3.1.11 DESIGN OF ANCHORS FOR FATIGUE
The design of structural elements to resist fatigue loading can have a significant effect on the connection design . The reader is referred to relevant standards for additional information on this subject . Design of anchors for fatigue should consider the following points :
1 . The application of preload to prevent stress fluctuations in the anchor rod element may be complicated by gradual loss of preload over time , particularly in cases where cracking in the base material may occur , and the fact that many anchor designs do not provide sufficient gauge length to permit the development of a meaningful degree of preload strain .
2 . Design of anchor groups for fatigue is often far more critical than the design of a single anchor due to the unequal distribution of loads . Load distribution is affected by anchor slip as well as by the degree of annular gap between the anchor and the baseplate and the specific location of the anchor with respect to the hole in the baseplate . It is therefore recommended that where anchor groups are to be subjected to significant fatigue loading , the annular gap between the anchors and the baseplate be eliminated through the use of weld washers , grout , or other means .
3 . Secondary flexural stresses as generated by eccentricities or gaps in the connection may be critical to the fatigue behavior of the anchor .
3.1.12 DESIGN OF ANCHORS FOR FIRE
Building codes are generally silent on the need to design anchors specifically for fire conditions . It may be assumed , however , that structural connections to concrete or masonry involving sustained dead and live loads should be protected for fire exposure in the same manner as other structural steel elements , i . e ., through the use of appropriate fireproofing materials , concrete cover , etc .
In some cases , it may be necessary to ascertain the length of time over which unprotected anchorages will survive fire exposure . The design of anchors for fire conditions is predicated on the availability of test data for the performance of anchors subjected to a standardized time-temperature curve ( e . g ., ASTM E 119 , ISO 834 ) while under load .
3.1.13 DESIGN OF POST-INSTALLED REINFORCING BAR CONNECTIONS
Previous to this section , design of post-installed threaded rod and rebar have followed the anchoring provisions of ACI 318 Chapter 17 and CSA A23.3 Annex D . Another common and long-standing application of anchoring adhesives is the installation of deformed reinforcing bars in holes drilled in concrete to emulate the behavior of cast-inplace reinforcing bars .
This section is a supplement to the Hilti North America Post-Installed Reinforcing Bar Guide and is an alternative to considering the post-installed rebar as an " anchor ". Refer to the Guide for a comprehensive description of post-installed reinforcing bar design with Hilti adhesive anchor systems . Contact Hilti Technical Services with questions .
Adhesive anchor systems are qualified in accordance with ICC-ES Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements ( AC308 ). Hilti HIT-RE 500 V3 and HIT-HY 200 V3 adhesives are recognized for use with post-installed reinforcing bars in ICC-ES Evaluation Service Reports ESR-3814 and ESR-4868 . Based on these recognitions , reinforcing bars installed with HIT-RE 500 V3 and HIT-HY 200 V3 may now be designed using two methods :
1 . Development and splice length provisions in ACI 318 ( Chapters 18 and 25 ) and CSA A23.3 ( Chapters 12 and 21 )
2 . Anchoring to concrete provisions in ACI 318 Chapter 17 and CSA A23.3 Annex D .
Within this section , development and splice lengths are provided according to ACI 318 Chapter 25 and CSA A23.3 Chapter 12 calculations ( see item 1 above ). In addition , embedment depths provided for anchorage calculations correspond to development of reinforcing bars following an approach outlined in a paper published in the ACI Structural Journal ( see item 2 above ).
Post-installed reinforcing bar installations in accordance with ACI 318 and CSA A23.3 can also be designed using Hilti ’ s PROFIS Anchor and PROFIS Rebar software . You can access PROFIS Anchor and PROFIS Rebar at www . hilti . com .
DEVELOPMENT AND SPLICING USING ACI 318 CHAPTER 25 PROVISIONS
ACI 318 Chapter 25 contains provisions for reinforcing bar development and splice lengths in non-seismic applications . Development lengths are assumed to preclude concrete
concrete splitting and reinforcing bar pullout failure prior to “ development ” ( attainment ) of bar yield stress . Although the term “ lap splice ” implies direct transfer of stress from bar to bar , forces between bars are transferred via struts and hoop stresses in the concrete . The ICC-ES acceptance criteria for adhesive anchors in concrete , AC308 , now includes procedures and requirements for the recognition of postinstalled designed reinforcing using the development length provisions of ACI 318 Chapters 18 and 25 . Hilti HIT-RE 500 V3 and HIT-HY 200 V3 are recognized in ICC-ES ESR-3814 and ESR-4868 , respectively , for this purpose .
24 Anchor Fastening Technical Guide Edition 22 | 3.0 ANCHORING SYSTEMS | 3.1 ANCHOR PRINCIPLES AND DESIGN Hilti , Inc . 1-800-879-8000 | en español 1-800-879-5000 | www . hilti . com | Hilti ( Canada ) Corporation | www . hilti . ca | 1-800-363-4458