"Rules" you must design by:
Building Codes | Design Standards | Local Entities | Design Philosophy
- Building codes:
- Developed throughout the world for the design and control of material quality.
- Adopted by cities and counties to become the legal authority.
- 3 model codes Þ provide the framework
of local codes.
- Uniform Building Code: Western U.S. - Specializing in seismic.
(ICBO - International Conference of Building Officials). - The BOCA National Building Code: Northern U.S. - Specializing
in snow
(Building Official and Code Administration). - Standard Building Code: Southern U.S. - Specializing in wind.
(SBCCI - Southern Building Code Congress International)
- Uniform Building Code: Western U.S. - Specializing in seismic.
- UBC will be taken as the authoritative guide in this class because:
- We are in the western U.S.
- It is the most widely used.
- It reflects the most current seismic/wood/masonry requirements.
- In the Fall of 1998, we focused on the 1994 version of the
UBC.
- This version has been reorganized and is arranged differently from earlier codes.
- We are now, Fall of 1999, updating this web site to reflect
the 1997 version of the UBC.
- The seismic section of thes 1997 version has changed considerably.
- Future direction for U.S. code:
- International code.
- 1 U.S. code called the International Building Code, IBC.
- ICBO, BOCA, SBCCI have formed a single entity, the International Code Council, ICC.
- May be in place by Spring of 2000.
- International code.
- Design Standards.
- Represent the latest structural recommendations.
- Usually produced by one or more industry associations.
- Often referenced heavily by the building codes.
- For wood:
- 1997 National Design Specifications for Wood Construction
(NDS) published by the Americal
Forest and Paper Association (AF&PA) and the American
Wood Council (AWC).
- Design specifications for solid sawn lumber and glued laminated timber.
- Design values for various species groupings and grades.
- Address: 1111 19th Street N.W., Suite 800
Washington, D.C. 20036
(202) 463 - 2700 - Although we will be referencing the '97 NDS in this class, note that the '97 UBC relies on an earlier version the 1991 NDS.
- Timber construction manual by American Institute of Timber
Construction (AITC).
- Structural glued-laminated timber authority.
- AITC Glulams
- 1997 National Design Specifications for Wood Construction
(NDS) published by the Americal
Forest and Paper Association (AF&PA) and the American
Wood Council (AWC).
- For masonry:
- 1992 ACI 530-92/ASCE-92/TMS402-92 Building Code Requirements for masonry structures.
- The 1999 version is now available and it includes a number
of new provisions:
- It is reformated.
- Includes prestressed masonry, inspection and quality assurance, hot weather masonry, and adhered veneer products.
- Often called the 530 code or the MSJC code.
- Where MSJC = Masonry Standards Joint Committee with members
from:
- ACI - American Concrete Institute.
- ASCE - American Society of Civil Engineers
- TMS - The Masonry Society
- CMR - Council for Masonry Research.
- Developed a single standard that was mechanics-based for both clay and concrete masonry.
- How local entities use model codes and design standards.
(the following figure was adapted and modified from Masonry Today, Portland Cement Association, Vol. 7, No. 1, Summer 1997.)
- For the case of Masonry, the BOCA and SBC codes adopts the MSJC code which in turn adopts the MSJC Specifications with references to the ASTM standards.
- The UBC does not reference the MSJC. It contains its own masonry design provisions and publishes its own materials, testing, and installation standards.
- It appears that the masonry provisions in the IBC will be a blend
of requirements taken from the three codes.
- Because the ASTM standards and the MSJC are consensus documents, however, the ICC will most likely heavily reference these in the development of the IBC criteria.
- Design Philosophy
- In this class we will use the older Working Stress Design (WSD) approach that is also known as Allowable Stress Design (ASD).
- This approach is still the most appropriate for wood and masonry, even though both industry groups have made attempts to develop strength procedures.
- This author believes, however, that these strength efforts are still at the development stage and will not be readily used by the design community for some time yet.
- The basic WSD approach is:
- Straight - line, elastic stress assumption (the induced-stresses are within the linear, elastic range of the material's behavior)
-
Actual stress £ Allowable stress ß ß Stress developed in a structural member due to actual (service or working) loads. A function of the material's strength and behavior for that particular stress under consideration. - Example: consider the following simple beam to demonstrate
the WSD procedure:
- This beam experiences shear and bending stresses and could
fail in either mode.
- The basic strength approach (which is also referred to
as the load resistance factor design or LRFD) is:
- Instead of focusing on the yield stress as a design target, strength design uses the ultimate strength as its target. Design equations are based upon forces and moments vs. stresses.
- Factored loads £ design strength.
- Example: consider the previous beam, checking it for
bending. The basic strength equation could look something
like:
- This beam experiences shear and bending stresses and could
fail in either mode.
- Units
- U.S. Customary
- Both materials are slow to adopt SI units because of modular construction where wall systems are based upon 16" lengths and roofs are based upon 4' X 8' rectangles.
- Although many projects have employed a "soft" conversion (designing
in US, but converting numbers to SI), its the "hard" conversion
that is difficult to employ.
- Hard conversion will require re-tooling of manufacturing and construction processes to be compatible with SI modulation.
