As governed by multiple-bar bond strength :
h ef , bond , m
= 1 A n A ( 1 . 25 ƒ )
Nao bars b y
ф b
A Na τ k , uncr πd a with minimum c a intended to preclude edge effects .
A In Equations ( 6 ) and ( 7 ),( Nco
· n bars A
A Nc
) and (
Nao
· n bars
) be taken as less than 1.0 .
A Na shall not
Note : Anchorage embedments published in the Hilti North American Product Technical Guide are based on assumptions that are intended to achieve development of 125 % of the nominal yield stress in reinforcing bars . In some cases , the recommended bar embedment exceeds the 20 bar diameter limit established in ACI 318 Chapter 17 for the applicability of the uniform bond model . It is Hilti ' s view that the conservatism of the underlying assumptions , taken in aggregate , is sufficient to offset any reduction in the effective bond stress associated with these bond lengths . The designer may elect to employ alternate design assumptions for bar development based on the specific conditions for a given design .
Edge distance : To account for the effect of edge distance on the concrete resistance , minimum edge distance is calculated as the greater of 10d b
( τ k , uncr
/ 1100 psi ) 0 . 5 and 1.5h ef , breakout
. In addition , for uncracked concrete , the minimum edge distance may be governed by the value of c ac
, the critical edge distance for splitting failure , where the design assumes uncracked concrete and there is no reinforcing to control splitting cracks .
General assumptions : Embedment depths in Tables 91 through 93 and 96 through 98 in Sec . 3.2.3 , and Tables 85 through 87 and 90 through 92 in Sec . 3.2.4 , are predicated on the assumptions that 1 ) edge distances are no less than c Na and c ac as defined by ACI 318 Chapter 17 and AC308 , respectively , 2 ) all bars in the group are loaded equally , 3 ) uncracked concrete conditions apply , 4 ) that orthogonal bars are spaced far enough way to preclude edge and spacing effects , 5 ) bars are NOT subject to sustained tension , and 6 ) that the number of bars in a linear array , n bars
, is equal to 10 .
Note : Tables 91 through 93 and 96 through 98 in Sec . 3.2.3 , and Tables 85 through 87 and 90 through 92 in Sec . 3.2.4 , provide calculated embedment depths , edge distances , and spacing values corresponding to the stated assumptions that are intended to develop 125 % of nominal yield in Grade 60 reinforcing bars under non-earthquake conditions ( i . e ., SDC A and B ). The use of other assumptions ( e . g ., bond values corresponding to cracked concrete or seismic loading , omission of the bar overstrength multiplier , etc .) will result in different embedment depths , spacings , and edge distances that may be appropriate for specific design conditions . Consult Hilti Technical Services for further information . bars in linear 24-inch-on-center array using anchor theory Requirement : Provide post-installed starter bars for a new wall on an existing lightly reinforced slab-on-grade as shown in the figure below installed with HIT-RE 500-V3 . Analysis indicates that there will be no cracking during service loading and no sustained tensile loads on the reinforcing bars .
A-A c a , min
# 5 at 24 in . O . C . ca , min
Section views of wall-to-slab starter bars
h ef
A
A s = 24-in .
Step 1 : Establish requirements for the new bars
( N ) Wall
( E ) Slab
Existing construction ( E ) 12-inch thick foundation , 6000 psi normal weight concrete , Gr . 60 reinforcement .
New construction ( N ) 10-inch wide wall as shown , 5000 psi normal weight concrete , Gr . 60 reinforcement , # 5 bars at 24−inch on-center spacing .
Step 2 : Determine the development length for the wall starter bars using anchor theory
From Table 85 in Sec . 3.2.4 , a # 5 bar with f ' c = 6000 psi produces h ef = 9 inches with c a
≥ 25 inches .
Step 3 : Specification
Gr . 60 # 5 reinforcing bars installed at an 9-inch embedment with Hilti HIT-RE 500 V3 at 24-inch O . C . no less than 25 inches from all edges . Install per Hilti Instructions for Use . Do not damage existing reinforcing . Roughen interface to 1 / 4-inch amplitude prior to placement of post-installed bars .
Note : ACI 318 and ICC Evaluation Service Reports refer to the manufacturer instructions for use as the Manufacturer ’ s Published Installation Instructions ( MPII ).
Design example — development of wall-to-slab starter
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
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