Slab refers to a common structural component of modern building. It is generally horizontal and contains lesser thickness with regards to its span. Proper care should be taken for slab design as the complete structural design of the building is dependent on it. The loads taken for its design calculations should be accurate and they differ in relation to the type of structure and its purpose.

Direct Design Method alias DDM as well as Coefficient Method are used to design the slabs. Slabs are primarily categorized as either one way or two ways. If the proportion of longer dimension of the slab panel to the shorter dimension is more than or equivalent to 2 then it is defined as one way slab. If, it is below 2 then it is described as two way slab. Several residential and office buildings which contain rooms have two way slab.

In other words, slabs which mainly deviate in one direction are called as one-way slabs. When slabs are supported by columns which are positioned typically in rows to facilitate the slabs deviating in two directions, they are generally described as two-way slabs.

The main variation among the two types of slabs - In one way slab load is delivered to one direction only that is the smaller one and therefore, primary reinforcement is presented parallel to the span while temperature or shrinkage reinforcement is presented perpendicular to the primary reinforcement. In two way slab, load is supported on four sides and proportion of longer span to shorter span is not more than 2. In two way slab, load is delivered in both the directions. Therefore, primary reinforcement is presented in both directions for resisting the loads.

It is recommended to create the design of slab with the use of excel sheet as the process will be very simple and lots of time will be saved. Given below, the sample spreadsheet for creating the design of two ways slab with the help of coefficient method. The steps of design are as follow:-

Input the following data (highlighted cells). The trial thickness is achieved with the formula h=perimeter/180 in ft. Then discover the panel dimension ratio ‘m’ and recognize the case of slab (provided in the drop down list). The spreadsheet is associated with Two Adjacent Edges Discontinuous and the value of m is 0.8.

Download Two Way Slab Design Spreadsheet

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