Rigid pavement longitudinal joint design: with pavement slab width 7.5 m, thickness 20 cm, and working stress 1400 kg/cm², what is a reasonable spacing for 10 mm tie bars to keep joints tight under service?

Introduction / Context:
Tie bars hold longitudinal joints of concrete pavements tightly closed, preventing lane separation due to temperature and shrinkage. Their spacing depends on bar diameter, slab thickness, joint working stress, and expected tensile demand from slab movements.

Given Data / Assumptions:

• Slab width = 7.5 m; thickness = 20 cm.
• Tie bar diameter = 10 mm; working stress = 1400 kg/cm².
• Objective: reasonable, standard-practice spacing for service conditions.

Concept / Approach:
A typical approach distributes joint traction demand among multiple bars so the steel stress does not exceed the working limit while offering adequate bond length. For 10 mm bars in 20 cm slabs, spacings on the order of 25–40 cm are commonly adopted; 30 cm is a widely used practical value balancing steel quantity and performance.

Step-by-Step Solution:

Verification / Alternative check:
Comparing to standard design tables shows 10–12 mm bars at 0.25–0.40 m spacing are typical for 18–22 cm slabs; 0.30 m lies centrally in that range.

Why Other Options Are Wrong:
10 cm and 20 cm are uneconomical; 40–50 cm may permit excessive joint opening and stress in bars under temperature drop.

Common Pitfalls:
Confusing tie bars (for longitudinal joints) with dowel bars (for transverse load transfer); ignoring bond and development length requirements.

Final Answer:
30 cm