Building suspended floors that are acceptably flat and level is one of the many challenges that contractors face. Every elevated floor deflects or sags slightly under its own weight, whether supported by steel beams or a cast-in-place concrete frame. Structural drawings generally require that individual floor framing members have a slight camber, or hump, in their profile prior to construction. When cambered floor framing members are allowed to deflect, they ideally will move to a level position. When everything works right, the contractor's finished surface is a perfect complement to structural deflection.
But buildings come in many shapes and sizes, and as the available materials and floor framing approaches are brought together, unique combinations are created; the resulting floor systems do not always deflect as the engineer expects. That's why the successful contractor must remain flexible and be ready to respond to jobsite developments. Success depends on two things—an effective preconstruction planning program and the ability to identify and adjust to unexpected conditions.
The goal in constructing any project is to meet and to exceed the requirements of the specifications. When evaluating construction of floors, the following standards, depending on the structural system, apply:
- Structural steel must be properly erected.
- Steel connections must conform to the contract document requirements.
- Concrete reinforcement must be placed and maintained in the proper location.
- Concrete mix design, strength, and slump must conform to the specification.
- Finished floor surfaces must meet the specified tolerances for levelness and flatness.
On a major construction site in Plano, Texas, the joint venture HCB/Zachary teamed up with Capform/Dalcan. To meet the challenges of this job, HCB/Zachary used a floor construction monitoring program called Flor-Comp, developed by Structural Services, Inc., of Dallas. Flor-Comp generates reliable information to assist the design/construction team in responding to jobsite developments, thus producing the best possible product for the owner.
The essential elements of Flor-Comp are:
- preconstruction planning and meetings to minimize potential problems
- gathering information during construction to allow evaluation of the work
- responding to unexpected results by adjusting the design or construction
- confirming that the adjustments are successful.
When establishing what systems are needed to achieve the quality standards, the project team first develops a clear understanding of the project and identifies the necessary steps. This starts with a preconstruction conference where the key participants review the requirements of the contract documents, address critical items, and coordinate the quality efforts of all participants.
Controlling the elevation of the supporting platform requires that engineering controls be established. The monitoring program for a structural steel frame provides key information about critical components such as base plate, column splice, and beam-to-column connection elevations, along with deflection of typical framing members.
On a cast-in-place concrete frame, the contractor should select forming and shoring systems and take this plan to the preconstruction conference. Forms and shoring should be designed to allow safe, easy removal, while protecting the structure from excessive deflection at early ages.
Evaluating concrete mix designs, delivery systems, and finishing techniques provides an opportunity to achieve the quality standards. Each decision will impact the flatness and levelness of the finished floor. Concrete mixes must develop adequate strength while providing good consolidation, consistent set time, and workability. Subcontractors selected for the project must be capable of producing work that conforms to the quality standards. Concrete finishing techniques must produce the desired results.
The preconstruction meeting is a good opportunity to address the team's plan for coping with isolated locations where actual deflection of the floor might be different from what is expected. Discussing jobsite controls for structural steel, formwork, reinforcing steel, concrete, and finished surface profiles will help ensure that backup systems are ready. Changes and substitutions in materials or admixtures should not be made without notifying and obtaining approval by the rest of the design/construction team. Use the pre-construction conference to discuss the importance of consistency with the concrete producer, and emphasize the need for uniform materials and batching.