While the County took immediate steps to address falling concrete in 2013 and 2014, described in the January 2015 summary inspection report, the Parks Department and County engineers knew two more things needed to happen: they needed to find a short-term solution to protect employees and visitors from falling concrete and they needed to develop a long-term plan for the Domes to address a wide range of issues including needed maintenance, described in Planning for the Future of the Domes. This section describes the short-term work during 2016 to address falling concrete that allowed the Show Dome to re-open on April 29 and the entire facility to re-open on October 29, a week ahead of schedule.
In asking how best to protect employees and visitors, the team of Parks employees, County engineers, and consultants faced a question well outside conventional engineering: the Domes are unique both as structures and as conservatory collections. The Domes are each 85’ high and 140’ wide; they filled with living plants – some quite rare and valuable – with specific growing requirements; inside conditions vary from arid to humid, and all three structures leak.
To narrow their search for short-term protection inside the Domes, the County team used several criteria to evaluate possible options. These included:
Staff areas must be protected as well as pedestrian paths
Ease and duration of installation process
Availability of materials
Lifespan of option (5 year minimum, up to 10+ years)
Impact on future inspection; solution must not limit ability to monitor condition of Domes
Impact on plants, both during installation and afterwards
Impact on visitor experience
Any requirements to modify vegetation and/or habitat
The team investigated three basic options and numerous variations within each: covering the walkways; covering the frame edges from which concrete was falling; applying mesh or netting on the inside of the structure.
In summary, they concluded that:
Covering the walkways would not protect the staff and would diminish the visitor experience
Applying netting or mesh to the 5,100 connection points across the three Domes would be time-consuming and expensive compared to other options
Covering the inside of the structures with some type of netting would best fit the criteria and was generally the simplest option
*Poly will not allow Show Dome to open in May due to lead time
Red indicates an unacceptable condition
Ensuring the Domes Are Safe for Visitors
Beginning in mid-March 2016 the County’s contractor installed wire mesh onto the Show Dome structure. The process began by clamping brackets onto the concrete frame of the Dome. These anchored the netting to the existing concrete frames. In some cases the brackets needed to be covered with flashing to keep them from touching other metal elements of the structure in order to prevent possible rusting.
Metal Bracket installed on concrete frame of Show Dome
Metal bracket installed with insulation next to metal on frame.
The second step was to connect cables to the brackets using stainless steel shackles. The cables will support the netting.
Cable attached to bracket.
Finally, the netting was attached to the cables with hog ties. The overlapping layers of netting were also secured together with hog ties to keep concrete pieces from slipping from between layers. The contractor installed over 5,000 hogties in the Show Dome alone! The netting is ½” stainless steel wire, chosen because the holes are small enough to trap concrete pieces and because the stainless steel should be durable over the next few years while long term plans are developed and implemented.
Sample of mesh attached with hog ties to cable inside Show Dome, March 2016
Work in the Show Dome was completed so that it could re-open on April 29. The Show Dome was addressed first because it houses few permanent plants, making it easier to maneuver equipment within. Also, with its changing exhibits of flowers and seasonal displays, the Show Dome is the most sought-after location for weddings and celebrations, and County staff was anxious to disrupt as few planned events as possible. Work on the other two Domes has been completed, and the entire facility re-opened to the public on October 29, 2016 – a week ahead of schedule.
Cost for the netting safety solution was $834,000, which included the planning and testing to determine the best solution to falling concrete, as well as the acquisition of the materials and installation and time spent managing the project.