FAILURE CHAIN · EP008 · SOURCES
Silver Bridge collapse (Point Pleasant, WV, 15 Dec 1967)
How to read this page. Each row is one claim. "Source and page" gives the document and the page in it. "Verbatim" is the exact text from that page. Status: VERIFIED and FINDING are stated by the official report; INFERENCE is the report's own reconstruction; TESTIMONY is attributed evidence; CONTESTED means the sources disagree.
Sources
| Key | Document | Public copy |
|---|---|---|
| ntsb-har-71-01-silver-bridge-1970.pdf | National Transportation Safety Board, Highway Accident Report NTSB-HAR-71-1: Collapse of U.S. 35 Highway Bridge, Point Pleasant, West Virginia, December 15, 1967, adopted December 16, 1970. | open |
A · Identity, synopsis, cause
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-001 | The report is NTSB-HAR-71-1. The NTSB adopted it on 16 December 1970. | ntsb-har-71-01-silver-bridge-1970.pdf, PDF p.1 (cover, unnumbered) | "Adopted: DECEMBER 16, 1970" | VERIFIED | The cover also reads "REPORT NUMBER: NTSB-HAR-71-1". The PDF p.8 header was image-checked as "December 16, 1970"; the OCR misreads it as "15". The signature page (PDF p.135, printed 128) also says 16 December 1970. |
| N-002 | This final report supplements an interim report issued on 4 October 1968. The interim report covered the bridge's design, construction, operation and maintenance from its completion in 1928 to its collapse. | PDF p.8, printed p.1 | "supple[m]ents the interim report issued October 4, 1968 … The interim report included desc[r]iptions of the design, construction, operation, and maintenance of the bridge from its completion in 1928 until its collapse in 1967." | VERIFIED | This is the only construction date the final report gives: "completion in 1928". It gives no opening day and no start-of-construction date; do not invent them. The interim report is not in sources/. The OCR's "1957" and "1948" in this paragraph are misreads; the image shows 1967 and 1968. |
| N-003 | The public hearing was held in Charleston, WV, on 10–13 May 1968. | PDF p.8, printed p.1 | "public hearing held in Charleston, West Virginia, May 10 through May 13, inclusive, 19[6]8." | VERIFIED | The OCR reads "1948". The image shows 1968. |
| N-004 | The bridge connected Point Pleasant, WV, with Kanauga, Ohio. It collapsed at about 5 p.m. EST on 15 December 1967. | PDF p.16, printed p.9 | "[The U. S.] 35 Highway Bridge connecting Point Pleasant, West Virginia, with Kanauga, Ohio, collapsed at approximately 5 p.m. (EST) December 15, 1967." | VERIFIED | Image-checked. "Approximately 5 p.m." is the only time the report gives. Do not give a minute-level time from this source. |
| N-005 | 46 people died and 9 were injured. | PDF p.16, printed p.9 | "Forty-six persons died in the accident, nine were injured" | VERIFIED | Image-checked. The numbers are spelled out on the page. |
| N-006 | 31 of the 37 vehicles on the bridge fell with it: 24 into the Ohio River and 7 onto the Ohio shore. No pedestrians were on the bridge. | PDF p.16, printed p.9 | "31 of the 37 vehicles on the bridge fell with the bridge. Twenty-four vehicles fell into the Ohio River and seven fell on the Ohio shore[.] There were no pedestrians on the bridge at the time of collapse." | VERIFIED | Image-checked. 24 + 7 = 31. The 6 vehicles that did not fall are not itemized here. |
| N-007 | The first structural failure was a cleavage (brittle) fracture in the lower limb of the eye of eyebar 330, at joint C13N. C13N was the first chain joint west of the Ohio tower. | PDF p.16, printed p.9 | "The initial failure in the bridge structure was a cleavage fracture in the lower limb of the eye of eyebar 330 (north bar, north chai[n], Ohio side span) at joint C13N, the first eyebar chain joint west of the Ohio tower of the bridge." | FINDING | "Cleavage" means brittle fracture. Location: north chain, Ohio side span, the upstream side. |
| N-008 | A ductile fracture in the upper limb then freed eyebar 330 from the chain. Its sister bar, eyebar 33, immediately slipped off the C13N pin, and the north chain parted. | PDF p.16, printed p.9 | "The cleavage fracture was followed by a ductile fracture in the upper limb of the eye of eyebar 330 at joint C13N, separating eyebar 330 from the chain. Immediately following the separation of eyebar 330 from joint C13N, the sister eyebar 33 slipped from the C13N joint pin, re[sulting] in the separation of the north chain at that location." | FINDING | The order is fixed: 330 broke first, then 33 slipped. See N-047 for why the "walk-off first" theory was rejected. |
| N-009 | The collapse began in the Ohio side span and moved east toward West Virginia. Within about one minute, the 700-ft center span, both 380-ft side spans and the towers were down. | PDF p.16, printed p.9 | "The coll[apse] of the bridge began in the Ohio [side] span, moving eastward toward the West Virginia shore, with the result that within a period of about 1 minute, the 700-foot center span, the two 380-foot side spans, and the towers had collapsed." | CONTESTED | 700 ft and 380 ft were image-checked. The "about 1 minute" figure conflicts with the seven-step reconstruction, which ends at 6–10 seconds (N-054). A survey on PDF p.22 gives the West Virginia side-span pier distance as "370 feet shown on the drawings" (N-061). Use 380 ft as the synopsis figure. |
| N-010 | Cause: the cleavage fracture in eyebar 330 at joint C13N, in the north suspension chain of the Ohio side span. | PDF p.133, printed p.126 | "The Safety Board finds that the cause of the bridge collapse was the cleavage fracture in the lower limb of the eye of eyebar 330 at joi[n]t C13N of the north eyebar suspension chain in the Ohio side [s]pan." | FINDING | The same wording appears in the synopsis (PDF p.16). |
| N-011 | The fracture came from a flaw that grew to critical size over the bridge's 40-year life, through stress corrosion and corrosion fatigue acting together. | PDF p.133, printed p.126 | "The fracture was caused by the development of a critical size flaw over the 40-year life of the structure as the result of the joint action of stress corrosion and corrosion fatigue." | FINDING | 40-year life was image-checked on the synopsis page. Keep "joint action". The Board did not pick one mechanism (N-019 and N-058). |
| N-012 | Contributing cause 1: in 1927, when the bridge was designed, stress corrosion and corrosion fatigue were not known to occur in this kind of bridge steel under ordinary rural exposure. | PDF p.133, printed p.126 | "In 1927, when the bridge was designed, the phenomena of stress corrosion and corrosion fatigue were not known to occur in the classes of bridge material used under conditions of exposure normally encountered in rural areas" | FINDING | The design year is given as 1927 here and as 1926 elsewhere (N-064). |
| N-013 | Contributing cause 2: the flaw was in a place that could not be seen during visual inspection. | PDF p.133, printed p.126 | "The location of the flaw was inaccessible to visual inspection" | FINDING | |
| N-014 | Contributing cause 3: no inspection method known in 1970 could have found the flaw without taking the eyebar joint apart. | PDF p.133, printed p.126 | "The flaw could not have been detected by any inspection method known in the state of the art today without disassembly of the eyebar joint." | FINDING | "Today" means 1970. |
| N-015 | Once the north chain separated at C13N, total collapse was certain, because the towers stood on rocker seats. | PDF p.8, printed p.1 | "When the north eyebar chain was separated at joint C13N, total collapse of the bridge was a certainty due to its design with the towers resting on rocker seats." | FINDING | Foreword wording, restating the interim report. Pair it with N-030 (only two bars per link). |
| N-016 | Eyebars 330 and 33 formed the north-chain link between joints C11 and C13. C13 was the first joint west of the Ohio tower, and the north leg of the Ohio tower was joint C15N. | PDF p.8, printed p.1 | "Eyebar 330 and its sister eyebar 33 were located in the north suspension chain of the bridge between joints C[11] and C13. C13 was the first joint west of the Ohio tower. The north leg of the Ohio tower was joint [C15N]." | VERIFIED | The OCR reads "CISN". The image shows C15N. 330 was the north bar and 33 the south bar (PDF p.17). |
B · Conclusions A1–A7 (sequence of events)
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-017 | A1: Total collapse required a failure in a chain or a tower. The directions in which the towers fell put that failure at the Ohio tower or west of it, in the north chain or its supports. | PDF p.128, printed p.121 | "The total collapse [o]f the structure required the failure of some element in the supporting chains or towers. The directions in which the towers fell indicate that this failure was at the Ohio tower or west of this point in the Ohio side span, and in the north chain or its supporting elements." | FINDING | Both towers fell toward West Virginia (N-044). |
| N-018 | A2: The north leg of the Ohio tower did not fail. The fractures in the chain bent post and in gusset plate U7N came from abnormal loads that the traffic just before collapse could not have produced. That leaves a failure in the chain itself. | PDF p.128, printed p.121 | "Examination of the Ohio tower wreckage showed no failure in the north leg … The only remaining failure in the chain or its supporting eleme[nts] in the Ohio side span which could have led to collapse is a [failure] of some element in the chain itself." | FINDING | This is the elimination logic. |
| N-019 | A3: Joint C13N began to separate because of the brittle fracture in eyebar 330. After that, eyebar 33 slid off the south end of the pin. | PDF p.128, printed p.121 | "[The] joint at C13N, the first joint in the north chain west of the O[hio] tower, began to separate because of the brittle fracture in eyebar No. 330 … Subsequent to this fracture, eyebar No[.] 33 (the southerly bar of this pair) slid off the south end of the pin, causing complete separation of the north chain at this point." | FINDING | The OCR's lowercase "the" at the start is the page's "The". |
| N-020 | A4(a): The small crack was big enough, at the stress computed for that spot, to cause the brittle fracture with no extra dynamic load. | PDF p.128, printed p.121 | "The small crack which existed prior to the collapse was large enough to account for the brittle fracture in the special steel of which the eyebars were made at the stress level computed to exist at this location, without any additional dynamic effects." | FINDING | This is the key line against "a truck jolt broke it". |
| N-021 | A4(b): The crack probably started at a small corrosion pit. | PDF p.128, printed p.121 | "This small crack probably initiated at a small corrosion pit." | FINDING | Keep "probably". |
| N-022 | A4(c): Stress-corrosion cracking and corrosion fatigue grew the crack together. The evidence does not show which one dominated. | PDF p.128, printed p.121 | "The crack grew to critical size by the joint action of stress-corrosion cracking and corrosion-fatigue. The available evide[n]ce is not sufficient to permit a definite conclusion as to which mechanism was predominant." | FINDING | This conflicts with the analysis, which leans toward stress corrosion (N-058). |
| N-023 | A5: Because the crack was so small and sat inside the pinhole, it could not have been found while the bridge stood: not by the inspection methods used, and not by any 1970 field method, without taking the joint apart. | PDF p.129, printed p.122 | "The small size of the critical crack in eyebar No. 330, and its location on the inside surface of the hole, precluded its being found while the structure was intact, by the inspection techniques used, or by any other inspection technique available at this time for use in the field on heavy structures, without disassembly of the joint." | FINDING | Image-checked. "Inspection techniques used" implies the bridge was inspected, but this report does not describe how or when (N-079). |
| N-024 | A6: Other fractures that might have sent a shock wave into the chain were studied. Some started at small existing cracks, but the evidence shows they happened after the collapse had begun. | PDF p.129, printed p.122 | "although some of these fractures occurred at points of additional pre-existent cracks in the structure[,] there is sufficient evidence to demonstrate that these fractures occurred after the process of collapse had begun." | FINDING | Image-checked. "Pre-existent cracks" elsewhere in the structure is a real fact, but none of them was the trigger. |
| N-025 | A7: Ordinary rust did not reduce the main members below what they needed to carry, either their design loads or the loads just before collapse. Some secondary parts were deeply rusted. | PDF p.129, printed p.122 | "Although there was deep rusting of some secondary elements[] such as stay plates, l[a]cing bars, a[n]d diaphragms, there is no [i]ndication that the net critical[] sections of main members were reduced in cross section to the point where they were inadequate to carry the intended loads or those imposed by the loading just prior to collapse." | FINDING | This refutes "the bridge rusted through". The deadly corrosion was microscopic pitting inside the pinhole, not general rust. |
C · Conclusions B1–B7 (elements that contributed)
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-026 | B (preamble): The failure came from several trends that were normal engineering practice in the 1920s, combined with a slow crack-growth process that was little known when the bridge was built. | PDF p.129, printed p.122 | "The failure of the Point Pleasant Bridge was a result of the convergence of several trends, each of which was common in engineering practice in the era in which it was designed, and the existence of a subtle form of time-dependent crack growth of which little was known at the time of its construction" | FINDING | This is the spine's framing line: no villain. |
| N-027 | B1: There was a trend toward stronger steels. The eyebars were a heat-treated steel with relatively high carbon content. | PDF p.129, printed p.122 | "The trend toward use of higher strength materials for steel structures. The steel in the eyebars was a heat treated, relatively high carbon steel (compared to ordinary structural carbon steel)." | FINDING | |
| N-028 | B2: The eyebars were allowed a working stress of 50,000 psi, which is 67 percent of the specified 75,000 psi elastic limit. About 75–80 percent of the stress came from the bridge's own weight. | PDF p.129, printed p.122 | "The allowable stress for the eyebars was set at 50,000 psi. or 67 percent [o]f the elastic limit of 75[,]000 psi. specified for the material. Typically, 75 to 80 percent of the applied stress was due to the weight of the structure itself." | FINDING | Image-checked. The page prints "75 000" with no comma. 50/75 = 66.7%, so 67% is consistent. The analysis says "approximately 75 percent" (N-066). Use "about three-quarters". |
| N-029 | B3: Some secondary and local stresses were not computed, a practice that was common for eyebars. The fabricator only had to show by static test that the high-stress area in the eye did not limit the bar's capacity. | PDF p.129, printed p.122 | "The practice of not computing certain secondary stresses or local effects where these were produced by static loads, and where the range of stress due to traffic loads and other transient effects was small[.] This practice was particularly common for eyebars" | FINDING | See N-068 on primary-only analysis. |
| N-030 | B4: In the 1920s, stress-corrosion crack growth was known only in a few metals under harsh conditions, such as boilers, chemical and food containers and machine parts. By today's knowledge, the stress at the edge of the eyebar hole was too high for this material without special corrosion protection. | PDF p.130, printed p.123 | "In the light of present day knowledge, the stress at the edge of the hole in the eyebars was too high for a material subject to crack growth by either of these mechanisms without special corrosion protection." | FINDING | This is hindsight, and the report says so. |
| N-031 | B5: Water could collect in a pocket next to a point of high stress, as it can in any eyebar joint with enough clearance between the pin and the hole. | PDF p.130, printed p.123 | "There was a water [collection] pocket adjacent to a point of high stress, as there is in any eyebar construction, where there is sufficient clearance between the pin and the pinhole surface to permit entry of water." | FINDING | See N-059 (the capillary space at the "90 degree" position). |
| N-032 | B6: That point of high stress could not be reached for inspection. | PDF p.130, printed p.123 | "This point of high stress was not accessible for inspection." | FINDING | |
| N-033 | B7: Each chain link had only two eyebars, so once eyebar 330 broke, the whole chain was bound to fail. With three or more bars per link, one broken bar might not have caused disaster. | PDF p.130, printed p.123 | "The use of only two eyebars per link in the eyebar chain. This made the total failure of the chain inevitable once the fracture occurred in eyebar No. 330. Had there been t[h]ree or more eyebars per link, there would have been the possibility that the failure of one bar would not have led to disaster" | FINDING | This is the redundancy beat, the core "chain" metaphor of the episode. |
D · Conclusions C1–C4 and D1–D4
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-034 | C1: This exact combination of factors is rare. The only other U.S. bridge with all of them was at St. Marys, WV, which had been closed since early in the investigation. | PDF p.130, printed p.123 | "The relatively rare combination of all the factors cited above for the Point Pleasant Bridge makes the recurrence of this exact type of failure remote[.] The only other bridge in this country to combine all these factors is at St. Marys, West Virginia, and it has been closed since early in this investigation." | FINDING | |
| N-035 | C2: Many other bridges have one or more of these factors, and no one knows exactly which combinations are critical. | PDF p.130, printed p.123 | "There are, however, many other structures which possess one or more of these factors as features in their designs. It is not precisely known what the critical combinations may be" | FINDING | |
| N-036 | C3: Better inspection will catch visible damage. Small hidden flaws in susceptible materials can still exist, and sometimes the critical flaw size is below what current inspection devices can detect. | PDF p.130, printed p.123 | "the possibility of small flaws in critical elements made of material susceptible to stress[-]corrosion, corrosion-fatigue and other time dependent flaw growth phenomena does exist." | FINDING | |
| N-037 | C4: The bridge-safety program should be accelerated: identify susceptible materials, set critical flaw sizes, build new field inspection equipment, create design safeguards, develop repair techniques, and learn more about loading history and bridge life. It also says 100 percent inspection would probably be impractical. | PDF p.131, printed p.124 | "One hundred percent inspection will probably prove impractical and extremely expensive." | FINDING | C4 items (a)–(f) are on PDF pp.130–131. The page also says "Develop a new generation of inspection equipment for use under field conditions". |
| N-038 | D1: The DOT's work on inspection standards and inspector training, required by the Federal-Aid Highway Act of 1968, is a positive step for bridges on the Federal-Aid System. | PDF p.131, printed p.124 | "The intensive actions of the Department of Transportation to establish standards for the proper safety inspections of bridges, and training programs for bridge inspectors as required by the Federal-Aid-Highway Act of 1968, are positive steps to i[n]crease the safety of highway bridges in the Federal-Aid-System." | FINDING | |
| N-039 | D2: More than 70 percent of about 563,500 U.S. highway bridges are not on the Federal-Aid System. 94 percent of about 373,000 bridges on county, rural and city roads were built before 1935. | PDF p.131, printed p.124 | "Over 70 percent of the approximate total of 563,500 highway bridges in the United States are not in the Fede[r]al-Aid-System, and 94 percent of the approximate number of 373,000 bridges on county secondary roads, rural roads, and city streets were built prior to 1935." | FINDING | Image-checked. It matches the facts section (N-085, N-086): 343,000 / 373,000 = 92%, not 94%. The report rounds or uses other data; see audit. |
| N-040 | D3: There is no requirement for authorities that own bridges off the Federal-Aid System to adopt the new federal inspection standards. | PDF p.132, printed p.125 | "there is no requirement that such authorities implement the intent of these documents." | FINDING | |
| N-041 | D4: The 1968 Act created a split. Federal-Aid bridges must meet strict federal inspection standards, while most of the nation's bridges need not, unless they adopt them voluntarily. | PDF p.132, printed p.125 | "bridges in the Federal-Aid System are required to meet rigorous Federal standards for inspection and maintenance, while the majority of the bridges in the country are not subject to those standards, except as voluntarily adopted." | FINDING |
E · Recommendations
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-042 | Recommendation 1: The Secretary of Transportation should expand research to (a) identify materials prone to slow flaw growth, (b) find critical flaw sizes, (c) develop equipment to detect flaws in standing bridges, (d) find critical locations, (e–f) set design and material standards, (g) develop repair techniques, and (h) learn more about loading history and bridge life expectancy. | PDF p.134, printed p.127 | "Develop inspection equipment capable of detecting critical or near critical flaws in standing bridge structures" | FINDING | This is item (c). Item (e): "ensure protection against fai[l]ures of material such as occurred in the Point Pleasant Bridge". |
| N-043 | Recommendation 2: The Secretary should explore how to make the 1968 Act's bridge-safety requirements mandatory for all U.S. highway bridges, through state adoption or federal law. | PDF p.134, printed p.127 | "The Secretary of Transportation explore the alternatives for action to assure mandatory application of the bridge safety requirements of the 1968 Federal-Aid-Highway Act to all highway bridges in the United States" | FINDING | It continues on PDF p.135: "or the enactment of Federal legislation applicable to all highway bridges." |
| N-044 | Recommendation 3: The Secretary should consider proposing federal aid to repair bridges that are not on the Federal-Aid System. | PDF p.135, printed p.128 | "The Secretary of Transportation consider the advis[a]bility of proposing a program of Federal aid to ensure the adequate repair of all bridges n[o]t in the Federal-Aid-System." | FINDING | The report was signed by Chairman John H. Reed and members Laurel, McAdams, Thayer and Burgess. |
F · Collapse sequence
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-045 | Salvage showed that both towers fell toward West Virginia. That ruled out a chain break in the main span or the WV side span, so a chain failure had to be in the Ohio side span. | PDF p.23, printed p.16 | "positive evidence from the salvage operation showed that both towers fell toward the West Virginia shore. This permitted elimination of the possibility of a failure in the eyebar chains in either the central span or the West Virginia side span." | VERIFIED | This is good for a graphic: tower fall direction points to the break. |
| N-046 | The only chain failure in the Ohio side span was the separation at joint C13N. | PDF p.23, printed p.16 | "The only failure in the eyebar chain within the Ohio side span was the separation of the joint at C13N." | VERIFIED | |
| N-047 | Investigators rejected the theory that eyebar 33 "walked off" its pin first. The burr shows no progressive steps, eyebar 330's fracture shows no out-of-plane bending, and a model test could not reproduce a walk-off, while a simulated 330 fracture matched the wreckage. | PDF p.101, printed p.94 | "There are several types of evidence which eliminate the possibility that eyebar No. 33 slipped off or "walked off" the end of pin C13N." | FINDING | The walk-off would have doubled the load on 330 (PDF p.19). The NBS burr finding: "formed in a single step as the bar slid off the end of the pin" (PDF p.41, printed p.34). |
| N-048 | The pin from joint C13N was never found, despite three searches. Dredging did recover the broken-off outboard piece of eyebar 330's eye. | PDF p.18, printed p.11 | "had been successful in locating the outboard piece from the fractured eye of eyebar No. 330, but they had not located the pin from joint C13N in spite of three separate searches." | VERIFIED | This is a nice "missing piece" beat. |
| N-049 | Step 1 (t = 1.0 s): after the lower limb broke, the joint took about a second to finish tearing through the upper limb. In the model test this took 1.2 s. The chain lengthened about 3 inches. | PDF p.108, printed p.101 | "Some short period of time, on the order of a second, was required to complete the rupture of eyebar No. 330 through the upper limb of its C13 head. This process required 1.2 seconds in the model test." | INFERENCE | All step times are counted from the brittle fracture and computed from free-fall rates. The report says "this analysis assumes". |
| N-050 | Step 2 (t = 1.2 s): with 330 fully broken, the C13N pin rotated and eyebar 33 slid off its south end, leaving a burr. | PDF p.110, printed p.103 | "the final fracture of the upper limb of the C13 eye of eyebar No[.] 330 permitted the pin at C13N to rotate about a vertical axis, so that eyebar No. 33 slid off the south end of this pin." | INFERENCE | Eyebar 33's final resting place "remains a mystery" (same page). |
| N-051 | The sudden release of chain tension travelled as a wave at about 14,000 ft/s and reached the anchorage in about 0.024 seconds. | PDF p.111, printed p.104 | "traveling as a rarefaction wave at acoustic velocity (about 14000 ft./sec.) from C1[1]N through U7N, the top of the chain bent post, and then to the anchorage, reached that point in about 0.024 seconds." | INFERENCE | Introduced with "believed to have been approximately as follows". |
| N-052 | With the chain slack, the north truss of the main span dropped in near free fall. In the middle of the span the truss's upper chord was the eyebar chain itself, so the truss could not hold itself up. | PDF p.112, printed p.105 | "the upper chord in the middle portion of the span consisted of the eyebar chain, Without the original chain tension, these eyebars could take very little load in compression before they began to buckle. The main span north truss therefore dropped in essentially free fall" | INFERENCE | This supports the design point that the chain served as the top chord of the stiffening truss. In the side spans the eyebars from U0 to U7 also served as the truss top chord ("participation in the stiffening truss", PDF p.105). Plate 1 (PDF p.13) shows truss members gusseted into the eyebar joint. |
| N-053 | By t = 2.0 s the north edge of the main span had dropped about 16 ft, and the top of the Ohio tower's north leg was about 8 ft east of normal. By t = 4.0 s the Ohio side span collapse was virtually complete. | PDF pp.113–115, printed pp.106–108 | "The collapse of the Ohio side span was virtually complete." | INFERENCE | That sentence is on PDF p.115 (Step 6, "Time = 4.0 seconds"). The 16 ft figure is on PDF p.113/114. |
| N-054 | Step 7 (6 to 10 s): the West Virginia tower rotated toward West Virginia and appears to have been the last part to fall into the water. | PDF p.116, printed p.109 | "It appears that the West Virginia tower was the last part to fall into the water. It fell toward West Virginia and slightly downstream of its normal position" | INFERENCE | The step header reads "Time = 6 to 10 seconds" (PDF p.116). This conflicts with the synopsis's "about 1 minute" (N-009). |
| N-055 | The Ohio tower's south leg broke about 69 ft below its top. A second fracture about 26 ft below the saddle came from a violent collision with the north leg. | PDF p.28, printed p.21 | "Further bending resulted in failures in the tower bracing system and a fracture through the south leg about 69 feet below the top of the tower." | INFERENCE | From the Hechtman scar analysis (Reference 14). |
| N-056 | Witness Wesley F. Wears, on a dock about a quarter mile downstream, said the Ohio towers fell first, the center span "fell straight down", and "the bridge was all down in a matter of five seconds as I estimate it". | PDF p.117, printed p.110 | "the bridge was all down in a matter of five seconds as I estimate it" | VERIFIED | This is a witness estimate. The report says distant witnesses were "generally in accord" with the reconstruction. |
| N-057 | Survivors near panel points 3 and 4 felt a short drop, then a pause, before the full fall. In the middle of the main span, one person got out of the back seat of a two-door car between the first 3-ft drop and the final fall. | PDF p.121, printed p.114 | "a witness was able to get out of the back seat of a two door car between the time it dropped the first three feet and the final fall." | VERIFIED | The report gives an explanation, "possibly due to ... cantilever action", which is an INFERENCE. |
G · Crack, mechanism, Bureau of Standards
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-058 | Stress corrosion vs corrosion fatigue: the analysis section concludes stress corrosion "appears" dominant, while admitting evidence of transgranular cracking that fits corrosion fatigue. | PDF p.105, printed p.98 | "It therefore appears that the stress-corrosion was th[e] dominant mechanism[,] in spite of the fact that there is evidence" | CONTESTED | Image-checked. This conflicts with Conclusion A4(c) (N-022), which says no definite conclusion is possible. On camera, say what the conclusions say: both mechanisms, and which one dominated is unresolved. |
| N-059 | The crack sat at the "90 degree" position on the hole surface. That point had the most pin-hole movement (fretting) and a tapered capillary gap that could trap contaminants from rain water. Fretting is believed to have helped start the pits. | PDF p.102, printed p.95 | "It was also favorable for stress corrosion because of the geometry of the hole, which provided a tapered capillary space at this point which could collect and concentrate contaminants dissolved in rain water. It is believed that fretting was a factor in the initiation of these pits." | INFERENCE | "Believed". Professor Starkey (Ohio State) found fretting evidence on some pins (same page). |
| N-060 | The National Bureau of Standards (NBS) first found a small radial crack about 1/8 inch deep running from the eyebar hole surface in the plane of the fracture. It started at a point that touched the pin. | PDF p.18, printed p.11 | "the [N]ational Bureau of Standards had revealed that there was a small radial crack about 1/8-inch deep extending from the eyebar hole surface in the plane of the fracture. The origin of this crack was at a point which was in contact with the pin in the assembled structure." | VERIFIED | Image-checked: "1/8-inch deep". This is the interim-era description; the final NBS description is N-061. |
| N-061 | The fracture started from a small semicircular crack of about 1/8-inch radius plus an auxiliary crack of about 1/16-inch radius. Both were on the inside surface of the pinhole near the bar's south face. | PDF p.39, printed p.32 | "The fracture of the [lower] limb of the C[1]3 head of this eyebar was precipitated by the existence of a small semi-circular crack about 1/8-inch in radius and an auxiliary crack about 1/[1]6-inch in radius (See Figure 7). Both of these small cracks originated on the inside surface of the pinhole near the south face of the bar" | VERIFIED | Image-checked. The OCR reads "1/l6". Units: 1/8 inch is the radius of a semicircle, so the crack was about 1/8 inch deep. Battelle measured the primary flaw as 0.12" × 0.28" (PDF p.54, printed p.47). Figure 7 (PDF p.40) is the NBS photo. Also printed p.32: "a plane roughly through the center of the pin at right angles to the longitudinal axis of the eyebar". |
| N-062 | Nearby cracks of the same kind were traced to small corrosion pits on the pinhole surface. They ran straight into the metal, at right angles to the main stress. | PDF p.39, printed p.32 | "Sectioning and examination of these cracks under high magnification indicate that they originated from small corrosion pits on the pinhole surface and penetrated radially into the eyebar material, approximately at right angles to the lines of principal stress." | VERIFIED | Other cracks lay about 1/16 inch from the fracture plane and up to about 1/2 inch away. |
| N-063 | The old crack faces were coated with dark oxides that looked different from the fresh rust on the rest of the fracture. This shows the crack existed before the collapse. | PDF p.39, printed p.32 | "The faces of both the pre-existent crack associated with the main fracture and the similar cracks in adjacent areas were covered with dark oxides of a distinctly different color and texture than the surface rusting which developed on the remainder of the fracture surface." | VERIFIED | This is good visual evidence (dark versus orange). |
| N-064 | NBS microprobe work found more sulfur compounds than normal on the crack surface. This suggests that sulfur-bearing gases such as sulfur dioxide or hydrogen sulfide may have entered the cracks and driven stress-corrosion growth. | PDF p.44, printed p.37 | "Microprobe analyses indicated the presence of more than normal amounts of sulfur compounds in the crack surface. This indicates that sulfur bearing gases such as sulfur dioxide or hydrogen-sulfide in the atmosphere may have penetrated into the cracks" | INFERENCE | "May have". Do not claim "industrial pollution caused it" as fact. |
| N-065 | In an NBS lab test, a piece of eyebar 330 held under stress in a hydrogen-sulfide solution cracked extensively after an additional 49 days. | PDF p.44, printed p.37 | "The specimen was returned to the corrosion cell for an additional 49 days and, after this exposure, exhibited extensive cracking." | VERIFIED | Test stress: 113,000 psi outer fiber, which is a lab condition, not the field stress. |
| N-066 | NBS issued seven reports (References 17–23). On 31 December 1968 the Board announced by press release that labs had found minute cracks inside the fractured head of eyebar 330, with stress corrosion suspected. | PDF p.32, printed p.25 / PDF p.8, printed p.1 | "The results of the investigations conducted at the National Bureau of Standards are documented in a series of seven reports from that laboratory (References 17 through 23)." | VERIFIED | Press release, PDF p.8: "The Safety Board issued a press release on December 31, 1968, describing the discovery during laboratory examinations of evidence of a se[r]ies of minute cracks". |
| N-067 | Battelle cut off and lab-tested 30 eyebar heads. Five showed positive signs of cracks on the pinhole surface. | PDF p.53, printed p.46 | "Thirty eyebar heads were therefore burned off and taken to the Battelle laboratories at Columbus for examination under more favorable conditions. … The net result of this program was that positive indications of cracks on the pinhole surface were found in five of the eyebar heads." | VERIFIED | Field dye-penetrant and magnetic-particle checks had been "inconclusive" (same page). |
| N-068 | Fracture mechanics: a flaw the size of eyebar 330's (0.12" × 0.28") needed about 88,000 psi to cause a brittle fracture using Battelle's toughness value. U.S. Steel's lower toughness value gives 75,000 psi. Local stress at the hole edge was likely near those levels (N-074). | PDF p.54, printed p.47; PDF p.72, printed p.65 | "indicates that a unit stress of 88,000 psi is required. This is about 10 per[]cent above the yield strength of the material" | INFERENCE | U.S. Steel, PDF p.72: "The indicated failure stress for the critical flaw in eyebar No. 330 based on this lower value of the critical stress intensity factor is 75,000 psi." Do not confuse this 75,000 psi with the 75,000 psi specified elastic limit (N-028). |
| N-069 | A similar tight crack in another eyebar (C9-C11, north chain, south bar) was opened in the lab. Its black oxides were still wet with water. | PDF p.73, printed p.66 | "When first examined, the black oxides in region A were noted to be wet with water." | VERIFIED | This is a strong visual detail. "Within five minutes, the surface was dry." |
| N-070 | The working group agreed that a corrosion process produced the crack in 330 and similar cracks in other bars. The data could not settle whether it was stress corrosion or corrosion fatigue, and no more cracked eyebars were left to study. | PDF p.103, printed p.96 | "it was agreed that the small oxide-covered crack which led to the rapid fracture of eyebar No. 330, similar nearby secondary cracks, and similar cracks in other eyebars were produced by a corrosion process." | FINDING | This is the task-group statement quoted by the Board. |
H · Material and design
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-071 | The eyebars were made from a special U.S. Steel steel developed a few years earlier. It had been used in eyebars on only one other bridge, at Florianópolis, Brazil, and was basically a heat-treated "1060" carbon steel. | PDF p.91, printed p.84 | "The eyebars of the chain were made from a special steel of the U. S. Steel Corporation which had been developed a few years earlier and had been used in the eyebars of one other bridge at Florianopolis, Brazil. This steel was basically a heat treated "1060" carbon steel." | VERIFIED | The trusses, hangers, towers and floor used ordinary A7-24 steel (same page). D. B. Steinman designed the Florianópolis bridge (PDF p.125). |
| N-072 | Heat treatment: the bars were quenched in water from about 1600°F and tempered at 1150–1200°F. The result was uneven, a "slack-quenched" steel with a hard martensite skin 1/4"–3/8" thick and a softer core. | PDF p.32, printed p.25 | "The heat treatment which consisted of quenching in water from the austenitizing temperature (approxi[]mately 1600°F.) and tempering from between 1150 and 1200°F. produced a non-homogeneous micro-structure. It may therefore be characterized as a "slack-quenched" steel" | VERIFIED | PDF p.94 (printed p.87) gives 850–900°C quench and 600–650°C for 2 hours. These are compatible in °C. |
| N-073 | Eyebar 330's steel was not unusual. It matched the 1927 mill-test bars and met the specification, including the 75,000 psi elastic limit. | PDF p.41, printed p.34 | "The material in eyebar No. 330 did not appear to differ in any important respect from other eyebar material removed from the structure." | VERIFIED | PDF p.95 (printed p.88): "the elastic limit value of 75,000 psi was satisfied." This refutes "a defective bar". |
| N-074 | The eyebar steel had low fracture toughness at about 32°F, the approximate temperature at collapse: 2 to 4 ft-lb in Charpy tests. | PDF p.41, printed p.34 | "this material had limited fracture toughness (2 to 4 foot pounds in the Charpy tests) at 32°F., the approximate temperature at the time of the bridge collapse" | VERIFIED | The truss-steel section says "at 30°F" (N-090). Say "around freezing". |
| N-075 | The bridge was designed and erected in 1926–1927 and completed in 1928. | PDF p.121, printed p.114 | "the design and erection of the Point Pleasant Bridge in 1926 and 1927." | CONTESTED | Contributing cause 1 says "In 1927, when the bridge was designed". The Foreword says "the era of 1926 when the Point Pleasant Bridge was designed". Completion: "1928" (N-002). Safe phrasing: "designed in the late 1920s, opened in 1928". The report does not give an opening ceremony date. |
| N-076 | The eyebar chain was an "alternate" design. Its designers chose an allowable stress of 50,000 psi, the consultants approved it, and the steel's minimum elastic limit was 75,000 psi, a safety factor of 1.50. The designers judged this reasonable because about 75 percent of the chain stress came from the bridge's own weight. | PDF p.125, printed p.118 | "The designers of the eyebar chain alternate for the Point Pleasant Bridge selected an allowable stress for the eyebar chain of 50,000 psi. This was approved by the consultants. This material was to be manufactured so as to produce a minimum [e]lastic limit of 75,000 pounds/sq. in. This provides a nominal factor of safety on the elastic limit of 1.50." | VERIFIED | Image-checked. The report does not name the designer firm in this passage. The same page: "approximately 75 percent of the stress in the eyebar chain elements was due to the weight of the structure". |
| N-077 | Comparison: at Florianópolis, Steinman used 46,500 psi for a chain of essentially the same steel, a factor of 1.61. Wire-cable bridges of that era typically used 1.6–1.7. | PDF p.125, printed p.118 | "In the design of the Florianopolis bridge in Brazil, D. B. Steinman used an allowable stress of 46,500 psi. for an eyebar chain composed of essen[]tially identical material. This would yield a factor of safety on the elastic limit of 1.61." | VERIFIED | Point Pleasant's margin was slimmer, but the report attributes this to judgment, not to error. |
| N-078 | The original design calculations followed normal practice of the time and contained no mistakes or significant errors. At the moment of collapse, stresses in the critical members were well below the design maximums. | PDF p.22, printed p.15 | "the original design had been executed in accordance with normal engineer[]ing practice in use at the time of the original design, and that it was without mistakes or significant errors in the original stress computations … the stresses in critical members of the eyebar chain and trusses produced by the loading on the structure at the time of collapse were well below the specified maximum stresses provided for in the original design." | VERIFIED | The only error found was a minor dead-load error in member L13-L15, "of no significance as regards the collapse". |
| N-079 | The designers computed only primary stresses. They did not account for bending from stiff truss joints, distortion of the chain-bent frame, or eyebar heads that might not rotate freely on their pins. No dynamic allowance was made for the chain, towers or stiffening truss. | PDF p.23, printed p.16 | "Only primary stresses in the members of the eyebar chain and the stiffening stresses were considered. … possible effects in the eyebar heads if they did not rotate freely on the pins were also ignored." | VERIFIED | Also: "No allowance for dynamic effects was included in the analysis of eyebar chain, towers or stiffening truss." The floor system got a 30% impact allowance (PDF p.96). |
| N-080 | The stress concentration at the edge of an eyebar hole (about 2.77 times the shank stress) was known in the 1920s. Under dead load alone, the metal at the hole edge probably yielded. Stresses on the order of 85,000 psi there "appear likely". | PDF p.99, printed p.92 | "Stresses on the order of 85,000 psi therefore appear likely, in spite of the fact that pin bending might have caused higher strains on one face than the other." | INFERENCE | Nominal dead-load stress in 330's shank was 36,000 psi (same page). Battelle measured residual stresses up to 27,325 psi at the pinhole edge (PDF p.54). |
| N-081 | Design live load for the chains: 1,400 lb per foot of bridge, about 50 lb per square foot of deck. | PDF p.25, printed p.18 | "The chains of this bridge were designed to carry a live load of 1400 pounds/foot applied at the deck level, which is approximately 50 pounds/square foot on the deck." | CONTESTED | Image-checked. PDF p.126 (printed p.119) prints "a live load of 14,000 pounds/linear ft. of bridge plus a 42,000 lb. concentrated load", also image-checked. That is a 10× conflict. 1,400 fits the 50 psf statement, so 14,000 is probably a typo. Avoid quoting either number on screen. |
| N-082 | The bridge's design live load was heavier than a modern (1931 AASHO) H20 loading on two lanes. No reduction was taken for the unlikelihood of full-length loading. | PDF p.126, printed p.119 | "This is in excess of the 640 lbs./ft./lane for a modern H20 loading on two lanes (as the structure was actually used), and no reduction was taken for the improbability of obtaining such loads over the long loaded lengths" | VERIFIED | This refutes "designed for Model T loads". The report says the design loads exceeded the H20 standard of its day. |
| N-083 | Plate 1 shows a typical chain joint: a joint pin with two sets of eyebars, truss members gusseted into the joint, and a retaining pin with double nuts at each end. Plate 2 shows the makeup of joint C13 north, with a hanger hung from the pin. | PDF p.13, printed p.6 (Plate 1); PDF p.14, printed p.7 (Plate 2); IMAGE-READ (rotated plate, OCR garbled) | "The makeup of the retaining pin, retainer plates and the use of double nuts on each end of the retaining pin were common to all eyebar joints except at the tops of the two towers and at the connections of the eyebar chain with the chain bent posts." | VERIFIED | Read from the rotated page image; the OCR is garbled. The Plate 2 caption: "This plate shows makeup of joint C13 north." These are good reference images for the C13N graphic. |
I · Loading at collapse (vs. "overloaded")
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-084 | At collapse, the live load in eyebar C11-C13 (the 330/33 link) was only 237.3 kips, about 41 percent of design live load. The traffic stretched from the west end to just past the center of the main span. | PDF p.105, printed p.98 | "The live load at the ti[m]e of collapse in eyebar C11-C1[3] was only 237.3 kips, or about 41 percent of design live load. This was due to a load extending from the west end of the structure to just beyond the center of the main span." | VERIFIED | Image-checked. This is the main rebuttal to "overloaded". Live load is only part of total stress, since about 75% was dead load. |
| N-085 | The report's loading table lists the actual load at collapse as 40% of design stress. | PDF p.100, printed p.93 | "40% Design stress - Actual load at time of collapse" | CONTESTED | Image-checked. 40% (stress, table) and 41% (live load, text) are close, but they measure different things. Use "about 40 percent". |
| N-086 | 1964 traffic was only about 16 percent heavy vehicles. The collapse-day load was probably an upper bound on peak loads, reached 20–30 times a day at most. Ordinary fatigue failure was not likely. | PDF p.100, printed p.93 | "The interim report (Reference 2) showed that the typical traffic in 1964 was a mixture containing only about 16 percent heavy vehicles." | INFERENCE | "Ordinary fatigue failure is therefore not likely" is the report's conclusion. The cycle estimate is 300,000–450,000 over 40 years. |
| N-087 | Traffic at collapse: standing westbound traffic filled the north side of the deck from the Ohio shore to the middle of the main span. Eastbound, two heavily loaded dump trucks and five cars were moving as a group. | PDF p.24, printed p.17 | "the deck adjacent to the north truss was occupied by standing traffic from the Ohio shore to the middle of the main span. … The eastbound traffic consisted of the two heavily loaded dump trucks and five passenger vehicles moving as a group across the structure." | VERIFIED | Standing traffic on the span was unusual: "the traffic only occasionally backed up far enough to place standing vehicles out on the span" (PDF p.120). |
| N-088 | The Board believes most of the unusual vibration people felt came from the two dump trucks (moving at 10–15 mph) passing people who were stopped on the bridge. | PDF p.120, printed p.113 | "It is the belief of the Board that most of the unusual vibrations noted were due to the passage of these trucks, They were felt by the people in the west bound vehicles because they were standing still on the bridge." | INFERENCE | The vibration came from the trucks, but the trucks did not break the bridge. Divers found both trucks "on the bottom near the center of the main span" (same page). |
| N-089 | If the bridge was weak near panel point 13, how did the two heavy trucks pass it and reach mid-span? This was listed as an open question after the interim report. | PDF p.19, printed p.12 | "how did the two heavily loaded dump trucks which were in the east bound lane successfu[l]ly pass this point and reach the center of the main span before collapse occurred?" | VERIFIED | The answer is in the reconstruction: the crack was critical at static stress (N-020). It can be used as a mystery hook. |
J · Weather, witnesses, external causes ruled out
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-090 | The temperature was about 30–32°F. The truss steel (A7-24) was working well below its transition temperature, so fractures could spread at low energy. | PDF p.46, printed p.39 | "This material was ope[r]ating well below its "15 foot pound transition temperature" at the time of collapse of the structure (at 30°F.)" | CONTESTED | Image-checked: 30°F here, but 32°F on PDF p.41 and PDF p.93. The reconstruction assumed "a 36°F. drop from 68°F." (PDF p.107), which also gives 32°F. Say "around freezing". No other weather (precipitation or sky) is given. |
| N-091 | The wind at collapse was about 6 mph, blowing along the bridge. A Tacoma Narrows-style wind failure was highly improbable. | PDF p.24, printed p.17 | "the wind was blowing in a direction parallel to the axis of the bridge and at a velocity of about six mph." | VERIFIED | George Vincent testified to this in May 1968. |
| N-092 | Army Ordnance inspection of all salvaged vehicles found no explosion evidence, and no sabotage evidence was found in the structure. | PDF p.24, printed p.17 | "showed no evidence of explosions in any of the vehicles. Subsequent inspections of the structural members at the reassembly site [h]ave not produced any indication of explosions in critical members, and no other evidence of deliberate sabotage by cutting or burning has been found." | VERIFIED | |
| N-093 | "Sonic boom" rumors were checked. No suitable aircraft were operating nearby, and there were no damage complaints. The "sonic boom" sounds witnesses heard were the bridge's own fractures. | PDF p.25, printed p.18 | "A check with nearby military installations indicated that no aircraft likely to produce such effects were operating in the vicinity of the Point Pleasant Bridge at that time, and there were no other complaints of even minor damage in this area." | VERIFIED | The noise attribution is on PDF p.120: "loud cracking and popping noises, presumably due to fractures". The reported duration of noise ranges from "8 or 10 to as much as 60 seconds". |
| N-094 | A woman in Vehicle 38 had started onto the West Virginia side span. She felt it shaking badly, stopped, and backed off onto the approach span, "saving herself and others". | PDF p.120, printed p.113 | "felt it was shaking so badly she stopped and backed off to the approach span, saving herself and others. This, however, was after the collapse had begun" | VERIFIED | The report does not name her. Do not invent a name. |
K · Inspection, St. Marys, salvage, reassembly, national statistics
| ID | Claim | Source and page | Verbatim | Status | Notes |
|---|---|---|---|---|---|
| N-095 | The corroded eyebar heads and pinholes could not be reached for any maintenance while the bridge stood. Pitting loss was under 3 percent of the eyebar head, and "substantially less than one percent" of the critical section through the pinhole. | PDF p.29, printed p.22 | "The corroded portions of the eyebar heads and pin holes were not accessible for maintenance of any type while the structure was standing." | VERIFIED | Quoted from the Modjeski & Masters "Corrosion Survey of the Silver Bridge". The pre-1967 inspection history (dates and methods) is NOT in this final report. It points to the interim report for "operation, and maintenance", and A5 refers only to "the inspection techniques used". Gate 1 needs the interim report SS-H-2 for inspection dates. |
| N-096 | The St. Marys, WV bridge was a near duplicate. FHWA's Office of Research finished vibration and strain tests on it in May 1968 (spring 1968). West Virginia then closed it as a precaution. | PDF p.30, printed p.23; PDF p.9, printed p.2 | "The field work to make experimental measurements of the vibration characteristics and check certain secondary effects was completed in May of 1968 by the Structures and Applied Mechanics Division of the Office of Research, Federal Highway Administration." | VERIFIED | Closure, PDF p.9: "the State of West Virginia closed the St. Marys Bridge, a sister structure to the Point Pleasant Bridge, as a safety precautionary measure". The report gives no closure date, only "since early in this investigation" (C1) and its mention in the 31 Dec 1968 press release. Do not say "closed in 1969" or "1971" from this source. |
| N-097 | The St. Marys tests showed that a moving truck caused only small dynamic strains, and that wind excitation of this kind of bridge was improbable. The extensive tests "have shown the first two [dynamic live load, secondary stresses] to be incapable of producing significant stresses in critical members." | PDF p.101, printed p.94 | "The extensive experi[]ments on the St. Marys Bridge have shown the first two to be incapable of producing significant stresses in critical members." | FINDING | Example from PDF p.30: the dynamic increment was "only about 480 psi" of bending stress in a hanger. |
| N-098 | Salvage and reassembly: the Army Corps of Engineers recovered the bridge from the river. Wreckage was laid out at a reassembly site. By October 1968 about 90 percent of the eyebar chains and 70 percent of the trusses had been placed. FHWA finished the job in October 1969 with about 90 percent of all available wreckage identified and placed. | PDF p.26, printed p.19 | "This work was completed in October 1969 with approximately 90 percent of all available wreckage identified and placed." | VERIFIED | Corps, PDF p.9: "The Corps of Engineers, U. S. Army, com[]pleted the massive recovery of the parts of the bridge from the Ohio River". By October 1968 the West Virginia State Road Commission had placed "approximately 90 percent of the eyebar chains a[n]d 70 percent of the stiffening trusses". Earlier, by the interim report, about 60 percent of the main members had been placed (PDF p.17). |
Things the report does NOT say (popular-retelling check)
| ID | Claim | What the record says | Ledger rows |
|---|---|---|---|
| X-01 | The Mothman, a curse, or other paranormal links | The report does not mention any of these. Its logic tree lists only engineering and external causes (substructure, overstress, superstructure defect, wind, sabotage, vehicle collision, sonic boom), and every external cause was eliminated. | N-092, N-093 |
| X-02 | "Overloaded by modern heavy trucks" | The live load in the critical link was about 41% of design live load. Stresses at collapse were "well below the specified maximum stresses". The design live load exceeded a modern H20 two-lane loading. The crack was critical "without any additional dynamic effects". The trucks explain the vibration people felt, not the failure. | N-020, N-078, N-082, N-084, N-088 |
| X-03 | "It was never inspected" | The report does not say this. A5 refers to "the inspection techniques used". It says the flaw was inaccessible and could not be detected without disassembly. The final report does not list the bridge's inspection dates or methods; that material is in the interim report. Both "never inspected" and "inspected annually by X" are unsupported by this source. | N-013, N-014, N-023, N-095 |
| X-04 | "Rust ate through the chain" | General rust did not reduce the main members' capacity (A7). Pitting removed less than 1% of the critical section. The killer was a roughly 1/8-inch crack that grew from a corrosion pit inside the pinhole. | N-025, N-061, N-095 |
| X-05 | "Metal fatigue from 40 years of traffic" | "An ordinary fatigue failure is therefore not likely." The mechanism was stress corrosion and corrosion fatigue, meaning corrosion-assisted growth. Battelle said plain fatigue was "probably not in itself the primary method" (PDF p.61). | N-011, N-086 |
| X-06 | "A defective or bad batch of steel" | Eyebar 330 "did not appear to differ in any important respect" from other bars and met the specification. The steel did have low toughness at freezing temperatures, which is a property of the material, not a defect. | N-073, N-074 |
| X-07 | "Design or calculation error" | The original computations were "without mistakes or significant errors" and followed normal practice. The report blames practices that were standard at the time (higher allowables, uncomputed local stresses, two-bar links) and knowledge that did not exist yet. | N-026 to N-033, N-078 |
| X-08 | "Eyebar 33 worked loose (missing cap) and triggered it" | This theory was considered and explicitly eliminated: 330 fractured first, then 33 slid off. | N-008, N-047 |
| X-09 | "Wind, or a Tacoma-style oscillation" | The wind was about 6 mph and parallel to the bridge. Aeroelastic excitation was "highly improbable" and was eliminated. | N-091 |
| X-10 | "It fell in seconds" / "it fell in a minute" | The report says both: the synopsis says "about 1 minute", the reconstruction says 6–10 seconds, and a witness estimated 5 seconds. Attribute whichever figure is used. | N-009, N-054, N-056 |
| X-11 | Named designer or company blamed; "the cheap alternate design" | The report notes that the chain was an "alternate" design approved by the consultants, but names no culpable party and gives no cost motive. Do not add a cost motive from this source. | N-076 |
| X-12 | "Named the Silver Bridge for its aluminum paint" | The report uses the name "Silver Bridge" (Figure 2a; reference titles) but never explains it. It mentions aluminum paint layers only in the hanger 17N analysis. The paint origin needs another source. | N-083 |