Bridge Guidelines for Selection of Bridge Components
Types of Bridges
Bridges are classified in various ways based on function, length, superstructure type, materials, and other criteria as per **IRC:5-2015** and related codes. Understanding these classifications helps in selecting appropriate components during planning and design.
Figure 1: Common Classification of Bridges by Superstructure and Substructure Types
Figure 2: Examples of Bridge Superstructure Configurations
Classification as per IRC:5-2015
- By Function:
- River Bridge / Bridge over Stream
- Viaduct
- Flyover / Grade Separator
- Road Over Bridge (ROB)
- Road Under Bridge (RUB)
- Foot Over Bridge (FOB)
- Underpass / Subway
- Overpass
- Submersible Bridge
- By Length:
- Culvert (as defined in IRC:5 Clause 101.13)
- Minor Bridge: Total length up to 60 m
- Major Bridge: Total length more than 60 m
- By Superstructure Type:
- Slab Bridge
- Girder/Slab (T-Beam, Box Girder)
- Arch Bridge
- Cable-Stayed Bridge
- Suspension Bridge
- Truss Bridge
- By Materials:
- RCC / PSC
- Steel / Composite
- Timber (rarely used now)
- By Span:
- Minor Span (< 20-30 m: Solid Slab)
- Medium Span (30-100 m: T-Beam, Box Girder)
- Long Span (> 100 m: Cable-Stayed, Suspension, Arch)
Selection Guidelines for Key Bridge Components
Selection of bridge components (superstructure, substructure, foundation, bearings, etc.) depends on span, site conditions, hydraulics, soil strata, economy, and constructability. Maharashtra PWD follows IRC codes with state-specific guidelines.
1. Superstructure Type Selection
- Solid Slab: Economical for spans up to 10-15 m (IRC:112).
- T-Beam / Voided Slab: 15-30 m spans.
- Box Girder (PSC): 30-60 m, good for continuity and aesthetics.
- Steel/Composite Girder: Longer spans or where rapid construction is needed (IRC:24).
- Extradosed / Cable-Stayed: Spans > 100 m.
2. Foundation Type Selection
Refer to the earlier table on span-to-height ratios and soil conditions for preliminary selection.
3. Bearings and Expansion Joints
- Use elastomeric/pot bearings for most RCC/PSC bridges (IRC:83).
- Modular joints for longer bridges.
4. Hydraulic and Scour Considerations
- Afflux, linear waterway, and scour depth as per IRC:78 and IRC:SP:13.
- Provide scour protection (aprons, riprap) in flood-prone areas.
Always cross-reference latest IRC codes (e.g., IRC:6 for loads, IRC:112 for concrete bridges) and perform site-specific analysis for final selection.
Common Types of Bridge Superstructures
Bridge superstructures can be broadly classified into several types based on structural behavior, span capability, aesthetics, and construction methodology. The most commonly used types in modern bridge engineering are:
- Slab
- Girder with Deck Slab
- Arch Type
- Suspension
- Cable-Stayed
- Truss Type
Figure: Classification of Common Bridge Superstructure Types
Arch Bridge
Arch bridges work primarily in compression, transferring loads through the curved arch to the abutments. They are aesthetically pleasing and efficient for medium to long spans (typically 40–500 m). Material: RCC, PSC, or steel.
Hydraulic Lift Bridges (Movable Bridges)
Also known as bascule or vertical lift bridges, these are movable structures that allow ship passage. Used where navigation clearance is required. Rare in India but seen in some canal/river crossings.
Truss Bridge
Truss bridges use triangular frameworks to distribute loads efficiently. Common in steel construction for railway and longer road spans (50–300 m). They offer high strength-to-weight ratio but require regular maintenance against corrosion.
Cable-Stayed Bridge
Cable-stayed bridges feature cables directly connecting the deck to one or more towers (pylons). Ideal for spans of 200–1000 m. They are economical compared to suspension bridges and offer striking aesthetics. Signature examples in India: Bandra-Worli Sea Link, Mumbai.
- Slab & Girder with Deck Slab: Most common for spans up to 50 m (economical, simple construction).
- Arch: Suitable where strong abutments are possible and aesthetic appeal is desired.
- Truss: Preferred for railway bridges or where material efficiency is critical.
- Cable-Stayed & Suspension: For long spans (>200 m) over rivers/seas (e.g., signature bridges).
- Movable Bridges: Only where navigation requirements mandate vertical clearance.
Final selection depends on span length, site constraints (hydraulics, geology), budget, construction time, and aesthetic requirements. Always refer to latest IRC codes (IRC:5, IRC:6, IRC:112) for detailed design criteria.
An Ideal Submersible Bridge Should Necessarily Have the Following Characteristics
Submersible bridges (also known as causeways or low-level bridges) are designed to be overtopped during high floods. They are economical solutions for minor crossings in rural or low-traffic areas where full high-level bridges are not justified. As per IRC:SP:13 and Maharashtra PWD guidelines, an ideal submersible bridge should satisfy the following site and design conditions:
- Open foundations keyed into rock.
- Firm and defined banks.
- Both banks at almost the same level.
- Straight nallah / river reach (no sharp bends).
- Ordinary Flood Level (O.F.L.) about 1.0 m below bank level.
- Height of bridge deck above bed level up to 6 m.
- Spans up to 10 m.
- Solid slab superstructure.
Span Arrangement for Submersible Bridges
- The height of a submersible bridge from the bed level is generally about 5 m to 8 m. Therefore, spans up to 10 m are desirable.
- Such span arrangements typically require solid slab superstructures, which provide greater stability during floods due to their mass and low obstruction to flow.
- Longer spans would require girder-and-slab arrangements, which are not desirable for submersible bridges as they offer more obstruction to flood waters, increasing afflux and scour potential.
Foundation for Submersible Bridges
- The ideal situation is to rest foundations directly on rock (open foundations keyed into sound rock).
- When the founding stratum is non-scourable (rock), there are minimal issues related to stability, durability, and long-term maintenance.
- In cases of weak soil strata with limited scour depth, raft foundations can be a viable solution. Raft foundations distribute loads over a larger area and provide enhanced stability by bridging over minor unevenness or local scour pockets.
- Lower construction cost compared to high-level bridges.
- Faster execution.
- Minimal disruption to natural waterway during normal flows.
- Traffic disruption during monsoons (bridge gets submerged).
- Higher maintenance due to flood damage potential.
- Not suitable for National/State Highways or high-traffic routes.
Stoppers on Downstream Side
During floods, there is a possibility that the superstructure may slide due to its buoyant weight and the horizontal forces exerted by fast-flowing water currents. To prevent displacement of the superstructure, it is essential to provide downstream stoppers. These stoppers are typically cast monolithically with or firmly anchored to the pier cap/abutment and bear against the downstream face of the deck slab or girder.
Kerbs and Railings
Kerbs and railings on submersible bridges should be designed to offer minimum resistance to flood water flow:
- Kerb height should be limited to the minimum required (typically 250 mm above the slab level).
- Discontinuous kerbs are preferred to allow smoother passage of water over the deck.
- Railings should be of collapsible or removable type (e.g., crash barriers that can be folded or easily dismantled before monsoon) to avoid obstruction to high-velocity flood flows.
Wearing Coat
The choice of wearing coat is critical for durability under repeated submergence:
- Concrete wearing coat is preferred over bituminous wearing coat for submersible bridges, especially for shorter spans. Concrete is more resistant to prolonged submersion and less prone to stripping or disintegration in water.
- However, concrete wearing coats are not desirable for longer spans as they tend to develop cracks due to flexural deflection of the superstructure.
- In longer spans, bituminous wearing coat (e.g., mastic asphalt or dense bituminous macadam) is recommended, despite requiring more frequent maintenance and repairs after floods.
- For spans ≤ 10 m (solid slab): 50–75 mm thick M40/M50 concrete wearing coat with wire mesh reinforcement.
- For longer spans: Bituminous wearing coat with proper waterproofing layer.
- Provide adequate slope (camber) and drainage arrangements to prevent water stagnation on the deck.
High Level Submersible Bridge
A high-level submersible bridge is a special type of bridge designed to be overtopped only during extraordinary floods (e.g., the 2005 floods in Maharashtra). Unlike conventional submersible bridges that get submerged frequently, high-level submersible bridges remain functional for most flood events and are overtopped only during extreme, rare floods (typically 1 in 50 or 1 in 100 year return period). This design balances economy with improved traffic continuity during normal monsoon seasons.
- Deck level set higher than ordinary high flood level (HFL) but lower than the calculated level for a full high-level bridge.
- Provides all-weather connectivity for most of the year.
- Cost-effective alternative to expensive high-level bridges in low-traffic rural areas.
Selection of Type of Foundation
Foundation Types
Generally, two broad categories of foundations are adopted for bridge structures:
- Shallow Foundations
- Open foundations
- Raft foundations
- Deep Foundations
- Pile foundations
- Well foundations
Selection of Foundation
The choice of foundation depends on several site-specific factors including soil strata, depth to hard rock, scour depth, hydraulic conditions, span length, seismic zone, and economic considerations. The following guidelines (as per IRC:78-2014, IRC:SP:13, and Maharashtra PWD practices) are commonly used for preliminary selection:
| Foundation Type | Typical Conditions for Selection | Advantages | Limitations |
|---|---|---|---|
| Open Foundation | Hard rock or firm strata available at shallow depth Economic excavation depth Low to moderate scour |
Economical Simple construction Fast execution |
Not suitable for deep scour or weak soils Limited to smaller spans |
| Raft Foundation | Weak or compressible soils Hard rock not available up to economic depth Moderate spans with low scour |
Distributes load over large area Resists differential settlement Good for submersible/high-level submersible bridges |
Higher concrete volume Requires good scour protection |
| Pile Foundation | Deep soft soils High scour depth Large spans Where open/raft not feasible |
High load-carrying capacity Minimal settlement Suitable for deep water/scour |
More expensive Requires specialized equipment Time-consuming |
| Well Foundation | Deep scour (rivers with sandy bed) Very large spans/major bridges Uncertain soil strata |
Excellent stability against scour High lateral resistance Proven for major Indian rivers |
Highly skilled construction Time-consuming sinking process Costly for minor bridges |
- Conduct detailed geotechnical investigation (minimum 1 borehole per pier/abutment).
- Estimate maximum scour depth as per IRC:78 (Lacey’s or modified Lacey’s formula).
- Foundations must be taken below maximum scour level by at least 2–3 times diameter/depth for safety.
- For submersible/high-level submersible bridges: Prefer open or raft on rock/firm strata.
- For major rivers with high scour: Pile or well foundations are mandatory.
Final selection should be based on detailed soil report, hydraulic analysis, and life-cycle cost comparison.
Guidelines for Selection of Foundation Type Based on Span to Height Ratio
The choice of foundation for bridge piers and abutments depends on various factors, including soil conditions, depth to hard strata, span length, and economic considerations. The table below provides recommended span-to-height ratios for different foundation types, commonly followed in Indian bridge design practice (as per IRC guidelines and field experience).
| Type of Foundation | Span to Height Ratio | Remarks |
|---|---|---|
| Raft | 1 to 1.25 | Hard rock not available up to economic depth |
| Open | 1.25 to 1.5 | Hard rock available up to economic depth |
| Pile | 1.25 to 1.75 | Suitable for larger spans Hard rock not available up to economic depth |
| Well | 1.5 to 2 | Suitable for larger spans Hard rock not available up to economic depth |
- Span to Height Ratio refers to the ratio of the bridge span length to the height of the pier/abutment from foundation level to superstructure bearing level.
- Lower ratios (e.g., 1–1.25) indicate stockier piers suitable for raft or open foundations in stable strata.
- Higher ratios (slender piers) typically require deep foundations like piles or wells to resist overturning and ensure stability.
- Selection also depends on geotechnical investigation results, scour depth, seismic zone, and hydraulic considerations (as per IRC:6, IRC:78, and IRC:SP:13).
- In flood-prone areas (common in Maharashtra), deep foundations (pile/well) are preferred even for moderate spans to counter scour.
This table serves as a quick reference for preliminary foundation selection during planning and design stages. Final choice must be validated through detailed soil investigation and structural analysis.
Open Foundation
Open foundations are the most preferred type of foundation for bridge structures whenever site conditions permit. They should be adopted when:
- Good founding strata (hard rock or dense soil) is available at shallow depth.
- Dewatering during construction is manageable and not excessive.
For RCC piers, RCC footings are preferred over plain cement concrete (PCC) footings due to higher strength, better durability, and ability to resist tensile stresses.
Well Foundation
Well foundations are deep foundations commonly used for major bridges in India, especially over rivers with deep scour and uncertain soil strata. The shape of the well can be:
- Single Circular
- Double D-Type
- Dumb-bell Type
- Twin Circular
Figure: Common Shapes of Well Foundations
Important Points Regarding Well Foundations
- Well foundations are highly effective in deep scour conditions (common in alluvial rivers of Maharashtra and North India).
- They provide excellent resistance against lateral forces, overturning, and scour due to large embedded depth and mass.
- Sinking is done by dredging inside the well while adding curb sections progressively (open sinking, pneumatic sinking for difficult strata).
- Bottom plug, filling, and top plug are critical construction stages requiring strict quality control (as per IRC:78-2014).
- Tilt and shift during sinking must be monitored and corrected within permissible limits (generally 1 in 100 for tilt).
- Suitable for major bridges with large spans and heavy loads.
- Requires skilled labor and specialized equipment; more time-consuming and expensive than open/raft foundations.
- Double-D and twin-circular wells are preferred for wide piers to reduce skin friction and improve stability.
- Well foundations are mandatory when maximum scour depth exceeds economic excavation limit for open foundations.
- Minimum embedment below scour level: 1/3 to 1/2 of well height or as per design.
- Steining thickness and reinforcement as per IRC:45 and IRC:78.
- Regular monitoring of tilt, shift, and sand blows during sinking is essential for safety.
While well foundations are robust and time-tested (used extensively in iconic Indian bridges like Howrah Bridge, Vembanad Bridge), they should only be adopted when shallow foundations are not feasible due to soil or hydraulic conditions.
Important Points Regarding Well Foundations (Continued)
-
a. Large Diameter Wells:
If the external diameter of a single circular well exceeds 12 m, the relevant provisions of Clause 708.1.2 of IRC:78-2000 shall apply. (This typically involves additional structural checks for hoop tension, buckling, and construction methodology.) -
b. Minimum Steining Thickness:
The steining thickness of the well shall not be less than 500 mm and shall satisfy the following empirical relationship:$$ h = k d \sqrt{L} $$where:
- $ h $ = minimum thickness of steining (in metres)
- $ d $ = external diameter of circular well (in metres)
- $ L $ = depth of well in metres below the top of well cap or Lowest Water Level (LWL), whichever is greater
- $ k $ = constant depending on material:
- 0.03 for wells in cement concrete
- 0.05 for brick masonry
- 0.05 for twin-D wells
- The formula ensures adequate hoop strength to resist soil and water pressures during sinking and service.
- For most modern RCC wells, $ k = 0.03 $ is used.
- Steining is heavily reinforced (both circular and vertical steel) to handle tensile stresses during sinking (as per IRC:78-2014, Clause 708).
- Minimum 500 mm thickness provides sufficient rigidity and durability against abrasion and impact during sinking.
-
c. Concrete Grade for Steining:
In case of PCC wells, the concrete shall not be leaner than M15. Under conditions of severe exposure (e.g., aggressive water or soil), steining shall not be leaner than M20.
The horizontal annular section of well steining shall be checked for ovalisation moments, taking into account side earth pressure. -
d. Cutting Edge and Well Curb:
Mild Steel (M.S.) cutting edge shall have a minimum weight of 40 kg/m to facilitate sinking through all types of strata.
For the well curb, the internal angle should be kept between 30° and 37°. The well curb shall not be leaner than RCC M25. -
e. Bottom Plug and Filling:
The bottom plug shall be designed such that its top is not lower than 300 mm above the top of the curb sump (provided below the level of the cutting edge).
Well filling above the bottom plug shall generally be done with sand. A top plug of minimum 300 mm thickness in M15 concrete shall be provided over the filling.
Raft Foundations
Types of Raft Foundations
The raft foundations commonly used in bridge construction can be broadly classified into three categories:
- R.C.C. Solid Slab Raft
- R.C.C. Channel Raft
- Raft for Box Bridges
Figure: Typical Raft Foundation Bridge
Guidelines for Use of Raft Foundations
- To be avoided for major wide streams such as Godavari, Tapi, Krishna, Penganga, etc. Raft foundations are more suitable for low-height bridges on soft or sandy strata.
- Not to be provided where sand mining and consequent lowering of the river bed is anticipated.
- The top of the raft shall be placed 0.60 m below the Lowest Bed Level (LBL).
- Provision shall be made to tie cutoff walls in the current direction if they become exposed due to sand lifting. Cross cutoff walls shall invariably be provided in each or alternate spans.
When Raft Foundation is NOT Recommended
Raft foundations, however, are not recommended in the following cases:
- Spans greater than 10 m (becomes uneconomical).
- Bridge foundations that cannot be inspected during their service life.
- Serious dewatering problems due to large inflow or standing water.
- Situations where open foundations are feasible.
Scour Protection for Raft Foundations
The size of the stones used in the launching apron is of prime importance. It depends on the velocity of water at the bed level to prevent the apron from being washed away, which could endanger the raft foundation. Stone size and apron thickness must be carefully designed.
If stones of the required size are not economically available, alternatives such as concrete blocks, precast concrete stones, or wire crates (gabions) may be used. Details of wire crates are provided in IRC:89 Appendix 1.
While determining stone size, the velocity of flow at the bed level should be considered. Using maximum velocity occurring at some depth below the surface would result in unnecessarily large stones.
- The minimum weight of individual stones in the apron shall not be less than 40 kg.
- It is desirable to provide larger stones or concrete blocks near the piers on the downstream side, as scour is most predominant in this location.
Figure: Recommended Stone Sizes for Different Velocities in Launching Apron
When the velocity at bed level exceeds 4.0 m/sec, the required stone weight becomes quite large and may be difficult to source. In such cases, consider concrete blocks or crate alternatives for practical and economical protection.
Selection of Substructure Type
Type designs available in Maharashtra PWD provide sufficient guidance for dimensions of PCC piers and abutments up to a height of 10 m. These designs are intended for non-seismic zones only.
For pier heights exceeding these limits or in seismic zones, RCC piers of appropriate dimensions must be designed specifically.
Selection of Superstructure Type
As per Maharashtra PWD policy, standard spans for bridges shall henceforth be adopted from 5 m to 40 m in multiples of 5 m only (e.g., 5 m, 10 m, 15 m, 20 m, 25 m, 30 m, 35 m, 40 m, etc.). This standardization promotes economy, ease of design, and faster construction using type designs.
Figure: Standardized Span Configurations for Bridges
- Utilization of approved type designs reduces design time and errors.
- Economy through repetition of formwork and materials.
- Faster approval and execution.
- Consistency in quality and maintenance.
Non-standard spans should be avoided unless justified by site constraints (e.g., hydraulic requirements or existing structures).
Guidelines for Selection of Superstructure
a) For Spans up to 15 m
The following superstructure types shall be allowed:
- Solid slab
- Portal frame
- Arch portal
- Box cell
- Composite construction
b) For Spans between 10 m and 20 m
- Submersible bridges: Solid slab or spine slab superstructure shall be provided for span lengths of 5 m, 10 m, 15 m, and 20 m.
- High-level bridges: RCC girder, portal frame, or arch bridges shall be provided.
c) For Spans More Than 20 m
- RCC girder (precast or cast-in-situ): Up to 25 m span
- PSC girder (precast or cast-in-situ): 30 m to 40 m span
- PSC box girder: For spans more than 40 m
- Steel girders with concrete deck slab: For spans more than 30–45 m
d) Continuity of Superstructure
Continuous superstructure shall not be allowed except for two-span continuous configurations. Superstructures constructed by the balanced cantilever method may be permitted only in exceptional cases due to difficult site conditions (e.g., deep backwater, deep valleys) where launching or lifting of precast girders is not feasible.
e) Transverse Spacing of Girders
For ease of execution and uniformity, the transverse spacing of girders shall generally be fixed at 2.5 m, irrespective of the bridge width, footpaths, etc.
f) Provision for Services (OFC, Water Pipelines, etc.)
Specific arrangements shall be provided in the end portions of the slab to accommodate services like Optical Fiber Cables (OFC) or water pipelines. Services should preferably be routed over the pier cap in suitable pipe arrangements. In the case of PSC superstructures, services shall not be accommodated by drilling hooks or J-bolts into the girders.
g) Superstructure Types to be Completely Banned
- Superstructure with articulation joints
- Balanced cantilever construction in service (except as permitted under clause d)
- Superstructure with central hinge
- Articulation joints and central hinges have historically led to maintenance issues and reduced durability.
- Excessive continuity increases complexity and risk of cracking without specialized design.
- Banning problematic types ensures long-term performance, reduced maintenance, and safety.
Standard Superstructure Types for Submersible and High-Level Bridges
The following table provides the approved superstructure types, span lengths, and carriageway widths for submersible and high-level bridges as per Maharashtra PWD guidelines. Standardization ensures economy, uniformity, and use of type designs.
| Sr. No. | Description of Superstructure | Submersible Type | High-Level Type | Remarks | ||
|---|---|---|---|---|---|---|
| Span Length | Width of Bridge | Span Length | Width of Bridge | |||
| 1 | RCC Solid Slab | 5 m, 10 m, 15 m | 7.5 m and 11.55 m | 5 m, 10 m, 15 m | 7.5 m and 11.00 m | |
| 2 | RCC Spine Slab | 15 m, 20 m | 7.5 m and 11.55 m | — | — | |
| 3 | RCC Box Cell | 3 m, 7 m, 8 m | 7.5 m and 11.55 m | 3 m, 7 m, 8 m | — | |
| 4 | RCC T-Beam & Slab (Cast-in-situ) | 10 m, 20 m, 25 m | 7.5 m and 11.55 m | 10 m, 20 m, 25 m | 7.5 m and 11.00 m | |
| 5 | Precast Girder and Slab | — | — | 10 m, 20 m, 25 m | 7.5 m and 11.00 m | |
| 6 | Composite Girder and Slab | — | — | 30 m, 35 m, 40 m | 7.5 m and 11.00 m | RCC slab and steel plate girder |
| 7 | Bridge cum Bandhara | 5 m, 10 m | 7.5 m and 11.55 m | — | — | |
| 8 | Arch Bridges | — | — | 5 m, 10 m | 7.5 m and 11.00 m | |
- Widths: 7.5 m (single lane + footpath) and 11.00–11.55 m (two-lane with footpaths).
- Submersible bridges are limited to shorter spans and solid/slab designs to minimize obstruction to flood flow.
- High-level bridges use longer spans with girder systems for better hydraulic efficiency and all-weather traffic.
- Standardization to these spans and widths allows use of approved type designs, reducing design time and ensuring consistency.
Additional Guidelines for Submersible Bridges
For submersible bridges, spans up to 20 m shall be preferred. The recommended superstructure types are:
- Solid slab spans
- Spine slab spans
- T-girder
Spans longer than 20 m shall not be provided, as they attract heavy current pressure and are liable to be washed away during floods.
In exceptional cases where obligatory spans of odd length are required (e.g., for flyovers at road junctions or navigational clearances of 50 m or more), composite superstructure with plate girders may be permitted. This is the only deviation from standard spans allowed.
Selection of Railing / Crash Barrier
The present practice of using RCC Sanchi-type parapets for high-level bridges has led to frequent damage due to increased vehicle speeds and traffic volume. RCC parapets are difficult to maintain and restore after accidents.
Henceforth, RCC Sanchi-type railings shall not be provided. Instead, RCC crash barriers shall be used for high-level bridges. The height of the crash barrier shall be 1.5 m and designed for high containment level to ensure vehicle safety.
For submersible bridges, the traditional MS angle and GI pipe railings are often not removed before monsoons, causing additional obstruction to flood flow and endangering the superstructure. Therefore, angle and pipe railings shall no longer be used. Instead, “W” beam metal crash barriers shall be provided.
Selection of Type of Returns
Return walls (wing walls) retain the approach embankment and guide traffic. Common types include:
- Riding Return: Used where abutments have back batter. Adjusts the batter so that the vertical face of the return wall is separated by an expansion joint uniformly throughout its height.
- Gravity Wall: Resists earth pressure through self-weight. Typically masonry or mass concrete. Suitable for heights up to 6 m.
- Cantilever Wall: Thin RCC section resisting pressure through structural strength. Suitable up to 6 m height.
- Counterfort Wall: Counterforts on the backfill side strengthen the main wall. Used when height exceeds 6 m.
- Buttress Wall: Buttresses on the same side as backfill. Alternative to counterfort for heights > 6 m.
- Tied Back Wall or Box Return: Suitable for high walls and where returns are needed on both sides. Provides excellent stability.
Grade of Concrete for Bridge Components (as per IRC)
It is recommended to use a uniform grade of concrete for all bridge components (except leveling course and annular filling in wells) to simplify construction and quality control.
- Konkan Region (severe, very severe, and extreme exposure conditions): M40
- Rest of Maharashtra (moderate exposure conditions): M30
- Pre-stressed Concrete Components: Minimum M35
Grade of Steel
For bridges in the Konkan region (classified under severe, very severe, and extreme exposure conditions due to high humidity, salinity, and aggressive environment), only corrosion-resistant reinforcement (CRS or HCR steel bars) from reputed manufacturers such as TATA, SAIL, or Jindal shall be used.
Figure: Corrosion-Resistant Reinforcement Bars (CRS/HCR)
Bearings
Bearings are critical components that transfer all forces from the superstructure to the substructure while accommodating movements (translation and rotation) due to temperature, creep, shrinkage, and live loads. Proper selection is essential for longevity and performance. Span length significantly influences bearing size, pedestal dimensions, and expansion joint gaps.
Recommended Selection of Bearings
- Spans up to and including 10 m (solid slab superstructure): Tar Paper Bearings
- Spans > 10 m and < 25 m: Elastomeric (Neoprene) Bearings
- Larger spans: POT/PTFE Bearings
Use of MSM (Metallic Sliding with Mirror) bearings and spherical bearings shall be encouraged for improved performance and durability.
The following bearing types shall be completely banned:
- Cut roller bearings
- Concrete/steel roller bearings
- Rocker bearings
Inspection and Maintenance:
- Bearings shall be inspected twice a year, and records maintained.
- Replacement cycle as per manufacturer/design life must be strictly observed.
Types of Bearings (General Classification)
- Pure Resting: Tar paper bearings (for spans up to 10 m) – Simple, economical, no movement accommodation beyond minor compression.
- Sliding: Allows sliding movement; applicable to small spans but currently not recommended due to maintenance issues.
- Roller: Steel rollers permit longitudinal movement; high maintenance (corrosion, dust accumulation) – banned.
- Rocker: Allows rotational movement but no sliding; steel rocker bearings have maintenance issues – banned.
Elastomeric Bearings
Elastomeric bearings consist of one or more internal layers of elastomer bonded to internal steel laminates through vulcanization. They accommodate translation and/or rotation of the superstructure through elastic deformation.
Recommended for spans from 10 m to 25 m (as per IRC:83 Part II – 1987).
POT-PTFE Bearings
Used for larger spans exceeding 25 m (as per IRC:83 Part III – 2002). These are high-capacity bearings suitable for heavy loads and multi-directional movements.
- a. Fixed POT Bearing: Bears and transmits vertical load and horizontal force in any direction while allowing rotation about any horizontal axis (no horizontal movement).
- b. Free Sliding POT-cum-PTFE Bearing: Bears vertical load, allows movement in any horizontal direction, and accommodates rotation.
- c. Guided Sliding POT-cum-PTFE Bearing: Bears vertical load, transmits horizontal force in one direction only, allows movement perpendicular to that direction, and accommodates rotation.
- d. Free PTFE Sliding Assembly: Bears vertical load, transmits horizontal force in one direction, and allows movement perpendicular to it.
- e. Guided PTFE Sliding Assembly: Similar to free but with guidance in one direction.
Other Bearing Types
- Metallic Guide Bearings: Sliding assembly with restraint in one direction to transmit horizontal force. Allows movement perpendicular to the force and rotation about a vertical axis. Cannot bear vertical load. Minimum height above affluxed design HFL: 500 mm.
- Pin Bearing: Consists of a metal pin within a cylinder. Transmits horizontal force in any direction, accommodates rotation, but cannot bear vertical load.
Degrees of Freedom (DOF) in Bearings
Bearings are classified based on the movements they permit:
- Fixed: No translation, allows rotation (e.g., Fixed POT).
- Unidirectional: Translation in one direction + rotation (e.g., Guided Sliding).
- Multidirectional: Translation in all horizontal directions + rotation (e.g., Free Sliding POT-PTFE).
- Prefer modern bearings (Elastomeric, POT-PTFE, Spherical) for low maintenance and seismic performance.
- Avoid obsolete types (roller, rocker) due to high maintenance and corrosion risks.
- Always follow IRC:83 (all parts) for design, testing, and installation.
- Provide dust seals, corrosion protection, and access for inspection/replacement.
Degrees of Freedom and Capabilities of Various Bearing Types
The following table summarizes the translational and rotational movements permitted, as well as loading resisted, for different types of bridge bearings. √ indicates permitted/resisted, X indicates not permitted, S indicates some resistance.
| Type of Bearing | Translation Permitted | Rotation Permitted | Loading Resisted | |||||
|---|---|---|---|---|---|---|---|---|
| Longitudinal | Transverse | Longitudinal | Transverse | Plan | Vertical | Longitudinal | Transverse | |
| Roller | ||||||||
| Single Cylindrical | √ | X | √ | X | X | √ | X | S |
| Multiple Cylindrical | √ | X | X | X | X | √ | X | S |
| Non-Cylindrical | √ | X | √ | X | X | √ | X | S |
| Rocker | ||||||||
| Linear | X | X | √ | X | X | √ | √ | S |
| Point | X | X | √ | √ | √ | √ | √ | √ |
| Knuckle | ||||||||
| Pin | X | X | √ | X | X | √ | √ | S |
| Leaf | X | X | √ | X | X | √ | √ | √ |
| Cylindrical | X | S | √ | X | X | X | √ | S |
| Spherical | X | X | √ | √ | √ | √ | √ | √ |
| Plane Sliding | √ | √ | X | X | X | √ | √ | S |
| Elastomeric | ||||||||
| Unreinforced | √ | √ | √ | √ | √ | √ | √ | √ |
| Laminated | √ | √ | √ | √ | √ | √ | √ | √ |
| Guided Pot | ||||||||
| Longitudinal | √ | X | √ | S | X | X | X | √ |
| Transverse | X | √ | S | X | X | X | √ | X |
Application of Bearings
| Type of Bearing | Movement Capacity in One Direction (mm) | Rotation (radians) | Typical Application | Steel | Concrete | |
|---|---|---|---|---|---|---|
| Straight | Curved | |||||
| Steel Roller | 100 | 0.19 | √ | - | √ | - |
| Steel Sliding | 25 | 0.08 | √ | - | √ | - |
| Pot | No limit | 0.04 | √ | √ | √ | √ |
| Disc | No limit | 0.04 | √ | √ | √ | √ |
| Spherical | No limit | - | √ | √ | √ | √ |
| Plain Elastomeric | 10 | Negligible | √ | √ | - | √ |
| Laminated Elastomeric | 60 | 0.025 | √ | √ | - | √ |
RE Wall Function
Reinforced Earth (RE) walls are primarily used to retain earth, especially behind abutments of Road Over Bridges (ROB) and in approach embankments.
Not suitable for river bridges due to potential scour, flood exposure, and hydraulic interference.
RE Wall Design
In RE wall systems:
- Horizontal (lateral earth) loads are resisted entirely by the geogrids/reinforcing strips.
- Facia panels are not designed to resist lateral loads; they primarily serve as facing for aesthetics and erosion protection.
Expansion Joints
In bridge planning, efforts shall be made to keep the number of expansion joints to the bare minimum. For this purpose, deck continuity (integral or semi-integral construction) shall be extensively adopted for spans greater than 10 m.
- For spans ≤ 30 m: MS cover plate resting on MS angles (with or without compressible joint filler) is recommended.
- For spans > 30 m: Expansion joints shall be provided as per IRC:SP:69-2011 (Guidelines for Design of Expansion Joints).
During maintenance or relaying of bituminous wearing course, the expansion joint gap often gets filled with bitumen, leading to clogging and undue forces on the superstructure. This must be avoided by:
- Placing thermocol pads or suitable compressible fillers during BT laying.
- Temporarily welding MS flats across the joint (if required), ensuring smooth riding quality post-work.
Water Spouts
Water spouts are essential to rapidly drain rainwater from the deck surface, preventing ponding and hydroplaning risks. The deck camber or super-elevation directs water towards kerbs, from where spouts discharge it away from the structure.
Spacing guideline: One water spout per 20 sq.m. of deck area is considered adequate.
Weep Holes
Adequate weep holes shall be provided in:
- Abutments
- Riding returns
- Solid returns
- Outer walls of box returns
Spacing:
- Horizontally: Not more than 2000 mm c/c
- Vertically: Not more than 1000 mm c/c (staggered arrangement)
Weep holes shall extend up to the bed level to relieve pore water pressure behind the wall.
Additional Resource for Bridge Hydraulics
For detailed guidance on bridge project planning, General Arrangement Drawings (GAD), and hydraulics, refer to:
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