Influence of cyclic loading on bond condition for post-installed adhesive anchor
Hiroshi Suzuki（Japan Atomic Energy Agency） Tomohisa Mukai（Building Research Instritute）
Takahiko Tanuma（Building Research Institute） Koichi Matsuzawa（Building Research Institute）
1. Introduction
A post-installed adhesive anchor is generally employed for seismic retrofitting and renewal
construction work for reinforced concrete structures. Bond degradation of that may cause serious
accidents involving human lives like “SASAGO tunnel ceiling collapse” occurred in 2012. Therefore,
it is important to investigate the bond strength quantitatively, to establish more reliable
construction quality control of the post-installed adhesive anchor. The bond strength between
adhesive and rebar or between adhesive and concrete may be affected by their bond conditions.
Accordingly, the measurement of the stress distribution along the embedded anchor bar must be
helpful to understand its bond condition. In our previous experiment in 2015A0163, it wasdemonstrated that the neutron diffraction can be a useful technique to measure the stress
distribution of the anchor bar embedded in concrete, and it was found that the stress distribution
along the embedded anchor bar shows different trend depending on the type of adhesive. On theother hand, considering a seismic design using the post-installed adhesive anchor, it is necessary toinvestigate bond degradation due to cyclic loading. In recent the 2016 Kumamoto earthquake, verystrong earthquakes measuring 7 on the intensity scale occurred twice within 2 days, and manybuildings including RC structures damaged by first quake were collapsed at the second strong
quake. Considering this case, therefore, the post-installed adhesive anchor must be designed tokeep stable state against multiple huge earthquakes occurred within a short period. In this study,
therefore, the stress distributions along the embedded anchor bar are measured under cyclicloading using neutron diffraction, and the deterioration mechanism of the bond condition will bediscussed based on results change in the stress distribution.
2. Experiment
Specimen. The cylinder-shaped specimen with 67 mm in diameter and 150 mm in height, coveringwith a steel tube with 3 mm in thickness is prepared. The deformed rebars with a diameter of 10mm was fixed in the anchor hole by injection of epoxy resin or cement adhesive. The specificationsof the samples and the loading histories for each sample are listed in Table 1.
Optical layout. The experiment was conducted using BL19, TAKUMI, in J-PARC MLF. The 5 mmradial collimators are installed, and the incident beam size was set to be 10 mm in width and 10mm in height. The pull-out loadings are applied to the anchor bar, and stress distribution along theembedded anchor bar was measured every loading conditions.
Table 1 The specifications of the samples and the loading histories
SampleLength of
Bonded region

Adhesive

No. 42150 mm

Epoxy

1kN > 17kN > (34kN) > 17kN > (51kN) > 17kN

No. 1850 mm

Epoxy

1kN > 5.6kN > 17kN > 5.6kN

No. 2850 mm

Cement

1kN > 10.7kN

No. 2250 mm

Epoxy acrylate

Loading history
No strain measurement at load in parentheses

1kN > 2.6kN > 8.2kN

13. Results
The result of the No. 42 sample is only discussed in this experimental report. The stress
distributions along the anchor bar from the loading edge of the sample are shown in Fig. 1. This is arelative change in the stress distribution from the initial variation measured under 1 kN of tensileloading. Under applying 17 kN as a long-period loading condition, the stresses gradually decease tozero toward the free edge of the sample at X=150 mm. The plateau region appeared from X= 35 mm
to 55 mm in Fig. 1 might be caused by local bond degradation due to poor filling of the epoxy resin
between rebar and concrete. After unloading to 17 kN from 34 kN as a short-period loading
condition, the stress distribution cannot return to initial variation before applying a short-periodloading. Instead, the stresses increase in the region from X=0 mm to 85 mm probably due to bonddegradation in the corresponding region, and relatively larger bond degradation appears at X=55mm and 85 mm locally. Especially, the local bond degradation at X=55 mm is the result furtherdevelopment of bond degradation appeared under initial loading of 17 kN. After unloading to 17 kN
from 51 kN as an ultimate loading condition, the stresses increase more in the region from X=0 mm
to 105 mm due to homogeneous degradation in the corresponding region.

Fig. 1 Relative stress distribution measured by neutron diffraction.

4. Conclusion
In this experiment, a change in stress distribution of the post-installed adhesive anchor in
response to the cyclic loading was investigated using neutron diffraction. As a result, it was foundthat bond degradation appears in the post-installed adhesive anchor subjected to overloading, andthat the bond degradation develops more after second overloading if it is higher than firstoverloading. In our future work, a long-term durability of the post-installed adhesive anchor undercreep will be investigated by measuring a change in the stress distribution using neutron
diffraction.
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