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[vikram.jeet]

Substructures :-

Abutments :-
River Bridges provided with various types of Abutments -

1) Mass concrete Abutments with Mix 1:2:4 and surface reinforcements,,

2) Non Spill through abutments with Rcc Columns and Screen wall

3) Spill through abutments with Rcc Columns and stone pitching at front (river side)

1)  Mass abutments resist earth pressures and other loadings through its mass(weight) and various sections along ht of Abutment were analysed to keep tensile stresses within limits on tension side,, compressive stress may not govern. Uplift from base to be considered.

2) Non spill through Abutments  - Rcc columns were provided beneath each Main Girder and additionally two columns at corners of abutments,  Rcc columns emerge out from Well cap in care of well foundations. A rcc wall facing earth side id provided to resist earth pressure and other forces,  and transfer to rcc columns. Use of Dr VK Raina paper for analysing rcc section was made.

3) Spill through abutments are  with rcc columns as above but, without screen wall and earth fill is sloped inside and protected by stone pitching /now a days Gabion.

[vikram.jeet]

Substructures :-

Piers and Pier caps :-

Pier is designed to carry DL and LL,, moments due to horizontal forces of braking and  temperature (thermal) ,, water current forces.

Since Simply supported span era due to manual designs,, the bearings one span were fixed and other  span free .

Pier section is checked for Max LL case with vehicle train causing Max reaction  ,, Minimum LL case with  LL placed distantly to cause minimum reaction but full braking horz force.,  and No LL case. Also pier sections need to be checked under one span, ie, span on one side existing case.  It was called one span collapsed condition earlier.
Wiind /EQ cases were also checked  , but EQ govern over wind in  conc Bridges.

Pier caps were cantilevered  from piers.

Governing cases were sometimes Minimum LL case, but full moments ,, but calculations were presented with all cases, so as to get the checking easy by MOST,  State PWD's Or Proof reader.

[vikram.jeet]

Superstructure:-


Bridges in Himachal Pradesh,,  were single lane , and  two longitudinal  girders scheme  with rcc deck slab was adopted. I intermediate x girders and End X girders  wete provided as stated earlier.  Since most of spans of various Bridges in HP over Khads were single spans > 20 m ,, Prestressed  post tensioned Girders were adopted. .


In X section single lane Road width on bridge was 4.25m  plus 0.225 m kerb on each side plus 0.150 m railing each side  as bridge x section.

Where  Bridges are two lane with roadway width 7.5 m, Three girders scheme was adopted.

Fior smaller spans upto 20 - 30 m Neoprene bearings were used  ,, but for higher spans Roller bearing at ond end and rocker hearing at other end were being used.

In Roller rocker bearings, the load shared by fixed rocker bearing is as per IRC 6
H = (B/2 +T)  or ( B-T) whichever higher.

For neoprene bearings forces were shared equally at each end.


Legend :-
B = Braking force  from Vehicle train
T =  Thermal force = u*W
  
W = (DL +LL) reaction

[vikram.jeet]

Dear Er Prashant ji,,

Whatever being stated by me in yr subject post, date back to about  40-45 yrs ,  computerisation  and availability of very potent softwares has made the life of Bridge structural engineers  , I should not use word easy,, which is not in dictionary of Republic of Structural engineers. ,  but little convenient but associated with faster demands. on job fronts.

So the ongoing discussion s fm my end csn be used to have s visualisation of bridge designs and only a first aid  Treatment  but for you, the experienced Structural person,  SKY IS THE LIMIT if you venture in bridge field too.

Just sharing  to let budding engineers also to know the vintage design  approach in bridge designs.

Thanks and beast rgds

[vikram.jeet]

Superstructure s :-

Cross girders function id to distribute the vehicle loads equally among longitudinal Girders,, in case loads are placed centric to bridge deck x section,  but  vehicle can take any position on bridge deck and due to eccentricity of Loads,, the loafs distribution to various longitudinal girders needs to be worked out based on popular and acceptable Curbon's Principle.

The Intermediate X girders can be 300 mm wide and depth wise these are at least of depth = 0.75* Depth of main long girders. Regarding it's design,, it was designed spanning between long girders for (self DL + Panel DL of slab  + plus wheel load  reaction from both sides assuming deck slab transferring that to  x girder.

End x Girder role is very important. It  is generally 600 mm to 900 width and having depth same as Longitudinal girders. It was also designed as explained for intermediate x girder  since bearings are placed beneath junction point of main long girders and End x girder.  
End x girders are additionally designed for JACKING CONDITION OF DECK,, Jacks are put  under End X girder on both sides of long girder junction and bearings are placed / for future replacement & maintenance.. Wt of DL of deck on long girders as vertical load with end x girder spanning between jack points.

[vikram.jeet]

Superstructure :-

Sequence of presentation of calculations in M/s GILCON  , delhi as devised by Dr VK Raina,, Chief of Organisation ( who used to reports to Sri Subba Rao, now Late ,CMD Gammons  ) as th GILCON was sister concern of Gammon India Ltd.

A2 tracing papers were cut into three long sheets. Each sheet accomodates 5 Big pages.  Blue prints of these ling cut tracings (blank ) were taken by Office ferro printer and handed over to concerned Engineer. Sample old bridge calcs were taken by the engineer, just to follow sequence. The design was written by the Engineer with pencil.  Each part of design was enclosed  as Table 1 , Table 2 etc. This was done to interconnect reference of one table to other.

The manuscripts of design written by one engineer was given to other engineer of same level for checking. Once the manuscript is checked,  it is passed to the original engineer who wrote manuscript. The  blank Tracing sheets (which were taken fir blue print earlier) were also handed over to manuscript engineer for writing the design calculations in pencil based on corrected manuscript.

Once tracings are ready in design calculations,, it's ferro prints were taken and a file is made and sent to Senior Engineer, who also check. Once satisfied, the drgs which were also simultaneously in preparation were finalised and checked by manuscript engineer and rechecked by senior engineer including head draftsman.

Final design calculations and drgs set was then taken by senior engineer to Dr VR Kittur (then Deputy chief of Gilcon) who also check and final checking by Dr Vk Raina .
The design calculations and drgs once approved by Dr Raina,  more ferro copies were taken to form File volumes and despatched to MOST/State PWD /Proof Reader appointed by Client department.

Sri VR Kittur took over from Dr VK Raina who joined UNDP.

Sharing some memories of working in a professional, dedi c ated Consultancy firm

[vikram.jeet]

Presentation of manual calculations :-

Superstructure s :-
Sheet 1
Table 1 - Design criteria, Notes on design,, Materials stresses , Loadings

Table  2 -  Deck x sec ,, outer girder section properties,, Inner Gurder Sec properties

Table 3- Self Del's,, Main Girders and deck slab, X girders loads
Super imposed DL's  -wearing coat loading,, loads of karbs & Railing

Table  4-lmpact Factors,

Sheet 2  

Table 1 - Reaction Factors  calculations of various Vehicular loading for Inner and outer girders


Sheet  3 - Live Load Bending moments at various sections of Span
This was presented in Tabular form with sections Midspan,, 1/4th span, 1/8th span, Face of End Block  along top horizontal  
And Vehicle Class loadings along vertical - one lane Class A,  Two lanes of class A,  One lane of Class 70R (wheeled) ,, one Lane of 70R (tracked) .

For each section of span ILD iwere  drawn and Loads were placed on it at critical position to give maximum BM. These are multiplied with Impact factor as well Reaction Factors to present BM outer Girders and BM inner girders

Sheet 4  - Live Load shear Force at various sections  :- done on same lines

Sheet 5   - Self DL BM,, BM due to SIDL (wearing coat plus Kerbs and Railings)
SF due to  self DL and SIDL were also worked out . These were were multiplied with reaction factors ( since no eccentricity,  equal distribution)

[vikram.jeet]

Structural design calculations presentation:-
(continued fm previous post)

Sheet 6 -
Table1 - Braking (Horizontal forces) and their moments  in LL direction at bearing level

Table 2 - Horizontal forces due to temperature and their moments at bearing level

Table 3 - Recap of forces and Moments at various sections of bridge span

Table 4 - Stresses due to DLs and Live loads at various sections

Sheet  7

Table 1  -  Notes on prestressing , cable / tendons used,, sheathing dia used,, UTS of cables / tendons ,  slp of  cables / tendons,    type of jack and jacking pressure
Slip for 12/7 cable = 6mm
Slip for 12T13 Tendons = 10mm

Table 2  Losses in prestress

[vikram.jeet]

Superstructure :-

Presentation of design calculations
(continued fm previous post)

Sheet 7
Table 1 ,, Table 2  - already discussed in previous post

Table 3 -  
Cable profiling  diagram in elevation clearly showing position of  it's centerline from girder soffit and it's position at end with parabolic profile ,, dividing span into small parts to detail parabolic profile including mid span, 1/4 th span,, 1/8th span and FOEB (face of end block)

Each cable profile was covered in one table separately giving profile diagram in elevation, and also in plan bending near end Block face. Losses due to friction along length of cable,, as well  change in angle in Elevation and also in plan were worked  out in tabular form at various sections including Midspan, 1/4 th span, 1/8th span and FOEB  . Prestress forces prior to SLIP   were worked out for each set of cables. .

Sheet  8 - Prestress forces for  cables prior to slip (as explained above)

Sheet-  9  :-  Cable force  diagram plotting  cable forces as worked out above along y axis and various sections along length  were plotted. This diagram is before slip
After allowing for slip ,, the cable forces drop and it is being worked out by trial and error.
In same table  extension of cables also worked out for each set of cables.

Sheets 10 - same as above for other cables

Sheet 11 :-
Table 1 - Total Prestress forces and Moments at various sections

Table 2 - Stresses due to Prestress at various sections

Taile 3 -  Prestress Losses of  Shrinkage, Creep  ,, Elastic shortening of concrete ,, relaxation of steel  worked out

Table 4 - Percentage losses worked out for Stage prestressing
Stage 1 -  DL loads (Girders plus deck slab + Prestress stage 1)
Stage 2 - SIDLs except Wearing coat plus stage 2 PS
Stage 3  - wearing coat  plus stage 3 PS


Sheet 12
Table 1 - Summary of stresses at Extreme Fibers

Table 2 - Check for  section as per Ultimate Load theory
This was mandatory as subject design was done under Elastic theory

Table 3 - SF at various sections due to prestress
Table 4 : Net SF  at various sections

Sheet 13
Table 1 - Un-tensioned reinforcement in girders
Table 2 Shear reinforcement at various sections in girders

[vikram.jeet]

Superstructure:
Presentation of design calculations :-

Sheet 13 - Table 1 &table 2 - as per previous post

Table 3 - Design of Intermediate X Girders,  RCC

Table 4 - Design of End X Girders  RCC
Design under jacking condition also yo be presented

Sheet 14 -  Design of Deck slab
Deck slab thickness generally was 200mm to 250 mm st that time but now it has to be more as per revised requirements.
Table 1 Deck X section was drawn showing Deck slab along with chamfers. Design criteria also given

Table 2 Self DL,, SIDL in form of wearing coat and Kerbs & Railings were worked for slab design.

Deck slab is designed as one way slab spanning between main longitudinal girders .
In three girders scheme for two lanes bridge deck, the slab is continuous  two span.

ILD's for Two span continuous beams are drawn based on  BM coefficient s given in STEEL DESIGNER'S MANUAL.  
Table 3  &4 - For each  Load class tyres are placed fir maximum span moments,  Maximum support moments considering dispersion along span . The moments do obtained were converted by dividing with effective width of that load.



Sheet 15

Table 1 , 2&3 - as above for other lod classes

Table 4 :- Recap of DL and  Live Liad moments for various loadings to mark Governkng Values


Sheet 16
Table 1 :- Design calculations for check for MOR of  slab  and  working out reinforcement in deck slab  .  Distribution reinforcement calculations.
  
Table 2 - Check of slab  for shear

Table 3 Design of Kerb s and Railings