Lab Statistics – How Much Wood?

Wood for testing
Wood for testing

Like many people with desk jobs, I just have to get up and walk around every once in a while. Most of my walks are through our connector test lab at our home office in Pleasanton, California. The lab technicians install a lot of products for testing, so in addition to stretching my legs, I like to quiz them for ideas on things we can do to make installation faster and easier for our products.

Discarded wood from testing
Discarded wood from testing

During one of my walks this week, a lab technician was finishing up a rather extensive test setup that consumed a large quantity of lumber, screws, and truss plates. I asked him how it was going and he commented, “Testing isn’t exactly environmentally friendly, is it?”

Before I could even respond, he added, “I guess that’s just part of the price of building safer buildings.” I like the way he thinks.

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So, What's Behind A Screw's Allowable Load?

This is Part 2 of a four-part series I’ll be doing on how connectors, fasteners, anchors and cold-formed steel systems are load rated. Read Part 1 and Part 1A.
These loads just can’t be right! Occasionally, I get this statement from engineers. This happens when they have been specifying commodity fasteners based on NDS load values and they get their first look at our higher screw values. Then the call comes in. They want to talk to someone to confirm what they are seeing is correct. I assure them the loads are right and give them this brief overview of how we got here:
Our first structural screw, the Simpson Strong-Tie(R) Strong-Drive(R) SDS, was originally load rated by plugging the bending yield strength and diameter into the NDS yield limit equations and using the load value from the governing failure mode. As later editions of the NDS modified the calculations and we did more testing, we found that the tested ultimate load of the SDS screw could be as much as ten times greater than the allowable load generated from the NDS equations.
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So, What’s Behind A Screw’s Allowable Load?

This is Part 2 of a four-part series I’ll be doing on how connectors, fasteners, anchors and cold-formed steel systems are load rated. Read Part 1 and Part 1A.

These loads just can’t be right! Occasionally, I get this statement from engineers. This happens when they have been specifying commodity fasteners based on NDS load values and they get their first look at our higher screw values. Then the call comes in. They want to talk to someone to confirm what they are seeing is correct. I assure them the loads are right and give them this brief overview of how we got here:

Our first structural screw, the Simpson Strong-Tie(R) Strong-Drive(R) SDS, was originally load rated by plugging the bending yield strength and diameter into the NDS yield limit equations and using the load value from the governing failure mode. As later editions of the NDS modified the calculations and we did more testing, we found that the tested ultimate load of the SDS screw could be as much as ten times greater than the allowable load generated from the NDS equations.

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Soft-Story Retrofits

In February 2007 I had the opportunity to volunteer for a Soft-Story Sidewalk Survey for the San Francisco Department of Building Inspection. The purpose of the survey was to inventory buildings in San Francisco that appeared superficially to have soft or weak first stories. The volunteers were given a list of addresses to review and we recorded if the building was more than three stories tall, had five or more dwellings, and estimated what percentage of the ground level had openings in the walls. No structural analysis going on, just counting stories, mailboxes, doors and windows.

San Francisco soft-story structure. Photo credit: USGS.
San Francisco soft-story structure failure. Photo credit: USGS.
A collapsed house in San Francisco from the 1989 Loma Prieta earthquake. Photo credit: Adam Teitelbaum, AFP, Getty Images.
A collapsed soft-story in San Francisco from the 1989 Loma Prieta earthquake. Photo credit: Adam Teitelbaum, AFP, Getty Images.

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Tell Us Your Genuine Story for a Chance To Win!

You may have noticed that the cover of our new 2013-14 Wood Construction Connectors Catalog features the word GENUINE. What do we mean by Genuine Simpson Strong-Tie Connectors? It’s really based on our roots and our founder Barclay Simpson, who made his very first connector for a customer in 1956. Barc believed in doing whatever it took to help the customer succeed.Today, helping the customer remains our number one priority. Whether that’s being on a jobsite to help with a product installation, spending endless hours on R&D and product testing or making sure our products get to our customers on time. This is what we promise to do everyday, and we do it genuinely.Continue Reading

Building Drift – Do You Check It?

Guest Blogger Sam Hensen, Simpson Strong-Tie Southeast Engineering Manager
Sam Hensen

[Simpson Strong-Tie note: Sam Hensen is the Simpson Strong-Tie Engineering Manager for the Southeast U.S. and the latest blogger for the Structural Engineering Blog. For more on Sam, see his bio here.]

Just as bending and shear checks performed on gravity loaded beams do not ensure that the beam will comply with required deflection limitations, adherence to allowable shears and aspect ratio limits  on shearwalls does not mean the structure will comply with required drift limitations. Shearwalls that are too flexible may prevent the structure from meeting drift limitations even if the shearwall design has adequate strength.

Seismic

For seismic load applications, section 12.12.1 of ASCE7-10 states that the design story drift of the structure shall not exceed the allowable drift listed in table 12.12-1. For light-frame buildings, the maximum permitted drift is 2.5% of the story height. This limitation is put in place not merely for serviceability reasons, but is an inherent effect of current seismic design provisions that is required to be checked to ensure life safety.

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Congratulations to the "Creative Use of Our Product" Contest Winners!

 

Engineered Desk: Winning photo of the Creative Use of Our Product contest. Photo credit: Alan Hanson, Simpson Strong-Tie.

Thank you to everyone who participated in our “Creative Use of Our Product” contest! This was our most popular post yet. Based on comments received, the Top 5 photos were:
1. Engineered Desk
2. Statue of David
3. Top Flange Spoiler Bracket
4. & 5. (Tie): Truss Coffee Table and HD Trailer Hitch Adapter
The winners of the Simpson Strong-Tie Prize Pack, chosen randomly among all comments on the post are:
1. Kimberly T., Brea, CA
2. Natalie D., Pleasanton, CA
3. Zoran P., Vaughan ON
4. Evan L., Pullman, WA
5. Mary P., Franklin, WI
Congratulations to the winners.
If you’d like automatic email updates when a new blog entry is posted (usually once a week), sign up here.

Congratulations to the “Creative Use of Our Product” Contest Winners!

 

Engineered Desk: Winning photo of the Creative Use of Our Product contest. Photo credit: Alan Hanson, Simpson Strong-Tie.

Thank you to everyone who participated in our “Creative Use of Our Product” contest! This was our most popular post yet. Based on comments received, the Top 5 photos were:

1. Engineered Desk

2. Statue of David

3. Top Flange Spoiler Bracket

4. & 5. (Tie): Truss Coffee Table and HD Trailer Hitch Adapter

The winners of the Simpson Strong-Tie Prize Pack, chosen randomly among all comments on the post are:

1. Kimberly T., Brea, CA

2. Natalie D., Pleasanton, CA

3. Zoran P., Vaughan ON

4. Evan L., Pullman, WA

5. Mary P., Franklin, WI

Congratulations to the winners.

If you’d like automatic email updates when a new blog entry is posted (usually once a week), sign up here.

Corrosion: The Issues, Code Requirements, Research and Solutions

When you hear $452 billion, what comes to mind? Perhaps the annual state budgets of California, Texas, Florida or New York? Maybe the combined net worth of Bill Gates, Larry Ellison, or the Walton Family? While those would be good guesses, I bet you didn’t think of corrosion! According to a May 2012 Congressional Briefing hosted by NACE International and ASM International, corrosion-related costs are a staggering 3.1% of the U.S. GDP, which is more than the individual budgets of those states above, and the combined net worth of the top 15 people listed on the Forbes 400: The Richest People in America.

Corrosion of metallic surfaces is an electrochemical process typically involving an anode, electrolyte and a cathode. An anode is a metal zone which loses electrons when exposed to an electrolyte, an electrolyte is a non-metal electrical conductor, and a cathode is the zone where an oxidizing agent (e.g., oxygen) gains the electrons. While there are many different forms of corrosion (e.g., pitting, intergranular, wet storage stain, etc.), and various sources of causes (e.g., treated lumber, moisture level, temperature, atmosphere, air quality, etc.), other factors such as exposure related to time of wetness are equally important. In a study presented in Dr. X.G. Zhang’s book Corrosion and Electrochemistry of Zinc, time of wetness is 50% greater near the top of a structure compared to the bottom, leading to greater corrosion.

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Load Testing, Last Day To Enter Our Contest, And Happy Holidays!

With all of the frenzy that happens before (and during) the holidays, I won’t be doing full blog posts this or next week. But, I did want to remind you that this Thursday (12/20) is the last day to enter our “Creative Uses of Our Product” contest. We’ll post our five winners to the blog next week.

This week will be a short snapshot into what we were doing yesterday. We are always testing products and usually the only people who stop by to watch the tests besides the lab technicians are an R&D engineer and occasionally the product manager. As valuable as testing is, the simple day-to-day stuff just doesn’t generate much excitement – crushing bowling balls is fun and gets a crowd, but we save that for orientation classes.

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