PART THREE: Analysis of Photographic Evidence
Bomb Damage Analysis Of Alfred P. Murrah Federal Building
Oklahoma City, Oklahoma
PART THREE
Analysis of Photographic Evidence

A careful examination of photos showing the "A" row columns and the large header from the third floor reveals absolutely no air blast shock wave fracture, which is consistent with the pressure falloff with distance from the truck bomb. The cleaned-up building structure (Tab 4) shows that the failure line across the roof goes all the way to the ground except around columns B4 and Bs at the second and third floor levels. Reinforcement rods stripped out of beams and floors extend straight down on all floors. Columns A3, A5, A7, and B3 collapsed straight down as the apparent result of demolition charges at the column juncture with the third floor for column B3 and with the third floor level header for columns A3, A5, and A7. The even numbered columns (A2, A4, A6, and A8) in Row A collapsed straight down because they were supported at the third floor by the header, which necessarily failed with the demolition of its conjunctions with columns A3, A5, and A7. When columns A2 through A8 collapsed straight down, the roof and floor fracture lines at all floors acted as an instant hinge line, which would have given all floors collapsing down a slight tug toward column row B. Because of the collapse of column B3, the floors were cropped closer to the north side of columns B4, B5, which resulted in damage by falling debris to sheet rock on columns B4 and B5 at the third floor level.

The so-called "pit" area behind columns B4 and B5 was caused either by the blast from the truck bomb pushing out the ceilings of the first and second floors or from the demolition charge on column B3. From the third floor it would look like a "pit" into which much debris fell. The blast pressure in this area would have been sufficient to exceed the ultimate yield design strength of the floor. There were large areas at this pressure being held only by the floor-thick, reinforced concrete around the 20-inch reinforced concrete columns in the B row. The floor of the first floor could not be blown downward, because it was a heavy concrete slab on compacted earth. The ceilings of the first and second floors nearer the truck between the A and B column rows could also have been blown upward initially.

Although the truck bomb had insufficient power to destroy columns, the bomb was clearly responsible for ripping out some floors at the second and third floor levels.

Photographic Evidence of Demolition Charges

Turning next to the demolition charges in the building, refer to the picture at Tab 5. Here you see column A9 with no spalling as one would expect with the blast pressures involved and the decorative indents are unmarred. Note also the grooves at the top of the column and across the header. When the demolition charge on column A7 went off, the charge instantly left a 40 foot cantilevered header supporting column A8. Cascading columns and beams from above probably snapped off the end with a clear structural fracture, including rugged cracks and rough surfaces. There is a large unseen beam extending from behind the column, between the decorative groves, back to the first floor header. This beam adds considerable rigidity to the lower oddnumbered columns in Row A.

Turning next to Tab 6, the stub of column B3 has been cleared, showing the bare reinforcement rods at the third floor level. The large header from the third floor level has fallen almost straight down with what appears to be demolition charge damage clearly evident to the right of column A3. The exposed reinforcement rods are clearly seen at the header end to the right of column A3. It appears that the demolition charge pulverized the header and columns out to about two feet from the juncture. Column A3 is standing there with the clean reinforcement rods clearly extended. Also, the architectural decorative band is clearly evident without blemish (indicating no blast damage in excess of yield strength). In this picture, the failure of the header at column As is still covered with rubble, and is not visible. However, the discontinuity in the slope of the header on either side of the column As location clearly shows that it failed in the region of its juncture with column As.

Tab 7 shows the localized damage to the header at the position of column As, the closest column to the truck bomb crater. The end of the beam on which the men are standing shows evidence of a demolition charge at its juncture with column As. Several feet of the beam juncture appear to have been pulverized away by a demolition charge and the ends jammed together in the collapse. The blast pressure from the truck bomb would have been in the 400 pounds per square inch region__a factor of 10 below the yield strength of concrete.

Tab 8 shows the localized demolition damage at the juncture of column A7 and the header. The same telltale demolition charge evidence is clear. The straight edge of the decorative grove at the juncture can be seen on both the column and the header.

In my discussions with the building architect, who was on the scene as an advisor throughout much of the cleanup, he told me that the residual building was structurally sound and that the Murrah Building could have been rebuilt. This is totally consistent with the collapse of columns with demolition charges because the inflicted structural damage is more localized.

Discussions above have been limited to the reinforced concrete structure of the Murrah Building. Reinforced concrete columns are hard targets for highexplosive bombs. Structures that have large areas for blast loading and low mass can be destroyed at considerable range from a large blast. That is why glass, plaster, and light structures were destroyed at considerable distance from the Murrah Building, but not reinforced concrete columns. Five pounds of blast pressure will flatten most frame houses.

...next PART FOUR: Conclusion and Appendix Oklahoma City Bomb Report Index Page

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