And from 'atmospheric pressure,' should I infer that the wood is not being exposed to the steam in a closed vessel?  (Steve Yasgur)

That is correct, although the vessel is closed in the sense that the contents are surrounded by a chamber ( say a plywood box), just not air/pressure tight, which could get dangerous in a hurry. Most boxes have an exit port on the bottom for the steam and pressure, opposite to the steam inlet, to remove water and spent steam.

An experiment you should try ( and you may have already done this)  is to warm a piece of scrap bamboo on a hot pipe or in front of a heat gun and try to flex it as you do so.  You will find a temperature at which the bamboo ( as you will also with hardwood) can be bent easily.  This is the temperature  at which you need to get the wood/bamboo to do a permanent straightening, as you have melted some of the bamboo structural components. On cooling, the bamboo will largely retain this shape if held this way as these bamboo biopolymers harden up again.  Binding the strips together or in Harry Boyd's binding form with a string which will not stretch in the heat or moisture should do the trick. One advantage of the steam box is that you do the whole strip instead of a short piece. If you do it in short areas, when you straighten the next area this may bring this just straightened area out of whack. Ever happened to you?.

So, if your goal is to bend the strip until it is straight, get it to this temperature and then hold it there. Cooling it now will fix this shape. .. This temperature is below the boiling point of water at atmospheric pressure ( 212F), so no need to pressurize a vessel. IIRC, about 180F is sufficient for hickory to make those Bent wood chairs and rockers  - popular long before electric heating was available and steam was the method of choice. Interestingly, hardwoods are easier to bend than softwoods.

Reading some of the old timey literature, makers heated the bamboo until the juice stopped oozing out the ends and then a little longer.

Here is but one example of a simple steam bender that will handle strips.

Searching for "wood steam bending" and "bamboo steam bending" will produce a plethora of examples with all sorts of materials of construction.  Just never seal it up tight.  A comment in the above article says it takes less than 5 minutes to heat 1/4 inch thick piece of wood ( once the steam box is at temperature)  This is the case, since water vapor has a much higher heat capacity than air..  In the case of bamboo, this will take longer, as the bamboo juices need more time to ooze out.

I have never done this with bamboo, but there are plenty of examples ( bamboo furniture for example and, of course, old time rod makers) to convince me it is very doable.  Oh, and no toast/burning problems with this method and leave it as long as you want in the steam chamber. This will give maximum protection to the power fibers.  You can also do many pieces at the same time, so no need to fire up the steam box very often. 

Do it outside if you can, as it does drip water. A catch pan may be necessary if you choose to do it inside. As always, be careful with steam as it can produce some deep (remember that high heat capacity) nasty burns. Wear insulating gloves when removing the bamboo.  (Dave Burley)

Tim Abbott did a wonderful demo on heating and pressing nodes with steam at the Merritt, BC gathering about six years ago. His vise is a work of art. Robert Kope makes vises which function somewhat similarly but from a completely different design.

With Tim's advice, I made a non-pressurized steam chamber for heating nodes. Even after several revisions I found the steam never got the bamboo quite hot enough to straighten and press nodes TO MY SATISFACTION. Later I learned that those who use steam sometimes also heat the jaws of the vise, and I wasn't willing to go that direction. (Harry Boyd)

In the meantime, I realized that soaking the strips ( as I think you do) and then heating them to above 212F would produce internal steam.  Not the same, but similar.  (Dave Burley)

Seems like soaking  and heating  would produce steam, doesn't it? I haven't soaked strips in 6-7 years, though that method is still detailed in my articles. Soaking for 3-4 days works quite well, but I never know I'm going to be heating and pressing or displacing nodes 3-4 days in advance. Besides, with a little practice I find that heating dry allows me to be more consistent in hitting the "sweet spot" temperature so no nodes pop back out in the oven. (Harry Boyd)

I think as long as the bamboo is wet its temperature is 212F independent of the oven temperature, until the bamboo is dry. This will make it more complicated to control.  Steam from an exterior source can only be 212F.  (Dave Burley)

In my first shop the bamboo was stored in very dry conditions. My storage area now has much more moisture/humidity. The first time I heated/pressed nodes there was an amazing difference. Storage can make a big difference!! If you store your cane in a very dry area, soaking WILL make a difference and you probably NEED to soak! If you store your cane in an area where the humidity is high, you probably won't need to soak. That's my scientific testing! LOL or BS, whatever you want to call it!  (David Dziadosz)

You know where I live, 52' from the river. The humidity is high and my bamboo is stored in a room about the same distance from the river.

I still find soaking will help a whole lot when Displacing nodes and drying in the oven with MD's Fixtures. Soaking prevents burning of the nodal area and I find it does not harden the nodes as dry heating does.

As I said many times, the beauty of all of this is, you can do as you like and it still ends up as a bamboo rod that will catch fish.  (Tony Spezio)

In no way was I trying to say soak/don't soak! LOL I was commenting on what someone said about not soaking now. And that maybe it didn't have to be soaked if the area where the cane had been stored had a higher moisture level. And the distinct difference between the two different places I have had cane stored.

Noticed I didn't say if I soak or don't soak!

Now, I think I'll go soak my head! Been out picking Blackberries! And the Misses baked a pie and having a scoop of ice cream on top!  (David Dziadosz)