COMMONLY
ASKED
QUESTIONS
|
Information taken from the
award-winning program Conceptual Selection Process: Guide and Workbook from Alfred Benesch
& Company. Awarded at the 26th Annual Engineering Excellence Awards Program 1997 by
the Consulting Engineers Council of Illinois |
 |
CONCRETE REINFORCING
STEEL INSTITUTE
ECONOMIC BUILDING
SYSTEMS
This is the first issue of a new publication
addressing questions commonly asked by engineers, architects, owners, developers and
contractors. This issue addresses reinforced concrete building systems and discusses
questions often brought up in the very early or conceptual stage of building design. The
answers contained herein were taken from an award-winning program developed by Alfred
Benesch & Company of Chicago, Illinois. A Value Engineering Study of the
"Conceptual Selection Process" led to the establishment of a clear and precise
process to identify all the pertinent and important factors to consider in building
design, and then to weigh those factors against project criteria to evaluate and select
the optimal design for the building owners.
What are the best building framing
systems for ease of construction and economy?
Flat plate and flat slab systems are the most economical
building systems because they provide the shortest floor-to-floor heights, and they have
simple and fast construction. They offer the following features:
• Can be constructed in the shortest time with
the least field labor.
• Utilizes the simplest formwork and reinforcing
steel layout.
• Provides flexibility in layout of columns,
partitions, openings, etc.
• Allows direct application of ceiling finish
resulting in cost and time savings.
How does floor-to-floor height affect
building costs?
Floor-to-floor height consists of the floor-to-ceiling height, the
depth of the framing system and space for utilities. Elements related to building height
that affect cost are building envelope, columns, walls, fire proofing and vertical runs of
the utilities. By limiting the depth of the framing system, economy can be achieved. Lower
height means lower cost. Generally, the reinforced concrete flat plate and flat slab
systems require half the structural depth of beam and slab structures. With proper
planning of utility placement, the two systems will offer economical design. This was
demonstrated in the Key Center at Fountain Plaza project in Buffalo, NY.
The project architect/engineer stated,
"After the construction manager performed comparative pricing, it was determined that
up to $1.5 million would be saved by using cast-in-place concrete versus steel frame. The
flat slab system offered potential for lower floor-to-floor heights, which reduced the
cost of all vertical elements (exterior walls, staircases, elevators, mechanical systems)
while allowing for unobstructed ceiling space to run mechanical and electrical
distribution systems."
How does a flat plate differ from a
flat slab?
The two-way flat slab system is very similar to the two-way flat plate
system. Flat slabs require drop panels at columns to support heavier loading. In some
applications the flat slab system can use less concrete and reinforcement than a flat
plate system. Buildings that best utilize the flat plate system are hotels, condominiums
and apartments. It is usually recommended for light to moderate loading. Economical spans
range up to 35 feet. In addition to these building types, flat slabs can be economically
used for offices, warehouses, industrial plants and other buildings with moderate to heavy
loads. Spans can economically range up to 40 feet.
ENGINEERING
INFORMATION PROGRAM-JUNE 1997 |
