Final Report Summary - CONFIRE (Fire Resistance of Connections in a Composite Floor System)
Project Work and Results:
In CONFIRE Project, the proposed four research objectives were successfully completed. With the project start, Bogazici University Structural Fire Research Group “BOUNFIRE” is formed, which has 9 members including 3 female graduate students. The findings of the project were disseminated via several international conferences and peer-reviewed publications. The details of the progress were also published on Project website (http://www.ce.boun.edu.tr/selamet(si apre in una nuova finestra)). The results of this project is highly related to the mitigation of natural hazard risks, which is one of priorities as a funded activity in “Environment European Research Area”.
Europe has one of the worst fire loss records in the industrialized world as demonstrated by the large number of fire-related deaths and the volume of property destruction. The direct financial cost amounted to 15 billion Euros in 2008 among the associated countries in Europe. Further, the cost for providing fire protection to buildings amounted to almost 12 billion Euros in 2008. CONFIRE Project investigates the steel connections in a steel beam-concrete slab floor system under fire and aims to use a performance-based approach to the fire resilience of connections in a full structural system. The ultimate goal is to design floors in tall buildings such that the risk to life safety to building occupants and fire fighters in the event of a fire is minimized and the fire is contained within the floor without partial or global collapse of the building. Steel-framed floors with thin concrete slabs are generally used in modern high-rise buildings in Europe. The project numerically and experimentally investigated the thermal and mechanical behavior of these floor systems and aimed to fully understand the governing fundamentals during a compartment fire. The goal has been to answer the following questions:
- Is it possible to avoid fire protection on the steel members in the secondary (gravity) beams in composite floors? Such conclusion will save millions of Euros to the steel industry in Europe.
- If the secondary beams do not fail under a severe fire, do the connections remain intact?
- What is the mechanical and thermal interaction between the steel members and the concrete slab in the floor system? At what deflections is the tensile membrane action triggered?
The first objective was to collect data of existing tall buildings relevant to structural fire safety.
- After investigating over 40 tall buildings in Istanbul, the tallest steel building Hilton by Doubletree in Istanbul, Turkey was chosen as a case study (see attached Figure 1). From the detailed blueprints, a large (9.5m x 6m) composite floor from this building was selected, which is then modeled in CAD software (see Figure 2a, 2b). The composite floor consisted of a 120mm thick concrete slab, four perimeter (main) beams, two secondary (gravity) beams connected via shear connection. The numerical and experimental analyses were carried out to observe the fire performance of this composite floor. The composite floor is heated for 90 minutes with a standard fire curve (ISO834) and it is consequently air-cooled. The secondary beams (see Figure 1) are left without fire protection whereas the main beams are protected against fire and remain almost at ambient (room) temperature.
The second objective was to create a numerical model of the selected composite floor.
- Using a widely used commercially available finite element software ABAQUS, the three dimensional model of the composite floor system was created and then the thermal and mechanical response of the composite floor system to a 90-minute standard fire (ISO834) was simulated. The three-dimensional model is shown in Figure 3. The analysis used sophisticated tools to simulate the interaction between the concrete slab and the steel beam members as well as the steel connection components in contact. Briefly, the results suggest that the floor experiences large vertical deflections; however, the concrete slab on top of the steel frame remains intact and does not collapse. This enhanced performance is due to a geometrical and mechanical phenomenon in slabs called “the tensile membrane action”. Although the concrete slab remains stable, the shear connections lose their structural integrity and fail in the cooling phase of fire. This is an important conclusion of CONFIRE Project: The shear connections in large composite floors are not designed to sustain a severe fire loading.
The third objective was to manufacture the composite floor and conduct a fire experiment.
- In order to validate the conclusions from the numerical model, the full-scale composite floor is manufactured. Since the largest fire furnace is about 5m by 5m in layout and the floor specimen is 9.5m by 6m, an original method had to be developed for this project. Only a quarter of the composite floor was constructed with symmetric boundaries on two edges (see Figure 4). The quarter of the compartment was specifically designed to behave like a full size compartment with these special boundaries, which allow vertical deflection but does not allow rotation on the floor edges. This methodology is a first in experimental research in structural fire engineering and a patent application at Bogazici University is currently in progress. The quarter composite floor with patent-pending special boundary conditions was subjected to gravity loading only. An original contribution of CONFIRE Project was to assess the mechanical response of the floor by measuring strains in the steel reinforcement in the concrete slab. The strain measurements validated the effectiveness of the patent-pending design. The composite floor is then subjected to 90-minute standard fire curve. During the fire test, images were captured inside and outside of the furnace to record the overall deformation of the composite floor. In addition, thermo-couples at various locations measured the temperatures. The strain gauges provided a full strain-map of the floor and quantitatively confirmed the formation of the enhance load carrying mechanism “the tensile membrane action”. The locations of the strain gauges were carefully selected such that the strain gauges were not significantly affected by the elevated temperatures. At the end of the fire test, the compartment deflected as much as 500mm and no visible failure occurred in the structure although significant deformations and local buckling was observed in the shear connection. The results of the fire experiment such as floor vertical deflection and temperature readings closely agreed with the results from the numerical simulation.
Use and Impact:
CONFIRE Project has several important contributions to the structural fire engineering research and to the general public. As target groups, the findings of CONFIRE project will contribute to students, researchers, fire testing laboratories, and structural fire consultants.
1) The fire test and the numerical model show that the composite floor survives the fire although the shear connections perform weakly. With strengthening the connections, it is possible to use no fire protection on the secondary beam in floors. This project has a major socio-economic impact since avoiding fire protection will create significant savings in construction and highly benefit the steel industry.
2) A specialized mechanical device for symmetric boundary conditions (see Figure 4):
A quarter section of the composite floor with special boundary conditions is designed, which behaves like a full-size compartment. This type of mechanical device is used for the first time in the structural fire research field and it has major implications in fire testing of large compartments in furnaces. Using this device, compartments up to 10m in length could be tested in conventional furnaces all around the world. The patent application for the mechanical device is filed at the Technology Transfer Office at Bogazici University.
3) Advanced finite element techniques such as convergence and stabilization, coupling and contact interaction methodologies for three dimensional solid element models.
4) The results of CONFIRE Project facilitated the launch of a new project: Structural Fire Reliability Assessment of High-Rise Buildings. New proposals to ERC and TUBITAK (The Scientific and Technological Research Council of Turkey) are currently prepared.
New Project Abstract:
The practice of structural fire safety engineering remains to be case-specific and the estimation of fire resistance of structures is mostly deterministic. Many researchers in structural fire engineering utilize the performance-based design method but these studies do not include the inherent uncertainties in both the demand and capacity. The financial district of Istanbul in a major city will be taken as a case study. Parameters such as building type and height, structural system, number of floors, floor area, number of elevators and stairs, the use of fire suppression systems, evacuation routes will be provided by the municipalities in order to develop a probabilistic methodology to estimate the fire safety of these structures. The analysis will be conducted by three main categories as hazard, structural response and loss domain, and each of these domains include random variables such as maximum fire temperature, deflection and strength and damage of structural components. The findings of this research will provide essential information on the fire safety risk of each tall building in a densely populated financial district. It will allow the municipalities and fire brigades to have a probabilistic risk assessment of these structures and develop evacuation and human rescue plans accordingly in case of a fire hazard. Further, this research will provide useful data to insurance companies to estimate fire hazard insurance premiums.
Marie-Curie Fellow:
Dr. Serdar Selamet
Assistant Professor
Department of Civil Engineering
Bogazici University
34342 Bebek, Istanbul TURKEY
email: serdar.selamet@boun.edu.tr
office: +90-212-3596430
cell: +90-533-2391254
http://www.ce.boun.edu.tr/selamet(si apre in una nuova finestra)
In CONFIRE Project, the proposed four research objectives were successfully completed. With the project start, Bogazici University Structural Fire Research Group “BOUNFIRE” is formed, which has 9 members including 3 female graduate students. The findings of the project were disseminated via several international conferences and peer-reviewed publications. The details of the progress were also published on Project website (http://www.ce.boun.edu.tr/selamet(si apre in una nuova finestra)). The results of this project is highly related to the mitigation of natural hazard risks, which is one of priorities as a funded activity in “Environment European Research Area”.
Europe has one of the worst fire loss records in the industrialized world as demonstrated by the large number of fire-related deaths and the volume of property destruction. The direct financial cost amounted to 15 billion Euros in 2008 among the associated countries in Europe. Further, the cost for providing fire protection to buildings amounted to almost 12 billion Euros in 2008. CONFIRE Project investigates the steel connections in a steel beam-concrete slab floor system under fire and aims to use a performance-based approach to the fire resilience of connections in a full structural system. The ultimate goal is to design floors in tall buildings such that the risk to life safety to building occupants and fire fighters in the event of a fire is minimized and the fire is contained within the floor without partial or global collapse of the building. Steel-framed floors with thin concrete slabs are generally used in modern high-rise buildings in Europe. The project numerically and experimentally investigated the thermal and mechanical behavior of these floor systems and aimed to fully understand the governing fundamentals during a compartment fire. The goal has been to answer the following questions:
- Is it possible to avoid fire protection on the steel members in the secondary (gravity) beams in composite floors? Such conclusion will save millions of Euros to the steel industry in Europe.
- If the secondary beams do not fail under a severe fire, do the connections remain intact?
- What is the mechanical and thermal interaction between the steel members and the concrete slab in the floor system? At what deflections is the tensile membrane action triggered?
The first objective was to collect data of existing tall buildings relevant to structural fire safety.
- After investigating over 40 tall buildings in Istanbul, the tallest steel building Hilton by Doubletree in Istanbul, Turkey was chosen as a case study (see attached Figure 1). From the detailed blueprints, a large (9.5m x 6m) composite floor from this building was selected, which is then modeled in CAD software (see Figure 2a, 2b). The composite floor consisted of a 120mm thick concrete slab, four perimeter (main) beams, two secondary (gravity) beams connected via shear connection. The numerical and experimental analyses were carried out to observe the fire performance of this composite floor. The composite floor is heated for 90 minutes with a standard fire curve (ISO834) and it is consequently air-cooled. The secondary beams (see Figure 1) are left without fire protection whereas the main beams are protected against fire and remain almost at ambient (room) temperature.
The second objective was to create a numerical model of the selected composite floor.
- Using a widely used commercially available finite element software ABAQUS, the three dimensional model of the composite floor system was created and then the thermal and mechanical response of the composite floor system to a 90-minute standard fire (ISO834) was simulated. The three-dimensional model is shown in Figure 3. The analysis used sophisticated tools to simulate the interaction between the concrete slab and the steel beam members as well as the steel connection components in contact. Briefly, the results suggest that the floor experiences large vertical deflections; however, the concrete slab on top of the steel frame remains intact and does not collapse. This enhanced performance is due to a geometrical and mechanical phenomenon in slabs called “the tensile membrane action”. Although the concrete slab remains stable, the shear connections lose their structural integrity and fail in the cooling phase of fire. This is an important conclusion of CONFIRE Project: The shear connections in large composite floors are not designed to sustain a severe fire loading.
The third objective was to manufacture the composite floor and conduct a fire experiment.
- In order to validate the conclusions from the numerical model, the full-scale composite floor is manufactured. Since the largest fire furnace is about 5m by 5m in layout and the floor specimen is 9.5m by 6m, an original method had to be developed for this project. Only a quarter of the composite floor was constructed with symmetric boundaries on two edges (see Figure 4). The quarter of the compartment was specifically designed to behave like a full size compartment with these special boundaries, which allow vertical deflection but does not allow rotation on the floor edges. This methodology is a first in experimental research in structural fire engineering and a patent application at Bogazici University is currently in progress. The quarter composite floor with patent-pending special boundary conditions was subjected to gravity loading only. An original contribution of CONFIRE Project was to assess the mechanical response of the floor by measuring strains in the steel reinforcement in the concrete slab. The strain measurements validated the effectiveness of the patent-pending design. The composite floor is then subjected to 90-minute standard fire curve. During the fire test, images were captured inside and outside of the furnace to record the overall deformation of the composite floor. In addition, thermo-couples at various locations measured the temperatures. The strain gauges provided a full strain-map of the floor and quantitatively confirmed the formation of the enhance load carrying mechanism “the tensile membrane action”. The locations of the strain gauges were carefully selected such that the strain gauges were not significantly affected by the elevated temperatures. At the end of the fire test, the compartment deflected as much as 500mm and no visible failure occurred in the structure although significant deformations and local buckling was observed in the shear connection. The results of the fire experiment such as floor vertical deflection and temperature readings closely agreed with the results from the numerical simulation.
Use and Impact:
CONFIRE Project has several important contributions to the structural fire engineering research and to the general public. As target groups, the findings of CONFIRE project will contribute to students, researchers, fire testing laboratories, and structural fire consultants.
1) The fire test and the numerical model show that the composite floor survives the fire although the shear connections perform weakly. With strengthening the connections, it is possible to use no fire protection on the secondary beam in floors. This project has a major socio-economic impact since avoiding fire protection will create significant savings in construction and highly benefit the steel industry.
2) A specialized mechanical device for symmetric boundary conditions (see Figure 4):
A quarter section of the composite floor with special boundary conditions is designed, which behaves like a full-size compartment. This type of mechanical device is used for the first time in the structural fire research field and it has major implications in fire testing of large compartments in furnaces. Using this device, compartments up to 10m in length could be tested in conventional furnaces all around the world. The patent application for the mechanical device is filed at the Technology Transfer Office at Bogazici University.
3) Advanced finite element techniques such as convergence and stabilization, coupling and contact interaction methodologies for three dimensional solid element models.
4) The results of CONFIRE Project facilitated the launch of a new project: Structural Fire Reliability Assessment of High-Rise Buildings. New proposals to ERC and TUBITAK (The Scientific and Technological Research Council of Turkey) are currently prepared.
New Project Abstract:
The practice of structural fire safety engineering remains to be case-specific and the estimation of fire resistance of structures is mostly deterministic. Many researchers in structural fire engineering utilize the performance-based design method but these studies do not include the inherent uncertainties in both the demand and capacity. The financial district of Istanbul in a major city will be taken as a case study. Parameters such as building type and height, structural system, number of floors, floor area, number of elevators and stairs, the use of fire suppression systems, evacuation routes will be provided by the municipalities in order to develop a probabilistic methodology to estimate the fire safety of these structures. The analysis will be conducted by three main categories as hazard, structural response and loss domain, and each of these domains include random variables such as maximum fire temperature, deflection and strength and damage of structural components. The findings of this research will provide essential information on the fire safety risk of each tall building in a densely populated financial district. It will allow the municipalities and fire brigades to have a probabilistic risk assessment of these structures and develop evacuation and human rescue plans accordingly in case of a fire hazard. Further, this research will provide useful data to insurance companies to estimate fire hazard insurance premiums.
Marie-Curie Fellow:
Dr. Serdar Selamet
Assistant Professor
Department of Civil Engineering
Bogazici University
34342 Bebek, Istanbul TURKEY
email: serdar.selamet@boun.edu.tr
office: +90-212-3596430
cell: +90-533-2391254
http://www.ce.boun.edu.tr/selamet(si apre in una nuova finestra)
