Cold Frame Post Mortem

A photo is worth a thousand words, but still needs to be interpreted with words to make sense. I took a closer look at the nature of the catastrophic collapse of the cold frame. There were some variations, but there was a general pattern. All center ribs broke at a place between 6 and 12 inches up from where they attached to the raised bed.

There were also several ribs that were snapped at their base where they were attached to the raised bed.

A key to the sequence of events that probably happened lies in the evidence provided by the end ribs. These did not snap completely, but bent and developed stress fractures. On both sides where this evidence appeared, there were splits at the 6 inch to 12 inch area above the raised bed timbers. This is more visible in the segment on the right but still occurred in the segment on the left.

Finally, it is worthy of note that on just one of the middle ribs was there evidence of breakage near the top of the rib.


So, what probably happened is this: The snow and ice accumulated on the top of the cold frame. Unlike rain that runs off, a bond was formed that kept the snow and ice in place. The snow and ice gradually caused the ribs to flex downward. Being only 5 mm in width and designed to be easy to bend, to a point this flexibility is desirable. However, when the weight of the snow and ice accumulated sufficient weight, probably in near the middle (lengthwise), the ribs started to snap, which probably cascaded throughout the structure relatively quickly. The points with the greatest stress was near the 45 degree points of the arc at that point in time.

My next step is to consider re-engineering changes that will allow future frames to either deal with snow and ice better or to allow them to hold more weight.