1. Define the material properties. Activate the Data Entry menu if it s not already visible, and click on Materials.

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1 CE 533, Fall 2014 Guide for Using RISA3D 1 / 9 Example Structure. The procedure for calculating frequencies and modes shapes of a multidegree of freedom (MDOF) system will be demonstrated using the following example. 3 Story, 1 bay x 1 bay structure. Plan dimensions are 30 x 30. All floors have a 7" thick reinforced concrete slab (f c = 4 ksi, unit weight = 150 pcf). All four columns are W14x30 steel columns, I zz = 291 in 4 30' 10' 10' v3 v2 v1 10' 1. Define the material properties. Activate the Data Entry menu if it s not already visible, and click on Materials Select the Hot Rolled tab and A992. Make sure that the modulus is set to 29,000 ksi Select the Concrete tab and Conc4000NW (for 4000 psi normal weight concrete) and make sure Density = kcf.

2 CE 533, Fall 2014 Guide for Using RISA3D 2 / 9 2. Define the Sections. Select Section Sets from the Data Entry menu Select the Hot Rolled tab, type in a label (e.g. Columns ), select the W14x30 shape, select the A992 Material, and check that the moment of inertia about the strong axis (Izz) = 291 in Select the Concrete tab, type in a label (e.g. Slab ), specify a rectangular element 7 inches deep by 180 wide (half the building width). 3. Set up your drawing grid 3.1. If the Graphic Editing Toolbar is not visible, right click anywhere in the white part of the screen and select it.

3 CE 533, Fall 2014 Guide for Using RISA3D 3 / Select the Drawing Grid icon, type in 1@30 under X Axis and 3@10 under Y Axis. 4. Layout the structure. Select Draw Members, and 4.1. Draw the columns after selecting: Hot Rolled, Assign a Section Set, Columns (make sure to select the nodes at each level to provide an intersection for the slab floors).

4 CE 533, Fall 2014 Guide for Using RISA3D 4 / Draw the slab floors after selecting: Concrete, Assign a Section Set, Slabs Check that your model is input correctly by selecting Plot Options, Members, Wireframe, and Shape. 5. Specify the Boundary Conditions. Since we are building a 2 dimensional model and RISA is 3D program, the first task is to constrain the model to a single plane (the X Y plane). Then we specify the boundary conditions at the support (assume fixed base) To constrain the model to the X Y plane, select the Modify Boundary Conditions icon, then select Fixed and check the Use? box for Z Translation, X Rotation, and Y Rotation. Then select the Apply Entries to All Selected Joints, and select Apply.

5 CE 533, Fall 2014 Guide for Using RISA3D 5 / To specify the support conditions, select Reaction and check the Use? box for X Translation, Y Translation, and Z Rotation. The only difference between Fixed and Reaction boundary conditions is reactions are not calculated for Fixed Check the boundary conditions by selecting Boundary Conditions from the Data Entry menu. Your boundary conditions should appear as below. 6. Specify the Loads. RISA is set up for structural design in which the engineer checks the structural response to multiple combinations of loads. For this example, since we are only calculating the natural frequencies and mode shapes, we will only have one basic load case

6 CE 533, Fall 2014 Guide for Using RISA3D 6 / 9 (self weight, others could be super imposed dead load, live load, seismic loads,...) and one load combination (self weight times a factor of 1.0, others could be 1.2 D L,...) Select the Basic Load Cases icon and the Load Combinations icon and arrange the spreadsheets as shown below. On the Basic Load Case spreadsheet, type a label under BLC Description (e.g. self weight ) and type a 1 under Y Gravity to specify that the member self weights will be applied in the negative Y direction (downward). On the Load Combinations spreadsheet, type another label under Description (e.g. self weight only ) and type a 1 under BLC (refers to Line 1 of the BLC spreadsheet) and type a 1 under Factor 6.2. Check your model by calculating the structural response to self weight only. With Load Combination 1 selected, select the Solve Current icon. Display the deflected shape of the structure by selecting the Plot Options icon, the Deflection Diagrams tab, Load Combination, Include Undeflected Shadow and

7 CE 533, Fall 2014 Guide for Using RISA3D 7 / 9 Apply. Check the indicated deformations for reasonableness (e.g. no rotation at fixed base supports, small rotations at column to floor connection, etc.). 7. Calculate the Natural Frequencies and Mode Shapes To calculate the natural frequencies, select the Solution icon, Dynamics, and Solve. Select Start Solution on the Dynamics spreadsheet that pops up. The resulting frequencies are displayed to the right:

8 CE 533, Fall 2014 Guide for Using RISA3D 8 / To display the mode shape for Mode 1, select Plot Options, Deflection Diagrams, Mode Shape, Mode 1 Period.9371 Sec, Include Undeflected Shadow, and Apply. Display the mode shapes for the other modes using a similar procedure. Mode 2 Mode 3 8. Adjust the RISA model to match the hand calculated (spreadsheet) frequencies and mode shapes. We made several simplifying assumptions when calculating the frequencies and mode shapes by hand. 8.1 Make the following changes to your RISA model so that it s frequencies match the hand calculated frequencies. On the Boundary Conditions menu, Fix the rotation about the Z axis at all column slab joints.

9 CE 533, Fall 2014 Guide for Using RISA3D 9 / 9 On the Global Parameters menu, Solution tab: uncheck Shear Deformation On the Materials menu, specify a density of 0 for A992 steel. 8.2 Now compare the RISA vs. hand calculated frequencies and mode shapes. You can copy the RISA mode shapes into your Excel sheet and normalize them so that the maximum modal displacement equals 1.0 for each mode.