temperature stresses – due to the temperature differential between the top and bottom of the...

• Temperature Stresses – Due to the temperature differential between the top and bottom of the slab, curling stresses (similar to bending stresses) are induced at the bottom or top of the slab • Frictional stresses – Due to the contraction of slab due to shrinkage or

due to drop in temperature tensile stresses are induced at the middle portion of the slab • Wheel Load Stresses – CC slab is subjected to flexural stresses due to the wheel loads

Temperature Steel •Temperature steel is provided in the form of

wire fabric or bar mats at mid depth and isdiscontinued at joints.

•This temperature steel does not increase thestructural capacity of the slab

•Temperature steel is used to increase thespacing of contraction joints

•Temperature steel ties the cracked concretetogether and maintains load transfer throughaggregate interlock

Computations using Influence Charts

These charts can be used for any shape of contact area and any wheel/axle/gear configurationThe bending moment is obtained about point O in the direction n.

The contact areas are to be drawn to the scale shown and the number of blocks (N) with in the contact areas are counted from the respective charts.

The design methods are classified to three main groups as follows:

1. Theoretical methods; 2. Empirical methods; 3. Empirical-theoretical

methods.

Design of joints

1 - Expansion joints The purpose of the expansion joint is to allow

the expansion of the pavement due to rise in temperature with respect to construction temperature.

2 - Contraction joints The purpose of the contraction joint is to allow the

contraction of the slab due to fall in slab temperature below

the construction temperature.

Dowel bars The purpose of the dowel bar is to

evectively transfer the load between two concrete slabs and to keep the two

slabs in same height. The dowel bars are provided in the direction of the traffic (longitudinal). The design

considerations are: * Mild steel rounded bars, * bonded on one side and free on other

side

Tie bars In contrast to dowel bars, tie bars are

not load transfer devices, but serve as a means to tie two slabs. Hence, tie bars must be deformed or hooked and must be firmly anchored into the concrete to function properly. They are smaller than dowel bars and placed at large intervals. They are provided across longitudinal joints.