旧金山的Salesforce Transit中心的批准商店图纸上的记录工程师的注释似乎已经启动了对钢制制造商的指示，以切成2英寸的2英寸。x 4英寸。轮毂盖板梁的底部法兰的孔。这些孔受到了审查，这是对两个bridgelike梁的底部法兰的调查的一部分，横跨弗里蒙特街（Fremont Street）80英尺。

To date, investigators say the fractures resulted from low fracture toughness deep inside the 4-in.-thick flange plates, combined with normal microcracks from thermal cutting, the welding sequence and stress levels from loads, which are a function of design.

The 41⁄2-block-long hub opened in mid-August and closed Sept. 25. The 1.2-million-sq-ft facility, owned by the Transbay Joint Powers Authority (TJPA) and designed by Pelli Clarke Pelli Architects with engineer of record Thornton Tomasetti Inc. (TT), was built by the Webcor/Obayashi Joint Venture. Skanska USA Civil West is the steel subcontractor.

双梁有助于支撑一个屋顶公园，并通过中跨式衣架板在每个底部法兰的插槽上捡起二楼的公交车甲板。没有骨折的相同双梁跨越了附近的第一街。

该设施的麻烦打开了一些过程，质量控制和责任挑战，这些挑战挑战具有大型或厚的部分和异常设计的长跨钢结构。

Should there be extra scrutiny for nonstandard details such as the hanger assembly? Should mills be required to test fracture toughness deeper into thick plates? Should there be extra procedures for cuts added after design approval?

The list goes on: Should there be more required weld and cut sequences for heavy plates? Should fabricators always hire detailers directly, and should they be allowed to communicate with designers?

“有很多事情我们可以学习这个,” says Michael D. Engelhardt, a professor of engineering at the University of Texas at Austin. “People who write codes and standards should take this seriously,” says Engelhardt, who chairs the independent peer review panel formed by the area’s Metropolitan Transportation Commission. The panel is monitoring TJPA’s inquiry and scrutinizing the structure, especially for low-fracture toughness.

According to Robert Hazleton, president of the Herrick Corp., which fabricated the girders, the girder-hanger system “is a unique detail that requires a hole that is not covered by the code.”

“These holes needed dimensions and finishing requirements to be considered by the design team and detailed in contract documents,” he says.

其他than Hazleton, all parties involved decline to comment in any detail on the holes until after the investigation.

The fractures propagated from the cuts in the bottom flange, one on each side of the web. Cuts are at the junction of fillet web-flange-hanger welds and butt welds, where the two 40-ft-long flange plates meet to form a shallow V.

On shop drawing P537BB, dated Sept. 24, 2014, and posted on TJPA’s website, TT noted the need for a weld access hole in the web, by adding “MISSING WAH. [TT],” with an arrow pointing to the midspan of the web. There, the hanger plate thickens the web to as much as 4 in. before it slots through the bottom flange to pick up a tension member that hangs the bus deck. TT approved P537BB, as noted.

On Dec. 2, 2014, Skanska issued Request for Information 978 to Webcor/Obayashi. The note on the RFI, presumably offered by steel detailer Candraft, working for Skanska, not Herrick, said: “It is not clear what is meant by this approval comment. A WAH is not required in the 4" vertical plate but it seems WAHs are required where the [complete joint penetration] weld for the 4" flange plates terminates at the 4" vertical plate. Please refer to detail 9/S1-5026 and supply the dimensions for the WAHs if required.”

WebCor的RFI响应指出，在此位置WAH的尺寸是一种手段和方法问题，应“根据美国焊接协会的AWS D1.1”执行。TT补充说：“我们不同意请求的原因：信息不足。我们将此RFI归类为对手段和方法的澄清。”

Hazleton disagrees, saying the cuts are not WAHs based on their shape, size and flange location, and they were not needed for welding (ENR 12/24-31/18 p. 14). Even if they were, WAHs—typically in the web—are not a means and methods issue, he says. WAHs are covered by the American Institute of Steel Construction’s “Specification for Structural Steel Buildings.” The spec requires polishing and grinding to minimize stress concentrations.

The job’s timeline and fabrication sequence are important to understand why the First Street girders, which also have cuts, did not fracture, says Engelhardt.

Hazleton explains that in March 2015, an inspector armed with RFI 978 directed Herrick to cut the holes into the already-fabricated First Street girders. Soon after, Herrick received a revised shop drawing from Skanska, called P151 and dated April 4, 2015. P151 shows “cuts” in the bottom flanges—no longer noted as WAHs.

For Fremont girders, not yet completed in April, Herrick cut the holes before butt-welding bottom-flange plates. Shrinkage from cooling likely increased the cracks.

尽管询问仍在进行中，但绕过裂缝的螺栓固定固定会绕过裂缝，就像夹板一样，尽管仍在进行中。