We travel south of the border this #seismicsaturday to Baja California, Mexico. Featured is an observation platform at “El Mirador” (The Lookout) in San Pedro Mártir Nacional Park, at 9100 ft.
⛰️The platform is made with a cantilever steel truss structure. The main truss extends outward, reducing its depth as it goes (Fig. 2). Secondary truss structures go across, to tie the main trusses together (Fig. 3). Every single steel-to-steel connection is welded (Fig. 4). It is notable that not a single bolt was used on any of the steel-steel connections. Given the extreme temperature variations at 9100 ft, with sub-freezing temperatures in the winter and hot weather in Summer, it is interesting to think about thermal stresses that would develop in this stiff structure.
⛰️One thing that makes this structure unique is the way it is kept in place on the mountainside. A huge pile of rocks, kept in place by steel tubes and mesh (pic 5), serves as a counterweight, keeping the structure on the hillside. Furthermore, a bunch of oddly (and seemingly arbitrarily) angled steel plates are bolted to rocks on the mountain (pic 6). Your Seismic Outreach correspondent has never seen anything like this before.
⛰️In an area battered by rain in the Summer, freeze-thaw cycles in the Winter, and high humidity, painting the structure is important to prevent corrosion. Except for a little section to the right of the joint in pic 4, this structure has been well painted, and as such, doesn’t seem to show signs of corrosion.
From the cantilevered steel tubing, to the rock boulder counterweight, to the wacky steel plates anchored to the ground, engineers building the lookout came up with a creative solution to create a platform over a precipitous drop. The platform gives hikers a gorgeous (and nail-biting) view.