UNIT-I STANDARD SPECIFICATION FOR ROAD BRIDGE SECTION-B UNIT-I STANDARD SPECIFICATION FOR ROAD BRIDGE

contents IRC bridge code Determination of dead loads and live loads Wind loads Longitudinal forces Centrifugal forces Horizontal forces due to water current and buoyancy effect Earth pressure Temp. effect

Deformation stresses secondary stresses Erection stresses Seismic forces

IRC BRIDGE CODE: The Indian roads congress has formulated standard specification and codes of practice for road bridges with a view to establish a common procedure for the design and construction of road bridges in India. The specification are collectively known as the bridge code.

Determination of loads

It is carried by bridge member consists of its own weight. DEAD LOAD: The dead load carried by a bridge member consists of its own weight and the portions of the weight of the superstructure and any fixed loads supported by the member. It is carried by bridge member consists of its own weight.

There are 4 types of standard loadings for which road bridges are designed: IRC class AA loading: It consists of either a tracked vehicle 700 kN or a wheeled vehicle of 400 kN. E.g.: combat tank used by army . IRC class 70R loading: It consists of tracked vehicles of 700kN or a wheeled vehicle of total load of 1000kN . The tracked vehicle is similar to that of class AA. IRC class A loading: It consists of a wheel load train composed of a driving vehicle and trailers of specified axle spacing and loads. This loading adopted for permanent bridges and culverts. IRC class B loading: This loading is similar to class B loading but adopted for temporary structures.

WIND LOADS: The horizontal load used in the design of a structure to account for the effects of wind.

Longitudinal forces: longitudinal forces are caused in road bridges due to: Tractive effort caused through acceleration of the driving wheels Braking effect due to application of brakes to the wheels

Centrifugal forces: Centrifugal forces is given by eq. where a road bridge is located on a curve , the effects of centrifugal forces due to movement of vehicles should be taken into account . Centrifugal forces is given by eq. C= (wv^2)/12.95R

HORIZONTAL FORCES DUE TO WATER CURRENTS: Any part of a bridge structure which may be submerged in running water should be designed to sustain safely the horizontal pressure due to the force of the current.

Buoyancy effect: Buoyancy=density of fluid *vol. of object * gravity upward forces exerted by fluids on submerged objects. Buoyancy=density of fluid *vol. of object * gravity

Lets us take an example of buoyancy effect

This beach ball floats. Why?

Because the Buoyant Force is greater than the weight of the ball.

Earth pressure:  The pressure exerted on a structure, such as a wall, by the earth which it retains. There are 3 states of lateral earth pressure: At rest(Ko) Active earth pressure(wall move away from soil)=Ka Passive earth pressure(wall move into soil)=kp

Temperature effect: When steel structure is not free to expand or contrast under variation of temperature, the stresses due a variation of  30 C. From local main must be considered. The coefficient of expansion for steel and concrete is 0.00001. If we consider unequal variation of temperature, in some structures which are not affected by equal changes, we allowed only for  15 C. In two hinged arches and suspension bridges the equal change of temperature has an effect on the internal forces. In continuous bridges the equal change of temperature has no effect because the girders are free to expand, but the unequal change has an effect.

DEFORMATION STRESSES: Deformation stresses are considered for steel bridges only. It is defined as the bending stress in any member of an open –web girder caused by the vertical deflection of the girder combined with the rigidity of the joints.

Stress stain curve

Secondary stresses: In steel structure, secondary forces are those which caused due to eccentricity of connections, floor beam loads, cross girder, lateral wind loads, and the movement of support.

Erection stresses: The stresses that are likely to be induced in member during erection should be considered in design.

Seismic forces: Seismic force is generated due to earthquake. It is a natural disaster. It is a violent shaking of earth.

Effect of seismic forces:

Unit-II culverts

Introduction: A culvert is a closed conduit used to convey water from one area to another, usually from one side of a road to the other side. 

Classification of culverts: RCC slab culvert Pipe culvert Box culvert Stone arch culvert Steel girder culvert for railways.

RCC slab culvert:

Pipe culvert:

Box culvert:

Stone arch culvert:

Steel girder culvert for railways:

Design of RCC slab culvert: EXAMPLE FOR R.C. SLAB CULVERT: GIVEN DATA CULVERT TO BE STATE HIGHWAY. WIDTH OF BRIDGE = (GIVEN) NO FOOTPATH PROVIDED condition of exposure: ’moderate’ materials: concrete grade m25 steel-deformed bars to is : 1786 (grade fe415) clear span =given ht. OF VENT = GIVEN DEPTH OF FOUNDATION = GIVEN WEARING COURSE = GIVEN STEP-1 : DESIGN OF DECK SLAB PRELIMINARY DIMENSIONS DEAD LOAD BENDING MOMEMNT PER METRE WIDTH OF SLAB LIVE LOAD BENDING MOMENT

STEP-2 : DESIGN BENDING MOMENT STEP-3 : STRUCTURAL DESIGN OF DECK SLAB STEP-4 : CHECK FOR SHEAR STEP-5: DESIGN OF KERB

DESIGN OF BOX CULVERT: GIVEN DATA: Clear span =given Concrete grade M25 = 25 Mpa Clear height = given Steel grade Fe 415 = 415 Mpa Top slab thickness =given БSc (Concrete)= 8.33 Mpa Bottom slab thickness= given БSt (Steel) =200 Mpa Side wall thickness=given Modular ratio=10 Unit weight of concrete =24 kN/m3 n (for depth of neutral axis) =given Unit weight of earth= 18 kN/m3 j (for effective depth)=given Unit weight of water =10 kN/m3 k (for moment of resistance) =1.105 Mpa Co-efficient of earth pressure at rest =0.5.

Total cushion on top 0.0m. Thickness of wearing coat=given load calculation Top slab Dead load Live load 2. Bottom slab Total load(DL+LL) 3.Side wall 4. Base pressure

Moment calculation top slab Bottom slab Side wall Distribution factor: Moment distribution: Braking force: Design of section: design moment Top slab Side walls Check for shear: