First of all, I want to clarify that I am far from being a structural engineer and I am sure the system is perfectly safe as it is. The following is just an idea without any data behind it. Also, since I am not a native speaker, I might express my question a bit more complicated than necessary, but here we go:
In all the designs I have seen on the website and YouTube, the edges of the blocks line up, effectively slicing the chassis like a loaf of bread, held together by the bowties.
Would alternating the blocks (similar to how we construct brick walls) not add an extra layer of safety without too much effort? Let’s consider the connecting sides of two wall boxes on the same floor as a crack in an otherwise whole wall, which is patched up by the ties. If there are unforeseen and extreme circumstances (like Godzilla doing jumping jacks next to the house or something) that lead to a catastrophic failure of some of the ties, the ties of the whole slice of the house are under more stress, right?
But if the floor/roof boxes that are resting on top of the wall have their “crack” located in the middle of the wall box underneath them, the forces would be more divided (that’s what I imagine).
Hi @fhein,
I think you make an excellent point, and even if you are not a structural engineer, it seems that you think like one
Maybe there is a way to have a version of Skylark like you say, but there a few things to solve if going in that direction.
The parallel with bricks might not be the most appropriate in my opinion. Bricks are full solid elements, so they can transmit forces through the entire surface. Skylack cassettes are essentially empty in the middle (except insulation). Because of the connections with beams, skylark vertical forces run on the side panels. If you alternate the blocks, my sense is that all the force coming from the beam will be concentrated on a small 18 mm x18 mm area. That won’t occur if the blocks are full solid like bricks
The second problem I see is uplifting forces. Imagine that your roof block is trying to fly away because of wind, and it is connected to the walls. What is preventing the wall to fly away if the blocks are alternated? You will need to somehow connect the blocks with a connector that restrain the uplifting (Bricks are heavier and the mortar in between acts in tension.)
Point two becomes relevant also when thinking at the walls racking. When racking, the wall is subjected to uplifting on one side, and therefore the connection needs to able to act in tension.
There might be ways to do that, but my sense is that the lower the number of connections and the more straight forward the load path, the better. Having said that, there are maybe better ways of doing than what we are currently doing now, so please keep challenging the Skylark system!
Coming back to Skylark in its current form, as you say we rely on bow ties to actually ‘tie’ the slices together. Therefore they are critical for structural purposes, i.e., if Godzilla takes them out, then the racking behaviour would be extremely compromised. But this is true for any structural /mechanical system in a way or another… For example, take any truss system, if you fail one single bolted connection then the whole thing will most likely fail abruptly. On a plane if you fail the connection between the wing and the body of the plane, then the whole plane fails.
What we normally do in structural engineering is:
We estimate the amount of load in a probabilistic way very conservatively (take earthquakes for example, we design with even with probability of 1/500 years). These numbers are given by the building code based on location.
We estimate the capacity of the structure very conservatively (we don’t use the average properties of materials, but the characteristic values. That means we take the 5th percentile capacity i.e. there is 95% probability that the material properties are stronger than what we assume)
We don’ just compare 1 and 2, but we also use further safety factors. For example, in timber connection we might reduce the capacity by dividing for 1.25.
We went thought this process for Skylark in its current form.
If you like math, we could argue that there is no 100% safe structure of any structural system, as there is always a non zero probability of collapse. For example, the loads given by the building code never took into account Godzilla because it never showed up in the historical data, so there might be a scenario where this happens. In practical terms, this whole design process guarantees that the structure is safe.
Well… we have or ups and downs, but I do think that with enough creative pessimism, even the Great Pyramid of Giza could, at least theoretically, tumble like a 1:5 replica of the Gau-Weinheim Bell Tower made entirely out of marbles (this one is for you)
I am certain that the system has the necessary safety buffer. My question/idea was born from a misunderstanding about the beam construction that I will explain further down.
But let’s just, for the sake of an argument, assume that a camera adds a pinch more than 10 pounds, and Godzilla is the size of the average human being. She (she laid eggs in the 1999 one) is now living in a Skylark house and tries to hang up some shelves. Since her eyes are on the sides of her head, her depth perspective could be better. Plus, she can barely hold a power tool with these thumbless lizard hands. So, after some missteps, she abandons the task, leaving five holes in a relatively straight line in the middle of one bowtie. Could that become a problem? Is it adding stress to the other ties in that row? Would an alternating approach relieve some stress in general by distributing the forces (in the direction towards the Earth’s center) more horizontally? Is there expected (significant) wear on the ties over time?
That is important information and it may conflict with my revised idea.
But the roof, beam, and wall blocks would still be connected with ties, with the only difference being that one beam would be connected to two wall blocks. I was not attempting to eliminate or even reduce the number of ties.
Now, here lies the root of my misunderstanding. I was envisioning a beam as a (more or less) closed simple box, which I then further simplified in my mind as a block capable of distributing vertical force over the entire surface area of its upper or lower panel. However, in reality, a beam appears more like a frame with a very small surface area.
So, what if you add a resting plate for the beam? By doing so, the beam would have the same surface area to distribute the forces as before.
In the end, there is still the issue regarding the number and distribution of the bow ties. For the floor boxes, if the middle bow tie connecting the lower floor with the upper beam were to be placed over the gap of two walls, perhaps two smaller bow ties could be placed on the left and right sides instead. However, if this arrangement is not beneficial to the stability of the system, it may not be a good idea to implement it.
Additional qestion: It appears to me that the bottom panels of the beams (room ceiling) serve a minimal structural purpose and are primarily in place to hold insulation (although I could be mistaken). Considering this, what if you manufacture these panels using thinner, more cost-effective materials or even omit them entirely? Instead, the insulation could be added after the final assembly, and the entire structure could be closed up using conventional materials such as plasterboard. This approach may also offer benefits for service installations.
So, what if you add a resting plate for the beam? By doing so, the beam would have the same surface area to distribute the forces as before.
I am not sure about this. Normally in beams, the shear is taken by the beam’s web while the moment is taken by the beam’s flanges. This is because the force follows the stiffness. So even if you add other plates to reinforce the support in a certain area, the load transfer will follow the sketch I sent you above from the beam into the column. In other words, I cannot see any way to transfer the load into the columns evenly on the 4 faces. It will be transferred on the side faces, because these are the faces supporting the beam’s web. You could think about using more webs, but I think it will use more material than needed.
Additional qestion: It appears to me that the bottom panels of the beams (room ceiling) serve a minimal structural purpose and are primarily in place to hold insulation (although I could be mistaken).
Not really, at least to my understanding of the system behaviour. The bottom panels and the tabs specifically create the necessary tensile forces to hold the section together. In fact, those are the points where the damage develops during load testing. If they were not engaged, you would not see any force transfer in that location. There is more information here if helpful https://www.youtube.com/live/MvMuF3SBPlE?feature=share
