The I-beams in the foreground were installed into the notches in the Trägersperre to block the road, although these appear to be too short to span the gap, perhaps US engineers cut them in half with a cutting torch to prevent them from being reused. But in any case, how were the I-beams secured into the notches? Some photos show two bolt heads in the notches, but what did they connect to? I have several books on fortifications, three on the Siegfried Line itself, yet I cannot find any photos showing how this was done. Anyone have a copy of Panzersperren und andere Hindernisse by chance? Some Trägersperre have large storage boxes fixed to the outsides of them, surely these boxes must have held the requisite parts to secure the I-beams, what else would they be used for? Beer coolers?
To your question, I wouldn’t think they would need to be secured. The time and effort involved in removing them from the angled notches would be sufficient to achieve the desired effect of slowing down an advancing armor column. In the first photo, it does appear that the beams were blown apart with either dynamite or thermite if you look at the ends, which gives an indication of how difficult they would have been to get out of the way once set in place. The beam in the last photo looks like it’s set for a couple of guys to shove it forward with a couple of prybars to let it fall into place in the notches.
Sorry, but the explanation of dropping the beams in unsecured does not account for the obvious bolt heads / mounting studs clearly visible in the photos.
Obviously, something else was done to fasten the beams into the notches, otherwise, why bother installing the bolts? Assuming that anti-tank gun defenses have been dealt with, an enemy tank would merely need to drive up to the Trägersperre, loop a choker cable around the beam, attach it to the tow shackle and yank it out of the way. Repeat as necessary. This would be a pretty weak link considering the cost and effort of building over 100 km of Dragon’s Teeth across your border. Perhaps the beams were installed and the bolts were screwed down across the edges to secure them in place. Even better if they used a special type of fastener, something akin to a security Torx-head bolt, a 5-sided fire hydrant bolt or the T-handled locking tool they used to open panzer engine decks. This would slow the enemy down enough for the defenders to bring in reinforcements to the area to deal with the problem. Still, I would like to find a clear photo with the beams installed. If no other apparatus is visible, then they were probably just bolted into place.
I also find it interesting that they numbered each slot in the above photo. This implies that whatever device was used to secure the beams had a unique size, spacing or other dimensional issues, otherwise why the numbers? 5 slots, 5 beams. Do they need Count von Count from Sesame Street to help them keep track of the number of beams? Maybe one of their fingers got shot off.
It is rather humorous that they originally painted all the Dragon’s Teeth green to “blend into the surroundings”. Like you wouldn’t notice them, especially from the air? Later model, larger teeth that were commonly added behind existing rows were left unpainted. Notice that the above Trägersperre are painted white, presumably so that drivers would not run into them at night, the first photo I posted actually has a group of reflectors mounted on the leading edge. Which raises the question about why they wasted the time painting the other Trägersperre with “camouflage” that resembles a pineapple plantion.
I’m no expert but I’d suggest the reason the supports were designed in that arc’ed way was specifically to prevent the cross-beams being just yanked out. The slots are at acute angles, you’d need a crane…which admittedly wouldn’t have held up clearance for very long, but enough to prevent any AFV from doing it. Or as demonstrated the beams could be just cut in half.
Overall a fairly naff defensive system unless also littered with mines – I’m sure I’ve seem some footage of a bulldozer just piling up earth over the pyramids to create a roadway across them.
Here’s my suggestion: They’re sliders. Maybe even on springs.
The way the concrete was poured and the shape of the arc makes it impossible to install/remove the Bars from the front. The rack in photo #4 has them aligned and you can see that the slots are narrower at the top. Being Germans, they probably had a special Sd.Kfz Truck to install/remove the bars. The allies did not. It actually shows the bars started in Photo 4.
Also looking at photo 4 and the beam alignment, It seems that the “I” part would align where the bolts come up out of the concrete making it difficult for a hole through the steel.
And I think the suggestion that the bars were torched apart in the other photo is probably correct.
Later model, larger teeth that were commonly added behind existing rows were left unpainted. Notice that the above Trägersperre are painted white, presumably so that drivers would not run into them at night, the first photo I posted actually has a group of reflectors mounted on the leading edge. Which raises the question about why they wasted the time painting the other Trägersperre with “camouflage” that resembles a pineapple plantion. 
