My work also has those upside U bikes racks. We have tonnes of them all bunched together. In theory there's enough to hold hundreds but in reality the pedals and handlebars get in the way and actually prevent that from happening. Also the U's are attached to a steel beam on the ground so they're also impossible to clear of snow in the winter (and as such they don't get cleared either).

Here's the culprit:
(http://www.equiparc.com/en-5911.html)