DEMOLITION OF A PULP MILL IN AN OPERATING PAPER FACILITY

by Merle E. Brander and John J. Jeanquart

Introduction

If you would ask people on the street what a structural engineer does, the most frequent response would probably be, “I don’t know”. A few people may know that structural engineers design buildings or additions or modifications to buildings; but you would seldom hear that structural engineers design for demolition of buildings. Yet, it is crucial that demolition, particularly demolition of a structure within an operating facility, include structural engineering to establish the loading and proper sequence of demolition to prevent unplanned collapse that could endanger workers, damage adjacent structures and equipment, or interrupt mill operations.

Setting The Stage

A major integrated papermaking facility, consisting of a pulp mill, a paper mill, and converting operations, was constructed on a site in various stages beginning in 1916. As the output of the company increased over time, additional structures were added to the site, resulting in a facility with partially intermingled processes and operations. By the time the company ceased on-site pulp operations several years ago, several pulp mill buildings also were serving secondary functions unrelated to the pulp operations. For example, one of the buildings housed the facility’s main water pump and piping; some retired pulp mill buildings contained components of the electrical system that served other still active buildings. In addition, some structural members of the pulp mill buildingsÊ still served a primary function, as they were shared with other still active buildings.

When demolition was being considered, the size and complexity of the project, the number and variety of equipment inside the buildings, the interior location of the buildings, the lack of physical separation, and the incomplete operational separation convinced the Owner that the demolition proposed required the attention of a structural engineer. The costs associated with shutdown of operations in the vicinity of the proposed demolition would have been prohibitive; the only reasonable course of action was to conduct the demolition without interrupting the operations in surrounding buildings.

Defining The Problems

The demolition project proposed involved 10 buildings for a total of approximately 39,000 square feet. More than half of the perimeter of the demolition area involved walls that were shared with other structures that were to remain and continue operating. When demolition was to be undertaken, not only was it necessary to assure the structural integrity of all the other buildings sharing those walls, but also to assure that the environmental conditions within those buildings would remain appropriate for personnel functioning in those buildings, including specifically maintenance of fire protection and escape and firefighting access. In addition, with the pulp mill housing electrical systems and water systems on which operations in other buildings were relying, those had to be adequately addressed if operations were to continue uninterrupted.

Because the pulp mill buildings were constructed before hazards associated with various materials were known, consideration had to be given to the likely possibility that the buildings would contain lead paint, asbestos, and other materials commonly in use at the time of construction. It was also necessary to account for other hazardous materials, such as sulfur, ammonia, and lead in mortar inside digesters and accumulators, known to be common in industrial facilities, and for other existing conditions, such as the presence of underground piping, that could pose a hazard or interrupt operations if encountered.

Pre-Demolition Activities

Before demolition activity began, we met with the Owner representative to discuss the project scope and likely cost. A demolition sequence had been proposed as part of Condition Survey of the Pulp Mill buildings done by Brander in 1996. That involved repairs that had already been done, as well as the following:

A survey to determine if hazardous materials had been used in any of the pipes, tanks, or other equipment on the property or building, and tests and purging to eliminate any hazards found or suspected.

A checklist of items within the pulp mills to be removed or relocated prior to demolition, such as fire suppression, electrical, automation, and water piping systems, and development of a plan for the removal or relocation.

Drawings and specifications for demolition of the existing buildings and structural components and for severing the buildings scheduled to be demolished from the adjacent buildings that were to remain intact.

Demolition of the Pulp Mill buildings and structural components, following all applicable OSHA safety requirements.

The 1996 Condition Survey of the pulp mill buildings served as the OSHA required survey by a competent person. Since mill personnel had already taken action to assure the stability of the structures shortly after issuance of the Condition Survey report, it was only necessary to verify that conditions remained as previously noted to be assured of the structural integrity of the buildings being addressed.

Specifying The Demolition

It was determined by the Owner’s engineer and Brander that the demolition project would be done under a single prime contract with a general contractor, with one of three listed prequalified demolition contractors serving as subcontractor to the general contractor. In the specifications, the project was defined as follows:

1. Demolition of existing Pulp Mill Buildings, involving numerous buildings, most of which are steel-framed structures with masonry walls, cast-in-place concrete slabs, and precast concrete, steel, or wood roof decks and smooth surface asbestos-containing builtup roofing systems. The buildings are at various levels and collectively contain digesters, pressure accumulators, stone towers, and numerous other structures and equipment, such as chests, tanks, chip bins, elevators, conveyors, mechanical equipment, conduit, piping, etc.

2. Demolition of peripheral concrete tanks, tank foundations, containment structures, and peripheral buildings constructed primarily of masonry walls with concrete foundations, all of which are to be assumed to be deep foundations.

3. Detachment of buildings being demolished from existing buildings that are to remain, and reinforcement and closure of those existing buildings, with closure to include construction of a new wall, construction of new roof framing and decking, installation of bracing for existing masonry walls, infilling of all penetrations through masonry walls, installation of new doors, and installation of platforms.

The Owner accepted responsibility, either in-house or under separate contract, for state-required asbestos assessment and removal, for identification and relocation of all active electrical or mechanical lines or equipment, and for emptying all chests and tanks. Contractors were advised to include in their bids the costs for dealing with lead paint. The specifications were prepared with disclosure of all known hazardous materials and contractors were offered the opportunity to tour the buildings to determine the types and numbers of items requiring special handling and disposal. Since even with the best prior planning, there are things that cannot be known until they are uncovered, there was a provision in the specifications for unit price payments for truly hidden conditions.

Each set of drawings included 15 demolition drawings and 20 structural drawings. The demolition drawings included plans of each floor to be demolished, as well as a cross section to identify the structures, equipment, and elevation changes, based on which volumes and areas could be calculated for bidding. The structural drawings included a sequence of structural reinforcement for walls of buildings that were to remain. Structural drawings also included details and plans for new roofs and walls to be installed after demolition, door and wall opening infill schedules, and windows for exterior walls.

Demolition

To facilitate coordination of the project and keep the Owner informed about the project, weekly meetings were held. During the meetings, questions could be answered as they arose so that work could proceed uninterrupted. The demolition work proceeded safely and on schedule, with only minor delays resulting in a demolition project that turned out to be less troublesome than a routine construction project.

Cost Considerations

The owner had initially requested funding for the demolition based on a cost estimate from a local contractor, provided without the benefit of drawings and specifications. After drawings and specifications were prepared and were used in the preparation of lump sum bids, it was found that the project cost was approximately 40% lower than originally expected, a substantial savings considering the size of the project.

The Role Of The Structural Engineer

The institutional role of the structural engineer developed when architects could no longer rely on a craftsman or builder to use and understand the properties and performance capabilities of the materials that were being produced. To have a builder take a building down and reconstruct adjacent buildings without being qualified to evaluate the support conditions and understand the integration of the materials needed for reconstruction exposes the building Owner to unnecessary risks and costs. A qualified structural engineer can reduce the risk and cost, allowing for demolition and rehabilitation even as the Owner’s facility continues to operate.

Structural Engineering in the 21st Century, ASCE

Proceedings of the 1999 Structures Congress

April 18-21, 1999

New Orleans, Louisiana