The Norman Transcript

March 17, 2014

Moore City council considers storm-resistant building code upgrades

By Joy Hampton
The Norman Transcript

NORMAN — Moore Strong may be more than just an inspiring slogan for recovery from the May 20 tornado if city leaders approve building code upgrades tonight.

The Moore City Council will consider 11 recommendations by structural engineering experts for residential building codes.

If adopted, those code changes could make new homes in Moore more likely to survive a tornado.

At the request of city leaders, Dr. Chris Ramseyer, University of Oklahoma engineering professor, presented findings and recommendations for consideration to the Moore City Council on Feb. 18. Tonight, those proposals are on the agenda for possible adoption into the city building code.

Ramseyer is the director of OU’s Fears Structural Engineering Laboratory, where structural theories are put to the test to gain real-life answers grounded in science. The city of Moore asked

Ramseyer to provide recommendations for a rational or scientific approach to high-wind design. Ramseyer specializes in structural design and teaches steel and concrete design classes to undergrads as well as graduate students at the university.

Currently, residential building codes in Oklahoma are based on the 2009 International Residential Code that requires homes to withstand 90 mile per hour winds with three-second gusts.

Ramseyer’s finding are based on International Building Code standards which are higher standards developed for commercial buildings rather than the IRC standards. Findings are also based on tests performed at the Fears lab. The 11 recommendations would make homes stronger and able to withstand an EF-3 tornado or winds up to 135 miles per hour.

Ramseyer was part of a National Science Foundation team that looked at tornado damage. As a structural engineer, Ramseyer and the team tried to answer the question, “How does a tornado interact with a house?”

The team was composed of five universities with 25 students and faculty participating, each with different specialties. The team found a neighborhood in south Oklahoma City that was hit by the May 20 tornado. That subdivision was new and all of the homes were unoccupied. Ramseyer said the houses were “robust structures.” The builder, Ideal Homes, is known for constructing homes with tornado safe elements.

“They use a very nice bracing system and clip system,” Ramseyer said.

That vacant neighborhood — the Wildflower addition — provided just what the team needed to study how a tornado interacts with a residential structure.

Two of the homes were completely wiped off the foundations, one was piled with debris and two other homes were standing but had some damage.

Wind speed within a tornado can’t be measured. The Enhanced Fujita Scale rates the strength of tornadoes based on the damage they cause and wind speeds are estimated by that damage.

In the Wildflower housing addition, there was only 70 feet between the house that suffered EF-5 tornado damage and the home that suffered EF-2 wind damage.  That was something the team found surprising and shocking.

Based on the study of those houses, the loads and strengths outlined by the IBC principles, and the results of testing at the Fears Lab, Ramseyer presented 11 points that could bring Moore’s residential building codes to improve the wind rating to 135 miles per hour while keeping costs low. Ramseyer said estimates indicate these upgrades in code would only increase construction costs by $1 per square foot, thus keeping housing affordable.

While these upgrades, if adopted by the Moore City Council tonight, will make homes more likely to survive tornadoes, the code changes would not make homes a safe shelter for residents in major tornado events.

“For true safety, you have to be in a shelter,” Ramseyer said.

The code changes would help homes — and the property contained in those homes — have a greater chance of surviving some of Oklahoma’s most extreme weather events, at least up to EF-3.

By making a house more likely to survive a tornado, it also protects neighboring homes because a destroyed home results in debris that is thrown at other homes, inflicting damage to those nearby structures, Ramseyer said.

While Oklahoma has great early warning systems, there are also people who get caught off guard and may be in their homes when a tornado strikes. Additionally, pets may be in the home and at risk.

“By going to 135 miles per hour, you are more likely to have a structure that is still standing and more likely to survive inside that structure,” he said.

Ramseyer stressed that homes still need tornado-safe shelters, however, and people should stay informed about weather and be prepared to take shelter.

“The state of Oklahoma is better prepared then any other state as far as notifications,” he said.

Some lessons learned in the study indicate that it is possible for an affordable home to provide shelter close to an EF-5 tornado. The data suggests that impact resistant windows are not warranted. Everyone in storm shelters survived and that is still the best place to wait out a tornado. Vehicles are not storm shelters.

One point of weakness in current building standards is that garage doors are not required to be wind rated even to 90 miles per hour. Often a garage door will bend in a tornado and let the wind inflate the garage like blowing up a balloon, Ramseyer said. That causes failure to walls, then the roof of the garage, exposing the attic and allowing a tornado to then deconstruct a house.

In very simple, layman’s terms, the 11 residential building code recommendations under consideration by Moore City Council tonight include:

1. Roof sheathing — larger nails, closer together with sheathing of OSB or plywood

2. Roof framing — more rafters, closer together

3. Roof connections — better connections for compression and tension include nail plates or steel connection plates with improved connections on rafters, web members, purlins, kickers and bracing connections, includes connections to interior brace wall top plates or ceiling joists

4. Gable end walls connections — tie gable end walls to the structure with steel connection plates or straps and make sure the improved connections are included at the top and bottom of the gable end wall

5. Gable end wall construction — use OSB or plywood sheathing with 8d ring shank or 10d nails on four inches on center along the edges and six inches on center in the field (bigger nails, closer together)

6. Roof framing anchors — hurricane clip or framing anchor on all rafter to wall connections

7. Two story detailing — nail upper and lower story wall sheathing to common rim board

8. Wall sheathing — using continuous sheathing on all walls. Garage doors are to be framed using the sheathed portal frame method. No form of intermittent bracing is allowed on an outer wall.

9. Increased nailing for sheathing — more nails, closer together

10. Sheathing detailing — extend structural wood sheathing to lap the sill plate (this is specific to a type of foundation seldom found in Oklahoma)

11. Garage doors — wind rated garage doors

Joy Hampton

366-3544

jhampton@normantranscript

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