Slab is one of the basic parts of a building. Slab being the first element to be designed has pretty much importance as the whole structural design is based on the design of slab. the loads considered for its design calculations are carefully chosen and vary according to the type of structure and its purpose. Slabs can be designed by Direct Design Method known as DDM and another method for design is Coefficient Method which is the easier one. Slabs are mainly of two types; either one way or two way. If the ratio of longer dimension of the slab panel to the shorter dimension is greater than or equal to 2 then it is designed as one way slab. If less than 2 then it is designed as a two way slab. Most of residential and office buildings have rooms that have two way slab. The basic difference between the two types of slabs is that: In one way slab load is carried by one direction only that is the shorter one and hence main reinforcement is provided parallel to the span whereas temperature or shrinkage reinforcement is provided perpendicular to the main reinforcement. While in a two way slab load is carried by both the directions (longer and shorter) and accordingly main reinforcement is provided in both directions to withstand the loads. Design of a slab using excel sheet is much easier and time saving. So today I am going to share with you my excel sheet for the design of two way slab using coefficient method. First I will explain the steps of design briefly:
Input the following data (highlighted cells). The trial thickness is obtained by the formula h=perimeter/180 in ft. Then find out the panel dimension ratio ‘m’ and identify the case of slab (given in the drop down list). My case is Two Adjacent Edges Discontinuous and the value of m is 0.8
Calculate the Negative Moments at continuous ends for long and short direction by the formula Ma,neg=Ca,neg x Wu x La x La (lb-in)
In the same way calculate positive moments at midspan.
Calculate negative moments at discontinuous ends as Ma,neg=Ma,pos/2 (lb-in)
Then calculate the reinforcement for long and short direction at the three places i.e continuous end, midspan and discontinuous end.
Check the slab against shear.
This is the output of the design.
Here the detailing of reinforcement is shown in the diagram.
So viewers here is the Excel Sheet Excel Sheet for Two Way Slab. Keep visiting Knowledgeoverflow for more and also see other tutorials like Cantilever Retaining Wall Design.