--- title: "Expansion and construction joints, positions" subject: "Building Technology" chapter: 10 key: "semester_6/building_technology:joints-expansion-construction-positions" source: https://www.bctengineer.com/q/semester_6/building_technology/joints-expansion-construction-positions site: BCT Engineering --- # Expansion and construction joints, positions Building Technology · Chapter 10: Causes and prevention of cracks in buildings - Asked in: 2062 Poush (old course) - Video: [Types of Joints in concrete || Expansion joints in concrete | Construction, Contraction, Isolation,](https://www.youtube.com/watch?v=3qh8MW-sfCE) — civilogy - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/joints-expansion-construction-positions - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-10 ## Question Describe the joints in the structure. Illustrate the types of joints. Explain briefly the expansion and construction joints and their probable positions in the structure. ## Short answer Joints are planned breaks for movement or staged concreting. Expansion joints are 20-25 mm gaps filled with compressible filler and sealant, placed every 30-45 m in long walls, slabs, and roofs. Construction joints are placed where concreting stops, in low-shear zones: slabs and beams in the middle third of the span, columns at the top of footing and 75 mm below the beam soffit. ## Answer A **joint** is a planned break or gap in a structure, provided to allow movement or to stop concreting. It reduces random cracking. #### Types of joints 1. **Expansion joint:** allows thermal expansion. 2. **Contraction (control) joint:** controls shrinkage cracks. 3. **Construction joint:** at a stopping place of concreting. 4. **Settlement joint:** between parts that settle differently. 5. **Sliding joint:** between slab and wall, for horizontal movement. 6. **Seismic joint:** between blocks, to avoid pounding. #### Expansion joint An **expansion joint** is a gap of 20-25 mm provided through the full depth of the structure above the foundation to allow expansion and contraction due to temperature, so that cracks do not form. It is used at intervals of 30-45 m in buildings, and in long walls, slabs, roofs and parapets. ```text Expansion joint in a wall/slab slab | 25 mm gap | slab =====| |===== wall | filler | wall | (bitumen) | | sealant on top foundation continuous below ``` The gap is filled with a compressible filler (bitumen-impregnated fibre board, cork, rubber) and sealed on top with a sealant. The two parts are fully separated, often by a double column or wall. **Positions:** at 30-45 m intervals along long buildings; where the plan changes shape (L, T, U); where the height or foundation level changes; between wings, and between old and new portions; in long parapets, roofs, retaining walls and pavements. #### Construction joint A **construction joint** is made where concrete placing is stopped and resumed after the earlier concrete has set, because the structure cannot be cast in a single operation. It must be located where shear and bending are small, and it must give good bond between old and new concrete. **Positions (IS 456 / IS 11817):** - **Slabs:** in the middle third of the span, at right angles to the main reinforcement. - **Beams:** in the middle third of the span (where secondary beams frame into girders, the joint in the girder is offset by at least twice the width of the secondary beam). - **Columns:** at the top of the footing, and about 75 mm below the lowest beam/slab soffit (or below the haunch/capital). - **Walls:** at openings, at junctions, and in the middle third. ```text Slab/beam Column ___________|___________ |slab| |<-L/3->|joint|<-L/3->| | beam | col ---- joint just below beam ===footing=== joint at top of footing ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A joint is: A. A reinforcement bar B. An accidental crack C. A planned break or gap that allows movement or a stopping point of concreting D. A type of mortar Answer: C. Joints reduce random cracking. (Key point: Joint definition) 2. Expansion joints are placed: A. Only in the foundation B. At every 3 m C. Only at corners of rooms D. At 30-45 m intervals and where plan shape or height changes Answer: D. L, T, U shapes and height changes need them. (Key point: Expansion joint positions) 3. A construction joint in a beam is located: A. In the middle third of span B. At the support C. At the top flange D. At the column face Answer: A. Shear is small there. (Key point: Beam construction joint) ## Related in Building Technology - [Construction joints in structure](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aconstruction-joint) — Building Technology, chapter 10, asked 2× - [Why joints are necessary; expansion joint](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Ajoints-why-expansion) — Building Technology, chapter 10, asked 2× - [Expansion joint in a residential building](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aexpansion-joint-350wall) — Building Technology, chapter 10 ## Related in other subjects - [Pipe joints; expansion joint](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Apipe-joints-expansion-joint) — Water Supply Engineering, chapter 8, asked 3× - [ANOVA: shear force of bolts at three positions](https://www.bctengineer.com/question.md?key=semester_5%2Fprobability_and_statistics%3Aanova-bolts-three-positions) — Probability and Statistics, chapter 6 - [Why ductile detailing is needed in joints](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Awhy-ductile-detailing-is-needed-in) — Design of RCC Structure, chapter 12 - [Define ductility; ductility in joints](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Adefine-ductility-ductility-in-joints) — Design of RCC Structure, chapter 12