Waffle Slab

QUESTION 1 Give 4 merits and 2 demerits of waffle slab floor system. Where the system is

considered more appropriate compared to beam and slab system? ANSWER

Merits: a. Reduc Reduced ed dead dead weigh weightt b. Aesth Aestheti etical cally ly plea pleasi sing ng c. Lighting Lighting fixtures fixtures can be conceal concealed ed in the the ribs ribs d. Can be used used for long long spans spans without without excessiv excessive e beam projections projections Demerits: a. Cost Cost of shu shutte tterin ring g is larg large e b. Large surface surface area : extra extra heat transfer and extra extra plastering plastering  This system system is preferred preferred over over beam and slab slab system system at places places where where aesthetic aesthetic and architectural architectural features are important. This system is a good option to reduce weight of roof and the amount of  material consumed. The system is preferred in large halls for public usage.

QUESTION 2 What are the 2 forms of waffle slab system? Give relative merits, demerits and at

least one case example of each. Which form is more commonly adopted and why? ANSWER

 The 2 types of forms are: o

o

Waffle slab with wide shallow beams around the periphery  →

Not as symmetric as solid plane system

→

Example: NBCC House at Bhikaji Cama Place

Waffle slab with solid panels around corners →

System is difficult to analyze

→

Less commonly adopted

→

Requires square grid

→

Example: Hero Honda factory at Gurgaon

Waffle slab with shallow beam around the periphery is more commonly used as it is easier to design and analyze. Moreover, this can be applied to asymmetric spans.

QUESTION 3 Draw a typical section through a waffle slab floor indicating all structural

components. Give thumb rules for fixing preliminary sizes of the structural members of waffle slab system. Why wide-shallow peripheral beams and not narrow-deep beams are normally provided in waffle slab systems?

 Thumb rules: Slab thickness: 75mm -100mm Beam thickness: span/20 –span/25 Column: span/15  Taper thickness: 120-150 mm Distance between two waffle: 800-1200mm Span determined by the distance between two columns. Structural shuttering: 25mm thik with 4mm dia structural steel bars

QUESTION 4 What are precast shuttering units for waffle slab floor system construction? What

are their demerits compared to in-situ shuttering? Explain with neat sketches, the arrangement of anchoring and integrating precast shuttering units with the in-situ construction. ANSWER

Precast shuttering units in the shape of the waffle are cast on the ground with ample reinforcement. They are lifted to the base of the roof and suspended with the help of rods and wooden base. After setting of the main slab, the precast units are set with it and form a part of  the slab. Demerits: A large no. of units has to be cast Setting up of the wooden shuttering unit at the roof level is cumbersome Uneconomic when used on small scale

Units cannot be reused Pre cast units can be cast beforehand therefore time can be saved during the roof construction

QUESTION 5 Plan and draw to an appropriate scale structural arrangement for a plan size of a

building 32m x 32m with the column spacing of 8m and four storey high with each storey of  4.6m. Draw typical floor plan and typical section with complete dimensions with suitable assumptions where ever required. Show detailed section if considered appropriate. Plan and draw both alternatives: I.

With wide shallow peripheral beams

II.

With solid panels around columns  Assume concrete mix M25