I'm really pleased to have Tony Huynh as a guest blogger today. His take on structural integrity for our nation's bridges is an important message, not only for civil engineers, but for our entire country. Also, make sure you check out his awesome animated visual that explains how different types of bridges are built at the end of the post. 

The Role of Civil Engineers in Building Bridges

Infrastructure remains top of mind priority in the United States. According to Newsweek, there are over 50,000 “crumbling” bridges across the nation — that’s about 8% of the total number of bridges in the U.S. It’s also estimated that if you put the number of bridges that currently need repair end to end, they would reach from New York City to Miami. In all, the US has around 620 thousand bridges which are crossed an estimated 188 million times each day by commuters going to work or trucks carrying goods. These bridges are economic necessities that would cripple a community if they were not traversable.  

According to Bridgemasters, it would take about $120B to begin to put America’s bridges back on track. While there is a general call across the land for the government to help fix, modernize, and updating our bridges, civil engineers know that the problem is pervasive.

When there is a dangerous situation in the US, a response is often expected from from the US Army Corps of Civil Engineers (USACE) which relies on a workforce of around 40 thousand civilian and active duty personnel. This is our line of defense when it comes to taking care of our infrastructure.

When Bridges Collapse

A recent bridge collapse in Genoa, Italy that led to over 30 deaths provided stark reminder of the consequences of allowing bridges to deteriorate. The specific structure, made over 50 years ago with reinforced and pre-stressed concrete, is an example of a common method of bridge building which faces stress, decay, erosion, and undermined safety today. Something as simple as a lightning strike (which has been partially blamed as a cause for the bridge collapse) could be a real concern for structure. Environmental factors are the biggest risks that civil engineers need to account for when designing bridges:

Climate Change

Rising tides and increased storm ferocity are two factors that civil engineers contend with with when creating better support models for bridges.

Floods

Higher sea level due to warmer oceanic temperatures means that flooding has become more severe globally. Unfortunately, over 50% of bridge collapse are caused by floods, according to the American Society of Civil Engineers. The waters can corrode the foundations of bridges, pummel the bridge with debris, and lift a bridge deck off its foundations.

Storms

In 2017, a bridge collapsed after being pummeled by hurricane Harvey. Civil engineers took what they could from this incident to improve design, particularly how air pockets created by these storms can disrupt gravity and friction in bridges, allowing them to give away under the pressure.

Earthquakes

The effect of earthquakes on bridges is generally linked to the ground type that a bridge is supported by. During an earthquake some of the  soil effectively liquifies causing a loss of bridge integrity that could lead to bridge collapse. In addition, when soft soil is laid over a hard layer of bedrock it can amplify the effects of a quake.

How Civil Engineers Can Prevent Bridge Collapse

Civil engineers play an important role in the planning, construction, and ongoing maintenance of our nation's bridges in order to support their function, safety, and integrity. Here are a few ways civil engineers can combat environmental factors:

• Design bridges higher than historic flood levels to avoid the possibility of lifted supports and debris collisions.
• Allow water or large debris to pass through bridges, creating better resistance during floods.
• Use clear span bridges that go over a channel without exposed supports.
• Make sure design standards outlined by the American Society of Civil Engineers are surpassed.
• Using cable-stay bridges can help anticipate the failure of any one element due to the bridge’s consistent and reinforced design.
• Create custom, flexible fabrication so that specific bridges can withstand earthquakes.
• Test scale models with comparable materials under rigorous conditions.

The largest culprit when it comes to structural damage or bridge collapse is poor construction and maintenance. Higher standards for earthquake protection have been in place since the 1990s, but a majority of current bridges were built prior to that time.

Updating bridge integrity has never been more crucial than it is today. It’s imperative that we look to our civil engineers for answers and employ them on a mission of protecting bridges before there is a major collapse.

Bridge building requires intensive study from qualified civil engineers.This infographic from BigRentz gives a layman’s view of how bridges are constructed and what the challenges are.

Please include attribution to BigRentz with this graphic.