Curing-Curing is important in achieving satisfactory results in any grout

installation. Normally this is accomplished by placing water-saturated rags over all exposed grout surfaces as soon as possible after grout placement.

These rags should be maintained wet and in place for at least 24 hr after which the exposed surface of the grout is coated with a curing compound if secondary grouting will not follow. Where secondary grouting is to follow, continue the water curing for 7 days, or until placement of the second grout. Proprietary grouts should be cured according to the manufacturer’s recommendations.

5.7 -Field problems

5.7.1 Cast-in-Place Systems-The c o m m o n problem encountered in the preconcreting stage is interference with existing reinforcement. In this case a decision has to be made whether to move the anchorage or move the reinforcement. In weighing the consequences of each, the Field Engineer, perhaps after consulting the Engineer-of-Record, establishes which has priority.

Another common problem is to discover, after the concrete has hardened, that the anchorage has shifted during the placement of the concrete, and that the base plate will not fit in place, or that there is insufficient thread projecting to fully engage the nut. These problems can and should be avoided by proper inspection, or by use of sleeved or adjustable anchors. The specifications should cover these possibilities, and state that it is the contractor’s responsibility to take necessary precautions and corrective measures. Actions taken when field errors are discovered should have the approval of the Engineer-of-Record.

Bending of protruding bolts is discouraged because the bending stress which results from the eccentricity of the service load, when added to the design axial and shear stresses, can often exceed the yield strength of the bolt. In welding to compensate for insufficient thread being engaged by the nut, care should be taken that the weld acting alone will develop the strength of the bolt, because the capacity of the welds and the engaged threads are not additive. When any embedded anchor is not installed within allowable tolerances, the structural adequacy of the installation should

be verified by the Engineer-of-Record and, if necessary, the design should be modified.

The single most helpful practice for avoiding the problem of cast-in-place anchor bolts not fitting the base plates is to make holes in column and machinery base plates oversize, and then grout the annular space after the base plate is in place, or use specially designed washers. The following schedule of oversize holes is recommended.

- Bolts less than 1 in. diameter - 5/16 in.

oversize

- Bolts 1 to 2 in. diameter - l/2 in. oversize - Bolts over 2 in. diameter - 1 in. oversize 5.7.2 Post-installed systems-A common field problem in post-installed systems is interference with the in-place reinforcement. The location of that reinforcement can be determined magnetically or radiographically. Sometimes, it is simply discovered when the drill bit, drilling the hole, hits steel. When an anchorage interferes with any in-place reinforcement, the Engineer-of-Record should decide on the remedy. Wherever possible, the anchorage itself should be shifted to a new location where there is no interference. Moment reinforcement should never be welded or cut.

W i t h d u e c o n s i d e r a t i o n , t e m p e r a t u r e reinforcement can be cut.

A second problem is excessive slip in pretensioning the bolt. This can be indicative of an oversized hole or a faulty anchoring device.

When excessive slip occurs, the assembly should be reinstalled in the hole and the pretensioning applied such that the slip does not exceed the allowable limit (i.e., resulting embedment is adequate). Sometimes the entire anchor will have to be replaced, or possibly the hole drilled to a larger size and the next larger sized anchor installed.

CHAPTER 6-REQUIREMENTS IN EXISTING CODES AND SPECIFICATIONS

6.1 -Introduction

Sources of information relating to codes and specifications on anchorage to concrete are presented in this section. Sources are referenced in alphabetical order. American and international documents are included in this state-of-the-art review.

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6.2 -Existing codes and specifications 6.2.1 American Association of State Highway Transportation Officials (AASHTO)

6.2.1.1 Standard Specification for Highway Bridges -For composite bridge decks, AASHTO uses the ultimate capacity of stud shear connectors and a reduction factor of 0.85 for design.

Design checks are required for horizontal shear under working loads. Working loads are compared to allowable loads which include a reduction for fatigue.

AASHTO Section 1.7.56 bases the number, required embedment, and size of anchor bolt on the span of the bridge, and requires that the anchor bolt be swedged or threaded to insure a satisfactory grip on material such as the grout.

AASHTO requires that anchor bolts subject to tension be designed to engage a mass of concrete which will provide a resistance equal to one and one-half times the calculated uplift.

6.2.2 American Concrete Institute (ACI) 6.2.2.1 ACI 318, Building Code Requirements for Reinforced Concrete - ACI 318-63 contained allowable bond values for plain (smooth) bars.

Many engineers have used these values for determining embedment requirements for cast-in-place anchor bolts. The current edition of ACI 318 does not give allowable bond values for plain or deformed bars. Section 12.6.1 states “Any mechanical device capable of developing the strength of reinforcement without damage to concrete may be used as anchorage.” Section 15.8.3.3 of ACI 318 states “Anchor bolts and mechanical connectors shall be designed to reach their design strength prior to anchorage failure or failure of surrounding concrete.”

6.2.2.2 ACI 349, Code Requirements for N u c l e a r S a f e t y R e l a t e d C o n c r e t e Structures-Appendix B of ACI 349 gives comprehensive procedures for designing anchorages and steel embedments that are used to transmit loads from attachments to reinforced concrete structures governed by ACI 349. The basic philosophy of anchorage requirements in ACI 349 is consistent with the ultimate strength design philosophy of reinforced concrete. The failure mechanism is controlled by requiring yielding of the steel anchor prior to brittle failure of the concrete.

This design method considers not only traditional design parameters, i.e., steel strength, concrete strength, and anchor size, but also other

variables such as anchor type or form, spacing, edge distance, nature of the anchor load, thickness of the concrete member, and concrete stress in the anchor zone. Concrete strength is critical to assure that the reinforced concrete structure exhibits ductile failure, which is also an ACI 318 requirement. Note, however, that many of the post-installed systems feature the brittle concrete-cone failure.

The commentary of ACI 349, Appendix B, provides an excellent source of information on types of anchorage devices, design requirements, modes of failure, and testing.

6.2.3 American Institute of Steel Construction (AISC)

6.2.3.1 Manual of Steel Construction -The AISC “Specification for the Design, Fabrication, and Erection of Structural Steel for Buildings” sets allowable bolt stresses in Sections 1.5.2 and 1.6.3.

These values apply to certain cast-in-place and grouted anchor bolts and are valid for allowable anchor steel stresses, but no values are given which relate to the transfer of these stresses to the surrounding concrete.

The AISC specification gives allowable values in shear for stud shear connectors used for composite design in Table 1.11-4. The listed values cannot be used for anchor bolts of the same size. The values used in Table 1.11-4 are based on equations derived from a testing program and the ultimate strength of the composite member, using a factor of safety of 2.0.

The AISC code commentary contains the following warning:

“The values of q in Table 1.11-4 must not be confused with shear connection values suitable for use when the required number is measured by the parameter where V is the total shear at any given cross-section. Such a misuse could result in providing less than half the number required by Formulas 1.11-3, 1.11-4, or 1.11-5.”

The AISC specification also gives setting tolerances for bolts used to anchor structural members; however, these tolerances are unsuitable for anchoring machinery.

6.2.4 American Society for Testing and Materials (ASTM)

6.2.4.1 Annual Book of Standards - Volume 04.07 contains test standard ASTM E 488,

“Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements.” This test standard describes procedures for determining the

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static, dynamic, and fatigue tensile and shear strengths of cast-in-place, chemical, grouted, and expansion anchors.

Volume 15.08, Fasteners, contains various ASTM specifications for the steel used for bolts, including A 193, A 307, A 325, A 449, and A 490.

6.2.5 Construction Industry Research and Information Association (CIRA) (Great Britain).

6.2.5.1 Section and Use of Fixings in Concrete and Masonry (Guide 4) - CIRA Guide 4, is a comprehensive guide on the selection and use of anchors installed in concrete. Three main categories of anchor types are covered. These include cast-in-place, expansion, and bonded anchors. The guide also covers behavior of fastener assemblies under load, design considerations, limitations, durability, testing, and practical considerations.

6.2.6 Institut Bautechnik (IfBT)(West Germany)

6.2.6.1 Tests to Evaluate the Strength of Metallic Expansion Bolts for Anchorage in Concrete with an of 20 MPa (2500 psi) or Greater-Approvals are based on results of tests carried out by licensed universities.

In the tests the proper functioning of the anchors under extreme conditions are checked, and tests to evaluate allowable loads for design are performed.

For evaluating allowable conditions of use (e.g., allowable loads, required edge distance, and spacing), a sufficient number of tests have to be performed to calculate a statistically reliable confidence level for the failure loads [5 percent fractile (or 95 percentile) of failure loads]. A safety factor of 3 is applied to the determined 5 percent fractile of the failure loads to account for the variations of the concrete tensile strength and of jobsite installation quality. For reasons of simplicity, one value for the allowable load is given per anchor size which is valid for all loading directions (tension, shear, combined tension, and shear). Expected displacements of anchors under allowable loads are given which should be taken into account in the design of the fastened element (when appropriate).

6.2.7 International Conference of Building Officials (ICBO)

6.2.7.1 U n i f o r m B u i l d i n g C o d e ( 1 9 8 5 Edition) -The Uniform Building Code (UBC), Table 26-G sets forth allowable shear and tension loads for cast-in-place bolts of at least ASTM A

307 quality or better.

The table assumes an anchor spacing of 12 anchor diameters. The spacing may be reduced down to 6 anchor diameters with a 50 percent reduction in allowable load values. A minimum edge distance of 6 anchor diameters is required.

Edge distance may also be reduced up to 50 percent, provided that the listed values are reduced in equal proportion. Tension values listed in the table may be increased 100 percent when

“special inspection” is provided. UBC Section 2719, on anchor bolts for steel column bases, does not provide design values for anchor bolts, but simply states that “Anchor bolts shall be designed to provide resistance to all conditions of tension and shear at the bases of columns.” The section on steel column anchorage does not refer to Table No. 26-G. Application of this table to steel column anchorage would greatly affect current design practice because of the requirement in Table No. 26-G of a minimum spacing of 6 anchor diameters.

6.2.8 Precast/Prestressed Concrete Institute (PCI) 6.2.8.1 PCI Design Handbook-The handbook gives equations for shear and tension load allowables for headed shear stud anchors.

Combined loading, as well as required edge distances and anchor spacing for groups of anchors, are covered.

Based on a review of past design methods and actual testing and modeling, the PCI Connection Details Committee recommends the use of a projected cone model to define the actual bolt tension at which concrete failure will occur. The PCI cone surface equation is:

= 2.8 + (6.1) where

= 1.0 for normal weight concrete

= 0.85 for sand lightweight concrete

= 0.75 for all lightweight concrete embedment, in.

= diameter of anchor or stud head, in.

= specified 28-day compressive strength of concrete, psi

P_IlC = nominal tensile capacity of anchor as governed by concrete failure In anchor bolt design where the concrete does not fail, the anchor bolt fails via a combination of tension and shear. The PCI equation for

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combined tension and shear strength is:

where

= strength reduction factor

= applied factored tension load P =nominal tension strength of

anchor

= applied factored shear load = nominal shear strength of anchor

as governed by steel failure In-depth discussions of these equations may be found in Klingner and Mendonca (1982) and Shaikh and Yi (1985).

6.2.9 The Board (Great Britain) 6.2.9.1 The Assessment of Torque-Expanded Anchor Bolts When Used in Dense Aggregate Concrete (M.O.A. T. No. 19:1981) -This document presents the procedures for deriving design information and classifies ten different types of expansion anchors according to the mechanism for achieving expansion. It considers the effects of different types of loading conditions and typically requires a minimum of 277 tests (for six different anchor diameters) to calculate safe working loads as the lower of:

a. The 5 percent exclusion value (or 95th percentile, calculated by regression analysis or other statistical techniques), then divided by three or,

b. The mean of the loads determined at a displacement of 0.1 mm (0.004 in.) under direct tension or,

c. The mean of the loads determined at a displacement of 1.0 mm (0.039 in.) under direct shear.

6.2.10 UEAtc (Union European of

The UEAtc Directives for the Assessment of Anchor Bolts (December, 1986) is a European code for the assessment and approval of anchor bolts. The document has been adopted by the Common Market Countries of Germany, U.K., France, Austria, Italy, Spain, Ireland, Netherlands, Portugal, Denmark, and Belgium.

6.2.11 Nuclear Regulatory Commission (NRC) Bulletin 79-02 and 79-14).

Anchor bolt design methods have been revised based on the United States NRC Office of Inspection and Enforcement Bulletins No. 79-02

and 79-14. Only Class I piping (piping used to safely shut down a nuclear power plant) was impacted by Bulletins 79-02 and 79-14. The NRC requires that during anchor bolt design, the following must be considered: baseplate flexibility, (i.e., baseplate prying action that increases anchor bolt loading), performance of anchors due to cyclic loading, anchor performance in masonry walls, the effect of pipe support loads on masonry walls, and the maximum support load considered for anchor bolt design. Concrete expansion anchors must have the following minimum factor of safety between the bolt design load and the bolt ultimate capacity determined from static load tests, (e.g., published data from the anchor bolt manufacturer) which simulate the installation conditions, (i.e., type of concrete and its strength properties): (1) a safety factor of 4:1 - for wedge-and sleeve-type anchor bolts, (2) a safety factor of 5:l - for shell-type anchor bolts.

The bolt ultimate capacity should account for the effects of shear and tension interaction, minimum edge distance, and proper bolt spacing.

A summary of the USNRC criteria is found in USNRC “Anchor Bolt Study Data Survey and Dynamic Testing” by the Hanford Engineering Development Laboratory.

6.2.12 Draft 1 Regulatory Guide MS 129-4

“Anchoring Component and Structural Supports in Concrete”

This draft guide from the U.S. Nuclear Regulatory Commission provides the criteria for acceptance, qualification, design, installation, and inspection for steel embedments anchored in concrete. It also provides information on the acceptability for NRC licensing actions in accordance with Appendix B, of ACI 349-80.

6.3 -Application and development of codes ASTM E 488 is the only existing American standard exclusively and specifically concerned with testing to determine the performance of all types of concrete anchors. It is not intended to describe design procedures for anchorage connections, nor to identify characteristics which affect performance in conditions other than as-tested. ICBO has also published a limited test standard for expansion anchors only.

ACI 349, Appendix B, specifies anchorage design and applies ultimate strength design philosophy to all types of anchorages. Other American codes limit their consideration to

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in-place or grouted anchorages. The Uniform Building Code (UBC) allows for alternative devices as specified in the code, generally applying the same conditions as specified for cast-in-place anchors.

American codes generally base recommended design procedures on ultimate strength data.

European codes recommend the criterion of displacement (slip) for post-concreting anchors, supported by ultimate strength data derived by regression analysis of other statistically reliable techniques.

Codes cannot address all the conditions applicable to a particular design or absolve the designer of the responsibility to check the relevance of code data for a given design. New and technically reliable information will inevitably be developed between publication dates of amendments to existing codes. Designers are encouraged to maintain familiarity with ongoing research and other developments and to supplement the provisions of governing codes with such information as it becomes available.

6.4 - References

ACI Committee 318,1989, “Building Code Requirements for Reinforced Concrete (ACI 318-89) and Commentary - ACI 318R-89, American Concrete Institute, Detroit, MI, November.

ACI Committee 349, 1990, “Code Requirements for Nuclear Safety Related Concrete Structures (ACI 349-90) and Commentary - ACI 349R-90, American Concrete Institute, Detroit, MI, March.

Fasteners. 1988 Annual Book of Standards, Volume 15.08, American Society for Testing and Materials, Philadelphia, PA, January, 1988.

Klingner, R.E. and Mendonca, J.A., (1982a) “Tensile Capacity of Short anchor Bolts and Welded Studs: A Literature Review,” ACI Journal, Proceedings, V. 79, No. 1, July-August.

Manual of Steel Construction. Eight Edition, American Institute of Steel Construction, Inc., New York, NY, 1980.

Paterson, W.S., “Selection and Use of Fixings in Concrete and Masonry”, CIRA Guide 4, Construction Industry Research and Information Association, London, England, October, 1977.

PCI Design Handbook, Third Edition, Prestressed Concrete Institute, Chicago, IL, 1980.

zur Beurteilung d e r v o n zwangsweise s p r e i z e n d e n aus MetaIl nach d e r Verankerung in Normalbeton Bn 250” (Tests to Evaluate the Load Capacity of Metal Expansion Anchors Fastened into Normal Concrete, Bn250), Institute for Construction (IfBT), Berlin, West Germany, January 1974.

Shaikh, A.P., Yi, W., “In-Place Strength of Welded Headed Studs,” PCI Journal, V.30, No. 2, March-April, 1985.

“Standard Specification for Highway Bridges”, Twelfth Edition, American Association of State Highway Transportation Officials, 1977.

“Standard Test Methods for Strength of Anchors in Concrete and Masonry Elements”, (ASTM E488-88), 1988 Annual Book of ASTM Standards, Volume 04.07, American Society for Testing and Materials, Philadelphia, PA, October, 1988.

“The Assessment of Torque-Expanded Anchor Bolts when used in Dense Aggregate Concrete”, M.O.A.T. No. 19:1981,

Board, Watford, Herts., England, January, 1981.

“UEAtc directives for the Assessment of Anchor Bolts”, M.O.A.T. No. 42:1986, European Union of

December, 1986.

Uniform Building Code, International Conference of Building Officials, Whittier, CA. 1985.

USNRC “Anchor Bolt Study Data Survey and Dynamic Testing”, Hanford Engineering Development Laboratory, NUREG/CR-2999, December, 1982.

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APPENDIX A-CONVERSION FACTORS: = number of anchors

355.1R-71

= distance between center of anchors

= summation of projected areas of individual stress cones,

= net bearing area of head of embedded anchorage, in.’

= net bearing area of head of embedded anchorage, in.’

In document ACI 355.1R.pdf (Page 66-71)