The Bridge to Terabithia

This project was part of the 'Finite Element Application to structures' class, where it was given to model a Pedestrian bridge as an architect and also design it as a Structural Engineer. The criteria for the design of the bridge are as follows:

• Withstand wind speed of 100-120 mph
• Bear the weight of a Newfoundland puppy(don't be fooled by the term puppy! they weigh like horses)
• Located over a canyon, connecting the 2 sides with a span of 150 ft
• Be careful to prevent the lock-in phenomena

The conditions of the surrounding area is as shown in figure 1.1.( all dimensions are in ft)

Given conditions of project

To catch the user's eye and to promote a sense of awe, a design idea of an arch-sparred cable bridge was put forward in our group of 4. The deck of the bridge is made up of a re-inforced concrete beam of width 12 in, which consists of W beams ( W6x8.5; W8x35 and W24x103). The supporting structure of the bridge is the arch which is a rectangular hollow tube, the diameter of the arch being 60ft. The arch is tied down to the bridge by 2 inch high strength tension cables running from the center of the arch to the center of the deck.

Model of the Cable Stayed Bridge in SAP2000

Loads Applied:

• Dead Load 

          Concrete Deck     -  150 lb/ft3

          Structural Steel      - 490 lb/ft3

          Railing                  -  95 plf ( pound per linear foot)  

• Live Load  

          Pedestrian Loading   -  149 lb/ft2

          Equestrian Loading   -  0.26 kip (applied to a 2x2 in area to check fro punching shear)

• Wind Load 

The wind load acting is in 2 directions: the horizontal and the other in the vertical actin from under the bridge pushing it upwards

          Horizontal         -  61.36 mph

          Vertical             -  0.24  klf ( applied at quarter point of deck width)

Frequency Check:

As per AASHTO LRFD, the first fundamental frequency in the vertical direction,

          f  > 2.6 * ln (180/ dead load of deck)

so as to counteract any mode shapes generated from the repetitive forces on the bridge, like running or walking. This refers to the phenomenon of 'lock-in'. It is said to occur when the random frequencies of loading synchronize to match with the lateral frequency of the bridge. This point could cause high vibrations of the bridge, leading to failure. This condition has been seen in the Millennium Bridge, London, within the first two days of opening the bridge to the public.

Deflection Check:

The deflection limits of a pedestrian bridge as per AASHTO is that the bridge's lateral and vertical deflections should not exceed,     

                 delta   <  (1/500) * span length

With the span length of 150ft,      delta  <  3.6 in

Actual deflections of the bridge: 

                 Vertical : 2.75in;      Lateral : 2.05in

So the bridge is safe from any abnormal deflections.

With the use of the software Revit ARCH, the idea of our bridge came to life as in the below pictures.

                                             

Final view of bridge (not to scale)

The entire cost of the above project was estimated to be around $200,000

The final requirement for this project was to create a video presentation good enough to sell the bridge to an  architectural committee. The video presentation created is as follows:

Visual Programming Using Revit-Dynamo

PROJECT 2 – ARCH 653




Fig 1. Building Facade

DESCRIPTION:

For project 2, we were to extend the level of functionality and creativity of the BIM model that was created in the first project. For these applications, the use of Visual Programming i.e., Revit Dynamo has become essential. As the projects get more complex, it is not possible to control all the parameters in the modelling interface.

I have chosen the same building model that I had used for project 1, on which I first ran this test process of controlling the parameters. Later, I also tried using this Dynamo file on other different shapes to see if a new parameter had to be included, but it was not necessary.

This time I have used Octagonal curtain panels with a circular void form in them. The aim of my project is to control the size of those openings using the colors of the panels. Apart from my building model, I have used the same dynamo file at various places to show a few more examples.

My curtain panels are ‘Octagonal’ Curtain Panels by pattern shown in fig., which are created with a thickness of 1 feet. A circular void is cut at the center of that curtain panel with a particular radius, which I named as the “Opening radius”. At the end of this project, the change in color, changes the radius of the opening. The change in radius is specified by us in the Dynamo coding.

      Fig 2. Octagonal Curtain Panel

 

RANDOMIZING USING EXCEL:

After applying the curtain panels on the divided surface, it is time to change the color of the panels with Dynamo. In order to randomize the color of the panels, I have used an Excel sheet with the function “RANDBETWEEN” to alternate the panels with 5 different colors. This function updates the sheet with random display of numbers from ‘0 to 4’. These numbers should vary in a specific number of cells, equal to the number of panels in the divided surface of the building.

Fig 3. the random values from Excel sheet

                                     

EXPLANATION FOR THE DYNAMO CODE:

The Dynamo code has a lot of nodes, which if sequentially laid, makes a proper code. Dynamo tool is pretty recent and so it does not have all the nodes, which can be normally done in a revit environment. If the user does not know what node to use, this process would not be productive. This does not make it easier for the user to use Dynamo and can be considered as the critics during the growing stages of Dynamo.

The following is the Dynamo code used for my project.

       Fig 4. Dynamo code for random colors controlling size of openings and thickness

There are 4 things that we need to get from the Revit Interface when using Dynamo:

1. The Divided Surface
2. Parameter 1 - Material/Color of object
3. Parameter 2 - Opening
4. Parameter 3 - Thickness       

                    Fig 5. Dynamo code- Divided Surface Families Node

 

The ‘Select divided surface Families’ Node is used to select the divided surfaces from the Revit Environment. The ‘Watch’ node connected to it shows all the selected panel by the IDs and the shape of the panel selected is also mentioned in the list of lists. This list is flattened into one list with the help of ‘Flatten Completely’ node. Multiple surface can also be selected using many instances of this node and then grouping them. However, using this node multiple times to select different surfaces on objects might pose a task, as the process can be complicated.

Fig 6. List Node for Materials/Colors

 

There are more than one material color and more than 1 radius values, so a ‘list’ option is used to group them individually.

Fig 7. list node for values of Openings and Thickness

Since my model has many divided surfaces, all the lists of panels are put through a ‘flatten completely’ node, so that all the panels are put under just a single list, which is then plugged into the final node ‘Set Element Parameter’. This parameter actually shows the result in the actual Revit mass family.

Python Script: This is also used in the Dynamo code, instead of many ‘if-else’ nodes. The python script comes in handy as a big If-else statement. This script basically takes one color as input, based on which a radius value and a thickness value is selected. These are automatically changed if the chosen color changes. 

For example if the Material color is Glass, corresponding radius for the opening is 4 ft and thickness is 3 ft. And if the color is 'Default- Blue', corresponding radius for the opening is 2 ft and thickness is 4 ft.

Without the python script, this would be make the Dynamo screen look too clustered with a lot of nodes. Hence a python script is used to simplify this process.

The Excel file controls the randomness of the colors, the list of material colors and the list of radius values are given as Input to the Python Script node.

Simultaneously there is another python script in the Dynamo code, which helps in changing the value of the thickness of the curtain panels based on the value of the colors.

FINAL FAÇADE AND EXAMPLES:

Below are few examples of models that I have created with the curtain panels changing in every picture that is shown. The figures below shows obviously the different colors, thickness and changing opening sizes.

L-shaped building

Sphere

Crescent

Star

Colorful Chessboard

                    Video also found at :     http://www.youtube.com/watch?v=wblfaCwKLEk

Mid-Term Project 1

Description:

In-order to model the high rise, which has unique shapes of walls at alternating floors, the mass model is first created with the required parameters. The parameters are related to each other so that the entire mass is controlled by these parameters. The footprint of the building that is modelled is as shown in figure 1.

                                             Fig 1. Footprint of the High-Rise

Modelling:

The parameters are pretty simple for this building. Before the boundaries are drawn, the parameters should be aligned to the references lines and not the boundary surfaces. If aligned to the boundary surfaces, constraint errors are going to pop up. Revit is not convenient to use when many errors of such kind commonly arise.

Fig 2. References Lines for the building

The smaller square at the 2^nd level is drawn to create a void from the 20^th floor to the 25^th floor on the shorter leg of the L-shaped building. The final Mass Model is as shown below in Figure 3.

                                        

  Fig 3.  Parametric Mass model- Screenshot 1   

The various parameters assigned and their relation to other parameters are as follows:

           Fig 4. Parameters Used

Changing the above parameters we get the following screenshots:

Fig 5. Screenshot 2 _ Variation in Length

Fig 6. Screenshot 3_ Variation in Width

Fig 7. Screenshot 4_Variation in Height

                                                                                            

My goal for this project was to create curved walls for every floor, but with alternating frequencies. Since the curve and frequencies come into play, a custom made curtain panel is made using the formulae of a Sine Curve. That panel is fitted into the divided surface of a wall in the mass model and the parameters are assigned to it.

             Fig 8.  Custom Curtain Panel 

         Fig 9.   Project Envelope (Façade)

Up-to this point, all the models are made in the family files. Now this family is loaded into a new project, where the model is further worked on, where a site, walls, floors, roof, rooms, furniture etc., are placed in the building. With the mass form as guidance walls and floors are created and then the mass for can be turned off as per settings.

Fig 10. Building Exterior-Wire Frame Model

Renderings of the Building:

Exterior Rendering

Interior Rendering (Lobby)

Critics on Revit Modelling Application:

 Without coding, using on modeling tools of Revit becomes hectic, for example, custom and unique color for a 100 panels. This becomes too cumbersome if manually done. And also as stated before, Revit takes the constraints in modelling very seriously. If not parameterized correctly, errors pop up very easily. So the user has to have thought over all the necessary details.