www.sefindia.org

[Jagdishdhantole]

Dear Safians,

I have to design a Blast Resistance Building as the provision of ASCE for an Indian Plant.
Blast over pressure is very Nominal (0.9 ksi only).

The two adjacent walls and roof will be affecting while blast occurs.
please suggest me how to Conceptualized this building.

Regards
Jagdish

[AMIT DUTT]

Dear Jagdish ,
The walls have to be RCC . A equivalent static approach can be applied also . I will mail you this ,similar formulations  as ASCE method are given .
You can do an FEM model

[Yogesh.Pisal]

Dear Jagdish,

I think you are talking about 0.9 psi and not 0.9 ksi.

(0.9 ksi = 900 psi = 620.5 t/m2 is very very high and it is impossible to design the building for such a huge pressure)

If the pressure is 0.9 psi, then you dont need to worry about your design.
OISD 163 minimum requirement norms will be enough for safe blast resistant design.

If you need to do the calculations then you can adopt
1. Static method of design
2. Dynamic method - Non linear time history analysis.

Refer to earlier posts on this topic for the detailed description on this topic.

Regards,
Yogesh Pisal

[Yogesh.Pisal]

Dear Amit,

FEM analysis is always accurate and better provided it is carried out properly / accurately. But, my experience is that most of the people use to take FEM analysis very lightly.

If meshing is done without giving much attention and convergence is not checked, then FEM analysis can lead you to very poor results.

Regards,
Yogesh Pisal

[Jagdishdhantole]

Dear Yogesh & Amit,

it was my mistake, over pressure = 0.9 psi.

OISD provisions can be followed as it is very less pressure, but I have to perform Detailed calculation and that is as per AISC provisions too.

I will search some releted topic also here.

Dear Amit,
I will be waiting for your reference calculations.

I wish to design this with FEM approach.
Let me explain the Boundary Condition,
RCC wall be supported by Columns and it is simply supported with the Top (roof) & Bottom (grade) Beams.

please tell how to check convergence for this condition.

Thanks & Regards
Jagdish

[AMIT DUTT]

Dear Yogesh.Pisal,
If we make the discretization properly ,aspect ratio 1:1 of the four noded elements & idealize the boundary conditions properly there should not be any problem.
FEM is a numerical solution & not a closed form solution where a shape function (displacement profile is chosen )
How do we check convergence in a STAAD PRO model

[Yogesh.Pisal]

Dear Amit,

I will like to share my personal experience here. I was involved in the design of sump. Normal practise is to use Moody's chart to find the moments in wall.

But, I did that using FEM (in STAADpro). Size of the wall panel is about 4m (W) x 6m (H) x 0.30m (tk). Size of the plate element is about 0.5m x 0.5m (Aspect ratio equal to 1). I was surprised to see the moment of 55kNm by FEM as compared to 82kNm by Moody's chart.

On the instruction from my boss, I did one more iteration with plate size 0.4m x 0.4m. I got higher moment with this plate size (discretisation). Then successively I reduced mesh size and checked moments in the plate.

Finally for the size of 0.1m x 0.1m I got the moment equal to 81.5 kNm (Almost equal to the moment as per Moody's chart). Further discretization does not alter the moment significantly. This means solution has converged.

Apart from simply decreasing the mesh size, One need to take special precautions while meshing for complex geometries (e.g. you need to have close meshing at corners, at openings etc)

Regards,
Yogesh Pisal

[AMIT DUTT]

Dear Yogesh ,
YOu maybe  correct . I will try this out in a small FEM model .

Dear Jagdish,
I do not have any calculation as such but it is the DEP (Shell Standard) .
Similar to the ASCE method of Blast load .

[vishnuvardhan]

Dear,

I am actually designing a structure subjected to blast loads as per IS 4991. I have calculated the pressure values for front face, sides, and rear face as per IS 4991. I need analyze this structure by time history method using staad pro software.

Can any one let me know how to apply the blast pressure values for each time interval in staad pro.

with regards,
vishnu vardhan

[Yogesh.Pisal]

Dear Er Vishnu,

Blast Load is pressure time history. You need to work out time history at each node on front wall, side wall, roof & rear wall. Here it is important to work out start time of each time history carefully as the time history on different nodes will be having different arrival time.

Note the following
1. STAAD will be doing only linear analysis and generally we prefer to perform non linear analysis for blast
2. Convergence shall be checked for plate stresses
3. I will recommend you to design the building by SDOF idealization as per ASCE manual rather than using STAAD.
    If we want to be more precise, then we should use more Sophisticated software like ANSYS, Abaqus etc

Best Regards,
Yogesh Pisal