slab design
Unit 7 - Reinforced concrete slabs.
(Study time allocation – 15 hours)
Introduction.
The topic of reinforced concrete slabs is somewhat related to that of beams but also needs to be considered as a separate unit.
Types of slab.
1. Single span solid slab.
2. Single span ribbed slab.
3. Two way “waffle” slab.
4. Flat slab – No column drops
5. Flat slab showing column drop.
Analysis of slabs.
Theoretically all slabs span to a greater or lesser extent in both directions. In practice many slabs are designed to only span in one direction and although there will be a small moment in the orthogonal direction in practice it is neglected. According to classical plate theory, a two way spanning slab is subject to the following forces; Mx, My, Mxy, Myx, Vx and Vy.
In practice we only design for Mx and My and provide restraint against twisting at corners (applies to external slabs).
Slab analysis can be undertaken using grillages or finite element analysis. In this course we will only examine simple techniques including the yield line method of analysis.
One way spanning slabs.
Analysed as a continuous “beam” strip spanning between beams and subject to the most unfavourable set of loads. Moment re-distribution (as with beams) may be undertaken)
.
Reinforcement in singly spanning slabs.
The main reinforcement is positioned with the least cover and as such provides the maximum resisting moment. Transverse reinforcement is used to form a mesh. Sometimes reinforcement mesh is purchased as a manufactured item but often the reinforcement “mesh” is built before being placed.
Reinforcing mesh. Stronger in one direction than the other
Building a reinforcing mesh. Probably for two-way spanning slab
Slab reinforcement at a column head.
Bending moments and shear forces in singly spanning slabs.
Two-way
(Study time allocation – 15 hours)
Introduction.
The topic of reinforced concrete slabs is somewhat related to that of beams but also needs to be considered as a separate unit.
Types of slab.
1. Single span solid slab.
2. Single span ribbed slab.
3. Two way “waffle” slab.
4. Flat slab – No column drops
5. Flat slab showing column drop.
Analysis of slabs.
Theoretically all slabs span to a greater or lesser extent in both directions. In practice many slabs are designed to only span in one direction and although there will be a small moment in the orthogonal direction in practice it is neglected. According to classical plate theory, a two way spanning slab is subject to the following forces; Mx, My, Mxy, Myx, Vx and Vy.
In practice we only design for Mx and My and provide restraint against twisting at corners (applies to external slabs).
Slab analysis can be undertaken using grillages or finite element analysis. In this course we will only examine simple techniques including the yield line method of analysis.
One way spanning slabs.
Analysed as a continuous “beam” strip spanning between beams and subject to the most unfavourable set of loads. Moment re-distribution (as with beams) may be undertaken)
.
Reinforcement in singly spanning slabs.
The main reinforcement is positioned with the least cover and as such provides the maximum resisting moment. Transverse reinforcement is used to form a mesh. Sometimes reinforcement mesh is purchased as a manufactured item but often the reinforcement “mesh” is built before being placed.
Reinforcing mesh. Stronger in one direction than the other
Building a reinforcing mesh. Probably for two-way spanning slab
Slab reinforcement at a column head.
Bending moments and shear forces in singly spanning slabs.
Two-way