Brudis & Associates, Inc. (BAI) provided structural inspection services and designed repairs to an existing dox plank floor system at Wellwood International School utilizing poured-in-place reinforced concrete beams. This innovative, cost-saving approach was used in lieu of the more expensive, common practice of cutting out and replacing the entire floor section. Replacing the entire floor section often requires designing additional structural support which would increase costs to the client, expand the construction schedule beyond summer break, and generate more waste to be dumped into landfills.
Structural Analysis. Prior to development of the design for the floor repair, BAI provided a visual inspection of the dox plank floor system via the crawl space. The areas of concern were grouped into 5 general categories based on the type of damage and the condition of the floor system: a) Mechanical Penetration b) Mild distress c) Mid-Stage Distress d) Advanced Distress and e) Block Failure; Four areas located within the south wing (including the cafeteria and kitchen) were categorized as “Block Failure” and warranted immediate replacement.
The dox plank system was developed in the 1950s as a low cost, light weight, easily constructed floor system alternative. The dox plank system consists of precast hollow core CMU blocks suspended on steel reinforcing rods spanning between support walls or beams (see Figure 1). Deterioration to the dox plank system is most typically associated with moisture causing the supporting rebar to corrode. As an expansive process, this corrosion typically exerts outward force on the bedding mortar and dox plank unit, ultimately causing the mortar to spall and the bottom face of the block to shatter. There were numerous locations where pipe penetrations have left broken blockwork and several places where the rebar was cut and pulled out of the mechanic’s way. Leaks in the plumbing may have accelerated the corrosion process.
Structural Design. The goal for this alternative design was to provide a permanent support solution while minimizing impact to the surrounding building elements such as CMU partition walls, built-in counters and work stations and to minimize impact to the mechanical, electrical and plumbing systems running along and through the floor. The repair and strengthening of the existing dox plank floor was accomplished by designing new reinforced concrete beams installed under the existing floor. The concrete beams were designed to support all loads on the floor using current building code requirements.
Concrete for the beams was poured through cored holes in the top of the floor. This method ensured a complete monolithic pour of the beams and damaged dox plank. Installation of the new concrete beams ensured the entire floor system, partition walls, and furnishings did not have to be removed and replaced. Additionally, this method minimized the finish work typically required with this type of floor replacement and reduced net debris disposal and overall costs. Most importantly, the structural integrity of the floor was brought up to modern building code standards, ensuring the safety of the teachers, faculty and nearly 500 students that attend Wellwood International School.