Experiment 3: Study of Deflection in Structural Members
1. Aim
To observe deflection in structural members, identify related problems, analyze possible reasons, and suggest suitable treatment and preventive strategies.
2. Objectives
- To study the nature and extent of deflections in beams, slabs, and other structural members.
- To identify structural and serviceability issues caused by excessive deflection.
- To analyze possible reasons for observed deflections.
- To propose remedial and preventive measures for minimizing deflections.
- To relate findings with provisions of relevant IS codes and explore case studies from literature for practical understanding.
3. Theoretical Background
Deflection in structural members refers to the displacement of a member under load. While some deflection is inevitable and permissible, excessive deflection can affect aesthetics, functionality, and structural safety.
- Common causes: overloading, insufficient stiffness, poor quality of materials, creep, shrinkage, or improper design.
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IS Codes:
- IS 456: 2000 (Plain and Reinforced Concrete – Code of Practice) specifies permissible deflections for RC structures.
- IS 800: 2007 (General Construction in Steel – Code of Practice) provides deflection limits for steel structures.
- Students are encouraged to go through case studies in literature to understand real-life implications of excessive deflection and its remedies.
4. Procedure (Sample – for reference only)
- Select structural members such as beams, slabs, or cantilevers in nearby buildings.
- Observe any visible deflections or serviceability issues (e.g., sagging, cracks due to bending).
- Record details including location, span, member size, visible deflection (if measurable), and associated issues.
- Capture clear, properly labelled, captioned, and numbered photographs of observed cases.
- Compare observations with permissible limits specified in IS codes.
- Analyze possible reasons for excessive deflection.
- Suggest treatment and preventive measures supported by IS codes and case studies.
5. Observations & Data Recording (Sample Table – for reference only)
| Sr. No. |
Structural Member |
Span/Size |
Observed Deflection (approx.) |
Possible Cause |
Effect on Structure/Serviceability |
Suggested Remedy |
| 1 |
RCC Beam (mid-span) |
4.5 m |
~15 mm |
Overloading, creep |
Sagging, plaster cracks |
External prestressing, section strengthening |
| 2 |
Slab panel |
3 m × 4 m |
~10 mm |
Insufficient thickness |
Ponding of water, tile cracks |
Increase slab depth (future), add topping |
Students must fill a minimum of 5–6 entries with properly captured, labelled, numbered, and captioned photographs attached in their report.
6. Analysis (Sample – for reference only)
- Compare observed deflections with permissible limits from IS codes.
- Discuss whether deflections are within safe/unsafe limits.
- Correlate observations with possible material, structural, or environmental causes.
- Support analysis with at least one relevant case study from literature.
7. Treatment Strategies (Sample – for reference only)
- Structural strengthening (jacketing, addition of supports, external prestressing).
- Load reduction or redistribution where feasible.
- Use of stiffer materials in future construction.
- Preventive measures like adequate member sizing, proper reinforcement detailing, and control of long-term effects (creep and shrinkage).
8. Results (Sample – for reference only)
- Nature and extent of deflections observed.
- Comparison with permissible values from IS codes.
- Causes and possible impacts of observed deflections.
- Suggested remedies and preventive strategies.
- Insights from related case studies.
9. References / Suggested Reading
- IS 456:2000 – Section on Serviceability & Deflection Limits
- “Structural Analysis” – R.C. Hibbeler
- Journal papers on deflection behavior of beams and slabs
Note: Students are encouraged to add more references based on their observations and literature review.
10. Viva Questions (Sample: for reference only - Do not write in the final report)
- What are the permissible limits of deflection in beams as per IS 456?
- How does creep and shrinkage influence deflection in RCC members?
- What are the main differences between short-term and long-term deflection?
- How do deflection criteria differ for RCC and steel members?
- Can you name a case study where excessive deflection led to structural/serviceability failure?