Construction joints – locations: Which statement about locating construction joints is MOST appropriate for structural performance and workmanship?

Introduction / Context:
Construction joints are unavoidable because concrete cannot always be placed continuously. Their positions must be chosen to minimize structural penalties and ensure good bonding between pours.

Given Data / Assumptions:

• Monolithic RC framing with columns, beams, and slabs.
• Cold joints avoided by proper surface preparation and bonding.
• Load paths and shear distributions are considered.

Concept / Approach:
In columns, stopping the pour slightly below the beam soffit allows the next pour to fully integrate the beam–column junction. In flexural members (beams/slabs), joints are preferably located away from supports where shear is highest; placing within the middle third (near a region of lower shear and sometimes lower moment depending on load case) reduces the adverse effect. The overarching rule is to select locations of least shear, ensuring adequate roughening, cleaning, and bonding grout before resuming concreting.

Step-by-Step Solution:
Identify critical shear regions → near supports.Avoid joints there; choose midspan regions where practical.For columns, avoid at beam–column interface; stop pour a few cm below beam soffit.Thus (a), (b), and (c) are all consistent → choose “All of the above.”

Verification / Alternative check:
Standard detailing manuals recommend such joint locations along with roughening and bonding slurry at restart.

Why Other Options Are Wrong:
Selecting only one ignores valid complementary guidance; “None” contradicts established practice.

Common Pitfalls:
Placing joints at supports; failing to roughen and clean the old concrete; not providing shear keys where needed.

Final Answer:
All of the above are appropriate recommendations.