Logan Meeting House Seismic Retrofit

Project Background

• On March 18, 2020, the Magna Earthquake incapacitated concrete masonry unit (CMU) buildings near Salt Lake City, UT 1
• Seismologists predict Utah is overdue for a magnitude 7.2 earthquake
• The structure at 792 N 500 E can be updated to meet the current ASCE 41-17 seismic code²

Deficient Components

From site visits and structure as-built plans, we diagnosed the following possible structural deficiencies:

• Shear stress capacity in CMU shear walls
• Strength of flexible diaphragms
• Rigid connections on building gas lines
• Gravity and seismic load paths
• Partition wall bracing
• Suspended Ceiling Seismic Bracing

Evaluation Criteria

Alternative solutions for each deficiencies were ranked and evaluated by:

• Safety Does the solution meet current code standards?
• Cost Is the solution economically feasible? Constructability Is the solution easy to implement?
• Aesthetic Value Does the solution fit the current building aesthetic?
• Usability Does the solution preserve the building’s function?

Seismic Upgrade Design

Truss Redesign

This truss model includes stress ratios. The building has many existing trusses, and some of them require redesign to function more effectively.

Wall Capacity Design

The addition of drags in key locations provides load paths for lateral forces in shear walls.

Blocking Design

This picture was taken inside the existing building. Wood blocking like this is used to increase shear capacity and connect various structural components in the building. TTE's design specifys additional blocking in many locations.

Strap Design

Straps are used to connect walls to roof sheathing. This prevents walls from tipping due to cross-plane forces by distributing load into the sheathing.

Out-Of-Plane Bracing Design

This perpendicular connection between the masonry wall and the truss above allows out-of-plane forces that act on the wall to transfer into the truss. This prevents the wall from tipping over.

Suspended Ceiling Bracing Design

This picture was taken in the engineering building on campus. This suspended ceiling design uses diagonal cables to prevent lateral shifting of the ceiling and compression struts to prevent upward motion of the ceiling. TTE recommends this design for the meetinghouse.