Univ Minor Rc Bridges

8/12/2019 Univ Minor Rc Bridges

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MINOR PROJECT TOPIC:Reinforced Concrete Bridges

BY

ZUBER AHMED

Enrolment No. MUR-1101408

Roll No. MUM-CV-SE-04

M.Tech(P/T) Structures (5th Semester)

18 June 2014 1


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Types of RC Bridges:

1. Slab Bridges.

2. Girder and Slab (T-beam) Bridges.

3. Hollow Girder Bridges.4. Balanced Cantilever Bridges.

5. Rigid Frame Bridges.

6. Arch Bridges.

7. Bow String Girder Bridges.

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T-Beam Bridges

Most commonly adopted type bridge in the span range of 10 to 25 m.

Main longitudinal girders are designed as T-beams.

Deck slab is casted monolithically with the girders.

Superstructure may be arranged to conform one of three types:

1. Girder, Slab and Diaphragm type.

2. Girder and slab type.

3. Girder, Slab and Cross beam type.

Longest single span of T-beam 35m for Advai bridge in Goa.



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T-BEAM BRIDGES



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Components of a T-Beam Bridge

Deck Slab.

Cantilever portion.

Footpaths, if provided, Krebs and handrails. Longitudinal Girders, considered in design to be of

T-section.

Cross beams or diaphragms.

Wearing course.



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COMPONENTS OF T-BEAM BRIDGE



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BAR CURTAILMENT FOR T-BEAM



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Design Of Longitudinal Girders Such ribs are used when cross beams are not used

The reactions on two longitudinal girder can be found byassuming the supports of the deck slab as un-yielding. With

three or more longitudinal girders the load distribution isestimated using the methods:

1. CourbonsMethod.

2. Hendry-Jaegar Method.

3. Morice and Little version of Guyon and MassonetMethod.



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Hollow Girder Bridges

These bridges are economical in span range of 25 to 30m

These bridges are not preferred these days

Components of girder are:

1. Cantilever portion including the kerb2. Top slab carrying the roadway

3. Webs (Exterior webs & Central Webs)

4. Diaphragms (Two end & three intermediate

diaphragms)



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HOLLOW GIRDER BRIDGES



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Balanced Cantilever Bridges Continuous spans are used.

Governing bending moments can be minimized.

Good for medium span ranging from 35m to 60m.

One disadvantage is that it requires a more skill on part of

designer and more elaborating detailing of reinforcements.

Advantages over simply supported girder designs are:

1. Less concrete, steel and formwork are required.

2. Reactions at piers are vertical and central.

3. Requires only one bearing at every pier.

4. Fewer expansion bearings are needed, resulting in lowerfirst cost and maintenance.



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Continuous Girder bridges

It is not connected monolithically to supports

They are suitable when unyielding supports are available

BM and shears of bridge are evaluated using influence lines

Disadvantages over simply supported girder bridges are:1. Should not be used where unyielding foundations cannot

be obtained at reasonable cost

2. Detailing and placing of reinforcements need extra care

3. Sequence of placing concrete & removing formwork to becarefully planned

4. Design is more complicated being statically indeterminate



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Advantages of over simply supported girder bridges:

1. Depth of decking at mid-span will be much smaller.

2. Quantities of steel and concrete will be less, resulting inreduced cost. Reduced depth of deck leads to decreasein cost of approach ramps and earthwork.

3. One bearing required as against two bearings requiredfor simply supported designs.

4. Fewer expansion joints will be required. Elimination ofjoints enhances the riding quality over the bridge.

5. Since bearing are placed on centre lines of the piers,reactions are transmitted centrally to the piers.

6. Suffers less vibration and deflection.



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CONTINUOUS GIRDER BRIDGES

C



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Rigid Frame Bridges

Consists of parallel girders which are rigidly connected to thesupporting columns or piers.

Types of rigid frames normally used in bridge construction:

1. Single span openings in case of bridges over railway tracks.2. Two-span bridge with base of column fixed or hinged.

3. An aesthetically pleasing structure over restricted highways.

Advantages over continuous bridges:

1. No bearings are needed at supports.2. Rigid connections result in more stable supports.

3. In view of slender dimensions, supporting piers cause theleast obstruction to view for traffic below the bridge.



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RIGID FRAME BRIDGES

R



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Arch Bridges

Used advantageously in span range of 35m to 200m. Aesthetic elegance and functional clarity.

Arch can be in the form of arch slab or arch ribs.

Various types of Arches namely:

1. Fixed Arch.

2. Two-hinged arch.

3. Three-hinged arch.

Arch axis is generally governed by:

1. Span and rise from the road gradient.2. Economical shape from point of view of saving materials.

3. Beauty of the intrados.

4. Rise-span ratio.



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A fixed arch is statically indeterminate and its analysisis based on the use of the following assumptions:

1. Span length remains unaltered.

2. Abutments remain fixed in position, and there is novertical displacement at the abutments.

Two-hinge arch is indeterminate to first degree. Itsanalysis is based on following assumptions:

1. Span length remains unchanged.

2. Abutments remain in position, but arch axis may rotate. Three-hinged arch is statically determinate and its

analysis is quite simple.



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Bow String Girder Bridge Consists of two arches tied horizontally at springing by tiemembers, so that reactions at support will only be vertical.

Normally used in span range of 30 to 35m.

Applicable in situations where unyielding abutments requiredfor arches are not available and good headroom is requiredunder the bridge adjacent to abutments.

Girder is supported on pin bearings on one end to permit

rotations and roller bearings at other to provide for expansion. Overall economy is not quite apparent due to less quantitiesusage of material but it would require costly formwork .

Enhanced aesthetic appearance merits attention.



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BOW & STRING GIRDER BRIDGES



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Pier Cap Analysis:

Pier Cap Literature Review.

Pier Cap Analysis Concept .

Pier Cap Analysis Calculations &Results.



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Pier Cap Literature Review:

Definition:Pier cap is the structural element that transfer the load

form the superstructure elements to the substructure elements, located

at the junction of two spans .



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Pier Cap (Types & Specifications):

Pier caps can come in different types like:

Single column (Hammerhead).

Solid Wall. Multi-column or pile bent.

The selection of the pier type depends on:

Required load capacity.

Superstructure Geometry.

Site conditions.

Cost Consideration.

Aesthetics.18 June 2014 24ZUBER AHMED


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1- Single Column (Hammerhead)



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2- Solid Wall



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Pier Cap Literature Review:3- Multi-Column or Pile Bent



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Information to be identified from analysis process:

Preliminary pier dimensions .

Applied load form superstructure.

Pier dead load.

Pier live load.

Material properties.



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Pier Cap Analysis Concept:Girder Reactions

Pier Own WeightLive Load on Bridge Deck



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Pier Cap Analysis Calculations &Results:

Minimum Height of Concrete Structure:



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Pier Cap Analysis Calculations &Result:

Pier height:

Pier Width:

Cross section area:

Pier own weight:

mL

h 65.15.18

30

5.18

mhw 825.0265.1

2

236125.1825.0*65.1* mwh

mkNAw concappierLD 03125.3436125.1*25.



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Bridge Components Design:

Design of Bridge Slab (Deck).

Design of Bridge Girder.

Design of Bridge Pier Cap.



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Bridge Deck (Slab) Design Concept & theory :

Design of Rectangle Section Involves two cases:

Case 1:Unrestricted sectional Dimensions.

Assume steel ratio ()min ()max.

Determine concrete dimensions accordingly (b,d & h).

Case 2:Pre-determined sectional dimensions.

Determine area of steel (As ) from given dimensions.

Ensure that (As)min As (As)max.



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Design of RC Section Requires Determination of:

1. Concrete Dimensions:

Beam width ( b ). Depth of steel reinforcement ( d ).

Section height .h = d + cover-to-center of steel.

2. Area of steel reinforcement ( As).

3. Ensure safety requirements ( As)min As ( As)max.



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Determine steel ratio ():

Using ACI Equation

Use of Tables from Appendix B

Choose the appropriate Table (B.8 up to B.10) according to (fc) and (fy).

Calculate the term (Rn) and then select ( ) accordingly.



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Important Notes:

If you find < min then, choose min.

If you find > max

Increase Section Depth ORAdd Compression Steel



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Bridge Deck (Slab) DesignConcept & theory

:

Calculate Area of steel:

Determine number of steels bars = As/Dia. of Bar

Check available width and steel distribution.



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Design of Rect. Section:

STEP 1: Assume bar size and then determine db.

STEP 2: Assume cover.

STEP 3: Compute depth of steel reinforcement ( d )

STEP 4: Determine ( ) from Tables or ACI Equation.

STEP 5: Ensure that min max.

STEP 6: Determine As.



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Bridge Girder (Design Concept):Main target is to determine the location of the neutral axis.

Two cases:

Case 1:

N.A falls in the flange (a hf).

Section above N.A is rectangular.

Same procedure as R-sections BUT different formula for the

calculation of As(max).



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Bridge Girder (Design Concept):

Compare the values of Mu& Mflange if:

Mu< Mflange a < hf

Mu> Mflange a > hf

Where:

Mu= Moment from applied forces (Obtained by Analysis).Mflange= Moment carried by flange.



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Case 1:

Mu


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Design of Rect. Section STEP 1: Assume bar size.

STEP 2: Assume cover.

STEP 3: Compute depth of steel reinforcement ( d ).



STEP 6: Determine As.



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Case 2:

Mu>Mflange a >hf

Design concept of T-Section



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Bridge Girder (Design Concept):STEP 1: determining the N.A position.

STEP 2: Dividing the compress area into two rectangles.

STEP 3: Calculating Asf& M

uw.


STEP 5: Calculating Asw.


STEP 7: Determine As(Total).



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Bridge Pier Caps Design:

According to reinforcement concrete (RC) design concept,the design of bridge pier caps follows the rectangularsection design method which is used in slab design.



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