Firm offers new approaches that achieve savings for owners.

The success of building projects is often determined by the speed of construction. Since time equals money, innovative designs that reduce construction time offer significant savings.

Weidlinger Associates, a consulting engineering firm that provides total services in structural, transportation, civil engineering and advanced technology throughout the U.S., Europe and Asia, has successfully reduced construction time on numerous projects utilizing the Up/Up method, which permits simultaneous construction of the below grade structure and the superstructure; Tree construction that speeds erection of structural steel by eliminating on-site welding and the Low Floor-to-Floor technique that minimizes story heights thereby adding valuable square footage without exceeding height limitations.

A successful project incorporates the method of construction into the design of the structural systems.

For buildings with basements, a common bottleneck in the schedule is completing below grade construction prior to beginning the superstructure. The Up/Up construction method allows the superstructure to begin immediately after the foundation is in place and does not depend on completing the below grade structure.

The sequence of construction for this method is:

* Excavate the site and install the foundations using conventional construction practices.

* Erect the steel building columns from the foundation level to the ground level and erect the ground level framing.

* Erect the superstructure framing and simultaneously construct the below grade structure

* Install the architectural elements and MEP systems immediately behind the structural systems.

Several weeks or months are saved in the critical path by simultaneously going "up" with the superstructure while working "up" from the foundation level, according to Dr. Kirmani. Since most basement levels are used for parking or mechanical rooms requiring minimal finishes, their construction is taken off the critical path, reducing the risk of project delays.

In conventional construction, the steel moment frame that laterally stabilizes the building is field welded at the time of its erection. To meet building code requirements, the rigid connection welds are tested before superstructure construction can continue. These welds, which must be laid down in several passes must be clear of flaws before they are accepted. Field welding is not well controlled and often requires corrective actions to meet building code criteria. Testing and re-welding can cause delays in the project's completion.

"Tree" construction is designed to eliminate field welding of these frames. As in conventional construction, the rigid joint is made with a full penetration welded connection. The difference is that this difficult and time consuming activity is completed in the fabricator's shop. The "tree" section, which is typically 15 feet and fits on a truck, is then delivered complete to the site and erected and joined to other "trees" with bolted connections.

Shop welding has several direct cost advantages including significant savings on field labor, which is approximately 150% that of shop labor. Also, productivity is better due to better welding access and the work is not weather dependent.

Concrete, which is not cost effective in many areas, has traditionally been used by structural engineers to minimize floor heights. Weidlinger Associates has applied certain techniques to structural steel framing systems to achieve the benefits of low floor to floor heights that make structural steel cost competitive with concrete.

Floor to floor height -- the distance from the top of a floor to the top of the next floor -- consists of three elements: the distance from the top of a floor to the architectural ceiling; the depth of the floor construction; and the 'sandwich' space for various building systems, which include HVAC, electrical, communications, plumbing and fire protection. It is this "sandwich" space where Weidlinger engineers find the greatest opportunity to minimize floor-to-floor heights. Floor to ceiling heights are often not flexible as they relate to building usage and code requirements.

Elimination or reduction of this space requires an understanding of the function of the architectural and MEP elements that compete for the same space as the beams and girders. One obvious method of integrating these elements in the same space is through the use of beam web penetrations which permit ducts and pipes to pass through the beams instead of beneath them.

This beam web penetration, either reinforced or unreinforced is generally expensive, especially if executed in the field. Field rework costs are substantially greater than shop fabrication costs. Weidlinger has achieved optimal results with careful coordination between the structural and mechanical disciplines in the conceptual stage of the project. Understanding how all the systems need to be accommodated within the ceiling space allows the structural engineer an opportunity to play a creative role in integrating beams and girders with the other elements housed within the space. The elements that compete for space in the ceiling include ductwork, piping, conduits and cable trays. Of these elements, the ductwork requires the greatest space and should be coordinated with the structure during the design phase. Beam penetrations should be clearly noted on the contract documents.