Building Codes Archives - Page 12 of 13 -

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.

Taking Wood-Framed Construction to New Heights

When I had more hair and less of it was gray, I worked on a project as an assistant engineer doing the calculations for a mixed-use building in San Jose, California. Final design consisted of four stories of wood framing over a concrete podium slab and another level of below-grade parking. At that time, my firm had designed many two- and three-story residential buildings, but common thinking was you switched to steel or concrete for taller structures because of perceived limitations in wood-framed construction.Continue Reading

Out-of-Plane Wall Anchorage Design

While the Simpson Strong-Tie Tye Gilb R&D lab in Stockton is a large testing facility, the world’s largest R&D lab is Mother Nature herself. Natural disasters such as earthquakes or storms put our engineering designs to the test. In this week’s blog post, I’ll be turning attention to wall anchorage for out-of-plane forces and the lessons we have learned from Mother Nature so far.

The 1979 building code incorporated many of the lessons learned from the 1971 San Fernando earthquake. In 1994, Mother Nature put the 1979 building code to the test with the January 17 Northridge earthquake. The Northridge earthquake showed that some of the increased design and detailing requirements in the 1979 building code worked well to improve performance over what was observed in 1971. However, it also revealed to researchers that acceleration at the roof level of single story warehouse buildings were three to four times the ground acceleration. The combination of higher than expected acceleration and excessive deformation of the wall anchorage assembly caused many wall anchorage failures.

Figure 1 Out-of-Plane Wall Anchorage Assembly

Several changes in the design forces used for wall anchorage and additional detailing requirements were incorporated in the 1997 Uniform Building Code. The requirements have been refined with each new building code, but overall the requirements and design forces have remained about the same under the current International Building Code. Wall anchorage design is governed by ASCE 7-05 and ASCE 7-10 Section 12.11. These provisions aim to mitigate the brittle wall anchorage failures observed in past earthquakes by increasing the design force and in Seismic Design Categories C through F, requiring:Continue Reading

So, What’s Behind A Structural Connector’s Allowable Load?

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

Today I did my presentation for the WoodWorks webinar on Testing and Product Evaluation of Products for Wood-framed Construction. We covered a lot of material regarding code requirements for using alternate materials or construction methods, how testing and evaluation criteria are developed, and some specifics on several Acceptance Criteria (AC’s) that are commonly used for connector evaluations. We also discussed some specific testing requirements, so I thought it would be timely to discuss some of those issues in this week’s blog post.

So, how are structural connectors for light frame wood construction load rated? What’s behind the allowable loads information published in Simpson Strong-Tie literature or wood connector evaluation reports? These are things that you might find yourself wondering while driving to the office or jobsite, or on a Sunday afternoon while enjoying your favorite iced tea or barley-based beverage.

The short answer is: testing, calculations, and of course, sound engineering judgment.

So, What's Behind A Structural Connector's Allowable Load?

This is Part 1 of a four-part series I’ll be doing on how connectors, fasteners, anchors and cold-formed steel systems are load rated.
Today I did my presentation for the WoodWorks webinar on Testing and Product Evaluation of Products for Wood-framed Construction. We covered a lot of material regarding code requirements for using alternate materials or construction methods, how testing and evaluation criteria are developed, and some specifics on several Acceptance Criteria (AC’s) that are commonly used for connector evaluations. We also discussed some specific testing requirements, so I thought it would be timely to discuss some of those issues in this week’s blog post.
So, how are structural connectors for light frame wood construction load rated? What’s behind the allowable loads information published in Simpson Strong-Tie literature or wood connector evaluation reports? These are things that you might find yourself wondering while driving to the office or jobsite, or on a Sunday afternoon while enjoying your favorite iced tea or barley-based beverage.
The short answer is: testing, calculations, and of course, sound engineering judgment.
Continue Reading

Join Me for a WoodWorks Webinar on Acceptance Criteria and Testing Methods for Connectors

I have the privilege of presenting a free WoodWorks webinar, “Testing and Product Evaluation of Products for Wood-framed Construction” on Thursday, October 25 at 10 am PST. Here is the webinar description:

Products that are not covered by the code are used in many if not all buildings. While the code permits a single engineer to review and submit to a building official and a single building official to review and approve a product not covered by the code, many feel a more robust process is needed to ensure that these products meet the code intent. Also, many code or evaluation reports are used not just for one project, but for multitudes of projects in numerous locations. Test setups can affect the performance and load rating of products.

Several private entities have been created over the years to assist the industry by developing public and transparent processes to develop test requirements, load rating requirements, design and detailing requirements, and ongoing quality compliance as well as product evaluation methodologies. This webinar will discuss various acceptance criteria and testing methods used for products used in wood construction, such as ASTM D7147 and ICC-ES AC155 to further advance the knowledge of these test methods and processes for those in the wood construction industry.

This will be a great opportunity for those of us who work in wood frame construction to discuss code and test requirements for connectors and other products for wood. I hope you’ll consider joining us! To register for the webinar, click here.

– Paul

What are your thoughts? Visit the blog and leave a comment!

“Sunny With A Chance Of Earthquake”

With scientists predicting a 99% chance of a 6.7 magnitude earthquake striking Southern California within the next 30 years, California weather forecasters may want to remind residents that the location which gives lots of golden sunshine year round is also one of high seismic risk.

Recent earthquakes in cities similar to Los Angeles, San Francisco and Memphis have served as a reminder of the damage and disruption a major earthquake can have on a community. Through lessons learned from past earthquakes and research performed by the construction industry, there are many tools available geared toward residential buildings to reduce damage and resist collapse.

Cantilever Floor Induced Load Path Concerns

IBC Section 1604.9 requires structural members, systems, components and cladding be designed to resist forces due to earthquakes and wind, with consideration of overturning, sliding and uplift. It also states that a continuous load path be provided for transmitting these forces to the foundation. Seems obvious to engineers that a continuous load path is needed, but it’s still nice to have the code say so.

But what happens if your structure’s upper and lower story walls do not stack? How do you create the required continuous load path? As engineers, we try to steer the architect towards eliminating the offset, making things line up, and keeping construction simple. But architectural requirements cannot always accommodate simple, and non-stacking walls occur all the time.

Confidence in Code Reports

Every building uses products that are not specifically covered in the building code. IBC Section 104.11 permits this if the “alternative material” is found to comply with the code intent by the building official after review of supporting information, such as research reports and tests.

Reviewing product data might be a challenge for some building departments, as they vary in size and expertise around the country. Some of the questions they might ask are:

1. What, if any, criteria was used to evaluate the product (e.g., test protocol, load rating methodology),

2. Was the criteria developed based on a single individual or a single company’s opinion or was there at least some involvement of others in the construction industry,

3. Are there any potential conflicts of interest in the parties wanting to use the product or the company who evaluated the product, and

4. Are there other tests or analyses that need to be completed prior to accepting the products use in the jurisdiction?

Top 3 Roof Deck Design Considerations for High Wind Events

Was it JFK who said, “The time to repair the roof is when the sun is shining?” He was likely using the roof as an analogy for the economy, but I take things literally and wanted to talk about roofs. The time to think about the design of your roof and its function in a high wind event like a hurricane or tornado is right now.

During a high wind event, a roof deck is expected to perform many functions. It should prevent water intrusion from rain, withstand impacts and protect those inside from hail. It also needs to act as a diaphragm – transferring lateral loads to shear walls and resisting the vacuum effects of wind uplift forces.Continue Reading