Archive for the ‘Technical’ Category
Posted on September 2, 2008 - by Elliott
2008 SEAOC Convention
I am attending the 2008 SEAOC (Structural Engineers Association of California) Convention. It is being held September 23 - 27 on the Big Island, Hawaii. I have been to the last 4 out of 5 SEAOC Conventions and certainly would not miss one being held in Hawaii! Every year I attend I have come back to BJG energized about my profession.
Here are some of the sessions I plan on attending.
Report Cards for Building Seismic Safety: A Proposed Rating System for Earthqauke Performance of Buildings
This session is being giving by the SEAONC Existing Buildings Committee. This is right inline with the training I took in 2006 to become a Safety Assessment Evaluator. This training, put on by SEAONC and the California Governor’s Office of Emergency Services is a 1 day course. From the SEAONC website:
When earthquake disaster strikes a community, there is an immediate need for damage inspections. The Structural Engineer’s Association of Northern California has teamed with the California Governor’s Office of Emergency Services (OES) to recruit, train, and maintain a group of licensed engineers who are ready to respond following a major earthquake to assess the safety of building structures. There are currently approximately 278 SEAONC members who are registered as Volunteer Safety Assessment Engineers. To activate such a large pool of volunteers, the SEAONC DES-ATC 20 Subcommittee has created a telephone and e-mail communication network in order to provide rapid response to the affected communities.
Best Design Practices for Seismic Evaluation and Preservation of Historic Buildings: Distinct Structural Systems and Benefit Cost Analyses
This session is exciting to me because it takes the evaluation part and extends it to a value and cost dimension. When is a certain structural system the most cost effective for the owner and occupants? This session has the potential shed some light on this subject.
Structual Implications of Green Roofs, Terraces, and Walls
I have not designed a green roof as of yet, however, I have always wondered about their effects on the load bearing systems in a building. What about water and rain retention? How does these additional loads affect the lateral (shear walls, moment frames, etc.) systems? This will be a very interesting session.
On a similar note, green is the hottest design item right now. It is interesting to look back three or four years ago at the proceedings and not find a single paper or presentation researching the structural implications of green design. However, you could find numerous papers (there seemed like there were entire afternoons devoted to the topic) on buckling restrained braced frames or unbonded braces. Now, there afternoons devoted to green design and only one presentation on buckling restrained braced frames.
Numerous Local Flavor Topics
There are always a number local topics presented at each convention. This is a neat way to become connected with the engineers in the area of the convention. This year there are presentations on Microzoned Design Maps of Topographic Wind Effects and Exposure in the Building Codes of the State of Hawaii and Performance of the Kawaihae Harbor Port Facility Resulting from teh 2006 Earthquake.
Social Programs
On top of the technical sessions there are ample opportunities for socializing and networking. There are themed welcome receptions and cocktail hours, younger member receptions, and the all important President’s Cup where the different sections (Northern, Central and Southern California as well as San Diego) compete against each other in mental and physical competitions.
I will report back after the conference to give everyone an update on the conference. Stay tuned! Additionally, if you will be in attendance, let me know in the comments what sessions you are looking forward to.
Posted on September 2, 2008 - by Teresa
2007 CBC Exit Distance with ESFR Sprinkler Systems
Background
One of our core areas of business is the design of industrial buildings. Some are build to suit (specifically designed and built with a tenant in mind) while others are speculative shells, no tenants. We have noticed a shift by fire departments after this most recent code adoption cycle, 2006 IBC/ 2007 CBC, with respect to the maximum exiting distance and ESFR (early suppression, fast response) sprinkler systems and smoke/heat vents. In both California and Nevada we have faced resistance from the fire department when completing tenant improvements in these large industrial buildings.
For the sake of this article we will use the following as a case study building:
Occupancies (These are the typical and also most conservative assumptions for this building type.):
- S-1: Moderate Hazard Storage and
- F-1: Factory Industrial Moderate-hazard, and also portions of
- B: Business Group (office)
Dimensions:
- 550’ wide and exit travel distances around 290’
Sprinklers:
- ESFR sprinkler system with skylights, smoke/heat vents sometimes although not always provided.
Rendering for a recent project included below:
In the past
The 2001 CBC exit travel distance for a building with automatic sprinkler systems and with most occupancy types is 250’ per section 1004.2.5.2.2. This allows for a building to be a little less than 500’ wide (because travel distance is on an angle). The 2001 CBC Section 1004.2.5.2.5 states that “the travel distance… may be increased to 400 feet (121 920 mm) if the building is equipped with an automatic sprinkler system throughout and is also provided with smoke and heat ventilation as specified in Section 906.” Section 906 describes the requirements for smoke and heat vents and refers to the Fire Code for high-piled combustible stock, which is one of the most common uses for large industrial buildings. The Fire Code had an exception that smoke and heat venting was not required with ESFR (Early Suppression Fast Response) sprinkler systems. This makes sense as ESFR sprinkler systems work best when the heat reaches the sprinkler head and starts the flow of water. Smoke and heat vents have a negative impact on ESFR systems as they let heat escape delaying the response time of the sprinkler system. In the past all jurisdictions that we had worked with had accepted the line of reasoning that ESFR sprinkler systems would allow for the maximum exit travel distance of 400’, equivalent to sprinklered buildings with smoke/heat vents, which in turn would allow buildings to be a little less than 800’ wide.
The “new” code
CBC 2007 (and IBC 2006) Section 1016 provides a table with exit access travel distances. The typical S-1 and F-1 occupancies are limited to 200’ without a sprinkler system and 250’ with a sprinkler system, in line with the 2001 CBC requirements. There is an increase in section 1016.2 to 400’ in one story buildings when roof vents are provided, this all sounds familiar. The referenced section 910 for roof vents provides an exception 910.1 #1 that states that automatic smoke and heat vents are not required in areas protected by ESFR sprinkler systems. This all seems to provide the potential for the same line of reasoning.
Now the fire marshals have to decide if the intent of the code is to allow a 400’ travel distance for ESFR sprinkler systems without smoke and heat vents. Certainly it makes sense that this well performing sprinkler system would be acceptable for the maximum code allowed travel distance.
However we are noticing a trend that fire marshals are looking very closely at this very topic. If you have a 550’+ wide building (travel distance roughly 290’), with an ESFR sprinklers system and no smoke vents what are your options if the fire marshal insists that smoke vents are required for a travel distance over 250’? We see the following as options:
- We can block off an internal 50’+/- wide strip of the building shortening the exit distance – this is meant to be a silly suggestion as it would drastically effect the function of the space.
- We can add internal corridors at each exit to limit travel distance, although this certainly impedes the use of the building along the end bays where forklift traffic is critical.
- We can down grade the occupancy type for this speculative building to F-2 and S-2, low-hazard factory industrial and storage, which per the exit travel distance table 1016.1 allows for a 400’ travel distance with sprinklers only. Although this also limits the prospective tenant options.
- Or we can replace the existing skylights with automatic smoke/heat vents. This system would then meet the letter of the code for a 400’ travel distance for S-1 and F-1 occupancy. Although also lessens the effectiveness of the ESFR system.
We had two recent scares where this issue came up. In one building it turned out the fire department had originally required smoke and heat vents as a plan check item and they were installed with the shell, thereby meeting the requirements of the code. In the other building we were able to show that the tenant required only an S-2 rating as described above. We anticipate that this trend will continue and that smoke/heat vents will be required with ESFR sprinkler system where the larger travel distance is necessary.
The Up Side
There is an argument (see links below) that smoke and heat vents with ESFR sprinkler systems is a good idea because they work as a backup, in case there is an earthquake that ruptures the water service and then there is a fire, at least the smoke vents would activate allowing occupants time to exit.
More to Consider
An argument we disagree with for these facilities is that smoke and heat vents can help with smoke removal after the fire. While this is true there are other better options available from opening the skylights manually to opening the dock doors that can easily be employed without lessening the effectiveness of the ESFR sprinkler system as automatic smoke and heat vents do.
The Summary
Code transitions can be painful for all of us. This transition has seemingly provided the jurisdictions an opportunity to review past decisions and decide if they do or don’t apply to the current code. There is no specific language regarding travel distance with ESFR sprinkler systems so it’s up to interpretation. It doesn’t seem worth it to hope the original interpretation sticks through the tenant improvements. Our take away: for existing projects work with the fire marshal to find the least painful patch and for future projects include automatic smoke/heat vents with ESFR sprinklers where the width of the building requires a travel distance greater than 250’.
References
Articles to reference for State Fire Marshall proposed changes regarding this issue:
- http://osfm.fire.ca.gov/codedevelopment/codedevelopment_2007cacodeadopcycle.php
- http://osfm.fire.ca.gov/codedevelopment/pdf/title24/part9-45-dayET.pdf (see page 9 & 17 for proposed code change)
- http://osfm.fire.ca.gov/codedevelopment/pdf/title24/part9-45-dayISOR.pdf (see page 7 & 10 for reasoning)
Posted on December 5, 2007 - by Elliott
Brace Yourself for the 2006 IBC
The 2006 International Building Code (IBC) is coming and for some jurisdictions it is already here. Las Vegas has already seen its adoption; Northern Nevada and California are close behind. BJG has studied up and is providing you with the following story of the 2006 IBC and your building’s braced frame particularly with respect to industrial buildings.
Not so long ago, the concentric braced frame was a thing of simplicity and reliability. Inexpensive to implement and relatively simple to design, it was an important system of choice for economical structures where the architectural floor plan could accommodate the brace layout. Several typical braced frame configurations are shown immediately below and will be discussed later where appropriate.
A typical braced frame “works” by transferring horizontal forces to foundations by pushing or pulling on the diagonal steel member. See Figure 8 for an illustration. Engineers have tried many varieties of braced frames over the centuries. Some have performed well, some have performed poorly and some have been “just ok”. Much of what we have learned has been by seeing what does and does not work in earthquakes. (more…)
