Pick up the correct statement(s) about joints in concrete structures:
Correct Answer: D. All of the above
📚 Detailed Explanation: All Three Statements About Joints Are Correct
Why D (All options are correct) is correct: Each of the three statements accurately describes a principle governing the design and use of construction and expansion joints in concrete structures. All three are correct and mutually consistent.
Analysis of Each Statement
| Statement | Correct? | Explanation |
|---|---|---|
| A. Construction joints must be planned at their locations | ✓ TRUE | Good engineering practice requires construction joints to be shown on the structural drawings and specified in the method statement. Unplanned/accidental joints (cold joints) are defects. Planned joints are located at positions of minimum BM and SF, and their surfaces are properly prepared. |
| B. Expansion joints accommodate thermal expansion | ✓ TRUE | The primary function of expansion joints is to provide space for the concrete to expand when temperature rises, preventing compressive buckling and cracking. The gap (filled with compressible filler) absorbs thermal expansion ΔL = α·L·ΔT. |
| C. Construction joints help control shrinkage cracks | ✓ TRUE | By dividing a large concrete element into sequential pours, construction joints release accumulated shrinkage strains at planned locations. Shrinkage in each section is smaller than in the continuous element. This prevents uncontrolled random shrinkage cracking. |
Joint Functions Summary
| Joint Type | Primary Function | Secondary Function |
|---|---|---|
| Construction Joint | Work-sequence interface; structural continuity | Shrinkage crack control; staged construction logistics |
| Expansion Joint | Thermal expansion accommodation; prevent buckling | Accommodates differential settlement in L/T/H-shaped buildings |
| Contraction Joint | Control shrinkage cracking location | Allows gradual opening without structural damage |
| Isolation Joint | Separates structure from adjacent structure/foundation | Allows differential settlement without stress transfer |
- Construction joints must be planned; unplanned (accidental cold joints) are structural defects.
- Expansion joints accommodate thermal expansion — their primary purpose.
- Construction joints also control shrinkage cracks by dividing pours into manageable segments.