11 Different category of Crash barriers There are three categories of crash barrier for different application.CategoryApplicationContainment forP-1: Normal ContainmentBridges carrying expressway, or equivalent15KN vehicle at 110Km/hr and 200 angle of impactP-2: Low ContainmentAll other bridges except bridge over railways15KN vehicle at 80Km/hr and 200 angle of impactP-3: High ContainmentAll hazardous and high risk locations,over busy railway lines, complex interchanges, etc.300KN vehicle at 60Km/hr and 200 angle of impact
12 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: mmMinimum 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 forintermediate section (for P-3)
13 IRC Codal ProvisionsMinimum 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)
21 Bridge RailingsRailings 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
22 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.
23 KERBSA line of raised concrete section, forming an edge between carriageway and railing/footpath/median.
25 FootpathFootpath 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
30 Drainage spout Disposal of rainwater from bridge surface Spacing shall not exceed 10m.100mm dia Galvanised/PVC pipe or any other corrosive resistant materialDischarge from drainage spout shall be kept away from the deck structure (down pipes upto 500mm above H.F.L)
31 WEARING COATA 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%
32 Type of Wearing coat Bituminous Wearing coat Cement concrete wearing coat)
33 Bituminous wearing coat Bituminous wearing coat shall comprise of following typesType 1: Bituminous concrete 5omm Thick laid in single layerType 2: Bituminous concrete 40mm thick overlaid with25mm thick mastic asphaltType 3: Stone Matrix Asphalt 50mm thick laid in single layerType 4: Mastic Asphalt 50mm thick laid in single layerBefore laying wearing coat the deck surface shall be thoroughly cleaned and tack coat shall be applied.
34 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.
35 AbutmentsAbutments 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.
38 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
39 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 of IRC: )
40 FUNCTIONS OF AN ABUTMENT Distributes the loads from bridge ends to the ground/foundationWithstands any loads that are directly imposed on it.Retains the fill of approach embankment behind it.
42 Types of Abutments Full-Retaining/Full-depth Abutment Semi-Retaining/ Partial depth AbutmentSill/Stub AbutmentSpill-through/open AbutmentCounter fort AbutmentU-AbutmentBox type AbutmentNon-load bearing abutment.Integral Abutment
43 Full-Retaining/Full-depth Abutment A full-retaining abutment is built at the bottom of the embankment and must retain the entire roadway embankment.
44 Full-Retaining Abutment(Contd…) This type of abutment is generally most costly.But it reduces the span length and superstructure costFull-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.
45 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.
46 Semi-Retaining/Partial depth Abutment The Semi-retaining abutment is built somewhere between the bottom and top of the roadway embankment.
47 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
48 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.
49 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 costSill type abutment eliminates the difficulties of obtaining adequate compaction adjacent to the relatively highwalls of closed abutments.
50 Spill-through/open Abutment Spill through abutment is an abutment where soil is allowed to spill through gaps, along the length of abutment.
51 Spill-Through Abutment Here columns are placed below deck beam and gap in between is free to spill earth.
52 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.
53 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.
54 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 .
55 Counter fort AbutmentCounter fort Abutments are similar to counter fort retaining walls designed for large vertical loads.
58 U-AbutmentA U-abutment is an abutment whose wing walls are perpendicular to the bridge seat.
59 Box type AbutmentWhen 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
60 Non-load bearing abutment Abutment, which supports the end span of less than 5m.
63 Forces Acting on Abutments Dead load due to superstructureLive load on superstructureSelf weight of the abutmentLongitudinal forces due to tractive effort and brakingForces due to temperature variation and concrete shrinkageEarth pressure due to backfillThrust due to effect of live loads on the fill at the rear of the abutment (i.e effect of live load surcharge)
64 Design of Abutment c) Stability against Sliding: 1) Assumption of Preliminary Dimension2) Checking for Stability against overturning, base pressure and Slidinga) Stability against overturning:The factor of safety against overturning should be grater than 2.0b)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 1.53) Structural design of various component
66 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.
67 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.
68 Back fill Behind Abutment (Ref:IRC:78-2014,Appendix-6)
69 Return wallA vertical wall adjacent to abutment generally parallel to road to retain approach embankment and raised up to the top of roadIn 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 of IRC: )Return walls are provided at right angle to the abutments.
70 Wing wallsA 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.
72 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 of IRC: )
73 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 banks2. Splayed wing walls: used for bridges across rivers.They provide smooth entry and exit to the water. The splay is usually 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
74 Fly wing wallsThese 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.
76 Approach slabAn approach slab is a transition slab of reinforced concrete laid on immediate approaches to a bridge with one end resting on dirt wall/abutment.
77 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.
78 IRC Provision for approach slab The minimum length of approach slab shall be 3.5m .Minimum grade of concrete: RCC M-30The 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.
80 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.
81 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
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