Item 414 – Forms and Falseworks
414.1 Description
This item shall consist of designing, constructing and removing forms and
falsework to temporarily support concrete, girders and other structural
elements until the structure is completed to the point it can support
itself.
414.2. Material Requirements
414.2.1 Formwork
The materials used for smooth form finish shall be plywood, tempered
concrete-form-grade hardboard, metal, plastic, paper or other acceptable
materials capable of producing the desired finish for form-facing
materials. Form-facing materials with raised grain, torn surfaces, word
edges, patches, dents, or other defects that will impair the texture of
concrete surfaces shall not be permitted, No form-facing material shall be
specified for rough form finish.
414.2.1.1 Formwork Accessories
Formwork accessories that are partially or wholly embedded on concrete,
including ties and hangers shall be commercially manufactured. The use of
non fabricated wire form ties shall not be permitted. Where indicated in
the Contract, use form ties with integral water barrier plates in walls.
414.2.1.2 Formwork Release Agents
Commercially manufactured formwork release agents shall be used to prevent
formwork absorption of moisture, prevent bond with concrete, and not stain
the concrete surfaces.
414.2.2 Falsework
The materials used in the falsework construction shall be of the quantity
and quality necessary to withstand the stresses imposed; it may be time or
steel or a combination of both. The workmanship shall be of such quality
that the falsework will support the loads imposed on it without excessive
settlement or take-up beyond as shown on the falsework drawings.
414.3 Construction Requirements
Falsework and Formworks design and drawings shall be in accordance, with
Item 407, Concrete Structures, Subsection 407.3.9 and 407.3.12,
respectively.
414.3.1.1 Formwork and Falsework Drawings
When complete details for forms and falseworks are not shown, prepare and
submit drawings to the Engineer showing the following:
1. Details for construction safe and adequate forms and falsework that
provide the necessary rigidity, support the loads imposed and produce in
the finished structure the required lines and grades. See subsection
414.3.1.2 for design loads. See Subsection 414.3.1.3 for design stresses,
loadings and deflections. See Subsection 414.3.2 for manufactured
assemblies.
2. The maximum applied structural load on the foundation material. Include
a drainage plan or description of how foundations will be protected from
saturation, erosion and/or scour see Subsection 414.3.3.1.
3. The description of all proposed material. Describe the material that is
not describable by standard nomenclature (such as AASHTO or ASTM specified)
based on manufacturer’s test recommended working loads. Provide evaluation
data for falsework material showing that the physical properties and
conditions of the material can support the loads assumed in the design.
4. The design calculations and material specification showing that the
proposed system will support the imposed concrete pressures and other
loads. Provide an outline of the proposed concrete placement operation
listing the equipment, labor and procedures to be used for the duration of
each operation. A superstructure placing diagram showing the concrete
placing sequence and construction joint locations is included.
5. Design calculations for proposed bridge falsework. A registered
professional engineer proficient in structural design shall design, sign
and seal the drawings. The falsework design calculations shall show the
stresses and deflections in load supporting members.
6. Anticipated total settlements of falsework and forms shall be shown.
Include falsework footing settlement and joint take-up. Design for
anticipated settlements not to exceed 20 millimeters. Design and detail on
falsework supporting deck slabs and overhangs on girder bridges so that
there will be no differential settlement between the girders and the deck
forms during placement of deck concrete. Design and construct the falsework
to elevations that include anticipated settlement during concrete placement
and required camber to compensate for member deflections during
construction.
7. Support system for form panels supporting concrete deck slabs and
overhangs on girder bridges.
8. Details for strengthening and protecting falsework over or adjacent to
roadways and railroads during each phase of erection and removal. See
Subsection 414.3.3.2.
9. Intended steel erection procedures with calculations in sufficient
detail to substantiate that the girder geometry will be correct. See
Subsection 414.3.3.3.
Details of proposed anchorage and ties for void forms shall be submitted.
See Subsection 414.3.4 for void form requirements.
Separate Falsework drawings for each structure shall be submitted to the
Engineer for approval, except for identical structures with identical
falsework design and details.
414.3.1.2 Design Loads for Forms and Falsework
414.3.1.21 Vertical Design Loads
Dead loads include the mass of concrete, reinforcing steel, forms and
falsework. Consider the entire superstructure, or any concrete mass being
supported by falsework to be a fluid dead load with no ability to support
itself. If the concrete is to be prestressed, design the falsework to
support any increase or readjusted loads caused by the prestressing forces.
The assumed density of concrete, reinforcing steel, and forms shall be not
less than 2600 kilograms per cubic meter for lightweight concrete.
Consider live loads to be actual mass of equipment to be supported by
falsework applied as concentrated loads at the point of contact plus a
uniform load of not less than 1000 Pascals applied over the area supported,
plus 1100 Newtons per meter applied at the outside edge of the deck
falsework overhangs.
The total vertical design load for falsework shall be the sum of vertical
dead and live loads. The total vertical design load used shall be not less
than 4800 Pascals.
414.3.1.2.2 Horizontal Design Loads
Use an assumed horizontal design load on falsework towers, bents frames and
other falsework and other falsework structures to verify lateral stability.
The assumed horizontal load is the sum of the actual horizontal loads due
to equipment construction sequence, or other causes and an allowance for
wind. However, in no case is the assumed horizontal load shall be less than
2 percent of the total supported dead load at the location under
consideration.
The minimum wind allowance for each heavy-duty steel shoring having a
vertical load carrying capacity exceeding 130 kilograms per leg is the sum
of the products of the wind impact area, shape factor and the applicable
wind pressure value for each height zone. The wind impact area is the total
projected area of all elements in the tower face normal to the applied
wind. Assume the shape factor for heavy duty shoring to be 2.2. Determine
wind pressure value from Table 1.
Table 1
Design Wind Pressure-Heavy Duty Steel Shoring
Height Zone Above Ground Meter
|
Wind Pressure Value-Pa
|
|
Adjacent Traffic
|
At Other Locations
|
|
0
9-15
15-30
Over 30
|
960
1200
1450
1675
|
720
960
1200
1450
|
The minimum wind allowance on all other types of falsework, including
falsework supported on heavy-duty shoring, is the sum of the products of
the wind impact area and the applicable wind pressure value for each height
zone. The wind impact area is the gross projected area of the falsework and
understrained portion of the permanent structure, excluding the areas
between falsework posts or towers where diagonal bracing is not used. Used
design wind pressures from Table 2.
Table 2
Design Wind Pressure-Other Types of Falsework
Height Zone Above Ground Meter
|
Wind Pressure Value-Pa
|
|
For Members Over and Bents Adjacent to Traffic Openings
|
At Other Locations
|
|
0
9-15
15-30
Over 30
|
320 Q
400 Q
480 Q
560 Q
|
240 Q
320 Q
400 Q
480 Q
|
Note: Q = 0.3+0.2W, but not more than 3. W is the width
of the falsework system in meters measure in the direction of the wind
force being considered.
414.3.1.2.3 Lateral Fluid Pressure
For concrete with retarding admixture, fly ash or other pozzolan
replacement for cement, design form, form ties and bracing for a lateral
fluid pressure based on concrete with a density of 2400 kilograms per cubic
meter. For concrete containing no pozzolans or admixtures, which affect the
time to initial set, the lateral fluid pressure shall be determined based
on concrete temperature and rate of placement according to ACI Standard
347R, Guide for Formwork for Concrete.
414.3.13 Design Stresses, Loads and Deflections for Forms and Falsework
The allowable maximum design stresses and loads listed in the section are
based on the use of undamaged high-quality material. If lesser quality
material is used, reduce the allowable stresses and loads. The following
maximum stresses, loads and deflections in the falsework design shall not
be exceeded.
414.3.1.3.1 For Timber
Compression perpendicular to the grain = 3100 kilopascals
Compression parallel to the grain (1) = 3009 megapascals
(L/d)2
Note: (1) Not to exceed 11 megapascals
Where:
L
= Unsupported length
d
= Least dimension of a square or rectangular column or the width of a
square of equivalent cross-sectional area for round columns
Flexural stress = 12.4 megapascals
Note: Reduced to 10 megapascals for members with a nominal depth of 200
millimeters or less
Horizontal shear = 1300 kilopascals
Axial tension = 8.3 megapascals
Defelction due to the mass of concrete may not exceed 1500 of the span even
if the deflection is compensated for by camber strips
Modulus of elasticity (E) for timber = 11.7 gigapascals
Maximum axial loading on timber piles = 400 kilonewtons
414.3.1.3.2 For Steel
For identified grades of steel the design stresses (other than stresses due
to flexural compression) specified in the Manual of Steel Construction as
published by the AISC shall not be exceeded.
When the grade of steel cannot be positively identified, the design
stresses other than stresses due to flexural compression shall not be
exceeded, either specified in the AISC Manual or ASTM A 36M structural
steel or the following:
Tension, axial and flexural = 150 megapscals
Compression, axial = 110 000 – 2.6(L/r)2 kilopascals
Note: L/r shall not exceed 120
Shear on the web gross section of rolled shapes = 100 megapascals
Web crippling for rolled shapes = 185 megapascals
For all grades of steel, do not exceed the following design stresses and
deflection:
Compression flexural(1) = 82 750 megapascals
(Ld/bt)
Note: (1) Note exceed 150 megapascals for unidentified steel or steel
conforming to ASTM A 36. Not to exceed 0.6 Fy for other
identified steel.
Where:
L
= Unsupported length
d
= Least dimension of a square or rectangular column or the width of a
square of equivalent cross-sectional area for round columns or the depth of
beams
b
= Width of the compression flange
t
= Thickness of the compression flange
r
= Radius of gyration of the member
Fy
= Specified minimum yield stress for the grade of steel used
Deflection due to the mass of concrete may not exceed 1/500 of the span
even if the deflection is compensated for by camber strips.
Modulus of Elasticity (E) for steel = 210 gigapascals
414.3.1.3.3 Other Requirements
Limit falsework spans supporting T-beam girder bridges to 4.3 meters plus
8.5 times the overall depth of T-beam girder.
414.3.2 Manufactured Assemblies
For jacks, brackets, columns, joist and other manufactured devices the
ultimate load carrying capacity of the assembly shall not exceed the
manufacturer's recommendations or 40 percent based on the manufacturer's
tests or additional tests ordered. The maximum allowable dead load
deflection of joists shall be 1 /500 of their spans.
Catalog or equivalent data shall be submitted to the Engineer showing the
manufacturer's recommendations or perform tests as necessary to demonstrate
the adequacy of any manufactured device proposed for use. No substitution
is allowed on manufacturer’s components unless the manufacturer's data
encompasses such substitutions or field tests reaffirm the integrity of the
system.
If a component of the falsework system consists of a steel frame tower
exceeding 2 or more levels high, the differential leg loading within the
steel tower unit shall not exceed 4 to 1. An exception may be approved if
the manufacturer of the steel frame certifies, based on manufacturer's
tests, that the proposed differential loadings are not detrimental to the
safe load carrying capacity of the steel frame.
414.3.3 Falsework Construction
The falsework construction shall be in accordance whenever applicable with
Item 407 Concrete Structures Subsection 407 .3.10 Falsework Construction.
414.3.3.1 Falsework Foundations
All ground elevations at proposed foundation location shall be verified
before design.
Where spread footing type foundation are used, determine the bearing
capacity of the soil. The maximum allowable bearing capacity for foundation
material, other than rock, is 190 kilo Pascals.
The edge of footing shall not be located closer than 300 millimeters from
the intersection of the bench and the top of the slope. Unless excavation
for footings is adequately supported by shoring, the edge of the footings
shall not be closer than 1.2 meters of the depth of excavation, whichever
is greater, from the edge of the excavation.
When falsework is supported by footings placed on paved, well-compacted
slopes of berm fills, do not strut the falsework to columns unless the
column is founded on rock or supported by piling.
The spread footings to support the footing design load at the assumed
bearing capacity of the soil shall be designed without exceeding
anticipated settlements. Steel reinforcement shall be provided in concrete
footings.
When individual steel towers have a maximum leg loads exceeding 130
kilonewtons, uniform settlement under all legs or each tower under all
loading conditions shall be provided.
Protect the foundation from adverse effects for the duration of its use.
414.3.3.2 Falsework Over or Adjacent to Roadways and Railroads
Falsework shall be designed and constructed with protection from vehicle
impact. This includes falsework posts that support members crossing over a
roadway or railroad and other falsework posts if they are located in the
row of falsework posts nearest to the roadway or railroad and if the
horizontal distance from the traffic side of the falsework to the edge of
pavement or to a point 3 meters from the centerline of track is less than
the total height of the falsework.
Additional features shall be provided to ensure that this falsework will
remain stable if subjected to impact by vehicles. Use vertical design loads
for these falsework posts, columns, and towers (but not footings) that are
greater than or equal to either of the following:
1. 150 percent of the design load calculated according to Subsection
414.3.1.2 but not including any increased or readjusted loads caused by
prestressing forces.
2. The increased or readjusted loads caused by prestressing forces.
Temporary traffic barriers shall be installed before erecting falsework
towers or columns adjacent to an open public roadway. Barries shall be
located so that falsework footings or pile caps are at least 75 millimeters
clear of concrete traffic barriers and all other falsework members are at
least 300 mm clear. Do not remove barriers until approved.
Use falsework columns that are steel with a minimum section modulus about
each axis of 156,000 cubic millimeters or sound timbers with a minimum
section modulus about each axis of 4,100,000 cubic millimeters.
Mechanically connect the base of each column or tower frame supporting
falsework over or immediately adjacent to an open public road to its
supporting footing or provide other lateral restraint to withstand a force
of not less than 9 kiloNewtons applied to the base of the column in any
direction. Mechanically connect such columns or frames to the falsework cap
or stringer to resist a horizontal force of not less than 4.5 kiloNewtons
in any direction. Neglect the effects of frictional resistance.
Brace or tie exterior girders, upon which overhanging bridge deck falsework
brackets are hung, to the adjacent interior girders as necessary to prevent
rotation of exterior girders or overstressing the exterior girder web.
Mechanically connect all exterior falsework stringers and stringers
adjacent to the end of discontinuous caps, the stringer or stringers over
points of minimum vertical clearance and every fifth remaining stringer to
the falsework cap or framing. Provide mechanical connections capable of
resisting load in any direction, including uplift on the stringer, if not
less than 2.2 kiloNewtons. Connections shall be installed before traffic is
allowed to pass beneath the span.
16 millimeters diameter or larger bolts to connect timber members shall be
used to brace falsework bents located adjacent to roadways or railroads.
Sheath falsework bents within 6 meters of the centerline of a railroad
track solid in the area between 1 and 5 meters above the track on the side
facing the track. Construct sheathing of plywood not less than 16
millimeters thick or lumber not less than 25 millimeters nominal thickness.
Adequate bracing shall be provided on such bents so that the bent resists
the required assumed horizontal load or 22 kiloNewtons, whichever is
greater, without the aid of sheathing.
Provide at least the minimum required vertical and horizontal clearances
through falsework for roadways, railroads, pedestrians and boats.
414.3.3.3 Falsework for Steel Structures
Falsework design loads shall consist of the mass of structural steel, the
load of supported erection equipment, and' all other supported by the
falsework.
Falsework and forms for concrete supported on steel structure shall be
designed so that loads are applied to girder webs within 150 millimeters of
flange or stiffener. Distribute the loads in a manner that does not produce
local distortion of the web. Do not use deck overhang forms that require
holes to be drilled into the girder webs.
Strut and tie exterior girders supporting overhanging deck falsework
brackets to adjacent interior girders to prevent distortion and
overstressing of the exterior girder web.
Do not apply loads to existing, new or partially completed structures that
exceed the load carrying capacity of any part of the structure according to
the load factor design methods of the AASHTO Bridge Design Specifications
using load group IB.
Build supporting falsework that will accommodate the proposed method of
erection without overstressing the structural steel, as required and will
produce the required final structural geometry, intended continuity and
structural action.
414.3.4 Forms
The forms construction shall be in accordance whenever applicable, with
Item 407, Concrete Structures Subsection 407 .3.13, Formwork Construction.
Form panels to be used shall be in good condition free of defects on
exposed surfaces. If form panel material other than plywood is used, it
shall have flexural strength, modulus of elasticity and other physical
properties equal to or greater than the physical properties for the type of
plywood specified.
Furnish and place form panels for exposed surfaces in uniform widths of not
less than 1 meter and in uniform lengths of not less than 2 meters except
where the width of the member formed is less than 1 meter.
Arrange panels in symmetrical patterns conforming to the general lines of
the structure. Place panels for vertical surfaces with the long dimension
horizontal and with horizontal joints level and continuous. For walls with
sloping footings which do not about other walls, panels may be placed with
the long dimension parallel to the footing.
Form panels shall be precisely aligned .on each side of the panel joint by
means of supports or fasteners common to both panels.
Use form ties and anchors that can be removed without damaging the concrete
surface. Construct metal ties or anchorages within the forms to permit
their removal to a depth of at least 25 millimeters from the face without
damage to the concrete. Fill cavities with cement mortar and finish to a
sound, smooth, uniform colored surface.
Support roadway slab forms of box girder type structures on wales or
similar supports fastened, as nearly as possible, to the top of the web
walls.
Form exposed curved surfaces to follow the shape of the curve, except on
retaining walls that follow a horizontal curve. The wall stems may be a
series of short chords if all of the following apply:
1. Chords within the panel are the same length.
2. Chords do not vary from a true curve by more than 15 millimeters at any
point.
3. All panel points are on the true curve.
When architectural treatment is required, make the angle points for chords
in wall stems fall at vertical rustication joints.
Earth cuts as forms for vertical or sloping surfaces shall not be used
unless otherwise required or permitted by the Contract.
414.3.4.1 Stay in Place Deck Forms
Use permanent or stay inplace forms only when permitted by the contract.
Fabricate permanent steel bridge deck forms and supports from steel
conforming to ASTM A 653M coating designation 2600, any grade except grade
340 class 3.
Install forms according to accepted fabrication and erection drawings. Do
not rest form sheets directly on the top of stringer or floor beam flanges.
Securely fasten sheets to form supports. Place from supports in direct
contact with the stringer flange or floor beam. Make all attachments with
permissible welds, bolts or clips. Do not weld from supports to flanges of
steels not considered weldable or to portions of flanges subject to tensile
stresses.
Clean with wire brush and paint 2 coats of zinc dust zinc-oxide primer (FSS
TT-P-641 type II no color added) any permanently exposed form metal where
the galvanized coating has been damaged. Minor heat discoloration in areas
of welds need not be touched up.
Locate transverse construction joints in slabs at the bottom of a flute.
Field drill 6 millimeter diameter weep holes at not less than 300
millimeters on center along the line of the joint.
414.3.4.2 Void Forms
Store void forms in a dry location to prevent distortion. Secure the forms
using anchors and ties which leave a minimum of metal or other supporting
material exposed at the bottom of finished slab.
Make the outside surface of the forms waterproof. Cover the ends with
waterproof mortar tight caps. Use premolded 6 millimeters thick rubber
joint filler around the perimeter of the caps to permit expansion.
Provide a PVC vent near each void form. Construct vents so the vent tube
shall not extend more than 13 millimeters below the bottom surface of the
finished concrete after form removal. Protect void from the weather until
concrete is placed.
414.3.4.3 Metal Forms
The specification for forms relative to design, mortar tightness, filleted
corners, beveled projection, bracing, alignment, removal, reuse and oiling
also apply to metal forms.
414.3.5 Removal of Forms and Falsework
The removal of forms and falsework shall be in accordance whenever
applicable, with Item 407 Concrete Structures, Subsection 407.3.11 Removing
Falsework and Subsection 407.3.14 Removal of Forms and Falsework.
Where necessary remove all forms except the following:
1. Interior soffit forms for roadway deck slabs of cast-in-place box
girders.
2. Forms for the interior voids of precast members
3. Forms for abutments or piers when no permanent access is available into
the cells or voids.
Install a reshoring system if falsework supporting the sides of girders
stems with slopes steeper than 1: 1 are removed before placing deck slab
concrete. Design the reshoring system with lateral supports which resist
all rotational forces acting on the stem, including those caused by the
placement of deck slab concrete. Install the lateral supports immediately
after each form panel is removed and before release of supports for the
adjacent form panel.
414.3.6 Acceptance
Forms and falsework (including design, construction, and removal) shall be
evaluated and approved by the Engineer.
When the falsework installation is complete and before concrete placement
or removal begins, the falsework shall be inspected by the Engineer. The
Engineer shall certify in writing that the installation conforms to the
contract, the approved falsework drawings (including approved changes) and
acceptable engineering practices.
414.4 Method of Measurement
When the Contract stipulates that payment will be made for forms and
falsework on lump-sum basis, the Pay Item will include all materials and
accessories needed in the work.
Whenever the Bill of Quantities does not contain an item for form and
falsework, the work will not be paid directly but will be considered as a
subsidiary obligation of the contractor under other Contract Items.
414.5 Basis of Payment
The accepted quantities measured as prescribe in Subsection 414.4, shall be
paid for at the Contract lump-sum price for Forms and Falsework which price
and payment shall be full compensation for designing, constructing and
removing forms and falsework, all materials and accessories needed and for
furnishing all labor equipment tools and incidentals necessary to complete
the item.
Payment will be made under:
Pay Item Number
|
Description
|
Unit of Measurement
|
414
|
Forms and Falsework
|
Lump Sum
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