For example, specifying permitted irregularities supports are provided. The formwork should be suitable for more stringent than those allowed for a Class D surface the support of such runways without significant deflections, Table 5. As a matter of prac- 5. Where a particular situation involves several types of generally accepted tolerances on 5.
Shoring fication section. The reversal of bending moments in the slab over the shore or reshore below may 5. If reshores do not align with ACI This Generally, the moment induced by the slab dead loads will section provides a summary of ways of evaluating surface not be reversed by the effect of having the upper shore offset variations due to forming quality but is not intended for eval- in location from the reshore below.
Reshores should be uation of surface defects, such as surface voids bugholes prevented from falling by such means as spring clips at the and blowholes , and honeycomb attributable to placing and top of reshores and positively attaching perimeter reshores consolidation deficiencies. These are more fully explained back into the interior of the structure with appropriate lacing by ACI Allowable irregularities or bracing. The reshoring plan should be submitted to the are designated either abrupt or gradual.
Multi-tier shoring—single-post shoring in two or sheathing, or liners, or from defects in forming materials are more tiers—is a dangerous practice and is not recommended considered abrupt irregularities.
Irregularities resulting from refer to Fig. All members should be straight and true or warped surfaces. In measuring irregularities of plane without twists or bends. Special attention should be given surfaces, the straightedge can be placed anywhere on the to beam and slab construction or one- and two-way joist surface in any direction. Inclined shores should be cate other irregularity limits where needed; or the concrete braced securely against slipping, sliding, or buckling.
The surface tolerances as specified in ACI , 5. Wedges may be cut and installed to achieve , 2. Connections of shore heads to other framing to public view where appearance is of special importance.
Class C is a general standard for permanently exposed 5. Class D is a generally accomplished by the use of sand jacks, jacks, or minimum-quality requirement for surfaces where roughness wedges beneath the supporting members. For the special is not objectionable, usually applied where surfaces will be problems associated with the construction of centering for permanently concealed. Special limits 5. Improper positioning of shore from floor to floor can create bending stresses for which the slab was not designed.
Formwork should be anchored to the shores below so that undesired movement of any part of the formwork system will be prevented during concrete placement. Such anchorages should be installed in such a way as to allow for anticipated take-up, settlement, or deflection of the formwork members. Additional height of formwork should be provided to allow for closure of form joints, settlements of mudsills, shrinkage of lumber, and elastic shortening and dead load deflections of form members.
Where appropriate, the dimen- sional value of the expected shortening effects may be stated in the formwork design drawings.
Positive means of adjustment wedges or jacks should be provided to permit realignment or readjustment of shores if settlement occurs. Adjustment during or after concrete placement should not be performed. This information is useful for the next time the forms are used in sequences of erection and removal of shoring and reshoring a similar configuration.
Formwork should be continuously on the formwork drawings. The strength can be determined Some corrections that may be possible are stopping excess by tests on field-cured specimens or on in-place concrete. It should be clearly sent. The temperature of the concrete while curing, not the stated if a minimum time after placement is a requirement to ambient air temperature, is an important factor in the strength strip forms in addition to the normal minimum compressive gain of concrete.
The curing time and concrete temperature strength requirement. When forms 5. If forms are removed before the specified curing is element. Walls, columns, and beam sides can usually be completed, measures should be taken to continue the curing stripped at fairly low concrete strengths.
Soffits of slabs, and provide adequate thermal protection for the concrete. In no case should supporting forms and shores acceptable methods of determining field strength.
Shores supporting post-tensioned construction tect should be consulted and methods discussed in ACI should not be removed until sufficient tensioning force is should be used for determining appropriate form removal applied to support the dead load, formwork, and anticipated criteria.
The elapsed times shown in Table 5. The times shown represent a cumulative beam sides, and piers can be removed before horizontal number of days, or hours, not necessarily consecutive, during forms for beams and slabs. Conversely, if ambient temperatures remain below 5. Shorter stripping times listed for live load When standard beam or cylinder tests are used to determine to dead load ratios greater than 1.
Table 5. Reshores should be placed as soon as practicable after stripping operations are complete but not later than the end of the working day in which stripping occurs.
Where reshores are required to implement early stripping while minimizing sag or creep rather than for distribution of superimposed construction loads as covered in 5.
Ambient air temperature loads will be distributed among all members connected by is only used in this case to show a minimum ambient air reshores.
Concrete temperature in relation to the removal of forms and shores. Reuse of form inside forms can vary depending on the type of forms used material and shores is an obvious economy. Furthermore, and any methods that are employed to reduce heat loss from the speed of construction in this type of work permits other unformed surfaces, such as the top of a wall or top of a slab.
The shoring that supports freshly ambient air temperature affects concrete strength gain. The loads imposed should not structures exceed the safe capacity of each floor providing support. For This section discusses methods of shoring and reshoring this reason, shoring or reshoring should be provided for a of multistory structures and provides general guidance and sufficient number of floors to distribute the imposed construc- considerations.
ACI Kabaila ; Agarwal and Gardner ; Stivaros and 5. Reshoring is used to distribute construc- inclined support members designed to carry the weight of tion loads to the lower floors. This requires the new slab or construction live loads. The weight of intermediate slabs is structural member to deflect and support its own weight and not included because each slab carries its own weight before existing construction loads applied before the installation of reshores are put in place. It is assumed that the reshores carry no load at Once the tier of reshores in contact with grade has been the time of installation.
Afterward, additional construction removed, the assumption is made that the system of slabs. The slabs interconnected by reshores will shores below, an analysis should be made to determine deflect equally during addition or removal of loads.
Loads whether or not detrimental stresses are produced in the will be distributed among the slabs in proportion to their slab. This condition seldom occurs in reshoring because the developed stiffness. The deflection of concrete slabs can be bending stresses normally caused by the offset reshores are considered elastic, that is, neglecting shrinkage and creep.
Where slabs are designed shoring system is used. Such systems tend to shift most of for light live loads or on long spans where the loads on the the imposed construction loads to the upper floors, which shores are heavy, care should be exercised in placing the have less strength.
Addition or removal of loads may be due shores so that the loads on the shores do not cause excessive to construction activity or to removing shores or reshores in punching shear or bending stress in the slab. Shore loads are determined by equilibrium of While reshoring is under way, no construction loads forces at each floor level.
Slabs are allowed to support their own weight, reducing the When placing reshores, care should be taken not to preload load in the reshores. Combination of shores and reshores the lower floor and not to remove the normal deflection of usually requires fewer levels of interconnected slabs, thus the slab above. The reshore is simply a strut and should freeing more areas for other trades.
The drop-head shore has a head that can be removed until the supported slab or member has attained lowered to remove forming components without removing sufficient strength to support itself and all applied loads. Later Shores should be removed or released before reshore the shore may be retracted and resnugged to act as a reshore.
Premature reshore removal can be dangerous as it It can also be used as a backshore or preshore. Removal opera- 5. Preshores and the The design and placement of shores and reshores for post- panels they support remain in place until the remainder of tensioned construction requires more consideration than for the complete bay has been stripped and backshored, a small normal reinforced concrete.
The stressing of post-tensioning area at a time. These methods are not recommended unless tendons can cause overloads to occur in shores, reshores, or performed under careful supervision by the formwork engi- other temporary supports.
When a slab is post-tensioned, the force in because excessively high slab and shore stresses can develop. The magnitude of the load can approach the Reshoring is one of the most critical operations in form- dead load of half the slab span on both sides of the beam.
Operations or girder shores or reshores will be required. Additionally, should be performed so that areas of new construction will special attention should be given to locations where a post- not be required to support combined dead and construction tensioned beam intersects a post-tensioned girder with no loads in excess of their capacity, as determined by design column at the intersection.
Post-tensioning forces at these load and developed concrete strength at the time of stripping points due to accumulated dead load transfer can be substan- and reshoring. Shores should not be located so as to alter the pattern of Similar load transfer situations occur in post-tensioned stress determined in the structural analysis of the completed bridge construction.
When shores above are not directly over quality required in the finished product. In general, it consists of an inside tect should define their expectations in the contract docu- tensile member and external holding devices. Form ties are ments and reference specific locations where the critical made to a range of specifications, depending on the manu- appearance s applies.
Refer to Chapter 7 for architectural facturer. These manufacturers also publish recommended concrete provisions. Their suggested working loads range from to more than 50, lb 4. Manufacturers produce numerous types of 6. Refer to ACI SP-4 for a describes the formwork materials commonly used in the description of commonly available tie systems. United States and provides extensive related data for form 6. Useful specification and design information is also secure formwork to previously placed concrete of adequate available from manufacturers and suppliers.
Table 6. The devices are normally embedded in a previous indicates specific sources of design and specification data concrete placement or drilled in or fastened to a previous for formwork materials. This tabulated information should concrete placement or other suitable structural member. The not be interpreted to exclude the use of any other materials actual load-carrying capacity of the anchors depends on that can meet quality and safety requirements established for their shape and material, the strength and type of concrete the finished work.
It can be in direct contact tion in the member. When anchoring to other elements, with the concrete or separated from it by a form liner. Manufacturers publish design data tion loads to supporting members, such as joists or studs. They may be fabricated from important considerations include: wire, flat metal pieces, plastic, or combinations of these a Strength materials.
Horizontal e Surface characteristics imparted to the concrete such as reinforcing bar spacers are used as reinforcing bar supports. Consideration tors and abrasion from slipforming should be given to any environmental effects on the rein- h Workability for cutting, drilling, and attaching fasteners forcing bar spacer material, such as corrosion, and visibility i Adaptability to weather and extreme field conditions, on the exposed concrete surface.
Spacers may affect the temperature, and moisture surface finish appearance of the concrete. Removable portions f Cost and durability of all ties should be of a type that can be readily removed g Ability to accommodate required contours and shapes without damage to the concrete and that leaves the smallest practicable holes to be filled.
Removable portions should be. Domes and pans for concrete joist construction Glass fiber-reinforced plastic Hurd , a Custom-made forms for special architectural effects. Form ties Form lining and insulation Cellular plastics ACI SP-4 Stay-in-place wall forms Other plastics, including ABS, poly- Form liners, both rigid and flexible, for decorative concrete propylene, polyethylene, polyvinyl Hurd chloride, polyurethane Chamfer and rustication formers Hold formwork secure against loads and pressures from Form ties, anchors, and hangers Safety factors recommended in 4.
If used as a facing material in contact with fresh concrete, it should be nonreac- tive to concrete or concrete containing calcium chloride. In addition, the handbooks, standards, specifications, and other data sources cited herein are listed in more detail in ACI SP-4 and in the references cited in Chapter 8 and Chapter 10 of this document.
Additional information is available in place. It is that can have a critical influence on formwork for cast-in- important to minimize mortar leakage at form ties. Tilt-up, precast architectural Form hangers should support all construction loads concrete, and concrete receiving coatings or plasters that imposed on the formwork supported by the hangers.
Form hide the surface color and texture are not considered herein. Architectural concrete Where the concrete surface is exposed and appearance should be specifically designated as such in the contract is important, the proper type of form tie or hanger will not documents. Particular care should be taken in the selec- leave exposed metal at the surface.
Noncorrosive materials tion of materials, design, and construction of the formwork, should be used when tie holes are left unpatched, exposing and placing and consolidation of the concrete to eliminate the tie to possible corrosion. The character of the concrete surface to be 6. Special attention should be given to closure facture or in the field to serve one or more of the following techniques, concealment of joints in formwork materials, purposes: and to the sealing of forms to minimize mortar leakage.
They start at the design stage and d Seal the contact surface of the form from intrusion of carry through to the completed project. Factors affecting moisture the surface appearance of the concrete can also include the 6.
They may be applied permanently to certain dure. Chemicals can have an effect on the final product, form materials during manufacture, but are normally applied whether used as additives in the mixture; applied directly to the form before each use. When applying in the field, be to the concrete, such as curing compounds; or applied indi- careful to avoid coating adjacent construction joint surfaces rectly, such as form release agents.
Even after the structure is or reinforcing steel. These and other influencing factors recommendations should be followed in the use of coat- should be identified and their effects evaluated during the ings, sealers, and release agents. Independent verification initial design stages. The single most important factor for of product performance is recommended before use.
When the success of architectural concrete construction is quality concrete surface color is critical, effects of the coating, workmanship. Where 7.
The best way for the contractor to achieve be sure that adhesion of such surface treatments will not this uniformity is to maintain consistency in all construc- be impaired or prevented by use of the coating, sealers, or tion practices.
Forming materials should remain the same release agent. Also, consider bonding requirements of subse- throughout the project, and release agents should be applied quent concrete placements. Follow the manufacturer recom- uniformly and consistently. Placement and consolidation of mendations when applying form release agents. A common the concrete should be standardized so that uniform density problem is applying too much material, which can nega- is achieved.
Stripping and curing sequences should be tively affect the surface of the concrete. The architect can use the latest information available in the zontal long-span member is sagging. The architect should art of forming and concrete technology during the design be aware that horizontal members are checked for compli- process to keep plans in line with the budget for the struc- ance with tolerances and camber before the removal of the ture.
Intricacies and irregularities, however, can raise the forms and shores. Determining the correct amount of camber budget to a point that outweighs the aesthetic contributions is not an exact science. If the calculated camber for a specific of the architectural concrete. The architect can make form member does not result in its deflection to a straight line, the reuse possible by standardizing building elements such as result will be a convex or concave concrete surface.
The increased tion joints, and expansion joints should be shown on the size of these uninterrupted areas will contribute to forming design drawings or the architect should specify a review economy and greater uniformity of appearance.
A prebid of the proposed location of all of these details as shown on conference with qualified contractors will bring out many the formwork drawings. Some guidance on joint locations practical considerations before the design is finalized. Because it 7. Specifying a preconstruction areas on a scale and module suitable to the size of available mockup prepared and finished by the contractor for approval materials and prevailing construction practices.
If this is not by the architect using proposed form materials; jointing tech- aesthetically satisfactory, dummy joints can be introduced niques; and form surface treatments such as wetting, oiling, to give a smaller pattern. Actual joints between sheathing or lacquering should be a requirement for all architectural materials can be masked by means of rustication strips concrete.
Once such a mockup has been completed to the attached to the form face. Rustication strips at horizontal satisfaction of the architect and owner, it should remain at and vertical construction joints can also create crisp edges the site for the duration of the work as a standard with which accented by shadow lines instead of the potential ragged the rest of the work should comply.
Special Design reference samples, which are smaller specimens care should be taken during placement and vibration to mini- of concrete with the proposed surface appearance, may also mize surface voids bugholes and honeycombing that form be created for approval by the architect that can help define when air is trapped beneath horizontal rustications.
Small samples like these, Sometimes construction joints in beams can be concealed kept at the job site for reference, are not as good as a full- above the support columns and joints in floors above their scale mockup, but can be helpful in defining mockup require- supporting beams instead of in the more customary regions.
The samples should be large enough to adequately of low shear in beams and slabs, usually the middle third of represent the surface of the concrete desired. The samples the span. Several 7. It would be helpful for all architectural Architects frequently integrate tie holes into the visual design concrete to include a required mockup so that the contractors quality of the surface. If this is planned and any effects or can demonstrate they are capable of producing the desired materials other than those provided in 7.
The mockup should be approved in writing by the should be clearly specified as to both location and type. Where tie holes are to be patched or filled, the architect It can be helpful to specify viewing conditions under should specify the treatment desired and specify examples which the concrete surfaces will be evaluated for compli- of the patches as part of the mockup. For positive control of required achievable, and economically feasible.
ACI R and cover, the architect can specify appropriate side form spacers may be consulted for further discussions concerning toler- as defined in 6. The architect should specify sufficient cover to allow 7.
The architect should, however, specify as aggregate exposure and tooling. The maximum thickness any additional camber required to compensate for structural of any material to be removed should be added to basic deflection or optical sag the illusion that a perfectly hori- required cover. The other suitable materials can all be used as sheathing or facing same spacers that will be used on the finished work should materials. Select the grade or class of material needed for be incorporated in the mockup.
Be sure that 7. Procedures for controlling the tectural concrete, especially when close to or in contact with rusting of steel forms should be carefully followed. Suitable materials include stainless steel, epoxy- 7. Stainless steel is often the best choice enough to meet the architectural specifications.
It is not required struc- 7. Wood, rigid plastic, elastomeric materials, and glass 7. The carefully detailed and fabricated. Some of these considerations include tie spacing 7. Because these factors can influence form design, they ties and 1 in. The ties should should be fully reviewed at the beginning of the form design not be fitted with lugs, cones, washers, or other devices that process.
Ties should be tight fitting or can be subjected to external vibration, revibration, set tie holes in the form should be sealed to minimize leakage at retarding admixtures, high-range water-reducing admix- the holes. If textured surfaces are to be formed, ties should tures, and slumps greater than those assumed for deter- be carefully evaluated with regard to fit, pattern, mortar mining the lateral pressure as noted in 4.
Particular care leakage, and aesthetics. In ment and vibration. The number and location of the side most cases, deflections govern design rather than bending form spacers should be adequate for job conditions. Deflections of sheathing, studs, A contributing factor to reinforcing spacers being visible and wales should be designed so that the finished surface at exposed concrete surfaces is the amount of load that meets the architectural specifications.
If the reinforcing steel is installed plumb, satisfactory for most architectural formwork refer to ACI straight, and with the correct spacing where it protrudes and ACI R. Forms bow with reuse; therefore, more from previous castings, there should not be an extraordinary bulging will occur in the formed surface after several uses amount of force required between these elements and the of the same form.
This effect should be considered when spacer should be there only to prevent the reinforcing bar designing forms. Given is a chance that the legs of the spacers can leave imprints in the capacity of the available tie and the area it supports, the the sheathing that will result in visible spacers. Where wood forms are used, stress-graded lumber or two-way joist systems in areas that are considered archi- equivalent free of twists and warps should be used for tectural, the architect and engineer should coordinate their structural members.
Form material should be sized and posi- requirements to be sure the architectural effect is consistent tioned to limit deflections within the requirements of the with the forming method and material specified.
Joints of sheathing materials should be Forms that will be reused should be carefully inspected backed with structural members to minimize offsets.
If the holes are to be exposed as part of the archi- unable to perform as designed. If tie holes are not to formwork should be carefully installed to produce neat and be exposed, ties should be located at rustication marks, symmetrical joint patterns, unless otherwise specified.
Joints control joints, or other points where the visual effect will be should be either vertical or horizontal and, where possible, minimized. Look Inside. ACI R. Edition, July Complete Document. Guide to Formwork for Concrete. These items are not eligible for return.
We are unable to find iTunes on your computer. Click I Have iTunes to open it now. Considerations specific to architectural concrete are also outlined in a separate chapter. Separate chapters deal with design, construction, and materials for formwork. The concluding chapter on formwork for special methods of construction includes slipforming, preplaced-aggregate concrete, tremie concrete, precast concrete, and prestressed concrete. Guide to Formed Concrete Surfaces.
Description Objectives of safety, quality, and economy are given priority in these guidelines for formwork. The full and complete returned product will be accepted if returned within 60 days of receipt and in salable condition. What you can do with a Secure PDF: A slip form system is fabricated and mockup test is conducted to verify the performances of the developed techniques through the construction of 10 m-high pylon with a hollow section.
Our policy towards aci guide to formwork for concrete use of cookies Techstreet, a Clarivate Analytics brand, uses cookies to improve your online experience. Visit FileOpen to see the full gide. You can change your cookie settings through your browser. The construction market of super-high-rise buildings and long-span bridges has recognized unprecedented expansion owing to the development of high performance and high strength materials and the advances achieved in the design and construction technologies.
A guide to neuropsychological report writing. In the erection of concrete pylons, slip forming represents the latest method offering the advantage of reducing drastically the construction duration compared to other methods by adopting automated slip-up of the forms and enabling hour continuous placing.
Other sections are devoted to formwork for bridges, shells, mass concrete, and underground work.
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