Tie bars are installed in longitudinal joints in cement concrete pavements. These joints are created to allow for the natural expansion and contraction of concrete due to temperature changes and other factors. Tie bars play a crucial role in maintaining the structural integrity and preventing the development of cracks in the pavement.

Expansion and Contraction Joints:
- Expansion joints are designed to accommodate the expansion of concrete caused by temperature changes. They provide space for the concrete to expand without causing excessive stress on the pavement.
- Contraction joints, on the other hand, are created to control the cracking caused by the contraction of concrete due to temperature drops. They help to prevent random cracking by providing predetermined locations for the concrete to crack.

Warping Joints:
- Warping joints are typically used in concrete pavements that experience warping or curling due to temperature changes or moisture variations. These joints allow the pavement to expand and contract without causing damage.

Longitudinal Joints:
- Longitudinal joints are the joints created between adjacent slabs of concrete pavement that run parallel to the direction of traffic. These joints are necessary to accommodate the movement and prevent the development of cracks.
- Tie bars are installed in these longitudinal joints to provide load transfer between the adjacent slabs, ensuring that they act as a single unit under traffic loads.
- Tie bars are typically made of steel and are placed across the joint at regular intervals. They are anchored into the concrete on either side of the joint and are designed to resist the tensile forces that occur due to traffic loads.
- The tie bars help to distribute the load evenly across the joint, reducing the potential for differential settlement and cracking.
- They also help to maintain the ride quality of the pavement by preventing vertical displacement at the joint.

In conclusion, tie bars are installed in longitudinal joints in cement concrete pavements to provide load transfer and prevent the development of cracks. They play a critical role in maintaining the structural integrity and ride quality of the pavement.