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AS AN OWNER
or property manager with a parking structure in your facility portfolio,
what can you do to help protect your business from trip and fall hazards on
your deteriorating parking structure stairs? How do you maintain stairs that
are aged and continue to deteriorate no matter what you or your building
engineer does to preserve them?
With a large number of parking structures now 20 or more years old, many
stair towers are in various stages of deterioration. Some of these stairs
present tripping hazards, or are no longer compatible with current building
codes. These problems could potentially be a liability to the owner. This
article will examine some of the common deteriorating stair conditions and
discuss reasons for continued deterioration, facts about repairs and the
service life that can be expected. It will outline an action plan that can
be implemented to address problems and will present a few tips to help limit
trip and fall hazards on existing deteriorated stairs.
METAL PAN/CONCRETE-FILLED STAIRS A
common economical stair design for new construction is metal pan stairs with
concrete infill. The metal framing is sheet steel with thin sections of
concrete placed in the stair treads and landings for the walking surfaces.
These thin sections of concrete (usually less than two inches thick)
typically do not contain any steel reinforcement and are susceptible to
cracking.
DETERIORATION/CORROSION PROCESS Concrete
filled metal pan stairs deteriorate and corrode when concrete sections
placed in shallow areas tend to crack due to shrinkage, thermal movement and
varying load conditions. Once the concrete cracks or shrinks, moisture
penetrates to the metal substrate and is trapped in the pan below. Moisture,
oxygen and unprotected steel, the
three key ingredients for corrosion to take place, are then present in the
metal pan section of the stairs. Additionally, trapped moisture can freeze
and expand in an environment that experiences freeze/thaw thermal cycles,
causing further cracking and damage to the concrete.
Deicer salts applied to the stair also accelerates the corrosion process, so
placing snowmelt on stairs to prevent slips and falls may be increasing trip
and fall potential by accelerating the corrosion process. Once the corrosion
process begins, the steel expands, causing high tensile forces, which crack
the concrete and further accelerate the deterioration process. More severe
conditions occur when sectional loss of steel from the corrosion process
destroys the structural integrity of the metal pan stairs.
PRECAST CONCRETE OR CAST IN PLACE CONCRETE STAIRS
Another type of common stair construction consists of precast or cast in
place concrete treads and risers along with metal railing.
One potential problem is that concrete surfaces are susceptible to moisture
penetration. Once moisture and chlorides penetrate to the reinforcing steel
in the concrete, corrosion of the steel can occur.
Another problem is called scaling concrete, or failure of the cement paste
at the top surface of the concrete. Scaling can be identified by the
characteristic flaking of the top surface of the concrete, which creates
small “pockets” in the surface and exposes the aggregate. Scaling concrete
can potentially impair the serviceability of the walking surface by creating
loose debris, which may potentially cause a trip or slip hazard.
Scaling typically occurs in locations that experience a large number of
freeze/thaw cycles, or by high service use of concrete that is relatively
weak due to poor durability characteristics.
REPAIR OPTIONS AND EXPECTED SERVICE LIFE OF REPAIRS
Now that we know some of the causes of deterioration in concrete and metal
stairs, what can be done to help correct the problems and maintain
serviceable stairs?
A common repair strategy for metal pan stairs with mild corrosion is a
series of restorative steps such as sandblasting, repairing metal, replacing
worn treads or landings and repainting the metal components of the stairs.
Some of the common repairs required in this type of program are as follows:
■
Installation of supplemental steel where
corrosion has deteriorated the steel and
caused cross sectional loss of the steel
pan section, stringer or supports
■
Re-weld failed welds on metal pans, support angles and hand
railings Sandblast and priming of any metal that
exhibits corrosion
or rusting
■
Replacement of concrete in the metal stair pans
■
Painting of all metal sections of the stair tower
These repair methods are
cost effective for a mildly deteriorated stair condition and can usually
extend the service life of the stairs another five to seven years (with
proper maintenance) before replacement or other major repairs are
required.
METAL PAN STAIRS-REPLACEMENT OF TREADS
A common repair strategy for metal pan stairs that have severe
deterioration to the concrete treads and landings, but only mild
corrosion to the metal stringers and framing of the stair tower, is to
keep the existing stringers and framing and replace the stair treads and
risers.
This repair strategy requires the removal of the existing concrete metal
pan stairs and risers and the replacement of treads and landings with
individual precast concrete or galvanized metal treads
risers and landings. Existing metal framing, stringers and hand railings
are utilized and require the installation of supplemental steel,
sandblasting and painting of the existing framing system. Additional
hand railing may be required to satisfy current building codes.
This repair strategy could have a service life of 10-15 years depending
on the overall condition of the existing framing components and whether
the stairs are properly maintained.
METAL PAN STAIRS – REPLACEMENT WITH PRECAST
STAIRS
One strategy for severely corroded and deteriorated stairs is completely
replacing the stairs and framing of the stair tower with precast
concrete stairs and framing. Demolition of the existing stairs and stair
framing system is required and new precast concrete framing members,
stairs, treads, risers and wall panels are installed. Design of this
type of stair replacement could also incorporate enclosing the stair
tower with precast spandrel panels and windows, which would offer a
service life of 25 plus years with proper maintenance.
As with any capital expenditure, a life cycle cost analysis of the
repair options should
be considered for any stair replacement or modification program.
An action plan should include the following:
■
Seek the expertise of a restoration engineering firm that can
evaluate the stair conditions, develop repair
strategies and accurately provide a construction budget
in-line with
the overall goals for the property.
■
Work with the restoration engineering firm and allow them to develop
construction documents for either the repairs or
replacement of the
stairs.
■
Follow through with the construction process on the repair or
construction of the stairs.
■
Implement an annual maintenance program for the future to maintain
the new or repaired stairs to help limit the future
repair costs.
Here are a few tips to
potentially limit trip and fall hazards on existing stairs: Clean all
stairs and landings of trash, debris, sand, dirt or loose impediments,
and inspect all hand railings for loose anchorages.
■
Check all walking surfaces for deteriorated or cracked concrete,
loose stair nosing or any other potential trip hazards.
If any of these
are present, take the necessary measures to implement
temporary
repairs to help limit the trip hazards.
■
Check lighting for proper function and check for dark areas. Replace
burned out bulbs and broken light fixtures
as required.
■
Check hardware and door closures for proper operations if
applicable.
These are just a few
proactive measures to take while assessing the overall condition of
stairs and developing long-term repair strategy.
IN CONCLUSION
We have discussed a few common types of stair construction and some of
the causes of corrosion and deterioration to concrete and metal sections
of the stairs. Once the source of the deterioration is identified,
proactive measures can be taken to either slow the deterioration process
or replace the stairs completely, creating a stair life compatible to
the remaining service life of the parking structure.
While repairs and/or replacement of stairs is a major undertaking,
planning, budgeting and seeking professional assistance throughout the
project can make the experience easier.
fm
Ray Charbonneau is
with Walker Restoration Consultants and may be contacted at (866)
972-2640.
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