Church Beam Repair
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In the mid 1990's termites were detected in the sacristy of the church and treatment was initiated. This eliminated the termites. What went unnoticed was their handiwork. One of the beams that support the roof is surrounded by brick and so the damage to the footing of this beam was not visible. Over the years the beam has deflected ever so slightly and this was mistakenly attributed to normal movement. In 2006 however, the beam bent a considerable amount, 1 3/4 inches at the greatest point of deflection. The following picture shows the deflection visible from the inside of the church.
The black material should not be visible. This shows how much the beam has deflected. If this picture were from a greater distance, the top and bottom portions of the beam would be shown to have not moved. Only the middle 4 feet has bent from the original shape. This is the deflection that we are talking about.
During the investigation into why the beam was deflecting, we were made aware of the treatment for termites in the 1990's. So we removed the brick wall surrounding the footing and this is what we found:
The surface is certainly not smooth like it is in the church. At some points a rod can be inserted all the way through the beam, over 12 inches.
Looking up, this is where the beam penetrates into the church at about 8 feet high. In the church the beam looks fine at that point but just behind the wall....
So what does this mean? Simply put the beam foot had to be reconstructed to restore the structural integrity. Initially what was thought was that after years in a weakened state, the beam fatigued and began giving away at an accelerated rate in 2006. This was incorrect. As it turns out, the termites reappeared. This is something not discovered until the repair was almost completed. Interestingly, after computer modeling, the structural engineer determined that the beam could fail completely and other than a loud noise, not much would change. The way the church is constructed, the remaining supports have already taken up most of the load from that beam. Nice to have friends! Anyway, after structural consultation with engineer Mike Stenstrom, a row of pews was removed to allow for the installation of temporary supports by Jerry Zimmerman and his crew. There are four and this is what they look like:
There are two on each side of the church. So why are there four supports if only one foot of the beam is damaged? What we have in the church is a hinged support structure. The 'hinge' is at the top of each arch. The arch itself is constructed of two separate beams that connect at the top of the arch or at the hinge. At that point each beam is pushing against each other so that they hold each other up. But at the foot, the beam wants to move in the opposite direction, horizontally away from the foot of the other beam. This is called thrust. Normally this thrust is arrested at the foundation where the beam foot sits in a metal 'shoe'. This keeps it from slipping off of the foundation. All the thrust force is transferred to the foundation that way. To keep the shoes from moving, they are fastened to a concrete beam that runs from the shoe on one side of the church to the shoe that is on the opposite side of the church. This way the thrust at one shoe is effectively counteracted by the thrust at the opposite shoe. Neat isn't it? Neat until you lose the foot of one beam.
So the four temporary supports alleviate the thrust by providing support for the entire hinged arch. They essentially held up that whole arch. Theoretically the legs could be cut off both sides of the beam and nothing would happen. This theory was not tested. Anyway, four are needed instead of just 2 because this is what the foundation can support at any point can support safely. The beam running across under the floor is capable of supporting the 88,000 pounds of thrust as long as we spread the load to four points. With the supports in place the work proceeded safely.
And how is a foot repaired? There are multiple options but the problem with most of the options is that there would be visible changes to the beam within the church. Since aesthetics is something of more than a little value, a process was selected that is used primarily on supporting deteriorated or weakened concrete. This requires a three step process.
Step one is to remove all of the damaged wood. Outside the church this is not a problem but we can not afford to damage the exterior of the beams that are visible inside the church. So we have to maintain the beauty of the beams while restoring structural integrity. Fortunately the little termites were eliminated before they got into the church. Perhaps they were not Catholic termites. The following pictures show the same areas as those photographed above only this time showing various stages when damaged wood has been removed leaving only strands of good wood.
You may wonder how in the world this beam can be supporting anything. The answer of course is that it can't. This goes to show how well this church is constructed. This beam is providing no support for the roof and still there was not have a structural problem.
Again, looking up, this is where the beam penetrates into the church at about 8 feet high. Shouldn't be able to see right through it should we? This was to be a solid beam, 12 inches thick and 33 inches wide before the termites feasted.
Pretty much all the damaged material has been removed. This is all that is left of the beam, about 4 strands of wood.
Should there really be a hole there? Not much left of the beam.
Back to the steps. Steps two and three are done by two separate contractors acting in unison. Step two is installation of wood to be used as filler material. Step three is the injection of epoxy to bind all of the filler wood together as one mass of material and then to apply the carbon fiber wrap to the wood to restore structural integrity. The carbon fiber wrap is what restores all of the structural strength.
Essentially where there was formally one big beam there is now smaller columns joined together. The pictures below show the creation of three columns of wood, the wrapping of one column, laying fiber on the second column and the filling in of the void between them with wood.
A little hard to see with the temporary wood wall behind it but we have laminated pieces of wood to create two columns. These were injected with epoxy and then wrapped with carbon fiber. Then the voids were filled in with two more columns and do the same thing.
Look at the picture to the left of this one, the rebuilt section of wood on the left is completely wrapped in the black carbon fiber material. There is also a sliver of black showing to the right and that is a layer added to the section on the right in the picture to the left. The void between those two columns has been filled in with wood and is ready for the next injection of epoxy and wrapping.
This is a closer view, this is where the beam penetrates into the church.
Naturally one would ask why we wrapped one column and only layered the second column and where is the third wood column. This has to do with the way in which this beam works. Let's take a little tour through engineering land before we return to the restoration narrative.
Engineering Land
The original beam was built from strips of wood laminated together to act as one monolithic member. As a monolithic member this beam has two forces acting upon it. The first is compression. The bottom half of the beam experiences this compression zone. The top half of the beam is in tension. The repair counteracts the tension forces and there is very little concern about the compression forces.Why not worry about failure of the compression zone? Think about when you bend a stick. The bottom part of the stick is in compression. The top part is in tension. Bend the stick enough and the stick will break from the outside, in the tension zone, down through the compression zone. It will not fail the other way. The compression zone area will not give way before the tension zone material. So if we can restore the tension strength, we have essentially repaired the beam.
So how did that little Engineering Land narrative explain the columns? It didn't, just showing off our vast knowledge of the mundane. No actually it will help explain what was done. By breaking the beam into columns multiple tension and compression zones are created, not just one. Looking at the pictures above, the area to the right that only has one layer of black material, that black material is the tension zone, everything to the right of it is a compression zone and that is one column. There is no reason to cover the wood to the right of the fabric because we don't need anymore tension zones in that area. The section that is completely wrapped creates two tension and compression zones. The left and right sides of the wrapped column are the tension zones. The area between them that is hidden by the wrap on the side is a compression zone and that is column two. The second compression zone created is in the void between the wrapped beam and the layered area. That area was filled with wood and is the third column. As we mover further to the left on the beam more layers of fabric are laid in to create narrower tension/compression zones. Each 1/16 inch layer of wrap is the equivalent of 1/4 inch steel. A minimum of two layers of fabric are used in each zone with a maximum of 4. The four layers are on the top of the beam and this layer extends into the church but is not visible.
One area of concern in the tension zone is the joint between the old beam and the new material. On the top of the beam, we have two 6 inch grooves cut two feet into the good old beam wood and down 6 feet past the joint. These grooves are filled with carbon fabric, epoxy and rebar. This spreads the tension force at the joint to the areas above and below the joint.
This is the beam covered in epoxy and ready for the final wrap.
This is where the beam penetrates into the church at about 8 feet high and is covered in epoxy.
Protective clothing is a must when working with the epoxy.
This is the beam with the final wrap done.
Again where it penetrates the church.The posts were removed, the floor repaired, brick closed up and the pews returned. Here are some additional pictures.
Bricking up the inside, say goodbye to the beam.
Lousy pictures, crummy photographer but look, almost back to normal.
Taking down a post.
Goodbye post, hopefully forever.There are two of the 14 beams that were surrounded by brick. After repairing the damaged beam, openings were left so that visual inspection of the beam for damage can take place. This was also be done on the other beam surrounded by brick that is not damaged. As a precaution the whole church was treated for termites.
And now for a little artistry. Isn't this a nice picture, light streaming through a brick opening? Nice except that we shouldn't be able to see this light, there should be a beam here.
The light is from a small opening that we created on the outside of the church. Looks like a skeleton or something from the Pirates of the Caribbean.