{QUESTION} On a current precast project we are supplying, a vast majority of the panels were out of plumb. We have determined the issue at the plant and corrected it, but a significant number of panels are already manufactured and the schedule does not permit time to replace them. What are our options?

{ANSWER} While no one likes to admit it, construction constraints, timelines, and budgets continue to be more and more demanding. Th is leaves no room for production errors, adding more pressure to precast concrete producers.

On a recent project, very demanding placement schedules required the precast supplier to cast 12 stories of architectural cladding weeks in advance, in preparation for a fast-paced placement. The members were about 30 feet long, 8 feet tall and 6 inches thick, with two window openings per panel.

With minimal onsite staging, multiple tower cranes, and fast-paced delivery coordination the order of 600 panels was installed. During the installation, it became evident that the panels were out of plumb horizontally, typically bowing inward 1 to 2 inches at the center of each panel. With strong concerns for the exterior barrier reliability and visual appearance, immediate action was required to meet the delivery date and ensure project quality.

Cooperation between all parties became critical to finding reasonable solutions and minimizing damages. Both cost and timeline made constructing new panels a last resort for this project.

All parties involved brainstormed for options to solve the problem, even taking into account the profile and location of the mechanical system to allow for enclosure within the interior wall framing. After drafts, calculations, and a field trial, a resolution was approved.

With dedication from designers, contractors, and many other supporting parties, a potential fix was designed to "push" the panels into the correct position.

The panels as originally installed did not have a mid-span connection allowing horizontal flexibility. Also, the cable design within the panels could not withstand the additional outward forces required to straighten each panel individually. The fix included installing an additional anchor at mid-span. Th is pushed the middle of the panel plumb, while the anchors at the end held the panel in place.

Designing a fix to a problem on the fly too often runs into a "catch" that requires re-thinking the plan. To achieve the correct position of the panels, an outward force was required at mid-height. The repair required a mechanical system to be anchored to the existing castin- place deck slab to push against and straighten the panel.

This was easier said than done, as the existing slab was a recently poured, post-tensioned slab with transverse cables near the desired position of the required anchors. The exact location of the mechanical system had to be fieldadjusted to avoid damaging the existing post-tensioned cables while maintaining the ability to complete the fix.

With the cooperation of multiple trades, crane operators, employees willing to work long shifts, and many more willing parties, about 50 panels per floor were straightened to acceptable tolerances. Anchors were drilled into the slab after scanning with ground penetrating radar to locate the existing post-tensioned cables—almost 1200 holes—without incident.

The mechanical system was engaged and extended while monitoring the panels for position and distress. Once at the desired location, the mechanical system was secured and wall framing reinstalled to conceal the fix.

As the construction industry continues to push the envelope with design and construction schedules, issues like this will most certainly continue to arise. Striving to learn from these experiences, and continuing to refine our processes and products will most certainly help limit these issues, but likely not completely eliminate them.

Contributed by Braun Intertec. Visit www.braunintertec.com.