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.
-
A40%
-
B50%
-
C60%
-
D70%
-
E30%
Answer
Correct Answer: 50%
Explanation
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:
1) Identify the controlling requirement for distribution steel where main bars are parallel to ribs.2) Adopt minimum transverse steel = 0.5 * (main steel at mid-span).3) Provide appropriate spacing to satisfy bar spacing and crack width limits.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%