Supporting a Fractured Building

Supporting a Fractured Building

BY JOHN P. O`CONNELL

A tremendous amount of shoring was erected throughout the Murrah Building`s fragile structure. Much of it was erected during the first days of the operation; however, shores were continually erected or improved throughout. They were used to protect members operating in dangerous areas and to stabilize the building`s remaining structural elements. In some areas, debris had to be removed before shores could be erected. (The base on which the shoring is assembled must be able to support the load being shored, or disastrous results can occur.) The majority of the shoring was done in the interior; a few shores were constructed outside of the structure, mainly to support sections of debris during removal operations. Rescue personnel installed the wood shoring; construction contractors erected four- and six- inch pipe shoring, much of which was tied together with angle iron straps for additional rigidity.

TYPES OF SHORES ERECTED

Flying raker. Numerous shores of this type were erected at this operation almost up until the last day of operations. They were used primarily to stabilize sections of concrete, generally pieces of broken floor slabs, while search and rescue operations were conducted in the area. The shores were constructed of one 4 3 4 propped under the concrete slab or anchored to it in a variety of ways. This type of shore was used as an initial safety shore to stabilize the leaning slabs while the areas around the piece were being cleared to the floor, making room to erect more substantial shores if necessary. In many cases, several of the flying rakers were assembled together; this made an excellent and stable shore that enabled workers to operate safely while searching for additional victims. A friction-type of shore, the flying raker is supported solely by the pressure applied to it from the concrete. A short wall plate of two-inch dimensional lumber should be anchored to the slab. Attaching the raker to this plate provides additional stability.

Solid-sole raker. Two solid-sole raker shores were erected on the first floor. They were used to support damaged and leaning sections of interior walls in the corridor used as a main accessway by all personnel. The wall plates, sole plates, and rakes of both shores were constructed of 4 3 4 lumber. The diagonal braces were constructed of 2 3 6 lumber.

Vertical shores. Vertical shores–the most common type used by rescue teams in any collapse situation–were widely used throughout the Murrah Building. Sixteen were erected in various locations on the first floor and two on the second floor. All were constructed of wood; 11 had 6 3 6 headers, sole plates, and posts; the elements of one were constructed of 4 3 6 lumber. The main components of the remaining vertical shores were erected with 4 3 4 lumber. The diagonal cross braces of all shores were of 2 3 6 lumber. The 4 3 4 shores were erected to support structurally unstable and damaged floor slabs. The 6 3 6 shores were used to support the much heavier beams that had been damaged in several places.

Laced posts. This type of shore is actually two vertical shores properly tied together to make an integral shore. It is very strong and extremely stable. Laced posts were erected in several areas where stability was a factor and not enough room was available to erect a series of shores. This type of shore can be constructed with 4 3 4 or 6 3 6 lumber; the latter was more prevalent at this operation. These posts are especially effective when stability is a factor and heavy loads must be supported–two problems experienced in several areas of the Murrah Building. Several of the laced posts were used under damaged floor slabs to prevent further collapse. The posts supported the slab`s edge and also counteracted lateral forces against the slab caused by the great amount of debris resting against it. This type of shore was also used under a heavily damaged area of a beam.

Vertical void shores. These shores are basically a smaller version of the vertical shore and usually are a little simpler to erect than the larger vertical shores; they generally serve a similar purpose. Several of these shores were erected at this rescue operation. Their advantages are that they can be erected quickly, are easy to maneuver, and use up quite a bit less lumber than box cribbing. Their wall plates, sole plates, and posts normally are constructed of 4 3 4 lumber; wedges are used to tighten the shore to its proper firmness–just enough to fully support the weight but not enough to move it.

Box cribbing. This is one of the stronger and more stable types of shores. The more material used for each tier, the stronger the crib. The height of the crib usually can be three times its width. Generally “4-by” multitier cribs were erected in this incident. They were consistently used to support sections of broken, cracked, or heavily dam -aged columns and beams. These cribs are extremely stable and can support extensive amounts of weight safely.

Pipe shores. Several of the first-responding task forces had installed some initial shoring using mechanical pipe shores and 4 3 4s and 4 3 6s. These pipe shores are commonly used in the construction industry, generally for supporting “green” concrete. A local contractor was able to supply several of these supports, erected during the initial stages of the operation. These shores, used strictly as vertical supports, were placed on 4 3 4s. Installing a 4 3 4 or 4 3 6 as a header made them effective full-length “dead” or vertical shores. Their one drawback was that they could not be diagonally braced, which made them less stable than the wooden dead shores.

Column bracing. The majority of this work was conducted over “the Pit” and was designed to stabilize compromised unsupported columns identified by the engineers. Construction contractors erected systems, designed by the structural engineers assigned to the FEMA incident support teams (ISTs), consisting of 4 3 6 pipe shoring tied together with angle iron straps for additional rigidity. The pipes were welded, erected, and bolted into the columns by contractor crews. Several of these column trusses were installed and tied together for additional stability. Truss braces were installed at Columns F20 and F22 at the second- and third-floor levels. Pipe knee braces were installed on the second floor at Columns F14, F16, and F18.

Wedges. Wedges play an extremely important role in any structural collapse operation. They have a variety of uses–all of which make the erection of rescue shoring that much faster and easier for the rescue workers in potentially hazardous situations. When used in conjunction with box cribbing, a wedge can quickly bring a crib into solid contact with an object that is on a different angle than the box crib itself. This will happen quite often when the support base of the cribbing is on the ground or a level floor underneath the object to be supported. Normally, the cribbing should be erected as level as possible for better stability. At some point, the crib must have full contact with the item being supported. If it is on an angle, this can easily be accomplished by using one wedge or a series of wedges.

When erecting vertical or dead shoring, wedges are an important part of the shore`s makeup. A set of wedges must be placed under each post, primarily to make sure the shore`s contact with the object to be stabilized is sufficient. The shore should be tight enough to take the full weight of the compromised object. The shore should not be used to lift the object in question. Wedges also will compensate for any differences in post lengths. Another advantage of wedges is they allow the shore to be continually adjusted, if necessary. Often, as debris is removed from above, the floor being stabilized starts to return to its original position. Continual adjustment of the wedges will ensure that the shore will continue to function properly.

LUMBER USED IN THE INCIDENT

Dozens of truckloads of lumber and materials were delivered to the scene. Evidence of the need for extensive shoring operations was apparent early in the operation. The call went out to all local lumber and construction suppliers, who promptly responded. Literally hundreds and hundreds of pieces of lumber in several sizes and shapes were brought to the site. Some of the most extensively used lumber sizes were 2 3 4, 2 3 6, 4 3 4, 4 3 6, 6 3 6, and 34-inch-thick plywood. n

(Left) Several different types of shores located in the same general area. A broken and heavily cracked beam is being supported by the box cribbing and two raker shores. The other long raker shore and the vertical pipe shores are supporting the damaged and loose slab of the second floor above. This area was the base for several shores because it was one of the first areas cleared of heavy debris down to the floor. All shoring must bear on solid ground; erecting shoring on debris is extremely dangerous and should never be done. The first shores erected were the vertical pipe shore and the longer flying raker shore. The longer flying raker was notched at the bottom to accept two wedges, which were tightened until the weight of the slab was supported by the raker. The base of the vertical pipe shores was erected on 6 3 6 timbers to gain sufficient height. These two shores were used to support the slab above as rescue members cleared debris from under the slab for shoring as well as search and rescue operations. The second and third shores constructed were the box cribbing under the beam and the flying raker shores against the face of the beam. The box cribbing was a 4 3 14-tier crib constructed of 4 3 4 24-inch-long lumber; wedges were also used to change the angle of the crib so it would have full bearing up to the beam. (Middle) Several feet to the left of the shoring depicted in the first photo, this broken section of column was hanging. It was still attached both to the remaining section of the column and the beam it was supporting originally. For operations to continue safely while other debris was being cleared and removed, this section of material had to be properly supported. A 3 3 10-tier crib was used; it was constructed from 4 3 4 lumber–more than enough to support the load above. (Right) The remaining shoring described in the first photo caption. Notice the double flying raker tied together and braced against the face of the cracked beam. Both pipe shores

(Left) Two flying raker shores propped against the remaining section of the second-floor slab. This slab was hanging precariously, and several victims were removed from this area. Considerable debris directly underneath this section of concrete made shoring difficult. The two raker shores were constructed of 4 3 4 lumber and placed into two pockets attached to a 2 3 4 section of lumber. The entire shore then was set in place and tightened; a diagonal brace then was attached to the rakers for additional stability. (Right) A 10-foot-long vertical pipe shore was also erected in the same area as the double flying raker shore. This shore was located on the east side of the beam on Column Line 18, between Columns E and F. It consisted of four pipe shores on top of a 4 3 4 sole plate and a 4 3 4 header. The slab was at a downward angle; as a result, wedges had to be placed along the length of the header so it would have proper bearing and support. The pipe shores were placed approximately three feet apart.

On the west side of Column E16, a section of broken column from an upper floor came to rest on a precariously unstable area of debris, which somehow had to be supported so rescuers could properly search and clear the area of debris. Two pieces of lumber–a 4 3 4 and a 4 3 6 (shown here)–were placed against the column section. A “V”-shaped notch was cut into the timber at the point at which it was placed against the corner of the column and then wedged into the floor.

(Left) The Pit area. On the left of the photo are two pipe shores installed by contractors. They were erected from column to column for additional lateral stability since the beams between the two columns had been destroyed and the columns were freestanding for two floors–bearing a major strain for which they were not designed. A plywood shoot was erected underneath the pipe bracing to expedite removal of loose debris to an area where it would be picked up by a Bobcat® loader. Several sections of the upper floor slabs came to rest on the edge of the Pit. Here, several 4 3 4 pieces of lumber were placed under the loose slabs as supports. They were also tied together to add additional stability to the shores. This gave rescuers a safe area in which to operate. (Right) The base of a flying raker anchored to the floor. A double 2 3 4 was laid on the ground-floor slab, and holes were drilled into the lumber and the floor slab. Then, sections of rebar were hammered into the holes. Wedges were then placed at the back of the flying raker and tightened–tightening the raker against the item to be shored and also the rebar against the concrete floor, giving the raker its support.

Some of the shoring erected in the Cave. The photo was taken after the bulk of the debris had been removed. The original entrance to the Cave was to the left; members had to crawl in and erect a series of shores before they could safely operate. Two vertical void shores were erected underneath a series of unsupported utility pipes. They were constructed of 4 3 4 lumber and wedges were placed at the bottom of the sole plate and header. Behind the two shores, two box cribs were erected. The cribs were placed under the second-floor slab, which had thousands of pounds of debris on top of it. Both box cribs were constructed alike: 3 3 7-tier cribs of 4 3 4 lumber. Wedges were placed above the top tier to spread the full bearing of the slab to the ground floor. After the shoring was accomplished, operations in this area continued for several days.

(Bottom left) This shoring was erected underneath the beam in Column Line 18, between Columns E and F, located on the first floor. The debris behind the shoring was the start of the Pit. These two types of vertical shores were erected side by side. The shore to the left was erected earlier than the shore on the right. The shore to the left has a header of 4 3 6 lumber with two interior posts consisting of 4 3 4 lumber with adjustable “feet”; the outside post consisted of two adjustable pipe shores. No sole plate was installed; the shores all bore directly on the first-floor concrete slab. Note there was no diagonal bracing–when using metal pipe shoring, diagonal bracing is difficult to accomplish. The shore to the right was constructed entirely of wood; the header and sole plate were constructed of 4 3 6 lumber. The posts were constructed from 4 3 6 lumber; the diagonal braces were 2 3 6, as were the cleats. Wedges were installed under the posts to tighten the posts properly. The last step was to attach the diagonal braces. The braces tied the entire shore together so it acted as one unit and provided resistance against any lateral pressures that might be applied against the shore. If debris from the large pile suddenly were to fall against the shoring, the all-wooden shore would be subject to less damage than if it were tied together as one unit. The shore on the left easily could have its posts dislodged or knocked out of plumb, thereby causing a major stability problem. (Bottom right) One of several vertical or dead shores erected at the incident. As a safety measure, these vertical shores were erected underneath the beams that had incurred damage. The height of the floor to the underside of the beams was approximately 12 feet; this was typical throughout the structure. The average width of the beams was five feet. The headers and sole plates were roughly six feet long with three posts assembled within that area. The headers, sole plates, and posts all were cons

(Left) The anchor point of the raker shore after the raker was erected against the leaning wall and the setting of the anchors. A space was left between the sole plate and the anchor blocks for installation of a set of wedges. A 4 3 4 and 4 3 6, each four feet long, were anchored into the concrete floor of the building–providing a solid foundation against which the sole plate could be secured. The wedges were tightened after the blocks were anchored. By installing these wedges, the sole plate was tightened up against the wall and against the anchor blocks–solidly locking the raker shore into position. Note the wedges behind the rake used to tighten the rake against the wall for full contact and proper transference of the weight from the leaning wall to the floor. Behind the wedges is the bottom cleat, which is nailed to the sole plate to support the wedges and rake. For additional stability, the team erecting this shoring also gusset-plated the connection points of the raker shore. (Right) A solid-sole type raker shore installed to support the heavily damaged interior partitions. The wall plate, sole plate, and rake were constructed from 4 3 4s. This type of raker shore is best suited for interior operations and installation onto a solid bearing, such as the concrete floor shown here. Two 2 3 4 diagonal braces were also installed on the rake for added strength.

A pneumatic nailer used by one team. It was attached to an air cylinder with a regulator and length of air hose, making the tool very portable and easy to maneuver around the collapse area. This type of nailer is invaluable in erecting rescue shoring. It nails without vibration and is much faster than conventional methods. It should be in all shoring tool caches.

(Left) In the center of this photo, a laced post shore was constructed from 6 3 6 timbers, 2 3 6 braces, and four-inch-thick wedges. The shore supported the heavily damaged third-floor beam along the Column 18 line between the E and F columns. Just to the left of the laced post, the majority of the beam had been almost totally destroyed, offering no real support to the slab above. Since the location of the laced post would be almost the center of the damaged beam, it was an excellent shore for holding up the remaining slab support. Two 6 3 6 headers and two 6 3 6 sole plates were used to evenly spread the load across the beam. The shore was laterally tied together at the top, bottom, and center–along all sides; this ties the shore solidly together as one unit. A series of diagonal braces was installed on the lower and upper halves of each of the four sides of the shore. The diagonals oppose each other, making an “X”-brace type of pattern–creating a considerably strong and effective shore that would help support against any eccentric or torsional loads that might adversely affect the laced post. Several of these shores were erected. This type of shore is excellent when a single shore had to be installed. It was extremely stable and able to stand alone without any problems or loss of integrity. (Right) The same laced post with a 4 3 6 dead shore erected adjacent to it. This shore was eight feet long and was also used to support the cracked F/E-18 beam.

A view of the start of the Forest from the southwest side of the shoring. Four 6 3 6 timber vertical shores were erected underneath the beam between Columns F16 and E16. This shoring had to be erected when–early in the incident–the beam cracked at the north end of the F column line and dropped several inches. The four dead shores were erected individually to immediately support the damaged concrete; they were erected with 6 3 6 headers, sole plates, and posts for maximum strength. After the shores were in place, they were diagonally braced in the opposite direction on both sides of the shore to further tie them together–making all four shores one support system. The shores shown here held up not only for the two-week operation but also when the building was demolished and the remaining structure came down on top of them.

(Left) The Smart Level® used in several locations of the structure. It was most efficient for monitoring movement of the several columns with questionable integrity. It was attached to the columns and visually monitored from a safe distance by using surveyors` transits. The digital readout indicated if movement had occurred. On-site engineers continually monitored the levels for the duration of the rescue operation. (Right) Whenever task forces erected shoring on-site, the shore was documented in a set of master drawings. This documentation was an ongoing process that lasted from the first until the last day. Information noted included the type of shore, its location, its size, and the type of material used in its construction.

JOHN P. O`CONNELL has been a firefighter with the City of New York (NY) Fire Department for 16 years and, as a member of Rescue Company 3 in the Bronx, has more than eight years of collapse rescue experience. He is an instructor of shoring and building collapse at FDNY`s Training Academy and has been involved in the writing and teaching of the department`s collapse and shoring training curriculum. O`Connell is a member of New York Task Force 1 of FEMA`s urban search and rescue network and is a rescue specialist instructor for FEMA. He is a New York state-certified fire instructor and spent more than 10 years in the building construction industry. He served as shoring adviser for the Fema IST at the Oklahoma City Bombing.