Curious Civil Engineer

Jacks are essential tools in prestressing operations and are used to apply tension to strands within tendons. There are two main types of jacks: A. Mono-Strand Jack A mono-strand jack is primarily used in building construction, where tendons typically consist of a small number of strands (usually 3 to 4). This type of jack is designed to stress each strand individually, ensuring precise control over the tensioning process. Since buildings generally have shorter tendons compared to bridges, stressing strands one by one is a practical and efficient approach in this context. construction management: concrete construction bridge construction:How to become a bridge engineer B. Multi strands jack:  In bridge construction, where tendons contain a significantly larger number of strands, using a mono-strand jack would be impractical. Stressing strands one by one in such cases would not only be time-consuming but also increase the risk of strand entrapment. Ther...

Concrete placement should not be permitted if the ambient temperature exceeds 38°C to 40°C . hence, it is recommended to place concrete when temperature is less than 35°C . If the temperature reaches 35°C or more, special precautions must be taken, as hot weather accelerates water evaporation from the concrete. This rapid evaporation negatively affects the hydration process, leading to reduced concrete strength and durability. Adverse Effects of Hot Weather on Concrete Increased Shrinkage – high temperatures cause excessive moisture loss, leading to greater shrinkage in concrete. Higher Risk of Cracking – Rapid drying can induce thermal and plastic shrinkage cracks. Reduced Durability – Increased evaporation increase concrete porosity, compromising its long-term strength and resistance to environmental factors. construction management: concrete construction bridge construction:How to become a bridge engineer Special Measures to Mitigate Hot Weather Effects To minimize ...

1. Anchorage Anchorage is a device used to secure prestressing steel and is installed at the edge of a concrete member or the prestressing end. There are two main types of anchorage: Dead-end anchorage : Embedded within the concrete, providing a fixed termination point for the prestressing tendons. Live-end anchorage : Positioned at the edge of the concrete member, where prestressing occurs. The jacking operation is done at the live end anchorage and the applied load is transferred to concrete members after the completion of tendon jacking. construction management: concrete construction bridge construction:How to become a bridge engineer Anchorage device consists of: anchorage device A. Bearing plate :  Typically round or rectangular, its primary function is to transfer the prestressing force from the tendons to the concrete. bearing plate and wedging plate B. Wedging plate:  This component holds the stra...

Pre-tensioning In pre-tensioning, the prestressing reinforcement (strands or bars) are tensioned before the casting of concrete. Once the concrete gains sufficient strength, the prestressing force is transferred from the tendons to the concrete. Stages of Pre-tensioning: Tendon Placement & Tensioning High-strength steel strands are stretched between two end abutments (bulkheads) within a prestressing bed. Concrete Casting Concrete is cast around the tensioned tendons and left to cure. Transfer of Prestress After the concrete attains the required strength, the tendons are cut loose from the abutments. The prestress is transferred to the concrete due to the bond between the tendons and the hardened concrete. Effects of Prestressing The concrete undergoes elastic shortening due to the prestressing force. If tendons are placed eccentrically, the member develops a camber (upward deflection). Post-tensioning In post-tensioning, concrete is cast first , and after it gain...

Prestressed concrete technology is widely used across the world due to its numerous advantages. The capacity of reinforced concrete members is inherently limited. When subjected to loads, reinforced concrete tends to crack, reducing the structure’s durability by allowing water and harmful substances to penetrate. To address this issue, prestressing is implemented to enhance the load-bearing capacity of concrete members. This is achieved by compressing the concrete using high-tensile cables, ensuring that any applied load must first counteract the pre-existing compression before exerting stress on the member itself. Prestressing can be categorized into two methods: Pre-tensioning: The cables are tensioned before casting the concrete. Post-tensioning: The cables are tensioned after the concrete has been cast and gained sufficient strength. This technique offers several benefits, including increased structural strength, enhanced durability, a higher span-to-d...