Per Pa Ration of Bridge Project

8/2/2019 Per Pa Ration of Bridge Project

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CHAPTER 2

PERPARATION OF BRIDGE PROJECT

II. PREPARATION OF BRIDGE PROJECT:

After joining the Design Circle the initial phase of studying the literature is completed . Then the preparation of bridgeproject work should be taken in hand. Various stages in project preparation are described below. The following pointsneeds to be considered before preparation of project :-

II.1. SURVEY DATA -Scrutiny :

Scrutiny of survey data received from the field officers is the first step in Designs Circle, Survey data should be as per thechecklist given in I.R.C. clause 102 and as per Designs Circle Circular, Dated 18.09.74. the guidelines for the preparationof Survey data are issued by Design Circle under letter No.BC/CIR/93 dated 31.01.61.

The observations, certain clarifications, and/or additional data /information required if any communicated to the ExecutiveEngineer ,Road Project Division.

Thereafter ,the site inspection by the Superintending Engineer ,Designs Circle for the bridges having length more than60m is arranged and site is finalised. It is not necessary that site suggested by Road Project Division is approved . If somemore study of better sites is necessary, Superintending Engineer, Design Circle issues instructions for collectingadditional data .

Some important points to be seen in survey data are detailed below :

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(i) Alignment of the proposed road along with the new bridge . What are the alternatives tired and dependingon the standard of road whether geometry of road is wisely proposed or otherwise .

Typical sketch of right angled and skew crossing is shown in the sketch.Fig.II.1 SKEW AND SQUARE CROSSING

(ii) Cross section at different proper locations are taken , drawn and L/S and R/S are correctly marked .(iii) Information about dams ,weirs on u/s and d/s of the proposed bridge .

(iv) The possibility of subsequent changes in the catchments characteristics like afforestation , deforstation,Urban development etc.(v) The catchment area plan should be properly drawn and certified by the Executive Engineer Road Project

Division .(vi) Counter plan is to be attached. This is very important since it gives better idea about site from

consideration of outflanking, submergence of nearby village etc. Topo-sheet may be referred for feelingconfident about the site .

(vii) Nearness of village on u/s and d/s sides.(viii) The effect of afflux on areas in the vicinity. Limitation on afflux should be reported. Effect of submergence

should be studied .(ix) Trial pits are generally taken for a depth of 1.5 m to 2m only which do not give true picture of the founding

strata. Trial pits for sufficient depth or trial bores should be plotted to show different strata below bed todecide type of foundation .

(x) In case of navigational channels, the clearances (horizontal and vertical ) are not generally supplied withthe survey data which delays the project.

(xi) H.F.L. from enquiry should be realistic . Else it may lead to unnecessary high level bridge some times thecalculated discharge does not tally with Inglis discharge creating confusion .

(xii) O.F.L. is to be assessed properly for submersible bridges with due consideration to permissibleinterruptions to traffic as per IRC codes.

(xiii) The rugosity coefficients are properly taken to depict the exact nalla characteristics for bed and bank .(xiv) The value of silt factor reported is either by guess or by Laboratory test results should be considered more

reliable .

Thus detailed survey data obtained from the Road Project Division is scrutinised ,and clarification/additional information sought. Thus the work of project preparation start in Designs Circle .

While proceeding with the project, methodology proposed to be adopted for preparation of the projectshould be got approved from Superintending Engineer, Design Circle. Certain assumptions, type ofstructures considered to be proposed , method of analysis and design etc. need be crystallised beforedetailed proposal is prepared. This would save time as corrections in the calculations and on the drawingscan be minimised .

II.2 HYDRAULIC CALCULATIONS & HYDRAULIC DESIGN OF THE BRIDGE

Hydraulics is the essential feature of bridge design. Fair assessment of flood levels, and maximum flood dischargeexpected to occur at bridge site during design life of bridge, and maximum scour levels are essential aspects ofbridge hydraulics. The faulty determination of these parameters may lead to failure of structures. While doinghydraulic calculations attention should be paid to the following :

(1) The river cross section should be truly representative. The cross section should not be vitiated by artificial cutsetc.

If the bridge site is along the exiting natural crossing , the cross section for the hydraulics should be across thenearby natural undisturbed channel. The cross section within 100m U/S and D/S may be quite useful inaddition to the c/s at 250m D/S and U/S. Generally existing cross section of river is disturbed due to presenttraffic crossing the river. In case of disturbed cross sections , exact length of bridge can not be ascertained,hence cross section at 10 m D/S and U/S will give representation of site condition. For fixing up the location ofabutments, cross sections at 10m U/S and D/S should be used in such cases.

(2) Spill channels should be properly located, marked and created for .

(3) Appropriate coefficient of rugosity should be used . The same rugosity coefficient should not be used for bedand banks, as the nature of stream changes according to properties of material and vegetation growth etc.

(4) The reasonableness of computed velocity should be judged in relation to bed material. For example bouldersand low velocity do not generally go together.

(5) In tidal creeks the possibility of high tides and floods coinciding should be kept in view. In such cases dischargeby usual ways i.e. by Mannings formula may workout to be more than Inglis discharge. This difference will bemore as we approach the sea.

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(6) The adoption of either the observed H.F.L. obtained by local enquiry or the computed H.F.L as design levelshould be done judiciously. The observed H.F.L. may be affluxed by obstructions like rice fields, bounds,blocking of spill channels etc.

(7) Details of various levels are explained as below .

(i) HFL (observed) - Highest flood levels ever recorded. (50 years record)

(ii) HFL (Inglis) - Flood level giving Mannings discharge equal toInglis discharge .

(iii) HFL(Modified) - Flood level giving Mannings discharge equal to ModifiedInglis discharge .

(iii) O. F.L. - Ordinary flood level. This is level of floodwhen clearted by bridge without submergence will not give

more than permissible interruption to traffic during floods .

Maximum permissible interruptions

(i) Bridges on SH, MDR with interruption to traffic for 6 times a year and theperiod not exceeding 12 hours at a time .

(ii) Bridge on ODR, 6 times a year and not exceeding 24 hours at a time .(iii) Bridges on VR , 6 times a year and not exceeding 72 hours at a time.

Although record of rainfall exists to some extent, the actual record of rainfall is seldom available in suchsufficiency (50 years) as to enable the Engineer to infer precisely the worst flood conditions for designing

bridges. The current practice generally followed for calculating the discharge at the bridge site is by usingempirical formulae as detailed below for various regions .

(1) Inglis Formula (for Western Ghats and Tapi Vally )

Q = 7000 AA + 4

Where Q = Discharge in cusecsA = Catchment area in sq. miles.

(2) Modified Inglis Formula : (Upper parts of western Ghats Annual rainfall


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The discharge is then calculated at the assumed H.F.L. by using Mannings formula. The discharge calculatedby Mannings formula is tallied with the discharge obtained from above empirical formulae. By trial and error theH.F.L.is fixed .

The discharge calculated by the Mannings formulae is tallied with the discharge by above empirical formulaefor the Catchment Area up to the bridge site. In the areas where Inglis flood is not excepted, the dischargecalculated by the Mannings formulae is tallied with the one either Modified Inglis formula or Dickens formula. Ifthe discharge calculated by the Mannings formulae is less than the above empirical formulae discharge, the

H.F.L. is raised suitably to get the designed H.F.L. and vice -versa. The bridge designed on the basis ofH.F.L.so fixed.

(4) Discharge by Mannings :

The discharge calculated as above from Inglis /Modified Inglis formula has to fairly tally with the dischargecalculated by Mannings formula i.e. area-velocity method will use hydraulic characteristics of stream.

Hydraulic characteristics of the channel influencing the maximum discharge are,

(a) Velocity of flow ,(b) Slope of stream,(c) Cross sectional area of stream ,(d) Shape and roughness of stream.

Mannings Velocity V( in m/sec) = 1 R 2/3 S 1/2

nand Q = A x V

Wherer n = Rugosity coefficient depending on roughness of bed &bank values shall be as given in table -1. Fore more detailed description of

the value refer Open Channel Hydraulics by Ven Te Chow. The exactvalues are given in Table -I.

R = A i.e. Hydraulic mean depth .P

A = Wetted Area in m2

P = Wetted Perimeter in m.

S = Hydraulic gradient

Q = Discharge n m3 /sec.

A = area of cross section in m2

V = velocities is respective compartments .

The discharge determined with the Mannings formula at H.F.L. shall generally be within 2%, variation with respect toInglis or Dickens discharge. The river cross section is divided in to no. of compartments depending upon the bedcharacteristic and velocity & discharge is calculated for each compartment . Maximum velocity is then considered fordesign. Total discharge is taken as sum as all compartmental discharges. The discharge at O.F.L.may also becalculated from Mannings formula. Generally O.F.L. discharge is 25% to 30% of the discharge at H.F.L.This may not , be true in all the cases .

TABLE 1 : Value of Regosity Coefficient (n)

1 R 2/3 S 1/2

n in the formula V = n

SrNo. Surface (Natural Stream) Perfect Good Fair Bad

1. Clear, straight bank, no rift ordeep pools .

2. Same as (1) but some weeds &stones

3. Winding some poles andshoals, clear

4. Same as (3) but more ineffective slope and section5 Same as (3) but some weeds and

stones

0.025

0.030

0.035

0.040

0.033

0.0275

0.0330

0.040

0.045

0.035

0.030

0.035

0.045

0.050

0.040

0.033

0.040

0.050

0.055

0.045

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6. Same as (4) but stony section

7. Sluggish river reaches rather weedy

8. Very weedy reaches

0.045

0.050

0.075

0.050

0.060

0.100

0.055

0.070

0.125

0.060

0.080

0.150

Note : As per Chao;s book , above values are applicable for streams having width less than 30 ft. IRC SP -13 alsospecifies the same values and may be adopted for major bridges also. However for more regorous estimation Chaosbook may be referred to . Variation in the velocity across the depth of Cannel is described in the sketch below.

Fig.II.2. CROSS SECTIN SECTION OF STREAM SHOWING VELOCITY CONTOURES

II. 2.1 OBSTRUCTION TO DISCHARGE :

The bridge proposal should not normally cause obstruction to the discharge of HFL. of more than 20% to 25%. Thisincludes the obstruction caused by the approach roads and bridge structure itself. The percentage of obstruction todischarge should be calculated for design H.F.L. , O.F.L. and flood level equal to road top level over bridge (forsubmersible bridges ) in each case and normally the limits shall be satisfied. However, if the afflux and velocity arelow then higher obstruction may not be objectionable. In case of raft foundations, it is reasonable to assume an totalcross sectional area as available 30cm above top of raft slab for calculating discharge through vents andcorresponding percentage obstruction and afflux .

Fig II. 3 RAFT FOUNDATION AS PER TYPE PLAN

II.2.2 DETERMINATION OF WATERWAY :

The area through which the water flows between channel bed and bridge superstructure is known as the waterway ofbridge. The linear measurement of this area along the bridge is known as waterway. This linear waterway equal tosum of all clear spans is called as effective linear waterway. Roughly linear waterway can be determined as below .

(a) Linear waterway at HFL /OFL = A/D

Where A = Wetted area of the discharging sections at HFL /OFL = A2 + A1 x Q1 + A3 X Q3

Q2 Q2

Where A1,A2,A3 Areas of compartments 1,2,and 3

Q1,Q2,Q3 Discharge of compartments 1,2,3,D = Maximum flood depth at HFL or OFL

= HFL/OFL -lowest bed level in central compartment .

For natural channels in alluvial beds and having undefined banks, effective linear waterway can be determined fromsome accepted rational formula. One such formula as per I.R.C. for regime conditions is given below

.Linear waterway W = c Q

Where Q = Design maximum discharge in m3/sec.C = A constant . Usually 4.8 for regime conditions

but may very from 4.5 to6.3 according tolocal conditions.

II.2.3 SCOUR DEPTH :

When the velocity of stream exceeds the limiting velocity, which the erodable particles of bed material can stand, thescour occurs. The normal scour depth is the depth of water on the middle of stream when it is carrying the peak flooddischarge .

The probable maximum depth of scour to be taken for the purpose of designing foundations of abutment and piers shallbe estimated after considering all local conditions. If possible the soundings for depth of scour shall be taken in the vicinityof bridge site during or immediately after the flood but before the score holes had time to silt up appreciably. Allowanceshall be made for increased depth resulting from

(a) The design discharge being greater than flood discharge .(b) The increased velocity due to obstruction to flow caused by construction of bridge .(c) The increase in score in the proximity of piers and abutments .

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Theoretically the score can be estimated as below. However , this method is applicable for natural Channel flowing innon coherent alluvium.

[ Qb2 ] 1/3

Mean depth of score dsm = 1.34 I Ksf I

Qb = Discharge in cumecs per meter width .

Ksf= the slit factor for representative sample of bed material obtained up to the level of deepest anticipated scour..= 1.76 dm

Where dm = Weighted mean particle diameter in mm.

The discharge per meter width (Qb) shall be maximum of ;(i) The total design discharge divided by effective linear waterway between abutments.(ii) The value obtained taking in to account any concentration of flow through a portion of the waterway

assessed from the study of the cross section of river. However these , modification may be applied forbridge length more than 60m .The unit discharge (Qb) for a high level bridge is obtained by dividing the total discharge by effective linearwaterway , For submersible bridges the unit discharge should be worked out by considering two layers .

(1) Bed to R.T.L.(2) R.T.L. to H.F.L.

In case of submersible bridges, the scour depth and afflux calculations are to be done simultaneously and involve

trial and error procedure .To provided for adequate margin of safety , the foundation shall be designed for a larger discharge which shouldbe a percent as mentioned below over design discharge . (IRC-78-1983 clause 703.1) The discharge worked outby Imperical formula be increased by :

Catchment up to 500 sq . m. - 30%500-5000 sq. km - 25to 30%5000- 25000 sq.m. - 20 to 10%More than 25000sq. m. - less than 10%

The value of Ksf for various grades of bed material is given in Table 2.

Table 2 : Value of silt factor (Ksf) for various bed materials.

Sr. no. Bed Material Grain size in mm Silt factor(Ksf)

1Silt: Fine 0.081 0.5Fine 0.120 0.6Fine 0.158 0.7Medium 0.233 0.85Standard 0.323 1.0

2 Sand : Medium 0.505 1.25Coarse 0.725 1.50Mixed with fine bajri 0.988 1.75Heavy 1.290 2.0

II.2.4 MAXIMUM DEPTH OF SCOUR FOR FOUNDATION DESIGN:

The maximum depth of scour below the highest flood level (H.F.L.) shall be estimated from value of mean depth ofscour (dsm) in following manner :

(a) for the design of piers and abutments located in a straight reach and having individual foundations without any

flood protection work .(i) In the vicinity of pier - 2.00 dsm.(ii) Near abutments - 1.27 dsm for approach retained.

- 2.00 dsm for scour all round .(iii) Raft foundations - 1.0 dsm (with u/s & d/s protection aprons)

(b) For the design of protection to raft foundations, shallow foundations or flood protection the scour depth shouldbe considered as follows :

(i.) in a straight reach - 1.27 dsm.(ii) at a moderate bend - 1.50 dsm.

(iii.) at a severe bend - 1.75 dsm .(iv) at a right angled bend - 2.00 dsm.

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These above scour values can be suitably increased if actual observation data is available on similar structures inthe vicinity .

In the following abnormal conditions, special studies should be undertaken for determining maximum scour depth forthe design of foundations.

(i) Bridge located in a bend of the river involving a curvilinear flow or excessive shoal formation .

(ii) Bridge located at a site where deep channel in the river hugs to one side .(iii) Bridge having very thick piers inducing heavy local scours.(iv) Where the obliquity of flow in the river is considerable .(v) Where a bridge is required to be constructed across a canal or across river downstream of storage

works, with the possibility of the relatively clear water inducing greater scour.(vi) Bridge in the vicinity of the dam, weir ,barrage or other irrigation structures where concentration of flow ,

aggradation /degradation of bed , etc., are likely to affect behaviour of structure .If a river is of flashy nature and the bed does not lend itself readily to the scouring effect of floods , theformula for dsm given above shall not apply. In such cases the maximum depth of scour shall be assessedfrom actual observations.

For bridges located across streams having bouldery beds the formula given in above para may be appliedwith a judicious choice of values for Db and Ksf and results may be compared with the actual observationsat site or from experience on similar structures near by and there performance .

II.3 Vertical Clearance :

It is the height from the design highest flood level with afflux of the Channel to the lowest point of bridgesuperstructure. Clearance shall also be provided according to navigational or anti - obstructionrequirement . Where these considerations do not arise, vertical clearance in case of high level bridgesshall be as follow:

Discharge Minimum Vertical Clearance(m3/sec.) (in mm)

Up to 0.3 1500.3 to 3.0 4503.0 to 30 600

30 to 300 900300 to 3000 1200above 3000 1500

In structures with metallic bearings, no part of the bearing shall be at a height less than 500 mm aboveaffluxed design highest flood level.

II . 4. Afflux : When the bridge is constructed, the abutment and pier structures as well as approaches on either sideclause the reduction of natural waterway area .the contraction of stream is desirable because it leads to tangiblesaving in the coast especially of alluvial streams whose natural surface is too large than required for stability .Therefore to carry maximum flood discharge within bridge portion ,the velocity under the bridge increases. Thisincreased velocity gives rise to sudden heading up of water on the upstream .This heading up phenomenon is

known as afflux .Greater the afflux, greater will be the velocity under downstream side of the bridge and greaterwill be the depth of foundations required .

Fig.II.5 AFFLUX AT A BRIDGE

Afflux should be as small as possible and generally shall not exceed 0.6m. where the foods spread over the banksis large , use of average velocity for calculating the afflux will give an erroneously low afflux . In such cases , thevelocity in the main channel /compartment should be used. The permissible afflux will be governed by thesubmergence effect on joining structures , fields etc. on upstream side.

The afflux is calculated by one of the following formulae :

(a) Afflux at H.F.L. by Molesworth formula (In case of high level bridge)

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V2

Afflux (ha) = ------- + 0.0153 [Q2] -1 17.86 [Q1]

Where V = Mean Velocity in m/sec.

Total design discharge (Mannings)= -------------------------------------------------Total area of channel (Mannings)

Q = Total design discharge in cum/sec.Q1 = Unobstructed discharge in cum/sec.

(b) Afflux at H.F.L. by submerged weir formula (in case of submersible bridge

Wetted area of channel at H.F.L. = Wa in m2Designed discharge (Mannings) = Qm3/sec.

Assume afflux = h in mAdditional area due to assumed afflux = A a in m2

= Length at HFL x h

Total area = W a + A a

Va = Velocity of approach

W a= ------------ x Mean Velocity (VM)

(W a + A a )

Design Discharge QVm = ----------------------------- = -------

Wetted area W a

V a2

Head due to Velocity of approach = ha = -----2g Where g is 9.81m/sec 2

Total head =H= h + ha

.[ H3/2- ha3/2 ]Q a = A a x 0.625 x 2/3 2g [ H ]

.Q b = A b x 0.8 2g H (2)

Where A b is unobstructed areaabove top of slab..

Q c = A c x 0.92g xH. (3)

Where A c is unobstructed areaabove of vent below soffitof slab.

Total Q = Q a + Q b + Q c

Thus this arrived Q should tally with design discharge .

II. 5. Selection of Type Foundation .

Next step is deciding the type of foundations as per the site conditions and as per the trial pits and /or bore resultsand also on the type of river flow, scour depths etc.

II. 6 Selection of Type Bridge.

Next step is to study of all the aspects of bridge site and also what type ofbridge is required to suit a particular site withrespect to hydraulics on the basis of percentages obstruction and afflux.

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III. COMPONENTS OF BRIDGE STRUCTURE:

Let us now study the bridge components and its adaptability and suitability at particular site conditions.

III.1 FOUNDATIONS:

Generally two types of foundations are adopted for bridge structures.

(i) Shallow foundations - Open foundations- Raft foundations

(ii ) Deep foundations - pi le foundations- Well foundations

III.1.1 Depth of foundations: The foundations shall be taken to such depth that they are safe against scour, or protected

for it. Apart from this, the depth should also be sufficient from consideration of bearing capacity, settlement ,stability and suitability of strata at the founding level and at sufficient depth below it .

(A) Depth of foundations in soil (Erodible strata)

(a) Depth of shallow foundations : Foundations may be taken down to a comparatively shallow depth below thebed surface provided a good bearing stratum is available and the foundation is protected against scour.

R.L. of foundation = Designed H.F.L. (Tallied H.F.L.) - Maximum scourDepth - Depth of Embedment (D.E.)

Where Depth of Embedment = Min.2.0m for piers and abutments with archesMin.1.2m for piers and abutments supportingother types of superstructure.

(b) Depth of deep foundations (in erodible strata)-

R.L. of foundation = Designed H.F.L. (Tallied H.F.L.) - 1.33* Maximum scourDepth.

(B) Depth of foundations in rock

The foundations R.L. in case of Hard Rock = R.L. of strata Hard Rock - 0.60m.

The foundation R.L. in soft rock /Exposed rock = R.L. of strata of Soft Rock /Exposed rock-1.50m. (weathered rock strata

is not considered while taking R.L. of rocktaking R.L. of rock top)

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Selection of particular type of foundation is a very important job as it affects the entire proposal for the bridge .e.g. if the rock is not available at shallow depth, the tendency may be for well foundation and because wells arecostly the situation may lead to adoption of bigger spans ,and the P.S.C. structures and may be SP-33have to beused. On the other hand if scour depth is less and flood depth is also reasonable small the raft foundation couldbe the choice. Then we have smaller spans. less height of bridge, may be a submersible bridge with permissibleinterruptions is felt sufficient.

Presence of soft/hard rock within 5 meters would attract open foundation depending upon the scour depth the

type of bridge and the height of the bridge above and below the bed level .Situation with 5m depth of foundationbelow bed and 2m to 3m heights of pier above bed may not be sound good .Alternative should be thought of insuch cases. So look for the strata where foundation can be rest. Start with open foundation. If the depth of strata isdeeper than 6m to 7m thick of well or piles. Simultaneously study scour depth and height of the bridge above bedlevel . If the scour depth is within 3.0 m and no problem of standing water , consider the possibility of raftfoundations.

Some important points which help preparing a bridge proposal are noted below.

- span to height ratio forRaft foundation be kept as 1.0 to 1.25Open foundation be kept as 1.25 to 1.50Well foundation be kept as1.5 to 2.0Pile foundations it should be 1.5 to 2.0

- The height of pier is measured from foundation to top of pier i.e. pier cap top.

- The dimensions of pier, abutment and well foundation be taken from type designs orfrom the I.R.C.Codes

- Proper uniform sitting of well foundation could be ensured by taking the foundation in torock by about 15cm.

- The raft foundation details be taken from the type of designs as applicable .

- Other similar designs prepared and approved by the Designs Circle should also bestudied and referred to.

- Open foundations are comparatively easy to be decided about.

- Anchorage of open foundation in to the rock shall be as per IRC-78 i.e. minimum 0.60min to hard and 1.50m into soft rock excluding scourable layers .

- Leveling course and annular filling should be proposed for open foundation. Annularfilling should be done with M10/M15 concrete up to rock level .

- Stability of foundation should be worked out. The beginner should obtain the standardcalculation sheets from office, and do the calculations manually to gain confidence. Further trials could be oncomputer. Software is available for checking the stability of the foundation and substructure .

Area under tension up to 20% is allowed by the I.R.C. code. However under seismic /barge impact conditions 25%of the area could be allowed under tension (except for bridge on National Highway ).

(1) Open : Open foundations are preferred over any other type . These are tobe provided when good founding strata is available at shallow depth and there is not much problem of dewatering.R.C.C. footings are preferred over P.C.C. footing in case of R.C.C. piers.

(2) Well :The shape of well can be, Single Circular , Double D-Type /DumbelType ,Twin Circular or Rectangular .

(3) Piles : Although piles can be designed as frication piles and end bearingpiles ,the states practise is to design only end bearing piles. Raker piles are also not preferred in bridgefoundations.

(4) Raft : The raft foundation can be deigned with attached or detached cut-offwalls .

III.1.2 More about raft foundation :

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In case of channels where the good foundable strata is not met with at a reasonable depth of about 3m and thatthe scour depth also is small, RAFT FOUNDATION could be considered as a better solution for such week &scourable strata.

The design circle has prepared type design designs for raft foundation. The latest type plan for raft foundationprepared by the Design Circle analysed raft of continuous beam on elastic foundation by using Heteneysequations. Earlier type design for the raft foundation was evolved considering the raft as a solid slab subjected toupward soil reaction. The cut off walls provided were not considered as structural elements but only for the

protection from scour. Later on the raft has been designed as channel section where the cut off walls play veryimportant role being a structural element. It is ,therefore, needless to say that in case of channel type of raft , thecut off walls shall be cast with utmost care, the concreting of cut off walls should be done in practically drycondition and the quality of concrete is ensured. Cross cut off walls should be invariably provided at the ends ofraft . These should be similar to main cut off walls .

The partial raft should be avoided. The pier height not exceeding 0.8 times span has been considered in the typeof designs. Different span to height ratio could be adopted if the raft is so designed. Computer programme isavailable for the analysis and design of raft foundations for both slab type and channel type.

While deciding the depth of cut off wall, the scour depth as work out by the formula.

1/3[ Qb2 ]

Dsm = 1.34 [ ------ ][ Ksf ]

is to be considered. It is not to be increased by any factor as incase of open/well foundations.

The top of the raft is kept generally 0.30 m below the lowest bed level and cut-off wall is taken generally 0.3mbelow design scour depth .

It is necessary in case of the raft foundation to have a perfect elastic bed and uniform properties. The raft slab aswell as cut off walls (for channel type of raft) should rest only and elastic bed .

The raft foundation with spans up to 10m have been done in the state. Spans more than 10m have not been tiredso far , the same could be tired if the site situation so warrants .

Upstream and downstream protection to raft foundation is considered necessary. Launching aprons are providedon upstream and downstream side . The width of apron is worked out as : (Please see para II.2.4.b)

1. The length u/s apron = 1.50 times the scour depth below bed level.2. The length of d/s apron = 2.00 times the scour depth below bed level.

The size of stone /block for the apron is worked out as per the formula given in IRC -89-1985 . The size of stonerequired for launching apron to resist mean design velocity (average velocity ) is given by the formula :

.V = 4.893 d

Where V = Mean design velocity in m/ sec at bed level .D = Diameter of stone in m.

Generally following size and weight of stone can be adopted for different velocities.

TABLE - 3:

Mean design velocity in Dia. Of stone in cm Weight of stone in Kg.m/sec.

Up to 2.5 30 40

3.0 38 76

3.5 51 184

4.0 67 417

4.5 85 852

5.0 104 1561

We find that when the velocity at bed level exceeds 4.0m / sec.the weight of stone required for apron is quitelarge.

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It may be difficult to get such large stones from quarries etc. We may , therefore think of concrete blocks orconcrete stone blocks or crates.

III. 2 SUBSTRUCTURE:

III.2.1 Type designs available would provided sufficient information about the dimensions of the P.C.C. piers andabutments up to the height of 10m. These type designs available are for non -seismic zones only . Forheights more than these R.C.C. pier of suitable dimensions will have to be considered.

For grade of concrete to be used refer Govt. Circular No. RMR- 1094/184/R-1 dated 12-6-96. Theprovisions of this circular differ from I.R.C. provisions ,which should be noted carefully . The circular isappended as Annexure -4.

III.2.2 Type design of R.C.C. piers are getting ready and could be referred even for seismic conditions. IRC-21-1972 allowed use of M-10 grade for mass concrete like solid piers and abutments . Our type designs ofP.C.C. piers and abutments. Our type designs of P.C.C. piers and abutments are prepared accordingly .In 1987 the code of practice IRC-21 was revised and in use today. This revised code does not permituse of M-10 grade concrete for bridge works. Further the permissible stress in various grades ofconcrete have been drastically reduced . This thus result in very heavy sections of piers and abutments. In fact the large number of bridges in Maharashtra have been constructed in past with M-10 concreteand they are functioning well .Looking to our experience , the Govt. of Maharashtra has issued circularpermitting use of M-10 grade concrete for piers and abutments and also solid returns behind abutment. (Govt. Circular No. RMR- 1094/184/R-1 dated 12.06.96 ).

III. 2.3 The proposed allowable compressive , tensile and shear stresses are as follows

(i) Flexural compression cb = 0.33 fck for all grade of concrete

(ii) Flexural tension tb = 0.033 fck for all grade of concrete

(iii) Shear As below.

(a) The available shear stress for R.C.C. members subject to flexural ,shear and members subject to axial

compression , the allowable shear stress carried by the concrete (c)shall be as per following table .

(Please refer IS- 456 -1978-Table 17)

TABLE- 4 : Permissible Shear Stress In Concrete c N/mm2

100 Asbd

Grade of concrete

M-15 M-20 M- 25 M-30 M- 35 M- 40

(1) (2) (3) (4) (5) (6) (7)

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0250.50.751.001.251.501.752.00

2.252.502.753.0 andabove

0.220.290.340.370.400.420.440.44

0.440.440.440.44

0.220.300.350.390.420.450.170.49

0.510.510.510.51

0.230.310.360.400.440.460.490.51

0.530.550.560.57

0.230.310.370.410.450.480.500.53

0.550.570.580.60

0.230.310.370.420.450.490.520.54

0.560.580.600.62

0.230.320.380.430.460.490.520.55

0.570.600.620.63

Note - As is that area of longitudinal tension reinforcement which continues at least one effective depth beyondthe section being considered except at supports where the full area of tension reinforcement may breused provided the detailing conforms to 304.6.2.3 of IRC: 21-1987 .

For slabs the allowable shear stress carried by concrete shall be K : c where k has values givenbellow

TABLE -5

Oberall depth 300 or 275 250 225 200 175 150 orOf slab in (mm) more less

K 1.00 1.05 1.10 1.15 1.20 1.25 1.30

Shear Reinforcement

(i) Where the design shear stress v exceeds the shear stress carried by concrete c shear reinforcementshall be provided as per the following equation :

Asw = (T- Tc) x bs

s(Sin +Cos) Aswbs as in IRC:21-1987 CI.304.7.4

s

(ii) The Type of shear reinforcement shall be in accordance with CI. 304.7.4.1 of IRC: 21-1987.

Minimum Shear Reinforcement

The minimum shear reinforcement calculated as per above equation shall not be less than :

Grade of barsS240 S415

Asw Min. 0.002bs 0.001bs

III. 2.3.1 In no case design shear stress calculated shall exceed the maximum permissible shear max as given below.

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max = 0.07fck or 2.5 MP a whichever is less.

III. 2.4 P.C.C. piers need the provided with surface reinforcement to cater for effects of temperature variations in thestructure. Such reinforcement is generally provided at 5 kg/Sq. m. area of the exposed surface. Thisreinforcement is also useful for having a good bond between two layers of concrete.

The top width of pier is dependent on type of structure i.e. solid slab, grider slab system, prestressed

concrete etc. The same therefore, need be carefully decided .Span length plays important role in decidingthe size of bearing and its pedestals and expansion gap, which also need be considered while deciding thetop width of pier .Prestrassed concrete construction warrants extra space for putting the prestrsseing jacks, which need be considered while deciding the top width of pier .Calculations are required with the help ofproperly drawn sketches .About 1.20m clear space between the faces of end diaphragms may beconsidered adequate for P.S.C. type of superstructures.

The batter given to the pier generally is 1:3, 1:25, 1:20,1:18 and some times 1:15 and 1:12 .This is as perthe stability calculations. The betters 1:15 and steeper do not look aesthetically pleasing and also result inincreased obstruction to flow of water and hence may be avoided if possible. It is prudent to have oneshape of pier for a bridge from asthetic point of view and also ease of work and economy due to repeateduse of centring .

III. 2.5 Forces to be considered for stability of piers and abutment are given in IRC-6 (Section -II) . The permissibleincrease in stresses in the various member under different load combinations are also given in the code .The same is summarised as below:

TABLE -7

Sr.No. Load combination * Increase in permissiblestresses.

1. Dead + Live NIL2. 1 + Secondary + Deformation +

Temperature15%

3. 2 + wind + wave pressure 331/3%4. 2 + seismic + wave pressure 50%5. 2 + barge impact + wind load 331/3%6. Dead + water current + buoyancy+

Earth pressure + erection + friction +Wind+ grade effect

331/3%

7. 6 + seismic - wind 50%

(* These values are not applicable for working out the base pressure for piers , abutment , returns etc. Thepermissible base pressure are given in I.R.C. 78 -1983 para 708)

Apart from above mentioned combinations, following load combinations should generally be checked .

1. Dead + Live + wind in transverse direction.

(i) Wind acting perpendicular to deck.(ii) 65% perpendicular and 35% along the deck . The wind velocity and method of computation of

forces is given IRC-6-1966(Section-II).

2. One span dislodged (i.e. smaller span not in position ) for pier and no span condition for abutment .

3. one span dislodged condition with Class A one train on span.

While considering the water current forces it is also assumed that the water flows at an angle of 20 o resulting the

transverse force on the pier.This force is quite substantial and is important on the stability analysis . Differential waterhead of 250 mm between opposite faces of the pier also need be considered in case of bridge with pucca floor orinerodible bed.

The effect of live load surcharge on the abutments shall be as per IRC-78-1983 Clause 714.4 .

It is further necessary to check the stability of pier of non-span condotion . The pire having no stabilising load fromsuperstructure may be found unsafe under particular load combinations ,e.g. water current .

Barge impact (in case of navigational channels) is one of the important factors in substructures design. The values ofbarge impact load should be judiciously consider depending on the weight of the moving barge .The highest point onthe pier where barge need to defined and constructed accordingly .Typical arrangement is shown here .

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Fig. III.1 HUNG TIMBER FENDER

Fig. III.2 CHRUSHABLE CONCRETE BOX TENDER ON THE FRANCIS SCOTTKEY BRIDGE.

Fig. III.3. OPEN FOUNDATION (NEW THANE CREEK BRIDGE)

All forces should be stated in a proper sequence. The combination of load & permissible base pressures. Specificrequirements for different types of foundations should be explained .

For important bridges from durability considerations the provisions of IRC-SP-33 shall have to be followed .(Refer Govt. Circular No. RMR-1094 /184/R-1 , dt. 12-6-1996 for applicability of IRC-SP-33).

(1) Piers : The various type and shapes of piers used by the department are as given below .The materials used for pier are Masonary , P.C.C.and R.C.C.The shapes adopted are Solid wall type , Circularcolumn, square column, rectangular , hollow circular , twin or multiple columns wit or without connected bydiaphragm . Some of the typical sections for piers are shown in following Figures.

Fig. III.4. SOLID WALL TYPE PIER

Fig .III.6 HAMMER HEAD PIER

Fig. III.5 SERIES OF COLUMNS FOR PIER

FiG.7 TWIN CIRCULAR PIER

Fig. III.8 SINGLE CIRCULAR PIER

Fig.9 R.C.C. HOLLOW PIER

(2) Abutment : Various types of abutments are used are gravity type , spill through type , counter fort type , boxtype . Typical sketches are shown bellow.

Fig. III10. SOLID ABUTMENT

Fig. III 11. SPILL THROUGH ABUTMENT

Fig. III 12. COUNTERFORT ABUTMENT

III.3 RETURNS : The type of returns used are solid gravity ,R.C.C. box, Tied back or flyback type

Fig. III 13. SOLID RETURN

Fig.III 14. SPLAYED RETURN

Fig. III 14 BOX RETURN

ELEVATION

Fig III.16 REINFORCED EARTH EMBANKMENT

III. 4. BEARINGS : Various type of bearings used are M,S. plate , cast steel rocket rollers ,neoprene ,PTFE, potbearing , R.C.C. roller . The selection of Bearings should be as follows :

1. Spans up to and including 10m for solid slab superstructure : Tar paper2. Span> 10m and


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Fig.III 21. P.T.F.E.PAD BEARING.

P.T.F.E. Bearings are for sliding or rotational movements .Proper selection would be necessary .Sufficient marginshould be kept for movement due to deflection in the structure. Stopper /Lugs need be provided to arrest excessivemovements in lateral direction due to centrifugal force etc.

III.5 SUPERSTRUCTURES

Various type of superstructures are arches , Masonary ,C.C.,R.C.C. Girder and deck slab ,Solid Slab , R.C.C. T-Beam Slab , R.C.C. Box Beam , Voided Slab, P.S.C. two Girder ,Three Girder ,Multi- Girder , Box Girder ,Simplysupported continuous Cantilever , Hammer head ,Bow string girder , Composit construction , cable stayed,suspension .

III.5.1 Selection of proper superstructure : Generally the following criteria should be followed for selection ofsuperstructure depending on span length.

1. Spans up to 10 R.C.C. solid slab .2. Spans > 10 to 15m R.C.C. solid slab / Ribbed slab/ 3 girder3. Spans > 15m to 20m R.C.C. 3 girder or Multi girder slab system . sl 4. Spans >

20m to 30m R.C.C. Box Type superstructure.5. Span > 30m to 60m P.S.C. Box girder.

For spans more than 60m the discussions should be held with Superintending Engineer, Designs Circle forselection of the type of superstructures .

2- girder system for two lane superstructure should not be proposed unless other alternativies are consideredunfeasible .

For spans up to 10m solid slab superstructure are found most suitable. As the span increases beyond 10m thethickness of solid slab poses difficulties during concreting.lot of construction joints are created in the structure ifdproper programme of concreting is not prepared and insisted upon .It is thus ,desirable to go for ribbed slab ormulti-girder system of deck slab . Spans between 10m to 15m could be conveniently covered in this manner.

Spans between 15m to 20m ,3-grider or multi -girder system would be desirable . Two girder system should beavoided as far as possible. In case of single lane bridge two - girder system is natural choice . But this systemshould not be preferred in severe exposure conditions. There is a school of though that damage to one girdermakes the entire structure unstable and unsafe and hence 3-girder system is to be preferred .

For spans between 20m and 30m R.C.C. box type superstructure is considered suitable. Use of R.C.C. girder andslab system might result in excessive deflections under live load . Box girder is a more desirable shape for thesuperstructure .

Beyond 30cm span , it is necessary to go for P.S.C. This enables us to somewhat restrict the deck height to thedesired level. Generally the spans may not exceeds 60m. However , if such situation occurs, the discussionsshould be held with Superintending Engineer ,Design Circle for deciding the type of superstructure. Theparameters influencing selection of superstructure need be studied .R.C.C. superstructure should be given suitable preconstruction camber. While estimating the deflection ofsuperstructure , the effect of shrinkage ,creep etc. over a period of about 15 years should be considered . In caseof P.S.C. superstructure precamber is generally not required. It should however be ensured that there will be nosagging in future .

Typical cross-section of the superstructure adopted by the departmentare given below:

Fig. III.22 SOLID SLAB

Fig. III 23. 2-GIRDER SYSTEM .

Fig. 24 . 3-GIRDER SYSTEM .

Fig.III.25 . 4-GIRDER SYSTEM.

Fig,III. 26 6- GIRDER SYSTEM

Fig. III.27 Girder System.

Fig. III.28 SINGLE CELL BOX

Fig. III. 29. TWO CELL BOXFig. III. 30 THREE CELL BOX .

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III.5.1.1 TYPE DESIGN

Type designs are available for solid slab and girder type superstructures. The type designs prepared byM.O.S.T. are also available for R.C.C. solid slab up to 10m , R.C.C. girder slab up to 24m and P.S.C. girderslab bridges up to 40m spans.

For box superstructure ,the type designs are to be done . However ,reference could be obtained from thealready approved designs of similar nature .

III.5.2 Type I and Type II structures . (PSC)

In case of P.S.C. structure as per I.S. -1343 three types of structures are defined. However in our case onlytype-I and type-II structures are allowed in the state in spite of I.R.C. provisions for type-I and type-II structuresare allowed in the state in spite of I.R.C. provisions for type-I only.

For type-I P.S.C. structures minimum compression of 5 kg. /cm2 is assumed under all loading conditions.Where as for type-II P.S.C. structures no tension is allowed under dead load +60% live load, but tension up to2/3 rd modulus of rupture of 7 day strength was allowed previously but now this stress limit is modified to20kg/cm2 (tension ) in moderate and 10kg/cm2 in severe exposure conditions .Generally for important and inserve atmospheric conditions ,type I structures are designed so that there will not be any cracking causingingress of moisture and there by leading to correction. For the bridge on less important routes and in dry climate, type II structures can be designed and constructed .

III.5.3 Minimum thickness:

Minimum thickness of deck slab is generally to be prescribed as 240mm either in case of box or girder slabsystem. This thickness is essential from practical point of view regarding placement of reinforcement , concreteand its proper compaction .

Minimum web thickness for box girder shall be 250 mm , however this should be increased in case of severeexposure conditions. All the specified minimum thickness are from durability point of view .

III.5.4 Methods of transverse analysis :

III.5.4.1 T- Girder slab system:

The longitudinal girders are connected by cross - girder at intermediate places and this arrangement supportsthe deck slab. Most complex problem in this case is determination of distribution of live loads between thelongitudinal girders. When there are only two longitudinal girders, the reaction of longitudinal girders can befound by assuming the supports of the deck slab as unyielding. With 3 or more girders , the load distribution canbe estimated using any one of the rational methods discussed as below .(a) Courbons method: Main assumption in this method is linear variation of deflection in transverse direction.

In view of simplicity this method is popular but it has its own limitation like.

(i) Ratio of span to width shall be grater than 2 but less than 4 .(ii ) Longitudinal girders are interconnected by symmetrical ly spaced cross girder of adequate tiffness.(iii) Cross girders extend to a depth of at least 0.75 of the depth of main girder.

(b) Hendry jaeger Method : Here it is assumed that cross girder can be replaced in the analysis by a uniformcontinuous transverse medium of equivalent stiffness.

(c) Morice -Little Method : Orthotropic plate theory is applied to concrete bridge system . This approach hasthe merit that a single set of distribution coefficient for two extreme cases of no torsion grillage and a fulltorsion grillage and a full torsion slab enable the distribution behaviour of any type of bridge to be found .

Design Circle is having computer programme for these types of analysis. Refer Essentials of bridgeEngineering by D. Johnson Victor .

III.5.4.2 Box girder bridge :

Detailed transverse analysis for box girder bridge is difficult to perform. Exact finite element model willhave to be generated to see the behaviour. In absence of rigorous analysis for the torsional moments andfor forces due to restrictions of warping torsion at ends , design moments and shear in longitudinaldirection are increased by 20% and transverse reinforcement steel by 5 % for simplicity and quick results .

Generally following procedure is followed for transverse analysis.

(i) Calculate bending moments in roadway slab consideration the slab considering the slab ,web and soffit slab as closed frame.

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(ii) Reinforcement in slabs, webs due to transverse moment is provided in addition to steelrequired to be provided in addition to steel required for shear or torsion.

(iii) Distorsion of box girder of box girder due to transverse moment is to be considered in thedesign .

III.6 EXPANSION JOINTS :

To cater for the expansion and contraction of superstructure suitable expansion joint is required to beprovided . The expansion joint is also supposed to be leak proof so that the superstructure ,bearings andpiers do not get damaged due to such leakage of rainwater etc.

Design Circle has issued some type designs for expansion joints which are being used commonly on thesmall span bridges.

1. Copper plate expansion joints.2. Sliding M.S. plate expansion joints .

The sliding M.S. plate joint have been extensively used in past .The experience of its performance ,however, is discouraging . The joints develops cracks in the bituminous wearing coat and during monsoongets further deteriorated. It also creates lot of noise as the vehicles pass over it .

The copper plate expansion joints has given satisfactory results (this joint is however susceptible totheft ).Up to 25mm gap, this type can be considered the best .

The two types expansion joints are described in the sketch.

Fig.III.31 DETAILS OF EXPANSION JOINTS BETWEEN R.C.C. SOLID SLAB

Fig.III.32. COPPER PLATE EXPANSION JOINTS.

Fig. III.33. DETAILS OF M.S. PLATE EXPANSION JOINTAND CEMENT CONCRETE WEARING COAT:

Fig. III.34. DETAILS OF COPPER PLATE EXPANSION JOINT

Fig. III.35 STRIP SEAL TYPE JOINT .

Fig. III.36 TYPICAL BOX SEAL MODULER EXPANSION JOINT .

Fig. III. 37. FIXING OF COMPRESSION SEAL JOINT.Most under circular dated RW/NH/33059/1/96-S&R 31-3-97 has prescribed different expansions joints suitable forparticular expansion .The details are as per table bellow .

TABLE :8 SUITABILITY CRITERIA FOR ADOPTION OF DIFFERENT TYPES OF EXPANSION JOINTS

Sr.No.

Typeexpansion

Suitability for adoption of joint Servicelife

Special consideration

1. Buried Simply supported spans up to 10 m 10years

Only for decks with bituminousasphaltic wearing coat.

2. Filler joint Fixed end of simply supported spans withinsignificant moment .

10years

The sealant and joint filler wood needreplacement if found damaged

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3. AsphalitcPlug joint

Simply supported spans for right or skewup to (20 degree)moderately curved orwide deck with maximum horizontalmovement not Exceeding 25mm

10years

Only for decks with bituminous/asphaltic wearing coat. not suitablefor bridge with longitudinal gradientmore than 2%and

crosscamber /superie-vationexceeding 3%. Not suitablefor curved spans and spansresting on yielding supports.

4. CompressionSeal joint

Simply support to continuous spans rightor skew(up to (20degree) moderatelycurved with maximum horizontalmovement not exceeding 40mm.

10years

Chloroprene/closed foam seal mayneed replacement during service .

5. ElastometricSlab seal joint

Simply support to continuous spans rightor skew(less than 70degree) moderatelycurved with maximum horizontalmovement not exceeding 50mm.

10years

Not suitable for bridges located inheavy reinfall area and spans restingon yielding support.

6. Simple steripSeal joint

Moderate to large Simply supported.cantilever continuous construction havingright ,skew or curved deck with maximumhorizontal movement up to 70mm .

25years

Elastometric seal may needreplacement during service.

7. Modular Strip/Box sealJoint.

Large to very large continuous/cantileverconstruction with right ,skew or curveddeck having maximum horizontalmovement in excess of 70mm .

25years

Elastometric seal may needreplacement during service

8. Special joints for special condition

For bridge having wide decks/ span lengthof more than 120m. or /and involvingcomplex moment / rotations in differentdirections /plans provisions of special typeof modular expansion joints such asswivel joists joints may be made.

25years

Elastometric seal may needreplacement during service.Provisions of these joints may bemade with prior approval of competent authority.

These are proprietary items for which 10 years warranty shall be insisted upon from the suppliers.

For larger expansion gaps , of about 50mm and more the joints has to be designed suitability . Other types of joints are :

1. Finger type joint (Cast steel )2. Strip seal joint (Elastomeric )3. Compression seal joint (Elastomeric )4. Slab seal joint (Elastomeric )5. Modular joints (Modules with Elastomeric )

The above joints are costly as compared to conventional joint described earlier . We are, however , left with nochoice for long span bridges but for adopting them. For details of material property refer M.O.S.T. specification forroads and Bridges 1997 edition.

The above item are presently patented and hence detailed design calculations are not generally mace available .It should be insisted upon .

For details of these joints refer literature given by the manufactures.

Extra care need be taken for maintaining line and level of the joint to match perfectly with the geometry of the decksurface .

III.7 PARAPET AND KERB

Deciding the type of railing , kerb etc. as per type of bridge i.e. high level or submersible .

(i) For high level :S.E.D.C.s Type drawings or bridge Sanchi type parapet as mentioned in designs criteriacan also be adopted. The choice of drawing is recommended in S.E.D.C.s Circular No.

(ii) For submersible Bridge : Railing shall be removable type .,Either pipe railing or collapsible type asshown in the type drawings can be adopted

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III.8. WEARING COAT :

Earlier up to 1980 R.C.C. wearing coat is generally adopted .Now as per Govt. in P.W.D. Circular No.CEC/1179/50677/CR-225/D-29-A dated 12.08.80, following type of wearing coat are generally provided forbuildings

Convensional Practice :

High level bridges : Bituminour 50mm DBM + 25 mm AC/SDCSubmersible bridges : C.C. M-20 with temperature steel .Long span bridges : Bituminous or C.C. M-20 with temperature steel .

The performance of C.C. wearing coat and long span bridges (Where deflections under live load areconsiderable ) is not found to be satisfactory . It develops cracks and spoils the riding quality . The crackedsurface also allows water to seep through the leads to corrossion in the main deck elements particularly in salineclimates .

Bituminous wearing coat with 50mm DBM + 25mm AC/SDC generally does not perform well during monsoon ,particularly in high rain fall area (> 1000 mm per annum). Better treatment consider today is -

12 mm Mastic Asphalt (as a water proofing layer)+ 50 mm DBM

+ 25 mm Mastic Asphalt (top surface sealant)

we may part with the 12mm. Thick Mastic Asphalt layer in areas where climate is not severe and that the rain fallis less than 1000mm per annum.

III.9. WATER SPOUTS :

Water spouts are required to drain out the rain water from the deck surface quickly ,. The deck has camber orsuper elevation which help rain water get quickly towards kerbs . The water spouts located near the kerb furtherdisposes the water out .

One water spout (as per M.O.S.T type deign No. SD-*303 ----) per 20 sq.m. of the deck area is consideredadequate .

Typical arrangement of rain water disposal is shown in following figure .

Fig. III.38. DETAILS OF DRANGE SPOUT

Fig. III. 39 FLY OVERS IN URBAN AREA (ARRANGEMET OF WATER SPOUT )

IV. SUBMERSIBLE BRIDGES :

On number of occasions we come across with very flat or shallow channels . the banks are not properly definedand the depth of channel is too small. The water spread at H.F.L. is too big. It becomes difficult to decide thelength of high level bridge covering the entire spread at H.F.L. by the bridge would be too uneconomical . Suchchannels are better for a submersible bridge with Road top level matching the general ground level. Theobstructions to flow due to approach should be practically NIL. Bank work in approaches for a submersible bridgeshould be minimised as it is very much susceptible to washouts during monsoon.

The percentage obstruction at O.F.L. (Ordinary Flood Level ) and R.T.L. should be worked out . At O.F.L. theobstructions may be aimed at about 20% .The value of at R.T.L. , however , are always higher (i.e. up to 40% ).This is due to obstruction to flow to superstructure .At H.F.L. however , the % obstructions should show aacceptable figure i.e. between 15% to 20% .

Premissible interruption for different category of roads have been specified by Govt. These are already stated in

previous chapter .

While deciding the R.L. to be cleared by the submersible bridge, the above limitations should be considered. Inabsence of detailed hydrographs, the various levels reported by Road Project Division have to be relied upon.The substructure is generally just resting on the substructure . The same , therefore , need to be stable by itselfduring floods. Solid Slabs superstructures are the best for submersible bridges. However ,Girder -slab , ribbedslab, box girder type superstructure are used for submersible bridges.Care , therefore need be taken for noentrapping of air , quick filling of box with water etc. Adequate No. of holes should be provided in thesuperstructure for escape of air etc.

Stoppers should be provided on d/s over the piers to add to the stability of the superstructure as an additional /precaution .

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V. ANTI CORROSIVE TREATMENT

Due to saline atmosphere, the steel get corroded due to electrochemical action.Not only the reinforcing steel butalso the standards /wires used for prestressing gets corroded . Adequate care, therefore , need to taken to protectthe bridge structure from this dangerous phenomenon. The concrete as well as steel need be provided with someanti-corrosive treatment. The bridges lying in coastal area are affected by corrosion. At place the atmosphere mayitself be corrosive due to heavy chemical industralisation . The channel may also carry waste produce from theindustries , which may lead to corrosion .

The anticorrosive treatment is required to be applied to concrete and reinforcement steel incase of saline andsevere exposure conditions .

(a) for reinforcement, at present C.E.C.R.I. specification (Phosphatic jelly treatment) and FBEC (fusion bondedepoxy coating ) treatment as per I.S. 13620-1995 are adopted. Both the treatments have certainadvantages and disadvantages , however the choice should be judiciously selected. Recently C.E.C.R.I.has developed CPCC ( cement polymer composite coating ) treatment ,thickness of coatings, effectivenessof coatings. The same could also be proposed being CECRI product .

(b) Anti Corrosive treatment for concrete surface.

(i) The Concrete surfaces that are in contact with earth of water -these surface are applied with zinc richcoal tar epoxy paint of primer plus 2 coats. This treatment can also be applied over linear of piles andpile caps .

(ii) The concrete surface in splash zone -Acque epoxy paint in three coats is applied as the surface isalternately in wet and dry condition .

(iii) The surface exposed to atmosphere - e.g. solid slabs ,girders and slab, outer faces of box girders.These are painted with epoxy coating in three coats as per C.E.C.R.I. specifications.

(iv) Inside faces of the box girder are applied with cement based paint .

VI. FUTURE PRESTRESSING ARRANGEMENTS:

In case of prestressed concrete structures , located in severe/ saline exposure conditions , provision of futureprestressing arrangement is felt necessary and should be obligatory. In case of box structures, the holes arekept in the end diaphragms at top portion. If intermediate diaphragms are provided then holes should be left inthese also keeping in view the alignment of external cables. It is preferable to get the cable profile approvedbefore approving the superstructure drawing . If the diaphragms are very wide /thick , then holes should berectangular in size to adjust the profile of alignment.

For prestressed structure , suitable arrangement for external prestressing should be decided at design stage .

Such arrangement should be for imparting about 20% of the prestressing force originally applied .

VII. USE OF COMPUTER FOR DESIGN OF BRIDGES :

At present there are 16 stand - alone personal computers in the design Circle .

List of software developed by the Designs Circle is attached as Annexure I. These all software are developed inhouse. Efforts are being made to develop more and more softwares. Recently purchased STADD-3 software isfound to be quite useful in analysis of structures .It is seen that for bridge structures ,ready made softwares arenot available in the market as a computer package . as soon as these becomes available , it should bepurchased for office use.It must be kept in mind that computer should be used as a tool for helping the designsand its scrutiny . After all it is the fell of structure , judgement of the expert that will count in final decision .Before using any of the programmes it is desirable that the Design Engineer does the calculations with his ownhands to get the fell of the problem .

VIII. HORIZONTAL AND VERTICAL GEOMETRY:

Aesthetics is a matter of taste and therefore it is not possible to codify the rules , which are to be followed in the

Designs of bridges. However few criteria like alignment (horizontal and vertical ) with proper geometrics can addto the architecture of bridge .

The approach gradients either for a valley curve or a summit curve shall have continuity without break . Thechange of slope should be gradual without any abrupt or sudden change . The approach to a bridge with a kinkas shown below shall be avoided .

(i) SUDDEN CHANGE OF GEADE (BAD)

(ii) GRADUAL CHANGE OF GRADE WITH TWO VERTICAL CURVES (GOOD)

(iii) GRADUAL CHANGE OF GRADE WITH ONE VERTICAL CURVE (BETTER)

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Fig. VIII.1 bridge with valley curve

(i) SUDDEN CHANGE OF GRADE (BAD)

(ii) GRADUAL CHANGE OF GRADE WITH TWO VERTICAL CURVES (GOOD))

(iii) GRADUAL CHANGE OF GRADE WITH ONE VERTICAL CURVE (BETTER)

FIG. VIII. 2 BRIDGES WITH SUMMIT CURVEThe approach gradients with the vertical curves at two ends with the bridge deck straight is preferable to thekink but a curve bridge deck in the vertical plane having single curvature will be most preferable .

IX. DESIGNS CRITERIA

Designs criteria is a guideline for contractors designer to design the structure with good Engineering practiceand in conformity with departmental specificationsSeparate criteria are devised for flyover and river / creek bridges .

The department has restricted use certain type of structures as mentioned below.

(1) Structures sensitive to unequal settlement of foundations resting on yielding type of foundations(2) Abutments resting on approach embankments .(3) Stability of overall structure endangered due to failure of one or more span/ spans.

(4) Superstructure with joints at the tip of long cantilevers with higher or gap slabs .(5) Structures with continuity only in deck slab, in transverse direction .(6) Piers in the form of multiple columns with isolated /separate footings resting on yielding type

strata .(7) Spill through type of abutments for river bridges where spilled earth is subjected to stream

velocity is more than 2m/sec. And tied back returns exceeding 3m in length .(8) Square ended piers for river bridges.(9) 2- girder slab system for superstructure in severe exposure .

(10) Piles in deep scour and navigational zone .Apart from this various limitations are given in the Designs Criteriain view of practices followed in the state .

X TRENDS AND PRACTISES FOLLOWED IN THE STATE:

There are no hard and fast rules for good engineering practices. However , from the experience of the department in theState , these practices are listed in the designs criteria . The prominent ones are as below .

(1) There shall be minimum number of expansion joints for better riding surface .(2) Shear strength of concrete is not considered as per I.R.C. Now the shear design is allowed as per

I.S. -456 hence this aspect is now taken care of .(3) Reduced area of contact is allowed up to 75% for load combinations II and III of I.R.C. -78 .(4) P.C.C. footings supporting R.C.C. columns are not permitted .(5) The provision of sump for well foundations in made obligatory . Anchors bars & Nos.32 dia .are

also made compulsory .(6) Minimum diameter. of piles is 750 mm for main bridge and 500mm for retaining structure.(7) Design with single row of piles is not accepted .(8) Pile foundations are not provided in flood zones or areas with deep scour or at locations where

navigation is allowed .(9) Any dimension of any element of counter-fort type abutment is not to be less than 300mm.(10) Hollow R.C.C.Pier are allowed with minimum thickness of wall as 300mm in moderate exposure

and 400mm in severe exposure condition .(11) The height of pedestal is limited to 500 mm .(12) Minimum deck slab thickness shall be 240mm and not less than

200mm at the trip of cantilever.(13) Minimum thickness of intermediate diaphragm wherever provided has

to be 300 mm and that of end diaphragm 5oomm .(14) In the absence of rigorous transverse analysis for box , design live load moments and shear forces

in longitudinal direction are increased by 20% and and transverse reinforcement steel be increased by 5%.(15) All prestressed members are provided with spare cables at 5% of total numbers required for

designs . This is needed in case of short fall in extensions of the designed cables.(16) Provision for imparting 20% of design prestress at a future date is made in the deck and suitable

anchorage , bulk heads are constructed for the purpose .

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(17) In case of submersible bridge sufficient vent holes are provided in box Superstructure to prevententrapping of air inside and to get water in to and out of box instantly.

(18) Bearings are to be provided preferably within external line of pier /abutment and below the web of box girders .

(19) Trapaper bearings are allowed up to 10m and restrained neoprene bearings are allowed up to40m span only.

(20) Anti- crash barriers are provided in high risk areas e.g. Intersections of important roads , tallbridges etc.

(21) Facilities for inspection of bridge are provided in case of tall bridges and those which posedifficulties in inspection .

(22) The bridge are designed for temperature gradient (t) of 35o centigrade for extreme atmosphericexposure and 25 o centigrade for moderate atmospheric expouser . The temperature indicated are total expansion/contraction aggregate value. (i.e. + 17.5 12.5 o )

The superstructure is also designed for effects of distribution of tempreture across the deck depth asshown in figure for calculation of the thermal forces , effect of E value of concrete should be taken as50% of instantaneous value so as to account for the effect of creep on thermal strains.

Fig. X.I. DESIGN TEMPERATURE DIFFERENCES

X. TYPES OF PRESTRESSING AND ITS PROPER USE:

Basically two types of prestressing and pretensioned and post tensioned are applied in bridge engineering.Generally pretensioning is very rarely used in the state because of its limitations like proximity and availability ofplant , size of member, number of units etc.Post tensioning system is mainly used in the state .Various system of prestressing are (a) Freyssinet, (b) Magnel-Blaton , (c) Gifford-Udall system .

Many of the post tensioning devices are covered by patents . In case of freyssinet systems, cable with a fixednumber of wires e.g. 12-5 or 12-7 or 19-7 are used .

Various system are explained in the accompanied sketch. The sheathing is generally of bright galvanised metalsheet of interlocking connection (0.3 to 0.5mm thickness).This can be manufactured at site.

Fig. XI.1 ANCHORAGE FOR FREYSSINET SYSTEM

Fig. XI.2 ANCHORAGE FOR MAGNET BLATTON SYSTEM

Fig. XI.3 ANCHORAGE FOR GOFFORD -UDAL SYSTEM

Fig. XI.4 ANCHORAGE FOR LEE MCCALLSYSTEM

XII. Preparation of first stage proposal for the bridgeThe technical note of the proposal should cover following chapters.(i) introduction : General site and area location and background should be mentioned here.

(i i)History : The history shall give the chronological l ist of the event so far occurred in finalising bridgeproposals .It shall include the date of receiving the survey data , scrutinising the data inthe design circle , receiving the compliance of the remarks raised by the Design Circle ,and dates of inspection of the site by various authorities . Mention shall also be made ofthe earlier proposal .Change in site as per directives of various authorities shall also bementioned .Typical background and peculiarity of site may also be mentioned in thissection if applicable .

(iii)Necessity : This should explain the necessity of bridge . How it will be facillitate the near by villagesand improve the road network . This also must state the requirement of high level orsubmersible bridge etc.

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(iV) Authority : If the work is approved administratively and if appearing in budget then its reference withamount should be stated . Or else priority given by the Chief Engineer should bementioned .

(v) Site selection : Site selection is a very important of site aspect . As per G.R. BDG - 1080/808308 (394)Desk -2 dated 03.11.80 the Designs

Circle is supposed to prepared bridge proposals for length more than 30m to For thelength of bridge between 30m to 60m, territonal S.E. is to finalise the site. However S.E.(Designs) has to finalise the site for bridge length more than 60m. Details of siteinspection , alternatives studied and justification for the proposed site should be narratedin this para.

(vi) Hydraulics This chapter of hydraulics should depict all the hydraulic characteristics of bridge site litecatchment,discharge ,surface characteristics, various water levels . The level to becleared by the bridge with justification should be explained .

(vii) Foundations : This should explain the type of foundations adopted depending on trial pit or trial boreresults with justification. The choice of type of foundations is discussed separately .

(viii) Proposal This para should detail the proposed bridge weather submersible or high level . In somecases high level submersible bridge is also proposed wherein the clearnce over H.F.L. isnormal and not standards as per I.R.C.T exact chainages of abutments with length ofbridge proposed is to be mentioned . How RTL/ Soffit levels are workedout has to bementioned as explained below :

H.F.L./ O.F.L. : ..m.(whichever is proposed to be cleared )+ Afflux (Assumed /actual ) :..m.+ vertical clearance : .m.

Soffit of slab /grider of superstructure : m.+ Girder height /Slab thickness/:.m.

Superstructure depth+ Wearing coat thickness :m.

Road top Level :.m.

(viii ) Standards : The para should state the type of loading for which the bridge is proposed to bedesigned .In case of bridge with footpath ,the loading should be mentioned Generally twolane bridge is designed for single lane of 70R wheeled / tracked or 2 lane of Class Awhichever produces worst effects. The single lane bridge is designed for one lane of classA only .Further the seismic zone of the bridge site with seismic zone of the bridge site withseismic coefficient , soil structure interaction factor and importance factor has to be clearlywritten .

(ix) Substructure This chapter should show the dimensions of substructures like abutments and piers alongwith grades of concrete proposed . if the sections can be taken directly from type planswell and good or else the stability calculations for piers /abutment is required to be done .Use of computer programmes can also be made .

(x) Superstructure. : This para should inform about the type of superstructure adopted reference of type plan ifadopted with grades of concrete and type of structures must be clearly given

(Xi) Miscellaneous : The miscellaneous item must spell out the provisions and details of wing walls/ returns,bearings , expansion joints, parapets , wearing coat , filling behind abutments ,anti-corrosive treatment , special provisions with respect to inspection of bridges etc. This sitethat are likely to be affected by the dewatering problem shall have specific mention so thatproper provision can be made in the estimate.

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(Xii) Approaches : The approaches may need some specific treatment is required . In case of blocking ofdischarge in approach area , provision of vents or otherwise and its details are to be given. In case of submersible approaches the type plan shall be used. For the approachesexpose to wave action , proper design has to be obtained preferably from MERI/CWPRS .

(xiii) Special points : The special points feature should include any points , which need special attention. If anydata is to be re-verified or some approvals are to be obtained from competent authoritiesthen it should appear here . Application severe exposure or SP-33 conditions which hasbearing on cost must have special mention. Special provision for formwork, centering ,

dewatering , slope , protection etc. Should be stated so that the same can be adequatelyincorporated in the estimate .

XIII . General Arrangement Drawing (G.A.D.)

Apart from above description, the proposal should contain the general arrangement drawing .A drawing shouldnecessarily contain L-section showing pier and abutment location , various levels, dimensions of pier / abutment ,plan and typical cross section . Further the notes about various assumptions of design should be written on thedrawing. Typical proforma of notes is attached as Annexure -2. Only applicable part of note has to be kept ondrawing. Apart from this material table should appear on drawing. Thus drawing should be self explanatory and tobe easy for preparation of estimate at field level. General guidelines to be followed for preparation of material tableare given in Annexure -3 .

The G.A.D so prepared should show sufficient details to enable preparation of detailed estimate . All dimensionand provisions should be clearly shown on the drawing .

Consider the whole proposal whether generally acceptable , workable , economical. A question should be askedat this stage weather there could be any better alternative.

For reference of the new comers a sample technical note and general arrangement drawing is attached as shownbelow .

The GAD also should have key plann showing bridge location, alignment , trail pit/bore result with location andthree bench mark position with values .

XIV. DETAILED ESTIMATE:

After preparation of the proposal, estimate will be prepared by the field officers on the basis of these technical noteand drawing. For the bridge length more than 60m. as per G.R. No. (Marathi) CEC -1083/(2008) /D-33 dated5.4.83 , the estimates are to be countersigned by the Designs Circle. Generally the measurements / provisions areto be critically verified .

XV . WORKING DRAWINGS :

After this next stage is inviting tenders. The tenders may be either on B-1/ B-2 i.e. on departmental design or on Cform i.e. On contractors own design. For B-1/B-2 type contracts the designs are to be prepared by Designs Circle& working drawings supplied to be concerned field officers. Generally for bridges with length more than 60m.tenders are invited on lump-sum basis (i.e. form C). For this type of works the designs criteria is to be given byDesigns Circle. On receipt of contractors technical proposals with the tender, this is to be scrutinised with respectto the tender conditions and accept stability or otherwise need be communicated to field officers. Thereafter animportant part is checking of contractors design after award of work.

(XVI). PREPARATION OF WORKING DRAWINGS :

Based on the site condition i.e. foundation level etc. , the detailed design with drawing is to be prepared forfoundation substructure, superstructure etc.

( XVII). CHECKING THE CONTRACTORS ALTERNATIVE DESIGN:

(1) Design criteria for contractors alternative design is to be studied in detail .

(2) Contractors design are to be checked based on the design criteria.

(XVII). REFERENCES :

1. Open channel hydraulics - Ven Te Chow .2. Essentials of bridge Engineering - D, Johnson Victor3. Bridge Engineering - Rakshit4. Concrete bridges - Design & practise -V. K. Raina5. Foundation design - Teng .

GUIDELINES FOR BRIDGE DESIGN

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ANNEXURES

ANNEXURE-1.

LIST OF SOFTWARES AVAILABLE IN DESIGNS CIRCLE (P.W.)

Sr.No.

Name ofprogram

Programmelanguage

Name ofprogrammer

Purpose of program

1 IL1 FORTRAN P.M. Baviskatr. To calculate Max SF and BM at user definedsections for passage of specified live load train

for simple span.2 IL2 FORTRAN P.M. Baviskatr. ----do for two span continuous beams-------3 IL3 FORTRAN P.M. Baviskatr. ----do for three span continuous beam-------4 FF1 LOTUS 123 P.M. Baviskatr. Analysis of rectangular R.C.C. section for

combined BM and Compression using firstprinciple.

5 FF2 LOTUS 123 P.M. Baviskatr. ---Do--- for BM and tension.6 FF4 LOTUS 123 P.M. Baviskatr. ----Do---for Tee section.7 RR FORTRAN P.M. Baviskatr. Analysis of rectangular RCC section for

combined BM and Compression.8 Note FORTRAN P.M. Baviskatr. Programme to generate Draft Technical Note to

be given with proposal9 AFFSUB LOTUS 123 P.M. Baviskatr. Calculations of Afflux and scouer depth for

submersible bridge using weir formulae .10 B12 FORTRAN P.M. Baviskatr. Analysis of rectangular RCC section for biaxial

BM and Compression

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11 UNIAX FORTRAN P.M. Baviskatr. Analysis of Circular RCC section for uniaxialBM and Compression

12 STAB98 FORTRAN P.M. Baviskatr. Programme to check stability and materialstresses at various levels in pier.

13 STHELP FORTRAN P.M. Baviskatr. Programme to generate input data for STAB98.FOR

14 CHINCH1 LOTUS 123 P.M. Baviskatr. Programme to check stability of submersibleabutment.

15 PRESTRE LOTUS 123 P.M. Baviskatr. Sample calculations of Design of Prestressessed superstructure.

16 NEO FORTRAN Y.E. Sakhalkar. To check the given dimensions of neoprenebearing for different load cases.

17 HYD4 FORTRAN Y.E. Sakhalkar. Hydraulic calculations for bridges .18 ABWELL MS EXCEL Y.E. Sakhalkar. Abutment well stability.19 SOLCP FORTRAN Y.E. Sakhalkar. Stresses in solid circular pier subjected to axial

load and moment.20 ABUT MS EXCEL Y.E. Sakhalkar. Abutment stability.21 FEMG FORTRAN S.K. Mukherjee.22 NBD FORTRAN S.K. Mukherjee.23 WATER CURRENT

FORCEMS EXCEL S.K. Mukherjee. Excel worksheets to calculate water current

forces.24 WIND CURRENT

FORCEMS EXCEL S.K. Mukherjee. Excel worksheets to calculate winder current

forces.25 SUMMARY OF

DEAD LOAD

MS EXCEL S.K. Mukherjee For design of pire,to calculate dead loads.

26 SUMMARY OFLOAD OPEN

FOUNDN

MS EXCEL S.K. Mukherjee For design of pire,to calculate dead loads.

27 SUMMARY OFLOAD WELL

FOUNDN

MS EXCEL S.K. Mukherjee To calculate total load for various combinationsfor well design

28 SUMMARY OFLOAD STEINING

LEVEL

MS EXCEL S.K. Mukherjee -----

29 REINFORCEDSECTION

MS EXCEL S.K. Mukherjee

30 SOLID CIRCULAR MS EXCEL S.K. Mukherjee To calculate stresses in steel and concrete for circular section

31 HOLLOWCIRCULAR

MS EXCEL S.K. Mukherjee To calculate stresses in steel and concrete for hollow section

32 Auto CAD C/S OFNALLAH AUTOCAD-R14 Hiranwar Programme to generete Lsection on Nalla for given bed levels33 SLAB RAFT FORTRAN Analysis of raft foundation(slab type)34 CHANNEL RAFT FORTRAN Analysis of raft foundation(channel Type)35 BEAM RAFT FORTRAN Analysis of raft foundation36 PIER STABILITY FORTRAN Programme to check abutment stability37 PIER STABILITY MS EXCEL Deotare -----38 COUNTER FORT

ABUTMENTSTABILITY

MS EXCEL Deotare Programme to check abutment stability

39 NEOPRENEBERING DESIGN

LOTUS 123 Worksheet for design of neoprene bearingdesign.

ANNEXURE -2: TYPE DESIGNS ISSUED BY THE DESIGN CIRCLE2.1 TYPE DESIGNS (1. FOUNDATIONS)

Sr.No

Drawing No. Description

1 Drg.No.I/a-3/1/1972 Details of well steining and curb 3m dia2 Drg.No.BR-I/A-3/2/1972 Notes and reinforced schedule of well stening and

curbe for 3m internal dia.3 Drg. No. 1/B-1/1/1972 Well anchorage details for pier well 3m (Twin well)4 Drg. No. BR-III/I/C-2/1/1972 Details of well steining & curb 4m internal dia.

Stening thick .0.7m

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5 Drg. No. BR-III/I/C-2/2/1972 Details of well steining & curb 5m internal dia.Stening thick .0.85m

6 Drg. No. BR-III/I/C-2/3/1972 Details of well steining & curb 6.20m internal dia.7 Drg. No. BR-1/C-2/4/1972 Detailes of well steining and curb 3m internal dia.8 Drg. No. BR-I/C-2/5/1972 Detailes of well steining and curb 5.60m internal

dia.9 Drg. No. BR-I/C-2/6/1972 Details of well steining & curb 4.2m internal dia.

Stening thickness .0.9m internal dia.

10 Drg. No. BR-I/C-2/7/1972 Details of well steining and curb 5.2m internal dia.11 Drg. No. BR-I/I/C/2/1/1972 Tentative details of steining & curb(for tapi bridge atIndgaon.)

12 Drg. No. BR-I/D-1/1972 Details of well cap under under abutment 6.20mdia.

13 Drg. No. BR-I/D-3/1972 Details of well cap and pier and abutment internaldia. 3m stening thickness 0.60

14 Drg. No. BR-I/D-3/1972 Details of well cap under pier 3 m internaldia.

15 Drg.No.BR-I/E-2/1/4/1972 General layout of type design for R.C.C. rafts onshallow foundation (Two way rafts slabs )

16 Drg. No. BR-I/E-2/2/4/1973 Details of reinforcement for bars two way raftsslabs.

17 Drg. No.BR-I/E-2/3/4/1972 Schedule or reinforcement for bars for R.C.C. raftson shallow foundations(Two ways rafts slab)

18 Drg.No.BR-III/I/E-2/4/4/1973 Details of reinforcement for two way.rafts onshallow foundations.

19 Drg.No.BR-III/I/E-2/1/5/1979 Type designs for R.C.C. rafts foundation for bridgeskey plan.

20 Drg.No.BR-III/i/2/5/1979/T.P. Type designs for R.C.Cum . Rafts foundations forbridges reinforcement arrangement.

21 Drg.No.BR-III/E-2/3/5/1979/ Type designs for R.C.C . rafts foundations forT.P. bridges schedules of two spans.

22 Drg.No.BR-III/I/E-2/4/5/1979/ Type designs for R.C.C . raft foundations forT.P. bridges schedule for more than two spans.

23 Drg.No.BR-III/I/E- Type designs for R.C.C . raft foundations for 2/5/5/1979/T.P. bridges schedule for single span.

24 Drg.No.BRN/CDR/178/92037 R.C.C. details of raft with cut-off wall walls.

(2.2) TYPE DESIGNS (II.SUB- STRUCTURE)

Sr.No. Drawing No. Description

1. Drg.No.II/G-1/1972. R.C.C. return 9m height2 Drg.No.II/G-2/1972. R.C.C. box return 4.5m height .3 Drg.No.II/G-3/1972. R.C.C. box return 3m height4 Drg.No.II/G-4/1972. R.C.C. box return 13.5m height5 Drg.No.II/G-5/1972. R.C.C. box return 13.5m height6 Drg.No.II/G-6/1972. Schedule of reinforcement for box return height 12m

& 13.5m only.7 Drg.No.II/G-7/1972. R.C.C. box return 6m height.8 Drg.No.II/G-8/1972. R.C.C. box return 7.5m height.9 Drg.No.II/G-9/1972. R.C.C. box return 12m & 7.5m clear .10 Drg.No.II/G-10/1972. Schedule of reinforcement for 3m ,6m ,9m&12-m

deep box return and statement of concrete and steelfor different .

11 Drg.No.II/G-11/1972. R.C.C. box return 10.5-m height.12 Drg.No.II/K-1/1972. details of abutment cap with dirt wall and pier caps

for T-beam and slab and R.C.C. solid slab(superseded)

13 Drg.No.BR-III/II-K/75001/T.P. Details abutment cap with dirt wall and pier capfor solid slab .

14 Drg.No.BR-III/K-1A/1972 Details abutment cap with dirt wall and pier capfor T beam and slab.

15 Drg.No.BR-II/N-1/1973T.P. Sketch showing surface reinforcement for pier abutments with mass concrete or c.c.1:3:6with plumb.

16 Drg.No.BL-IV/II/A &B/74007 Type section for abutment (with sol id slab deck )./TP.

17 Drg.No.BL-IV/II/A &B/74008 Type section for abutment(for T beam and slab/T.P. deck.

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18 Drg.No.BL-IV/II/E&F/ Type section for return walls and wing walls .74009/T.P.>

19 Drg.No.BL-IV/II-G/75025 R.C.C. box returns 13.5m ht.(H.Y.S.D.and c.c.M150)20 Drg.No.BL-IV/II-G/75026 R.C.C. box returns 12m and13.5m height .(H.Y.S.S.)21 Drg.No.BL-IV/II- R.C.C. box returns 12m and13.5m height(schedule of

G/75027/T.P. reinforcement).22 Drg.No.BL-IV/II-/75028/T.P. R.C.C. box returns 10.5m ht. (Schedule of

Per Pa Ration of Bridge Project

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