Unit - 6

Sub-Structure

6.1 Sub-Structure

Definition:

• The part of the bridge that helps the superstructure and distributes all bridge hundreds to below-floor bridge footings.
• The substructure includes the part of the bridge that helps the complete shape at the given surrounding soil.
• There are various designs because of the one of a kind soil situations for every bridge webpage and the one of a kind weights of the systems for every project.
• In a few cases, the character of the superstructure can even impact the selection of basis type, mainly whilst essential substructures are used. Designers are cautioned to contain certified geotechnical engineers early within side the bridge layout system to assist pick out the precise basis type.

Fig: Sub-structure

Key takeaways:

• The part of the bridge that helps the superstructure and distributes all bridge hundreds to below-floor bridge footings.

6.2 Types of foundations & their choice

• Foundation: The basis of a bridge shape creates a easy transition permitting the inner forces to waft among the bridge and the ground. Foundations are the ‘bridges’ or hyperlinks among the bridge and the ground.
• There are surely best kinds of bridge foundations – even though every has many variations – ‘spread’ foundations and ‘piled’ foundations. Both sorts need to switch forces into the soil below the bridge.

• The bridge basis is specifically crucial or essential because they need to hold the complete load of the bridge and the site visitors masses that it's going to byskip on. A bridge basis is the component constructed below the pier or abutment and over the essential soil or rock.
• The masses dispatched through the rules to the subordinate soil ought to now no longer reason soil shear failure or harming agreement of the superstructure. Here it's far mentioned approximately the bridge basis, bridge basis creation manner and varieties of bridge basis. Foundation is the considerable structural piece of bridges and it additionally the primary thing or phase a part of the bridge.
• It receives the masses from the piers or abutments and actions it to the soil. Reason for basis is to deliver the weight of bridge over an full-size bearing place and provide solidness of bridge in opposition to agreement and shifting. It is given effectively profound with the intention that it now no longer inspired through the scouring.

Spread Foundation:

• Spread foundations are as an alternative just like the snowshoes you may put on to save you sinking into deep snow – the stereotype is sort of a tennis racquet – in reality the French time period.
• The precept of a variety basis applies in case you had been ever unlucky sufficient to locate yourself stuck in quicksand. The exceptional recommendation isn't to conflict however to lie flat and nonetheless at the floor to try and unfold your weight. If no person is round to assist pull you out then try and swim – quicksand is liquefied sand and so is a good deal denser than water. Swimming in it is going to be very tough paintings however it can keep your life.

Shallow vs Deep Foundation

• Construction You don’t ought to be an architect to parent the comparison among a shallow basis and a deep basis. In any case, profundity isn’t the lone difference among the two. Every approach actions the weight to the floor in an sudden way. Shallow foundations often have a extensive base, which then, at that factor actions the load of the weight onto the topsoil. With a shallow basis, the real soil issues approximately the concern.
• Deep foundations are usually skinny and infiltrate through the pinnacle soil to deeper extra grounded layers of soil. Here, the full-size majority of the assist likewise comes from the grinding of soil pushing towards the perimeters of the basis.

Battered Piles

• This is the least complex strategy for underwater piling. Rather than a solitary pillar, battered piles utilize a few, similar to a curved fork. The piles are made by the profundity of the water. They are then dropped into the water from a canal boat where they are crashed into the delicate mud. The “tines” of the battered piles spread the weight in a few ways to offer most extreme help. Battered piles are normally utilized for more modest bridges in shallower water.

Key takeaways:

• The basis of a bridge shape creates a easy transition permitting the inner forces to waft among the bridge and the ground. Foundations are the ‘bridges’ or hyperlinks among the bridge and the ground.

6.3 Open, Pile and well foundation

Open foundation:

A shallow basis is appropriate for slight top shape, dry floor and difficult soil strata or stone, and so forth wherein the whole shape agreement might be inside ideal limits and the assisting soil strata is to be had inside 1.five to a few m under the mattress Level of the watercourse and while the scouring is minimum. This is greater most cost-efficient than a deep basis.

This sort of basis may be categorised into-

1. Spread foundation:

This sort of bridge basis is greater appropriate for slight top shape, dry floor and difficult soil strata or stone, and so forth wherein the whole shape agreement might be inside ideal limits and the assisting soil strata is to be had inside 1.five to a few m under the mattress Level.

B.    Raft foundation:

This kind of bridge basis is appropriate for the bridge wherein gentle clay and silt and the difficult soil isn't to be had inside affordable depth (1.five to 2.five m) underneath the river bed. It is pleasant appropriate in conditions wherein the allowable bearing ability of the soil is low and wherein is a opportunity of unequal agreement because of heavy load.

C.   Grillage foundation:

This sort of bridge basis is used to transmit heavy hundreds from substructure to the soils wherein the bearing ability is low. This is used to avoids deep excavations and gives the vital vicinity at the bottom to lessen the depth of stress to the assisting vicinity. This sort of basis is made of rolled metal joists (grillage beams) supplied in unmarried or double tires and positioned at a concrete pad.

Pile foundation:

• Pile basis: This kind of bridge basis is appropriate wherein the aid from the soil strata isn't sufficient, constructional or financial situations make it important to transmit hundreds of systems to strata which are past the attain of shallow foundations. Not handiest for helping the structure, however piles also are used to assist face up to uplift, overturning, and lateral forces.
• Pile foundations are built via riding finished and uninteresting method. In the case of the riding method, the gadgets are pushed into the desired founding degree or tough strata.
• Drilling in after which riding tubes packed with concrete. The tubes will be packed with concrete in special ways – they may be stuffed for the duration of or earlier than withdrawal, or via drilling unlined, partially covered, or completely covered boreholes earlier than being packed with concrete.
• A not unusualplace sort of pile is the “pushed pile” – those are normally metallic piles hat are knocked into the floor like big nails pushed into wood through hammering. But. The very last desire of pile relies upon at the floor situations and soil strata. If there may be mattress rock a few manner down then the piles may be pushed or forged in order that the masses are taken immediately to the rock – they may be referred to as stop-bearing piles.
• Bored piles are generally stop bearing with every so often pretty big diameters. However if there may be no bedrock close to sufficient to the floor then the piles can be pushed or forged into stiffer floor. The piles are then designed to transmit the weight to the floor through the friction among the surfaces of the pile and the floor. Driven piles can be stop bearing or friction piles or a mixture of both. The sources on this phase will describe a few applications, offer illustrations and examine the utility to brief span modular metallic bridges.

Fig: Pile foundation

Well foundation:

• Well basis is a form of deep basis that's usually furnished under the water degree for bridges. Cassions or properly had been in use for foundations of bridges and different systems because Roman and Mughal periods. The term ‘cassion’ is derived from the French phrase caisse this means that field or chest. Hence cassion way a field like structure, spherical or rectangular, that's sunk from the floor of both land or water to a few preferred depth.
• Well foundations are a kind of deep basis this is commonly supplied under the water stage for bridges; caissons or wells were used for foundations of bridges and different systems due to the fact Roman and Mughal instances due to the fact it's miles greater proper whilst the inspiration is subjected to huge lateral forces.
• The creation concepts of the powerful basis are similar to traditional wells sunk for underground water. The basis has been utilized in India for masses of years, i.e. the famous Taj Mahal in Agra stands on properly basis.

Shapes of Wells:

The common types of well shapes are:

(i) Single circular

(ii) Twin circular

(iii) Dumb well

(iv) Double-D

(v) Twin hexagonal

(vi) Twin octagonal

(vii) Rectangular.

Description of Parts (Elements) of Well:

1. Staining: It is the wall or shall of the well, manufactured from R.C.C. And which switch the burden to the curb. It acts as a enclosure for excavating the soil for the penetration of well.

2. Curb: It is a R.C.C. Ring beam with metal reducing facet below. The cross- segment of the cut back is wedge formed which enables the sinking of the properly. The cut back helps properly stening. The cut back is saved barely projected from the stoning to lessen the pores and skin friction.

3. Cutting facet: It is the bottom a part of the properly cut back which cuts the soil all through sinking.

4. Bottom plug: After crowning glory of properly sinking the lowest of properly is pluged with concrete. The backside plug that is restricted with the aid of using the properly cut back acts as a raft towards soil strain from below.

5. Back fill: The properly is dewatered after putting of the lowest plug and it's far backfilled with the aid of using sand or excavated material.

6. Top plug: It is a concrete plug furnished over the filling within the properly.

7. Well cap: It is a R.C.C. Slab furnished on the pinnacle of stening to transmit the burden of superstructure to the stening and over which pier is laid. The minimal thickness of the slab is ready 750 mm.

Key takeaways:

• Pile foundations are built via riding finished and uninteresting method. In the case of the riding method, the gadgets are pushed into the desired founding degree or tough strata.

6.4 Pneumatic Caissons

• A pneumatic caisson is a watertight container or cylinder-like shape this is closed on the pinnacle and open on the bottom, resting at the mattress of the waterbody. They are used for underwater production of foundations for bridge piers, abutments in rivers, and foundations for huge multi-tale buildings.
• They are designed to hold water out of the development sector and act as a seal that maintains the internal of the caisson dry for employees to perform paintings safely. The internal of the caisson is stored dry with the aid of using the usage of compressed air to pressure water out of the shape.
• This manner creates an hermetic operating chamber in which production activities, consisting of excavations, may be achieved safely. Pneumatic caissons are perfect for hard conditions in which it isn't always feasible to perform moist floor excavations withinside the open. However, this technique is complex, time-consuming, and comparatively high priced while in comparison to different kinds of caissons.

Advantages:

• The surrounding groundwater and soil is least affected because the compressed air fed into the operating chamber is managed to be same to the stress of groundwater
• Pneumatic caissons may be sunk in lots of exceptional soil conditions
• No transient earth maintaining systems are required because the caissons themselves grow to be the very last underground structure

Key takeaways:

• The surrounding groundwater and soil is least affected because the compressed air fed into the operating chamber is managed to be same to the stress of groundwater

6.5 Cofferdams

• A cofferdam is an enclosure constructed inside a frame of water to permit the enclosed region to be pumped out. This pumping creates a dry operating surroundings in order that the paintings may be achieved safely. Cofferdams are generally used for creation or restore of everlasting dams, oil platforms, bridge piers, etc., constructed inside or over water.
• These cofferdams are generally welded metal systems, with additives including sheet piles, wales, and move braces. Such systems are generally dismantled after the development paintings is completed.

Uses

• For dam production, cofferdams are generally constructed, one upstream and one downstream of the proposed dam, after an opportunity diversion tunnel or channel has been supplied for the river waft to skip the muse place of the dam.
• These cofferdams are normally a traditional embankment dam of each earth- and rock-fill, however concrete or a few sheet piling additionally can be used. Usually, upon finishing touch of the dam and related structures, the downstream coffer is eliminated and the upstream coffer is flooded because the diversion is closed and the reservoir starts to fill.
• Depending at the geography of a dam site, in a few applications, a "U"-fashioned cofferdam is used withinside the production of 1 1/2 of of a dam. When complete, the cofferdam is eliminated and a comparable one is created on the alternative facet of the river for the development of the dam's different 1/2 of. The cofferdam is likewise used occasionally withinside the shipbuilding and deliver restore industry, whilst it isn't always sensible to position a deliver in drydock for restore paintings or modernization.
• An instance of such an utility is the lengthening of ships. In a few instances a deliver is genuinely reduce in even as nevertheless withinside the water, and a brand new phase of deliver is floated in to extend the deliver. The reducing of the hull is achieved inner a cofferdam connected immediately to the hull of the deliver; the cofferdam is then indifferent earlier than the hull sections are floated apart.
• The cofferdam is later changed even as the hull sections are welded collectively again. As luxurious as this can be to accomplish, the usage of a drydock is probably even greater luxurious. See additionally caisson.
• A 100-ton open caisson that changed into decreased greater than a mile to the ocean ground in tries to forestall the waft of oil withinside the Deep water Horizon oil spill has been known as a cofferdam. A cofferdam over 1 mile lengthy changed into constructed to allow the development of the Livingstone Channel withinside the Detroit River Island.

Key takeaways:

• The cofferdam is later changed even as the hull sections are welded collectively again. As luxurious as this can be to accomplish, the usage of a drydock is probably even greater luxurious. See additionally caisson.

6.6 Abutment

• An abutment is the substructure on the ends of a bridge span or dam assisting its superstructure. Single-span bridges have abutments at every stop which give vertical and lateral guide for the span, in addition to performing as preserving partitions to face up to lateral motion of the earthen fill of the bridge approach.
• Multi-span bridges require piers to guide ends of spans unsupported through abutments Dam abutments are usually the perimeters of a valley or gorge, however can be synthetic that allows you to guide arch dams which includes Kurobe Dam in Japan. The civil engineering time period may discuss with the shape assisting one aspect of an arch, or masonry used to face up to the lateral forces of a vault. The impost or abacus of a column in classical structure may function an abutment to an arch.

6.7 Piers & Wing walls

Piers:

• The intermediate support for the super structure of a multi span bridge are known as piers.
• A pier essentially consists of two parts i.e. column shaft and foundation.

Types of pier:

1. Solid pier
2. Open pier

Wing wall:

• In a bridge, the wing partitions are adjoining to the abutments and act as keeping partitions. They are commonly built of the identical fabric as the ones of abutments. The wing partitions can both be connected to the abutment or be impartial of it. Wing partitions are supplied at each ends of the abutments to preserve the earth filling of the approaches.
• Their layout relies upon upon the character of the embankment and does now no longer rely upon the sort or elements of the bridge.
• The soil and fill helping the roadway and technique embankment are retained with the aid of using the wing partitions, which may be at a proper perspective to the abutment or splayed at specific angles. The wing partitions are commonly built on the identical time and of the identical substances because the abutments.

Key takeaways:

The intermediate support for the super structure of a multi span bridge are known as piers.

6.8 Their types general design

Wing walls can be classified according to their position in plan with respect to banks and abutments. The classification is as follows:

1. Straight wing walls: used for small bridges, on drains with low banks and for railway bridges in cities (weep holes are provided).
2. Splayed wing walls: used for bridges across rivers. They provide smooth entry and exit to the water. The splay is usually 45°. Their top width is 0.5 m, face batter 1 in 12 and back batter 1 in 6, weep holes are provided.
3. Return wing walls: used where banks are high and hard or firm. Their top width is 1.5 m and face is vertical and back battered 1 in 4. Scour can be a problem for wing walls and abutments both, as the water in the stream erodes the supporting soil.

6.9 Principles (empirical)

• Piers are maximum normally made from concrete, masonry or handled timber, and set up into organized holes or shafts.
• Piers can serve a comparable motive to piles, however aren't set up through hammers and feature the potential, if primarily based totally on a solid substrate, to assist a extra load. Pier shafts were excavated with widths of greater than 1.eight m and depths of greater than 30 m , able to helping high-upward push buildings.
• Piers also can be utilized in foundations as a way of elevating a shape from the ground, mainly if the shape is on a slope or close to a huge frame of water. They vary from traditional foundations in that they assist the structural load at some of awesome points. This commonly calls for much less excavation and soil disruption than different styles of foundation.
• The best cross-phase of a pier is rectangular or rectangular, despite the fact that different shapes are not unusualplace. In medieval architecture, drum piers (round supports), cruciform piers (cross-shaped), and compound piers (blended with pilasters, columns or shafts) had been not unusualplace architectural elements. Compound piers had been regularly used to shape an arcade of arches, assembly the ribs descending from the vaults above.
• The decrease phase of a pier can be widened to higher distribute the downward stress of a specially huge superstructure. Piers used for helping bridges are regularly set up withinside the shape of caissons, which might be sunk into function to the bearing stratum through excavating from the interior. For greater information, see Caisson.
• The term 'pier' can also be used to consult a marine shape that tasks right into a frame of water, supported through a sequence of columns, commonly permitting docking of marine craft, however extensively utilized for pleasure. The open shape of piers lets in water to go with the drift underneath, in assessment to greater stable wharfs or quays.

Key takeaways:

• Piers are maximum normally made from concrete, masonry or handled timber, and set up into organized holes or shafts.

6.10 Super Structure

• Definition: The part of the bridge that helps the deck and connects one substructure detail to another.
• Girders: Girders joins all of the pile caps collectively via way of means of extending over them. Girders also are known as beams, and provide help to the deck. This may be a unmarried span, or maybe more than one spans becoming a member of all of the bents, depending on the period of the bridge. Girders normally have a truss layout to enhance pressure and cargo resistibility. Hence, stress is speedy exceeded toward the foundation. Girders are mainly crafted from steel or concrete.
• Bearings: Bearings are structural individuals able to moving masses from the deck to the substructure. These displace stresses and cargo to the piers through the girders to permit motion among components of a bridge. The motion may be linear in addition to torsional. Bearings offer allowance among those components.
• Trusses: Trusses are made via way of means of becoming a member of triangular additives to divide masses and bending moments through the bridge. Some sorts are easy trusses, suspension, and additionally cantilever trusses. The truss community affords a floor for transportation which may be constructed as a deck truss, pony truss, or through truss. Each truss differs in how the visitors will pass at the bridge. Decks: Decks get the direct visitors load. Some primary decks may be product of concrete and additionally from steel. These encompass tour or on foot paths, drainage systems, curbs, growth additives, sidewalks and method slabs.
• Barriers: Mainly as a protection and safety feature, bridges have obstacles on the edges in their decks. These may be mainly designed fixtures, ropes, rails, fences, or concrete partitions for higher aesthetics.
• Arches: A bridge with arches has a whole lot of strength. Arches can assist manage the protection and cargo bearing cappotential of the bridge. The amount of arches and substances used for production could be very important. A area connecting the bridge pillars and deck beam is known as the spandrel. There may be open or closed spandrels relying at the arch layout.

Key takeaways:

The part of the bridge that helps the deck and connects one substructure detail to another.

6.11 Different structural forms

Basic forms

There are six basic bridge forms: the beam, the truss, the arch, the suspension, the cantilever, and the cable-stay.

Beam:

The beam bridge is the maximum not unusualplace bridge form. A beam contains vertical masses via way of means of bending. As the beam bridge bends, it undergoes horizontal compression at the top. At the equal time, the lowest of the beam is subjected to horizontal tension. The helps deliver the masses from the beam via way of means of compression vertically to the foundations.

Truss:

A single-span truss bridge is sort of a virtually supported beam as it incorporates vertical masses via way of means of bending. Bending results in compression withinside the pinnacle chords (or horizontal members), anxiety withinside the backside chords, and both anxiety or compression withinside the vertical and diagonal members, relying on their orientation. Trusses are famous due to the fact they use a highly small quantity of cloth to hold highly huge masses.

Arch

The arch bridge contains masses in the main via way of means of compression, which exerts on the muse each vertical and horizontal forces. Arch foundations have to consequently save you each vertical settling and horizontal sliding. In spite of the extra complex basis design, the shape itself typically calls for much less fabric than a beam bridge of the equal span.

Suspension:

A suspension bridge consists of vertical masses through curved cables in anxiety. These masses are transferred each to the towers, which convey them with the aid of using vertical compression to the ground, and to the anchorages, which should face up to the inward and every now and then vertical pull of the cables. The suspension bridge may be considered as an upside-down arch in anxiety with handiest the towers in compression. Because the deck is hung withinside the air, care should be taken to make certain that it does now no longer flow excessively beneathneath loading. The deck consequently should be both heavy or stiff or each.

Key takeaways:

A single-span truss bridge is sort of a virtually supported beam as it incorporates vertical masses via way of means of bending.

6.12 Rating and Maintenance

Rating and Maintenance of Bridges:

The renovation of bridge way the up-preserving of the bridge additives in suitable and serviceable circumstance for you to make sure an extended existence of the bridge as envisaged on the time of its layout and construction. Even if the bridges are properly designed and nicely constructed, periodic renovation, if needed, may be very important to hold them in suitable serviceable circumstance. Therefore, the bridges ought to be often inspected and nicely maintained.

The matters which require immediate attention and maintenance may be broadly stated as below:

(i) Approaches,

(ii) Protective Works,

(iii) Foundation,

(iv) Piers, abutments and wing walls,

(v) Bearings,

(vi) Superstructure,

(vii) Expansion Joints,

(viii) Wearing Coat,

(ix) Drainage Spouts,

(x) Hand Rails,

(xi) Foot Paths,

(xii) Utility Services.

Classification of Bridge Maintenance:

The bridge maintenance may be broadly classified into two type:

(a) Routine maintenance or annual maintenance

(b) Quarterly maintenance

6.13 Methods & Techniques of rating of existing bridges Inspection

1.Flexible bridge rating method

• Several bridge inspection requirements and situation evaluation practices were advanced across the globe. Some practices appoint 4 linguistic expressions to fee bridge factors whilst different practices use 5 or six, or undertake numerical rankings consisting of 1 to 9.
• This studies introduces a situation score technique that may perform below one-of-a-kind situation evaluation practices and account for uncertainties in situation evaluation by the Evidential Reasoning (ER) idea.
• The technique gives flexibility in phrases of the use of default factors and their weights or deciding on opportunity set of factors and situation score schemes. The carried out ER method money owed for uncertainties in situation score through treating the situation tests as probabilistic grades in preference to numerical values.
• The ER method calls for the project of preliminary fundamental ideals or possibilities, and commonly those preliminary ideals are assigned through an expert. Alternatively, this studies integrates the Monte Carlo Simulation (MCS) approach with the ER idea to quantitatively estimate the fundamental possibilities and to provide sturdy universal bridge situation rankings.
• The proposed technique is novel to the literature and has the subsequent features:

(1) bendy and may be used with any variety of bridge factors and any trendy of situation grades;

(2) intuitive and easy paired contrast approach is carried out to assess weights of the bridge factors;

(3) the MCS approach is incorporated with the ER method to quantify uncertainties related to the stochastic nature of the bridge deterioration process;

(4) the technique can characteristic with restricted statistics and may include new proof to replace the situation score;

(5) the very last score includes a couple of situation grades and is produced as a disbursed probabilistic evaluation reflecting the situation of the bridge factors collectively.

The proposed technique is illustrated with a actual case study, and ability destiny studies paintings is identified.

2.Stochastic method

• Bridge situation score is used to make essential selections concerning wishes evaluation and price range allocation. This take a look at analyzes using the bushy good judgment method to conquer uncertainty troubles related to the bridge situation evaluation process.
• The evaluation famous some of sensible problems related to the software of the bushy arithmetic to expand an usual bridge situation score.
• An opportunity probabilistic method to charge the bridge factors deliberating the uncertainty problem is advanced. The Analytic Hierarchy Process is followed to assess the structural significance of the numerous bridge factors. A approach is proposed to combination the situation score and the structural significance of the bridge factors into an usual bridge situation score.
• The advanced method makes use of the precise visible inspection consequences to carry out bridge situation score and blends flawlessly with the famous Markov chain method to version deterioration.

Key takeaways:

• Several bridge inspection requirements and situation evaluation practices were advanced across the globe. Some practices appoint 4 linguistic expressions to fee bridge factors whilst different practices use 5 or six, or undertake numerical rankings consisting of 1 to 9.

6.14 Repairs

Expansion Joint Repair and Replacement:

• Bridge growth joints permit visitors to hold seamlessly throughout a bridge structure. They additionally assist to house motion of the bridge, shrinkage, and versions in temperature that purpose the bridge to clearly make bigger and contract.
• However, as a bridge expands and contracts, the motion can bring about concrete cracking and spalling, main to leaks and the eventual failure of the growth joint.
• Any proof of cracking and spalling alongside growth joints ought to warrant restore or replacement. Expansion joints are one of the first factors of the bridge that need to be repaired to make bigger the bride’s lifespan. Monitoring and repairing those joints is an crucial step withinside the proactive preservation of a bridge.

Structural Steel Girder Rehabilitation:

• Structural metallic is extensively utilized in creation tasks and is one of the maximum generally used substances for bridge girders. While metallic is a flexible and sturdy cloth whilst nicely maintained, it is able to be afflicted by corrosion, fatigue, deformation, and rest whilst subjected to strain over time.
• If there may be any proof of those symptoms, a bridge's structural metallic can also additionally require rehabilitation. Structural metallic rehabilitation entails the straightening of bridge girders and different contributors if the bridge suffers effect harm or immoderate corrosion because of incorrect drainage of water from the bridge deck.
• This technique can also additionally contain welding and heating, changing bridge bearings, or make emergency repairs, relying at the diagnosis.

Substructure Replacement:

• Substructures are commonly crafted from concrete, steel, and wood, in a few cases. Each fabric is susceptible to special varieties of deterioration inclusive of erosion and corrosion.
• Wooden substructures will also be prone to fungal decay and different herbal processes. Experts can decide if a bridge is affected by a lack of bearing ability primarily based totally at the substructure’s footings and pilings, or is struggling a lack of ability primarily based totally at the corrosion of the bridge’s columns and piers.
• If there's any proof of deterioration, cracking, effect harm, shear harm or inadequate seismic ability, substructures may also want to get replaced or strengthened with new materials.

Superstructure Replacement:

• A bridge’s superstructure can go through many extraordinary forms of harm, each from the factors and from normal use over time. When figuring out among rehabilitation or alternative, each the structural integrity and visitors manipulate barriers need to be taken into consideration. For instance, if transient visitors regulations to facilitate bridge alternative isn't feasible, then rehabilitation can be the higher solution.
• On the flipside, while harm is intense sufficient that the superstructure can't be repaired or rehabilitated, the superstructure may also want to be demolished and changed. Superstructures are normally changed with new concrete slabs. UHPC field-solid connections also are a great restore solution. It’s been used withinside the US for over 10 years. Since 2006, over one hundred eighty field-solid UHPC initiatives were deployed, with over a hundred bridges withinside the USA with the aid of using 20 DOTs and with over eighty bridges in Canada with the aid of using five Provincial Ministries of Transportation.
• Visit this hyperlink for an interactive map showing bridges throughout americaA and Canada the use of UHPC. Also utilized in Accelerate Bridge Construction, field-solid UHPC connections for precast bridge factors have established to be the most powerful connection of the bridge deck system, wherein connections constituted of different cementitious substances was once the weakest hyperlink of a bridge. The FHWA posted a TechNote at the Design and Construction of Field-Cast UHPC Connections.

Key takeaways:

• Substructures are commonly crafted from concrete, steel, and wood, in a few cases. Each fabric is susceptible to special varieties of deterioration inclusive of erosion and corrosion.

6.15 Maintenance

• Maintenance of present day bridge infrastructure gives many challenges.
• Transportation engineering and upkeep employees ought to hold across the clock provider to tens of thousands and thousands of human beings every yr even as preserving tens of thousands and thousands of cubic meters of concrete disbursed at some point of their facilities.
• This infrastructure consists of bridges. Presently simplest a restricted wide variety of correct and inexpensive strategies exist to check those systems for integrity and protection in addition to insure that they meet authentic layout specifications. No unmarried generation can discover all bodily anomalies in and underneath the concrete, those strategies in conjunction with statistics fusion can help withinside the following investigations, to call a few: Locating voids and delaminations in bridge pavements and scour round bridge aid columns. Determining place and sorts of reinforcing metallic in concrete Ensuring fine manage on new concrete installations
• Infrared thermography and ground-penetrating radar had been advanced to discover voids and delaminations in concrete systems consisting of bridge decks, highways and airport pavements. Being capable of discover voids and delaminations approach the structural renovation engineer can degree the real cracking and weakening of concrete pavements earlier than catastrophic disasters can occur.
• Concrete objects, consisting of bridges, emit strength primarily based totally upon absolutely the temperature of its surfaces and the floor temperatures are structured upon the inner situations of the concrete. These inner situations can encompass bodily situations like: Density modifications in concrete Voids due to erosion under the concrete slabs Horizontal delaminations due to rust enlargement of rusting inner reinforcing metallic.
• Infrared thermographic radiometer or “IR Imager” locates those anomalous thermal situations. This tool can degree loads of thousand of man or woman temperature factors in line with 2d and convert this facts to thermal maps or temperature photographs of the concrete. By finding anomalous regions, or temperature styles which fluctuate from the background “norm” on those photographs, educated engineers can discover the precise anomalous regions that would result in catastrophic failure of concrete and its assisting soil and backfill systems.
• Ground-penetrating radar offers facts precious in figuring out such traits as: goal material, voids, fluids, soil or backfill strata, and amount of reinforcing metallic present.

Key takeaways:

Concrete objects, consisting of bridges, emit strength primarily based totally upon absolutely the temperature of its surfaces and the floor temperatures are structured upon the inner situations of the concrete.

6.16 Corrosion

• The number one motive of corrosion of metallic bridges is the publicity of the metallic to atmospheric conditions. This corrosion is significantly improved because of marine (salt spray) exposures and business environments. The handiest corrosion prevention approach for those systems is to offer a barrier coating (paint).
• Changes in environmental safety policies have delivered approximately transformation of the method to corrosion safety for metallic bridges. Until the mid- to late-1970s, surely all metallic bridges had been included from corrosion via way of means of a couple of skinny coats of lead- and chromate-containing alkyd paints carried out at once over mill scale at the fashioned metallic. Maintenance portray for prevention of corrosion become uncommon and usually become practiced on large bridge systems. Since the bulk of the metallic bridges withinside the interstate dual carriageway device had been built among 1950 and 1980, maximum of those systems had been firstly painted on this manner; therefore, a massive percent of the metallic bridges withinside the interstate device are included from corrosion via way of means of a coating device this is now past its beneficial provider life.
• Moreover, the paint device typically used for metallic bridge contributors consists of chromium and lead and may now not be used due to the results it has on human beings and the surroundings.
• The bridge engineers have a preference of both changing the lead-primarily based totally paints with a special coating or portray over the deteriorating areas. Removal of lead-primarily based totally paint incurs excessive prices related to the necessities to include all of the unsafe waste and debris. Developments include: (1) progressed and environmentally secure coating structures and

(2) methodologies to optimize the usage of those structures, such as “zone” portray (adjusting coating kinds and protection schedules primarily based totally at the aggressiveness of the surroundings inside special zones at the bridge). Overpainting strategies to put off the value of high priced paint elimination additionally were developed.

Key takeaways:

• The number one motive of corrosion of metallic bridges is the publicity of the metallic to atmospheric conditions. This corrosion is significantly improved because of marine (salt spray) exposures and business environments. The handiest corrosion prevention approach for those systems is to offer a barrier coating (paint).

6.17 Causes and prevention

Causes:

• Since the bulk of the metallic bridges withinside the interstate dual carriageway device had been built among 1950 and 1980, maximum of those systems had been firstly painted on this manner; therefore, a massive percent of the metallic bridges withinside the interstate device are included from corrosion via way of means of a coating device this is now past its beneficial provider life. Moreover, the paint device typically used for metallic bridge contributors consists of chromium and lead and may now not be used due to the results it has on human beings and the surroundings.
• The bridge engineers have a preference of both changing the lead-primarily based totally paints with a special coating or portray over the deteriorating areas. Removal of lead-primarily based totally paint incurs excessive prices related to the necessities to include all of the unsafe waste and debris.

Prevention:

• Cement concrete is a flexible constructing fabric and is the second one maximum fed on fabric withinside the world, after water. It is made the usage of Portland cement, coarse, and first-class aggregates, water and one or extra admixtures. Concrete is widely known for the convenience with which it's far made, for its capacity to be moulded in any form, and its excessive energy.
• The microstructure of concrete is such that it has capillary pores to the quantity of 28%, which relies upon fine of concrete and the presence of water on the time of blending of concrete. Concrete made with low w/c ratio is dense with decrease quantity of pores.
• These pores are created because of evaporation of extra loose water in the course of strengthening of concrete mass, and a concrete made with excessive w/c ratio may have pores inter linked and expand deep in the mass of concrete from its surface. More are the inter linked pores, extra is the convenience with which water can glide via the concrete (i.e. excessive permeability).
• The sturdiness of concrete is described as its capacity to carry out satisfactorily withinside the given publicity conditions, and it's far prompted with the aid of using the pore shape of the concrete. Inadequate sturdiness has been the motive of untimely screw ups of many concrete structures. The concrete undergoes deterioration because of corrosion of metallic reinforcement in concrete, sulphate assault, freeze-thaw assault, alkali-silica reaction, etc. Among them, the corrosion of metallic in concrete has been diagnosed as maximum extreme forms of assault answerable for deterioration of concrete.
• The corrosion of metallic consequences in growth in its quantity with the aid of using as much as 5-7 instances and the ensuing enlargement of metallic exerts tensile stresses in concrete upto approximately 70 MPa (ten thousand psi)  that's an awful lot much less than the tensile energy of concrete. These disruptive forces motive disintegration of concrete via improvement of cracks, delamination, and cracking main to lack of integrity of concrete, discount in load bearing capability and carrier existence of the bridges.
• The deformed carbon metallic is maximum susceptible to corrosion in comparison to standard carbon metallic. Before 1970's, simple carbon metallic reinforcement bars had been utilized in bridge structures. The use of deformed carbon metallic bars have come into use considering mid-70's. It isn't always the purpose of the writer to advocate using simple carbon metallic bars as reinforcement, however simplest to focus on the vulnerability of deformed carbon metallic bars to corrosion.
• A concrete bridge constructed throughout River Damodar in the course of mid 60's, the usage of simple carbon metallic bars as reinforcement, become examined these days with the aid of using CSIR-CRRI. No misery exhibited as cracks or spalling become observed at the bridge because of corrosion. Depth of carbonation (i.e. assault of carbon dioxide) become now no longer significant.

Key takeaways:

• Cement concrete is a flexible constructing fabric and is the second one maximum fed on fabric withinside the world, after water. It is made the usage of Portland cement, coarse, and first-class aggregates, water and one or extra admixtures. Concrete is widely known for the convenience with which it's far made, for its capacity to be moulded in any form, and its excessive energy.

6.18 Aesthetics

• A bridge makes up one detail of a dual carriageway or a metropolis street, which in flip is a detail withinside the grasp plan of a metropolis or a community. Hence, the characteristic of a bridge isn't always described through a bridge engineer.
• When the want arises to pass a river or a valley, or to attach points, the making plans requires the layout and production of a bridge. This want drives the cause of the bridge layout. The cause similarly defines the characteristic of the bridge. The characteristic of a bridge is hooked up primarily based totally on-site visitors making plans, along with socioeconomic and concrete research.
• This research discover how a great deal site visitors is expected for a sure layout existence of the bridge. The site visitors engineer determines the wide variety of lanes required primarily based totally at the quantity of the expected site visitors and the layout speed.
• The nearby topography and different nearby situations then decide the preferred geometry of the deck inclusive of the length, minimal span length, most grades, and minimal clearances. Once the characteristic of a bridge is determined, the bridge engineer selects the shape of the bridge to fulfill the given characteristic—as a result the motto “shape follows characteristic.” However, earlier than organising the shape of the bridge, the engineer have to recognize what cloth is to be had for the development of the bridge.

Key takeaways:

• A bridge makes up one detail of a dual carriageway or a metropolis street, which in flip is an detail withinside the grasp plan of a metropolis or a community. Hence, the characteristic of a bridge isn't always described through a bridge engineer.

References:

1. Pavement Design: Yoder and Witzak Wiley

2. Traffic Engineering: L.R.Kadiyali Khanna Publishers