SIOUX FALLS, S.D. (KELO) — Depending on where they are built and their use, buildings will have differing construction needs based on risk, said Nadim Wehbe, the John M. Hanson Professorship of Structural and Construction Engineering and head of the Department of Civil and Environmental Engineering at South Dakota State University in Brookings.
“The future trend if not the current trend is to design structures for resiliency based on their risk categories,” Wehbe said.
Changes based on extremes such as today’s predicted high winds including frequent gusts of at least 70 mph or the 200-mile F3 tornado that destroyed an Amazon warehouse in Illinois and a factory in Kentucky as well as other extremes in weather have prompted engineers to lean to resiliency in design, Wehbe said.
“Resiliency is the ability of a structure to function following a major event. Resiliency is also related to acceptable damage level,” Wehbe said.
As an example, Wehbe said a certain level of damage and even closure of a bridge that is not essential to function after an earthquake is acceptable. But it’s not acceptable for the bridge to collapse and cause loss of life, he said.
A major bridge that is needed for market use and emergency use must function after an earthquake even if it can’t carry full traffic, Wehbe said. A level of damage that does not close the bridge and still allows for limited traffic is acceptable, he said.
Resiliency that applies to earthquakes happened as major earthquakes caused changes to building codes in the 1980s 1990s and 2000. Buildings constructed now must meet standards to withstand certain levels of seismic activity, he said.
“The same thing could be said about designing for wind loads, Coastal areas that are subjected or prone to hurricanes, the building codes are very strict,” Wehbe said.
Now, maybe building codes should adopt certain requirements that are implemented in hurricane prone areas for tornadoes, Wehbe said.
A Dec. 10 tornado destroyed an Amazon warehouse in Edwardsville, Illinois, and a candle factory in Mayfield, Kentucky, which has been noted for its size, December date and the possibility it could be one large 200-mile long tornado or multiple tornados.
“The building codes classify structures based on risk categories. The risk category is related to the function of the structure,” Wehbe said. “In other words the risk to human lives and consequence of failure following a major event.”
A single-family home is in risk category 2 while a hospital, firehouse or similar building is in risk category 4.
A building in risk category 4 needs to function after a major event, Wehbe said.
Building codes use wind maps that apply to areas across the U.S. The maps are based on history and statistical analysis for wind events.
“A 115 mph wind for risk category 2 in our area is based on a return interval of 1 in 700 years. Such speeds might happen 1 time in 700,” Wehbe said.
The city of Sioux Falls has codes that require certain buildings to withstand various wind speeds, city building official Butch Warrington said in a Dec. 13 interview with KELOLAND News.
Amazon is building a 3 million-square-foot-five-story facility in Sioux Falls. Warrington said the building must be able to withstand 115 mph winds.
While houses, buildings, warehouses and factors are designed for 115 mph, the city has required schools to have a section that will withstand 200 mph wind since 2018, Warrington said. The new Thomas Jefferson High School and Ben Reifel Middle School would have those sections. The new school for the Harrisburg School District in Sioux Falls, for example, would also meet that section requirement.
The city also has a higher wind speed requirement of 115 for buildings of assembly such as a large event center, Warrington said.
Storm shelters are only required for emergency services such as the city’s 911 command center, he said
Wehbe said a building in risk category 4, is for an event with a return interval in 1 of 1,300 years.
Wehbe said it’s not economical to design structures for higher load levels than what codes prescribe. It is likely more practical to improve on certain details, he said.
Collapse Amazon warehouse in Edwardsville, Illinois, is similar to the collapse of a Home Depot facility in Joplin, Missouri, that happened a few years ago, Wehbe said.
The Amazon facility has tilt-up walls connected by the roof, Wehbe said.
Officials from Edwardsville and Madison County said in a Dec. 11 news conference that the warehouse house walls were 40-foot tall and made of 11-inch concrete that collapsed inward. The facility’s roof collapsed downward, officials said.
“The walls themselves are strong enough to withstand any load but looking at the collapse in these two facilities it seems like roof gave up first because of the suction pressure,” Wehbe said. “Once the roof is gone, the structure is gone, those walls are going to collapse.”
The details may be the key to improving the performance of these type of facilities, Wehbe said. Can the details of the connections be improved one area to consider, Wehbe said.