Miscellaneous Bridge Components Sri Naresh chandra Rout and Sri Nihar Ranjan Behera Asst.Executive Engineer(civil) ,PWD,Odisha

CONTENTS CRASH BARRIER RAILINGS KERBS FOOTPATH DRAINAGE SPOUTS WEARING COATS APPROACH SLAB ABUTMENTS &ITS TYPES WING WALLS RETURN WALLS FLY WING WALLS FILTER MEDIA WEEP HOLES BACKFILL BEHIND ABUTMENTS/WING WALLS/RETURN WALLS

What is Crash Barrier? A barrier provided at the side of carriageway designed to reduce the risk of serious accidents by guiding the errant vehicles back on the road.

CRASH BARRIER

CRASH BARRIER

Where do we provide crash barrier? All high level Bridges, Fly overs, interchanges and ROB’s. Approaches to Bridge Structure, where embankment height is more than 3m

Different types of Crash Barrier Rigid Barrier(e.g:Reinforced Concrete crash barrier ) Semi-Rigid Barrier(e.g ,Metal beam Crash barrier) Flexible Barrier(e.g: wire rope fencing)

Semi-Rigid Barrier (Metal Beam Crash Barrier)

Rigid Barrier(R.C.C Crash barrier)

Different category of Crash barriers There are three categories of crash barrier for different application. Category Application Containment for P-1: Normal Containment Bridges carrying expressway, or equivalent 15KN vehicle at 110Km/hr and 200 angle of impact P-2: Low Containment All other bridges except bridge over railways 15KN vehicle at 80Km/hr and 200 angle of impact P-3: High Containment All hazardous and high risk locations,over busy railway lines, complex interchanges, etc. 300KN vehicle at 60Km/hr and 200 angle of impact

IRC Codal Provisions Minimum grade of concrete: M-40 (for P1,P2,&P3) Ref: IRC:6-2014(Clause No.206.6) and IRC:5-2015(Cl.No.109.6) Minimum grade of concrete: M-40 (for P1,P2,&P3) Minimum Thickness of RC wall (at top):-175mm(for P1 &P2) :-250mm(for P-3) Minimum thickness at bottom: 500mm Minimum Height-900mm (for P-1 & P-2) & 1550mm(for P-3) Minimum Moment of Resistant at base of the wall for bending in vertical plane with reinforcement adjacent to the traffic face= 15KN-m/m(for P-1) = 7.5KN-m/m(for P-2) =100KN-m/m for end section and 75kN-m/m for intermediate section (for P-3)

IRC Codal Provisions Minimum Moment of Resistant for bending in Horizontal plane with reinforcement adjacent to the outer face =7.5KN-m/m(for P-1) = 3.75KN-m/m(for P-2) =40KN-m/m(for P-3)

Bridge Railings Bridge Railings are provided along each side of the bridge and erected on and above the kerb/deck for the protection of pedestrians or cyclist from falling over

Types of Railing Steel rolled section Tubular steel Cast-in-situ concrete Pre-cast concrete

Precast/Cast-in –situ concrete railings

Precast/Cast-in –situ concrete railings

Steel Railings

STEEL RAILING

Bridge Railings Railings for high level bridges,fly over and ROBs etc shall have a minimum 1.1m height above the adjacent roadway or footway safety kerb surface. When cycle track is located adjacent to the bridge railing, the height of the railing shall be minimum 1.25metres. Minimum grade of concrete for Railing=M-30

Railing(for submersible bridges) Railings for submersible bridge and vented causeway shall be either collapsible or removable during flood,so as to minimise obstruction to flow of water and passage of floating debris. It is preferable to provide perforated kerbs along with diamond shape guide posts for submersible bridges.

KERBS A line of raised concrete section, forming an edge between carriageway and railing/footpath/median.

KERBS(contd…)

Footpath Footpath is provided on either side of bridges for pedestrian using the roads in the interest of road safety. The width of footpath shall be minimum 1.5m and the width may be increased on bridges in urban areas. The loading shall be taken as 500kg/sq.m

FOOTPATH

Footpath

Drainage Spout

Drainage spout

Drainage spout Disposal of rainwater from bridge surface Spacing shall not exceed 10m. 100mm dia Galvanised/PVC pipe or any other corrosive resistant material Discharge from drainage spout shall be kept away from the deck structure (down pipes upto 500mm above H.F.L)

WEARING COAT A wearing coat/wearing course is provided over concrete bridge decks to protect the structural concrete from the direct wearing effects of traffic and also to provide the cross camber required for surface drainage. Cross camber:2.5%

Type of Wearing coat Bituminous Wearing coat Cement concrete wearing coat)

Bituminous wearing coat Bituminous wearing coat shall comprise of following types Type 1: Bituminous concrete 5omm Thick laid in single layer Type 2: Bituminous concrete 40mm thick overlaid with25mm thick mastic asphalt Type 3: Stone Matrix Asphalt 50mm thick laid in single layer Type 4: Mastic Asphalt 50mm thick laid in single layer Before laying wearing coat the deck surface shall be thoroughly cleaned and tack coat shall be applied.

Cement concrete wearing coat Cement concrete wearing coat may be adopted in isolated bridges/culverts where use of bituminous wearing coat is inconvenient. The thickness of C.C wearing coat shall be 75mm and concrete shall be minimum M-30 grade.

Abutments Abutments are end supports to the superstructure of a bridge and they retain earth on their back side which serves as an approach to the bridge.

Components of an Abutment

Components of an Abutment

Components of an Abutment An abutment generally consists of the following three distinct structural component 1) Stem/Breast wall 2)Wing walls 3) Back wall/Dirt wall

Components of an Abutment Stem/Breast wall : The stem/breast wall directly supports the dead and live loads of the superstructure and retains the earthfilling on the rear side. Wing walls: The wing walls are provided adjacent to abutment which act as an extensions of the breast wall,retains the earthfill without resisting any loads from the superstructure. Back wall/Dirt wall: A dirt wall is small retaining wall located just behind the bridge seat and it prevents the earthfill from approaches spilling on the bridge seat and bearings. Dirt wall shall be provided with minimum thickness of 200mm (Ref: Cl.710.6.4 of IRC:78-2014)

FUNCTIONS OF AN ABUTMENT Distributes the loads from bridge ends to the ground/foundation Withstands any loads that are directly imposed on it. Retains the fill of approach embankment behind it.

Primary function of an Abutment

Types of Abutments Full-Retaining/Full-depth Abutment Semi-Retaining/ Partial depth Abutment Sill/Stub Abutment Spill-through/open Abutment Counter fort Abutment U-Abutment Box type Abutment Non-load bearing abutment. Integral Abutment

Full-Retaining/Full-depth Abutment A full-retaining abutment is built at the bottom of the embankment and must retain the entire roadway embankment.

Full-Retaining Abutment(Contd…) This type of abutment is generally most costly. But it reduces the span length and superstructure cost Full-retaining abutments are desirable where right of way is critical. An objectionable feature of full-retaining abutments is the difficulty associated with placing and compacting material against the body and between wing walls.

Full-Retaing Abutment(contd…) Other Disadvantages of full-retaining abutments are 1) Minimum Horizontal Clearance 2) Settlement of Foundation 3) Minimum sight distance when the roadway underneath is on curved alignment 4) Collision hazard when abutment front face is not protected.

Semi-Retaining/Partial depth Abutment The Semi-retaining abutment is built somewhere between the bottom and top of the roadway embankment.

Semi-Retaining Abutment(contd…) It provides more horizontal clearance and sight distance than a full-retaining abutment. Since it is located on the embankment slope, it becomes less of a collision hazard for a vehicle that is out of control. They are primarily used in highway-highway crossings

Sill Abutment/Stub Abutment The Sill abutments are short abutment constructed at top of the embankment/ at the top of the slope after roadway embankment is close to final grade.

Sill-Abutment(Contd….) Sill abutments are the least expensive abutment type and are usually the easiest to construct. This abutment type results in a higher superstructure cost Sill type abutment eliminates the difficulties of obtaining adequate compaction adjacent to the relatively highwalls of closed abutments.

Spill-through/open Abutment Spill through abutment is an abutment where soil is allowed to spill through gaps, along the length of abutment.

Spill-Through Abutment Here columns are placed below deck beam and gap in between is free to spill earth.

Spill-Through Abutment (Contd…) Spill-through abutment consists of a beam that supports the bridge seat, two or more columns supporting the beam. The columns are embedded up to the bottom of the beam. Spilling of earth is not generally permitted above a level of 500mm below the bottom of bearing.

Spill-through/open Abutment(Contd…) A spill through /open abutment is mostly used where an additional span may be added to the bridge in the future. It is essentially a pier being used as an abutment.

Spill-through/open Abutment(contd…) Disadvantage: 1) it is very difficult to properly compact the embankment materials that must be placed around the columns and under the abutment cap. 2) Early settlement and erosion are problems frequently encountered .

Counter fort Abutment Counter fort Abutments are similar to counter fort retaining walls designed for large vertical loads.

Counter fort Abutment(Contd..)

U-Abutment

U-Abutment A U-abutment is an abutment whose wing walls are perpendicular to the bridge seat.

Box type Abutment When the return walls on two sides are integrated with abutment and a back wall parallel to abutment is provided at the end of return walls, the structure is called Box type abutment

Non-load bearing abutment Abutment, which supports the end span of less than 5m.

Integral Abutment

Integral Abutment

Forces Acting on Abutments Dead load due to superstructure Live load on superstructure Self weight of the abutment Longitudinal forces due to tractive effort and braking Forces due to temperature variation and concrete shrinkage Earth pressure due to backfill Thrust due to effect of live loads on the fill at the rear of the abutment (i.e effect of live load surcharge)

Design of Abutment c) Stability against Sliding: 1) Assumption of Preliminary Dimension 2) Checking for Stability against overturning, base pressure and Sliding a) Stability against overturning: The factor of safety against overturning should be grater than 2.0 b)Stability against base pressure: The maximum base stress should be less than the safe bearing capacity of soil. c) Stability against Sliding: The factor of safety against sliding should be more than 1.5 3) Structural design of various component

Details of Abutment

Drainage behind Abutment (Ref:IRC:78-2014,Appendix-6) Filter Media and Weep holes Filter Media : A layer of filter material well packed to a thickness of 600mm with smaller size towards the soil and bigger size towards the wall shall be provided over the entire surface behind abutment,wing/returns walls to the full height.

Drainage behind Abutment Weep Holes: Adequate number of weep holes not exceeding one metre spacing in both directions sholuld be provided to prevent any accumulation of water and building up of hydrostatic pressure behind walls. The weep holes should be provided above low water level.

Back fill Behind Abutment (Ref:IRC:78-2014,Appendix-6)

Return wall A vertical wall adjacent to abutment generally parallel to road to retain approach embankment and raised up to the top of road In addition to the earth pressure, return walls are designed to withstand a live-load surcharge equivalent to 1.2m height of earth fill (Ref: Cl.no.707.6.9 of IRC:78-2014) Return walls are provided at right angle to the abutments.

Wing walls A wall adjacent to abutment with its top upto road top level near abutment and sloping down up to ground level or a little above at the other end. These are generally at 450 to the alignment of road or parallel to the river and follows profile of earthen banks. Wing walls provide smooth entry of water into the bridge site and provide support and protect the embankment.

Wing walls(contd..)

Wing walls(contd..) The wing walls are designed primarily to withstand earth pressure in addition to self weight. Wing walls shall be of sufficient length to retain the roadway to the required extent and to provide protection against scour. The top of the wing/return walls shall be carried above the top of embankment by at least 100mm to prevent any soil from being blown or washed away by rain over its top(Ref:Cl.710.6 of IRC:78-2014)

Classification of wing walls Wing walls are classified according to their position in plan with respect to banks and abutments. 1. Straight wing walls: used for small bridges, on drains with low banks 2. Splayed wing walls: used for bridges across rivers.They provide smooth entry and exit to the water. The splay is usually 450 .Their top width is 0.5m,face batter 1 in 12 and back batter 1 in 6, weep holes are provided. 3. Return Wing walls: used where banks are high and hard or firm. Face is vertical and back battered 1 in 4. 4.Fly wing walls

Fly wing walls These are the wing walls cantilevering from abutment/return wall. Also called butter fly wing walls. They are provided when approach embankment height is not very high and there is no problem of errosion of earthen embankment during flood. The length of fly wing walls /cantilever return walls where adopted should not be more than 4.0m.

Fly wing wall

Approach slab An approach slab is a transition slab of reinforced concrete laid on immediate approaches to a bridge with one end resting on dirt wall/abutment.

Function of approach slab The approach slab which is usually provided on either side of bridge, function as an interface between the bridge structure and approach roadway. The slab serves to minimize bumps to traffic and the resulting impact to abutment due to potential differential settlement between the approach embankment and the abutment.

IRC Provision for approach slab The minimum length of approach slab shall be 3.5m . Minimum grade of concrete: RCC M-30 The slab should cover full width of the roadway and shall have a minimum thickness of 300mm at the ends with maximum thickness adjusted to suit the cross camber.

Approach slab

MINISTRY DRAWINGS (for Super-structure of Bridges) Here Ministry means Ministry of Road Transport & Highway,Govt. of India, New Delhi. Indian Road Congress(IRC) on behalf of Ministry, has published a number of Standard Plans of Superstructure for Highway Bridges for practicing engineers for preparation of estimates and construction in the field.

MINISTRY DRAWINGS (contd..) (for Super-structure of Bridges) The Standard plans contain a series of standard drawings for Solid Slab type superstructure, R.C.C T-Beam & Slab type superstructure and PSC Girder& RC Slab composite superstructure etc. The standard plans also contain drawings of bearing, wearing coat, railings and Miscellaneous items etc

MINISTRY DRAWINGS (contd..) (for R.C.C Slab Super-structure) Standard plans for 3.0m to 10.0m Span Reinforced Cement Concrete Solid Slab Structure with and without footpaths for Highways.

MINISTRY DRAWINGS (contd..) (for R.C.C Slab Super-structure)

Ministry Drawing(RCC Slab Bridge)

Ministry Drawing(RCC Slab Bridge)

MINISTRY DRAWINGS (contd..) (for R.C.C T-Beam & Slab Super-structure) Standard plans for Highway Bridges R.C.C.T-Beam & Slab Superstructure-Span from 10m to 24m.

MINISTRY DRAWINGS (contd..) (for R.C.C T-Beam & Slab Super-structure)

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