CIVL3811 Introduction to Fire Engineering Lecture Slides - Week 12 2022 PDF

Introduction to Fire Engineering CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1  Overview 1. Why fire design? 2. Progress of fire in a building 3. Con...

Introduction to Fire Engineering CIVL3811 Engineering Design and Construction School of Civil Engineering | Faculty of Engineering THE UNIVERSITY OF SYDNEY The University of Sydney Page 1  Overview 1. Why fire design? 2. Progress of fire in a building 3. Concrete behaviour at high temperature 4. Fire Limit States and Fire-resistance Period 5. Design for the Fire Resistance 6. Fire Protection in Buildings 7. References The University of Sydney Page 3  1. Why Fire Design? A tragic toll: Building fires in Australia 1966: The William Booth Memorial Home for Men at 462 Little Lonsdale Street, Melbourne (30 died) 1973: The Whiskey Au Go Go nightclub in Fortitude Valley, Brisbane (15 people died) 1975: Fire rips through the Savoy Hotel in Kings Cross, NSW (15 people died) 1981: Fire breaks out in the Pacific Nursing Home, in Sylvania Heights, NSW (16 died) 1981: The Rembrandt Hotel in Kings Cross, NSW (19 died) 1989: The Down Under Hostel at Kings Cross, NSW (6 died) 1991: The Palm Grove Hostel in Dungog, NSW (12 people died) 2000: A hostel in Childers, Queensland (15 backpackers died) 2011: A house at Slacks Creek, south of Brisbane (11 people died) The University of Sydney Page 4  1. Why Fire Design? World Trade Centre (WTC) Collapse Getty image Each tower was 64 m2, standing 411 m above street level. As a result of the attacks, a total of 2763 people died: 2192 civilians, 343 firefighters, and 71 law enforcement officers. The University of Sydney Page 5  1. Why Fire Design? World Trade Centre (WTC) Collapse The total weight of the structure was roughly 500,000 t, but wind load dominated the design. Building was designed to resist a 225 km/h hurricane—a total of lateral load of 5,000 t. To have more open area, the towers were designed as "tube in tube" structures, Perimeter columns provided the strength to the structure, wile gravity load shared with the steel box columns of the core. The University of Sydney Page 6  1. Why Fire Design? World Trade Centre (WTC) Collapse The perimeter elements were bridged by prefabricated floor trusses. http://www.tms.org/pubs/journals/jom/0112/eagar/eagar-0112.html The weak points were the angle clips that held the floor joists between the columns on the perimeter wall and the core structure. With a 700 Pa floor design allowable, each floor should have been able to support approximately 1,300 t beyond its own weight. However, the total weight of each tower was about 500,000 t. The University of Sydney Page 7  1. Why Fire Design? Control Fire in a concrete building can cause; Severe structural damage Total loss of contents Loss of life How to reduce possibility of damages; Detailed structural design The layout of the building Fire protection strategies The University of Sydney Page 8  2. Progress of Fire in a Building Ignition Growth Fully developed Cooling ▪ needs sufficient ▪ air must be provided by ▪ very high ambient ▪ fuel sources energy, Oxygen some form of ventilation temperatures depleted and the and Combustible ▪ thermal energy is ▪ a fall-off in the elastic temperature material transferred by radiation modulus and the yield decreases and convection to other strength of reinforcements material ▪ spalling of cover concrete ▪ hot gasses build up ▪ the capacity of members under ceiling and cause a can fall to the level of rapid spread of fire sustained loads (flameover) The University of Sydney Page 9  4. Fire Limit States and Fire-resistance Period Fire-related Limit State Strength: Fire integrity: Insulation: concerned with prevention of the spread of fire load capacity of the structural cracks/fissures form which the temperature on the remote face member is reduced and are wide enough to allow of the fire-separating member member cannot carry the flames or hot gasses to pass reaches 140ºC (combustible material sustained load through the member in contact with the surface could ignite) The University of Sydney Page 10  4. Fire Limit States and Fire-resistance Period Fire-resistance Period (FRP) Structural design objective: Allow: The limit states are NOT reached in less ✓ enough time for evacuation of the building than a specified time, called “the fire- ✓ recovery of contents resistance period” ✓ and for the initiation of fire-fighting procedures The standard fire-resistance periods are usually considered as; 30, 60, 90, 120, 180, and 240 mins. The selection of time depends on: the intended use of the building the type of construction building location (close to fire zone, in a commercial/business zone, …) The University of Sydney Figure 2.10.1 (AS1530.4): Standard time vs temperature curve Page 11  5. Design for Fire Resistance AS3600-2018, Section 5 Section 5 of AS3600 specifies the requirements for reinforced concrete members to meet the fire resistance levels (FRLs) required by the Building Code of Australia (BCA). Based on AS3600, the normal design procedure is to meet certain minimum cover and size limits according to a number of deemed-to-comply rules in Clauses 5.4 to 5.7, for Beams Columns Slabs Clause 5.8: Increasing fire resistance period by use of insulating materials. The University of Sydney Page 12  5. Design for Fire Resistance Design Performance Criteria A member shall be designed to have a fire resistance period (FRP) for structural adequacy, integrity and insulation of not less than the required fire resistance level (FRL). The FRP for a member shall be established by either one of the following methods: (a) Determined from the tabulated data and figures given in AS3600. Unless stated otherwise within Section 5 of AS3600, when using the tabulated data or figures no further checks are required concerning shear and torsion capacity or anchorage details. (b) Predicted by methods of calculation. In these cases, checks shall be made for bending, and where appropriate, shear, torsion and anchorage capacities. NOTE: Eurocode 2, Part 1.2 provides a method of calculation to predict the FRP of a member. The University of Sydney Page 13  5. Design for Fire Resistance Definitions Axis Distance (Cl 5.2.2-AS3600) Distance from the centre-line axis of a longitudinal bar to the nearest surface exposed to fire Axis distance (as) is a nominal value and no allowance for tolerance need be added. Circular Section Rectangular Section The University of Sydney Page 14  5. Design for Fire Resistance Definitions Ave. Axis Distance (Cl 5.2.1-AS3600) When reinforcement is arranged in several layers with the characteristic strength, fsy, and cross sectional area of Asy, the average axis distance, am, may be determined by 𝐴𝑠1 𝑓𝑠𝑦1 𝑎1 + 𝐴𝑠2 𝑓𝑠𝑦2 𝑎2 + ⋯ + 𝐴𝑠𝑛 𝑓𝑠𝑦𝑛 𝑎𝑛 σ 𝐴𝑠𝑖 𝑎𝑖 𝑎𝑚 = = 𝐴𝑠1 𝑓𝑠𝑦1 + 𝐴𝑠2 𝑓𝑠𝑦2 + ⋯ + 𝐴𝑠𝑛 𝑓𝑠𝑦𝑛 σ 𝐴𝑠𝑖 ai = axis distance of steel bar ‘i’ from the nearest exposed surface The University of Sydney Page 15  5. Design for Fire Resistance Fire Resistance Periods (FRPs) For Beams (Cl 5.4-AS3600) Structural adequacy of a beam is determined according to the exposed surfaces of the member to fire. Therefore ▪ for beams incorporated in roof or floor systems- refer to Cl 5.4.1 T-Beam (integrated slab) L-Beam (integrated slab) Band-Beam (integrated slab) ▪ for beams exposed to fire on all sides- refer to Cl 5.4.2 The University of Sydney Page 16  5. Design for Fire Resistance Beams Beams Incorporated in Roof or Floor Systems Structural adequacy of the beams are examined based on the exposed surfaces of the member to fire. Therefore Simply supported beams: Table 5.4.1(A) or Figure 5.4.1(A) Continuous beams: Table 5.4.1(B) or Figure 5.4.1(B) provided the beam— (i) has the upper surface integral with or protected by a slab; (ii) has a web of uniform width, or one which tapers uniformly over its depth; and (iii) is proportioned so that— (A) the beam width (b), measured at the centroid of the lowest level of longitudinal bottom reinforcement; and (B) the average axis distance to the longitudinal bottom reinforcement are not less than the values for that period given in the appropriate table or figure. The University of Sydney Page 17  5. Design for Fire Resistance Beams Rectangular Beams Exposed to Fire on All Sides Simply supported beams: Table 5.4.1(A) or Figure 5.4.1(A) Continuous beams: Table 5.4.1(B) or Figure 5.4.1(B) provided the beam is proportioned so that— (A) the total depth of the beam is not less than the least value of b for that period (B) the cross-sectional area of the beam is not less than twice the area of a square with a side equal to b determined as for Item (a); and (C) the average axis distance is not less than the value for that period determined using the minimum dimension of the beam for b in the relevant Table and applies to all longitudinal reinforcement. The University of Sydney Page 18  5. Design for Fire Resistance Beams Beams Incorporated in Roof or Floor Systems The University of Sydney Page 19  5. Design for Fire Resistance Beams Beams Incorporated in Roof or Floor Systems Linear interpolation between values given in the Tables and Figures in this Section is permitted. The University of Sydney Page 20  5. Design for Fire Resistance Beams Example 1: For a simply supported beam, determine the minimum required cover for FRP of 90 minutes. 50 40 Cover to bottom reinforcement= as > 40 mm Axis distance to the side reo= as > 40+10 = 50 mm In beams with only one layer of reinforcement, the axis distance to the side of the beam for the corner bars , shall be increased by 10 mm The University of Sydney Page 21  5. Design for Fire Resistance Fire Resistance Periods (FRPs) For Slabs (Cl 5.5-AS3600) Slabs are thin planar members (e.g. floors, bridge decks) which transmit transverse loads by bending action to their supports. https://goo.gl/images/O3IKqt One-way Slab Types of Slabs Solid Slab Hollow-core slab Ribbed or waffle slab The University of Sydney Page 22  5. Design for Fire Resistance Slabs Two fire limits should be considered for slabs; 1. Insulation 2. Structural adequacy 1. Insulation (Cl 5.5.1) It requires that the effective thickness of the slab is more than the values in Table 5.5.1 H Effective Thickness shall be taken as; Solid Slabs the actual thickness Hollow-core slabs the net cross-sectional area divided by the width of the cross-section Ribbed slabs the thickness of the solid slab between the webs of adjacent ribs The University of Sydney Page 23  5. Design for Fire Resistance Slabs 2. Structural Adequacy (Cl 5.5.2) Based on slab’s type, need to satisfy the following conditions; Solid or hollow-core slabs supported on beams or walls the slab is proportioned such that the average axis distance to the bottom reinforcement is not less than the value for that period given in the Table 5.5.2(B) One-way ribbed slabs (i) the width of the ribs and the axis distance to the lowest layer of the longitudinal bottom reinforcement in the slabs comply with the requirements for beams given in Clause 5.4.1; and (ii) the axis distance to the bottom reinforcement in the slab between the ribs is not less than that given in Table 5.5.2(B) The University of Sydney Page 24  5. Design for Fire Resistance Slabs The University of Sydney Page 25  5. Design for Fire Resistance Slabs 2. Structural Adequacy (Cl 5.5.2) Flat slabs (i) the average axis distance to the bottom layer of reinforcement is not less than the value in the Table 5.5.2(A) (ii) when the FRP is 90 min or more, at least 20% of the total top reinforcement in each direction over intermediate supports is continuous over the full span and placed in the column strip; Two-way ribbed slabs the width and the average axis distance to the longitudinal bottom reinforcement in the ribs, and the axis distance to the bottom reinforcement in the slab between the ribs, and the axis distance of the corner bar to the side face of the rib, is not less than the value in Tables 5.5.2(C) or Table 5.5.2(D) plus 10 mm. The University of Sydney Page 26  5. Design for Fire Resistance Slabs The University of Sydney Page 27  5. Design for Fire Resistance Slabs The University of Sydney Page 28  5. Design for Fire Resistance Slabs The University of Sydney Page 29  5. Design for Fire Resistance Slabs Example 2: Determine appropriate minimum slab thickness and the cover for the one-way simply supported slab, to satisfy structural adequacy based on AS3600 for a FRP of 120 mins. h N12@120mm cts Solution: We should use Cl 5.5.2 (b): (i) For solid of hollow-core slabs supported on beams or walls [see Table 5.5.2(B)], provided the slab is proportioned such that, for the appropriate support conditions, the average axis distance to the bottom reinforcement and tendons is not less than the value for that period given in the table. The University of Sydney Page 30  5. Design for Fire Resistance Slabs Solution (Cont.) The minimum distance required from edge of concrete to lowest layer of reinforcement is 40mm The University of Sydney Page 31  5. Design for Fire Resistance Slabs Solution (Cont.) For the depth of the slab, we should also check the effective depth of the one-way slab based on FRP insulation as provided in clause 5.5.1 which is given as; Therefore, the minimum thickness of the slab should be 120mm for FRP for insulation The University of Sydney Page 32  Material Response - Steel – Steel: – Becomes weaker at high temperature – Stiffness reduces – Thermal expansion https://www.steelconstruction.info/The_case_for_steel The University of Sydney Page 33  Fire Protection for single steel elements – How hot can the steel be allowed to reach, and still carry – prescribed loads? – How long must it remain below this temperature ie what is the – required FRL? – What protection is required to do this? The University of Sydney Page 34  Passive Fire Protection Systems Fire resistant structure Walls, floors and ceilings Fire isolated stairs Active Fire Protection Systems passageways Mechanical engineering systems Operate either manually or automatically on demand Smoke detection and alarm Sprinkler Thermal alarm Hydrant Fire stair pressurization Smoke exhaust system The University of Sydney Page 36  The benefits of active fire protection systems ❑ If active systems are installed in a newly constructed building, some relaxation in the passive requirements may be accepted by the building certifier. This might including: ❑ Larger fire compartments ❑ Open stairways between floors ❑ Reduction in constraints on building atriums ❑ Reduction in the fire resistance of walls ❑ Discount on the insurance premium The University of Sydney Page 37  Remember the BCA structure? Mandatory Performance Requirements Requirements Optional Deemed-to- Alternative means of satisfy Solutions compliance Provisions The University of Sydney Page 38  Combustion and Fire Spread ❑ On removing one or more of these factors combustion stops. ❑ Water is a most effective medium for absorbing heat. ❑ Foam or carbon dioxide is used for reducing the oxygen supply. ❑ The intensity of a fire depends on the amount of fuel present in the building. The University of Sydney Page 39  Fire Transfer/spread ❑ A fire spreads through a building by three principal mechanism: ❑ Conduction: occurs when heat is transferred directly through the structure from an adjacent fire. ❑ Convection: occurs when hot gases and smoke rise within a building, with the fire easily spreading from the ground to an upper floor by way of an open stairway or shaft. ❑ Radiation: transfers heat in a straight line from its sources to any adjacent combustible material. Radiation is a method of heat transfer that does not rely upon any contact between the heat source and the heated object. The University of Sydney Page 40  Hints for construction of buildings ❑ Reinforcing steel, encased in concrete, loses strengths rapidly if its temperature rises by conduction above about 400 C. ❑ Windows glass is more or less transparent to radiation, and this form of fire spread commonly occurs both inside a building, and between adjacent buildings if they are close enough to each other. ❑ In the event of fire the principal hazards are to: ❑ The occupants; ❑ The contents; ❑ The structure; and ❑ Adjacent buildings ❑ Large buildings are divided into a number of smaller fire compartments each having surrounding walls, floors and ceilings which will be structurally stable during a fire. The University of Sydney Page 41 Class of occupancy (NCC) ❑ The nature of the fire hazard depends on the type of building occupancy. ❑ The class of building occupancy indicates whether the principle risk is to people or property. Class 1 Houses (1a) and boarding houses (1b) Class 2 2 or more sole-occupancy units, i.e., flats and home units Class 3 Other residential buildings, hotels, schools, or detention buildings Class 4 A dwelling in a class 5, 6, 7, 8 or 9 building, e.g., a caretaker’s flat Class 5 Offices used for professional or commercial services Class 6 Shops or other buildings used for supply services to the public Class 7 Carparks (7a) and warehouses (7b) Class 8 Laboratories and factories Class 9 Public buildings; health care (9a), assembly (9b), aged care (9c) Class 10 Private garage or shed (10a) or a free standing structure (10b) The University of Sydney Page 42  Fire Resistant Construction ❑ These are defined in terms of the extend to which the walls, floors, roofs, columns, and beams withstand the burn-out of the building’s contents in the event of fire. ❑ The Three types of construction recognised by NCC A, B and C, are determined by the building’s class and rise in storeys. Fire Hazard Analysis ❑ Classification: The use of building ❑ Number of storeys: The rise in storeys at the external wall of the building ❑ Effective height: If the effective height exceeds 25 m different requirements come into play. ❑ Type of construction: Identifies which fire resistance levels are applicable to different elements ❑ Fire resistance levels: Fundamental to knowing what protection is required. ❑ Fire-isolated exits: Need to know whether an exit is a required fire-isolated. The University of Sydney Page 44  Active Fire Protection Systems Portable fire extinguishers Water supplies Detectors for smoke and heat Hydrants and hose reels Sprinklers The University of Sydney Page 46 Water supplies Fire hydrant systems Fire hose reel systems Sprinkler systems Domestic water supplies ❑ Water supplies are suitable for extinguishing Class A fires. ❑ In the city, the fire-fighting water required for hydrants, hose reels and sprinkler systems is normally supplied from a street main. ❑ In some rural areas, very large tanks or dams are necessary with enough storage capacity to completely extinguish a fire. The University of Sydney Page 50  Hydrants System Components ❑ Pipework and valve distribution ❑ Fire service booster ❑ Pump set ❑ Hydrant ❑ Hydrant valve and coupling ❑ Lay flat fire hose ❑ Nozzle The University of Sydney Page 51  Storage Tank / Water Pressure ❑ For building higher than 25 m, an elevated storage tank is required to provide water pressure to the hydrants. Such a tank must be located at the very top of a building. ❑ A 25,000 litre tank provides sufficient water for two hydrants. For small buildings a 16,000 litre tank may be adequate. ❑ For building more than 12 m height above street level, pumps are required to boost the water. The University of Sydney Page 53  Sprinklers ❑ Suitable for locations with special fire risks such as very large or high-rise buildings, underground car parks, warehouses or stores. ❑ Sprinkler systems are the most effective means of automatic fire protection yet devised. They have an outstanding record of successful operations in Australia. ❑ Remarkable discount from insurance companies for buildings where sprinklers have been installed. ❑ In accordance with NCC, an automatic sprinkler system is required in all buildings taller than 25 m. ❑ Sprinkler systems are intended to both detect and extinguish a fire. ❑ An array of sprinklers heads, at specified intervals, are connected to an overhead piping system containing water under high pressure. ❑ The heads are designed to operate when the ambient air temperature exceeds a selected value. ❑ A typical sprinkler head contains a glass bulb of fusible link which disintegrates about 65 C, allowing orifice open and spray water over a 3.5 m radius. The University of Sydney Page 54 Sprinkler Heads Quartzoid Bulb Type ❑ Sprinkler head is made on a glass or quartzoid bulb containing liquid. ❑ When temperature rises the liquid expands, breaking the bulb which is preventing the water passing. ❑ Bulbs are available in a range of duties as follows Temperature (C) Colour of Quartzoid Bulb Colour 57 Orange 68 Red 79 Yellow 93 Green 142 Blue 182 Mauve 204-260 Black The University of Sydney Page 56 Regulations and Standards for Compliance ❑ NCC/BCA Volume One: ❑ Section C Fire Resistance ❑ Section E Services and Equipment ❑ AS 1530 series, Fire Testing of Building Materials ❑ AS 1670 series, Fire Detection, Warning and Alarms ❑ AS 2118 series, Fire Sprinklers ❑ AS 2419 Hydrants ❑ AS 2441 Hose Reels ❑ AS 2444 Portable Extinguishers References for Expert Engineering Detail ❑ CIBSE (UK) Guides ❑ SFPE Society for Fire Protection Engineering (USA) www.sfpe.org ❑ NFPA National Fire Protection Association www.nfpa.org The University of Sydney Page 63  Fire Protection in Buildings AS3600 Recommendations Increasing FRPs by the addition of insulating materials (Cl 5.8) The FRP for insulation and structural adequacy of a concrete member may be increased by the addition to the surface of an insulating material, to provide increased thickness to the member or greater insulation to the longitudinal reinforcement, in accordance with the requirements of Clause 5.8. For slabs, the FRPs may be increased by the addition of toppings and/or the application of insulating materials to the soffit; for flat slabs and plates, only http://www.sekisuifoam.com the application of an insulating material to the soffit may be used to improve the structural adequacy. Under slab (soffit) insulation The University of Sydney Page 64  Fire protection The University of Sydney Page 65  Board protection / https://www.promat.com/en/construction/products-systems/products/boards/promatect-xs-pi2932 The University of Sydney Page 66  Spray protection https://www.youtube.com/watch?v=fOszR3oOkWU The University of Sydney Page 67  References – Obrart, A. (2016). Building Services Engineering for Architects and Building Design Professionals: A Guide to Integrated Design. Integral Publishing: Watsons Bay. – Grondzik, W. T., & Kwok, A. G. (2015). Mechanical and electrical equipment for buildings. John Wiley & Sons. – Board, A.B.C., 2016. National Construction Code. ABCB. – Stych, M. (2013). Are Building Services a necessary evil?. Building Engineering London, ARUP. Available at https://www.youtube.com/watch?v=6bHbM15sBMw&t=452s. CIBSE (UK) Guides SFPE Society for Fire Protection Engineering (USA) www.sfpe.org NFPA National Fire Protection Association www.nfpa.org The University of Sydney Page 68