Post Tension Brick Jack Arch

We are currently prefabricating 8 foot long brick jack arches for a project in Philadelphia that have no angle iron support under the brickwork. Oh the joys of design-build. Actually it has given us the chance to try a system that Ray Wethington invented, of using post tension #4 epoxy coated rebar through he length of the arch.

Post-tensioned is the descriptive term for a method of applying compression after pouring concrete and the curing process. 99% of the brick jack arches we prefabricate are set on steel angle irons, and it is the steel that carries the load of the weight above the masonry opening. We do make structural jack arches but code usually dictates steel reinforcement unless a historical variance is given.

For this job we are drilling a 1" hole into the brick before we prefab the arch. Then we are inserting the rebar that has a hook on one end and threaded on the other end. We then tighten a nut on the rebar threaded end giving the brick jack arch post tension strength. The dramatic effect is 8 foot straight spans with brick and joints visible from below.

Brick Arches of the Roman Colosseum

Walking up to the Colosseum through the modern streets of Rome with my wife Brigid made me feel alive. I felt proud to work for a company that designs brick arches because there is no greater proof of masonry’s mastery than in Rome. I also felt insignificant in the physical and historical scope of the Colosseum. The stories of thousands of people who had died and cheered on the spot I was standing are what movies are made of.

The exterior of the Colosseum is made from white travertine stone that was quarried from the local hillside and held together with iron clamps. I was surprised to learn that all of the interior was brick and mortar. I we walked through the arcades and hallways, the tour guide gave a short talk on the significance of Roman technological breakthroughs in the field of masonry. The Romans discovered that masonry strength was not compromised by adding arches to span openings. The strength of the masonry structure increases as weight is dispersed above an arch.

The structural brick arches of the seating areas held up as many as 80,000 people as well as the weight of the masonry above it. The arena itself has a brick underground structure that allowed for trap doors with people and animals below like in the movie Gladiator. The brick jack arches of the arena and ground level doors were brilliantly designed and built.

Using four foot long brick, the Romans constructed the jack arch for functionality. The jack arches that supported the arena floor have a 77 degree skew but the jack arches under the massive seating area are built with a 70 degree skew to support more weight above it. What a marvel of engineering.

48" 4J O/S 1/4" joint 3/4 bond

We often get jobs that are either renovations or additions, and the architect and masonry contractor want the new brickwork to match the existing building. Brick arches built decades ago were made without autoCAD and designed with form following function. What we pay close attention to when we need to match an old brick arch are: structure, bond, skew, striking tool, and joint width. Here is picture a bricklayer sent us.



He said he needs 16 jack arches with a 48" M.O.(masonry opening) for an addition to a YMCA on the Eastern shore. The picture he sent gives us enough info to go ahead with the design. It looks like the building is flemish bond but the four course tall jack arch is 3/4 bond but closer to 1/2 bond. This is common in older buildings because bricklayers did not usually build jack arches this height with flemish bond, too many little pieces. They wanted to use the full length of the brick and still achieve 4 course height (12 1/2"). It also looks like the jack arch joint is tighter and slick joint and the rest of the building is grapevine joint and 3/8". We decide to design the jack arch with 1/4" joints, a 70 degree skew, and 3/4 bond.



We were sent oversize handmade brick from the bricklayer to build the jack arches. The length of the handmade brick is 8". When we took the 8" brick and stood it up as a stretcher, then leaned it 70 degrees, we figured the max height of our flemish bond stretcher in the jack arch to be 7". The old YMCA jack arch was probably made from brick longer than 8" because the 3/4 bond looks closer to a 1/2 bond. Since handmade is a long as these brick get nowadays without ordering special slugs, we proceed to match the bond as best we can. If the jack arch is 12 1/2" tall with 1/4" joint it leaves us with a 5 1/4" bat. We then designed the jack arch the same way we always do here at Archway System, with a georgian style, double struck consistent joint.