Foundation Requirements
The document concludes Chapter 25 with detailed regulations for building foundations. Floor joists must maintain a minimum clearance of 18 inches from the ground (p. 165). Wood sills and plates in contact with masonry or concrete must be isolated using approved materials like slate-covered roofing or galvanized iron (p. 165). Permitted lumber for these locations must meet high durability standards, such as Heart Long Leaf Southern Yellow Pine or treated Cypress, with brush treatment prohibited except for end cuts (p. 165). Wood posts cannot rest directly on concrete floors; they require concrete floatings or metal plates (p. 165). Foundation walls under Type II buildings must have ventilated openings covered with non-corrosive wire mesh, proportioned at 2 square feet per 15 lineal feet of wall to ensure foundation-ventilation-requirements (p. 165-166). Loose wood storage under buildings is prohibited (p. 166).
Reinforced Concrete: Scope and Definitions
Chapter 26 establishes regulations for reinforced-concrete-design. These rules supplement the general building code and govern in cases of conflict (p. 166). Special concrete systems not covered by standard provisions may be reviewed by a “Board of Examiners for Special Construction” (p. 166). Key definitions include:
- Aggregate: Inert material mixed with cement and water (p. 167).
- Column: An upright compression member with length exceeding three times its least lateral dimension (p. 167).
- Flat Slab: A slab without beams or girders transferring loads to supports (p. 168).
- Water-Cement Ratio: Total water (including surface water) expressed in gallons per 94-lb sack of cement (p. 169).
Materials and Testing
Materials must conform to standards set by the american-society-for-testing-materials (ASTM). Portland cement must meet Specification C9-30 (p. 171). Aggregates must be clean, durable, and free from excessive deleterious materials like shale or silt (p. 171). Metal reinforcement must conform to Specifications A 15-35 (billet-steel) or A 16-35 (rail-steel) (p. 171-172). The building-inspector has the right to order tests for materials and completed structures, with load tests requiring a superimposed load of 1.5 times the live load plus 0.5 times the dead load for 24 hours (p. 170).
Concrete Quality and Stresses
Concrete quality is determined by the water-cement ratio. For average materials, specific ratios correspond to assumed 28-day compressive strengths, ranging from 1,500 to 3,000 psi (p. 172-173). When established by test, the water-cement ratio must yield a strength 15% higher than the minimum required (p. 173). Allowable unit stresses in concrete depend on the 28-day strength (). For example, extreme fiber stress in compression () is limited to (p. 176). Allowable stresses in reinforcement include 20,000 psi for tension in intermediate grade billet steel (p. 177).
Construction Practices
Concrete mixing must ensure uniform distribution and color, with mixing continuing for at least one minute after all ingredients are added (p. 178). Concrete must be placed continuously and thoroughly compacted (p. 179). Curing requires keeping exposed surfaces moist for at least 7 days (p. 179). In cold weather, concrete must be maintained at at least 50°F for 72 hours (p. 179). Forms must be substantial and tight, and reinforcement must be free from rust and scale before placement (p. 180-181). Protective concrete cover for reinforcement ranges from 1 inch in slabs to 3 inches in footings (p. 181). Construction joints must be located to minimize strength impairment, with horizontal joints requiring cleaning and roughening of the hardened surface (p. 181).
Design Assumptions and Notation
Design is based on working stresses and safe loads, assuming steel takes all tensile stress (p. 181). The ratio of modulus of elasticity of steel to concrete () is defined as (p. 182). The code provides extensive notation for design variables, including span lengths, moments, and reinforcement areas (p. 182-184). Design loads must account for all dead and live loads, with wind loads allowing a 50% increase in allowable unit stresses (p. 184).
Related Concepts
- reinforced-concrete-design
- foundation-ventilation-requirements
- building-material-specifications
- building-inspection-protocol
- structural-load-calculations