MAIN CONCERNS ABOUT ANCHOR RODS ON THE NEW BAY BRIDGE

Transcription

1 MAIN CONCERNS ABOUT ANCHOR RODS ON THE NEW BAY BRIDGE

2 MAIN CONCERNS ABOUT ANCHOR RODS ON THE NEW BAY BRIDGE Tower T1 Pier W2 November 29, 2013 Prepared by Yun Chung Materials Engineer (Retired) Alameda, California Lisa K. Thomas, P.E. Metallurgical and Materials Engineer Berkeley Research Company Berkeley, California

3 MAIN CONCERNS ABOUT ANCHOR RODS ON THE NEW BAY BRIDGE A B S T R A C T The TBPOC (Toll Bridge Program Oversight Committee) has managed the new San Francisco-Oakland Bay Bridge construction since The main section of the new Bay Bridge is a mile long self-anchored suspension (SAS) bridge, which is supported by a 525 foot high tower (T1) and two piers (E2 and W2). In March 2013, 32 of the 96 Grade BD (high strength steel) anchor rods, each 3 inches in diameter and up to 17 feet in length and up to 400 pounds, for the base plates of shear keys on E2 failed due to hydrogen embrittlement (HE) cracking. Shear keys are major earthquake stabilizers for the traffic decks of the SAS Bridge. It has 2306 Grade BD anchor rods, all of which can be subject to HE failures, depending on the metallurgical conditions of individual anchor rods. The TBPOC released a final report on the anchor rod failures in July This report gives a detailed account of their strategy in arriving at remedial resolutions for each of the 17 types of the 2306 Grade BD anchor rods. Central to this strategy is a construction of what is known as a KI SCC -hardness (or KI SCC - HRC) curve. (KI SCC - stress intensity factor for stress corrosion cracking (SCC)). 1,2 To do this, TBPOC- Caltrans constructed large scale Townsend KI SCC test rigs that are designed to utilize full size anchor rods as specimens. Despite the shear key anchor rod failures in March 2013 and uncertainty as to the remaining anchor rods, the new Bay Bridge was opened to traffic in September 2013 as scheduled. A review of the TBPOC report of July 2013 disclosed numerous technical errors. Their conclusions as to the cause of the shear key anchor rod failures were wrong. In October 2013, Chung and Thomas sent a review report, titled, High Strength Steel Anchor Rod Problems on the New Bay Bridge, to TBPOC- Caltrans. It points out some 200 errors and technically questionable or erroneous statements and divulged that most of TBPOC-Caltrans new supplementary requirements for replacement anchor rods, including a new CVN toughness requirement, will be ineffective. The TBPOC report has serious questions unanswered regarding the long term performance of the anchor rods for the main cable and the tower base. TBPOC-Caltrans are not even aware of the metallurgical characteristics of these anchor rods that would put their strategy of utilizing KI SCC -HRC curves for assuring the integrity of these anchor rods into question. This report has been prepared as a supplement to the Chung-Thomas previous review report of the TBPOC report. This supplement specifically focuses on the problems unique to the anchor rods for the main cable (also identified as PWS Parallel Wire Strands) and the tower base. This supplement is deemed necessary because TBPOC-Caltrans have been oblivious to the metallurgical conditions unique to these anchor rods, which may have HE susceptibility worse than other anchor rods, contrary to TBPOC- Caltrans expectations. TBPOC-Caltrans need to understand that these anchor rods have unique metallurgical characteristics that could adversely affect their HE susceptibility. This supplement explains why this might be so and what TBPOC-Caltrans need to do to characterize the HE susceptibility of the anchor rods for the main cable and the tower base. TBPOC-Caltrans need to construct KI SCC -HRC curves specifically for these anchor rods, separately from those for other anchor rods. 1 HRC Hardness in the Rockwell C scale. 2 In the July 8, 2013 TBPOC report, the term stress corrosion cracking (SCC) is used for the term environmental hydrogen embrittlement (EHE). Therefore, KI SCC is the same as KI EHE. In the case of high strength steel failures under static load in the atmosphere, however, EHE is preferred to SCC in the technical literature, including ASTM specifications.

4 Main Concerns About the Anchor Rods on the New Bay Bridge ii MAIN CONCERNS ABOUT ANCHOR RODS ON THE NEW BAY BRIDGE Table of Contents Page ABSTRACT i I. SUMMARY OF MAIN CONCERNS.. 1 (a) Anchor Rods with Rolled Threads. 1 (b) Anchor Rods for Tower Base. 2 II. PROBLEMS UNIQUE TO THE PWS ANCHOR RODS AND WHAT TBPOC-CALTRANS NEED TO DO. 3 III. TBPOC-CALTRANS REMEDIAL RESOLUTIONS FOR PWS ANCHOR RODS. 9 IV. PROBLEMS UNIQUE TO THE TOWER SADDLE TIE RODS AND TOWER BASE ANCHOR RODS 10 V. COMMENTS ON TBPOC-CALTRANS KI-HRC STRATEGY. 12 VI. CONCLUSIONS. 14

5 Main Concerns About the Anchor Rods on the New Bay Bridge 1 I. SUMMARY OF MAIN CONCERNS TBPOC-Caltrans believe that their July 8, 2013 report has addressed and resolved all the questions and issues regarding the high strength steel anchor rods on the new Bay Bridge. This is untrue. There are several important questions unanswered and TBPOC-Caltrans are not even aware of some metallurgical problems facing the long term performance integrity of fracture-critical anchor rods. The truth is that TBPOC-Caltrans have no idea about the susceptibility of the most fracture-critical anchor rods to hydrogen embrittlement (HE). Their testing protocols including the Townsend KI SCC (stress corrosion cracking) tests have completely missed the mark in connection with the validity of their remedial resolutions of the anchor rods for the main cable (Item 7, PWS Parallel Wire Strands) and of the tower base (Items 12 and 13). 3 The anchor rods for the PWS and the tower base are fracture-critical. It means that their failures can bring down the entire SAS Bridge. TBPOC-Caltrans are not cognizant of metallurgical problems unique to these anchor rods. Their remedial resolutions are unsatisfactory. Their Townsend KI SCC test protocols must be significantly augmented to provide valid assurance that these anchor rods will not fail due to hydrogen embrittlement (HE) during service. (a) Anchor Rods with Rolled Threads The only remedial requirement for the PWS anchor rods in the TBPOC report is dehumidification of the splay chambers where the PWS anchor rods are located. Is dehumidification alone sufficient to assure no HE failures in the PWS anchor rods? No, or it depends on their KI SCC data, which may be quite different from KI SCC for other anchor rods. TBPOC-Caltrans may be wrong if they think that one KI SCC -HRC curve is applicable to all anchor rods, including the PWS anchor rods. If this were the case, they could just use KI SCC data in the literature; there is no need for conducting the expensive Townsend KI SCC testing. TBPOC-Caltrans need to establish a KI SCC -HRC curve specifically for the PWS anchor rods. The results may provide a support for the dehumidification measure or a need for additional evaluation. The anchor rods for the PWS are each 3½ inches in diameter by feet in length. Of these, 217 have rolled threads and the rest (55) have cut threads. The threads of the former were formed by cold rolling of steel bars that were heat treated to high hardness (e.g., 38 HRC). The thread rolling operation cold worked the surface layer, altering the microstructure. The cold working would increase the metal hardness in the surface layer, about inch deep in this case. Both the high hardness and the cold worked microstructure would increase the susceptibility of the anchor rods to HE cracking. Their combined effects on KI SCC are unknown. Consequently, whether or not the dehumidification of the splay chambers 3 The stress intensity factor is a fracture mechanics term, often shortened and accepted erroneously as the stress intensity, as in the TBPOC report. In a stress analysis, for example, as required by the ASME (American Society of Mechanical Engineers) pressure vessel codes, the term stress intensity has an entirely different definition from that of the term stress intensity factor. Fracture mechanics can evaluate the effects of flaws or cracks on the stability of a solid, like steel. It was developed to define the stress state in the material ahead of a crack, where the effects of stress concentration at a notch or a crack tip are difficult to evaluate. The stress intensity factor is denoted by K, which relates to but is not the same as the stress, denoted by σ. KIc denotes a critical stress intensity factor in Mode I (one) where a crack would propagate by opening up due to rising tensile stresses. There are KII (for Mode II - sliding mode) and KIII (for Mode III - twisting mode). Most metal fractures occur in Mode I; therefore, KI is more important than KII or KIII. KIc is known as the fracture toughness and relates to and can be converted to Charpy V-notch (CVN) values using empirical equations. KI SCC denotes the critical stress intensity factor or the minimum stress intensity factor that can cause stress corrosion cracking in the material. Conversely, if an anchor rod is stressed so that its KI is below KI SCC, it will not develop SCC (or EHE). Thus, KI SCC is also known as the threshold stress intensity factor for stress corrosion cracking.

6 Main Concerns About the Anchor Rods on the New Bay Bridge 2 alone is sufficient to prevent HE failures is unknown. Also, the efficacy of dehumidification as described in the TBPOC report is questionable. TBPOC-Caltrans need to generate a KI SCC -HRC curve specifically and separately for the PWS anchor rods with cold rolled threads. Only the Townsend KI SCC test rig can do this because small size lab specimens cannot represent the effects of the cold worked surface layer on (environmental) HE cracking. Caltrans does not, however, even have hardness data for the surface layer of the rolled threads and their KI SCC test protocol is entirely inadequate in understanding the HE susceptibility of the PWS anchor rods with cold rolled threads. The SAS Bridge has other anchor rods with rolled threads, for example, Item 8, 25 Saddle Tie Rods, each 4 inches in diameter by 6 18 feet in length. TBPOC-Caltrans remedial resolution for Item 8 is Reduce Tension from the original 0.7Fu (70% of ultimate tensile strength) to an unspecified level. Only one sample from Item 8 was allocated for a KI SCC test. In addition, these 4 inch anchor rods have hardness distribution curves that are M-shaped rather than V-shaped, probably because of insufficient tempering. Consequently, these anchor rods would have high residual stresses, which could promote HE cracking. (b) Anchor Rods for Tower Base The only remedial requirement in the TBPOC report for the tower base anchor rods is reduction in tension. Is this sufficient? No. The tower base is secured to the foundation using 3 and 4 inch anchor rods, both 26 feet in length. There are 388 of the 3 inch (each 600 pounds) and 36 of the 4 inch anchor rods (each 1,100 pounds). Both the 3 and 4 inch anchor rods have hardness distribution curves across the diameter that are M-shaped as was for Item 8 mentioned above. This means that the surface hardness was lower than a maximum hardness (e.g., 40 HRC) which occurred at ½ inch from the surface. Anchor rods that are properly heat treated should show a V-shaped hardness distribution curve. The M-shaped hardness distribution curves would result if the anchor rods were not sufficiently tempered. Thus, these anchor rods would have high residual stresses. TBPOC-Caltrans have never taken the effects of residual stresses on HE cracking into consideration. TBPOC-Caltrans need to provide a metallurgical explanation as to why the tower base anchor rods have M-shaped hardness distribution curves and what their effects on HE susceptibility might be. They need to address the effects of residual stresses in these rods with M-shaped hardness distribution curves on HE cracking. Many SCC failures have occurred because of residual stresses alone without additional applied stresses. There is another new question for TBPOC-Caltrans: the effects of cathodic protection (CP) on HE cracking. Unlike most SCC failures, CP can promote HE failures in high strength steels. If the bottom ends of the tower base anchor rods are exposed to seawater intrusion, for whatever reasons, and if they are electrically connected to a CP system of the foundation, HE cracks could develop in the bottom threads of the anchor rods, leading to HE failures. TBPOC-Caltrans need to provide assurance that this scenario is not applicable to the tower base anchor rods.

7 Main Concerns About the Anchor Rods on the New Bay Bridge 3 II. PROBLEMS UNIQUE TO THE PWS ANCHOR RODS AND WHAT TBPOC-CALTRANS NEED TO DO Missing data See below Figure 1 A comparison of HRC plots across cross sections of PWS anchor rods between cut threads and rolled threads. cold worked surface layer Missing data cut threads rolled threads The 217 of the PWS anchor rods were manufactured by heat treating 4140 steel rounds and forming the threads by cold rolling rather than by thread cutting. The cold rolling will cold work the metal structure, resulting in a cold worked microstructure and increased hardness. Both the cold worked microstructure and the increased hardness would increase the susceptibility of the steel to HE cracking. In other words, the PWS anchor rods with cold rolled threads may be more susceptible to HE cracking than any other anchor rods on the new Bay Bridge, including the 740 anchor rods that are going to be replaced because of their high risk of HE cracking failures as calculated by FHWA engineers. (The FHWA s HE cracking assessment tool completely missed the mark because they, too, were not even aware of the effects of the cold work on hardness in the surface layer.) Figure 1 above from Caltrans File E17 illustrates average hardness data for the PWS anchor rods: the red curve for cut threads and the blue curve for rolled threads. Caltrans may have presented Figure 1 to imply erroneously that there are little differences in hardness distributions between anchor rods with rolled threads and those with cut threads and that the surface hardness is about 36 HRC for both rather than higher than 39 HRC. They have, however, missed the obvious point. The difference between them would be in the surface layer, in the first about 0.15 inch from the surface. Caltrans have paid no attention to this surface layer because they were unaware of the cold work effects of thread forming by cold rolling on hardness and microstructure. Distance from surface, inch Figure 2 A comparison of HRC in the surface layers of anchor rods with cold rolled threads against those with cut threads. Figure 2 at left shows imaginary hardness data in the cold worked surface layer of a PWS anchor rod with rolled threads. At the root surfaces of cold rolled threads, the metal hardness would have approached 40 HRC or higher, decreasing sharply to 36 HRC, probably within inch from the surface. In some PWS anchor rods, the maximum hardness at thread roots could have reached up to 43 HRC, which needs to be verified.

8 Main Concerns About the Anchor Rods on the New Bay Bridge 4 Caltrans, their contractors, and consultants have all missed this point. FHWA engineers neglected to consider the effects of cold thread rolling on HE failures when they calculated HE susceptibility risks using their own Greg Assessment Tool. Consensus is that the higher the hardness, the higher (or worse) the HE cracking susceptibility and that a cold worked structure would increase the HE cracking susceptibility. How bad the combined effects of the cold worked microstructure and the increased hardness on the HE cracking susceptibility on the 3½ inch PWS anchor rods might be is unknown. No laboratory test or field performance data on the HE cracking susceptibility of anchor rods with cold rolled threads, like the PWS anchor rods, are available in the open literature. No one before the new Bay Bridge project had produced anchor rods (or any other form of fasteners) by heat treating 4140 steel rods (around 3½-inches in diameter) to 38 HRC at the surface, cold rolled the threads, and hot dip galvanized them. This practice should have never been allowed in the first place. In terms of HE cracking susceptibility, the PWS anchor rods with rolled threads could stand by themselves because of the high hardness and the cold worked microstructure in the surface layer. This needs to be verified by conducting the Townsend KI SCC testing. None of Caltrans' hardness data is useful in evaluating the hardness of the PWS anchor rods with rolled threads because Caltrans hardness test protocol required the first hardness indentation to be made at 0.25 inch from the surface, well below the cold worked layer. Thus, TBPOC-Caltrans do not even know what the maximum hardness for the PWS anchor rods is, let alone their HE susceptibility. Their KI SCC testing protocol is woefully inadequate for the PWS anchor rods with rolled threads, to be discussed later. The absence of hardness data for the roots of rolled threads of PWS anchor rods with rolled threads precludes TBPOC-Caltrans from knowing whether the dehumidification of the splay chambers alone would be sufficient to assure their long term integrity. Furthermore, the splay chambers where the PWS anchor rods are located should be air tight, not water tight, as stated in the TBPOC report, and should have relative humidity monitored continuously to no higher than 50% throughout the chambers at all times. To assure the long term integrity of the PWS anchor rods, TBPOC-Caltrans need to determine that the HE cracking susceptibility of the PWS anchor rods with cold rolled threads is about the same as, higher, or lower than other anchor rods of equal hardness but with cut threads. One way to achieve this is to determine the maximum hardness and to establish a KI SCC -HRC (or KI EHE -HRC) curve. The latter is a curve of critical stress intensity factor for stress corrosion cracking (SCC) or for environmental hydrogen embrittlement (EHE) vs hardness. For the former, TBPOC-Caltrans completely ignored the effect of the cold working during thread rolling. The TBPOC report states on page 66 as follows.

9 Main Concerns About the Anchor Rods on the New Bay Bridge 5 The above statements indicate that Caltrans will construct a KI SCC -HRC curve to accommodate the range of ASTM A354 grade BD rod lengths and diameters. It will be discussed later that their plan is to construct a KI SCC -HRC curve using new anchor rods to be purchased and that this plan has several problems, to be discussed later. The lower half of Figure 33 of the TBPOC report is as follows. Step 1 Determine KI SCC In the box below (Step 2), the word Critical should be deleted. Note: Stress corrosion cracking (SCC) in the TBPOC report is the same as environmental hydrogen embrittlement (EHE) cracking. Step 2 Locate KI, not KI SCC, and HRC for individual rod on Townsend KI SCC -HRC curve Step 3 Classify HE susceptibility The purple boxes added for clarification Figure 3 The lower half of Figure 33 of the TBPOC report of July 8, 2013.

10 Critical Stress Intensity, KISCC, ksi in Main Concerns About the Anchor Rods on the New Bay Bridge 6 The steps outlined by red in Figure 3 require KI SCC (or KI EHE ) and surface hardness data. They are central to the TBPOC-Caltrans strategy in arriving at remedial resolutions for all the anchor rods on the new SAS Bridge. Caltrans data on surface hardness and KI SCC are, however, incomplete or erroneous for purposes of classifying the HE susceptibility according to the above steps. Also, Step 2 has an error. The word Critical is extraneous and should be deleted. KI (or K) would vary according to the stress, σ, or the pretension levels in the anchor rods; KI SCC is a material property, like a yield strength, that is unaffected by stress. This mix-up between KI and KI SCC is akin to the mix-ups between stress and strength in five places in the July 8, 2013 TBPOC report. TBPOC-Caltrans referred to the bottom KI SCC Zn coated curve with solid data points in Figure 4 below as the Townsend curve, which came from one of Townsend s research papers. This paper is referenced in Note 4 of ASTM A354 for hot dip galvanized Grade BD bolts. From H. E. Townsend, Jr.: Metallurgical Transactions A, v.6a, April 1975, pp Figure 4 (left) shows KI SCC = 75 ksi (1) KI SCC (or KI EHE ) decreases as hardness increases. 31 KI SCC = 32 ksi 36 HRC HRC Hardness, HRC (2) KI SCC for zinc coated (or hot dip galvanized) steel is significantly lower than that for uncoated steel. This is particularly so for HRC, the shaded range, specified for Grade BD anchor rods. This means that hot dip galvanizing increases HE susceptibility. (3) At 36 HRC, KI SCC is about 32 ksi in for hot dip galvanized steel and about 75 ksi in for uncoated steel. Figure 4 KI SCC vs hardness curves by Townsend: the bottom curve for galvanized steel and the middle curve for uncoated (black) steel. (TBPOC-Caltrans borrowed and presented the bottom curve in Figure 4 from a book by Prof. John Fisher and his co-authors during the May 8, 2013 BATA Briefing. Prof. Fisher and his co-authors introduced

11 Main Concerns About the Anchor Rods on the New Bay Bridge 7 errors in the above bottom curve when they reproduced it in their book. TBPOC-Caltrans blindly copied the graph from this book including the errors and mislabeled the graph as a critical stress curve The term critical stress is not the same as the term critical stress intensity or critical stress intensity factor. Along with the mix-up between KI and KI SCC in Figure 3, this is another one of several signs that Caltrans engineers lack expertise in fracture mechanics based KI SCC analyses.) Townsend established the above KI SCC -HRC curves using small precracked cantilever specimens (about ½ inch square). TBPOC-Caltrans constructed several KI SCC test rigs that would use full size anchor rods as specimens in accordance with a design by Townsend, shown below in Figures 5 and 6. Salt solution Hydraulic tensioners Salt solution chamber Full size anchor rod specimen 3.5% NaCl Salt solution chamber Figure 5 A KI SCC test rig designed by Townsend for Caltrans. Figure 6 Actual test rigs being prepared for KI SCC testing (Photo: Contra Costa Times) The above test rigs (Figures 5 and 6) are probably one of a kind. No one has done KI SCC tests using 3 inch diameter full size anchor rods as specimens. This is because, firstly, the above test rigs would be expensive to construct and carry out the tests and, secondly, for most threaded fasteners, the above test rig

12 Main Concerns About the Anchor Rods on the New Bay Bridge 8 would be no more advantageous than a laboratory desk top test setup. For example, using small specimens, the ASTM F1624 test can do most everything that the above Townsend KI SCC testing can do. 4 One exception would be KI SCC testing of the PWS anchor rods with rolled threads where small specimens cannot represent the localized conditions of the thread roots that were cold worked. The Townsend KI SCC testing protocol is given in Figure 32 on page 63 of the TBPOC report. TBPOC- Caltrans are, however, not utilizing the advantages of the above full size test rig as discussed below. The PWS anchor rods with cold rolled threads have a localized surface layer at the thread roots where the metal hardness and microstructure change drastically within a short distance (say, less than 0.15 inch) as illustrated in Figure 2. Because of these conditions, it would be almost impractical to determine the KI SCC - HRC curves using small precracked specimens in the same way as what Townsend did in his 1975 research paper. Also, Test V (the Raymond Test) may not be able to determine KI SCC for the PWS anchor rods with cold rolled threads for the same reason. Then, the main purpose and benefits of the above Townsend KI SCC test rig should have been to determine the KI SCC or (σ SCC ) for the PWS anchor rods with cold rolled threads. This is because a Townsend curve for other anchor rods with cut threads (except for the Tower base anchor rods, to be discussed later) can be estimated based on KI SCC -HRC data in the literature. In spite of this, the TBPOC-Caltrans test plan has not focused on the KI SCC for the PWS anchor rods with cold rolled threads. A portion of the overall test plan in Figure 28 on page 61 of the TBPOC report is reproduced blow. 30 ordered 4 ASTM F1624 Standard Test Method for Measurement of Hydrogen Embrittlement Threshold in Steel by the Incremental Step Loading Technique. Figure 7 A portion of Figure 28 of the TBPOC report of July 8, 2013.

13 Main Concerns About the Anchor Rods on the New Bay Bridge 9 The above test plan by TBPOC-Caltrans presents the following problems. (i) The double heat treated specimens under Note 8 are based on a misconception that double heat treatment would further harden the steel. This is as untrue as additional heat treatment contributed to the shear key anchor rod failures as discussed in the review report. (ii) A comparison between black and galvanized would not add data that are useful for evaluating the SAS anchor rods, all of which are hot dip galvanized. Townsend already showed that hot dip galvanizing increases the HE susceptibility in Figure 4. (iii) For Item 7, PWS Main Cable Anchor rods, 3½ inch in diameter, only 4 specimens were allocated for the Type IV Townsend KI SCC test. The *** indicates that the four specimens consist of 2 with rolled threads and 2 with cut threads. The 2 specimens with rolled threads would have to be selected probably at random without regard to the hardness at the thread roots because Caltrans has not produced any hardness data for the root of the cold rolled threads. These four specimens could only provide two data points in a KI SCC -HRC curve for anchor rods with rolled threads. They are hardly sufficient for constructing a KI SCC -HRC curve or characterizing the KI SCC for the PWS anchor rods with rolled threads. Consequently, TBPOC- Caltrans would not know if any of the PWS anchor rods with rolled threads will or will not develop SCC (or EHE) during service. III. TBPOC-CALTRANS REMEDIAL RESOLUTIONS FOR PWS ANCHOR RODS The TBPOC report states as follows on page The above statements are confusing as to exactly how TBPOC-Caltrans intend to have the risk of hydrogen-associated damage to the metallurgical structure of high-strength rods addressed for the SAS Bridge. The first sentence 1 sounds as if TBPOC-Caltrans will create a KI SCC -HRC curve similar to the Townsend curve, the bottom curve shown in Figure 4. This is not the same as Step 1, Determine KI SCC, in Figure 3 (or Figure 33 of the TBPOC report). The second sentence 2 in the above quotation is consistent with Step 2, except that it should be to locate KI-HRC, not KI SCC -HRC, for each rod on the Townsend curve. There are, however, several problems with this approach, as follows.

14 Main Concerns About the Anchor Rods on the New Bay Bridge 10 (i) The Townsend curve in the bottom of Figure 4 was constructed from using ½ inch square specimens. The 3 inch diameter Gr. BD anchor rods for the SAS bridge would have metallurgical characteristics different from the small lab specimens. Therefore, the Townsend curve in Figure 4, bottom, may not be used as a reference to judge if any of the individual Gr. BD anchor rods on the SAS Bridge could be susceptible or not susceptible to HE failures. (ii) The TBPOC-Caltrans test plan appears to focus on constructing a KI SCC -HRC curve using 10 specimens from Item 18, E Replacement Rods. This curve would look like the Townsend curve in the bottom of Figure 4 and may be applicable to most anchor rods for the SAS bridge, except for Item #7, the PWS Anchor Rods with rolled threads, and Items #12 and 13, the 3 and 4 tower base anchor rods that showed M-shaped hardness distribution curves. The KI SCC -HRC curves for Items #7, 12, and 13 may be so significantly different from the Townsend curve that new and separate KI SCC -HRC curves may need to be constructed. (iii) The 2013 replacements rods may have been ordered to meet the new supplementary requirements, including HRC. The SCC (or EHE) cracking problems are for anchor rods with higher hardness, HRC (or probably up to 43 HRC for PWS anchor rods with cold rolled threads.) (iv) A KI SCC -HRC curve established from cut thread specimens may not be used for assessing the KI SCC of the PWS anchor rods with rolled threads, again because of differences in metallurgical characteristics between them. To determine a KI SCC -HRC curve that is relevant to evaluating the HE susceptibility (or KI SCC ) of the PWS anchor rods with rolled threads, TBPOC-Caltrans need to do the following. (a) Recognize that the PWS anchor rods with rolled threads (and the tower base anchor rods) have metallurgical characteristics (and HE susceptibility) that are different from the anchor rods with cut threads. (b) Determine the hardness profiles for the surface layer at the roots of rolled threads for the installed PWS anchor rods. (c) Purchase 20 PWS anchor rods with rolled threads that would have duplicated the hardness range of the installed PWS anchor rods with rolled threads. (d) Establish a KI SCC -HRC curve using the full size specimen Townsend KI SCC test rig for the PWS anchor rods with rolled threads for an evaluation of the KI SCC (or σ SCC ) of the installed PWS anchor rods. IV. PROBLEMS UNIQUE TO THE TOWER SADDLE TIE RODS AND TOWER BASE ANCHOR RODS The hardness distribution curves of the 3 and 4 inch anchor rods for the tower base are peculiar for heat treated (i.e., quenched and tempered) 4140 steel rounds. When hardened and fully tempered (e.g., 2 hours or more at ºF following hardening or the metal temperature having reached ºF throughout the section), the maximum hardness is expected to be at the surface. Therefore, the hardness distribution curve across the diameter would be generally V-shaped as exemplified by Figure 1. Instead, many of the 3 and 4 inch anchor rods for the tower base have M-shaped hardness distribution curves.

15 Main Concerns About the Anchor Rods on the New Bay Bridge 11 Some examples of hardness distribution curves for Item 8, 4 inch Tower Saddle Tie Rods, and Items 12 and 13, 3 and 4 inch Tower Base Anchor Rods, are shown below. The maximum hardness (around 40 HRC) occurred about ½ inch from the surface and the hardness at the surface dropped to HRC. Figure 8 Examples of M-shaped HRC distribution curves. Both 3 and 4 inch anchor rods for the tower base have M-shaped hardness distribution curves, which indicate hardness higher than 40 HRC around ½ inch from the surface. In Table 10 of the TBPOC report, TBPOC-Caltrans reported HRC for Item 12 and HRC for Item 13. They ignored the hardness up to 40 HRC or higher at ½ inch from the surface and its implications on HE failures. High hardness like 40 HRC would be a concern from the point of HE cracking susceptibility regardless of whether it occurred at the surface or some distance from the surface. If the above peculiar hardness distribution curves resulted from insufficient tempering, there is a hidden problem in addition to the question of maximum hardness at ½ inch from the surface. This is that insufficient tempering would not have imparted the full benefit of lowering the residual stresses that are induced in the steel during hardening. This aspect of tempering on lowering the residual stresses is usually

16 Main Concerns About the Anchor Rods on the New Bay Bridge 12 overlooked because they would be low after sufficient (or complete) tempering. In this case, however, the effects of residual stresses in the 3 and 4 inch anchor rod for the tower base on HE susceptibility should be taken into consideration. This is because the tensile stress that can cause SCC (or EHE) would include residual stresses as well as applied stresses. Often, residual tensile stresses alone without applied stresses can cause SCC failures. The peculiar hardness distributions above and the potentially high residual stresses in the tower base anchor rods make them unsuitable for utilizing KI SCC data in the literature or conducting a KI SCC test using small specimens. Therefore, a KI SCC curve for the tower base anchor rods would have to be constructed using the Townsend KI SCC test rig in the same way as for the PWS anchor rods. To determine a KI SCC curve that is relevant to evaluating the HE susceptibility (or KI SCC ) of the tower base anchor rods, TBPOC-Caltrans need to do the following. (a) Recognize that the tower base anchor rods with M-shaped hardness distribution curves have metallurgical characteristics (and HE susceptibility) that are different from the anchor rods with V-shaped hardness distribution curves. (b) Provide a metallurgical explanation as to how the M-shaped hardness distribution resulted. Verify the explanation by conducting a heat treatment experiment that would duplicate the M- shaped hardness distribution. (c) Purchase 3 and 4 inch anchor rods that were heat treated to have an M-shaped hardness distribution. Using full size anchor rods, conduct a KI SCC test to construct a KI SCC -HRC curve. (Specimens could be shorter than the actual tower base anchor rods.) (d) Construct a KI SCC -HRC curve for both the 3 and the 4 inch anchor rods for the tower base as well as for the Tower Saddle Tie Rods. V. COMMENTS ON TBPOC-CALTRANS KI-HRC STRATEGY The purposes of constructing KI SCC -HRC curves are as follows according to the TBPOC report (p.66). Figure 34 of the TBPOC report is reproduced on the next page.

17 Critical Stress Intensity Factor, KISCC, or Stress Intensity Factor, KI, ksi in Main Concerns About the Anchor Rods on the New Bay Bridge 13 Tower Saddle Tie Rod 2 - Bearing and Shear Key Anchor Rods 3 - Shear Key Rods (top) Typical KI SCC HRC (Townsend) Curve Saddle Turned Rods PWS Main Cable Anchor Rods Bearing Rods (top) Tower Anchor Rods Tower Anchor Rods East Saddle Tie Rods Bearing Retainer Ring Plate Assembly Bearing Assembly Cable Band Anchor Rods 10 - Saddle Grillage 11 Outrigger Boom East Saddle Anchor Rods Surface Hardness, HRC Figure 9 Caltrans KI-HRC data as presented in Figure 34 of the TBPOC report of July 8, (The label for the ordinate has been changed from Critical Stress Intensity, ksi in in Figure 34.) The TBPOC presented the above figure without explanations as to what the horizontal bars or the dots would represent. It seems that the horizontal bars would represent the hardness range and the dots average HRC values for the anchor rods of the item numbers indicated. The HRC values by the dots correspond to those reported in Table 10 of the TBPOC report (page 53). In general, the higher the pretension level and the larger the anchor rod diameter, the higher the KI values. The dashed curve would represent a typical KI SCC -HRC curve, similar to the Townsend curve, the bottom curve in Figure 4. Figure 33 of the TBPOC report shows There are several problems with this methodology, as follows.

18 Main Concerns About the Anchor Rods on the New Bay Bridge 14 (i) As mentioned already, the word Critical should be deleted in the above step. (ii) The Townsend KI SCC -HRC curve, to be constructed of Item 18 (3 inch diameter anchor rods, purchased to the new supplementary requirements including HRC), would not be applicable to the PWS anchor rods with rolled threads and the tower base anchor rods that have M-shaped hardness distribution curves. (iii) The anchor rods for the main cable (PWS) and the tower base have metallurgical characteristics that would require separate KI SCC curves of their own. Also, the KI SCC calculations using the failure load for full size anchor rod specimens of the Townsend KI SCC test setup are not straightforward. This is because the full size anchor rod specimens are not precracked. Therefore, the KI or KI SCC calculations must involve some assumptions and shape factors, which can vary from one technical reference to another. For example, the shape factors cited in the book by Prof. Fisher and his coauthors in 1987 may be inconsistent with shape factors for a threaded rod in the latest literature. TBPOC-Caltrans must disclose full details of the Townsend KI SCC test, including the KI SCC calculations. The objective of the Townsend KI SCC test would be to calculate the threshold stress, σ SCC, below which the anchor rods will not fail due to HE. TBPOC-Caltrans need to show how the KI SCC data may be used to arrive at σ SCC. VI. CONCLUSIONS The July 8, 2013 TBPOC Report has many errors, from typographical to wrong conclusions as to the cause of the shear key anchor rod failures. Caltrans protocols for various laboratory and field tests, including KI SCC tests, on anchor rods missed the effects of cold rolled threads of anchor rods for the main cable (PWS) and of incomplete tempering during heat treatment of anchor rods for the tower base. TBPOC-Caltrans understanding of the hydrogen embrittlement susceptibility of these anchor rods is woefully inadequate and their remedial resolutions remain questionable. They need to check their Townsend KI SCC test to ascertain if the results are valid. Without valid KI SCC data, the TBPOC-Caltrans remedial rod-by-rod resolutions will be groundless. The July 8, 2013 TBPOC report on the new Bay Bridge anchor rod problems has all the characteristics of an un-reviewed or unedited draft or rough notes from which a more refined, comprehensive document was to be constructed. As issued, it cannot be considered a definitive professional engineering report intended to provide remedial resolutions for what was clearly a major materials engineering failure on a $6.4 billion project. TBPOC-Caltrans need to do more work, a lot more work, and present a new revised report on the anchor rod problems on the new Bay Bridge.