ATC/SEAOC Training Seminars Supplemental Material Session 3 The Load Path in Wood Frame Construction Prepared by John R. Henry, P.E. Senior Staff Engineer International Conference of Building Officials

A Specific Detailing Requirement: The Code Philosophy The Purpose: “The purpose of the earthquake provisions is primarily to safeguard against major structural failures and loss of life, not to limit damage or maintain function.” (Section 1624) A Specific Detailing Requirement: “Seismic and Wind Design. When the code prescribed wind design produces greater effects, the wind design shall govern, but detailing requirements and limitations prescribed in this section and referenced sections shall be followed. (Section 1626.3) 6

UBC Section 1605: “The Jewel in the Crown” Rationality: “Any system or method of construction to be used shall be based upon a rational analysis in accordance with well-established principles of mechanics.” Complete Load Path: “Such analysis shall result in a system which provides a complete load-path capable of transferring all loads from their point of origin to the load-resisting element.”

Specific Connection Requirements: Seismic Zones 2, 3 & 4 Anchorage of roof to walls and columns, and of walls and columns to foundations to resist uplift and sliding (Section 1605.2.3) Concrete and masonry walls shall be anchored to all floors, roofs, and other structural elements which provide support for the wall. (Section 1605.2.3) The anchorage shall provide a positive direct connection between the wall and floor or roof (Section 1633.2.8) 16

Specific Connection Requirements: Seismic Zones 2, 3 & 4 Connections which resist seismic forces are to be designed and detailed on the drawings (Section 1633.2.3) All parts of a structure shall be interconnected and connections shall be capable of transmitting the seismic force induced by the parts being connected. (Section 1633.2.5) A positive connection for resisting a horizontal force acting parallel to the member shall be provided for each beam, girder, or truss. (Section 1633.2.5) 16

Specific Connection Requirements Seismic Zones 2, 3 & 4 Collector elements shall be capable of transferring the seismic forces originating in other portions of the building to the element providing resistance to those forces (Section 1633.2.6) Diaphragms supporting concrete or masonry walls shall have continuous ties or struts between diaphragm chords. Added chords may be used to form subdiaphragms to transmit the anchorage forces. to the main cross-ties. (Section 1633.2.9 item 4) 17

Specific Connection Requirements Seismic Zones 2, 3 & 4 In seismic zones 3 and 4 anchorage (of concrete or masonry walls) shall not be done accomplished by the use of toenails or nails subject to withdrawal nor shall wood ledgers or framing be used in cross-grain bending or cross-grain tension, and the continuous ties required (above) shall be in addition to the diaphragm sheathing. (Section 1633.2.9 item 5) In addition, in seismic zones 3 and 4, diaphragm to wall anchorage using embedded straps shall have the straps attached to or hooked around the reinforcing steel or otherwise terminated so as to effectively transfer forces to the reinforcing steel. (Section 1633.2.8) 17

Wood Connection Requirements: Connections and anchorages shall be provided between the diaphragms and resisting elements. (Section 2315.1) All boundary members proportioned and spliced where necessary to transmit direct stresses. (Section 2315.3 & 2315.4) In Seismic zones 3 & 4, collector members provided to transmit tension and compression forces and detailed to distribute the shearing stresses (Section 2315.5.2) 18

Wood Connection Requirements: Openings in diaphragms shall be fully detailed on the plans and shall have their edges adequately reinforced. (Section 2315.1) Perimeter members at openings provided and detailed to distribute the shearing stresses (Section 2315.5.2) In seismic zone 3 and 4, exterior exit balconies and stairs shall be positively anchored to the primary structure. (Section 2320.13) 18

Specific Foundation Connection Requirements Seismic Zones 3 & 4: The foundation capable of transmitting design base shear and overturning forces from the structure into the supporting soil. (Section 1809.2) Connection of superstructure elements to foundation adequate to transmit design forces to the foundation the forces for which the foundation. (Section 1809.3) 18