AutoTight®
Catalog
3. Multi-Story Systems
SECTION 102 APPLICIBILITY
"102.1 General. Where there is a conflict between a general requirement and a specific requirement, the specific requirement shall be applicable. Where, in any specific case, different sections of this code specify different materials, methods of construction or other requirements, the most restrictive shall govern."
Designers in the State of California see CBC 2015 section101.7.3
COMMENTARY
Different codes references may conflict to the extent that material strengths are over stressed by 16%. In addition, some elongations may be understated by 36%. Unless the designer understands the conflict and uses the most conservative approach, the customer & building owner will not receive the required performance.
1604.4 (LOAD) ANALYSIS
Load effects on structural members and their connections shall be determined by methods of structural analysis that take into account equilibrium, general stability, geometric compatibility and both short-and long-term material properties. Members that tend to accumulate residual deformations under repeated service loads shall have included in their analysis the added eccentricities expected to occur during their service life. Any system or method of construction to be used shall be based on a rational analysis in accordance with well-established principles of mechanics. Such analysis shall result in a system that provides a complete load path capable of transferring loads from their point of origin to the load-resisting elements.
1604.4 (LOAD) ANALYSIS
The total lateral force shall be distributed to the various vertical elements of the lateral force-resisting system in proportion to their rigidities, considering the rigidity of the horizontal bracing system or diaphragm. Rigid elements assumed not to be a part of the lateral force-resisting system are permitted to be incorporated into buildings provided their effect on the action of the system is considered and provided for in the design. A diaphragm is rigid for the purpose of distribution of story shear and torsional moment when the lateral deformation of the diaphragm is less than or equal to two times the average story drift. Where required by ASCE 7, provisions shall be made for the increased forces induced on resisting elements of the structural system resulting from torsion due to eccentricity between the center of application of the lateral forces and the center of rigidity of the lateral force resisting system. Every structure shall be designed to resist the overturning effects caused by the lateral forces specified in this chapter. See Section 1609 for wind loads, Section 1610 for lateral soil loads and Section 1613 for earthquake loads.
SECTION 2303.7 SHRINKAGE
Consideration shall be given in design to the possible effect of cross-grain dimensional changes considered vertically which may occur in lumber fabricated in a green condition.
SECTION 2304.3.3 SHRINKAGE
Wood walls and bearing partitions shall not support more than two floors and a roof unless an analysis satisfactory to the building official shows that shrinkage of the wood framing will not have adverse effects on the structure on any plumbing, electrical or mechanical systems or other equipment installed therein due to excessive shrinkage or differential movement caused by shrinkage, The analysis shall also show what roof drainage system and the foregoing systems or equipment will not be adversely affected or, as an alternative , such systems shall be designed to accommodate the differential shrinkage or movements.
COMMENTARY
Hardware looseness of 1/2″ to 1″ or more is often introduced into buildings of 1 or 2 stories. Any system looseness results in increased drift in direct proportion to the looseness. Always use a TUD and examine walls for shrinkage and drift.
NDS SPECIAL DESIGN PROVISIONS FOR WIND AND SEISMIC
2015 EDITION ANSII/AWC SDPWS‐2015
SECTION 4.3.2 DEFLECTION
Calculations of shear wall deflection shall account for bending and shear deflections, fastener deformation, anchorage slip, and other contributing sources of deflection.
The shear wall deflection, d^sw, shall be permitted to be calculated by the use of the following equation.
Where: b = shear wall length, ft. Δa = total vertical elongation of wall anchorage system (including fastener slip, device elongation, rod elongation, etc.) at the induced unit shear in the shear wall, in. E = modulus of elasticity of end posts, psi. A = area of end post cross-section, square in. Ga = apparent shear wall shear stiffness from all slip and panel shear deformation, kips/in (from Column A, Tables 4.3A, 4.3B, 4.3C, 4.3D) h = shear wall height, ft. v = induced unit shear, lbs/ft d ^sw= maximum shear wall deflection.
COMMENTARY
In many cases wall drift governs the shear wall performance. This equation requires the designer to include all sources of vertical movement in the tie-down. This means: System elongation = ∑ of all items under load The TUD compensates for shrinkage but adds elongation. Either shrinkage is added or a TUD is used. If used then TUD DA +DR must be included.
Threaded Rod Allowable Strength Design
