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8. Rigid pavement design

Rigid pavements are highly rigid structures made mainly of cement concrete, built primarily to provide maximum load carrying capacity through slab action. The design principles revolve around factors such as modulus of sub-grade reaction, critical load positions, and types of stresses including temperature and frictional stresses. Comprehensive joint design considerations for expansion and contraction joints, as well as dowel and tie bars, are necessary to ensure durability and functionality.

Sections

Rigid pavement design

Rigid pavements are concrete slabs with limited flexural capacity under load, utilizing principles of elasticity and sub-grade reactions for design.

29 Section Overview

Start current section content and materials

29.1 Overview

This section provides an overview of rigid pavement design, highlighting its key characteristics, stress factors, and foundational concepts introduced by H. M. Westergaard.

29.1.1 Modulus of sub-grade reaction

This section details the modulus of sub-grade reaction as defined by Westergaard, explaining its significance in rigid pavement design.

29.1.2 Relative stiffness of slab to sub-grade

This section discusses the concept of the relative stiffness of a rigid pavement slab to its sub-grade, emphasizing the role of sub-grade deformation in assessing slab performance.

29.1.3 Critical load positions

Critical load positions in rigid pavement design refer to the specific areas on the pavement surface where the maximum stress occurs due to traffic loads.

29.1.4 Equivalent radius of resisting section

This section discusses the equivalent radius of the resisting section in rigid pavements and its relevance to bending moments under loading.

29.2 Wheel load stresses - Westergaard’s stress equation

This section explores Westergaard’s stress equations for analyzing wheel load stresses in rigid pavements, focusing on stress distribution at interior, edge, and corner regions.

29.3 Temperature stresses

Temperature stresses in cement concrete pavement are caused by variations in slab temperature, leading to warping and frictional stresses.

29.3.1 Warping stress

Warping stress in rigid pavements arises due to temperature variations across the slab, impacting its structural integrity.

29.3.2 Frictional stresses

This section defines frictional stresses in rigid pavements and presents its calculation.

29.4 Combination of stresses

This section discusses the critical combinations of stresses in rigid pavements caused by various factors, including temperature and load positions.

29.5 Design of joints

This section discusses the various types of joints used in rigid pavement design, including expansion joints, contraction joints, dowel bars, and tie bars, highlighting their purposes and design considerations.

29.5.1 Expansion joints

Expansion joints are designed to accommodate pavement expansion due to temperature increases, ensuring structural integrity.

29.5.2 Contraction joints

Contraction joints are essential in rigid pavements to allow for temperature-induced contraction.

29.5.3 Dowel bars

Dowel bars facilitate effective load transfer between adjacent concrete slabs, ensuring they remain level and aligned.

29.5.4 Tie bars

Tie bars are essential in rigid pavement design, primarily serving to connect two concrete slabs while maintaining their elevation.

29.6 Summary

This section summarizes the design principles of rigid pavements, focusing on key concepts such as the modulus of subgrade reaction and critical stresses.

29.7 Problems

This section focuses on the critical aspects of rigid pavement design, emphasizing the analysis of stress, joint design, and load transfer mechanisms.

Learning Objectives

  • Rigid pavements are primarily made of cement concrete, offering high rigidity under loads.

  • The effective design of rigid pavements incorporates critical load positions and various stress types.

  • Joint designs, like expansion and contraction joints, are essential for accommodating temperature variations and preventing structural damage.

Key Concepts

Modulus of Sub-grade Reaction

A measure of the sub-grade support provided to a slab, defining the relationship between pressure and deflection.

Critical Load Positions

Specific locations (interior, edge, corner) on a pavement slab where stress distributions are critically affected by vehicle loads.

Warping Stress

Stresses caused in the pavement due to temperature gradients resulting in slab deformation.

Frictional Stress

Stresses generated due to friction at the interface between the slab and the sub-grade.

Dowel Bars

Steel bars used to transfer loads between two concrete slabs and maintain their level.

Tie Bars

Bars used to keep two slabs tied together but do not transfer loads.

Practice Exercises

Total Questions

2

Estimated Time

4 min

Passing Score

70%

Instructions

  • Read each question carefully
  • You can use hints if you need help
  • Complete all questions before submitting

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