2012 Autodesk University

Autodesk University is an annual conference focused on keeping the design community up to date on the latest innovations, trends and technologies in design, drafting and visualization. Last year, Autodesk University was held in Las Vegas the week after Thanksgiving. Sadly, events always seem to conspire to prevent me from going to Vegas, but Simpson Strong-Tie was well represented by Frank Ding, our Engineering Analysis & Technical Computing Manager.

It was an exciting time attending my first Autodesk University in 2012. I have been to so many technical conferences during my professional career, but this one was quite different in scale, and the sheer size of it just blew me away. There were more than 8,000 attendees from 102 countries, more than 750 classes offered, and 163 exhibitors. I was impressed by the organization of such a large event, along with the online and mobile apps provided to help attendees manage their conference schedules.Continue Reading

Open Front Structure Wind Pressure Design

We received a request from Martin H., one of our blog readers, to discuss the method for determining roof wind pressures on an open front agricultural building. The inquiry was regarding clarification on analyzing the roof pressure when a combined external and interior pressure exists and whether these are additive.

Wind Pressure Figure

As can be seen in the above illustrations, the net design pressure on the roof is the sum of the uplift on the exterior surface and the uplift on the interior surface from any internal pressure. ASCE 7 provides a method for determining this pressure. Specifically, ASCE 7-10 will be used for the remainder of this post. Assuming the three remaining sides of the open front structure are walls without openings, the building will be classified as partially enclosed by the definitions of Section 26.2.

ASCE 7-10 provides for two methods for determining the Main Wind Force Resisting System (MWFRS) wind loads for partially enclosed buildings, the Directional Procedure in Chapter 27, and the Envelope Procedure in Chapter 28.

When using the Directional Procedure, the net wind load is calculated using the following equation:

P = qGCp – qi(GCpi)

When using the Envelope Procedure, the net wind load is calculated using the following equation:

 P = qh[(GCpf) – (GCpi)]  

In each of these equations, the first portion determines the pressure on the exterior surface, and the second portion determines the pressure on the interior surface. So the variable for calculating the internal pressure is the internal pressure coefficient GCpi.

The internal pressure coefficient is provided in Table 26.11-1 based on three different categories of building enclosure.

Enclosure Classification

(GCpi)
Open Buildings

0.00
Partially Enclosed Buildings

+0.55

-0.55
Enclosed Buildings

+0.18

-0.18

Table 26.11-1

In the case of an open front structure, it is assumed that the partially enclosed internal pressure coefficient must be used. This coefficient is 3x greater than when the building envelope is classified as enclosed. Use of this higher coefficient in the design will account for the interior pressure on the underside of the roof combined with the exterior pressure.

MWFRS versus C&C

Another somewhat related question: to what level loads should the roof anchorage forces be calculated, MWFRS or C&C (Component and Cladding)? I have often been asked this question, and wrote a Technical Note published by CFSEI (Cold-Formed Steel Engineers Institute) in July 2009.

What are your thoughts?

– Sam

Code Reports: Uniform Application of Code Intent in a Diverse Environment

Woodworks invited me to do a presentation on Testing and Evaluation of Products for Wood-framed Construction, and I found you can’t really talk about testing without talking about the test standards and criteria used in product evaluations. Usually the goal in testing to these standards is to show compliance with the intent of the building code and have the product listed in a code report.

Why not just follow the code?

Innovative architectural and structural building products not addressed by the building code are in every building. Revisions to the building code are considered on a three-year cycle and some standards are on a five-year cycle. Sometimes it may take several cycles to address a new building product.

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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.
Continue Reading

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.

Continue Reading

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.
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