Understanding Behaviour, Analysis and Design in RCC Structures
In reinforced cement concrete (RCC) buildings, slabs are essential structural elements that safely transfer loads to beams and columns. Based on structural behaviour and load transfer mechanism, slabs are mainly classified into one way slabs and two way slabs. Proper understanding of these slabs is very important for civil engineering students, site engineers, and practicing professionals.
---
One Way Slab
A one way slab is a slab in which the load is carried mainly in one direction, that is along the shorter span of the slab. When the slab is supported only on two opposite sides and the ratio of longer span to shorter span is greater than two, the slab behaves as a one way slab. In such slabs, bending occurs predominantly in one direction.
Main reinforcement is provided in the shorter span direction to resist bending moments, while minimum distribution steel is provided in the longer direction to control shrinkage and temperature stresses.
---
Analysis and Design of One Way Slab
Step 1: Preliminary Design
The effective depth of slab is determined using deflection control criteria.
The span to depth ratio is taken as 25 for simply supported slabs and 30 for continuous slabs.
The minimum overall depth should not be less than 100 mm for normal structures and 125 mm for earthquake resistant structures.
Step 2: Analysis of Slab
The slab is analyzed by considering a strip of one metre width acting as a beam. All loads such as self weight, floor finish, and live load are calculated. From the factored load, the maximum bending moment and shear force are obtained.
Step 3: Design of Slab
The depth of slab is first verified for safety.
The slab section is designed as a singly reinforced under-reinforced rectangular section. The area of tension steel is calculated using standard RCC design equations and should not be less than the minimum steel required by the code. Appropriate bar diameter and spacing are then selected.
Shear stress is checked, and generally slabs are safe in shear due to their smaller loading.
Step 4: Serviceability Check
Deflection is checked using permissible span to depth ratio limits with modification factors.
Step 5: Detailing of Reinforcement
Surplus bars are curtailed or bent as per codal recommendations. Development length at supports is checked carefully. Minimum distribution reinforcement is provided in the longer span direction.
---
Two Way Slab
A two way slab is a slab in which the load is transferred in both directions, along the shorter and longer spans. When a slab is supported on all four sides and the ratio of longer span to shorter span is less than or equal to two, it behaves as a two way slab.
In two way slabs, bending occurs in two perpendicular directions and reinforcement is required in both directions. Corners of the slab may also experience torsion depending on support conditions.
---
Analysis and Design of Two Way Slab
Step 1: Preliminary Design
The span to depth ratio is taken as 28 for simply supported slabs and 32 for continuous slabs.
The minimum depth should be 100 mm for normal structures and 125 mm for earthquake resistant design.
Step 2: Analysis of Slab
Two way slabs are analysed using the coefficient method as recommended by IS codes. Bending moments in both directions are calculated based on slab panel dimensions and support conditions.
Step 3: Design of Slab
The depth of slab is verified for strength.
The slab is designed as a singly reinforced under-reinforced rectangular section. Required reinforcement is calculated separately for both shorter and longer directions. Shear is mainly checked in the shorter direction.
Step 4: Serviceability Check
Deflection is checked in the shorter span direction using allowable span to depth ratios with modification factors.
Step 5: Detailing of Reinforcement
Bars are curtailed or bent as per detailing rules. Development length is checked at all supports. Torsion reinforcement is provided at discontinuous edges and slab corners as per codal provisions.
---
Conclusion
Both one way and two way slabs are widely used in RCC construction depending on span ratio and support conditions. Correct identification and proper design of slabs ensure safety, durability, and economy of structures. A clear understanding of slab behaviour, analysis procedures, and reinforcement detailing is essential for producing sound structural designs.
#CivilEngineering
#RCCDesign
#SlabDesign
#OneWaySlab
#TwoWaySlab
#StructuralEngineering
#SiteEngineer
#ConstructionLife
#EngineeringStudents
#IS456
#BuildingConstruction
#ConcreteStructure
#CivilNotes
#CivilEngineerLife
#GauravNepal
#GauravN
#GauravNCivil
#Damugaurav
#EngineeringBasics
#LearnCivil
No comments:
Post a Comment