Jack Arch

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Jack Arch

What is Jack Arch?

A shallow masonry arch constructed between steel beams or joists to support floor or roof loads, typically made of brick or concrete masonry units, commonly used in commercial and industrial construction to create fire-resistant floor and roof systems with structural steel framing.

Description

A jack arch is a shallow masonry arch constructed between steel beams or joists to support floor or roof loads, typically made of brick or concrete masonry units, commonly used in commercial and industrial construction to create fire-resistant floor and roof systems with structural steel framing. This structural system combines the strength of steel framing with the fire resistance and thermal mass of masonry construction. Jack arches are fundamental elements in traditional mill construction and continue to be used in modern fire-resistant building systems.

The primary purposes include providing fire-resistant floor and roof systems, supporting loads between steel beams, creating thermal mass for temperature control, offering durability and longevity, providing sound dampening properties, enabling large open spaces with steel framing, and meeting fire safety building code requirements.

Construction and design encompass shallow arch geometry, integration with steel beam systems, masonry unit selection, mortar joint design, load distribution mechanisms, and fire resistance characteristics.

FAQs

  • What is a jack arch?

    A jack arch is a shallow masonry arch constructed between steel beams or joists to support floor or roof loads, typically made of brick or concrete masonry units for fire-resistant construction.

  • Where are jack arches used?

    Jack arches are used in commercial and industrial buildings, mill construction, warehouses, and any application requiring fire-resistant floor or roof systems with steel framing.

  • What materials are used for jack arches?

    Common materials include brick (common or fire brick), concrete masonry units, fire-resistant mortars, and integration with structural steel beams for support.

  • How are jack arches constructed?

    Construction involves installing temporary centering, placing masonry units in an arch pattern between steel beams, using proper mortar joints, and curing before removing centering.

  • What are the fire resistance benefits?

    Jack arches provide excellent fire resistance, protect structural steel from heat, create fire-rated assemblies, and help compartmentalize buildings for fire safety.

  • How shallow can a jack arch be?

    Jack arches typically have rise-to-span ratios of 1:10 to 1:20, making them much shallower than traditional arches while still providing structural and fire benefits.

  • Are jack arches still used today?

    Yes, jack arches are still used in modern construction for fire-resistant systems, historic restoration, and applications requiring the unique benefits of masonry and steel construction.

Fun Fact

Fun Fact: Jack arches were extensively used in 19th-century mill buildings and are why many of these structures survived major fires that destroyed other buildings! The term “jack arch” comes from the use of “jack” meaning auxiliary or supporting, similar to jack rafters. Some jack arch buildings from the 1800s are still in use today, testament to their durability. Interestingly, modern jack arch systems can achieve fire ratings of 3+ hours while supporting heavy loads, making them valuable for high-rise construction and industrial applications!

CSI Code

04 20 00

NAHB Code

430