FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS

Transcription

1 INFORMATION PAPER IP 21/10 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS Tom Lennon and Danny Hopkin The use of Structural Insulated Panel (SIP) systems in construction in the UK has increased over the last decade where they are used as principal loadbearing elements and mainly as internal and external walls. This Information Paper summarises the results from an experimental programme funded by Communities and Local Government (CLG) to determine the performance of SIP systems exposed to a realistic fire scenario and provides some recommendations for designers, regulators, warranty providers, manufacturers and contractors. Four large-scale fire experiments were carried out on two storey structures incorporating SIP wall panels and a floor system comprising engineered floor joists. More detailed information from the project is available in a number of journal and conference papers [1-4]. INTRODUCTION Structural Insulated Panels (SIPs) are prefabricated lightweight units that form the principal loadbearing components used predominantly in residential and light industrial buildings [5]. They are a sandwich construction consisting of two structural facings bonded to a lightweight insulating core. In the UK the two face layers are generally formed from Oriented Strand Board (OSB). The insulated core is formed from a polymer-based foam such as polyurethane (PUR), polyisocyanurate (PIR), expanded polystyrene (EPS) or extruded polystyrene (XPS). SIPs are used mainly as internal or external walls and occasionally as roofs or floors. The use of SIPs in construction in the UK has been increasing in popularity over the last decade. The reasons for this include they are lightweight and strong, the prefabrication of panels results in reduced waste Large-scale fire tests of SIP system clad with masonry onsite and increased speed of erection, they are easily adaptable and they provide good thermal efficiency and airtightness when compared with more traditional forms of construction. As with all other forms of construction, SIPs must be tested to demonstrate their compliance with the requirements of the building regulations. Standard fire resistance tests [6] provide a good indication of the relative performance of elements of building construction subject to a specific scenario based on idealised loading and support conditions and a single thermal exposure corresponding to the standard fire curve.

2 2 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS IP 21/10 However, such testing and related assessments provide little information on the performance of a building system formed of a number of interconnected building elements exposed to a realistic fire scenario. This fact was recognised and the fire performance of SIP buildings was identified as a priority for future research in a project funded by the Department for Communities and Local Government (CLG) [7] in Subsequently, BRE has completed a research project funded by CLG to undertake an experimental programme to determine the performance of SIP systems exposed to a realistic fire scenario. This Information Paper summarises the results from the experimental programme and provides some recommendations for designers, regulators, warranty providers, manufacturers and contractors. Laboratory testing The laboratory programme comprised a number of tests on single panels with EPS and PUR cores protected with Type A or Type F gypsum plasterboard [8]. The tests included load tests at ambient temperature, unloaded panels subjected to a thermal exposure corresponding to the standard fire curve [6] and panels subject to a combination of applied load and heating. In total 30 experiments were performed on single SIPs of overall dimensions mm. All panels had two 15 mm-thick OSB skins with an insulated core of 120 mm. The results from the full experimental programme are summarised in Table 1. EXPERIMENTAL PROGRAMME The research into the fire performance of SIP structures consisted of a series of laboratory tests on single panels and four large-scale fire tests on two-storey SIP structures incorporating engineered floor joists. The experimental studies were supported by numerical modelling. Figure 2: Flush mounted and protruding electrical sockets in panel Figure 1: Combustion of panel on removal from the furnace

3 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS IP 21/10 3 Table 1: Summary of laboratory tests on single panels Test no. Test reference Results and comments Ultimate load tests at ambient temperature. Uniaxial compression to determine panel resistance 1 PUR L1 Ultimate load 331 kn. Failure due to sudden brittle crack propagating through the width and thickness of the OSB sheets. De-lamination close to crack site between OSB and insulation. 2 PUR L2 Ultimate load 293 kn. Failure due to sudden brittle crack propagating through the width and thickness of the OSB sheets. De-lamination close to crack site between OSB and insulation. 3 EPS L1 Ultimate load 647 kn due to presence of solid timber frame. Heat transfer tests. 30 minutes standard fire exposure with no load, 15 mm Type F plasterboard 4 PUR PUR PUR EPS EPS EPS 303 All tests completed without need to terminate. No indication of combustion behind plasterboard for duration of test. Mean temperatures at back of plasterboard were 303 C and 263 C for PUR and EPS respectively. Corresponding temperatures at the interface of the insulation with the back of the OSB on the fire side were 66 C and 84 C. Samples ignited when removed from the furnace once plasterboard removed and sufficient oxygen available for combustion (see Figure 1). Heat transfer tests. 60 minutes standard fire exposure with no load, 30 mm Type F plasterboard 10 PUR PUR PUR EPS EPS EPS 603 All tests completed without need to terminate. No indication of combustion behind plasterboard for duration of test. Mean temperatures at back of plasterboard were 139 C and 152 C for PUR and EPS respectively. Corresponding temperatures at the interface of the insulation with the back of the OSB on the fire side were 72 C and 60 C Heat transfer tests. 30 minutes standard fire exposure with no load, 12.5 mm Type A plasterboard 16 EPS 301W Tests terminated after approximately 20 minutes due to combustion of the OSB skin. Typical temperatures 17 EPS 302W behind plasterboard and at back of OSB were in excess of 300 C Heat transfer tests. 30 minutes standard fire exposure with no load, 15 mm Type F plasterboard fixed direct 18 PUR 301FD All tests completed without need to terminate. Temperatures at back of plasterboard were 103 C and 19 EPS 301FD 376 C for PUR and EPS respectively. Corresponding temperatures at the interface of the insulation with the back of the OSB on the fire side were 68 C and 70 C respectively Heat transfer tests. 30 minutes standard fire exposure with no load, 15 mm Type F plasterboard. Samples incorporated electrical sockets mounted either flush to plasterboard or protruding (Figure 2) 20 EPS 301P All tests completed without the need to terminate. Measured temperatures through depth of SIP panels 21 EPS 302P very similar to previous test results on panels without service penetrations Combined heat and load (130 kn) tests. 30 minutes standard fire exposure, 15 mm Type F plasterboard 22 PUR 301HL 23 PUR 302HL 24 PUR 303HL 25 EPS 301HL 26 EPS 302HL No load-bearing failure occurred. Temperature distribution similar to heat transfer tests. No discernible difference between PUR and EPS variants Combined heat and load (130 kn) tests. 60 minutes standard fire exposure, 30 mm Type F plasterboard 27 PUR 601HL 28 PUR 602HL 29 PUR 603HL 30 EPS 601HL No load-bearing failure occurred. Temperature distribution similar to heat transfer tests Notes: The fire exposure tests were carried out in accordance with BS [6] Tests 16 and 17: Standard wall board Tests 18 and 19: Lining screwed to OSB otherwise fixed via softwood battens Tests 20 and 21: Service penetrations (two double plug sockets).

4 4 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS IP 21/10 Large-scale fire tests Four large-scale fire tests have been undertaken on SIP structures incorporating engineered floor joists and protected from the effects of fire by plasterboard linings to the ceilings and walls. The order and configuration of the tests is shown in Table 2. In each case the overall dimensions of the test compartment were the same, with a floor area of 4 3 m and a height from floor to ceiling of 2.4 m. The first floor loading was identical in each case with an imposed load of 0.75 kn/m² spread uniformly over the first floor. The second floor load was varied as in Table 2 to represent either a two- (0.75 kn/m²) or fourstorey (2.25 kn/m²) building. Figure 3 shows two of the units in the test facility during the construction stage. The 30 and 60 minute design solutions were effectively representing a two-storey house and a multi-occupancy apartment dwelling respectively with the appropriate load level in place to simulate realistic conditions. In all cases the fire design was the same and was designed to give an equivalent severity to a 60 minute exposure in a standard furnace test [6]. The results from the large-scale fire tests are summarised in Table 3. Figure 4 shows the fire loading in place before ignition. Table 2: Summary of large-scale fire tests Test Design fire resistance period (min) Core material 2nd floor loading (kn/m²) F1 60 EPS 2.25 F2 30 EPS 0.75 F3 60 PUR 2.25 F4 30 PUR 0.75 Figure 4: Fire load within compartment prior to ignition Figure 3: Two of the test compartments during construction of the external masonry cladding

5 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS IP 21/10 5 Table 3: Summary of large-scale fire tests Test F1 F2 Results and comments Maximum atmosphere temperature approximately 1075 C after 52 minutes. Test continued up to cooling phase. Peak temperatures in floor void approximately 200 C with a corresponding maximum deflection of approximately 10 mm. Floor joists, resilient bars and party wall remained intact (Figure 5). The polystyrene core material had melted away in localised areas within the external walls. The location of the most significant damage coincided with an unsealed hole used for erection purposes which allowed sufficient air into the system to maintain combustion during the latter stages of the fire Maximum atmosphere temperature approximately 1078 C after 43 minutes. Test terminated after approximately 50 minutes due to runaway deflection of the floor caused by combustion of the OSB web of the engineered floor joists (Figure 6) once the integrity of the plasterboard lining the ceiling had been compromised. Peak temperatures in the floor void approximately 900 C with a corresponding maximum deflection of 203 mm. Much of the insulation core in the walls had melted away at the end of the test. However, there was no indication of any integrity failure of the wall panels Test F3 F4 Results and comments Maximum atmosphere temperature 1071 C after 51 minutes. Test continued up to cooling phase. Peak temperatures in floor void approximately 200 C with a corresponding maximum deflection of approximately 15 mm. Core temperatures largely unaffected by the fire for the duration of the test but continued to rise in the cooling phase. Some time after the initial fire had been extinguished localised combustion continued within the wall panels with the inner surface of the PUR involved. Although initially there was no evidence of any damage to the wall panels the post-test damage was significant (Figure 7). The inclusion of electrical sockets did not influence the temperature of the panels Maximum atmosphere temperature 1083 C after 49 minutes. Test terminated after approximately 50 minutes due to runaway deflection of the floor caused by combustion of the OSB web of the engineered floor joists once the integrity of the plasterboard lining the ceiling had been compromised (similar to Test F2). Peak temperatures in the floor void approximately 664 C with a corresponding maximum deflection of 120 mm. Although the temperature within the external wall panels continued to increase towards the end of the test, any combustion of the PUR insulation was quickly dealt with by the Fire Service. Temperatures within the core of the party wall remained low throughout the test. The inclusion of electrical sockets did not influence the temperature of the panels Batten Residual plasterboard Figure 5 (above left and right): Limited damage to floor joists and party wall. Test F1 Figure 6: Damage to engineered floor joists. Test F2 Figure 7: Damage to PUR wall panels. Test F3

6 6 FIRE PERFORMANCE OF STRUCTURAL INSULATED PANEL SYSTEMS IP 21/10 DISCUSSION Within the scope of the experimental work undertaken and supported by numerical modelling of the performance of SIP buildings in fire a number of important issues have been highlighted. The laboratory tests on individual panels have indicated that the specification of 15 or 30 mm Type F [8] plasterboard for applications where 30 or 60 minutes fire resistance respectively is required is sufficient to restrict the temperature rise within the insulated core to less than 100 C. At such temperatures the performance of the panel is independent of the type of insulation used. In order to assist in the correct specification of plasterboard linings for specific applications a number of graphs have been developed that are based on the validated heat transfer model produced as part of the research project. The graphs provide predicted temperature data behind the inner layer of OSB (corresponding to the maximum temperature of the insulation) for both a 60 minute and a 30 minute exposure for a range of different OSB and plasterboard thicknesses (Figures 8 and 9) based on plasterboard fixed to the panels via 25 mm softwood battens. The information should be seen in the light of typical delamination temperatures for EPS (100 C) and PUR (200 C) insulation from the literature [9]. Similar graphs are presented based on the average temperature of the inner layer of OSB in terms of the residual strength of timber at elevated temperature as given in EN [10] (Figures 10 and 11). The use of battens for fixing the internal lining reduces heat transfer to the panel and provides a void for services. Where such a service void is present the incorporation of penetrations for electrical sockets will not compromise the integrity of the panel. Rear of exp posed side OSB temperature (DegC) minutes BS exposure (Type F) 8 mm OSB (Type F) 10 mm OSB (Type F) 15 mm OSB (Type A) 8 mm OSB (Type A) 10 mm OSB (Type A) 15 mm OSB Plasterboard thickness (mm) Figure 8: Temperature of rear of inner layer of OSB for 30 minute fire exposure front OSB temperature (DegC) Mean f % of compressive strength (Type F) 8 mm OSB (Type F) 10 mm OSB (Type F) 15 mm OSB (Type A) 8 mm OSB (Type A) 10 mm OSB (Type A) 15 mm OSB 30 minutes BS exposure 25% of compressive strength th % of compressive strength Plasterboard thickness (mm) Figure 10: Temperature of mean inner layer of OSB for 30 minute fire exposure Rear of exp posed side OSB temperature (DegC) (Type F) 8 mm OSB (Type F) 10 mm OSB (Type F) 15 mm OSB (Type A) 8 mm OSB (Type A) 10 mm OSB (Type A) 15 mm OSB 60 minutes BS exposure Plasterboard thickness (mm) Figure 9: Temperature of rear of inner layer of OSB for 60 minute fire exposure front OSB temperature (DegC) Mean f % of compressive strength (Type F) 8 mm OSB (Type F) 10 mm OSB (Type F) 15 mm OSB (Type A) 8 mm OSB (Type A) 10 mm OSB (Type A) 15 mm OSB 60 minutes BS exposure 0% of compressive strength 100% of compressive strength Plasterboard thickness (mm) Figure 11: Temperature of mean inner layer of OSB for 60 minute fire exposure

7 FIRE PERFORMANCE PAGE HEADER OF STRUCTURAL RIGHT PAGE INSULATED HEADER PANEL LEAFLET SYSTEMS NUMBER IP 21/10 7 Table 4: Specification for specific periods of fire resistance Wall lining Ceiling lining Services Penetrations in SIP panels Recommended specification for fire resistance period of: 30 minutes 60 minutes 15 mm Type F plasterboard fixed to softwood battens All joints taped and sealed 15 mm Type F plasterboard fixed to resilient bars All joints taped and sealed Incorporated within service void formed by battens All penetrations to be adequately fire stopped Lifting holes to be sealed* following erection of panels 30 mm Type F plasterboard fixed to softwood battens All joints between layers staggered Exposed joints taped and sealed 30 mm Type F plasterboard fixed to resilient bars All joints between layers staggered Exposed joints taped and sealed Incorporated within service void formed by battens All penetrations to be adequately fire stopped Lifting holes to be sealed* following erection of panels *Material used to seal the hole should, as a minimum, provide the same level of protection as the material removed. The results and observations from the large-scale fire tests have confirmed the ability of a structure incorporating SIP wall panels and engineered floor joists to survive a real fire scenario with an equivalent severity of 60 minutes exposure to the standard fire curve. As with other forms of construction, the performance of the structure is very much dependent on the correct specification and installation of the internal linings. The mode of failure of such a structure has been shown to be runaway deflection of the floor plate due to ignition and rapid combustion of the web member of the engineered floor joists. The rate of deflection increases very rapidly as the floor system approaches collapse. Such a scenario is not influenced by the SIP system and would be the same for other panelised, framed or traditional masonry construction systems. RECOMMENDATIONS As mentioned above, the correct specification and installation of the internal linings to both the ceiling and the floor are critical to the performance of the system in a real fire situation. Based on the results and observations of both the tests on the individual panels and the largescale natural fire tests, supported by numerical studies, recommendations for achieving design fire resistance periods of 30 minutes and 60 minutes are given in Table 4. The graphs in Figures 8 to 11 provide information on the relationship between panel temperature and specification of OSB face layers and plasterboard linings and can be used by manufacturers to select a suitable combination to achieve the required performance. Installation should comply with the instructions and detailed guidance produced by the plasterboard supplier. Compliance with recommendations for minimum lengths of fixings and minimum centres between fixings is particularly important. REFERENCES [1] Lennon T, Hopkin D, El-Rimawi J and Silberschmidt V. Large scale natural fire tests on protected engineered timber floor systems, Fire Safety Journal [2] Hopkin D, Lennon T, Silberschmidt V and El-Rimawi J, A. laboratory study into the fire resistance performance of structural insulated panels (SIPs). Proceedings of 6th International Conference on Structures in Fire, Michigan 2 4 June, [3] Hopkin D, Lennon T, Silberschmidt V and El-Rimawai J. Full scale fire tests on structural insulated panel and engineered floor joist assemblies. Proceedings of 6th International Conference on Structures in Fire, Michigan 2 4 June [4] Hopkin D, El-Rimawi J, Silberschmidt V and Lennon T. Modelling the fire resistance of structural insulated panels: heat transfer. Proceedings of 12th International Conference on Fire Science and Engineering (INTERFLAM), 5 7 July [5] Bregulla J and Enjily V. An introduction to building with Structural Insulated Panels (SIPs), BRE Information Paper IP 13/04, BRE, Watford, [6] BSI. BS : Fire tests on building materials and structures Part 20: Method for the determination of the fire resistance of elements of construction (general principles), BSI, London, [7] Communities and Local Government. Innovative Construction Products and Techniques BD 2503, Communities and Local Government, London, January [8] BSI. BS EN 520: 2004, Gypsum plasterboards Definitions, requirements and test methods, BSI, London, [9] Ashby MF and Gibson LJ. Cellular solids: structure and properties. Cambridge University Press. Second edn [10] BSI. BS EN : 2004, Eurocode 5: Design of timber structures Part 1-2: General Structural fire design, BSI, London, FURTHER INFORMATION A full report on the test programme carried out by BRE will be published by CLG in due course. Further information on SIP technology is available at ACKNOWLEDGEMENTS The information presented in publication is based on work carried out by BRE under a contract placed by CLG. The views expressed are not necessarily those of CLG. The active participation of the UK SIP Association is gratefully acknowledged as is the significant contribution to the experimental programme made by Lafarge Plasterboard.

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