I’ve conducted hundreds of hands-on Science projects at an elementary
school in my neighborhood for many years, and I’ve learned something important.
Though the students enjoyed the hands-on experiments, the projects were more
meaningful to them when I gave them context.
So, as we embark on this bridge-building adventure, I'll provide an
overall context for the experiments in this book.
As I noted before, I purchase most of my supplies from the Dollar stores, Target, etc. I hope this affordability will enable parents and teachers to make use of my experiments more in their homes and classrooms.
A short summary of the history of bridge building
Humans first made bridges using wooden logs, planks and lashing
together sticks, bamboo poles, and tree branches. Eventually, humans started
building bridges with stones, and one of the oldest bridges still in use was a
stone arch bridge in Greece dating back to the Greek Bronze Age (13th
century BCE).
The Romans were the greatest bridge builders in ancient times. The
Roman built arch bridges that withstood extreme conditions, which would have
damaged earlier bridge designs. The Romans also used cement, which lessened the
changes in strength from stone to stone.
Many innovations took place in the bridge design during the 18th century from timber bridges to iron bridges. Following the Industrial Revolution in the 19th century, truss bridges were designed to carry larger loads (larger bridges, more freight, and people). But wrought iron didn't have enough tensile strength to meet the demands for ever bigger bridges. Later, much larger bridges were built with steel and their designs were influenced by Gustave Eiffel's ideas.
Nowadays, three basic types of bridges are used in
transportation. They are beam and truss bridges, arch bridges, and suspension
bridges.
