Fort Lewis 8-Plex Housing Units
Seismic Upgrades
This project consists of the evaluation of a represent-ative residential building consisting of eight, two-story living units for the purpose of effecting earthquake remediation measures sufficient for providing life safety performance level outlined in FEMA 273. The intent of this study and report was to apply the solutions proposed for a single building to thirty-seven similar buildings.
These 8-plex structures consist of an unreinforced masonry [URM] building with conventional continuous spread wall footings and slab on grade. The first floor is a 2 _” concrete slab on open web steel joists. The original roof is 2x6 decking on wood beams. To revise the pitch of the roof to a greater angle, roof trusses were constructed directly over the existing roof and sheathed with _” plywood to support composition shingles. The trusses bear directly on the original roof.
Vertical lateral load resisting elements are URM walls for the first floor concrete diaphragm and wood stud walls at the perimeter of the building for the roof diaphragm.
A cost estimate to accomplish the repairs identified to achieve the “Life Safety Level of Performance” in accordance with FEMA 273 was determined to be $137,000 per 8-plex building. The estimate was prepared using the government supplied PDS software & unit price book.
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DEFICIENCY
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PROPOSED SOLUTION
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| Vertical lateral load resisting elements in the longitudinal direction were inadequate to resist the seismic forces transferred by the first floor diaphragm. |
New shear walls (reinforced masonry) are proposed to be added in the longitudinal direction to resist the seismic forces. |
| Vertical lateral load resisting elements in the longitudinal direction were inadequate to resist seismic forces transferred by the roof diaphragm. |
Corner reinforcement for the openings in the wood stud wall are proposed to resist the shear and uplift forces in the walls. |
| No support for the URM walls at the roof in the transverse direction. |
New positive connections are proposed between the roof diaphragm and the top of the URM walls. |
| No support for URM walls at the floor level in the longitudinal direction only. |
New positive connections are proposed between the top of the wall (URM) and the floor diaphragm. |
| Inadequate shear transfer from top roof diaphragm to original roof diaphragm and from wood stud walls to concrete floor diaphragm. |
New fasteners are proposed to provide shear transfer from the wood stud walls to the diaphragm below. |
| Chimney lacks bracing at roof diaphragm. |
Chimney bracing to roof diaphragm is proposed to be installed. |
Key Project Features:
- Seismic Analysis per FEMA Standards
- PDS Cost Estimating System
- Coordination with JOC Contractor
