How to consider the diaphragm action of slab in the analysis for seismic loading?
If you are using IS: 1893 (Part-I)-2002 code for seismic analysis, there has been specific guideline on the consideration of diaphragm effect on the model. The code is allowing the designer to consider Rigid Diaphragm for reinforced concrete monolithic slab-beam floors or those consisting of prefabricated/ precast elements with topping reinforced screed. The following condition has been proposed to evaluate the flexibility of a diaphragm.
On evaluating the proper type of diaphragm, you need to model them in the model. STAAD.Pro allows you to model RIGID DIAPHRAGM. The following picture demonstrate the process that you can adopt to define rigid diaphragm in your model. A sample model has been attached.
Answer Verified By: SSV Consulting Engineers
FILE FOR RIGID DIAPHRAM.std
dear all,
in defining loads in reference load command, im just wondering why it is positive sign where the loads where going upward?
can you please explain? sorry for this question, please help
rekcah
The Reference Load itself has definition of mass in the loading type. In this load case, you need to provide a mass modelling- defining the masses in the three orthogonal directions (X, Y and Z). You need to apply the loading (100% od DL and required % of LL) in the three direction and the program compute the mass of the model accordingly. The program would simply compute seismic mass from this load cases.
Using +ve and -ve loads all together would lead to the cancelation of masses. Thus, it is suggested that you use unsigned loads.
thank you so much sir dsanju,
do you have any refernces that you can suggest or any link so that i can understand further about mass modelling?
i really appreciate your help
Please refer to the following section of Technical Reference Manual: