得益于监视视频，照片，2018年的建筑系统调查以及1979年的原始计划，结构工程师将12.5层的Champlain Towers South Towers South Residential Condominium的一部分致命的渐进式崩溃的可能序列拼凑在一起在佛罗里达州的Surfside。但是，6月24日的启动事件使这位40岁的钢筋混凝土结构中的一支机翼（约150英尺长）仍然是一个谜。
KCE结构工程师的创始人，总裁兼首席执行官Allyn Kilsheimer说：“我正在试图找到扳机。”他正在调查Surfside镇的崩溃。
致命事件的开始，至少杀死了11人，但仍失踪了150人，“似乎在基地附近……但是有很多问题，”基尔斯海默补充说。
Thesurveillance videofrom a nearby building that has been widely studied 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. “That one video [we have] doesn’t give you a 3D view of the building,” he says.
The wing of the residential building still left standing, looking from the east. The shear wall of the elevator-stair tower is in the center of the photo.
Photo by: Jeff Greenberg/Universal Images Group via Getty Images
Reinforced Concrete with Flat Plate Slabs
The reinforced concrete building has flat-plate floor slabs. Flat plates are relatively thin concrete slabs supported directly on columns. The building is lightly braced by shear walls.
视频显示，故障发生在建筑物的中央朝南周围，这是计划中的脂肪。L失败的长腿在足迹的北侧向西延伸至西。加利福尼亚大学伯克利分校的结构工程教授杰克·莫赫尔（Jack Moehle）说：“在内部建筑物的建筑物中，失败可能开始更高，但在视频中不可见。”
The video also shows a “very rapid vertical collapse of the interior portion of the building, with relatively little apparent side sway,” says Moehle.
The north side of the long leg followed the south side collapse, almost immediately. “That is apparent from the video,” 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.
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 Bell. In the second part of the collapse, the floors are a little offset from one another because of this effect, he adds.
尚普兰塔（Champlain Towers South）于1981年完成。一个失败的理论是，在L-In-In-In-In-In-In-In-In-In-In-In-In-the建筑物弯道附近可能存在问题。
Imagery © 2021 Data SIO, NOAA, U.S. Navy, NGA, GEBCO, IBCAO, Landsat / Copernicus, Google, Imagery © 2021 Maxar Technologies, Map data © 2021
Shorter Wing Left Standing
故障停在西方end of the midsection, near where the two legs of the L join, leaving the shorter leg of the L standing. The break was cleaner along the elevator and stair core on the southwest edge of the collapsed section, where there is a shear wall, says Bell.
贝尔补充说：“关于扳机有很多理论在循环。”
Some observers, who have studied the collapse video and photos, the2018 field survey report结构工程师弗兰克·莫比托（Frank P.
The deck sits over the one-level-basement parking garage, which fills the entire site, including and beyond the building’s footprint. The structural engineer for the development was Breiterman Jurado & Associates.
贝尔说，理论是，泳池甲板的混凝土板可能失败了，可能是由于防水恶化。
现场计划的顶部显示了失败的北翼，即L建筑计划的较长腿。剩下的部分在建筑物的西侧向北延伸。
由Surfside镇提供
Repair Estimate
在他的报告尚普兰塔公寓association, Morabito estimated the price of needed repairs at $9.1 million. The estimate for remediating the garage, the entrance and pool deck was the most expensive line item, with a cost of roughly $3.8 million. Remediation of the building’s façade would require an additional $3.2 million, according to Morabito. The repairs, which were planned for 2021 back in 2018, had just begun when the collapse occurred.
There are at least three theories about the trigger of the progressive collapse, beyond the pool deck slab: column failure, slab failure due to punching shear or failure of the pile foundation system, perhaps under the pool deck. Kilsheimer, Bell and others speculate there may have been more than one contributing factor, as in a perfect storm.
Progressive failure is caused either 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。
如果没有持续的底部加固the slab passing over the columns—a detail not required in 1981—then the slab can move downward relative to the column, redistributing load to adjacent slab-column connections, which in turn can fail. A slab that eventually lands on the floor below it overloads that floor system, and there is more punching shear, says Moehle, who has done extensive testing of concrete structures.
If the columns were the trigger, then it is likely but not certain that the collapse started at the bottom of the building where the axial loads are largest, adds Moehle. If it was the slab-column connection, then the failure could have started just about anywhere in the building and progressed downward in a vertical collapse that extended across the floor and down to the base.
照片中盘旋的区域显示了一列，钢筋像发束一样悬挂，在板块撞倒后，车辆和全部在其下方的地板上丢失了平板，这是由于刺穿剪切的。碎片堆的景色来自南部的北方。
原始照片由迈阿密戴德消防救援公司提供
Some photos of the debris suggest that the 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，它开始对钢筋的腐蚀，并补充了Moehle。腐蚀的最新加速可能加速了柱强度的损失。
One area of the pool deck simply ended up a level down, columns and all, with no sign of punching shear. It is possible that the pile foundations under that area sank because of the opening up of sinkhole or some other factor. The lowered deck could then have pulled down the rest of the structure.
另一个理论是，整个建筑物占地面积的差分定居点可能会导致内部力量的重新分配，并使某些成员过高。
“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 Editor Scott Judy contributed reporting for this article.
