Post-Installed Reinforcing in Fire Conditions
Post-Installed Reinforcing in Fire Conditions for Concrete Construction
Fires are unfortunately an occurrence that some buildings are exposed to over their service life. It is known that the fire can do significant damage to both the non-structural and structural elements of a building during a fire. The model building codes are constructed to allow the occupants to exit safely and hopefully to limit the damage from the fire. Both the International Building Code( IBC) in the United States and the National Building Code of Canada( NBC-C) have provisions to create fire barriers to limit fire spread if a fire should break out.
In concrete and masonry structures, engineers today can use ACI / TMS 216.1 Code Requirements for Determining Fire Resistance of Concrete and Masonry Construction Assemblies to examine how the building structural elements will be affected when exposed to the high temperatures in a fire. ACI 216.1 provides information on the design of concrete walls, floors, and roofs, which make up the primary fire rated assemblies in a structure, as well as providing information on the effects of the fire on steel reinforcing, and the design of concrete beams and columns. There are also design considerations for steel columns encased in concrete and provisions for fire consideration in masonry structures.
However, there are no provisions within ACI 216.1 or other reference codes in the United States or Canada that considers the effects of fire on post-installed anchors such as post-installed reinforcing with adhesive anchoring systems that is used to develop the rebar just like cast-in rebar. Designing post-installed anchors for fire exposure has been more common in Europe, primarily due to the high number of tunnels where fires are extremely dangerous. In Europe, there are testing and design standards which are used by designers to evaluate post-installed anchors in fire conditions.
In conjunction with ACI 216.1 and a new test and evaluation acceptance criteria implemented by ICC Evaluation Services( ICC-ES), this document is intended to provide a methodology that designers using ACI 318 or CSA A23.3 can use to evaluate post-installed rebar connections with Hilti adhesives for rebar development during a fire event.
ICC-ES Acceptance Criteria for Post-Installed Adhesive Anchors in Concrete Elements( AC308) was updated in 2015 so that post-installed rebar with adhesive could be qualified to show equivalence with cast-in rebar for development length calculations. Hilti has qualified HIT-RE 500 V3 with ICC-ES for use with ACI 318 Chapter 25 rebar development equations within ESR 3814. Refer to the Hilti North American Product Technical Guide: Post-Installed Reinforcing Guide, dated November 2022( Rebar Tech Guide), for more information on designing postinstalled rebar connections with Hilti adhesive anchors.
AC308 was subsequently updated in 2022 with testing provisions for fire exposure and updated again with a new criteria number, AC308( 24) in 2024. Hilti has performed the new tests for fire evaluation in AC308( 24) and ESR-3814 has been updated with data for use in fire conditions for post-installed rebar development connections. Refer to ESR-3814 and Section 4.0 of this document for data related to tests in fire conditions with HIT-RE 500 V3. For the first time, designers and building officials have a tool related to performance of post-installed anchors in fire for the United States or Canada and do not have to rely on European information.
In addition, Hilti has a new adhesive product, HIT-FP 700 R, which is a brand-new injectable cementitious adhesive which has very little sensitivity to high heat. Previously, cementitious, inorganic adhesives were not recognized by AC308( 24) or ACI 355.4. However, in 2024 ACI published ACI 355.5-24 which is a new testing provision for post-installed reinforcing bar systems, and this incorporated test for both organic and inorganic adhesive systems and also included the fire testing provisions from AC308( 24). Subsequently, ICC-ES published the Acceptance Criteria for Post-Installed Reinforcing Bars in Concrete Elements( AC581( 24)) which mirrors ACI 355.5 and allows manufacturers to obtain an ICC-ES Evaluation Report for inorganic post-installed reinforcing bar systems including evaluation of the system for fire conditions.
Hilti HIT-FP 700 R has been tested to all of the provisions of ACI 355.5 and AC581( 24) and Hilti is now the first manufacturer to have an inorganic, cementitious adhesive with an ICC-ES Evaluation Report, ESR-5891, including evaluation of fire tests. Technical data for rebar development is provided in Section 3.0 of this document for designs in fire and non-fire( ambient temperature) conditions.
Design for Rebar Development in Fire Conditions
The design methodology in this section is meant to be used in conjunction with standard rebar development calculations in ACI 318 Chapter 25 and CSA A23.3 Chapter 12 and with fire exposure based on a time to temperature curve established in ASTM E119 Standard Test Methods for Fire Tests of Building Construction and Materials. In general, the design will determine whether the development length needed at ambient temperature will need to be increased due to fire exposure to account for the potential loss in bond stress in the concrete that has been heated.
For the design the following information is needed:
• The development length of the post-installed rebar at ambient temperature.
• The fire duration rating of the connection, such as 30, 60, 90, 120, 180, or 240 minutes.
• The temperature in the concrete at the specific concrete cover distance of the rebar.
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