House deformation joint setting

Deformation joints in buildings are a common feature in construction engineering. When structures vary in size, shape, and height, and are built on different geological conditions, it is crucial to account for factors such as temperature changes, settlement, and seismic activity. Neglecting these elements can lead to cracks or even structural damage. Below, the types of construction joints and their placement principles are explained in detail to help guide future construction practices. 1. **Expansion Joint (Temperature Deformation Joint)** The primary purpose of an expansion joint is to prevent serious deformation and cracking caused by temperature fluctuations and material shrinkage. To avoid vertical wall cracks due to temperature differences and wall shrinkage, the joint should be placed where stress concentration from temperature and shrinkage is most likely to occur. The spacing between expansion joints can be calculated based on specific formulas or referenced from Table 6.3.1 of the masonry structure design code (GB2003-2001). For example, with insulated roofs and floors, the maximum spacing can be up to 50 meters, while without insulation, it reduces to 40 meters. These joints are typically fully separated from the foundation to allow independent movement. 2. **Settlement Joint** A settlement joint is a permanent joint designed to prevent cracks caused by uneven foundation settlement. It helps control shear cracks by allowing the structure to deform freely without generating additional internal forces. The location of these joints should be at points where the building’s geometry changes, such as corners, height or load differences, or where the soil has varying compressibility. Unlike expansion joints, settlement joints require the foundation to be completely disconnected from the superstructure. The width of the joint depends on the number of storeys, ranging from 50–80 mm for 2–3 storeys to over 120 mm for more than five storeys. It's important not to fill the joint with materials that could restrict movement. 3. **Seismic Joint** To enhance a building's earthquake resistance, seismic joints are required when there are significant height differences, load variations, or structural rigidity differences. According to the Seismic Design Code (GB50011-2001), these joints must be placed along the full height of the building and include walls on both sides. For high-rise reinforced concrete buildings, the minimum width of the seismic joint depends on the building height and seismic intensity. In frame structures, the width may be as low as 70 mm for shorter buildings, increasing with height. These joints should be combined with expansion and settlement joints for optimal performance. 4. **Post-Casting Strip** A post-casting strip is a temporary joint used during the construction of cast-in-place concrete structures to manage thermal and shrinkage stresses. These strips are typically placed every 30–40 meters, with a width of 70–100 cm. After two to four weeks, the gap is filled with high-strength, non-shrinkage cement to ensure a continuous and stable structure. While this method helps prevent cracking, it also increases construction complexity and cost. Therefore, careful planning is essential to minimize the need for such joints. In modern architecture, complex designs often make it challenging to avoid joints. However, excessive use of joints can complicate construction, increase material usage, and reduce structural integrity. In seismic zones, improper joints can lead to collisions between building segments during earthquakes, causing additional damage. To mitigate this, architects and engineers should integrate joint considerations early in the design phase, aiming for minimal or no joints where possible.

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