Curve / Circular Ramp Beam Example

You can model a ramp beam / ring beam. Circular ramp/spiral slab is beyond the scope of the program.  Attached a sample modelling for your references only. 

Generally, it is recommended that separate the model of  circular ramp / spiral staircase from main building model, if possible. This will be more productive as it is easier to set up, analyze and troubleshoot.

It is not possible to model sloping slabs supported by spiral / curve beams; as the slab will not be perfectly planar & hence, the slab loads cannot be correctly captured. Hence, the slab loads should be separately calculated and enter onto the curve beams via Edit Loads. 

The following are general steps to model the circular ramp beam :

1. Draw the few curve axes (e.g. 4 axes) to complete a circle (refer to snapshot below). Based on project layout, you may split the circle to more curve axes segments.

2. Draw all the columns and enter corresponding Del-Z values. 

You may skip to enter the Del-Z value for column first. You can do it later after adjustment of Del-Z beams.

 

      

3. Draw the curve beams and enter corresponding Del-Z value. You can open 3D view and plan view side by side to check whether Del-Z value is assigned correctly. 

   

 How to differentiate i-end or j-end of a beam as shown below.

Selecting the beam will also display the I and J symbol on screen  

      

4. Enter Del-Z value accordingly for columns if you skip them in step (2). 

5. Display and verify the analytical model progressively to ensure member wireframe are connected  : 

a.  Create a 3D view >  By default a "Solid" or "Rendered" model is shown 

b.  Press F11 or "CTRL + D"  consecutively > this will cycle to various Display Style (Rendered, Flat, Hidden Line, Linear)

c.  Ensure "Linear" is active > This is the 3D analytical wireframe model 

d.  Verify the members are connected properly by zooming in common joints of interest (by zooming in joint of interest.

Below is an example where members are not connected analytical but appears to be connected in solid rendered view. 

6. Run Building Analysis and check the connectivity of members between columns and beams after Building Analysis is done. 

1. Go to Analysis Tab > Analytical Model > General, click "Connectivity Issue" to check connectivity of members. 
   
2. Check displacement of members is reasonable, as displacements is a direct reflection of internal member forces. If displacement is unreasonable, member forces are consequently wrong. 
   
3. Refer to all guidance as highlighted in this e-learning video : 15 – Post-Analysis Processes & Analytical Model. 

By default, the torsion stiffness of beam maybe set to 0.01 = 1% in Material and Section Effective Stiffness Factors.

Thus, due to the curve beams, you may need to adjust / increase it to utilize more of the curve beam stiffness, based on your engineering judgement. 

7. Since the ramp slab cannot be modelled in Prota, you will need to input the manual loading to your curve beam by select corresponding beam, right-click > Edit Member Loads.

8. As stated in step (2)  or step (4), please enter Del-Z of column correctly in order effective length is calculated correctly. Besides, you can also enter LEN (Storey) value to span the column height more than 1 storey. 

      

9.  As the beam is slanted, thus some of beam at above floor will supported by column below and it might have cantilever beam mark for that corresponding beam. 

1. Since it is supported by column below, you can assign corresponding beam as both ends supported. This is to avoid wrong design checking and detailing will be performed at design stage. 
   
2. To assign cantilever beam to non-cantilever beam, please select corresponding beam(s), right-click > Mark Free End of Cantilever Beam > Both Ends Supported. 

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