Engineering Fallacies

By Howard Cook, Founder and General Manager of Bay Area Retrofit

Engineer Misconceptions.

Imagination

 

How do I Find a Good Engineer?

This is a difficult decision.   You want your retrofit done right and it is natural to think an engineer is the way to go.  After all, engineers design construction projects every day and will make sure your house is retrofitted correctly.

Bay Area Structural Engineers

Which engineer should I choose?

There are some problems with this assumption:

Very few engineers do this kind of work on a regular basis and universally they don’t know how to practice the subject.  Wood frame construction, let alone seismic retrofitting, is not even on the curriculum at many universities such as UC Berkeley.

Engineers shy away from it because the liability is extremely high and the pay is low.  Plus few engineers want to spend the day crawling under houses. Home inspection engineers, most often recommended  by realtors, specialize in home inspections, not retrofit designs, and are usually not the best choice.

When interviewing engineers make sure are familiar with empirical evidence showing how and why houses are damaged, lab tests done in government and private research laboratories, or have taken the time to study old building codes or the science behind existing retrofit guidelines.  The information is hard to find but for someone interested it is there to be found. Unfortunately very few engineers have the time or desire to study the subject.

In many cases this results in engineers “making things up”,basing their designs on conjecture rather than science.

Using Angle Irons

Angle Iron Brace

Ineffective Hardware recommended by a Bay Area Structural Engineer

The drawing on the left is called a construction detail and tells a contractor how to build something.  This detail illustrates something called an Angle Iron Brace.  The photograph to the right is a photograph of the same.  The efficacy of Angle Iron Braces has been called into serious question by many prominent structural engineers. Calculations done by Kelly Cobeen, one of the most prestigious wood frame seismic engineers in the country did some calculations, found angle irons to be ineffective.   Angle irons were briefly reviewed by the Los Angeles Residential Retrofit Guidelines Committee in 1994 and was unanimously rejected as being ineffective.

There are some exceptional engineers and recently we received a few sets of plans from an engineer who not only understood engineering principles, but she also has a good sense of cost-effectiveness.  This however is an exception rather than a rule and one must be very careful when hiring an engineer or a contractor for the reasons described below.

The construction detail below is very similar.

  • The purple arrow points at a steel strap that has zero earthquake resistance.  This hardware is not recommended in any seismic retrofit guideline.
  • The blue green arrow also points at a bolt that bolts the bottom of a post to a small block of cement.  This is not required in new construction for houses built directly on top of an earthquake fault or any of the retrofit guidelines.
  • The red arrow points at a another type of hardware that has zero resistance to earthquakes.
  • ALL of these things are deemed unnecessary by all seismic retrofit guidelines.
  • Lastly, the green arrow points at a T912 hardware that does not even exist!  See what I mean about engineers making things up?

Bolted Block

The Most Seriously Flawed Construction Detail.

Szumski

 

The chart on the left is from a local civil engineer who recommends a procedure called the Nailed Blocking Method.  This method has been discredited by research scientists at the largest shear research laboratory in the world because the nails split the blocks.
These blocks are an untested system and the least desirable according to research scientists   affiliated with the largest shear wall testing laboratory in the world who presented their opinion to the Code Committee that was developing a guideline knows as Standard Plan A.  The conclusion of their top research scientists was:

“Based on my professional opinion, I would judge the retrofit strategies in the following order, from most preferred to least preferred.

1.) Flush-cut mudsill method

2.) Reverse block method

3.) Stapled blocking method

4.) Nailed blocking method

I have chosen to order the retrofit strategies based on several reasons. First, the flush-cut mudsill and the reverse block method are the closest retrofit strategies to a conventionally built shear wall. Hence I have a great deal of confidence in either of these methods. I believe the flush cut method would be more practical for most retrofits, but the reverse block method would be an acceptable alternative.

This is an excellent video on all the methods listed above.

Another common misunderstanding

The red arrow below points at a piece of hardware that is supposed to strengthen a connection that will not fail.   The interesting thing about this construction detail is that there is not a single case in all of the earthquakes in the United States of this existing connection ever failing.   Nor is the need to strengthen this connection found in any of the many retrofit guidelines including the International Existing Building Code.  The detail on the right is from the International Existing Building Code.  Notice the blue arrow.   No hardware can be seen here and points to the fact that no retrofit guideline recommends this expensive and unnecessary hardware.

Typical Ineffective Construction Detail by a Bay Area Structural Engineer

                                

 FEMA Approved Hardware without this Hardware

 

 

 

 

 

 

 

 

 

Research is Necessary

Finally, the California Building Code only has five sentences that address seismic retrofitting.  This leaves much to the imagination of the engineer or contractor and is the reason designs can be so wildly different.  It also results in recommendations that have no basis in science or observed damage from earthquakes.

A seismic retrofit engineer or contractor should be familiar with old building codes and the ability to determine how strong your house already is, should know about  Tests on the performance of wood and should be familiar with shear wall tests.   Most important, a contractor or engineer must be familiar with the kinds of damage that occurred in previous earthquakes.

You also want your engineer or contractor to be familiar with the photographs available for viewing at the Pacific Earthquake Engineering Institute at U.C. Berkeley.  This is the largest collection of such photographs in the world    Most engineers just don’t have the time or the desire to do this research.  Whoever you decide to use, be sure that they  can answer at least one of  these basic questions. 

 

 

                         

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