自从千禧塔的所谓修复导致高层突然下沉和倾斜更多以来，首次公开发表讲话，修复的首席设计师周四作证说，这座建筑可以倾斜超过 6 英尺，并且仍然可以安全地承受大地震.
“正如湾区的每个人都知道的那样，随着我们一直在安装新桩，建筑物的沉降和倾斜有所增加，”结构工程师 Ron Hamburger 在旧金山监事会政府监督委员会面前说. “增长并不像媒体希望你相信的那么戏剧化。”
该塔目前向西倾斜 23 英寸，向北倾斜 9.5 英寸，其中包括自 5 月以来新增的约 6 英寸向西倾斜。
在承认他对安装工作开始后不久会加速下沉和倾斜表示担忧的同时，汉堡说工程师们已经吸取了重要的经验教训，即在不增加倾斜和下沉的情况下，将桩固定在两侧的基岩上的方法。
汉堡说，在最近对新安装方法进行的测试中，该建筑物的沉降量可以忽略不计，该方法旨在限制两个可疑因素——挖掘过程中的土壤流失和施工过程中的振动。
“我们已经成功地减轻了振动，”汉堡说，并补充说，在修改后的挖掘过程中，工作人员还限制了从地基周围带走的土壤量。
但本周公布的数据——随着在 Mission Street 新安装 100 英尺长的钢套管的工作恢复——显示高层建筑沉降了十分之一英寸，引发了向西倾斜四分之一英寸的更多倾斜。在采取任何措施限制地面损失或振动之前，这与 8 月份导致修复项目停止的每周费率大致相同。
在他的证词中，汉堡淡化了当前倾斜率造成任何问题的可能性——重申他认为甚至不需要修复来保护建筑物的安全。
他指出，一项新的分析表明，这座建筑可以向西倾斜超过六英尺半，向北倾斜近三英尺——并且在大地震中仍然安全地幸存下来。
他说：“我们得出的结论是，建筑物仍然能够安全地抵抗考虑到如此大的倾斜程度的最大地震震动，”他说，但表示倾斜以维持建筑物电梯和管道系统运行的“实际最大值”已经开启。 40 英寸的数量级，大约是它的一半。
他说，即使是下限，也能在达到“实际最大值”之前提供近一英尺多的额外倾斜余量。
汉堡还说，40 英寸的水平大约是根据土壤条件可以预期的建筑物的最大数量，如果没有进行任何修复工作。
至于 6.5 英尺倾斜水平汉堡现在说这座建筑可以在地震中幸存下来，旧金山主管亚伦佩斯金 - 在 NBC 湾区首次报告修复问题后召集听证会 - 持怀疑态度。
“这对我来说听起来很可笑，”佩斯金在听证会上说。 “在北加州地震多发地区，建筑物可以在泥泞中倾斜六英尺半，而不是地震或生命安全隐患。我想对它进行第三组观察。”
汉堡强调，建筑物不太可能倾斜那么多，因为完成的修复将阻止沉降，甚至扭转一些倾斜。他指出，工程师现在建议使用 42 根桩，而不是原来的 52 根，并且可以根据未来几周将桩沉入基岩的关键计划测试结果进一步减少这一数字。
Fix Designer Says Millennium Tower Could Tilt 6.5 Feet, Still Withstand Major Quake
Speaking publicly for the first time since the so-called fix of the Millennium Tower caused the high-rise to suddenly sink and tilt more, the fix’s lead designer testified Thursday that the building could lean more than six feet and still safely withstand a massive earthquake.
“As everyone in the Bay Area is aware, as we’ve been installing the new piles, there has been an increase in settlement and tilting of the building” said structural engineer Ron Hamburger before the government oversight committee of the San Francisco Board of Supervisors. “The increase is not as dramatic as the media would have you believe.”
The tower is currently leaning 23 inches to the west and 9.5 inches to the north, which includes about six inches of newly added tilt to the west just since May.
While acknowledging he had concerns about the accelerated sinking and tilting soon after installation work began, Hamburger said engineers have since learned important lessons on ways to anchor the project with piles sunk to bedrock on two sides without adding to tilting and sinking.
Hamburger said the building experienced negligible amount of settlement during a recent test conducted of new installation methods designed to limit two suspected factors – soil lost during digging and vibration during construction.
“We have successfully mitigated the vibration,” Hamburger said, adding that crews also limited the amount of soil taken away from around the foundation in the revised digging process.
But data released this week – as work resumed with new installation of 100-foot long steel casings on Mission Street – show the high rise settled one tenth of an inch, triggering a quarter-inch of more tilt to the west. That’s roughly the same weekly rate that triggered a halt to the fix project back in August, before any measures were taken to limit ground loss or vibration.
During his testimony, Hamburger downplayed the potential that current rates of tilting pose any issue – restating his belief that the fix was not even needed to preserve the building’s safety.
He pointed to a new analysis showing the building could tilt just over six and half feet to the west and nearly three feet to the north -- and still safely survive a massive quake.
“We’ve concluded that the building is still able to safely resist this maximum considered earthquake shaking with that amount of tilting,” he said, but indicated the “practical maximum” for tilting to maintain operations for the building’s elevators and plumbing systems is on the order of 40 inches, about half as much.
Even the lower limit, he said, provides a margin of nearly a foot more of additional tilting before the “practical maximum” is reached.
Hamburger also said that 40-inch level was about maximum amount of the building could be expected to experience based on soil conditions, had no fix work ever been done.
As to the 6.5-foot tilt level Hamburger now says the building could survive in a quake, San Francisco Supervisor Aaron Peskin -- who convened the hearing after NBC Bay Area first reported about the fix problems -- was dubious.
“That sounds just ludicrous to me,” Peskin said at the hearing. “That a building can tilt six and a half feet in the muck in an earthquake prone part of Northern California and not be a seismic or life safety hazard. I would like to have a third set of eyes on that.”
Hamburger stressed it’s not likely the building would tilt that much, given that the completed fix will arrest the settlement and even reverse some of the tilting. He noted that engineers now propose relying on 42 piles, instead of the original 52, and could reduce that number further, based on the outcome of a key planned test of sinking a pile to bedrock in coming weeks.
