In a simply supported reinforced concrete slab, distribution (secondary) reinforcement is provided primarily to handle which effects and functions?

Introduction / Context:
Reinforced concrete slabs have main (primary) reinforcement in the direction of the principal bending. Distribution (secondary) reinforcement runs orthogonally and serves multiple serviceability functions beyond mere strength in the main span direction.

Given Data / Assumptions:

• Simply supported slab with predominant one-way action.
• Ordinary room temperature variations and drying shrinkage are present.
• Local loads may occur due to point or line contacts (e.g., partitions, wheel loads).

Concept / Approach:
Distribution steel limits crack widths and spacing caused by temperature gradients and drying shrinkage; it also helps distribute local wheel or impact loads over a wider area, reducing stress concentrations and improving serviceability. Though not sized for primary flexure, it is indispensable for crack control and load sharing.

Step-by-Step Solution:
Identify the main causes of secondary cracking: temperature and shrinkage.Recognize load spread: orthogonal bars help spread wheel/point loads to main reinforcement.Therefore, its role encompasses load distribution plus restraint of temperature and shrinkage strains.

Verification / Alternative check:
Crack control provisions in design standards set minimum percentages for distribution steel based on bar size, spacing, and exposure. Field experience confirms slabs with inadequate secondary steel exhibit wider crack patterns and local punching or rutting near concentrated loads.

Why Other Options Are Wrong:
Each single-cause option is incomplete. The correct role is multi-faceted, including both environmental strain effects and load distribution.

Common Pitfalls:
Reducing distribution steel as a cost-saving measure often leads to surface cracking, durability problems, and poor performance under localized loads.

Final Answer:
All the above (load distribution as well as temperature and shrinkage effects).