review of the failed e2 embedded anchor rod...

D R A F T R E P O R T

Review of the Failed E2 Embedded

Anchor Rod Boroscope Investigation

Rev. 3: April 17, 2014

For:

San Francisco-Oakland Bay Bridge (SFOBB)

SAS Pier E2 Anchor Bolts Study

By:

Bay Area Management Consultants (BAMC) for the Bay Area Toll

Authority (BATA) Oakland Bay Bridge

SAS pier E2 Anchor Bolts Study

By the Bay Area Management Consultants (BAMC) For the Bay Area Toll

Report Background

Bay Area Management Consultants (BAMC):

BAMC is a joint venture of URS Corporation and Hatch Mott MacDonald (HMM) Corporations.

BAMC was retained by BATA (Bay Area Toll Authority) to provide program management oversight

services for the State of California’s Toll Bridge Seismic Retrofit Program. BAMC was selected

through a public competitively based Request for Proposal (RFP) process in 2005 pursuant to services

required by the 2005 California Law AB144. In the performance of those services, BAMC was

requested by BATA to conduct a review of the Caltrans boroscope investigation which focused on all

the boroscope videos taken of the anchor rods that had been installed in 2008, specifically, the E2

S1/S2 rods that failed in March of 2013 on the San Francisco-Oakland Bay Bridge’s Self-Anchored

Suspension span.

The following report summarizes the findings of the review and observations from the boroscope

videos taken by Jason Gramlick of Caltrans during March 2013.

Authors:

Alan Cavendish-Tribe, Hatch Mott MacDonald

Stephen Christoffersen, URS Corporation

Contributors:

Ted S Hall - Hatch Mott MacDonald

Alan Cavendish-Tribe - Hatch Mott MacDonald

Steven Matty - URS Corporation

Stephen Christoffersen - URS Corporation

Dr. Jeff Gorman - Dominion Engineering, Inc. (sub-consultant to BAMC)

Mark Lisin - Lisin Metallurgical Services (sub-consultant to BAMC)

Melissa Pedersen - Hatch Mott MacDonald

Cover Photograph:

The cover photo is of the fractured surfaces of two of the nine failed rod ends recovered from the shear

keys S1 & S2 ducts for testing and analysis. The S2-H6 exhibit on the right demonstrates a 360 degree

uniform exposure to hydrogen embrittlement and axisymmetric loading. Whereas S2-A8 fracture

displays a local exposure to hydrogen embrittlement (100 degree), which may be due to the initial

localized stress corrosion crack dominating the fracture or possible asymmetric loading.

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TABLE OF CONTENTS

1. Introduction ..................................................................................................................................... 1

2. Background ..................................................................................................................................... 2

3. Inspection Results .......................................................................................................................... 4

4. Discussion ...................................................................................................................................... 7

5. Conclusion .................................................................................................................................... 11

6. Appendices ................................................................................................................................... 13

6.1 Boroscope Photographs

6.2 Lisin Metallurgical Services Report

6.3 Dr. J. Gorman Paper

6.4 Cover of Caltrans "Rainwater Chronology in the S1/S2 Shear Key GR 354BD Anchor Rods"

List of Tables:

Table 1: S1 and S2 Fractured Anchor Rod Summary .................................................................... 3 Table 2: Boroscope Test Results/Physical Observations ................................................................ 6

Table 3: Water Test ......................................................................................................................... 8

List of Figures:

Figure 1: Embedded Anchor Rods .................................................................................................. 1

Figure 2: S1 and S2 Anchor Rod Layout ........................................................................................ 2 Figure 3: Top Hat Detail ................................................................................................................. 5

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Review of the Boroscope Investigation for the Failed E2 Embedded Anchor Rods

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1. Introduction

In March 2013, 32 of the 96 San Francisco-Oakland Bay Bridge’s (SFOBB) Self-

Anchored Suspension span’s (SAS) S1 & S2 shear key anchor rods failed near the

bottom nut within days after being tensioned to 0.75Fu and seated at .70Fu

(Fu=140ksi). The rods fabricated during 2008 in accordance with ASTM A-354 BD ,

were 3-inch diameter, 9 or 17-feet in length, and hot-dipped galvanized. The rods were

assembled in 2008 into 7-inch diameter pipe sleeves. These were grouted five years

later on January 22nd-24th 2013. Tensioning was done on March 2nd 2013. Nine (9) of

the 32 failed rods were extracted from their sleeves in order to assess the possible cause

of failure. Once these rods were removed, boroscope examinations were successfully

performed down the length of four rod cavities and recorded by video. Two of the four

revealed sections of the fractured rod had dropped further into the top-hat cavity and

were submerged in water. The area of the entombed, severed end of the rods was the

primary focus of this review. This report describes the results of the boroscope

examination as well as a discussion of other relevant findings and observations noted as

the review proceeded.

Figure 1: Embedded Anchor Rods

Figure 1 displays the embedded anchor rods in yellow securing shear key S2 to the

cross beam of pier E2. The inset photo (bottom left) was taken in 2008 during the

installation of the anchor rod / pipe sleeve assemblies prior to the concrete being poured

for the pier E2 cross beam.

By design, the Pier E2 shear keys and bearings require high strength anchor rods to

have a minimum ultimate tensile strength (UTS) of 140 ksi and when installed a

preload of 70% UTS. This combination of highly stressed high strength rods makes

these susceptible to Stress Corrosion and therefore appropriate protection is necessary.

Shear Key S2.

7” Diameter Pipe

Sleeves

Bearing Plate

Top Hat Section


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2. Background

On March 8, 2013, several days after being tensioned, the nuts on nine shear key rods

were observed to be ‘lifted’ approximately 2 inches off the top of the base plate of

shear keys S1 and S2. Within the next four days, another 20 nuts were found in a

similar condition. The decision was made to reduce the tension on the remaining rods

to 0.45Fu. During that process three more rods failed, bringing a total of 32 broken

anchor rods. Figure 2 identifies which rods failed and their location (layout). Table 1

shows what dates the broken rods were found and their respective lengths and shear key

(summary).

Figure 2: S1 and S2 Anchor Rod Layout


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Date of Discovery # of Failures by Location Total # of Failures by Date

S1 Shear Keys S2 Shear Keys

9 Feet 1.5 Inches 17 Feet 2.125 Inches

9 Feet 1.5 Inches

17 Feet 2.125 Inches

3/8/2013 0 B7, G1, G2, H7 B4, B6 A6, H6, H8 9

3/9/2013 B4 C8, E7 0 H3 4

3/11/2013 0 A6, A8, B3, C1, E8, H2

0 A2, G1 8

3/12/2013 H4 H3 0 0 2

3/13/2013 0 A1, A7, G7, H1 H4 A3 6

3/14/2013 0 A2, B2 0 0 2*

3/15/2013 0 0 0 A8 1*

Total Failures by Location

2 19 3 8 32

Notes:

1. There are 2 different length rods-9'1.5" and 17'2.125"

2. *=failed when jacking to reduce load from .7Fu to .45Fu

3. Shear keys 3 & 4 and Bearing Rods were not tensioned at this time

4. 9 Rods were removed for examination

5. 4 Rod cavities were examined by video boroscope

6. March 10, 2013 was a Sunday and may be why no report of a failure

7. S2-A8 is location of water sample

Table 1 - S1 and S2 Fractured Anchor Rod Summary

The decision was made to extract nine of the broken rods as part of a root-cause analysis effort

and to help determine whether the embedded remains could be utilized in the remedial works.

The rods had to be pulled and cut every few feet due to overhead restrictions. It became

obvious that all rods had failed near the bottom nut and the removed sections appeared to be

undamaged. A boroscope examination was conducted on March 12th, 13th, 14th and 17th to

observe the rod cavity and lower nut area. This inspection was conducted by Caltrans. The

inspector was Jason Gramlick, Associate Steel Inspector at Caltrans, Vallejo office, using a GE

Inspection Technologies XLGO Video boroscope with a standard field of view tip and no

applied magnification.


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3. Inspection Results

For orientation purposes, Figure 2 shows the design of the rod, nut and pipe sleeve assembly.

The 7-inch diameter galvanized sleeve connects from the top of the Pier cap to a bottom

bearing plate. Beneath this plate is welded an 8-inch sleeve, approximately 2.5-feet long,

referred to as a ‘top hat’. Before the shear keys were set in place, the anchor rods rested on the

bottom of the top hat. Once the shear keys were aligned over the rods, the rods were lifted,

grouted, cured for 28 days and then tensioned. The grout injection line connected to the

bottom of the top hat with the pumping supply originally designed as coming up from

underside of the cross beam. There are two (2), 25 mm (1 inch) grout holes in the bottom

bearing plate which allow the grout to flow up through the rod sleeve to the shear key base

plate on top of the Pier. However, these grout holes are shown to be half covered on the

bottom by the nut-washer assembly and half covered on the top side by the smaller 7-inch

diameter sleeve.

To assist in the interpretation of the boroscope videos, the review began with an examination

of the fractured rod ends that had been removed from shear keys S1 & S2. Appendix 1

contains image clips taken from the videos and a summary of the findings are in Table 2 of

this report. Due to the findings this review also considered other construction information,

including the laboratory analysis of the water sample that had been extracted from one of the

failed anchor-rod ducts.

Boroscope Investigation of the SFOBB Failed E2 Embedded Anchor Rods

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Figure 3: Top Hat Detail


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Table 2 - Boroscope Test Results/Physical Observations

Date Rod

Length

LOCATION

Examination of the Fractured Rod

End

Boroscope Examination OTHER COMMENTS

2013 Arc of Hydrogen

Embrittlement*

HE as % of

cross

section*

Did Anchor

Rod drop into

Top Hat

Water

evidence in

Sleeve/Top Hat

Rust

deposits

4-17 17 S1-G1 210 30 no yes Yes From Boroscope video failed anchor rod end is close (tight ?) to

the bearing plate, not submerged in water but beads of water can

be seen in the thread, so the rod end may be sitting in water.

17 S1-H3 200 30

3-14 17 S1-A7 360 40 yes yes From Boroscope video the failed anchor rod end has dropped

away from the bearing plate and is submerged in water.

17 S2-A3 160 30

3-13 17 S2-A6

no no Yes From Boroscope video failed anchor rod end is close (tight ?) to

the bearing plate, not submerged in water and no evidence of

water. The fracture surface is corroded and partially covered with

debris.

17 S2-A8 105 15 yes ? yes – water

sample

extracted

Water sample was extracted for analysis, not examined by

borescope. (In order to extract water it is anticipated there was a

grout void that allowed the failed anchor rod end to drop away

from the bearing plate, exposing the trapped water)

3-12 9 S2-H4 310 30 Boroscope inspection was not successful.

3-12 17 S2-H6 360 50 yes yes From Boroscope video Failed anchor rod end has dropped away

from the bearing plate and is submerged in water. (Look carefully

at the surface of the water, you can see the washer, nut and

fractured face of the rod through the water)

17 S2-A2 180 20

Notes:

*= crack morphology observed on removed mating fracture surfaces

8 of the 9 removed rods were available for visual examination in February 2014


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4. Discussion

The most significant boroscope finding was that of standing water being seen in the bottom of

the sleeves and in some cases the failed end of the rod and nut assembly not being tight up

against the bottom bearing plate. Inquiries were made as to how these conditions could exist.

The following describes what was discovered.

The shear key S1 & S2 embedded anchor rods were fabricated in 2008, delivered to the site and

assembled in their sleeves and installed in Pier E2 that same year immediately prior to the

concrete pour. As previously noted the rods sat un-tensioned on the bottom of the top hat and

squarely covering the grout injection port. The sleeves were specified to be covered and

protected from the environment. This was not done for the complete time. There was very

limited access to this area, as the Pier was not connected to any decking. There are photographs

which show no covering over the totally exposed and isolated shear key anchor sleeves.

Furthermore, there are documented records of an airtight fitting being used to lift the rod

sufficiently to uncover the injection port, and the application of compressed air to blow water

that had accumulated during the layup period, out through the bottom grout injection port and

connected plumbing. (Pumping water out by suction was not feasible due to the access

restriction at the bottom bearing plate between the top hat and rod sleeve, as well as the spherical

washer restricting access to the very bottom of the top hat). Note: This is a draft report and

includes the information provided by Bill Casey on April 16, 2014 entitled “Rainwater

Chronology” in the S1/S2 Shear Key GR 354BD Anchor Rods” (see appendices for cover of

presentation), which does not show the actual grouting operation about which information has

been requested. The “Rainwater Chronology” slide presentation documents repeated exposure of

the 2008 rods to rainwater for extended periods of time during construction.

A water sample was gathered once the rods were removed and sent to a laboratory for analysis to

determine the source of the water. The results were that the pH level was extremely caustic with

a level greater than 13. The high pH combined together with the chemical analysis of the

sample, it was determined that the grout had contaminated the water in the bottom of the

sleeve/top hat prior to and during curing. This would therefore indicate the water was present

prior to the grouting operation. If the grout had been injected from the bottom of the top hat, the

water should have been displaced upwards by the grout pushing it up the duct.

There is well established data which indicate that zinc coating will aggressively corrode in such a

caustic environment. This corrosion would result in generating high concentrations of hydrogen

that could be absorbed into the steel in both the stressed and un-stressed condition. Refer to

Dominion Engineering Inc report in Appendix 3.The results of the water analysis, supplied by

Rami Boundouki of METS, are shown in Table 3.


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Table 3: Water Test

Table 1. Water

Test Results Parameter

Result

pH 13.04

Conductivity 31 mS

Chloride 44 mg Cl-/L

Sulfate 128 mg SO42-/L

Nitrate 1.5 mg NO32-/L

Nitrite 293 mg NO2-/L

Sodium 3940mg Na+/L

Potassium 990 mg K+/L

Magnesium ND

Calcium 96 mg Ca2+/L

Carbonate 2,040 mg/L as CaCO3

Bicarbonate ND

Organic compounds ND

Chromium <1 mg Cr/L

Iron ND

Aluminum 29.2 mg Al/L

Zinc 32.8 mg Zn/L

Total dissolved solids 11,200 mg/L

A contributing factor that lead to the water accumulation was a field modification where the

grout injection line was rerouted from under the bottom of the cross beam, in accordance with

the approved-for construction- plan shown in Figure 2, to a longer and more circuitous path

where the injection port was now on the top of the Pier. This essentially removed a natural

gravity drain that would have prevented the accumulation of water in the top hat.

The question of how/why the fractured section of the rod and nut weren’t tight against the

bottom bearing plate arose. The expectation for the boroscope examination was for the grout to

support the fractured end of the rod, complete with nut and washer, up against the bearing plate.

However it appears that beneath the bearing plate, there were cavities in the grout and that in

some instances the entombed piece had ‘dropped’ down in the top hat following the fracture,

which could only occur if the top hat was not filled with grout. The probable cause for this is

that the rerouted grout injection line was not allowing grout to flow effectively, thus enabling the

grout to displace the water – pushing it up the anchor rod sleeve. It is also understood that in

order to complete the grout operation, in a number of instances it was necessary to pour/gravity

fed grout into the rod sleeve from above, i.e., not using the grout injection pipe. If the top hat

was filled with water and grout was poured down the sleeve, the water would not have been

displaced, causing it to be trapped below the bearing plate. This would explain the existence of

the water-filled voids and the presence of water observed in the boroscope videos.


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The following photographs were taken during construction of the Pier E2 cross beam in 2008.

The photograph above shows the pipe sleeves, containing the anchor rods. The white 19mm

PVC grout injection pipes are visible adjacent to their respective sleeve assemblies.

The photograph above shows the bearing plate, the top hat and the 19mm grout injection pipe.

The photograph above shows the finishing work to the grout injection plumbing to bring the

injection port to above the concrete cross beam and outside the footprint of the shear key.

Pipe sleeve containing an anchor

rod

Grout injection pipe

Pipe sleeve

Bearing plate

Top hat

Grout injection pipe

19mm pipe fittings for the

finishing works to the

grout injection pipes


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The photograph above (courtesy of Caltrans) shows the 19mm grout injection pipes for each of

the pipe sleeves positioned outside of the shear key footprint.

While examining the fracture surfaces of the failed rod ends that had been removed from shear

keys S1 & S2, it was noted that some exhibited symmetrical hydrogen embrittlement cracking

and that others exhibited a non-uniform pattern, where crack propagation was dominant in a

localized area. This is characterized by a visual crack path that leads to a point of origin on the

circumference. Please refer to Lisin Metallurgical Services report in Appendix 2 for a detailed

explanation.

In all instances, the nine failed rods fractured at the first full thread engagement with the lower

nut. The possible reasons for this are two fold; 1) the highest stress intensity due to the thread

geometry will be at that first thread; 2) the volume of water trapped below the bearing plate will

vary, but provided the bottom of the nut is submerged in water, capillary action would ensure the

threaded contact area between the nut and rod is wet, therefore the location of highest stress

intensity will always be subjected to stress corrosion. Therefore, capillary action may still have

facilitated stress corrosion at the first thread anchor rod S2-A6, even though it appeared dry

during the boroscope examination. Note: This is a draft report and some further consideration is

being given to the grout process in respect of the plumbing and possible effect of head loss

during the grout operation.

Two rows of grout injection pipes


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The photographs above from the Caltrans “Rainwater Chronology” slide presentation, dated

April 16, 2014 (see appendices for cover of presentation) shows the corrosion effects that

repeated exposure to rainwater was having on the 2008 S1/S2 rods. This underscores the

continued presence of rainwater in the pipe sleeves, even though there were several significant

attempts made to keep this water out of the pipe sleeves.

5. Conclusion

One third of the S1 & S2 shear key anchor rods experienced delayed cracking failures.

Approximately 25 percent of these were extracted from their grouted sleeves. A boroscope

inspection was subsequently performed which indicated that the grouting operation was not

entirely successful and resulted in a void immediately below the bearing plate containing

entrapped water. This would suggest that the anchor rods that sat in water for part of the time

since being installed in 2008 and the same water had become caustic during the grouting

operation giving cause to accelerated corrosion during the 28-day cure period prior to rod

tensioning and to stress corrosion/hydrogen embrittlement after tensioning.

The examination of the fractured surfaces of the rods that had been extracted assessed the

possibility of asymmetric loading being a common cause of failure. Since 2 rods exhibited

uniform hydrogen embrittlement, 360 degrees and 1 rod exhibited 310 degrees of hydrogen

embrittlement, this demonstrates that some of the failed rods were subjected to axisymmetric

loading and therefore asymmetric loading or bending may only be a contributory factor for some

of the anchor rods.

Without any further records it is difficult to predict with any degree of certainty that all 96 of

these rods were subject to the same conditions as the rods that failed. However, it is clear that

the approved design for the installation and grouting of all 96 E2-embedded anchor rod

assemblies had not been followed. Three (3) of the four (4) anchor rod cavities examined with a

boroscope contained entrapped water and fifth anchor rod cavity also contained entrapped water

that was subsequently analyzed. It therefore suggests that the modified grout operation had been


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ineffective, resulting in water-filled voids existing immediately below the bearing plate in the

same vicinity as the hydrogen embrittlement fracture location. The laboratory analysis of the

water taken at this same location also confirmed that the entrapped water had become highly

corrosive as a result of the caustic materials that leeched from the grout.

Note: With regard to the anchoring of the Pier E2 shear keys, all 96 embedded rods that are the subject of this

report were abandoned, since it was not feasible to rework this detail. An alternative design was engineered and

constructed in late 2013.

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6. Appendices

Appendices: Boroscope Investigation of the SFOBB Failed E2 Embedded Anchor Rods

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Appendix 1

Boroscope Photographs

The inset photographs shown on the following pages, identified by letters A thru E have

been clipped from the original boroscope video. The other photographs have been taken in

the office with some identical pieces of anchor rod, spherical nut and washer, in an attempt

to show the orientation of the fractured rod assembly being observed through the

boroscope.

Exhibit 1: This is a sample spherical washer and the mating spherical nut assembled on a short

piece of anchor rods. The purpose of this photo is only to assist the reader of this report to

interpret the boroscope images.

Anchor Rod

Spherical surface of the nut which seats in the washer

Spherical seat of the washer

Exhibit 1


EXHIBIT 2 3-AUG-16 16

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Shear Key 1 Video Captures Anchor Rod S1 – G1

Video recorded on April 17, 2013 (video of S1-G1 but filed as S1 – XX). Failed anchor rod end is close (tight ?) to the bearing plate. It is not submerged in water, but beads of water can be seen in the thread, so the rod end may be sitting in water.

Though the fracture surface is not submerged in water, the surface appears wet with evidence of water beads in the thread.

Washer

Nut

Fracture surface of anchor rod

Mock-up photo to show orientation of rod end which is square and central to the washer


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BAMC EXHIBIT 3

Shear Key 1 Video Captures(cont.) Anchor Rod S1 – A7

Video recorded on March 14 and March 18, 2013. Failed anchor rod end have dropped away from the bearing plate and are submerged in water.

This shows the face of the washer which was bearing on the bearing plate s the failed rod end has dropped in the water,

Gap between the nut and washer

Spherical face of the nut.

Mock-up photo taken in office to show orientation of S1-A7 rod end

S1- A7 was revisited four days later after the original boroscope examination, having adding some tap water in an attempt to improve visibility. Little improvement was noted.


EXHIBIT 4 3-AUG-16 18

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Shear Key 2 Video Captures Anchor Rod S2 – A6

Video recorded on March 13, 2013. Failed anchor rod end is close (tight ?) to the bearing plate, not submerged in water and no evidence of water. The fracture surface is corroded and partially covered with debris.

Fracture surface of the anchor rod

Nut

Even though water is not visible, significant corrosion has occurred to the thread and nut.

Washer

Exposed end of the thread

A

B

Mock-up photo to show orientation of S2 –A6 rod end


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Shear Key 2 Video Captures (cont.) Anchor Rod S2 – A8

Boroscope inspection was performed at this location.

Water sample was extracted at this location for analysis, refer to Table 3 for test results.

Anchor Rod S2 – H4

Boroscope inspection at this location was unsuccessful.


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BAMC EXHIBIT 5

Shear Key 2 Video Captures (cont.) Anchor Rod S2 – H6

Video recorded on March 12, 2013

Failed anchor rod end has dropped away from the bearing plate and is submerged in water. (Look carefully at the surface of the water, you can see the washer, nut and fractured face of the rod through

the water)

Mock-up to show orientation of S2 –H6 rod end

Fracture surface of the anchor rod

Nut

Washer

Bearing Plate

Grout in the upper section of the anchor sleeve

A

Washer

Corner of the nut

Spherical surface of the nut

Appendices: Lisen Metallurgical Services Report

Appendix 2

Lisin Metallurgical Services Report

Appendices: Jeff Gorman Report

Appendix 3

Dr. Jeff Gorman Report

Appendices: Jeff Gorman Report

Appendix 4

Rainwater Chronology in the S1/S2 Shear Key GR 354BD Anchor Rod

Blockouts and Shear Key/Bearing Erection/Construction

review of the failed e2 embedded anchor rod...

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