PROJECT REPORTPROJECT REPORT

DESIGN CONCEPTS OF BOW STRING GIRDER (40 M SPAN) OF ROAD OVERBRIDGE AND DESIGN OF SUB STRUCTURE FOR THE SAME.

PRESENTED BYPRESENTED BY1. R.M.MEENA

(XEN/C/JU/NWR)

2. SIVA KUMAR (AXEN/Designs/MTP®/MS/S.R.)

3. L.N.LOKHARE (AXEN/C/KTT/WCR)

4. L.B.SINGH MAURYA (Vice Principal/SRETC/TBM/S.R.)

INTEGRATED COURSE INTEGRATED COURSE BATCH NO-514BATCH NO-514

PROJECT GUIDE

Sri.G. Bansal

COURSE DIRECTOR

Sri A.K.Rai

INTRODUCTIONINTRODUCTIONOn Indian Railway there are 16471 Nos of

manned level crossings and 19284 Nos of unmanned level crossings as on date. These Level crossings are affecting the safe & effective functioning of Railways. The Level crossings are the accident prone zones and causes delay of trains due to detention by road traffic at gate.

INTRODUCTION- contINTRODUCTION- cont

There are loss of valuable human life and Railways properties due to accidents taking place on this level crossings. Keeping safety point of view it become necessary to replace these level crossings by ROB/RUB..

INTRODUCTION- contINTRODUCTION- cont Replacing the level crossings with

ROB/RUB are being done by Railways in a phased manner based upon its TVU. Where ever possible ROB is preferable over RUB due to its less maintenance, effective usefulness, even though the initial cost of ROB is more.

SCOPE OF THE PROJECTSCOPE OF THE PROJECT

The ROB comprises following different structure:-

1. Main railway span (40 m)2. Approach spans having 20 m spans3. Abutment4. Reinforced earth retaining wall beyond

abutment on the approaches where height is less than 4.0 m

SCOPE OF THE PROJECT - contSCOPE OF THE PROJECT - cont

As far as super structure is concerned only design concept of Bow string girder is emphasized. However for substructure complete design is made and enclosed.

ELEMENTS OF BOW STRING ELEMENTS OF BOW STRING GIRDERGIRDER

MAIN I- GIRDER

Main I- girder is purely a tension member because of its geometry. This member is proposed as a prestressed member .The amount the prestressing required shall be less since the same required only nullify the tension.

MAIN I GIRDER

ARCH MEMBERSUSPENDERS

ARCH MEMBERARCH MEMBERArch member is always in compression

and hence RCC is sufficient to take this load. A member size of 450x900 at supports and 450x600 at crown is normally sufficient to carry the compression for this 40 meter span.

SUSPENDERSSUSPENDERSSince suspenders are pure tension

members and it does not requires any flexural rigidity , these members can be provided as HTS strands firmly anchored between main I beams and arch members

CROSS GIRDERCROSS GIRDERCross girder can be of RCC, which spans

between main I -girders. The spacing of cross girders is kept as 4.15 meter & the span is 8.0 meter. At the top of cross girder, a continuous slab of span of 4.15 meter and thickness of 230 mm is provided. Over the slab road-wearing surface as per IRC, specification is provided.

4150

CROSS GIRDER

C LINE OF SPANLC LINE OF BEARINGL

41500

PLAN AT DECK LEVEL

BOW STRING

8m

LOADINGLOADINGLive load

Load as per IRC-6

Combinations are1. Single lane 70R wheeled/track vehicle2. Two lane IRC –class A, wheeled

ADVANTAGES OF BOW ADVANTAGES OF BOW STRING OVER DECK TYPE STRING OVER DECK TYPE

GIRDERSGIRDERS

There is some considerable savings in depth of construction in case of bow string girder compared to typical deck type girder Due to reduced depth of construction, the over all length of ROB get reduced and overall economy achieved

2500

ROAD SURFACE

7500

BOX GIRDER TYPE ROB

DEPTH OF CONSTRUCTION=2.50m

2400

BOW STRING GIRDER

7500

1000

ROAD SURFACE

DEPTH OF CONSTRUCTION=1.0m

BOW STRING GIRDER TYPE ROB

DESIGN CONCEPT OF BOW DESIGN CONCEPT OF BOW STRING GIRDERSTRING GIRDER

LIVE LOADLike our railway bridge rules, these IRC

codes does not provide any EUDL,so for the above rolling loads maximum bending moment and shear force shall be worked out using STAAD-PRO 2003 software. However a manual calculation is also shown. Due provision for impact is also considered as per the code.

DEAD LOADDEAD LOAD

This comprise of dead load of all element of bow string span ,the carriage way wearing coat, foot path and other miscellaneous load such as cables, parapets, crash barriers have been considered

WIND LOADWIND LOAD

Wind load is arrived at as per IS 875 part-III.the wind intensity multiplied by the projected area gives the wind load on the structure.

SUB STRUCTURESUB STRUCTURE The substructure consists of two numbers

of 1.80 meter dia column spaced at 8.0 meter apart. The depth of trestle beam is fixed as 1.25 meter for stiffness and other practical consideration such as requirement during construction and replacement of bearing.

ELEVATION OF SUBSTRUCTURE

PILE CAP

PILE 1.0m dia

COLUMN 1.80m dia1.80m

1.25m

8.0m

4

Rail level

6.525m

LOADS AND OMENTS LOADS AND OMENTS ON COLUMNON COLUMN

As we know the the column is critical at the pile cap level . Maximum moments will come at this level which are all explained through the following sketches. Algebraically adding all the moments the column section is designed

SESMIC LOAD SESMIC LOAD

Lateral Seismic Coefficient=0.04Importance Factor =1.5 (for important

bridges)Foundation system factor =1.0 (for pile

foundation) Design for seismic

force=.04x1.5x1.0=.06

SESMIC LOADSESMIC LOAD

Code followed IRC 78 Even though the seismic load does not

affect the super structure, the impact on the substructure design is considerable.

Seismic Zone III

Lumped mass of super structure

Adjoining span -20m Bow string span- 40m

Leve

r ar

m

Pile cap

Pile1.DUE TO DEAD LOAD

Adjoining span -20m Bow string span- 40m

Leve

r ar

m

Pile cap

Pile

Lumped mass of trestle beam

2.DUE TO DL OF SUB STRUCTURE

Adjoining span -20m Bow string span- 40m

Pile cap

Pile

Higher loadLower load

xy

Un balanced moment =higher load * y-lower load *x

Adjoining span -20m Bow string span- 40m

Leve

r ar

m

Pile cap

Pile

1.83 m

4. DUE TO LIVE LOAD

FoundationFoundationThe foundation system consists of four no

of 1.0m dia pile spaced at 3.0m apart. The piles are proposed to be founded on hard strata, which is available at 25.0m depth. The piles are of bored cast in situ.

FoundationFoundation

Max. vertical Load in pile workout to be :- under seismic condition = 264 tonnes under normal loads = 214 tonnes lateral load per pile = 14 tonnes

FoundationFoundation Vertical load bearing capacity of pile = 320 tThe above capacity of piles is based on soil

capacity at site. The pile derives its capacity both from friction as well as end bearing.

FOUNDATIONFOUNDATION Reinforcement design of pile

The length of fixity of pile below ground level “Le” is found based on lateral modulus of subgrade reaction of the pile

The moment on pile = Horizontal load x Le

Based on the moment and the vertical load on the pile,the reinceforcement of the pile is designed

L1=2.5m

L=22.5m

5.318m

Le

CALCULATION OF LENGTH OF FIXITY OF PILE

Pile cap