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vikram.jeet
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PostPosted: Thu Nov 30, 2023 4:27 pm    Post subject: Reply with quote

Er Prashant ji,,

The manual design philosophy in Bridge designs is being  discussed by me here is just to have understanding,  but now a days computer work out the critical cases inherently.

But for any designer understand ing is very important to be able to have perfect modelling.
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PostPosted: Fri Dec 01, 2023 7:33 am    Post subject: Search for mentor Reply with quote

vikram.jeet wrote:

Er Prashant ji,,

The manual design philosophy in Bridge designs is being  discussed by me here is just to have understanding,  but now a days computer work out the critical cases inherently.

But for any designer understand ing is very important to be able to have perfect modelling.


Dear Sir
I agree with your above reply, I am interested in understanding the design philosophy of bridges and hence interested in manual designs and then proceed further to computer modelling and analysis.
I will be in touch with you regarding the subject.
Thank you  
Prashant.
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vikram.jeet
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PostPosted: Fri Dec 01, 2023 4:26 pm    Post subject: Reply with quote

Manual design  calculations were presented in two volumes generally :-

Volume 1 -  substructures  ( Foundations, abutments, piers,,design including design of bearings

Volume 2 - Superstructure design  ( Design of girders,  Deck slab,, kerbs,  railing, now Crash  Bariers )


Foundations :- for river Bridge s, in case bridges located in hill terrains, open Foundations were adopted based on sbc of rock strata

But in rivers in  Plains Well foundations were adopted with separate design for Abutment wells and Pier wells

Abutment and it's Foundations were also checked under  Deck not existing  during construction stage / superstructure washed condition  and permissible stresses were were increased under such conditions .
Piers were also checked under one span existing conditions
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 2:14 am    Post subject: Reply with quote

Dear Prashant ji,,

Again reiterate that sharing whatever little I know about bridges  is I only a first aid effect,, but there is need for you to have a mentor, expert in bridges  having spent his life in bridge designs.

I sm just recalling some tips from manual era.

Hope you may bear with.

Thanks and regds
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 3:16 am    Post subject: Reply with quote

Well Foundations :-

These were designed considering skin friction of sides as well as base area .

Wells are subject to vertical loads from superstructure and horizontal forces (causing Moments) from temperatures and braking  ,, water current forces under normal conditions and additional   horizontal  forces under Wind/EQ.  
Abutments well also subject to Earth pressures and there was practice to provide eccentricity of superstructure (centerline brgs) wrt to centerline well to decimate at least  some percentage of earth pressures.

Wells were also designed for additional moments of  TILTS AND SHIFTS. pl refer to IRC codes.

During execution if tilt of well and shift of well exceed the limits taken in design as per IRC,, the design needs to be seen again with actually value of tilt and shift and stresses to be checked, to be within permissible limits. If Wells are shifted and tilted more and design is not ok with such,, there is need to correct at site .

Well caps are generally 1.5 to 2.5 m thickness  to transfer loads anc moments to well steining.

Features of well foundations are - Cutting Edge at base of steel made of Angle iron with stiffners beneath with steining cast over it and sinking.
RCC well steining analysed as annular section subject to loads and moments. Use of Dr VK Raina papers was extensively made. WSM was permitted in IRC Codes.

Bottom Plug :- once well sunk to it's founding level it is plugged at bottom with 1.5 to 2.0 m concrete mass.

Sand filling

Intermediate plug :- at about LWL, I think, not sure,

Sand filling

Well cap



May please verify as I am recalling and not quoting from book
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 3:25 am    Post subject: Reply with quote

Tilt and shift to be taken in design ad per IRC 78

TILT = 1 in 80

SHIFT =150 mm

Both to be taken additive
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 4:05 am    Post subject: Reply with quote

Well foundations :-

Well foundation is deep foundation. The Passive less active pressures  are analysed, earlier, using Bombay Committee Method which is I think, now included in IRC 45.


Pile Foundations :- These were popular for Flyovers and city bridges,  but  for Rivers, pile foundations were not adopted due to deep scouring situations under HFL (Flooding period) .
I think piles are now adopted for low scouring situations,, but rivers like Ganga and Yamuna,, bridging is still on well foundations,, if not wrong,.
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 4:43 am    Post subject: Reply with quote

Open Foundations :-

Open foundations for Bridge structures are feasible on Rocky strata.

When I joined GILCON delhi as tiny tot designer ,, the work on Himachal bridges was in progress  and single span, mostly, bridges were there with abutments foundations in Rock,,
Few bridges were having main central long span in Prestressed and smaller end spans,i n Rcc, Also tackled Legship Bridge West sikkim having 50m box Girder main  span, straight    and 20m rcc end spans (same box) curved to align with roads on either side to make S shape in plan.

Design is usual,, but IRC code allowed redistribution of pressure by permitting 20percent upliftment under normal conditions and 33percent under seismic conditions.  Use of Wyane C Teng's Charts wrre followed to work out base pressures on footings subjected to vertical load and Bi axial moments.

Open foundations were provided with rock anchors as a mandatory measure,, NOT  to be considered in design.
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 8:00 am    Post subject: Reply with quote

Bridge Loadings :-
Please refer to IRC 6


FOUNDATIONS & SUBSTRUCTURE :-

VERTICAL LOADS & THEIR MOMENTS
(Moments To be worked out separately for L-L direction and T-T direction
,  where LL is along Longitudinal and TT is along Transverse  direction )

Due to DL and  Live loads from superstructure transferred through Bearings
Eccentricity of Live loads in transverse direction will cause M(TT)

Moments due to( Tilt + Shift) in well foundations

HORIZONTAL LOADS AND THEIR MOMENTS
Due Temperature and braking  forces (Depending on type of bearings adopted)
Centrifugal forces in curved decks
Eath pressures
Water current forces on piers and abutments


Earthquake  horizontal  and vertical forces and moments  ( generally govrns in concrete  deckings RCC/PSC)/
Wind horizontal forces and moments (Generally significant vs EQ)
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vikram.jeet
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PostPosted: Sat Dec 02, 2023 11:52 am    Post subject: Reply with quote

Bearings :-

Role of bearing is very important in Bridges. Bearings transfer super structure loads to sub structures - Abutments and  Piers.

Earlier,  (as I know in late seventies)   bearings were of three types extensively used in Bridges.

Metallic Roller and Rocker bearing for heavy loads,  made of Forged Steel

Neoprene Bearings  for medium range loads

Pot bearings just came into mrkt, but not popular

Later advanced version of pot bearings  - PTFE bearings with fixed type,, free type are, now a days the only prefered bearings

For small Bridges plate on plate bearings
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