Theory and design of Structures

The difference between the two is enormous. This would lead to a design failure if it isn't examined carefully. If automeshing is applied to wall objects, don't select the visible joints at the foundation level and display the joint reaction for selections. Rather, just display the whole reaction and joints with "~" prefix would be displayed and they are joints generated by automeshing. Make sure to include them in your design. @theoryanddesignofstructures

Now rather than selecting and showing the reaction at the two nodes, display support or spring reaction option is used. Here in this case the reaction at the joints generated by the automeshing is displayed, if we sum up these values the total would be 17334.25 KN. @theoryanddesignofstructures

The reaction that the shear wall element in the ETABS model is supposed to bring to the foundation is shown in the picture by selecting the two joint objects at the two ends of the wall. Automeshing for the wall element is assigned. If the vertical reactions at the two joints from this table is summed up the value would be 4791.72 KN. @theoryanddesignofstructures

Correction Ds/4 instead of Ds/6 Thanks for commenting.

Flat plate(notice the direct connection between the slab and the column). @theoryanddesignofstructures

Flat slab( notice the column head and drop panel at the column slab junction). @theoryanddesignofstructures

Slab directly supported on columns( without beams or beams only at the perimeter of the building) are called Flat slabs or flat plates. What is the Difference between flat slab and flat plate? Flat slab is one with either drop panel or column capital(or both at the same time) that helps reduce shear stress on the column slab junction. On the other hand flat plates are slabs systems with the slab connected to the column directly. Flat slabs can bridge larger spans when compared to flat plates. Due to shear demand and deflection requirement the span flat plates can bridge is very small. According to macgregor and whites book, mechanics and design of reinforced concrete Structures, flat plates are most economical for spans from 15 to 20ft [4.5 to 6 m] and flat slabs are used for spans of 20 to 30 ft[6 to 9 m]. Flat slab or plates can be analyzed using several methods of structural analysis. Some of these methods are: ✅DDM(direct design method), ✅EFM(equivalent frame method), ✅FEM(finite element method), ✅Grillage method, ✅Yeild line method and ✅Strip method of analysis. @theoryanddesignofstructures

As a conclusion, If one chooses to use drop panel it would have an extra advantage of reducing the required slab thickness and reinforcement while this advantage cann't be obtained from shear caps. shear caps only serve to reduced shear stress. @theoryanddesignofstructures

Drop panel would look something like this. it would appear to be larger than a shear cap. @theoryanddesignofstructures

Shear cap looks small as shown in this picture( I amnot stating this is shear cap, but it looks like it). @theoryanddesignofstructures

According to article 8.2.5 in order to refer a given thickening around column as a shear cap, it shall project below the slab soffit( no specific dimension required) and it shall extend horizontally a distance equal to the projection below the slab soffit( Dp). @theoryanddesignofstructures

Therefore any given "drop panel" if it doesn't satisfy the above requirement it cannot be referred as drop panel. But, it has the possibility of being shear cap...let's see. @theoryanddesignofstructures

If we take the grid system in the picture, according to article 8.2.4(b) the drop panel shall extend( for column C1 for example) L1/6, L2/6,N2/6 and N3/6 in each direction. @theoryanddesignofstructures

According to Article 8.2.4(a) Dp shall be greater than or equal to Ds/6. @theoryanddesignofstructures

ACI 318-14, Art. 8.2.4 and 8.2.5 @theoryanddesignofstructures

Shear cap vs drop panel Flat slab design is usually associated with punching shear. In order to reduce the shear stress induced around columns designers usually increase the slab thickness near the column. This increase in thickness in the vicinity of columns is usually called "drop panel". Is it technically correct to call every thickness increase around columns drop panel? The answer to this question is NO! And let's see an article from ACI 318-14 to arrive at a correct naming/term. @theoryanddesignofstructures

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