31-03-2014, 04:42 PM
NOTES ON DESIGN OF STEEL PARKING STRUCTURES- INCLUDING SEISMIC EFFECTS
DESIGN OF STEEL PARKING .pdf (Size: 322.24 KB / Downloads: 407)
Introduction
The need for multi-story parking structures has grown considerably over the years and will
continue to grow as metropolitan densities increase. There are several key issues, which need to
be addressed in the design of multi-story parking structures. They are:
Site considerations, environmental and neighborhood impacts and traffic access
Number of parking spaces, car circulations, ramps and other architectural aspects
Security and safety
Structural aspects (particularly in highly seismic areas, seismic design aspects)
Cost and speed of construction
Life cycle cost of maintenance
Fire resistance and/or need for fireproofing.
The first three items in the above list, to great extent, are impacted by the decisions of
architects. Items 4 to 6 in above list, also are impacted by architectural aspects, however, these
three items are primarily impacted by the structural design and decisions made by the structural
engineers. Today, structural steel provides viable systems that address the above key issues. In
the past, a large percentage of parking structures throughout the country were designed and built
using reinforced concrete structures. However, since 1980’
s in many regions of the US including
seismic areas such as California, more and more steel parking structures have been designed and
built. According to Emile Troup (1989), nearly three out of every five car parks for which
contracts were awarded in 1987 in New England were steel. He attributes this increase in use of
steel structures in open parking structures to the fact that as a result of research and testing done
in 1970’
s the issue of fire-proofing of steel structures in car parks was put to rest and the use of
“unprotected steel“ in parking structures was accepted (Troup, 1989). Because of extensive
research and testing of bare steel structures subjected to fire, the fire codes no longer have very
stringent requirement for fire protection of steel car parking structures. This development, along
with education and dissemination of information on viability and economy of using steel structures
in car parking, may have been instrumental in visible increase in design and construction of steel
parking structures.
General Aspects of Design of Parking Structures
Design of car parking involves good combination of information on not only building
design but also bridge design. Like bridges, in many cases, especially in open car parks, there are
very few non-structural elements and the car park building, as a bridge is primarily a bare
structure with minimal mechanical and non-structural elements. According to Emile Troup: “ In
many cases the structure – the deck and frame – is the car park. The concept and design of the
deck and frame will largely determine the success of the facility: its cost and its ability to perform,
relatively problem free, for the design life expectancy. Therefore, it is recommended that the
structural engineer for the car park share the lead role as building designer, in close association
with others charged with developing the optimum parking concept.” The April 2001 issue of the
Modern Steel Construction magazine (MSC, 2001) featured six articles on various aspects of
steel parking structures. In almost all case studies, the prominent role of structural engineer and
the impact of structural engineering decisions on making the projects highly successful are very
clear. The reader is urged to refer to the articles for very useful information and case studies on
efficient design and construction of modern steel parking structures.
Fire Code Requirements
Recent years have witnessed appearance of an increasing number of open-deck, multi-level
parking structures that have unprotected steel framing. This growth of unprotected steel framed
open-deck parking structures is in recognition that fire severity in this type of structure is actually
quite low.
The American Iron and Steel institute (AISI) and the Municipal Parking Congress
conducted research in order to provide a new, statistically reliable basis for evaluating the fire
protection requirements and the insurance rates of parking structures. To accurately document an
actual fire severity and its effects on parking decks, an intensive study was conducted in Scranton,
PA on 15 October 1972. In this study, AISI sponsored a full-scale fire test using a newly erected,
multi-level parking structure. This full-scale fire test was conducted while the facility was in
normal daytime operation.
The principal objective of AISI was to make a comprehensive and totally objective
determination of the effects of a burning auto on bare structural steel framing. During this 50
minute test period the maximum recorded steel temperature on a steel girder, located directly
above the burning auto, was 440°F. Within the same test period, this girder showed a maximum
deflection of 1 5/8” and a maximum elongation of 1/8”. After the completion of the test, both the
deflection and elongation readings returned to zero.