Week 8 Challenge

WEEK 8 CHALLENGE SOLUTIONS

1. AIM:

Applying Load Exercise

For the structure modelled in previous exercise. Apply following loads

• Form a Load case as DL for Dead Load
• Apply Self weight
• Apply member load of 3 kN/m on the rafter
• Apply member load of 6 kN/m on the secondary beams
• Apply point load of 20 kN at node intersecting inclined member on the top chord.
• Form a Load case as LL for Live Load
• Apply member load of 4 kN/m on the rafter
• Apply member load of 7.5 kN/m on the secondary beams
• Form load combination 1.5DL+1.5LL

Procedure:

Open the previous challenge

• Go to Loading tab and select Load Case Details.
• Then click Add, Select Dead load and name it as DL as shown below.

• Now select DL load case, and click Add.
• Then click Selfweight Load and give -1 factor of load at Y direction.

• Now select Member Load, then give input as -3 kN/m for Rafter and -6 kN/m for Secondary beams along GY direction.

• Then select Nodal Load, give input as -20 kN.

• Assign all Dead Load to the structure as shown below.

Go to Utilities - Groups. Highlight the top chord/rafter

Now assign the member load of 3kN/m to the rafter

Highlight secondary beams from Groups and assign -6kN/m on it

To assign nodal load of 20kN go to nodes cursor and select the required nodes

• Again add Load Cases Details as Live Load and name it as LL.
• And add -4 kN/m and -7.5 kN/m of Member Load for Rafter and Secondary beams respectively.

Now click on LL and start adding member loads in it

Utilities - Group. Highlight top chord / rafter members

Click on Add to define the load combinations

2. AIM:

Find Maximum Force and Minimum Force for member and present the STAAD result.

Continue previous challenge, Run the analysis and find following results on the member mentioned

• Run the analysis
• Find the Maximum Moment in the Secondary beam for 1.5DL+1.5LL case
• Find the Maximum Axial force on the inclined bracing and identify the member having the maximum force for 1.5DL+1.5LL case
• Identify Bottom chord of Truss having Maximum shear Force & Maximum moment for 1.5DL+1.5LL case and present the values.

Procedure:

Go to Analysis and Design - Define Commands

• Then click Run Analysis.

• Now select Postprocessing to see the Results.
• Then choose the Load Combinations.

Click on Beam results to view the bending moment

The maximum moment for 1.5DL + 1.5LL is 52.922 kNm

Now view the BM results of the inclined bracings

Create a group in the analytical modelling for inclined members

Click on Mz in the View Results. Annotate - Choose member in the group

Right click on the table - Results Setup- Group

Similarly view the axial forces

Now view the max SF and BM for bottom chord under the load combination

3. AIM:

View and Rectify the Warning, instabilities in the structure

For the attached STAAD file identify the Warnings and fix the same and run the analysis.

Procedure:

• Open the STAAD File given in the attachment.
• Run the analysis

We can notice 0 errors and 8 warnings in the structure

Go to Analytical model to view nodes 47 and 48

Direction 3,4,5,6 means there is no stiffness or reaction against translation in Z axis, rotation in X, Y and Z axis

Toggle off the Truss specification to the members supporting the nodes. ie let them be normal beams carrying the moment too

Method 2:

Select the 2 nodes that were in warning condition. Under Node specification, fix the dependant direction as below to introduce stiffness where ever zero stiffness was present

4. AIM:

Design Parameter exercise

In continuation to challenge 1, Apply Design parameter for structure modelled for code IS800:2007.

• Effective Length Lx, Ly, Lz for beams, Truss elements
• Effective length factors Ky, Kz for Columns
• Apply other design parameters for respective members

Procedure:

Go to Analysis and Design - Steel

Choose the code as IS 800

Click on Define parameters

Add the following parameters

Since we have pinned ends , Ky = 1

Lx,Ly for rafters = purlin spacing = cos 20 = 3m/hyp = 3.19 (assume as 1.5), for columns (assume girt spacing )= 1.8

Lz taken as the height of the column = 10m, for rafter = 15m(half the span)

Also include Take off and Check code commands

Now run the analysis

Check the utilization ratios. It could be seen that the purlins and rafters have a very high utilization ratio. The member size needs to be altered