This case involves a summertime campground facility built in 1951, and nestled high in the Sierra Nevada mountains. Over the winter, the camp was inaccessible and as the snow melted and the caretakers returned, they noticed an exterior wall in the main building that was bowed in by several inches. Eventually GEI was called in for an examination.
Our inspection discovered the following:
- A portion of the first story exterior wall of the main building had moved and cracked.
- The exterior stairway to the second floor of the main building had collapsed.
- The roof structure was sagging.
- The foundations were cracked.
- There was dry rot and insect damage at the base of some of the walls.
- A visit to the attic showed that there had been repairs to the roof structure in the past.
- The roof ridge beam in the vicinity of the earlier repairs was crushed.
- Some of the purlins in the roof structure also were broken.
- Some of the replacement posts in the attic had moved as well.
The next step was an evaluation of the observations. Starting at the foundations, there had been some soil movement over the past number of years, but it was not serious and was not the prime cause of the observed damages.
The dry rot and insect damage needed repairs, but also had not yet seriously compromised the strength of the walls.
We discovered that there were really two separate issues-the wall and the roof, although both had been damaged by snow.
Researching the snow loads, we found that for the years of 1947 to 2004, the heaviest snowfall was in 1951-1952, with the maximum total annual snowfall of 444 inches. The greatest total monthly snowfall was in January 1952, and was 127 inches. We did not have all the data for the current snow season yet, but the incomplete data projected that the maximum total annual snowfall would be 157 inches. The deepest snowfall was recorded in January with an approximate depth of 70 inches. This indicated that there were heavier snowfalls prior and/or during the construction of the building. Also, the retrofit to the roof structure indicated structural problems with the roof structure were recognized and corrected in the past. We also detected evidence of multiple roofing materials. An excessive load from roofing materials, construction equipment and roofers walking on the roof during re-roofing can also damage a roof structure. Generally a building movement of this nature is caused by excessive or unbalanced snow load on the roof structure, and poor design/construction practices. In this case, it was not a single event, but the cumulative effect on a roof that was not designed/constructed to take the snow loads that it was annually subjected to.
The issue of the damaged wall was also interesting. There was another building a few feet away, whose peaked roof shed snow into the walkway between the two buildings. Over the course of the winter, the snow slid off the roof of the second building and filled up the walkway between the buildings. A winter caretaker reported that the snow was up to nine feet deep between the two buildings during the winter. The buildup of packed snow delivered a lateral thrust against the wall, which was never designed to resist such a pressure. The result was a series of broken 2 by 6 vertical wall studs and a five inch inward deflection in the wall.
The main building was in an eminent collapse mode. It lost its structural integrity and could not resist any new forces or loads. The weight of the building itself, more lateral movement in the wall, or a moderate wind/earthquake load would have caused the total collapse of the building. It was therefore a hazard to the public; and was ‘red tagged” until repairs could be accomplished.
While it was inconvenient for the camp operators to use alternate facilities , our engineer averted disaster by his timely analysis. If a thunderstorm had occurred while the lodge was filled with little campers, the story would not have had a happy ending. The protection of the public is a responsibility that our engineers take very seriously.