--- title: "Building shape in plan and elevation" subject: "Building Technology" chapter: 11 key: "semester_6/building_technology:building-shape-plan-elevation" source: https://www.bctengineer.com/q/semester_6/building_technology/building-shape-plan-elevation site: BCT Engineering --- # Building shape in plan and elevation Building Technology · Chapter 11: Earthquake protection & Retrofitting in building - Asked in: 2072 Magh, 6 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/building_technology/building-shape-plan-elevation - Whole chapter: https://www.bctengineer.com/md/semester_6/building_technology/chapter-11 ## Question Discuss building shape in plan and elevation. ## Short answer In plan, simple symmetrical shapes (square, rectangle) are best; avoid L, T, U shapes or separate with seismic joints. Length:width ≤3. In elevation, maintain uniform mass and stiffness, avoid sudden changes like soft storeys or set-backs, and ensure continuous walls and columns from foundation to roof. ## Answer Building shape strongly influences how the structure behaves in an earthquake, so the shape is decided at the planning stage. #### Shape in plan - **Best:** square, rectangle or circle. These are symmetrical, load paths are direct, and there is no stress concentration. - **Poor:** L, T, U, H, Y and cross shapes. The wings vibrate differently, and stress concentrates at the re-entrant (inside) corners, causing torsion and damage there. - **Remedy:** divide complex plans into simple rectangular blocks separated by seismic joints (gaps), or add strong ties/diaphragms at the junctions. - **Aspect ratio:** length/width preferably not more than 3 (2 is better). - **Projections** such as cantilever balconies should be small (not more than about 1.2 m), and the centres of mass and rigidity should be close together. ```text Good plans Poor plans +-------+ (o) +--+ +--+ | | | | | | +-------+ | +---+ | U-shape +---------+ ``` #### Shape in elevation - **Best:** a uniform, regular box shape, or one whose size reduces gradually with height. - **Poor:** sudden changes such as set-backs, large overhangs, an open (soft) ground storey, heavy top floors, floating columns, and short columns on a slope. - **Principles:** mass, stiffness and strength should be uniform or reduce gradually with height; walls and columns should be continuous from the foundation; avoid a very tall, slender building on a small base (overturning). - A soft storey (open ground floor for parking) concentrates damage on that floor; add shear walls or bracing. ```text Good Poor (set-back) Poor (soft storey) +------+ +--+ +------+ | | | | | | | | +--+ +--+ | | | | | | +------+ | | | | | | | | open ground storey +------+ +--------+ +-+--+-+ ``` ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Why are L, T, U and H plans poor in earthquakes? A. Wings vibrate differently and stress concentrates at re-entrant corners, causing torsion B. They have too much open floor area C. They are always heavier than rectangles D. They need more bricks per wall Answer: A. Different vibration of wings and stress at inside corners cause torsion and damage. (Key point: Poor plan shapes) 2. How is a complex plan made safer? A. Make the walls thicker everywhere B. Divide it into simple rectangular blocks separated by seismic joints C. Add a heavy top floor D. Increase the cantilever projections Answer: B. Seismic gaps (or strong ties) let each simple block move on its own. (Key point: Remedy for complex plans) 3. What happens in a building with an open (soft) ground storey? A. The ground floor becomes the strongest part B. The upper floors collapse first C. Damage concentrates on that floor, so shear walls or bracing are added D. Nothing, as the load is uniform Answer: C. The sudden stiffness drop concentrates damage at the soft storey. (Key point: Soft storey) 4. Which elevation principle is correct? A. Heavier floors should be placed at the top B. Columns can be discontinued at the first floor C. Sudden set-backs improve stability D. Mass, stiffness and strength should be uniform or reduce gradually with height Answer: D. Sudden changes and heavy tops cause stress concentration; walls and columns should be continuous. (Key point: Elevation principle) ## Related in Building Technology - [Functions of door and window; battened door elevation](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Adoor-window-functions-battened) — Building Technology, chapter 6 - [Essential requirements and types of stair by shape](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-requirements-shape-types) — Building Technology, chapter 5 - [Plan and vertical section of panelled door](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apanelled-door-plan-section) — Building Technology, chapter 6 - [Passive solar design and building layout](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Apassive-solar-design) — Building Technology, chapter 1 - [Staircase for public building (5.5 m × 6.5 m)](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Astair-public-5p5x6p5) — Building Technology, chapter 5 - [Open-well stair, 5.5 m by 3.5 m](https://www.bctengineer.com/question.md?key=semester_6%2Fbuilding_technology%3Aopen-well-stair-public-5p5m) — Building Technology, chapter 5 ## Related in other subjects - [Plan and elevation of English bond wall](https://www.bctengineer.com/question.md?key=semester_5%2Fconcrete_technology_and_masonry_structure%3Aenglish-bond-plan-elevation) — Concrete Technology and Masonry Structure, chapter 7, asked 2× - [Slab panel 2 for BM and SF (floor plan)](https://www.bctengineer.com/question.md?key=semester_7%2Fdesign_of_rcc_structure%3Aslab-panel-2-for-bm-and) — Design of RCC Structure, chapter 9 - [Typical job layout of a building project](https://www.bctengineer.com/question.md?key=semester_8%2Fconstruction_management%3Atypical-job-layout-building) — Construction Management, chapter 6, asked 4× - [Mat 18 m × 22 m, safe building weight](https://www.bctengineer.com/question.md?key=semester_5%2Ffoundation_engineering%3Amat-18x22-clay-ucs75) — Foundation Engineering, chapter 7, asked 2×