2009 IRC Bracing Provisions. 2009 bracing provisions are significantly different in organization, scope and detail from the previous version of the code. Quick overview. Check lists Examples. Sections 5537 and 6737 of the California Business & Professions Code:.
2009 bracing provisions are significantly different in organization,
scope and detail from the previous version of the code.
An unlicensed person may prepare construction documents for the following:
• Single-family dwellings of wood frame construction not more than two stories and
basement in height.
• Multiple dwellings containing no more than four dwelling units of wood frame construction not more than two stories and basement in height on any lawfully divided lot.
• Garages or other structures appurtenant to single-family dwelling or multiple dwellings of wood frame construction not more than two stories and basement in height.
• Agricultural and ranch buildings of wood frame construction unless the Building Official deems that an undue risk to the public health, safety or welfare is involved.
However, if any portion of any structure exempted by Section 5537(a) of the California Business & Professions Code deviates from substantial compliance with conventional framing requirements for wood frame construction found in the most recent edition of Title 24 of the California Code of Regulations or tables of limitation for wood frame construction, as defined by the applicable building code duly adopted by the local jurisdiction or the state, the Building Official shall require the preparation of construction documents for that portion by, or under the responsible control of, a Registered Design Professional.
The construction documents for that portion shall bear the stamp and signature of the licensee who is responsible for their preparation.
Page 43 CRC
TODAY’S COMPLEX HOUSE
With unusual or irregular shapes, along with high gravity or lateral(seismic) loads, many homes constructed in certain regions are engineered. For example, in Tacoma, Washington, 90 percent of all new houses constructed have an engineered load path. This is also true for new homes in parts of Florida, California, Oregon and other states.
For SDC E, the IRC contains provisions for reclassification of structures from SDC E to D2 (see
IRC Section R301.2.2.1.2) under the following circumstances:
• Where the structure is in a SDC D region based on in the International Building Code maps, or
• All exterior braced wall panels are in the same vertical plane from foundation to roof, and
• Floors do not cantilever over exterior walls, and
• Building meets IRC Section R301.2.2.2.5 requirements for “regularity”
For SDC E structures that do not meet these requirements, the prescriptive structural requirements of the IRC cannot be used and the IBC, or other referenced standards, must be used to design the structure.
As discussed in CHAPTER 4, the IRC places additional limitations on irregular portions of structures in higher Seismic Design Categories, as they may have physical features that are more vulnerable to seismic forces.
The problem with irregular buildings is that the irregular shape of the structure can cause the lateral loads to shift around in the building in unusual and difficult-to-predict load paths. Such structures are difficult to design and almost impossible to effectively specify using the prescriptive provisions of the IRC.
In order to permit some degree of building irregularity that the prescriptive provisions can safely accommodate, this section was developed. Those structures, or portions thereof, that are outside of these limitations are irregular shaped buildings and must be designed using the IBC to ensure that the building has adequate capacity and a load path to resist seismic forces.
Buildings having a regular shape can be constructed by following the prescriptive provisions of the IRC.
But there are some exceptions:
We are on pg 65 of the 2010 CRC
Setbacks or cantilevers do not exceed four times the nominal depth of the wood floor joists and ALL of the following conditions are met:
1. Floor joists are nominal 2x10 or larger and spaced not more than 16 inches on center. (Note that some engineered I-joist products are manufactured at 9-1/2-inch depths. These can be considered within the scope of this condition.)
2. The ratio of the backspan to cantilever is at least 2:1.
3. Floor joists at the ends of braced wall panels are doubled.
4. A continuous rim joist is connected to ends of all cantilevered joists.
5. Gravity loads at the end of the cantilever are limited to uniform wall and roof loads and the headers in the wall must have a span of 8 feet or less.
2. When a section of floor or roof is not laterally
supported by shear walls or braced wall lines
on all edges.
Exception: Portions of floors that do not support shear walls or braced wall panels above, or roofs, shall be permitted to extend no more than 6 feet (1829 mm) beyond a shear wall or braced wall line.
3. When the end of a braced wall panel occurs over an opening in the wall below and ends at a horizontal distance greater than 1 foot from the edge of the opening. This provision is applicable to shear walls and braced wall panels offset in plane and to braced wall panels offset out of plane as permitted by the exception to Item 1 above.
4. When an opening in a floor or roof exceeds the lesser of 12 feet or 50 percent of the least floor or roof dimension. (no exceptions)
5. When portions of a floor level are vertically offset.
IRC Section R502.6.1 states that joist framing must be lapped a minimum of 3 inches and face nailed together with three 10d nails. As an alternate, a wood or metal splice with equal strength is permitted. These measures address the problems associated with floor-offset irregularities.
6. When shear walls and braced wall lines do not occur in two perpendicular directions.
No exceptions allowed
Note that an angled corner as described in IRC Section R602.10.1.3 (illustrated below) is not such an irregularity, but rather an architectural feature found on a basically rectangular structure.
This section permits the bracing that may be found on the angled portion to be counted towards the minimum length required for one wall. The angled corner is limited to 8 feet in length, thus minimizing its impact on the structural rectangularity of the building.
7. When stories above-grade partially or completely braced by wood wall framing in accordance with Section R602 or steel wall framing in accordance with Section R603 include masonry or concrete construction.
Exception: Fireplaces, chimneys and masonry veneer as permitted by this code. When this irregularity applies, the entire story shall be designed in accordance with accepted engineering practice.
2. Buildings located in Seismic Design Category E that conform to the following additional restrictions are permitted to be constructed in accordance with the provisions for Seismic Design Category D2 of this code:
2.1. All exterior shear wall lines or braced wall panels are in one plane vertically from the foundation to the uppermost story.
2.2. Floors shall not cantilever past the exterior walls.
2.3. The building meets all of the requirements of Section R301.2.2.2.5 for being considered as regular.
As illustrated , the information in the seismic bracing table is based on:
• Soil site classification D
• 10-foot wall height
• 10 psf floor dead load
• 15 psf roof and ceiling dead load
• Braced wall line spacing of 25 feet or less
Example 11.2 highlights: your pages 252-254
• The amount of bracing required is based on the greater amount required by the ≤85 mph
wind speed category and SDC D2.
• For a single-family dwelling located in SDC D0, D1 and D2, braced wall panels on the
second floor cannot be placed over an opening on the first floor except in certain cases
(IRC Section R301.2.2.2.5, Item 3, Exceptions).
• In SDC D0, D1 and D2, braced wall panels are not permitted to be located away from the
ends of braced wall lines except in certain cases and only with Method WSP (IRC Section
R602.10.1.4.1, Exception). WSP= Wood Structural Panels
• For structures in SDC D0, D1 and D2, braced wall line spacing is limited to 25 feet (IRC
• Describes how to compare the amount of bracing required to the amount of bracing provided.
We might want to prepare a SLO Co. B.D. policy handout asking for the designer to follow this format when they use the CRC without engineering.
And require braced wall lines to be indexed on a grid as in this example.
This and the following could also be incorporated into the CONVENTIONAL CONSTRUCTION per the CRC handout and used as a checklist for us and the designer to determine whether it meets the CRC requirements.