United States Nuclear Regulatory Commission - Protecting People and the Environment

Bulletin 79-02: Pipe Support Base Plate Designs Using Concrete Expansion Anchor Bolts

                               UNITED STATES 
                        NUCLEAR REGULATORY COMMISSION
                    OFFICE OF INSPECTION AND ENFORCEMENT
                           WASHINGTON, D.C. 20555
                                     
                                March 8, 1979

                                                      IE Bulletin No. 79-02 

PIPE SUPPORT BASE PLATE DESIGNS USING CONCRETE EXPANSION ANCHOR BOLTS 
Description of Circumstances: 

While performing inservice inspections during a March-April 1978 refueling 
outage at Millstone Unit 1, structural failures of piping supports for 
safety equipment were observed by the licensee. Subsequent licensee 
inspections of undamaged supports showed a large percentage of the concrete 
anchor bolts were not tightened properly. 

Deficiency reports, in accordance with 10 CFR 50.55(e), filed by Long Island
Lighting Company on Shoreham Unit 1, indicate that design of base plates 
using rigid plate assumptions has resulted in underestimation of loads on 
some anchor bolts. Initial investigation indicated that nearly fifty percent
of the base plates could not be assumed to behave as rigid plates. In 
addition, licensee inspection of anchor bolt installations at Shoreham has 
shown over fifty percent of the bolt installations to be deficient. 

Vendor Inspection Audits by NRC at Architect Engineering firms have shown a 
wide range of design practices and installation procedures which have been 
employed for the use of concrete expansion anchors. The current trends in 
the industry are toward more rigorous controls and verification of the 
installation of the bolts. 

The data available on dynamic testing of the concrete expansion anchors show
fatigue failures can occur at loads substantially below the bolt static 
capacities due to material imperfections or notch type stress risers. The 
data also show low cycle dynamic failures at loads below the bolt static 
capacities due to joint slippage. 

Action to be Taken by Licensees and Permit Holders: 

For pipe support base plates that use concrete expansion anchor bolts in 
Seismic Category I systems as defined by Regulatory Guide 1.29, "Seismic 
Design Classification" Revision 1, dated August 1973 or as defined in the 
applicable FSAR. 

1.   Verify that pipe support base plate flexibility was accounted for in 
     the calculation of anchor bolt loads. In lieu of supporting analysis 
     justifying the assumption of rigidity, the base plates 



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IE Bulletin No. 79-02                                        March 8, 1979 

     should be considered flexible if the unstiffened distance between the 
     member welded to the plate and the edge of the base plate is greater 
     than twice the thickness of the plate. If the base plate is determined 
     to be flexible, then recalculate the bolt loads using an appropriate 
     analysis which will account for the effects of shear - tension 
     interaction, minimum edge distance and proper bolt spacing. This is to 
     be done prior to testing of anchor bolts. These calculated bolt loads 
     are referred to hereafter as the bolt design loads. 

2.   Verify that the concrete expansion anchor bolts have the following 
     minimum factor of safety between the bolt design load and the bolt 
     ultimate capacity determined from static load tests (e.g. anchor bolt 
     manufacturer's) which simulate the actual conditions of installation 
     (i.e., type of concrete and its strength properties): 

     a.   Four - For wedge and sleeve type anchor bolts, 

     b.   Five - For shell type anchor bolts. 

3.   Describe, the design requirements if applicable for anchor bolts to 
     withstand cyclic loads (e.g. seismic loads and high cycle operating 
     loads). 

4.   Verify from, existing QC documentation that design requirements have 
     been met for each anchor bolt in the following areas: 

     (a)  Cyclic loads have been considered (e.g. anchor bolt preload  is 
          equal to or greater than bolt design load). In the case of the 
          shell type, assure that it is not in contact with the back of the 
          support plate prior to preload testing. 

     (b)  Specified design size and type is correctly installed (e.g. proper
          embedment depth). 

     If sufficient documentation does not exist, then initiate a testing 
     program that will assure that minimum design requirements have been met
     with respect to sub-items (a) and (b) above. A sampling technique is 
     acceptable. One acceptable technique is to randomly select and test one
     anchor bolt in each base plate (i.e. some supports may have more than 
     one base plate). The test should provide verification of sub-items (a) 
     and (b) above. If the test fails, all other bolts on that base plate 
     should be similarly tested. In any event, the test program should 
     assure that each Seismic Category 1 system will perform its intended 
     function. 






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IE Bulletin No. 79-02                                        March 8, 1979 

5.   All holders of operating licenses for power reactor facilities are 
     requested to complete items 1 through 4 within 120 days of date of 
     issuance of this Bulletin. A reactor shutdown is not required to be 
     initiated solely for purposes of this inspection above. Maintain 
     documentation of any sampling inspection of anchor bolts required by 
     item 4 on site and available for NRC inspection. Report in writing 
     within 120 days of date of Bulletin issuance, to the Director of the 
     appropriate NRC Regional Office, completion of your verification and 
     describe any discrepancies in meeting items 1 through 4 and, if 
     necessary, your plans and schedule for resolution. For planned action, 
     a final report is to be submitted upon completion of your action. A 
     copy of your report(s) should be sent to the United States Nuclear 
     Regulatory Commission, Office of Inspection and Enforcement, Division 
     of Reactor Operations Inspection, Washington, D.C. 20555. These 
     reporting requirements do not preclude nor substitute for the 
     applicable requirements to report - as set forth in the regulations and 
     license. 

6.   All holders of construction permits for power reactor facilities are 
     requested to complete items 1 though 4 for installed pipe 1 support 
     base plates with concrete anchor bolts within 120 days of date of 
     issuance of this Bulletin. For pipe support base plates which have not 
     yet been installed, document your actions to assure that items 1 though 
     4 will be satisfied. Maintain documentation of these actions on site 
     and available for NRC inspection. Report in writing within 120 days of 
     date of Bulletin issuance, to the Director of the appropriate NRC 
     Regional Office, completion of your review and describe any 
     discrepancies in meeting items 1 though 4 and, if necessary, your plans 
     and schedule for resolution. A copy of your report should be sent to 
     the United States Nuclear Regulatory Commission, Office of Inspection 
     and Enforcement, Division of Reactor Construction Inspection, 
     Washington, D.C. 20555. 

Approved by GAO B180225 (ROO72); clearance expires 7/31/80. Approval was 
given under a blanket clearance specifically for identified generic 
problems. 

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