Introduction: SonoGROTTO

sonoGROTTO, creates a human-scaled space of respite and repose on the busy sidewalk of Market Street in San Francisco. It is composed of hundreds of cardboard tubes fastened together to create a protected but open space. These tubes are carved, creating seats, windows, and an oculus to view the sky.

For this project you will need the following:


Software used: Rhinoceros 5.0, with the plug-in T-Splines by Autodesk


Whole pieces of Sono tubes: 1
Large (24” diameter), 20 Medium (10” diameter), 55 Small (6” diameter)-each are 12 feet tall); it’s great to have a few extra pieces in case mistakes are made when cutting each individual piece. Depending on the overall form you decide to make, the number of tubes will vary.

We are able to cut 235 pieces: 3 Large, 67 Medium, 165 Small

Connection pieces:

Bolts 1880 (.0174 lb per piece), 32.7 lbs.

Nuts 1880 (.005 lb per piece), 9.4 lbs.

Washers 3760 (.0198 lb per piece), 74.5 lbs.

Note: A total weight of 116.6 lbs. was added to the structure.

The following specs are provided for the products used.

Note: Each package comes with 100 pieces; determine how many packages you would need based on the expected tangent connections of your structure.

1” ¼ by 20 low strength zinc plated steel bolts

1/4” Internal diameter hex nuts

1/4” Internal diameter 1-1/4” outside diameter fender washers


300 lbs of sand

bags for the sand


A jig saw (this will be used to create the curved voids on the tubes, you can drill the tube first to that you may insert the saw blade to cut out the geometry

A circular saw (this will be used mainly to cut pieces that need trimmings or simple geometry)

A hand sander with medium grit

A power drill that could fit inside the 6” tubes to that you may be able to drill from the inside, with the following attachments:

A drill bit, slightly larger than ¼” diameter­

A square drive hex bit socket for tightening the hex nuts onto the bolts

1/4” wrench, to hold the hex nuts while tightening the bolts

Painter's/drafting tape for securing the paper template in place around the tubes

A rotary tool with spokes for initially marking the tubes of the cut lines

(It is also helpful to have multiples of these tools, especially if you have a group of people building the structure, that way production time will be much more efficient)

Step 1: Designing the 3D Model

The first step is to create the 3D model of your design. This was done using Rhino with a plug-in called T-Splines. Start by creating circular curves that correspond to the different sizes of cardboard tubes: 6", 10" and 24". Extrude these to the desired height (note that the tubes come in 12' lengths, we did ours in 10').

Array and pack the desired dimension of structure (we did a 10-foot cube). Once you determine the distribution of the tubes within your desired volume, trim the excess/overflow tubes on the sides to create sharp edge.

Using T-Splines, create the volume that you would use to create the void within. (This may take some time to get the desired geometry of the interior) Once you are satisfied with this volume, use it to Boolean out the interior space to create the carved volume.

Step 2: Creating Your Templates

Once your 3D model is created, group them in clusters that make sense for assembly. We created 3 different group types: foundation base, structural columns and the roof pieces. You can also break these group up into smaller aggregations.

After creating a logical grouping, color code them and plot them out to get a scaled footprint of the base and inverted roof plan. (You will use this to guide your assembly, check the extents of your plotter to know that maximum width you can print.) We also overlaid our plan templates in order to save paper.

For the tubes themselves, unroll each surfaces and label them accordingly; using the same system you used for the plans. We also overlaid the unrolled surfaces so that we saved some paper in the printing. (These templates were used in determining where to cut out the void on the tube.)

Step 3: Tube Fabrication and Aggregation

Tube Fabrication:

Once you've created and printed your templates, you can use them to wrap around the whole tube and tape them in place and mark the tubes using a rotary tool with spokes. When you remove the paper, trace the indentations with a pencil to create a more visible outline. Label the piece accordingly and repeat until each tube is fully used.

When you've marked all the pieces you need, you may begin cutting. You can use a circular saw for trimming ends and less curved cutouts. When you have pieces that cut a void through the tube, use the drill to make a hole, which you can use as an initial cut with the jig saw. It its best to leave between 1/8" to 1/4" offset, which you can sand off.

When all the pieces are cut, you can sand them down to create nice pristine edges.


Tube Aggregation:

Now that all your pieces are cut and sanded, you can begin aggregating them based on the grouping logic you've created with the help of the overlaid plan drawings we've created from the previous step. Lay the plot on a flat surface and place the pieces on their corresponding locations. You have have to move things a bit while as you pre-drill the tubes with a 4" and 2" distance from the edges. We found it to be easier to drill and bolt the pieces as we assemble the groupings. This way your pre-drilled holes will line up perfectly, rather than drilling all the holes at once and missing their alignment because the pieces haven't been bolted and fastened.

Hold the tubes in place by placing fender washers on the inside of the 2 tubes being joined, and secure with the bolt and hex nut. Use your power drill with the tightening attachment and a wrench on the other side to secure and tighten the connection.

Do this step until you've aggregated your groupings of tubes. It is best to group them in manageable size and weight so that 2-3 people can lift them.

Step 4: Overall Assembly

Once all the tube groupings are created, create the 2 halves that would make the overall form. We simply bisected the design along the path and made sure that the base, columns and roof pieces for each half would be able to stand structurally when erected in place. (See drawing/diagram of Structural Analyses)

When both halves are securely bolted, gather a group who can tilt each of the halves in place. When these halves are fitted into place, drill and bolt them in place at the roof. Depending on the height of your structure, you may need to use a ladder to reach into the roof tubes.

Step 5: Structural Analyses

This diagram served as our analysis of the structural considerations for the pavilion. You can use Rhino to calculate the volume of your designed structure, and use the weight of each tube type to determine the weight of your pieces. We've also provided the weight of each connecting pieces so that you may calculate the overall weight of bolts, washers and hex nuts that would be added to your total structural weight.

If you are unsure of the structural capacity/integrity of your design, check with a structural engineer.

Step 6: Process Models