As fire disasters continue to happen and with the emergence of engineering disciplines such as Structural Fire Engineering, structural engineers have started focusing on how fire and high heat events effect different structural components to bring safer and more resilient structures. For the fire safety of structural concrete connections using post-installed rebar with adhesive there have been strides in recent years to support the evaluation of post-installed rebar, designed with the development and splice provisions of the model code, for designated fire ratings. Below are frequently asked questions regarding post-installed rebar design with either HIT-FP 700 R or HIT-RE 500 V3 in fire-rated concrete assemblies.
 
Supporting resources:
 
Post-Installed Reinforcing in Fire Conditions Design Guide
 
Designing Post-installed Rebar for Fire Conditions using PROFIS Engineering Whitepaper
 
 
Is fire-rating post-installed rebar connections required by the model codes?
 
Yes, however, like cast-in rebar, it is dependent on the application. The International Building Code (IBC) and National Building Code of Canada (NBCC) provide the structural design requirements for fire resistance of buildings based on occupancy and structure type. Certain assemblies within the structure are given a designated fire-rating to allow proper egress of the building inhabitants during a fire event. When designing the assembly, each material within the assembly needs to either be specifically designed for a fire rating, such as cast-in rebar being designed with the cover requirements listed in the IBC/NBCC that relate to a specific fire rating, or through other prescriptive methods. For adhesives, the new optional “Bond Stress vs. Temperature of Post-installed Reinforcing Bar Applications Subject to Elevated Temperature/Fire” test in Acceptance Criteria (AC308) for Adhesive Anchors in Cracked an Uncracked Concrete allows engineers to design post-installed rebar with tested adhesives with the development length provisions of the model code to meet the fire rating of the applications assembly.

Which HILTI adhesives have been tested to be used in fire-rated concrete connections? 
 
In 2023, Hilti released HIT-FP 700 R which is the first inorganic cementitious adhesive on the market tested for use in fire-rated concrete-to-concrete connection. It is tested following the AC308 test criteria for evaluating deformed reinforcing bars for use in post-installed rebar connections, and the resulting technical data can be designed for use in fire-rated concrete connections using the development length provisions of the ACI or CSA code. Hilti’s HIT-RE 500 V3 has been tested to the new “Bond Stress vs. Temperature of Post-installed Reinforcing Bar Applications Subject to Elevated Temperature/Fire” test in AC308 and has the appropriate published table available in ICC-ESR 3814 for its use in fire-rated rebar connections.
Visit the product page for:
 
HIT-RE 500 V3
 
HIT-FP 700 R
 
Can I use HIT-FP 700 R for an anchoring application?
 
Hilti’s HIT-FP 700 R has been tested for use with the reinforcing bar development length provisions of the code available in ACI 318-19 Chapter 25 and CSA A23.3 -19 Chapter 12. It has not been tested per a test method to make its design compatible with the post-installed anchoring provisions of ACI 318-19 Chapter 17 or CSA A23.3-19 Annex D.
 
Should I replace RE-500 V3 with FP-700 moving forward?
 
Not necessarily. Both HIT-FP 700 R and HIT-RE 500 V3 have been tested for use in fire-rated reinforcing bar connections and each have benefits depending on the application. HIT-RE 500 V3 is a great option in connections where you have a variable temperature gradient along the embedded length such as post-installed rebar installed in a joint connection and may even have a lesser embedded length than HIT-FP 700 R in the same connection. HIT-FP 700 R demonstrates its benefit in extension type applications where the full embedded length is exposed to the same elevated temperature. In summary, when there is a larger concrete cover and protection from the fire, HIT-RE 500 V3 may still be the option with the smaller development length.


Why has fire design not been addressed previously?
 
Until late 2022 there was not a test method available to evaluate adhesive performance when exposed to heat. However, with the prevalence of post-installed connections in construction due to their ease of use and flexibility, the International Code Council Evaluation Services (ICC-ES) introduced a new optional testing protocol within AC308  for manufacturers to test for the “Bond Stress vs. Temperature of Post-installed Reinforcing Bar Applications Subject to Elevated Temperature/Fire” curve for adhesives exposed to heat in post-installed reinforcing bar connections.
 
Can HIT-FP 700 R and HIT-RE 500 V3 be designed in masonry fire-rated walls?
 
While masonry fire-rated walls are common, neither HIT-FP 700 R nor HIT-RE 500 V3 have been tested for use in masonry construction. They are currently only tested for use in cracked and uncracked concrete.
 
What is the load combination that I should be using when performing a fire design? 
 
The load combination for design is up to the engineer of record and local rules and regulations. ASCE 7 does offer a load combination for extraordinary events like fire which provides for half of the normal live load and some considerations of loads during the fire (Ak). It is up to the EOR (Engineers of Record) whether this is acceptable for their structure. 


Supporting Resources
 
Post-Installed Reinforcing in Fire Conditions Design Guide
 
Designing Post-installed Rebar for Fire Conditions using PROFIS Engineering Whitepaper
 
Log in or Register for PROFIS Engineering to get started on a fire-rated rebar design in the Concrete-to-Concrete Design module.