Rigidity is due to high modulus of elasticity of concrete. Cement concrete pavement is rested on soil foundation which can be treated as a spring offers the modulus of subgrade reaction.
Modulus of subgrade reaction (by Westergaard) K=p/Δ in kg/cm3
The radius of relative stiffness- Relative stiffness of slab with respect to subgrade is represented by the radius of relative stiffness and computed as
l is in cm (rad of relative stiffness),
h is slab thickness (in cm),
E is mod. Of Elasticity in kg/cm2
Poisson’s ratio -for concrete=0.15
Radius of resisting section
A small area of pavement is resisting a bending movement of a plate due to loading
Westergard has given a relation for radius of the resisting section in cm by
(When a <1.724h)
And b (in cm)=a, when a>1.724h
Where a is the radius of wheel load distribution in cm, h is slab thickness in cm
Goldbeck Corner load where P is corner load and h is slab thickness.
Westergaard’s Stress equation
Interior loading –
Edge loading –
l is the radius of relative stiffness in cm,
b is the radius of the resisting section in cm,
h is the thickness of slab in cm and Stress are in kg/cm2
These stresses are developed in cement concrete pavement due to variation in the slab temperature and resistance against deformation provided by the weight of slab and friction between slab and ground.
Daily variation will lead to warping of slab (Temp. difference between the top & bottom of the slab generates warping stress)
When the slab is warped down in day time, warping stress is tensile in nature at the bottom. During the night when the slab is warped up tensile stress developed at the top of the slab
The magnitude of warping stress is maximum at the interior region and are minimum at the corner region.
Due to seasonal variation of temp. expansion or contraction of pavement slab is resisted by friction offered by underlying surface
Frictional stresses are zero at free end and maximum at interior section
During summer when the slab is under expansion the frictional stress is compressive and during winter when the slab contracts frictional stresses are tensile
Pavement designs can be advanced according to the Rigid Pavement Design Manual (Document No. 625 010-006). The authorized pavement layout and the helping information can be covered withinside the District Project Design File.
The Pavement Design Package at least will consist of the subsequent items:
The Pavement Design Summary Sheet will show the approved pavement design and could be signed and sealed by using the District Pavement Design Engineer or the designated responsible Pavement Design Engineer. The District Design Engineer will sign for concurrence with the layout. The report replica will show Federal Highway Administration (FHWA) approval, if required, for Federal Aid Projects or Certification Acceptance as appropriate. Project place and outline of the kind of work, if now no longer clearly stated at the summary sheet. The foundation for the material properties used withinside the design signed and sealed where required, including if applicable for:
- Resilient Modulus (MR).
- Material properties used if different than those in the Design Manual.
- Concrete Pavement Rehabilitation (CPR) and Lane Widening
- Existing pavement layer information (layer types, thickness, and condition).
- A copy of the Pavement Coring and Evaluation Report.
- Drainage recommendations.
- The ESALD calculations are normally signed and certified by the Planning Office. The basis for the input data used for these calculations must be stated.
- Required slab thickness calculations.
- Documentation addressing any special features such as cross slope, coordination with adjacent projects, stage construction, drainage considerations, etc.
- Sketch of a possible construction sequence, including any widening and shoulders, to ensure constructability in accordance with the standards.
- A drawing of the rigid pavement design typical section or an adequate narrative description.
- Joint Design Details showing Plan View in areas where geometric changes occur
Central office approval of the pavement design isn’t required. designs are going to be monitored and periodically reviewed, in detail, for quality assurance and for functions of distinguishing and improving deficiencies in design policies, procedures, standards, and guidelines. For Federal Aid projects that are selected beneath the FHWA PODI (Projects of Division Interest) program, 2 copies of the approved Pavement style summary Sheet and one copy of the supporting documentation will be forwarded on to the suitable Federal road Administration (FHWA) Engineer for FHWA concurrence (concurrent with the transmission to the State Pavement style Engineer). solely inject or major parts of a project would like formal FHWA pavement style approval. Details love crossroads and shoulders are going to be handled as an area of the plans approval process. don’t send these copies to the business office for transmission to FHWA. The District can deal directly with the FHWA to resolve any questions. business office Pavement Management will be offered for help if requested by the District or FHWA. The FHWA will come back directly to the District one copy of the summary sheet with a signature denoting concurrence. This copy will be filed within the District Project style file.
REVISIONS DESIGN OF RIGID PAVEMENT
Changes made subsequent to formal distribution would require that a revised summary sheet be organized, a copy of which will be signed and sealed, distributed, and filed for permanent file withinside the Project Design File. Minor modifications can be noted in kind or ink at the original Pavement Design Summary Sheet with the responsible Professional Engineers initials and the date of the change. A reproduction of the revised unique must then be signed, dated, sealed, and filed for everlasting file. Major modifications may require that a whole new Pavement Design Summary Sheet be organized and processed, wherein case it shall observe that it supersedes a preceding layout. Copies of revised pavement designs consisting of backup facts documenting why the extrade is being made might be transmitted to the State Pavement Design Engineer and redistributed as appropriate. For intersection improvement, brief roadway connectors on bridge alternative projects, and roadway widening projects, the Modulus of Subgrade Reaction (K Value), 18-kip (80- kN) Equivalent Single Axle Loads (ESALD), and computation of slab thickness are normally not required. However, in all cases, a report describing how the pavement the design turned into advanced must be prepared, signed, and sealed.
Every attempt should be made to observe written procedures. Situations will occur in which following the pavement design system will bring about a required slab thickness that can’t be met. This may want to arise whilst a layout is needed in a widening area. The Pavement Design Engineer will exercise engineering judgment on what ought to be finished in those cases. When this occurs, the Pavement Design Engineer is suggested to record the project, make unique notes of the problem, and offer extra causes as to how the recommended design becomes developed. Consultation with different engineers (Construction, Drainage, Materials, etc.) is highly endorsed and ought to be stated withinside the design file.