Advances in sensors, concrete, nanotech are making structures – from bridges to office towers – safer, stronger and better looking

On August 1, 2007, the bridge carrying Interstate 35W across the Mississippi River at Minneapolis collapsed. Thirteen died, 145 were injured.

The powerful earthquake struck suddenly, shaking the seven-story building so hard it bent, cracked and swayed in response.

But this was no ordinary earthquake. In a groundbreaking series of tests, engineering researchers from UC San Diego’s Jacobs School of Engineering jarred a full-size 275-ton building erected on a shake table, duplicating ground motions recorded during the January 17, 1994 Northridge earthquake in Los Angeles, California.

Sprays of dirt flew out of a soil box that held a retaining wall as it violently shook from a simulated 7.4 magnitude earthquake. The wall was put to test recently by engineers at the UC San Diego Englekirk Structural Engineering Center, which has the largest outdoor shake table in the United States. During the first series of tests, led by Dawn Cheng, a UCSD engineering alumna and now a civil engineering professor at UC Davis, researchers investigated the seismic response of a semi-gravity reinforced concrete cantilever wall.

In order to make a concrete mix design that works, you should master all the concrete theories in combination with experiences of concreting at work. Here is some important things you need to know when design concrete mixes.

A. What do you need to know before designing concrete?

1. What are the strength requirements?

- Compressive (on cube or cylinder specimen) strength

- Flexural strength