Day 5 -- The Red Zone, Part II

Day 5

Yesterday, Day 4, was spent in the peripheral towns of Onna and Pagonica, both of which sustained heavy damage due to archaic and low-strength building materials (mostly stone rubble masonry with mud mortar). Onna, a small town of working class farmers and weathly country-dwellers, lost approximatley 40 of its 300 residents to the disaster. The field of crushed cars represents an eery reminder of the power of collapsing stone.

Today, Day 5, we returned to the Red Zone in the historic center of L' Aquila (pronounced with emphasis on the first syllable -- LA-quila), seeking to augment our Day 3 experience with more focussed investigations. We planned to focus on three building types: (i) Concrete frames, (ii) Churches, and (iii) Stone Masonry. We also planned to focus on issues related to lateral drift, repairability/occupiability, and non-structural life-safety issues.

The concrete frames with brick or tile infill appeared to exhibit the full spectrum of performance, from zero damage, to light cracking of the exterior plaster, to heavy cracking along the infill perimeters, to diagonal 'X' cracking within the infills, to partial fallout of the infills, to complete fallout of both wythes of infills, to a single story collapse, to full building collapse. Some buildings, such as the one below, displayed multiple stages of infill performance. We believe there are possible correlations between the (readily apparent) exterior infill damage and other, less apparent aspects of the performance, such as the amount of lateral seismic drift, the amount of damage to the reinforced concrete frame, the degree of interior damage, and the overall life-safety performance of the structure. These correlations may ultimatley be useful for improving the accuracy of rapid exterior visual inspections of large quantities of buildings, which currently suffer from under-sophistication.

Some structures, such as the one below, required no inferences as to their life-safety performance. Notice also that the interior partition beyond the beds is heavily cracked. After seeing this type of damage, I have not been sleeping as well -- I can only imagine what the occupants of this room must now endure.

We noticed that, in general, solid brick infill performed better than hollow clay tile infill, with the former more likely to remain intact. We believe this bodes well for our steel frame with brick infill buildings at home and solidified our concerns over hollow clay tile. It was noted by a colleague, however, that the solid brick infills were more likely to transfer large shear forces to the frame connections, which necessitates more careful consideration of these systems.

The large churches in L' Aquila continue to fascinate us. We obtained very brief access to view the interior of the Cathedral through the collapsed east wall. What appears most fascinating is the severity of the damage considering the building has apparently been retrofitted. The details of the retrofit remain unclear, but hopefully we can study the photos from our brief visit and better understand the failure.

We also continue to be fascinated by the emergence of heavy timbers -- basically de-barked trees -- in the collapsed brick walls. In one instance, shown below, a circle of timbers appears to be (not very well) functioning as a dome tension ring! In another instance, two overlapping timbers through the (now collapsed) gable wall appear to be tying the longitudinal walls together while steel ties with exposed bar terminators secure the front wall at the same elevation.

The stone masonry buildings comprise the greatest challenge to the restoration and revitalization of the city center of L' Aquila. They contibute greatly to the historic fabric of the city, provide considerable square footage of accessible (tourist) retail space, and unfortunately sustained the most structural damage of any structure type. Though the lessons implicit in these buildings are not necessarily directly transferrable to our buildings at home, we feel it necessary to devote at least a portion of our energies and attention to these structure, if for no other reason than to be a part of the 'solution' for L' Aquila.

These buildings typically have thick stone-masonry walls with either brick arch floors or "flat-arch" panels locked between transverse steel beams. Some of these buildings completely collapsed. Some sustained very little damage. The vast majority, however, experienced moderate to significant damage in the form of racking and dilation. The racking resulted in disjointed walls, expressed as visible separations and fallen debris (e.g. in stairwells and hallways), and the dilation resulted in precarious floor arches or floor segments, expressed as bowed walls at the floor levels and occassionally partially or completely collapsed floors, as shown below.

These buildings clearly have the potential to be very dangerous. Based on our observations, it is very difficult to draw the line between safe and unsafe, repairable and unrepairable, worthy and unworthy. The future of these buildings will be focussed on whether they can be reasonably repaired (preservation of historic fabric, restoration of structural stability, and economically viable) and re-occupied.

From a technical perspective, the addition of continuous cross-ties at a reasonable spacing seems most efficient, though only applicable to the better performing structures, where signifant dilation has not already occurred. Repairing the walls, perhaps by repointing, replastering, and then injection grouting, seems the next logical step for more heavily damaged walls (though still not heavily dilated). Though a topic of some debate, it seems that buildings with moderately to significantly dilated walls (therefore hiding de-stabilized arch floors) are compelling candidates for demolition. This process, however, will need to be one of collaboration and compromise between preservationists, structural engineers, funders, and the local community.

One particular example is shown below, observing the front and side walls, the front doorway, and the post-earthquake state of the stairway. Note the presence of longitudinal and transverse cross ties (with exterior rod terminators) aligned at the building perimeter walls. Also note the slight bowing of the walls at the Second Floor level. Lastly, imagine trying to navigate the exit stairs at 3:30am with bare feet on a cold April evening after enduring one of the most petrifying 30 seconds of your life.

Undoubtedly, 10 different people will have 10 different opinions on the fate of this buiding, all of which are likely valid.

As our trip nears its end, we continue to search for the 'forest through the trees' -- trying to find the overall lessons within the unbelieveable spectacles. It has become clear that performance is a relative term, that post-earthquake repairability and occupiability must be part of the conversation, and that planning for a disaster is much easier and much more effective than reacting to one.

Tomorrow, Day 6, we will attempt to access the main hospital in L' Aquila -- reports on which range from completely destroyed to barely damaged. We know there are lessons to be learned and we are anxious to find them and bring them home.

We hope everyone is well and thank you for your support and encouragement -- we look forward to sharing more lessons and experiences with you upon our return.

Please visit www.degenkolb.com/blog/ to view blog contributions from the Degenkolb team, including Ricardo Hernandez (Days 1, 2, and 4) from our Los Angeles office and Holly Razzano (Day 6) from the Oakland office.