Though the trigger may remain a mystery for some time, by the end of the week, the structural engineer probing the partial progressive collapse of a 40-year-old Surfside, Fla., residential condominium expects to complete a computer model of the unstable, 12-story remains of the building. The computer model of the still-standing wing of Champlain Towers South will initially be used to alert the search and rescue team to suspend operations if a hurricane is coming.
“我们正在收集数据和建造结构模型”，在原始图纸的帮助下，以预测不稳定塔可以承受的风力，以便在必要时“我们可以警告人们”撤离该地点，Allyn Kilsheimer说。KCE结构工程师的创始人。6月24日崩溃后第二天到达该地点的基尔斯海默（Kilsheimer）正在迈阿密海滩北部的苏尔菲斯市工作。
With a cyclone category 5 in the Caribbean that is expected to become Tropical Storm Elsa, the completion of the model could not be better timed. At a June 30 press conference in Surfside, Florida officials announced the storm, if it hit at all, would not have any impact on South Florida through Saturday. Officials also said they were tracking the storm and making appropriate preparations, including developing a plan to keep the debris of the tower from becoming projectiles.
Concurrently, KCE, with the geotechnical consultant Mueser Rutledge Consulting Engineers, is piecing together the complex puzzle of the collapse scenario, based on observations, measurements, a 2018 field survey, photos, a surveillance video and the original 1979 documents for the reinforced concrete structure. The investigators are also trying to sort out the locations of the two foundation types on the drawings: pressure-injected footings and 14-ft-square precast concrete piles.
“There may have been three collapses,” in quick succession, Kilsheimer speculates. Determining “why this happened is a long process of collecting data and creating computer models,” he adds.
表面停车区
An area of interest is the surface parking zone near the lobby entry drive that goes partly under the remaining wing. That slab for the parking, which is next to the grade-level pool deck, is the roof of a one-level basement garage that fills the site's entire footprint.
According to Kilsheimer, it appears, from the position of the cars that dropped a level—one car’s nose ended up pointing to the pool area—that the lobby slab columns moved sideways toward the pool deck, causing the pool deck to drop, which then pulled on the tower columns, causing them to fail. “This will not prove where it started,” he says. "That is not something we can determine in a hurry."
However, Kilsheimer has all but ruled out an overload from the parked cars as the trigger. “It could be that a drunk driver hit a column,” he says. “We don’t know yet.”
KCE和Mueser Rutledge很快将由另一个调查团队加入该网站。同样在新闻发布会上，美国商务部的国家标准与技术研究所宣布，它将很快对2002年《国家建筑安全团队法案》（National Construction Safetial Team Act）授予的授权授权的原因进行技术调查。
Fact-Finding Not Fault-Finding Investigation
"This is a fact-finding not a fault-finding technical investigation" that could take a couple years, said James Olthoff, NIST's director. The goal is to determine the cause of the collapse and make recommendations for changes in codes and standards, he said.
NIST材料和结构系统部门副局长朱迪思·米特拉尼·里斯特（Judith Mitrani-Resider并研究建新利luck筑物的设计，构建，修改和维护。
There was no announcement of when the team would be deployed. There were assurances, however, that there would be no interference with ongoing search and rescue operations. At the time of the press conference, there were 18 dead and 145 people still missing.
No one has been allowed into the remains of the evacuated building. That includes the basement level that fills the entire site. The only shoring posts installed to date were to create a tunnel of sorts through the debris pile to help rescue workers search for survivors.
迈阿密戴德县市长丹尼拉·莱文·卡瓦（Daniella Levine Cava）还在新闻发布会上说，该县正在审查其有关建筑物的规则，包括建筑物40岁时的重新认证。
似乎很明显，级别的平板上的悲剧性失败开始了，“但是有很多问题，”基尔斯海默说。他补充说：“我们每秒都在学习更多东西。”
The video taken from a nearby building, which has been widely studied, is helpful, but it starts a few seconds into the collapse. Kilsheimer, at the site since June 25, says he hopes other videos will surface, including one that shows the very beginning of the collapse. “The one video [we have] doesn’t give you a 3D view of the building,” he says.
The collapse may have started in the at-grade parking area alongside and under the elevated first occupied level of the remaining wing (at right, in photo) and brought down the adjacent pool deck. The deck likely sent a shock wave toward the east-to-west tower, which then collapsed into a pile of debris.
Chandan Khanna/AFP通过Getty Images摄
Sequence of the Debacle
就崩溃的顺序而言，有报道称目击者在坡度高架台球甲板和地面停车区周围听到噪音。照片显示了泳池甲板的一部分掉落到下面的地下室车库板上。S.K.说，崩溃会在坡度上通过地板系统（即车库屋顶）发出冲击波。S.K.总裁GhoshGhosh Associates LLC。
他补充说，在这种情况下，冲击波足够大，可以拆除一两个关键柱。“从那里，这是一次进行性崩溃。”
Engineers are concerned about a design that would then result in a progressive collapse of so much of the tower.
这座136个单位的尚普兰塔楼南部于1981年完成，由已故的纳特尔建筑（Nattel Construction）建造，这是已故项目共同开发者内森·里伯（Nathan Reiber）拥有的迈阿密海滩承包商。由已故的Breiterman Jurado＆Associates设计的钢筋混凝土建筑具有平板地板板和易于支撑的剪切墙。相对较薄的平板，在平板顶部附近轻轻加固，直接支撑在柱上。一级地下室填补了整个站点，包括建筑物的占地面积。
尚普兰塔South stood for 40 years. Area of pool deck nearest the building is under scrutiny. Grade-level site plan is inset.
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The building met all building codes in effect in 1979. But Florida codes have been greatly improved since then, agree sources. Still, the collapse raises questions about the condition of the rest of the older building stock in Florida.
Worry About Newer Buildings
该地区的一位结构工程师说：“每个人都担心，甚至对较新的建筑物都担心。”他强调，30至40年前，佛罗里达州的建设就像“野外西部”，但至少15年的过程“与美国其他任何地方一样严格”，并有规定的同行审查，以及一定程度的审查。结构。
尚普兰塔公寓刚刚开始了迈阿密戴德县要求的40年建筑重新认证计划。该过程要求注册工程师或建筑师提交有关建筑物系统“一般结构状况”的现场调查报告。
要求匿名的工程师说，40年的重新认证过程“不是一项重大评估”。“就像窗敷。”
On June 25, Surfside officials released public records related to Champlain Towers, including the 2018 survey report by structural engineer Morabito Consultants Inc. and the original 1979 plans by William M. Friedman and Associates Architects Inc. “The goal of our study was to understand and document the extent of the structural issues that require repair and/or remediation in the immediate or near future,” wrote Frank Morabito, the firm’s president, in the report.
Morabito indicated “that many of the previous garage repairs are failing resulting in additional concrete cracking, spalling and leaching of calcium carbonate deposits. At the underside of the entrance/pool deck where the slab had been epoxy-injected, new cracks were radiating from the originally repaired cracks.”
Morabito recommended the entrance/pool deck concrete slabs that were showing distress be removed and replaced in their entirety.
现场调查仅基于视觉观察。这位匿名工程师说：“该报告没有概述我们在其他地方没有看到一千次的任何[结构性恶化]。”他说：“没有危险信号。”
A letter recently sent from Champlain Towers condo association board president Jean Wodnicki to building residents and released to the media by family members, shed further light on the structure’s condition prior to collapse. A revised estimate dated Oct. 15, 2020, from Morabito—who was overseeing the recertification repairs—showed that costs had ballooned to nearly $15 million from the original $9.1 million.
In the memo to residents, Wodnicki “indicated that the concrete damage observed would begin to multiply exponentially over the years, and indeed the observable damage such as in the garage has gotten significantly worse since the initial inspection. When you can visually see the concrete spalling (cracking), that means that the rebar holding it together is rusting and deteriorating beneath the surface.”
“The concrete deterioration is accelerating,” wrote Wodnicki.
在2018年的估计中，“车库，入口和泳池甲板修复”的单个订单项目为380万美元。2020年的估计为410万美元。其中包括五个涵盖“防水”，“结构维修”和“其他维修”等工作的订单项目。
由于重新认证报告等，将出现有关责任和责任的主要问题。律师事务所Dorsey＆Whitney的合伙人埃里克·鲁齐卡（Eric Ruzicka）说：“我注意佛罗里达州的限制法规和安息。”
According to Ruzicka, under Florida Stat. 95.11(3)(c), an action founded on the design, planning or construction of a building must be commenced within four years from the time the defect is discovered or should have been discovered. No claim can be brought 10 years after completion of the work regardless of when it was discovered.
他说，该法规可能会消除参与原始开发，设计和建设的人的责任。Ruzicka补充说，相反，受害者及其家人的康复将仅限于参与建筑物的维护人员以及在过去四年中评估建筑物状况的人。
The progressive collapse of the east-west wing stopped at the shear wall elevator core, leaving much of the north-to-south wing standing but unstable.
Photo by Jeff Greenberg/Universal Images Group via Getty Images
监视视频表明，塔本身的崩溃开始在建筑物的中部朝南周边降低，这是计划中的胖子。L失败的长腿在足迹的北侧向西延伸至西。
视频还展示了一个“快速垂直collapse of the interior portion of the building, with relatively little apparent side sway,” says Jack Moehle, a professor of structural engineering at the University of California, Berkeley.
长腿的北侧几乎立即紧随南侧塌陷。接下来，建筑物的东端最近的大西洋驶向向西的中部。
The video shows the east end standing for a short while after the midsection collapsed, gradually leaning toward the midsection. Likely there was an imbalanced load due to loss of support from the portion of the building that collapsed, which dragged the remaining portion sideways until its gravity load-carrying capacity was exhausted and it also collapsed, says Glenn Bell, a forensic structural engineer and director of Collaborative Reporting for Safer Structures (CROSS-US), a division of the American Society of Civil Engineers’ Structural Engineering Institute (ASCE/SEI).
可能的崩溃可能不成比例
除了痛苦the pool deck slab, engineers speculate that column failure, slab failure due to punching shear or failure of the pile foundation system may have contributed to the progressive collapse. If the failure did start at the grade-level slab, and spread to the tower, the disaster could be considered a disproportionate collapse, which is a more specific type of progressive collapse. In a disproportionate collapse, the failure is out of proportion to the trigger because it spreads way beyond the trigger zone, in this case perhaps to the tower itself. By coincidence, ASCE/SEI expects to publish a Disproportionate Collapse Mitigation Standard in January.
Both progressive or disproportionate failure is caused by columns that fail axially due to axial over-stress or shear damage that progresses to axial failure or punching shear failure, says Moehle.
在打孔时，建筑物的一个平板中的一个或多个会在圆柱周围形成剪切故障，并相对于柱子掉落。如果平板上没有连续的底部加固，则列出了列（1981年不需要的细节），则平板可以相对于列向下移动，将负载重新分配到相邻的平板柱连接，从而又可能会失败。Moehle说，一块落在其下方地板上的平板使地板系统超负荷，还有更多的冲刺。
Some photos of the debris suggest that the tower collapse involved—at least as a secondary mechanism—punching shear failures. “This could have been a secondary aspect of the collapse, with the primary cause of the collapse being something else,” says Moehle, who adds that his observations are “very preliminary speculation.”
其他可能的促成因素：“合理”的海洋喷雾剂在40年以上增加了混凝土的氯化物含量，在达到临界点后，它开始腐蚀钢筋，并补充了Moehle。腐蚀的最新加速可能加速了柱强度的损失。另一个理论是，整个站点之间的差异解决可能导致内部力量的重新分配，并可能过于压力一些成员。
“It will be a long time before this has been thoroughly studied and thoughtfully considered” to give engineers the confidence to draw lessons about what happened, says Moehle.
ENR Southeast Editor Scott Judy contributed to this article
