Slab with main reinforcement parallel to a T-beam (rib): required transverse steel at mid-span State the minimum transverse reinforcement (as a percentage of the main reinforcement area) to be provided at mid-span when the main bars run parallel to the T-beam.

Introduction:
When slab main bars run parallel to supporting T-beams, adequate transverse steel is needed to control cracking, distribute loads to ribs, and resist shrinkage/temperature effects. Codes prescribe a minimum proportion relative to the main reinforcement at mid-span.

Given Data / Assumptions:

• Main bars are parallel to the T-beam direction.
• Transverse bars act as distribution and secondary reinforcement.
• Normal room exposure with typical slab thickness.

Concept / Approach:

The transverse steel should not be arbitrarily reduced because load transfer to ribs and crack control depend on a minimum amount. A widely used rule is to provide at least half of the main steel area at mid-span in the transverse direction.

Step-by-Step Solution:

Verification / Alternative check:

Check crack control and serviceability: spacing and bar diameter should satisfy service crack widths under working loads.

Why Other Options Are Wrong:

40% can under-reinforce for distribution; 60% and 70% are conservative but not required as a minimum; 30% is inadequate for load distribution between ribs.

Common Pitfalls:

Providing the same transverse steel at supports as mid-span without considering negative moments; using large diameters at wide spacing, which is less effective for crack control.

Final Answer:

50%