

• Replacing a whole bridge is considered the last resort in the process of upgrading the existing infrastructure; it is a drastic measure and possibly the costliest

RehabilitationRehabilitation

• means to restore, to make suitable, to put back in good condition, to re-establish on a firm, sound basis, to bring back to full use, to reinstate, to renew and to revive.

• Rehabilitation concerns mostly the whole bridge structure, including its primary structural members.

StrengtheningStrengthening

• means to increase load-carrying capacity by adding more material, additional components (e.g., external prestressing), and so on.

ModernizationModernization

• is a form of upgrading by adding new features, e.g., new traffic flow arrangement, new signs, new lighting, new barriers.

• This term is commonly applied to structures designed and constructed prior to availability of these modern features.

• However, modernization can also be considered in a wider meaning. For instance, upgrading of the bridge requires in many cases its strengthening, new traffic flow arrangement requires the widening of the bridge deck, and so on

RetrofitRetrofit

• is a strengthening procedure applied to an existing structure, not necessarily although in many cases related to seismic strength.

• It is applied usually after it is found that the original design is not sufficient in light of newly gained experience

• All the above mentioned terms define various actions concerning bridge works of different scale and importance.

• However, it is very difficult to consider these actions as fully separate ones. For instance, rehabilitation of a bridge often requires its adequate strengthening or replacement and repair of some of its elements, etc.

• Therefore, repair, replacement, rehabilitation, strengthening and modernization have usually many relations to each other and they may be considered to be the components of maintenance in its wider meaning

"Bridge"Bridge Rehabilitation"Rehabilitation"• its content also covers many technical and

economical problems related to other above mentioned bridgeworks performed to improve the technical condition and functional features of the structures.

• Bridge rehabilitation covers many complex engineering problems as well as economical ones.

• Moreover, in the recent few years, many modern rehabilitation methods and non-conventional material solutions to improve the durability of bridge structures have been developed

Focused on rehabilitation of Focused on rehabilitation of concrete bridgesconcrete bridges

• This is due to the fact that on the one hand they represent a great majority of the bridge population in many countries and on the other hand, their rehabilitation is in general much more complex than in the case of steel bridges.

• Moreover, maintenance works, e.g., anti-corrosive coatings, are usually performed more systematically on steel bridges. Therefore, their technical condition is generally better than the concrete ones.

Wooden and Stone bridgesWooden and Stone bridges

• Rehabilitation problems concerning wooden and stone bridges are neglected,

• because of their specific and unique character related in many cases to the historical merit of the structures

Focused on highway bridgesFocused on highway bridges

• This is due to several reasons. Highway bridges are much more numerous and therefore, their rehabilitation needs are more evident than those related to the railway bridges.

• Railway bridges, mostly built of steel, are generally in a better position, as the intensity of rail traffic and the increase of loads are less pronounced than in the case of highway bridges.

• On the other hand, however, the problems concerning rehabilitation of railway bridges are specific due to the fact that they were often built at the end of the XIXth century and at the beginning of the XXth century and exceeded their design life

AA Practical GuidePractical Guide

• Some problems concerning bridge rehabilitation in several countries are formulated according to more or less official guidelines, regulations and other engineering requirements, e.g.:

• L. G. Silano (ed.). Bridge inspection and Rehabilitation - A Practical Guide (John Wiley & Sons, Inc., 1993), 288 pp

Factors acting on bridge during Factors acting on bridge during their servicetheir service

• Bridge structures are subjected to many types of loadings and other influences resulting both from the live loads (mostly traffic effects) and exposure of the structures to the weather and environmental effects of various nature. The most important factors acting on bridges during their service are schematically shown in Fig. 3.1.

The most important factors acting on The most important factors acting on bridges during their servicebridges during their service

Deterioration and bridge damages Deterioration and bridge damages classificationsclassifications

• The classification relating to concrete bridges was developed within the framework of Reunion International des Laboratoires d'Essais et de Recherches sur les Materiaux et les Construction (RILEM 1991)

• The factors leading to bridge deterioration can be classified into four fundamental groups: (A) inner factors, (B) traffic load factors, (C) weather and environmental factors, (D) maintenance factors

InnerInner factorsfactors

are immanently connected with the structure itself. It means that the structure may contain some factors of degradation or causing special sensitivity to damage, e.g.:

• inadequacy of the design (including structural system) and building,

• quality of the materials,

• the age, etc.

• The age of bridges is a very important factor. In Europe, the life of the structural elements is generally between 60 and 120 years and is in accordance with many practical cases.

• On the other hand, however, a bad adaptation of the design to the service conditions or insufficient geometrical parameters (e.g., too small clearance) may endanger the good behavior of the structures

• It should also be pointed out that, in general, the bridge structural systems with discontinuous deflection line (e.g., the bridges of simple span type) are more sensitive to damage from traffic load than those with continuous deflection line (e.g., the bridges of continuous span type).

• This is due to the dynamic effects (impacts) produced by traffic load in the numerous expansion joints representing structural discontinuity as shown schematically in Fig. 3.2

Fig. 3.2. Structural system with (a) discontinuous and (b) continuous deflection line

TrafficTraffic loadload factorsfactors• are of external nature and are related to the exploitation

conditions. • It should be emphasized that the intensity and speed of the

road traffic as well as the concentration of loads by the heavy vehicles have enormously grown during the last few decades and therefore, many old bridges are not adapted to support, without damage, such an evolution, especially because of the evident increase of dynamic effects.

• It should also be noticed that "if the static load per axle does not grow, the axles are always nearer and so the load becomes more concentrated, which is very disadvantageous for certain elements of the bridges".

• The last remark, cited according to Ch. Van Begin, concerns especially bridge deck elements.

• The exploitation conditions may also be changed when the bridge is subjected to other types of live loads than predicted in the design.

• For instance, the old railway bridges were designed for operating under steam locomotive traffic and when the railway traction was modernized from steam to electric, many bridges, especially masonry ones, are shown to be damaged due to the different motion characteristics of electric locomotives (e.g., an evident growth of lateral dynamic effects)

WeatherWeather andand environmentalenvironmental factorsfactors

• are of climatic and atmospherically nature. • Some of them (e.g., season and diurnal

temperature changes, rainfalls or wind pressure) may be classified as objective ones, i.e., the factors directly independent of human activity in the domain of bridge engineering,

• while the others (e.g., atmospheric pollutions, aggressive chemicals in underground water or in rivers, effects of de-icing salts on structures) are dependent on human activity in the bridge engineering itself and in the other domains of technical activity.

• It should also be emphasized that the bridges, in contradistinction to many other structures (e.g., buildings of various types), are generally not covered by roofs or other protection elements and therefore, they are directly subjected to weather and environmental effects.

• These effects are, in many cases, more important for bridge durability than traffic load effects.

• Moreover, only certain factors are included in the design calculations, such as temperature changes or wind pressure, which usually belong to the standard design parameters.

• Majority of the other weather and environmental factors are not generally considered as design parameters and it is either impossible or very difficult to predict their development in time and harmful influence on the structures (e.g., intensity of atmospheric pollutions or aggressive chemicals in rivers)

MaintenanceMaintenance factorsfactors• are entirely related to the quality and intensity of

preservation measures, such as anti-corrosive protection, current conservation works, cleaning, etc.

• Maintenance is, in many cases, a decisive factor influencing bridge durability; inadequate routine maintenance leads, in general, to bridge degradation even if the structure is well constructed with the use of structural materials and equipment elements of high quality.

• Therefore, maintenance factors belong to those depending on human activity in the bridge engineering itself

ClassificationClassification

• Classification of factors leading to bridge deterioration performed according to the basic criteria denoted above by A, B, C, D and I, II is presented in Table 3.1.

TableTable 3.13.1 Classification of factors Classification of factors leading to bridge deterioration.leading to bridge deterioration.

A. Inner factors; I. Objective• A. I.1. The age of the bridge structure

A. Inner factors; II. Subjective• A.II.1. Quality of the study• A.II.2. Structural system itself--- sensitive to damage• A.II.3. Adequacy of the design to the actual service

conditions (including geometrical parameters)• A.II.4. Quality of the construction works at every stage• A.II.5. Quality of the structural materials and bridge

equipment elements (e.g., insulation expansion joints, drainage system elements, etc.)

B. Traffic load factors; II. Subjective (only)• B.II.1. The frequency, speed and concentration of

traffic loads (especially the heavy vehicles)• B.II.2. Dynamic effects (including fatigue damage

mostly in steel bridges)• B.II.3. Car or other accidents on the bridge• B.II.4. Overloading by the heavy vehicles• B.II.5. Impacts produced by the oversized vehicles

C. Weather and environmental factors; I. Objective• C.I.1. Atmospheric falls (e.g., rainfalls, snowfalls)• C.I.2. Variation of the water level in the rivers, straits, gulfs, etc.• C.I.3. Ice-float run-off and its pressure on bridge piers• C.I.4. Wind pressure and its effects on structural and secondary bridge

elements• C.I.5. The earth movements (including seismic effects)• C.I.6. Diurnal and season variation of ambient temperature leading to the

uniform thermal deformation of the bridge structures• C.I.7. Direct solar radiation on the bridge and other thermal effects

leading to the non uniform heat distribution in the bridge structures• C.I.8. Chloride attack originating from the action of sea water

The factors denoted by C.I.1, to C.I.5. may be in some cases of a catastrophic nature, e.g., flood, hurricane, earthquake, etc.

C. Weather and environmental factors; II. Subjective• C.II.1. Chloride attack originating from the use of de-icing

products (mainly salts) on road under the bridge• C.II.2. Frost destruction of concrete• C.II.3. Atmospheric falls containing aggressive chemicals

(e.g., "acid rains")• C.II.4. Penetration of CO; from atmosphere (carbonation

effect in concrete)• C.II.5. Aggressive chemicals in rivers and underground

water• C.II.6. Vagabond currents (e.g., in bridge structures over

the railroads with electric traction of direct current)• C.II.7. Fire

D. Maintenance factors; II. Subjective (only)• D.II.1. Structural, material and bridge equipment solutions easy or

difficult for maintenance works• D.II.2. Quality of inspection of any type (e.g., cursory, detailed, special

inspections)• D.II.3. Quality of routine maintenance works (e.g., cleaning, repair,

replacement of some elements of bridge equipment, etc.)• D.II.4. Renewal of anti-corrosive protection of structural and other

steel elements• D.II.5. The use of de-icing salts on the bridge roadway itself D.II.6.

Quality of the drainage system and its efficiency• D.II.7. Quality of the pavement on roadway (e.g., roughness,

permeability, etc.) or railway (e.g., geometrical tolerance)• D.II.8. State of pipelines of any types and other installations located on

the bridge

Bridge equipment elementsBridge equipment elements• It should be emphasized that besides the quality of the

structural materials, the bridge equipment elements (i.e., industrial components such as bearing devices, insulation, expansion joints, etc.) belong, in majority of the cases, to the decisive factors influencing bridge durability.

• In general, damage of bridge structures has its origin in permeable insulation of deck slabs, water infiltration through expansion joints and ineffective drainage system.

• Therefore, the use of the above mentioned elements with a high quality is technically and economically justified.

• In contemporary bridge engineering, the cost of all equipment elements generally varies from 15-20% of the total construction cost of the bridge, but in some cases, it may reach even 30-40%

• For instance, permeable insulation layer of deck slabs leads to water infiltration through concrete and the leaks appear on the bottom faces of these slabs and vertical faces of the girders.

• It should be noticed that rainwater is generally alkaline and dissolves Ca(OH)2 crystals in cement mortar, washing them out. It leads to a more porous structure of concrete and is very often manifested by the white efflorescences and even small stalactites on the bottom surface of the deck slabs

Many other damages caused by the low quality of bridge equipment elements or their inadequate solutions can be listed, such as

• lack of outlets for water behind the abutments causing leaks and washing out of Ca(OH)2 through the walls,

• leaking expansion joints and lack of their adequate dewatering,

• improper fixation of water outlets, • corroded rainwater pipes, • too short intermediate slabs between spans and

abutments, etc