Did You Know CHALLENGES With OVERLAPPING in Building Construction?
Reinforcement bar overlapping is a common practice in the construction industry to ensure the integrity and strength of concrete structures. However, several challenges and considerations arise when implementing overlapping techniques. The problems associated with reinforcement bar overlapping and today we discuss some relevant provisions from the Indian Standard Code IS 456:2000 and IS 13920:2016.
1.0 Problem with Overlapping in Building Construction
1. 1 Limitations on Bar Size
§ According to IS 456:2000 [Clause: 26.2.5.1], Amendment No. 3 (August 2007), lap splices should not be used for bars larger than 32 mm in diameter. For bars exceeding this size, they should be either welded or mechanically spliced. This limitation is imposed to ensure adequate strength and structural integrity.
1.2 Difficulty in Maintaining Joggling
§ During the process of lapping, a 1:6 slope, referred to as joggling, is recommended to enhance the bond between the overlapping bars. However, achieving and maintaining this slope can be challenging at construction sites, requiring extra attention and care from the workers.
1. 3 Staggering Complications
§ Staggering refers to the arrangement of overlapping bars in a way that avoids concentration of stresses at a single location. IS 13920 [Clause 7.3.2.2] suggests that overlapping should be maintained at the mid-height (H/2) of the column. However, ensuring proper staggering can be difficult, especially when dealing with complex reinforcement layouts.
1.4 Congestion in Column reinforcement:
§ The consequences of concrete congestion in column reinforcement can be significant. It may compromise the structural integrity of the column, reduce its load bearing capacity and affect the overall stability and safety of structure.
§ Other Impact of Congestion:
1. Difficulty in Concrete Placing in column
2. Having Improper Compaction
3. Decrease durability of structure due to Honeycombing
2.0Limitations on Overlap Length
2.1High-Stress Concentration
§ IS 456:2000 [Clause 26.2.5] recommends that more than 50% of a bar’s length should not be overlapped at a single location. Excessive overlapping at one location can lead to high-stress concentrations, particularly during seismic events, increasing the risk of joint failure. Adhering to these guidelines is crucial for the structural safety of the building.
2.2 Reduction in Column Size
§ Overlapping is the reduction in the effective area of the column. Overlapping requires additional space within the column, resulting in a reduced cross-sectional area available for concrete. According to IS 456:2000[Clause26.5.3.1], the maximum reinforcement provided in a column should be 4%, with a permissible 6% at the location of overlapping. This reduction in the column size can impact its load-carrying capacity.
2.3Dependency on Concrete Strength
§ It is important to note that the strength of the overlapping joint is depends on the surrounding concrete. The overlapping does not possess its own strength but rather depends on the strength of the concrete in which it is embedded. Therefore, ensuring proper concrete quality and sufficient
bonding between the bars.
Conclusion
Reinforcement bar overlapping plays a crucial role in reinforcing concrete structures and ensuring their strength and durability in building construction. However, it is essential to consider and address the challenges associated with overlapping to maintain structural integrity. Adhering to the relevant provisions of IS 456:2000 and IS 13920, such as limitations on bar size, maintaining proper slopes, staggering overlaps, and avoiding excessive overlapping, will help mitigate these challenges.