Moment frames
This remedial option considered the retrofit of the existing beam-to-column bolted connections and upgrades to the existing concrete pad footings supporting the interior columns. Under this scenario, the existing beam-to-column connections would be retrofitted with steel plates and additional welds in order to form moment connections at designated locations.
Drawbacks to this approach included construction and accessibility challenges associated with footing upgrades within the interior of the building. Additionally, the structural analysis confirmed, the calculated lateral deflections would likely result in continued cracking of the repaired masonry walls, due to the relative flexibility of a moment frame lateral system.
Reconstruction of stairwells
This remedial option had investigated the reconstruction of the five interior stairwells using reinforced concrete shear walls to resist the calculated lateral loads. It is important to note, the building stairs have varying levels of security/accessibility requirements depending on who is it (i.e. public, building staff, police, and/or persons on trial).
Significant challenges relating to constructability were identified with this approach. Additionally, it was determined it was infeasible to shut down any one stairwell during construction and still meet OBC exiting standards and building functionality requirements (i.e. separating public, staff, police, etc.) within the courthouse.
Interior bracing
This option reviewed the addition of interior braced bays within the building footprint. However, due to how the existing rooms and hallways were designed within the building, and changes in layouts from floor-to-floor, it was impossible to find enough suitable locations for braced bays from the roof level down to the foundation.
External precast concrete shear walls
With this retrofit scheme, the vertical lateral elements were placed outside of the building footprint. There were 13 external precast concrete shear walls positioned around the perimeter of the structure, with designated reinforced beam drag strut ‘load paths’ at the floor levels to transfer the inertial seismic forces. Nine of the precast shear walls were orientated parallel to the existing building walls and four were set perpendicular to the existing walls. Shear wall orientations and locations were selected to maximize efficiency of the new lateral system.
This option had a distinct advantage by having the shear walls constructed outside of the building footprint; this would simplify construction access, minimize building disruption during construction and the interior room, and hallway/room layouts within the building would remain unchanged after construction was complete. The interior work could be phased and completed off-hours in order to maintain building operations during the weekdays.
Based on the advantages outlined above, this option was ultimately the approach selected and used to develop construction drawings.
