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vikram.jeet
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PostPosted: Sat Dec 09, 2023 4:34 am    Post subject: Reply with quote

Presentation of Design Calculations - Why so much emphasis and importance

Each page sheet was having Table  No. And top title clearly stating what is given in this page sheet.

THIS WAS DONE TO PROVIDE REFERENCES And CROSS REFERENCE S.

FOR EXAMPLE -  REFER TABLE 2 OF SHEET 5 etc

The designs were presented for easy and convenient checking by Ministry of Surface Transport (MOST) ,, State PWDs Or their proof Consultants.

I salute Dr VK Raina,  a gem of Bridge and Structural Engineering,  a Living Legend, fir his  unique way of presentation of Bridge design calculations.

Main advantages :-
Easy and early checking by Departments and fast approvals

Less queries

Easily explained on phone and avoiding visits to Department  thereby saving in engineer time to devote to other projects

Even freshers can follow  the designs
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vikram.jeet
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PostPosted: Sat Dec 09, 2023 4:58 am    Post subject: Reply with quote

Some 15 yrs back posting on sefi forum,  post titled 'Dr VK Raina, World Class Engineer' initiated by Sri UH Varyani  saheb.

vikram.jeet wrote:
Dr VK Raina

He is definitely a gem of Bridge engineering,I think,still serving as Technical Advisor  
for the United Nations funded projects .
He is beyond description because of his accomplishments .
A Very dynamic ,living genius of structural engineering  
He has written many books and papers .His presentation of bridge designs was unique


My association with him was short,during late seventy, but has lasting effect on me and
still a guiding force.

He commanded respect from everyone because of his flamboyant personality,
clear oration and clarity of concepts. He is born technocrat and great practitioner


A hard task master with compassionate heart and always lived by example

I express my heartiest appreciation, gratitude and regards to this living legend
who was crowned as Prime Advisor in the technical position in UNDP ,a pride
for our Nation.


vikramjeet


Dear Sefians,
Dr.V.K.Raina,Ph.D,D.I.C,B.Sc(eng),is a top class bridge engineer of
world-wide fame.He is the author of nine books.I have recently read
his book'The World of Bridges'.
It is a pictorial journey through the history of bridge design.His
brief commentary is worth reading and meditating upon.He has proved
that brevity is the soul of wisdom.
He presently resides at NOIDA,near Delhi.We all would like to offer
him our best wishes and regards.I would request those engineers who
have worked with him to give more
details of his work and personality,for the benefit of us all.
with best wishes and regards,
uhvaryani







--

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vikram.jeet
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PostPosted: Sat Dec 09, 2023 5:10 am    Post subject: Reply with quote

Earlier posting regarding Mentor and Bridge Expert Dr VK Raina  initiated by Er Sri
Alok Bhowmick


vikram.jeet wrote:
Dear Mr Bhowmick

Thanks for posting this .It will inspire everyone as he is a living legend
and GEM of Bridge and structural engineering.

Dr VK Raina's interview

On structural engineering:

Engineering is not just doing sums, nor it is matter of blind adherence to graphs and formulae
It is more meaningful to have an approximate solution to an exact problem than an exact solution
to an approximated problem.A useful book does not have to be graveyards of dead Phd's

A technical profession such as Design and Construction of Bridges needs to move ahead
and thus real time practice must subordinate pure theory and yet the former needs an
analytical mind trained by that theory to carry out the practice.

Practical engineers must be conceptual more than perceptual, creative more than  
analytical , and more visual than merely mathematical.

Good engineering judgement comes out of experience and yet experience comes out
of bad engineering judgement.

best regards

vikramjeet



Dear All,
The CHRONICLE (New Jersey, USA) recently interviewed Dr V K Raina, …a familiar name in India, particularly for Bridge Engineers. ATTACHED is a copy of what they published. This is for reference of all Sefians.
With best wishes
Alok Bhowmick

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vikram.jeet
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PostPosted: Sat Dec 09, 2023 7:23 am    Post subject: Reply with quote

Prestressed concrete Mein Girders :- End Block Design

End Block :- the main girders which were generally 300 thick were thickened at about  750 to 900 m towards s ends with  flaring. The thickened Girder accomodate cables / Tendons  on pairs, which were running concentrically  about centerline girders to flare for end block. End block  to facilitate jacking.

End block female cones   are precast embeded sealed  at ends based on  respective profiling  .  End block  was designed based on accepted Guyon's Theory given in his book to arrive at dis of SPIRAL REINFORCEMENT AROUND TENDONS  AND NOS AND DF IA OF MESH REINFORCEMENT IN THE END BLOCK.

End block is subject to very high  compressive and splitting forces.
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vikram.jeet
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PostPosted: Sat Dec 09, 2023 4:29 pm    Post subject: Reply with quote

Superstructure - Prestressing


Bridge girders are mostly Prestressed post -  tensioned type.

The Girders are cast with un - Tensioned longitudinal reinforcement plus full shear reinforcement plus sheathings  laid and tied as per cable profile s  plus End block spiral reinforcement & vertical meshes.

Cables are stressed after   after concrete achieve its strength .
Pre stressing is fine in two/ three stages.

Cables are stressed and blocked when these achieve specified extension as mentioned in drgs.

Stressing is done simultaneously from both ends

Cables are then grouted in sheathing.

Losses in Prestress  :-
Friction loss  
While stressing the prestressing cables/ Tendons,, the friction between cables and sheathing from mid span towards end block based on distance create loss in PS,
Also angle turned in elevation as well as plan create loss. Both these losses sre  calculated in table s of cable profiles and working ps forces before slip.
Slip  Loss
This loss occurs when cable after stressing is  blocked.

This is also  worked out during calculations  and pd forces snd moments are worked out at various sections.

Other Losses to be worked out  (percentage wise) and algebrically accounted in SUMMARY OF STRESSES AT EXTREME FIBERS AS PER STAGE .
These ste :-
Losses due to Shrinkage of concrete
Creep
Elastic Shortening of concrete
Relaxation  of ps steel

These needs to be worked out,  as first trial these needs to be assumed as total 20-25percent , with PS1 as 12-15percent ,  PS 2 as 8- 10 percent  these losses are Excluding friction and Slip
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vikram.jeet
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PostPosted: Sun Dec 10, 2023 2:54 am    Post subject: Reply with quote

Prestress design vs Rcc design,,

In rcc design , if ,, higher reinforcement is provided than needed,, there is not any problem except slight more spending on reinf quantity.


But in Prestress ,, design requires precision ,, Over Dosage is as dangerous as under dosage.  ie to say that if by chance cables are kept more than required ,, it will cause high compressive stresses on cable side fibers and high tensile stresses on other side since cables are not at NA but eccentric to it. Pre Stress counters stresses due to DL plus LL. Bursting, splitting  occurs if prestress is in excess  OR  Loads are worked erroneously and structure can fail.  Hence prestress design requires high precision in calculations of Loads,, prestress.
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PostPosted: Sun Dec 10, 2023 2:51 pm    Post subject: Reply with quote

Substructures :-

All structure components - Foundations , Abutments,, Piers  in contact with earth /water  were provided with Mild steel reinforcement to have stresses  to ensure crack width control. Structure components above water level  - Abutment cap, Pier cap etc and Superstructure were provided with Torr steel. This was to ensure durability of foundations and substructures even though it was a costly provision,, but crack check was very stringent. I think now HYSD bars are slso used with new guidelines for crack width.  

In steel reinforcement  ,,IRC code 21  permit lesser permissible stresses vis a vis IS Code 456 ,,

Tensile stress in bending ,, eg
Fe415 - 2000 kg/cm2  in IRC 21 vs 2300 kg/cm2  in IS 456
Fe 250 - 1250 kg/cm2  in IRC 21 vs 1400 kg/cm2 in IS 456

Crack control check was different,  forcing designers to go for Mild steel reinforcement for buried structure components.
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PostPosted: Sat Dec 16, 2023 2:56 am    Post subject: Reply with quote

Approaches to River Bridges :-

In case of Approaches to River Bridges,,  options were/are :-

RCC Retaining walls on sides  

Sloping backfill protected by stone Pitching /gabions./ grassing  shrubs

RE wall option (in case of flyovers,, ROBs)  can not be adopted  due  River Bridges in close vicinity to rivers with saturation of backfill under HFL. RE wall is solely dependent on back fill friction  which is not available in saturated / submerged conditions .
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PostPosted: Tue Dec 19, 2023 7:37 am    Post subject: Reply with quote

Super structures :-

Notes Prestressing :-

Prestressing was done using 12 T13 Tendons  as per IRC 6006.
Salient features of these syrands are :

No of strands - 12

Nominal dia  of each strands /Tendons = 13 mm

Gross UTS  of tendons = 200 kg/mm2

Nominal steel area of Tendons = 1115 mm2

Recommend minimum sheath dia = 66 mm

Permissible stresses (As per IRC 18 )

Maximum Temporary stress in PS steel   = NOT greater than 0.70 *UTS
(After allowing for Slip  &  Elastic shortening)

Overstressing  = Not greater than 0.80* UTS  to allow for slipping of Anchorage OR  To achieve calculated extensions


Note this was as per old code IRC 18 ,, but pl follow latest from latest version only)
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vikram.jeet
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PostPosted: Tue Dec 19, 2023 11:11 am    Post subject: Reply with quote

Outdated but not out of Memory :-

Bridge design vintage approach, in absence of softwares / computers in India  , are being shared by me  is  just to emphasize that  100 percent inputs were  provided by the Consulting firm  and a fresh engineer can grow under mentorship of experts /  seniors of the field.

Now with softwares,, Indian design engineers  are achieving dream creations in Bridges .

One must agree not to invent wheel,, but philosophy of structures analysis and design as  fed in softwares needs to be understood and visulised by even modern day designers,, to  emerge as real professionals of the field.

Hence sharing this little manual design experience,,
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