We start with our basic bridge base.
On top of each base build your stack placing 2 chips on each half of the base and cover those 2 with another chip. Continue stacking on top of each other until it is high enough for your liking. Repeat over each pillar.
Then using one hand to support the stack, begin to place chips in between. Try to keep the sides even with chips so you do not topple your bridge.
Then fill in the middle to join your 2 stacks together. If you did 5 or 7 chips between your pillars, then you would need to put more chips to fill in the gap on each side. Once you join 2 pillars, you can remove the chips on the bottom which kept the pillars properly spaced. Fill in the other side where you haven't placed chips yet.
Now you can build several of these and put them together. Then begin your next layer if you wish to go higher. Just do the same thing you did with your first row. Now by this time your chips might not be 100% straight. Take 2 books and press them up from the front and back of the bridge at the same time. This will evenly align your bridge and keep it from toppling. And then you can go up another layer if you wish.
Now this bridge is straight, but if you curve your towers, you can make a full circle and build up. Eventually with the proper spacing you can also put a dome on the top of your tower of chips. Bridges look complex but are very easy to build. Just take your time and use your imagination and you will have no problem building awesome structures.