5 Steps to a Successful Soft-Story Retrofit

Last year, I gave a presentation at the annual National Council of Structural Engineers Associations (NCSEA) Summit in Orlando, Florida, titled “Becoming a Trusted Advisor: Communication and Selling Skills for Structural Engineers.” As this was a summit for the leaders of the structural engineers associations from across the country, I wasn’t sure how many people would find it valuable to spend their time learning about a very nontechnical topic. To my surprise and delight, the seminar ended up being standing-room only, and I was able to field some great questions from the audience about how they could improve their selling and communication skills. In the many conversations I had with the conference attendees after my presentation, the common theme was that engineers felt they needed more soft-skills training in order to better serve their clients. The problem, however, was finding the time to do so when faced with the daily grind of design work.

Structural Engineers In a Training for Seismic Retrofits

Presenting at the NCSEA Summit, I’m the tiny person in upper left hand corner.

When I started my first job as a design engineer at a structural engineering consulting firm straight out of school, I was very focused on improving and expanding my technical expertise. Whenever possible, I would attend building-code seminars, design reviews and new product solution presentations, all in an effort to learn more about structural engineering. What I found as I progressed through my career, however, was that no matter how much I learned or how hardworking I was, it didn’t really matter if I couldn’t successfully convey my knowledge or ideas to the person who really mattered most: the client.

Contractors discussing building plans with an engineer.

Contractors discussing building plans with an engineer.

How can an engineer be most effective in explaining a proposed action or solution to a client? You have to be able to effectively sell your idea by understanding the needs of your client as well as any reasons for hesitation. The importance of effective communication and persuasion is probably intuitive to anyone who’s been on the sales side of the business, but not something that occurs naturally to data-driven folks like engineers. As a result of recent legislation in California, however, structural engineers are starting to be inundated with questions from a group of folks who have suddenly found themselves responsible for seismically upgrading their properties: apartment building owners in San Francisco and Los Angeles.

Imagine for a moment that you are a building owner who has received a soft-story retrofit notice under the City of Los Angeles’ Ordinance 183893; you have zero knowledge of structural engineering or what this term “soft-story” even means. Who will be your trusted advisor to help you sort it out? The City of Los Angeles Department of Building and Safety (LADBS) has put together a helpful mandatory ordinance website that explains the programs and also offers an FAQ for building owners that lets them know the first step in the process: hire an engineer or architect licensed in the state of California to evaluate the building.

Simpson Strong-Tie Structural Engineer Annie Kao at a jobsite.

Checking out some soft story buildings in Los Angeles. The Los Angeles Times has a great map tool.

I’ve had the opportunity to be the first point of contact for a building owner after they received a mandatory notice, because it turns out some relatives own an apartment building with soft-story tuck-under parking. Panicked by the notice, they called me looking to understand why they were being forced to retrofit a building that “never had any problems in the past.” They were worried they would lose rent money due to tenants needing to relocate, worried about how to meet the requirements of the ordinance and, most importantly, worried about how much it was going to cost them. What they really wanted was a simple, straightforward answer to their questions, and I did my best to explain the necessity behind retrofitting these vulnerable buildings and give an estimated time frame and cost that I had learned from attending the first Los Angeles Retrofit Resource Fair in April 2016. With close to 18,000 buildings in the cities of San Francisco and Los Angeles alone that have been classified as “soft-story,” this equates to quite a number of building owners who will have similar questions and be searching for answers.

To help provide an additional resource, Simpson Strong-Tie will be hosting a webinar for building owners in the Los Angeles area who have received a mandatory soft-story retrofit notice. Jeff Ellis and I will be covering “5 Steps to a Successful Retrofit” and helping to set a clear project path for building owners. The five steps that Simpson Strong-Tie will be recommending are:

  1. Understanding the Seismic Retrofit Mandate
  2. Partnering with Design Professionals
  3. Submitting Building Plans with the Right Retrofit Product Solutions
  4. Communicating with Your Building Tenants
  5. Completing Your Soft-Story Retrofit

We encourage you to invite any clients or potential clients to attend this informative webinar, which will lay the foundation for great communication between the two of you. As part of the webinar, we will be asking the building owners for their comments, questions and feedback so we can better understand what information they need to make informed decisions, and we will be sure to share these with the structural engineering community in a future post. By working together to support better communication and understanding among all stakeholders in retrofit projects, we will be well on our way to creating stronger and more resilient communities!

For additional information or articles of interest, there are several resources available:

Great ShakeOut Earthquake Drill 2016

The Great ShakeOut Earthquake Drill is an annual opportunity for people in homes, schools and organizations to practice what to do during earthquakes and improve their preparedness. In a post I wrote last October about the Great ShakeOut, I reminisced about the first earthquake I had to stop, drop and cover for – the Livermore earthquake in January, 1980. This year got me thinking about how our evacuation drills work.

At Simpson Strong-Tie, we use the annual Great ShakeOut drill to practice our building evacuation procedures. Evacuation drills are simple in concept – alarms go off and you exit the building. We have volunteer safety wardens in different departments who confirm that everyone actually leaves their offices. There are always a few people who want to stay inside and finish up a blog post. Once the building is empty and we have all met up in the designated meeting area, we do a roll call and wait for the all-clear to get back to work.

Several years ago the alarms went off. While waiting for the drill to end, we were concerned to see fire fighters arrive and rush into the building. Realizing this was not a drill, there were some tense moments of waiting. The fire chief and our president eventually walked out of the building and our president was yelling for one of our engineers. Turns out the engineer (who shall remain nameless) was cooking a chicken for lunch. Yes, a whole chicken. The chicken didn’t make it – I’m not sure what the guilty engineer had for lunch afterwards. At least we received extra evacuation practice that year. We aren’t allowed to cook whole chickens in the kitchen anymore.

Simpson Strong-Tie is helping increase awareness about earthquake safety and encouraging our customers to participate in the Great ShakeOut, which takes place next Thursday on October 20. It’s the largest earthquake drill in the world. More than 43 million people around the world have already registered on the site.

On October 20, from noon to 2:00 p.m. (PST), earthquake preparedness experts from the Washington Emergency Management Division and FEMA will join scientists with the Washington Department of Natural Resources and the Pacific Northwest Seismic Network for a Reddit Ask Me Anything – an online Q&A. Our very own Emory Montague will be answering questions. The public is invited to ask questions here. (Just remember that this thread opens the day before the event and not sooner.)

Emory Montague from Simpson Strong-Tie

Emory, ready to answer some seismic-related questions.

We’re also providing resources on how to retrofit homes and buildings, and have information for engineers here and for homeowners here.

Earthquake risk is not just a California issue. According to the USGS, structures in 42 of 50 states are at risk for seismic damage. As many of you know, we have done a considerable amount of earthquake research, and are committed to helping our customers build safer, stronger homes and buildings. We continue to conduct extensive testing at our state-of-the-art Tye Gilb lab in Stockton, California. We have also worked with the City of San Francisco to offer education and retrofit solutions to address their mandatory soft-story building retrofit ordinance and have created a section on our website to give building owners and engineers information to help them meet the requirements of the ordinance.

Last year, Tim Kaucher, our Southwestern regional Engineering Manager, wrote about the City of Los Angeles’s Seismic Safety Plan in this post. Since that time, the City of Los Angeles has put that plan into action by adopting mandatory retrofit ordinances for both soft-story buildings and non-ductile concrete buildings. Fortunately, California has not had a damaging earthquake for some time now. As a structural engineer, I find it encouraging to see government policy makers resist complacency and enact laws to promote public safety.

Participating in the Great ShakeOut Earthquake Drill is a small thing we can all do to make ourselves more prepared for an earthquake. If your office hasn’t signed up for the Great ShakeOut Earthquake Drill, we encourage you to visit shakeout.org and do so now.

Seismic Bracing Requirements for Nonstructural Components

Have you ever been at home during an earthquake and the lights turned off due to a loss of power?  Imagine what it would be like to be in a hospital on an operating table during an earthquake or for a ceiling to fall on you while you are lying on your hospital bed.

One of the last things you want is to experience serious electrical, mechanical or plumbing failures during or after a seismic event. During the 1994 Northridge earthquake, 80%-90% of the damage to buildings was to nonstructural components. Ten key hospitals in the area were temporarily inoperable primarily because of water damage, broken glass, dangling light fixtures or lack of emergency power.

Complete loss of suspended ceilings and light fixtures in the 1994 Northridge Earthquake. (FEMA 74, 1994)

Complete loss of suspended ceilings and light fixtures in the 1994 Northridge Earthquake. (FEMA 74, 1994)

Broken sprinkler pipe at Olive View Hospital in Sylmar, California after the 1994 Northridggde, Earthquake. (FEMA 74, 1994)

Broken sprinkler pipe at Olive View Hospital in Sylmar, California after the 1994 Northridggde, Earthquake. (FEMA 74, 1994)

ASCE 7 has an entire chapter titled Seismic Design Requirement of Nonstructural Components (Chapter 13 of ASCE 7-10) that is devoted to provisions on seismic bracing of nonstructural components. Unfortunately, not a lot of Designers are aware of this part of the ASCE. This blog post will walk Designers through the ASCE 7 requirements.

Nonstructural components consist of architectural, mechanical, electrical and plumbing utilities. Chapter 13 of ASCE 7-10 establishes the minimum design criteria for nonstructural components permanently attached to structures. First, we need to introduce some of the terminology that is used in Chapter 13 of ASCE 7.

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  • Component – the mechanical equipment or utility.
  • Support – the method to transfer the loads from the component to the structure.
  • Attachment – the method of actual attachment to the structure.
  • Importance Factor (Ip) – identifies which components are required to be fully functioning during and after a seismic event. This factor also identifies components that may contain toxic chemicals, explosive substances, or hazardous material in excess of certain quantities. This is typically determined by the Designer.

Section 13.2.1 of ASCE 7 requires architectural, mechanical and electrical components to be designed and anchored per criteria listed in Table 13.2-1 below.

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Architectural components consist of furniture, interior partition walls, ceilings, lights, fans, exterior cladding, exterior walls, etc. This list may seem minor compared to structural components, but if these components are not properly secured, they can fall and hurt the occupants or prevent them from escaping a building during a seismic event. The risk of fire also increases during an earthquake, further endangering the occupants.

Failure of office partitions and ceilings during the Northridge 1994 Earthquake. (FEMA 74, 1994)

Failure of office partitions and ceilings during the Northridge 1994 Earthquake. (FEMA 74, 1994)

Damage to overloaded  storage racks during the 1994 Northridge Earthquake. (FEMA 74, 1994)

Damage to overloaded storage racks during the 1994 Northridge Earthquake. (FEMA 74, 1994)

Section 13.5 of ASCE 7-10 includes the necessary requirements for seismic bracing of architectural components. Table 13.5-1 provides various architectural components and the seismic coefficients required to determine the force level the attachments and supports are to be designed for.

Mechanical and electrical components consist of floor-mounted and suspended equipment. It also includes suspended distributed utilities such as ducts, pipes or conduits. These components are essential in providing the necessary functions of a building. In a hospital, these components are required to be fully functioning both during and after a seismic event. A disruption of these components can make an entire hospital building unusable. In order for hospitals to properly service the needs of the public after a seismic event, fully functioning equipment is essential.

Failed attachments to a chiller after the 1994 Northridge Earthquake. (FEMA 74, 1994)

Failed attachments to a chiller after the 1994 Northridge Earthquake. (FEMA 74, 1994)

Section 13.6 of ASCE 7-10 provides the requirements of seismic bracing for mechanical and electrical components. Table 13.6-1 provides a list of typical components and the coefficients required to determine the force level the attachments and supports are to be designed for.

Chapter 13 lists some typical requirements for which components are to be anchored and supported under specific conditions:

  1. Section 13.1.4 item 6c: Any component weighing more than 400 pounds.
  2. Section 13.1.4 item 6c: Any component where its center of gravity is more than 4 feet above the floor.
  3. Section 13.6.5.6 has specific electrical conduit size and weight requirements.
  4. Section 13.6.7 has specific size and weight requirements for suspended duct systems.
  5. Section 13.6.7 has specific size and weight requirements for suspended piping systems.

The chapter also has some general exceptions to the rules:

  1. 12 Inch Rule: When a distributed system such as conduit ducts or pipes are suspended from the structure with hangers less than 12 inches in length, seismic bracing is not required.
  2. If the support carrying multiple pipes or conduits weighs less than 10 pound/feet of lineal weight of the component, the seismic bracing of the support does not have to be considered.
Example of a support with multiple pipes and the hanger rod length. These exceptions do have limitations, which that are clearly listed in Ssections 13.6.5.6, 13.6.7 and 13.6.8.

Example of a support with multiple pipes and the hanger rod length.

These exceptions do have limitations that are clearly listed in Sections 13.6.5.6, 13.6.7 and 13.6.8.

These systems may not seem important in the structural systems of a building, but they are essential in allowing the building to function the way it was designed to serve the public. It is also important that occupants are able to escape a damaged building after a seismic event. Obstacles such as bookcases blocking exit doors or falling debris may prevent occupants from leaving a building after a seismic event.

It is important that Designers are aware of these code requirements and take the time to read and understand what is needed to provide a safe structure.

 

Report Back from Nepal – Assessing Seismic Damage from April/May Earthquakes

 Dr. H. Kit Miyamoto assessing damage in Nepal.

Dr. H. Kit Miyamoto assessing structural damage in Nepal.

This week’s post comes from Dr. H. Kit Miyamoto, S.E. Kit is CEO of Miyamoto International, a structural engineering firm and president of the nonprofit, Miyamoto Global Disaster Relief. He also is a California Seismic Safety Commissioner.

As soon as news spread that 7.8-magnitude and 7.3-magnitude earthquakes struck Nepal in April and May of this year, earthquake structural engineering experts from our firm, Miyamoto International, hopped on planes from three countries to offer assistance. We do this in hopes that our expertise and technical advice might help stricken communities recover; help them to build better and ultimately help save lives.

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Dr. H. Kit Miyamoto on site. Evidence of massive damage is present in the background.

While structural engineers are not first responders, we are well equipped to assess whether it is safe for people to return to homes, businesses, schools and critical-services buildings. We also can help people understand why some buildings stand while others collapse. This information is essential. It is the only way to protect people from future tragedy.

On touch down in Nepal, we found the airport filled with frightened people leaving the country. It is always a bit sobering to see people leaving while you head in.  We struck out for the hotel we could only hope was still standing. Once there, we found the building to be structurally sound, although uneasy guests opted to sleep in the courtyard, leaving us, the structural engineers, the only ones sleeping inside.

I expected the devastation in Kathmandu to be much greater than it was – we all did. Yet because the epicenter was about 50 miles from the capital, the quake’s power was partially dissipated by distance and the Kathmandu Valley’s soft river soil, which likely saved many lives and structures.

Nepal’s Minister of Education asked our team to examine some of the schools in remote areas.  We drove into a village to a horrible find: a large, three-story school reduced to a rubble pile of brick, concrete and broken desks. What we found were columns made of bricks without any reinforcement. This is something I saw in schools in Sichuan, China in 2008, where poor construction practices left tens of thousands of school children vulnerable to disaster. And yet, I have to say that Nepal was lucky. Although more than 7,000 of the country’s schools were severely damaged or destroyed, the quake hit midday on a Saturday when students were not in school. Had the quake hit in the middle of a school day, tens of thousands of students would have died.

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A look inside the collapsed school.

Driving out beyond the city, we found rural areas in the central and western regions particularly devastated, with entire villages destroyed and further isolated by road damage, closures, rugged terrain and the threat of landslides. As is the case in much of the world, unreinforced masonry construction presented the biggest problem. In rural Nepal – where traditional homes are made of stone, mud and wood – we found up to 90 percent of the structures destroyed. Whole villages were gone.

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Absolute devastation of a rural village.

Around the world, the experts involved in construction – from the engineer and contractor to the building inspector – have to invest in constructing safe buildings. No corruption. No excuses. Build as if your children are attending that school or living in those homes and we will begin to have seismically resilient cities.

Many of the newer high-rise buildings in Kathmandu have also exhibited crippling damage and we have assessed more than 30 of these to date. Even when building codes are adhered to, a big gap exists between what code provides and what society expects. Even in places like Los Angeles and San Francisco, people don’t understand that. At one meeting in Kathmandu, luxury condo owners were stunned and angry to learn that the building they bought into met standards, but was still too heavily damaged to occupy. These buildings are not usable now. The financial loss is enormous.

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An aerial view of the earthquake damage. 

We have to understand that people don’t have to die in earthquakes. Earthquakes don’t kill people; buildings kill people. Or more precisely, poorly constructed buildings. This is tragic and avoidable because we know how to design seismically strong buildings. When an earthquake strikes, our disaster response efforts include “knowledge transfer,” during which we train engineers, masons and contractors on simple seismic techniques that save lives and help communities “build back better.” Our profession has disaster-resilient solutions for new construction and retrofits.

At Miyamoto International, our mission is to save lives and positively impact economies through our work. In China, 169,000 lives were lost, including tens of thousands of students in 7,000 classrooms. In 2010 in Haiti, more than 200,000 people died. In Nepal, the earthquake killed more than 8,600 people. It doesn’t have to be this way.  Building seismically resilient cities is possible. It is achievable. We can save lives.

Midrise of Steel

Guest blogger Jeff Ellis, engineering manager

Guest blogger Jeff Ellis, engineering manager

The number of midrise structures constructed using light-frame cold-formed steel (CFS) certainly seems to be increasing each year. As with any material, there are benefits and challenges, especially in areas of moderate to high seismic risk. This post will discuss these as well as potential solutions.

Light-frame CFS midrise construction often uses ledger floor framing primarily to facilitate the load transfer detailing at the floor, tension anchorage (tie-downs or hold-downs) and compression chord studs or posts designed to resist the amplified seismic overturning loads. CFS framing is typically thin and singly symmetric.

Various CFS Construction Floor Framing Methods

Various CFS Construction Floor Framing Methods

 

 

 

 

 

 

Amplified Seismic Load

The AISI Lateral Design standard (AISI S213-07/S1-09) Section C5.1.2 requires that the nominal strength of uplift (tension) anchorage and the compression chord studs for shear walls resist the lesser of (1) the amplified seismic load or (2) the maximum load the system can deliver when the response modification coefficient, R, greater than 3. The amplified seismic load is defined as the load determined using the ASCE 7 seismic load combinations with the overstrength factor, Wo, which may be taken as 2.5 for CFS framed shear wall systems with flexible diaphragms.

Typically, the maximum the system can deliver to the uplift anchorage or chord studs is taken as the forces determined using the nominal shear strength of the shear wall assembly tabulated in the seismic shear wall table in S213 multiplied by 1.3. The S213 commentary accounts for the tabulated loads being based on Sequential Phased Displacement (SPD) rather than CUREE cyclic protocol and the degraded backbone curve. See the Structure magazine article that discusses the design of CFS framed lateral force-resisting systems.

Continuous Rod Tie-Down Systems

Light-framed CFS over three stories often use continuous rod tie-down systems rather than cold-formed steel hold-downs to resist shear wall overturning forces as they offer increased load capacity. Neglecting the dead load contribution, the amplified seismic load requirement for CFS shear walls using an R greater than 3 results in an 80% increase in the load used to size the continuous rod tie-down system compared to design level loads. For shear walls using an R greater than 3, it is important to note on the design drawings whether the uplift loads shown are ASD, LRFD, amplified ASD or amplified LRFD so the appropriate tie-down system may be designed.

Continuous Rod Tie-Down System Resisting Shear Wall Overturning Forces

Continuous Rod Tie-Down System Resisting Shear Wall Overturning Forces

Continuous rod tie-down systems are designed not only for strength, but also checked to ensure they do not deflect too much to cause the top of shear wall drift to exceed the code limit or to exceed the 0.20” vertical story deflection limit required by some jurisdictions and ICC-ES AC316. Take-up devices are used in CFS framed structures to take-up construction and settlement gaps that may occur.  AISI S200 Section C3.4.4 states that a gap of up to 1/8” might occur between the end of wall framing and the track. The vertical elongation of the continuous rod tie-down system includes rod elongation (PL/AE) and the take-up device deflection due to the seating increment and the deflection under load.

In addition, coordination is important in using continuous rod tie-down systems in CFS structures because the walls are often prefabricated offsite. An example is the consideration of the appropriate detail for the steel bearing plate installed at the floor sheathing in the story above to resist the uplift (tension) force from the story below.

One possible detail is to install the bearing plate in the bottom CFS track under all the CFS chord studs, but it’s important to ensure the bottom track flanges are deep enough to screw them to the stud flanges as the bearing plate can have a thickness of 1 ½” or more and typical tracks use 1 ¼” flanges. It is also important to ensure that the bearing plate width fits in the track. Another possible detail is to install the bearing plate under the CFS track under all the CFS chord studs.  However, then it must be cut into the floor sheathing and may cause the bottom track to be raised at the bearing plate. For this detail, the floor shear transfer must be detailed through the ledger into the CFS framing.

Continuous Rod Tie-Down System Steel Bearing Plate Coordination Issues

Continuous Rod Tie-Down System Steel Bearing Plate Coordination Issues

Concrete Tension Anchorage

The concrete tension anchorage is designed according to ACI 318 Appendix D using the continuous steel rod material and size in accordance with S213 to have the nominal strength to resist the lesser of the amplified seismic force or the maximum load the system can deliver. ACI 318-11 Section D.3.3.4.3 offers four force limits for design of concrete tension anchorage design in Seismic Design Category C through F:

(1)   The concrete nominal tension anchorage strength shall be greater than 1.2 times the ductile steel rod nominal tension anchorage strength

(2) The anchorage design strength shall be greater than the maximum tension force that can be delivered by a yielding attachment;

(3) The anchorage design strength shall be greater than the maximum tension force that can be delivered by a non-yielding attachment; and

(4) The anchorage design strength shall be greater than the amplified seismic force.

Typically either option (1) or (4) is used where (1) would lead to less concrete required than (4) if the bolt is efficiently sized while (4) would be required for such conditions as a vertical irregularity.  See the concrete anchorage and podium anchorage SE Blog posts for more details.

ACI 318-11 Section D.3.3.4.3 Anchorage Design Options

ACI 318-11 Section D.3.3.4.3 Anchorage Design Options

CFS Wall Stud Bracing

CFS studs are typically thin and singly symmetric and thus require bracing. AISI S211 (Wall Stud Design Standard) permits two types of bracing design that cannot be combined; sheathing based or steel based. There are limits on the stud axial strength when using sheathing braced design. It’s important to identify on the drawings that the sheathing braces the studs and another load combination must be used for the stud design.

2012 IBC Section 2211.4 requires stud bracing to be designed using either AISI S100 (North American Specification) or S211 (Wall Stud Design Standard). S100-07 Section D3.3 required nominal brace strength is to be 1% of the stud’s nominal compressive axial strength, but S100-12 Section D3.3 changes this to the required brace strength is to be 1% of the stud’s required compressive axial strength (demand load). In addition, D3.3 requires a certain stiffness for each brace. AISI S211 required brace strength is to be 2% of each stud’s required compressive axial strength for axially loaded studs and, for combined bending and axial loads, be designed for the combined brace force per S100 Section D3.2.2 and 2% of the stud’s required compressive axial strength.

There are two primary types of steel stud bracing systems: bridging and strap bracing. U-channel bridging extends through the stud punchouts and is attached to the stud with a clip, of which there are various solutions such as this post on Wall Stud Bridging.  Bridging bracing requires coordination with the building elements in the stud bay. It installs on one side of the wall, and does not bump out the wall sheathing. It also requires periodic anchorage to distribute the cumulative bracing loads to the structure for axially loaded studs often using strongback studs and does not require periodic anchorage for laterally loaded studs since the system is in equilibrium as the torsion in the stud is resisted by the U-channel bending.

Flat strap bracing is installed on either side of the wall and at locations other than the stud punchout. It bumps out the sheathing and requires periodic anchorage to distribute the cumulative bracing loads to the structure for axially and laterally loaded studs.

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Strap and Block Bracing

Strap and Block Stud Bracing Anchored Periodically to Structure Using Strongbacks

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Bridging and Clip Bracing Anchored Periodically to Structure Using Strongbacks

Bridging and Clip Bracing Anchored Periodically to Structure Using Strongbacks

Bridging and Clip Bracing Anchored Periodically to Structure Using Diagonal Strap Bracing

Bridging and Clip Bracing Anchored Periodically to Structure Using Diagonal Strap Bracing

Light-frame cold-formed steel construction has been used successfully for many projects, but there are challenges  that must be addressed to ensure code compliance and desired performance. Some beneficial resources for designing CFS structures are the SEAOC 2012 IBC Structural/Seismic Design Manual Volumes 1 and 2 and the Cold-Formed Steel Engineers Institute’s (CFSEI) website where you can find technical notes and design guides.

What have been some of your observations or challenges in designing cold-formed steel midrise structures?

Ignore Seismic Requirements When Wind Controls?

Prior to joining Simpson Strong-Tie, my career involved the design of projects in California’s San Francisco Bay Area. When designing the primary lateral force resisting system, I would have several pages of seismic base shear calculations and, oh yeah, a one- or two-line calculation of the wind forces – just to show that seismic governed. There was no need for complete wind analysis, since the seismic design and detailing requirements were more restrictive. Of course, building components such as parapets, cladding or roof screens needed a wind design. Unfortunately, when wind appears to control, meeting the seismic requirements is not so simple.

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