Safety Assessment Program Evaluator Student Manual

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CA Emergency Mgmt. Agency Safety Assessment Program Evaluator Manual April 2011Photo courtesy Global Emergency ManagementFigure 2-30 – Parapet failure into small building, 1989 Loma Prieta EarthquakeFigure 2-26 shows a house that has a porch with severe damage, and the entire house is racked,as evidenced by the leaning columns on either corner of the house. It does not take muchracking for a structure to be pushed into failure mode; this house was correctly tagged UNSAFE.Figure 2-27 shows an unreinforced masonry building with extensive damage. The question hereis, why did the pool come up out of the ground? There could be several reasons; if the pool issited in sandy soil with a high water table, liquefaction may have caused the pool to simplybecome buoyant and rise up out of the ground. Another cause may have been a scarp thatpushed the pool up. If the latter, it needs to be identified, by a geologist or geotechnical engineerif necessary, and the information supplied to the building department via the assessment form forthis building.Figure 2-28 shows a reinforced concrete column supporting a pedestrian overcrossing thatspalled away the concrete cover protecting the rebar. Upon closer examination in Figure 2-29, itis clear that the column is now in a type of failure mode. The rebar is bent, and there is adiagonal crack through the center of the column. These conditions indicate that a P-delta effectis at work, that is translating vertical load into lateral movement. The entire area should bebarricaded off, and tagged “AREA UNSAFE,” using a felt pen to insert the word AREA in frontof the word UNSAFE on the placard. The pedestrian overcrossing should also be barricaded atboth ends and placarded UNSAFE as well.Figure 2-30 shows great damage to a small building caused by masonry collapsing into it from amuch higher one. This should also be marked AREA UNSAFE, and barricaded off from thepublic. There is no need to endanger one‟s life by posting the front of the building; the posting56
CA Emergency Mgmt. Agency Safety Assessment Program Evaluator Manual April 2011can be on grape sticks or other posts around the barricaded buildings, which should include boththe tall building and the shorter one, so the public is not threatened by falling debris.2.5.3.2 Discussion of Collapse ZonesThe dangers from weakened structures are not isolated to earthquake disasters. For examples,one of the chief dangers facing fire fighters is the structural collapse that occurs while a structurefire is being fought. A common practice is to establish a safety zone around such a structure thatis at least the height of the structure. While buildings may collapse straight down as opposed toleaning over, there is no guarantee of how a weakened building may collapse, and it is too late toset up the safety zone when the building starts to fail, so the caution shown by such a safety zoneis definitely appropriate.Better yet, engineers with the Urban Search and Rescue teams are trained to create a safety zoneone and one-half times the height of the building. So, a weakened building that is 50 feet tallwould have a safety zone 75 feet in radius around it. This allows room for the building tocollapse and for the building debris to come to rest. This federally used rule of thumb is the onepreferred by the Safety Assessment Program.Obviously, if other buildings are situated within the safety zone (or “collapse zone”), they facethe peril of being damaged or destroyed by the collapsing structure. This situation makes itimperative that they be placarded UNSAFE. The danger from the weakened structure is toogreat to do otherwise. So, in the above example, buildings within the 75 foot radius around theweakened 50 foot high building would be tagged UNSAFE due to the collapse hazard from thetall building nearby.The following is an example of how these principles were used in the 2010 Baja Earthquake.Photo courtesy Fred Turner, EERIFigure 2-31 – 150 foot tall El Centro water tower57
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