SEISMIC ANALYSIS USING LUMPED MASS METHOD

Create the Geometry of the model and give member property.Provide all beam and column junctions as hinged and create a load case [i.e. DL+50%LL or 25%LL as per Code IS 1893 (Part 1) -2002]Then run analysis and view the result w.r.t the already created load case.Go to reaction tab and copy the reactions to the excel sheet.Delete the all the unwanted columns [ Fx, Fz, Mx, My…]Let nodes, load case and Fy column retainedReplace the load case column fully by Joint weight.Copy and paste it in the staad editor.Done…Detailed Procedure :

STEPS INVOLVED:

1. Creation of Geometry

2. Giving Member Property

3. Support Condition

4. Giving Loads :

Load 1 Dead Load

Load 2 Live Load

Load Comb 3

5. Specifying Analysis Type

6. Post Analysis Print

7. Design

8. Analysis.

(1) In this complete steps 1 to 6. Then follow the further steps for Lumped

Mass.

There are two parts.

Part 1 : Finding Joint Loads for Earth quake analysis.

Part 2: Applying Earthquake analysis.

Before Proceeding take a copy of Model created from step 1 to 6.

Part 1: To find Joint Loads:

1.To give pinned supports at all column nodes :

Main menu ‡ Select ‡ Beams parallel to ‡Y

Main menu‡ View ‡View selected objects only.

Main menu‡Commands ‡Support specifications ‡ Pinned ‡ Assign.

2. Apply Load:

(1) In Seismic Load for finding joint load we have to consider the following

Load case as per Table 8 (Clause 7.3.1 ) of IS 1893-2002.

1.0DL+0.25LL (If LL<3KN/m2)

1.0DL+0.50LL (If LL>3KN/m2)

Main menu ‡Edit ‡Edit input command file‡

In Load case below Live Load type the following:

Load Combination 3

1 1 2 0.25

Perform Analysis

Load List 3

Print Support Reaction

(2) Main Menu‡ Analysis ‡ Run Analysis ‡Done.

(3) Main Menu‡ View ‡Tables ‡ □ Support Reaction.

From support reaction Select only Joint No. and Force FY.

Copy and Paste the Joint No. and vertical reaction at the pinned supports

in a separate file named as “Joint Load “file.

Type Weight in between Joint No. and Force Fy as below:

(E.g) 16 WEIGHT 81.47

Close the File.

Part 2 : Applying Earthquake Analysis:

Go to original file of Model created from step 1 to 6. Then follow the steps

below:

DEFINING SEISMIC LOAD:

1. Main menu ‡ Commands‡ Loading ‡ Definitions‡Seismic Load‡

IS1893-2002

2. Seismic Parameter screen will appear. Select type:IS1893-2002.

□ Include Accidental Load

□ Generate .

3. IS1893-2002 Seismic Parameter screen will appear.

Select city or Zone. For Zone III Z=0.16 (Table 2 IS1893-2002)

Response Reduction Factor (RF) : (Table 7 IS1893-2002)

: 5 for SMRF

: 3 for OMRF

Importance Factor (I) : (Table 6 IS1893-2002)

: 1 for Ordinary Residential Building

: 1.5 for Important Building

Other Factors:

Rock or Soil sites Factor (SS) : (Clause 6.4.5 of IS1893-2002)

: 1 for hard soil (N>30)

: 2 for medium soil (10≤ N ≤ 30) for all soils.

: 3 for soft soils (N< 10)

Type of Structure (ST) (Optional) : (Clause 7.6 IS1893-2002)

=1 for RC Frame Building

= 2 for Steel Frame Building

= 3 for all other Building

Damping Ratio (DM) (Table 3 IS1893-2002): 0.05%

PX =Period in X Direction (Optional):

PZ =Period in Z Direction (Optional):

□ Generate ‡ Add ‡ Close.

4. Go to “ Joint Load” file .Copy the Joint Weight and apply them as

Seismic Weights. For this go to

Main menu ‡Edit‡ Edit Input Command file.

Below the Zone factor, copy and paste the JOINT WEIGHT as in the Joint Load

file.

1. Edit the Load case No.1 (Dead Load) and 2(Live Load) as Load case No. 5 &

6.

2. APPLYING SEISMIC LOAD:

(1) Click Load case details in the Data Area ‡Add.

Number: 1 Loading Type: Seismic

Title : Seismic X +ve ‡ Add.

Click Load Case 1 ‡ Add

Seismic Load § X Direction. Factor 1 ‡ Add. ‡ Close.

(2) Click Load case details in the Data Area ‡Add.

Number: 2 Loading Type: Seismic

Title : Seismic X -ve ‡ Add.

Click Load Case 2 ‡ Add

Seismic Load § X Direction. Factor:- 1 ‡ Add. ‡ Close.

(3) Click Load case details in the Data Area ‡Add.

Number: 3 Loading Type: Seismic

Title : Seismic Z +ve ‡ Add.

Click Load Case 1 ‡ Add

Seismic Load § Z Direction. Factor 1 ‡ Add. ‡ Close.

(4) Click Load case details in the Data Area ‡Add.

Number: 4 Loading Type: Seismic

Title : Seismic Z -ve ‡ Add.

Click Load Case 4 ‡ Add

Seismic Load § Z Direction. Factor: - 1 ‡ Add. ‡ Close.

LOAD COMBINATION:

Main menu ‡ Load Combinations‡

Loading No.7

Name: 1.5(DL+LL) Default: 1.5

Available Load case Load

cases

Factor

1. EQX+ve

2. EQX-ve

3. EQZ+ve

4. EQZ-ve

5. DL

6. LL

>

>>

<

<<

5

6

1.5

1.5

Add‡

Loading No.8 Name: 1.5(DL+EQX+ve)

Default : 1.5

Available Load case Load

cases

Factor

1. EQX+ve

2. EQX-ve

3. EQZ+ve

4. EQZ-ve

5. DL

6. LL

>

>>

<

<<

5

1

1.5

1.5

Add‡

In the similar way add the following load combination.

Load case No. Load case Factor

95 1.5

2 1.5

105 1.5

3 1.5

115 1.5

4 1.5

12

5 1.2

6 1.2

1 1.2

13

5 1.2

6 1.2

2 1.2

14

5 1.2

6 1.2

3 1.2

15

5 1.2

6 1.2

4 1.2

165 0.9

1 1.5

175 0.9

2 1.5

185 0.9

3 1.5

195 0.9

4 1.5

Add ‡ Close. (OR)

AUTO LOAD COMBINATION

Main menu ‡ Commands ‡ Loading ‡Edit Auto Loads ‡ Select Indian

Code

Select : New category say EQ

No. of rule :4

Rule No. Dead Live Seismic

1 1.5 1.5 --

2 1.5 -- 1.5

3 1.2 1.2 1.2

4 0.9 --- 1.5

Click Update Table ‡Close.

Click Load case details ‡ Add ‡ High light Auto Load Combination (in left

side).

Select : Indian code

Category: EQ ‡ Generate loads‡Add‡ Close.

Main menu‡Commands‡Loading‡ Load List (selecting Design loads) ‡

Load List.

Available Load Load list

1. EQ X+ve

2. EQ X-ve

3. EQ Z+ve

4. EQ Z-ve.

5.DL

6.LL

7. 1.5(DL+LL)

8. 1.5(DL+EQX+)

9. 1.5(DL-EQX-)

10. 1.5(DL+EQZ+)

11. 1.5(DL-EQZ-)

12. 1.2(DL+LL+EQX+)

13. 1.2(DL+LL+EQX-)

14. 1.2(DL+LL+EQZ+)

15. 1.2(DL+LL+EQZ-)

16. 0.9DL+1.5 EQX+

17. 0.9DL+1.5 EQX-

18. 0.9DL+1.5EQ Z+

19. 0.9DL+1.5EQ Z-

>

>>

<

<<

Load Comb

7 to 19

‡O.k. ‡ Close.

STEP 5 ( Analysis ):

From Main menu ‡ Commands – Analysis ‡ Perform Analysis ‡ § No

print ‡ OK.

STEP 6 (Post Analysis Print):

From Main Menu ‡ Commands ‡ Post Analysis Print ‡ Support Reactions

‡

§ To view ‡ OK.

STEP 7 ( Design) :

Page control ‡Click Design‡Concrete ‡Current code IS 456‡Define Parameters

‡Fc=30,000KN/m2 ‡Add. Fymain=415,000KN/m2 ‡Add.

Fysec=415,000KN/m2 ‡Add. Ratio=3%‡Add.

Click Command‡Design Beam ‡Add. Design Column ‡Add. Take

off‡Add‡Close.

Click Fck=30,000KN/m2 and select the entire structure ठAssign to

selected Beam‡ Assign ‡Yes. Click Fymain=415000KN/m2 and select

the entire structure ‡§ Assign to selected beam‡ Assign ‡Yes. Click

Fysec=415000KN/m2 and select the entire structure ठAssign to

selected beam‡ Assign ‡Yes. Click Ratio=3% and select the entire

structure ‡§ Assign to selected beam‡ Assign ‡Yes. Click Design

Beam ‡Select‡Beam parallel to ‡X and Beam parallel to ‡Z‡

§ Assign to selected beam‡ Assign ‡Yes . Click Design Column‡Select

‡ Beam parallel to Y‡§ Assign to selected beam‡ Assign ‡Yes ‡

Take off ‡ Assign ‡ Close.

Note: Save the File and Run the Program.

STEP 8 (Analysis):

From Main Menu ‡ ` Analysis ‡ Run Analysis ‡ Run Analysis ‡ Done.

Select the member and double click on it ‡ Shear bending ‡ Close.

NOTE:

This procedure is very useful in the older version of Staad Pro due to the fact that in

the OLDER version, load list in load cases differ from the load list in load definition.

In the latter version of Staad Pro 2007, you can just copy paste the loads from the

load cases to the seismic definition and let Staad will do the entire process of

analysing weights but of course there is a need to carefully change some load name,

e.g. instead of floor load that will be floor weights Member Load will be Member

weight etc. It's much easier.

This method of analyzing Earthquake analysis by direct method is explained

separately.