Problem Solving Article: Warehouse roof sag
Maintenance: Warehouse: Stucco ceiling panels cause roof sag. 

An Article from the Series of Problem Solving Articles in an Industrial Setting

The warehouse at the olive cannery that I worked at was part of an older, all wooden structure. A Valero convenience/gas store was located across the street from the warehouse.

I went over to the store one day to purchase a Pepsi Cola. I checked out the roof as I was returning to the warehouse.

The main roof of the warehouse was sagging in one section. This roofing section was due South of the warehouse loading dock.

I looked at the loading dock roof. It was wide enough for four trucks to be loaded at once. I called the Lead Mechanic of the warehouse maintenance unit to come to the loading dock to talk to me about the history.

Originally, the sunken loading dock had only been wide enough for two trucks. An increase in business required that the dock be enlarged to accommodate four trucks at once.

The dock was enlarged to 44 feet wide and the heigth to remain the same. The entire container of the truck would fit into the sunken floor and be level.

To save money on the installation cost, a used, laminated, wooden beam was purchased and installed to bridge and hold up the outer edge of the dock ceiling. The laminated beam was 48 feet in length.

Existing supports designed to just hold up the edge of the existing roof were used to mount the beam at each end. These supports were not designed to support the load of the roof and the beam with no intermediate supports.

Still, all would probably have been well but for the decision to stucco the underside of the loading dock ceiling. The stucco had been liberally applied and was 2 to 3 inches thick on the underside of the entire ceiling of nearly 2400 square feet.

That's a lot of cement and weight for a span of that size. The weight was dragging the laminate beam down and had allowed the laminated plates to start to separate and slip. 

The dock ceiling had bowed downward and outward. This pull was what had caused the warehouse roof to sag. Some of the roof support columns inside the warehouse had actually moved and were no longer in line.

I reported my findings to the Plant Manager and Company President. I suggested that we hire a Structural Engineer to examine the roof and dock ceiling.

The Structural Engineer came up with a plan to remove the stucco from the underside of the dock ceiling. The stucco was attached to 4' X 8' sheets of plywood.

The demolition contractor would have to remove the stucco and plywood from one section at a time to allow the loading dock to continue to be used. As the plywood was removed, sheets of plastic were installed to cover the holes and keep insects and birds out of the warehouse.

Two new laminated beam support columns were installed at the same time. The beam would have to be lifted while still attached to the roof and then the final beam rests welded into place on the support columns.

When all was ready, the contractor rented four large fork lifts to raise the laminated beam. Unfortunately, he didn't calculate his measurements correctly and the beam was installed about 6 inches shorter than it should have been. We would continue to have a small sag.

The beam was raised as high as possible by the forklifts and then the beam support rests on the columns were welded into place. The beam was lowered into place and then bolted to the rests, but not tight.

The laminated beam still had to be moved and jiggled to get existing holes in the laminate sections to line up. Once lined up, large bolts and nuts were installed to prevent slip of the laminate pieces.

The beam was then securely fastened to the support rests. Nearly all of the sag was removed from the loading dock ceiling.

Plywood sections 4' X 8' and 1/4" thick were installed and spray painted to make the dock ceiling. Lighting was reinstalled to permanent locations.

The warehouse roof sag was less, but still noticeable. I had the plant contractor relocate stacks of product to gain access to the roof support columns in the warehouse.

The roof was lifted slightly at each wooden column and then wedges were placed under the column to keep it permanently raised in place. Holes were drilled in the concrete floor and anchors mounted and then bolted to the columns to stabilize their positions.

All in all, a successful outcome to what could have been a disaster. The roof and/or loading dock ceiling could have suffered a cascading collapse at any time.

All warehouse personnel and truck drivers had been at severe risk. The company was at high risk to liability and consequences from a possible collapse.

This was all averted. Nobody still working at the plant could recall whether the loading dock expansion had been carried out from the plans of a structural engineering firm or whether the planning and installation had been carried out by plant personnel.

From the looks of the installation, I could not envision the scenario where any Engineer I knew of would lay claim to the design and installation of such a potential disaster. I would have to vote for design and installation by unqualified plant personnel trying to save the company money.

Feel free to copy this article in it's entirety as long as you include the credits below. Thank you for spreading the knowledge.

Author: Larry Bush 
Profile: Electrician in industrial, construction, marine, and food industries for 47 years, with 22 of those years in management.
URL: http://www.reliability-consultant.com