NORTH AMERICAN NEWS
Out of more than 150 individual rod results obtained from both quality control and quality assurance testing, five results were below specifications. All five involved one mechanical property - elongation. “The specification requires a minimum of 14% elongation, and 5 results were in the range of 12.5% - 13.6%, or 1.5% - 0.4% below specification.” Design and construction engineers reviewed those 2008 test results and the material was determined to be suitable for use. The remaining 192 rods for other shear keys and bearings were
manufactured in 2010. All of those rods passed QC/QA testing. As of 9th
April, those rods have been tensioned to about 70% of maximum
load. All of them have been visually inspected and “there’s been no indication of a problem,” according to Andrew Fremier, deputy executive director of BATA. Of the 2010 batch, ten rods have been selected for instrumentation to monitor bolt performance. An additional ten will be removed for destructive testing.
25th Solutions
Officials at the meeting said they are exploring a two-part solution. The first involves retrofitting the shear key where the embedded bolts failed. One retrofit idea design engineers are exploring involves placing a steel collar around the base. Theoretically they could also replace the embedded bolts, though officials quickly pointed to significant problems involving rebar congestion and accessibility. The second part of the solution is the continued monitoring of the 192 through bolts from the 2010 batch to determine whether or not they should be replaced. Officials expressed cautious optimism that they won’t encounter hydrogen problems with those bolts, but indicated they are exploring what it would take to replace them.
April: ‘Catastrophic failure’ of Bay Bridge bolts caused by hydrogen embrittlement
Oakland Bay Bridge officials confirmed the cause of 32 snapped anchor rods on the new US$6.4 billion eastern span of the bridge. “The failed rods suffered from hydrogen embrittlement,” Caltrans director Malcolm Dougherty announced at the 24th
in the 2008 bolts caused the threaded areas of bolts to become brittle and fracture under high tension.” T T 26
he rods were from one of two distinct batches of bolts manufactured by Ohio based Dyson Corporation. One batch included a total of 96 rods manufactured and installed in 2008. The “failed bolts” came from that
batch, which were embedded in concrete during construction. A second batch of anchor rods, totaling 192, are through bolts manufactured in 2010 and installed in 2011. None of those bolts, which have been under load since 9th
April have failed.
Dougherty said lack of uniformity in the steel microstructure of the 2008 bolts increased susceptibility to hydrogen embrittlement. Bridge officials have “substantially” expanded testing of the 2010 bolts to evaluate their disposition. Their investigation into the failure of the 2008 bolts and the conformity of the 2010 bolts includes analysis from a three-member expert panel currently evaluating both sets of bolts. Metropolitan Transportation Commission executive director
Steve Heminger conceded that Caltrans failed to provide adequate specifications to the manufacturer or mandate specific tests that would have revealed whether the bolts were susceptible to hydrogen embrittlement. “These bolts were sort of bought out of the catalog instead of being tailor made,” Heminger stated. “The bolts are the dumb end of the operation. The seismic devices are the smart end. You need something to hold them together. Frankly we would have used super glue if that had been appropriate.”
Two possible fixes The bridge project team has narrowed response to two options: either a steel collar or steel saddle. Both options will achieve the design intent of this system. The contractor is already engaged in process, and has already steel orders as well as lining up fabricator for both options.
IFI publishes handbooks on torque and mechanical fastening
The Industrial Fasteners Institute released two new critical handbooks, one authored and compiled by Bengt Blendulf on mechanical fastening and joining, and the other by Joe Greenslade on how to correctly tighten fasteners.
he Torque Book for Fasteners by Joe Greenslade features “all the engineering data in one place to calculate the correct tightening torque for all types of inch and metric fasteners”. “The question of ‘How much torque should be applied’
is the most frequent question I have heard from end users, directly and through suppliers, for the 42 years I have been in the fastener industry,” Greenslade told GlobalFastenerNews. “The ultimate audience is every installer of threaded fastener user in the world. I believe fastener distributors are the link in the chain that fields the question of tightening torque most frequently.” “When composing this book I realized that providing a
resource that only addressed how to calculate a suggested tightening torque value for bolts and accumulating the variables data in one place was still an incomplete resource of questions related to tightening,” Greenslade explained. “The content was expanded to include information on how
to determine how much torque has been applied to a completed assembly, what torque to apply to tapping screws, what torque to apply to set screws, how to address galling problems associated with tightening stainless steel bolts, and a brief explanation of alternative means of effectively tightening threaded fasteners other than by measuring torque. “In the very back of the book are several pages of worksheets
indicating which tables contain which variables so the user simply fills in the blanks in the worksheet and uses a calculator to multiply the variable which results in an answer in inch pounds, foot, pounds or Newton meters depending on the last multiple that is applied.”
Mechanical Fastening and Joining by Bengt Blendulf US$150/copy (outside US & Canada) + 25% shipping & handling Torque Book for Fasteners by IFI/Joe Greenslade US$75/copy (outside US & Canada) + 25% shipping & handling
Fastener + Fixing Magazine • Issue 81 May 2013 April meeting of the Bay Area Toll Authority in Oakland. “Excess hydrogen
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