Section 562 — Temporary Works

Description

562.01This work consists of the design, construction, inspection, maintenance, and removal of temporary works (such as shoring, bracing, cofferdams, falsework, forms, and formwork) for the construction and repair of permanent structures. This work also includes temporary facilities used in construction that do not become part of the perm anent structure.

Material

562.02Select material consistent with the safety and quality required by the design assumptions. Provide factory fabricated components of vertical shoring towers according to FHWA -RD-93-033, Certification Program for Bridge Temporary Works.

Design Requirements

562.03Design. Design temporary works that will support loads imposed and provide the necessary rigidity to produce the lines and grades shown in the plans for the final structure. Design temporary works according to the AASHTO, LRFD Bridge Design Specifications or AASHTO, Guide Design Specifications for Bridge Temporary Works . Ensure the design load on manufactured devices is within the load rating recommended by the manufacturer. Design falsework and forms that support deck slabs and overhangs on girder bridges to ensure no differential settlement between the girders and the deck forms during placement of deck concrete. Limit the calculated deflections of falsework and formwork members for cast- in-place concrete structures as follows:

(a)Falsework member vertical deflection. 1⁄360 of the span under the dead load of the concrete only, regardless of the fact that deflection may be compensated for by camber strips;

(b)Formwork (other than sheathing). 1⁄360 of the span under the dead load of the concrete only or the lateral pressure of fluid concrete only; and

(c)Formwork (sheathing). ⅛ inch or 1⁄270 of the center -to-center distance between studs, joists, form stiffeners, form fasteners, or wales. Design falsework and forms for concrete supported on steel structures to ensure loads are applied to girder webs within 6 inches of a flange or stiffener. Distribute the loads to avoid producing local distortion of the web. 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. Do not use deck overhang form brackets that require holes to be cast or drilled into the bridge girders. Do not apply loads to existing, new, or partially completed structures more than the load carrying capacity of any part of the structure as determined according to AASHTO, LRFD Bridge Design Specifications . 546 Do not use permanent or stay- in-place deck forms.

562.04Drawings. Submit drawings according to Subsection 104.06. Provide design calculations and supporting data in sufficient detail to allow a structural and safety review of the proposed design. Show informat ion to allow the design of components to be checked independently. Provide catalog or equivalent data indicating a manufactured device’s recommended safe load capacity. Indicate the proposed sequence, rate of placement, direction of placement, and location of construction joints when concrete placement is involved. Show anticipated total settlements and deflections of the falsework and forms. Include falsework footing settlements, joint take -up, and deflection of beams or girders. Submit the erection proced ure and temporary support system for girder erection. Include calculations in sufficient detail to substantiate that the girder geometry is correct. Provide supporting calculations showing the falsework design accommodates the erection procedure without overstressing the girder and produces the required final structural geometry, intended continuity, and structural action. Submit foundation design calculations and other relevant foundation design data for approval.

Construction Requirements

562.05Foundations. Determine the allowable bearing capacity of the foundation material that supports the temporary works. Perform load tests to verify proposed bearing capacity values that are in doubt, marginal or in other high -risk situations. Specified foundation support values for the permanent structure may be used in the design of falsework foundations if foundations are at the same elevation and on the same soil as those of the permanent structure. If temporary works are to be supported on temporary fill, construct the fill according to Section 204 and verify the bearing capacity of the placed material. Locate the edge of footings at least 12 inches from the intersection of the bench and the top of the slope. Locate the edg e of the footings at least 48 inches or the depth of excavation, whichever is greater from the edge of excavation, unless shoring adequately supports the footing excavation. Provide adequate site drainage and erosion control protection. If piles are used, capacities may be estimated and later confirmed during construction using standard procedures based on the driving characteristics of the pile. Determine ultimate pile capacity according to Section 551. The Contractor may use load tests to confirm the estimated capacities. Perform load tests to verify proposed bearing capacity values that are in doubt, marginal, or in other high- risk situations.

562.06Construction. Construct temporary works according to the approved drawings and the AASHTO, Construction Handbook for Bridge Temporary Works . Use material and workmanship consistent with that assumed in the approved drawings. Do not weld or use driven devices to fasten temporary works to portions of the permanent structure unle ss shown in the approved drawings. Place form panels for exposed surfaces in uniform widths of at least 36 inches and in uniform lengths of at least 6 feet, except where the width of the member formed is at least 36 inches. 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. Place panels with the long dimension parallel to the footing for walls with sloping footings and that do not abut other walls. Align form panels on each side of the panel joint by supports or fasteners common to both panels. Devices may be cast into the concrete for later use in supporting forms or for lifting precast me mbers. Do not use driven devices for fastening forms or form supports to concrete. Use form ties consisting of form bolts, clamps, or other devices necessary to prevent spreading of the forms during concrete placement. Do not use form ties consisting of tw isted wire loops. Make the angle points for chords in wall stems fall at vertical rustication joints when architectural treatment is required. 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 the following apply:

(a)Chords within the panel are the same length;

(b)Chords do not vary from a true curve by more than ½ inch at any point; and

(c)All panel points are on the true curve. Provide tell -tales with surveyed measurements, or other acceptable means, for accurate measurement of falsework settlement. Do not use the ground surface near falsework supports as a reference elevation. Record settlement to the nearest ⅛ inch during concrete placement. Discontinue concrete placement and take corrective action if settlement or deflections occur that deviate more than ⅜ inch from those shown on the approved drawings. If satisfactory corrective action is not taken before initial set, remove unacceptable concrete.

562.07Maintenance and Inspection . Inspect and maintain temporary works in an acceptable condition. Clearly mark the capacity on each manufactured component according to FHWA- RD-93-033. Perform an in -depth inspection of the temporary works in the presence of the CO no more than 24 hours before starting each concrete placement, or before allowing people to enter a cofferdam or excavation support structure. Perform inspections and provide certifications according to FHWA -RD-93- 033. Submit written results of the inspections before:

(a)Placing concrete;

(b)Allowing people to enter a cofferdam or excavation support structure; or

(c)Loading temporary works. Inspect other temporary works at least once a month to ensure they are functioning properly. Use a professional engineer to inspect cofferdams, shoring, support of excavation structures, and support systems for load tests before loading. For structures that qualify as bridges, perform an initial safety inspection for the temporary bridge structure according to the National Bridge Inspection Standards (NBIS) before opening the bridge to public traffic. Submit the initial bridge inspection report before opening the bridge to public traffic. 548 Perform other safety inspections according to the NBIS. Maintain the in -servic e temporary bridge structure throughout its service life. Submit bridge inspection reports within 7 days after completing the inspection.

562.08Removal. Remove temporary works, except as follows:

(a)Portions of driven falsework piles that are at least 36 inches below subgrade within roadbeds, 24 inches below the original ground or finished grade outside of roadbeds, or 24 inches below the established limits of a navigation channel;

(b)Footing forms where their removal would damage the structural integrity of th e cofferdams or other work; or

(c)Forms from enclosed cells where access is not provided. Remove temporary works to allow the structure to take the stresses of its own dead load uniformly and gradually. Remove temporary works upon completion of the work unless approved to remain. Do not disturb or damage the finished work. Remove debris and restore the area to its original or planned condition. The removed temporary works remain the property of the Contractor. After the concrete has been in place for 24 hours, removal of railing and barrier forms and forms that do not support the dead load of concrete members is allowed. Do not remove forms until the concrete has attain ed at least 500 pounds per square inch strength. Do not damage the surface when removing forms. Cure concrete according to Subsection 552.13 when forms are removed less than 7 days after concrete placement. Do not remove forms supporting the dead load of concrete members until the concrete has attain ed 90 percent of the design compressive strength and has been in place for at least 7 days. Do not remove falsework supporting any span of a simple span bridge until the concrete, excluding concrete above the bridge deck, has attain ed 90 percent of the design compressive strength and has been in-place at least 10 days. Do not remove falsework supporting any span of a continuous or rigid frame bridge until the concr ete in that span and in the adjacent portions of each adjoining span for a length equal to at least one -half of the length of the span where the falsework is to be released meets the requirements for simple span bridges. Do not release falsework for post -tensioned portions of structures until the prestressing steel has been tensioned. Remove falsework for arch bridges uniformly and gradually. Start at the crown and work toward the springing points. Remove falsework for adjacent arch spans simultaneously. Install a reshoring system if falsework supporting the sides of girder stems with slopes steeper than 1V:1H are removed before placing deck slab concrete. Design the reshoring system with lateral supports, which resist 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.

562.09Acceptance. Temporary works will be evaluated under Subsections 106.02, 106.03, and 106.04. Construction of temporary fill will be evaluated under Section 204.

Measurement an d Payment

562.10Do not measure temporary works for payment. See Subsection 109.05.