Prior to the erection of the
forms for each substructure unit, the Inspector should ensure that the
Contractor is placing the forms in the correct location. This should be accomplished by available methods
that do not require the use of instruments.
Footing concrete may be
placed against rock, hard shale, or sheeting.
All other concrete must be placed in substantial forms that are designed
and constructed so that finished concrete will conform to plan lines and
dimensions and will have a satisfactory surface. Forms for exposed surfaces are to be made of
acceptable materials that will produce a smooth surface with a minimum number
of joints. Acceptable materials include
sheet plywood, fabricated metal forms, fabricated metal frames with plywood
inserts, or dressed lumber of uniform thickness with a form liner of plywood,
hardboard, or sheet metal.
Previously used form lumber
and bent metal forms that will not produce an acceptable surface on concrete
when stripped, regardless of finish specified, are to be rejected. Exercise care to obtain as flush a fit as
possible at panel joints. When
rustication grooves are required, panel joints should, if possible, be made to
coincide.
The underside of a deck that
cantilevers out from the fascia beam is considered an exposed surface and
requires forms with smooth surfaces. The
underside of pier caps is considered an exposed surface and forms with smooth
surfaces should be used and cut to fit neatly around columns or piles.
The inside of all forms are
to be coated with a bond-breaker. If the
forms are not coated, and oiling is necessary, it should be done before placing
the reinforcing steel, or preferably, before assembly of the forms.
Forms must be adequately
braced and provided with walers and form ties that
are properly designed to maintain the proper dimension and alignment for the
proposed height and rate of concrete placement.
Some suppliers of form ties specify the height of concrete in feet
(meters) per hour that can be placed for their design. All form ties and anchor bolts used for form
support must be designed for removal of 2 inches (50 mm) in from the exposed
surfaces of concrete.
When forming pier,
intermediate of end diaphragms for prestressed or
post tensioned concrete members, care must be taken to avoid damaging
reinforcing steel, strands, or precast concrete. The Contractor should not
place post installed anchors in these members. They should properly brace
diaphragm forms externally or use approved form tie inserts cast into these
members.
Moldings for the 3/4-inch (19
mm) beveled edges and rustification grooves must be
surfaced on all sides and be of uniform section. The bevel strip should be nailed at sufficient
intervals to completely fill a corner or contact the form for the
full-length. Rustification
strips are fastened to the forms in such a manner that the molding will remain
in contact with the concrete when the forms are stripped and will not be removed
until the concrete has set sufficiently to avoid damage.
Weep holes through abutments
and retaining walls are formed in such a manner as to obtain a smooth, circular
opening. To form the hole, metal such as
downspouts or sonotube may be used and later removed,
or noncorrodible rigid plastic pipe may be used and
left in place, provided the gradient and inside diameter are in accordance with
508.03.
All scrap wood, dirt, and
other foreign material, including ponded water, must be removed from within the
forms prior to placing concrete. If the
forms are too deep or narrow to permit easy removal of foreign material from
the top, a temporary opening should be left at the bottom for removal of
foreign material. When necessary, an
opening must be provided for inspection.
Temporary openings must be made mortar tight after the forms have been
cleaned and inspected.
Forms should be inspected for
proper fit and for holes where leakage of cement paste may occur. Openings must be corrected in order to close
the hole and provide a smooth form surface.
Filler strips, plugs, and tin are commonly used to plug such
openings. Forms should be watched
closely during the placing of the concrete and any leaks must be corrected
immediately.
Before any concrete is
placed, form dimensions should be measured for compliance with the plan
requirements and approved change orders.
Measurements which result in concrete equal to or greater than plan
dimensions are considered verified plan dimensions. The measurements must be checked for
compliance with the plan dimensions and then recorded and filed in the project
records. A statement that the dimensions
have been checked and are in compliance with plan requirements is not
acceptable verification. The recording
may consist of any of the three following methods:
1. A tabulation of all the verified plan dimensions for
simple shapes.
2. A sketch on an appropriate form showing all the
verified plan dimensions.
3. The plan sheet for the structure unit with the verified
dimensions checked thereon.
Whatever method is used, the
Inspector should date and sign the sheet.
If checks are made on different days, dates should indicate the day each
check was made. If different inspectors
check parts of the measurements, each should initial those checks that he has
made.
If measurements are not in
compliance, make correction and recheck the dimensions before the concrete may
be placed.
Falsework is the system of temporary support of formwork for
concrete members. The falsework is to remain in place until the concrete members
have attained required strength and are self-supporting. This includes the system of supporting
formwork for deck slabs and pier caps.
For cast-in-place concrete
slab bridges, the Contractor must submit a falsework
working drawing per 501.05.B.3. No superstructure concrete can be placed
until the working drawing is received and the falsework
conforms to the submitted working drawings. The Contractor may substitute
elements of equal or greater strength if it does not involve a change in depth
that effects elevations. Any other
deviations from the accepted working drawing that the Contractor desires, or
that becomes necessary due to unforeseen conditions, must be covered by
submission of a revised working drawing.
Although ODOTs
acceptance of falsework working drawings is not
required, a review should be made at the project to ascertain that the existing
conditions shown in the working drawing are representative of those found in
the field. The absence of Department acceptance does not supersede the
Engineer’s authority as defined in 105.01.
The maximum deflection
permitted in the falsework of a slab bridge is
specified in 508.02. Camber equal to this deflection must be built
into the falsework to compensate for falsework deflection.
Camber equal to 1/800 of the span must be built into the falsework to compensate for deflection of the slab after falsework is released.
Also, camber which conforms to the vertical curvature of the profile
grade must be provided.
If unusual requirements for
span of an existing road or channel or restrictions due to vertical clearance
exist, contact the Office of Structural Engineering to evaluate acceptable site
specific camber requirements.
Falsework members must be of the section and length shown on
the submitted working drawings. Members
having a greater section modulus may be used; however, if this involved a
change in depth and affects elevations, details of modifications should be
included on a resubmission of the affected working drawing.
Steel members such as
stringers must be in good condition.
They must not show loss of section through rusting, excessive weldments, or holes that would affect their strength.
Timber shall be sound and of
the required size. Used timber that shows deterioration and stress cracks may
not perform its function and must not be used.
Piling must be driven to the
bearing called for on the submitted plans.
In order to determine the required blow count, it will be necessary for
the Contractor to perform dynamic load testing.
Allowance for consolidation
of wood wedges and blocking must be provided.
Using rough-cut timber, an allowance of 1/16 inch (2 mm) for each
contact surface will be necessary.
Where phased construction or
adjacent concrete decks are separated by an open joint or closure pour, forms
for the cantilevered edges of each slab must be supported independently from
the adjacent structure. This is
necessary to avoid movement of the forms due to differential deflections during
placing of the concrete.
The finishing machine must be
supported by the structure on which the concrete is being placed and
independent of any adjacent structure or support. If it is not, the finishing machine will not
move with the deck as the concrete is placed and can result in areas where the
superstructure concrete is either too thick or too thin.
Closure pours are normally
specified during phased construction when the cross bracing or diaphragms
between the phases are not in place prior to the placement of the
superstructure concrete. A closure pour
is not to eliminate traffic vibration, but to allow differential deflection to
take place between the phases when the superstructure concrete is placed. In order to properly place the superstructure
concrete, the closure pour should not be waived unless the deadload
deflection that occurs when the superstructure concrete is placed is less than
1/4 inch.
Prior to placing sidewalks,
safety curbs, or other superimposed concrete on the deck of a slab bridge, the falsework must be removed or released and allowed to
deflect.
For QC/QA Concrete, falsework may be removed when the conditions tabulated in
the table of section 511.14-1A
of the Construction and Material Specifications have been met. If QC/QA is not
being used, falsework may be removed when the
conditions tabulated in the table of section 511.14-1B
have been met. Any piling not removed
must be cut off at least to the slope line or rip rap line of the bed of
stream.
1. Received falsework working
drawings submitted per 501.05.B.3
for slab deck bridges.
2. Falsework constructed according to submitted drawings.
3. Document bearing obtained and number of falsework piling.
4. Number and size of bracing on falsework.
5. Protection during cold weather.
6. Forms oiled prior to steel placement.