This from Chi-Town Fire Photos:

Here are a few shots from the Still & Box TRT response at 3959 w Harrison on Thursday. It appeared a construction crew was replacing the sidewalk in the rear of the building which made the rear collapse. It was a vacant building and it appeared there was not any injuries. 

Building collapse at 3959 w Harrison in Chicago, 9/12/19

Chi-Town Fire Photos

Chicago FD Special Operations Battalion Chief

Chi-Town Fire Photos

Chicago fire trucks on scene

Chi-Town Fire Photos

Building collapse at 3959 w Harrison in Chicago, 9/12/19

Chi-Town Fire Photos

Chicago FD Engine 38

Chi-Town Fire Photos

Building collapse at 3959 w Harrison in Chicago, 9/12/19

Chi-Town Fire Photos