Project contact is Yelda Turkan, Oregon State University
Over the past decade, fires have caused significant losses, both financial and through loss of lives, in timber buildings during construction (USFA 2020). Buildings under construction or in development are largely unprotected as they are not yet equipped with active fire protection systems (sprinklers), and for those buildings that are not designed for exposed timber, multiple floors are left exposed at a time as the fire protection trade trails in schedule behind the erection of the mass timber structural elements. With the addition of Type IVA, B, and C in the 2021 International Building Code (IBC), the IBC also adopted stricter requirements for mass timber buildings under construction. Under-construction mass timber buildings require that the mass timber is protected with noncombustible material within four levels of any construction more than six stories above grade. However, limited research has occurred to demonstrate that this construction sequence results in the optimal balance of safety, property loss, and cost.
The goals of this project are to: (a) develop a methodology to couple multiple commonly-used computational tools to evaluate the sequence of installation of passive fire protection in mass timber buildings under construction fire scenarios, (b) develop an analytical framework that can be implemented by industry to evaluate the risk and impact of fire protection construction sequencing on a job site while balancing property loss, cost, and life safety of construction workers due to a construction fire, and (c) identify knowledge gaps in fire dynamics in timber buildings that would increase the accuracy of predicting fire spread in mass timber buildings under construction.
Fire separations and fire-resistance ratings are often required together but they are not interchangeable terms, nor are they necessarily mutually inclusive. The National Building Code of Canada (NBC)1 provides the following definitions: A fire separation is defined as “a construction assembly that acts as a barrier against the spread of fire.” A fire-resistance rating is defined as “the time in minutes or hours that a material or assembly of materials will withstand the passage of flame and the transmission of heat when exposed to fire under specified conditions of test and performance criteria, or as determined by extension or interpretation of information derived therefrom as prescribed in [the NBC].” In many buildings, the structural members such as beams and columns, and structural or non-structural assemblies such as walls and floors, are required to exhibit some degree of resistance to fire in order to prevent the spread of fire and smoke, and/or to minimize the risk of collapse of the building in the event of a fire. However, fire separations are assemblies that may or may not be required to have a specific fire-resistance rating, while structural members such as beams and columns that require a fireresistance rating to maintain the structural stability of a building in the event of a fire are not fire separations because they do not “act as a barrier against the spread of fire.”
Project contact is Erica Fischer, Oregon State University
Previous large-scale fire testing of mass timber buildings has occurred on a single floor of a building. The data collected from these experiments were used to demonstrate the fire performance of cross-laminated timber (CLT) buildings and to change the International Building Code (IBC) prescriptive fire protection design provisions for mass timber buildings. The scope of the tests was limited to compartment fires with varying levels of encapsulation. However, multi-story mass timber buildings are being constructed in the United States and fire science experts understand that fire threats can move beyond compartment fires and into travelling (moving fires) and vertical fire spread. In addition, many buildings are being proposed outside of the scope of the IBC prescriptive fire protection design approach (i.e. open floor plans), thereby requiring the employment of performance-based structural fire engineering. Performance-based structural fire engineering requires quantifying fire demands within the structure and calculating the resistance of the structure throughout the fire to provide safety to the occupants during egress, safety to fire fighters during and after the fire, and to ensure the building will not collapse introducing a threat of fire spread and damage to the surrounding buildings. To date, engineers are employing performance-based structural fire engineering on mass timber buildings; however, engineers are typically forced to make simplifications, be very conservative, and/or frequently use unproven assumptions. These simplifications and assumptions need to be tested experimentally to ensure that engineers are providing adequate levels of safety. Some of these assumptions include exterior wall and façade details that can prevent vertical fire spread, and detailing by engineers that considers the effects of charring during the decay phase of the fire.
The PIs have an opportunity to perform large-scale fire tests on a multi-story mass timber building in Corvallis, OR. Future large-scale fire tests will utilize a portion of the 10-story building being tested as a part of the Natural Hazards Engineering Research Infrastructure (NHERI) Tall Wood project (http://nheritallwood.mines.edu/). After the seismic testing of the 10-story building, the top four stories will be demolished and not utilized. Therefore, the research team will transport these floors to Corvallis to be re-assembled at the Corvallis Fire Training Center. In this preliminary stage, a multi-disciplinary team will perform computer simulation modeling of the fire tests, fully develop the scope of the tests and create a detailed experimental plan for the large-scale fire tests. The tests will be designed with considerations for the ability to address the following questions. These questions are consistent with future research needs that were identified by the Forest Products Laboratory  and the recent National Fire Protection Association (NFPA) Fire Safety in Tall Timber Buildings Workshop.
(1) How does the façade detailing of a mass timber building influence the vertical fire spread behavior?
(2) How can engineers better design mass timber buildings to enhance the safety for firefighters?
(3) How do glulam beam-to-column connections perform in real fires?
(4) What engineering solutions can be implemented within mass timber buildings to account for the behavior of the mass timber during the decay phase of the fire in the case that suppression is not available?
(5) How can engineers better design mass timber buildings to enhance the safety for fire fighters during the firefight and during overhaul/investigation?
To better evaluate failure of building elements and spread of fire beyond the room of fire origin, this thesis developed and integrated into CUrisk a barrier failure model and a fire spread model.
The role and position of the Fire Spread submodel were analyzed and changes to the system model and some other submodels were undertaken. With these modifications, CUrisk can employ the Fire Spread submodel to predict the fire hazard conditions in a building fire, and to use the results to predict the life risk and fire damages. Through a comprehensive case study of fire risk assessment of a six-storey residential building using the improved CUrisk, the Fire Spread submodel demonstrated the impacts of fire spread level on building occupant safety and fire losses.
The model performance was verified by comparing with the fire test measurements, which demonstrated good agreements. Comparable results are also predicted regarding the fall-off behaviour of the fire-exposed gypsum board as well as the charring behaviour. In addition, an example calculation was made using the probabilistic barrier failure model. Finally, a fire risk analysis case study was conducted on a six-storey apartment building with the purpose of showing the effect of wall barriers on fire risk. Results indicated that CUrisk can evaluate the impact of fire barriers on the fire risk with the new Barrie Failure submodel.