1. Anchor
Channel Systems
2. HAC
Portfolio
3. HAC
Applications
4. Design
Introduction
5. Base material
6. Loading
7. Anchor Channel
Design Code
8. Reinforcing
Bar Anchorage
9. Special Anchor
Channel Design
10. Design
Software
11. Best
Practices
12. Instructions
for Use
13. Field Fixes
14. Design
Example
5.3 CORROSION Galvanic Series of Metals and Alloys
Historically, allowable loads for anchors have been derived by
applying a global safety factor to the average ultimate value of
test results as shown in Eq. (5.2.1). 5.3.1 THE CORROSION PROCESS Corroded End (anodic, or least noble)
F
F all = ___
v (5.2.1)
F = mean ultimate value of test data (population sample)
v = global safety factor
Global safety factors of 3 for cast-in anchor channels have been
industry practice for nearly three decades. The global safety
factor is assumed to cover expected variations in field installation
conditions and in anchor performance from laboratory tests.
5.2.3 STATISTICAL EVALUATION OF DATA
Owen, D.B., (1962) Handbook of Statistical Tables, Section 5.3.
Reading: Addison-Wesley Publishing.
Type 304 Stainless (active)
Type 316 Stainless (active)
Lead tin solders
Lead
Tin
Where:
R k = characteristic resistance of the tested anchor
system 5.3.2.1 DIRECT CHEMICAL ATTACK
F = mean ultimate resistance of the tested anchor
system k = distribution value for test sample size n s = standard deviation of the test data Corrosion by direct chemical attack occurs when the base material is soluble in the
corroding medium. One method of mitigating these effects is to select a fastener that
is not susceptible to attack by the corroding chemical. Compatibility tables of various
chemical compounds with Hilti adhesive and epoxy fastening systems are provided in
this technical guide.
cv = coefficient of variation =
s
F
Thus, test series with low standard deviations are rewarded with
higher 5% fractile characteristic design values. This is typical of
ductile steel failure modes.
When selection of a base metal compatible with the corroding medium is not possible
or economical, another solution is to provide a coating that is resistant to the corroding
medium. This might include metallic coatings such as zinc or organic coatings such as
epoxies or fluorocarbons.
5.3.2.2 ELECTROCHEMICAL CONTACT CORROSION
All metals have an electrical potential relative to each other and are classified
accordingly in the galvanic series of metals and alloys. When metals of different
potential come into contact in the presence of an electrolyte (moisture), the metal with
more negative potential becomes the anode and corrodes, while the other becomes the
cathode and is galvanically protected.
The severity and rate of attack are influenced by:
a. Relative position of the contacting metals in the galvanic series
b. Relative surface areas of the contacting materials
c. Conductivity of the electrolyte
Nickel (active)
Inconel nickel-chromium alloy (active)
Hastelloy Alloy C (active)
Brasses
Copper
Bronzes
Copper-nickel alloys
Monel nickel-copper alloy
Nickel (passive)
Inconel nickel-chromium alloy
(passive)
Silver solder
Chromium-iron (passive)
Type 304 Stainless (passive)
Type 316 Stainless (passive)
Hastelloy Alloy C (passive)
Silver
Titanium
Graphite
Gold
Platinum
Protected End
(cathodic, or most noble)
Source: IFI Fastener Standards, 6th Edition
The 5% fractile characteristic value has been adopted by the
IBC as the basis for determining published design loads based
on anchor testing results for Strength Design. There is a 90%
probability that 95% of the test loads will exceed a 5% fractile
value. The 5% fractile value is calculated by subtracting a certain
number of standard deviations of the test results from the mean
based on the number of trials. See Eq. (5.2.2) and the referenced
statistical table by D. B. Owen. For a series of 5 trials, the 5%
fractile value is calculated by multiplying the standard deviations
by k = 3.401 and subtracting from the mean.
5.3.2 TYPES OF CORROSION
Experience from a large number of tests on anchors has shown
that ultimate loads generally approximate a normal Gaussian
probability density function as shown in Fig. 5.2.1. This allows
for the use of statistical evaluation techniques that relate the
resistance to the system performance variability associated with
a particular anchor.
(5.2.2)
Aluminum 1100
Cadmium
Aluminum 2024-T4
Steel or Iron
Cast Iron
Chromium-iron (active)
Ni-Resist cast iron
Note that global safety factors applied to the mean do not
explicitly account for the coefficient of variation, i.e., all anchors
are considered equal with respect to variability in the test data.
R k = F - k · s = F (1 - k · cv)
Magnesium
Magnesium alloys
Zinc
Where:
Fig. 5.2.1 Frequency distribution of anchor ultimate loads,
demonstrating the significance of the 5% fractile
Corrosion is defined as the chemical or electrochemical reaction between a material,
usually a metal, and its environment that produces a deterioration of the material and
its properties (ASTM G15). The corrosion process can be very complex and have many
contributing factors that lead to immediate or gradual destructive results. In anchorage
and fastener design, the most common types of corrosion are direct chemical attack
and electro-chemical contact.
5.2.2 ALLOWABLE LOADS
The effects of electro-chemical contact corrosion may be mitigated by:
a. Using similar metals close together in the electromotive force series,
b. Separating dissimilar metals with gaskets, plastic washers or paint with low electrical
conductivity. Materials typically used in these applications include:
1. High Density Polyethylene (HDPE)
2. Polytetrafluoroethylene (PTFE)
3. Polycarbonates
4. Neoprene/chloroprene
5. Cold galvanizing compound
6. Bituminous coatings or paint
Note: Specifiers must ensure that these materials are compatible with other anchorage
components in the service environment.
c. S
electing materials so that the fastener is the cathode, the most noble or protected
component
d. Providing drainage or weep holes to prevent entrapment of the electrolyte
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137