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�- -we Patterson Pass Business Center, Building#6 Page 3 Tracy, California Lateral Force Resisting System Lateral seismic forces will be generated at the building by horizontal earthquake ground accelerations acting on the mass of the structure. The resulting forces acting on the building are resisted by the OSB roof sheathing acting as a deep beam, or diaphragm, that spans between the exterior pre-cast concrete shear walls. The exterior walls transfer the lateral forces to the foundation primarily through shear. Pneumatically driven pins from the roof sheathing into the steel ledgers transfer the diaphragm shear forces into the ledgers and drag members. Bolts through the ledgers that are embedded in the wall panels transfer the shear forces from the ledgers to the concrete wall panels. Double-sided wall anchors bolted to the wood sub-purlins and embedded in the wall panels and the welded joist connections prevent the walls form separating from the roof framing during earthquake ground shaking. DESIGN REVIEW The building is assumed to have been designed according to the requirements of the 1997 edition of the Uniform Building Code (UBC). It appears that the design and construction of the building are in essential conformance with the requirements of 1997 edition of the UBC. The roof of the building was designed to support the code-specified live load of 20 pounds per square foot. Panelized roof systems, such as is present at this project, are designed with little, if any, reserve capacity. Additional loads (e.g. antennae, HVAC equipment) should not be placed on or suspended from the roof unless approved by an engineer. Anchorage of the heavy concrete wall panels to the roof diaphragm is required to prevent separation of the walls from the roof structure during moderate to strong earthquakes. Localized tearing of the roof sheathing may occur during moderate to strong ground shaking unless the wall anchorage forces are developed into the diaphragm by sub-diaphragms of adequate strength and stiffness. The design of the roof diaphragm at this project included wall anchorage and sub- diaphragms to reduce the potential for damage during an earthquake. The design of the wall anchorage elements appeared to equal or exceed the 1997 UBC requirements for Seismic Zone 3. The presence of wall anchors and sub-diaphragms was taken into account when determining the estimated seismic risk at the project. 05005.01 R. D. Boyens Engineering