Structural, Fire Resistance and Foundation Designs

Transcription

1 Seminar on Transitional Pre-fabricated Modular Housing Structural, Fire Resistance and Foundation Designs Prof. K F Chung, Prof. Asif Usmani & Dr. Andy Leung The Hong Kong Polytechnic University 3 November 2017

2 Structural Design for Transitional Pre-fabricated Modular Housing Professor K.F. Chung

3 Cold-formed Steel Technology Widely adopted in many industries Strip products with thicknesses 1.2 to 3.5 mm Press-braking or roll-forming into sections and panels Strength = 280, 350, 450, 500, 550 N/mm 2 (Structural steel: 275 and 355 N/mm 2 ) Jointing: Bolts, screws, and fire pins 3

4 Cold-formed Steel Technology Structural instability in thin gauge sections Codes of Practice for cold-formed steel structures: Structural Eurocode EN Hong Kong Steel Code BS5950: Part 5 Material strengths / Cross-section capacities / Member resistances / Connections and joints / System behaviour 4

5 Cold-formed Steel Technology Joints Bolts, screws and fire pins Different joint details 5

6 Cold-formed Steel Technology Modular steel framing We have a collaboration with the Steel Construction Institute in the U.K., and the China State Construction Engineering Corporation 中建钢构 in Shenzhen on a) effective use of high strength steel, and b) modular construction 模块化建筑. 6

7 The Steel Construction Institute Professional Publications SCI P276 Building Design Using Cold Formed Steel Sections Structural Design to BS :1998 Section Properties and Load Tables SCI P125 Building Design Using Cold Formed Steel Sections: Worked Examples SCI P129 Building design using cold formed steel sections: Fire protection SCI P299 Mini-Piles and Composite Ground Floors for Housing SCI P302 Modular Construction using Light Steel Framing. Design of Residential Buildings SCI P272 Modular Construction using Light Steel Framing. An Architect s Guide SCI P284 Modular Construction in Building Extensions SCI P348 Building Design Using Modules SCI P367 Energy efficient housing using light steel framing. Modular construction technology has been developed for 20 years in the U.K. with currently a total of 9 major suppliers and manufacturers. 7

8 On 6 th December 2015, Mr. Wan Gang, Head of Ministry of Science and Technology, the People s Republic of China presented the Official Plague of Chinese National Engineering Research Centre for Steel Construction (Hong Kong Branch) in the Hong Kong Science and Technology Parks, supported and congratulated by Mr. Nicholas Wei-Hsiung Yang, Secretary for Innovation and Technology Bureau, and Ms Annie Choi, Commissioner for Innovation and Technology of the Government of the Hong Kong SAR. Professor K.F. Chung was appointed Director of the CNERC. 8

9 CNERC for Steel Construction (Hong Kong Branch) Development Bureau of Government of Hong Kong SAR Construction Industry Council Chinese Iron and Steel Association Chinese Steel Construction Society Chinese Constructional Metal Structures Association Promoting sustainable infrastructure development in Hong Kong Promoting export of Hong Kong and Chinese Steel Construction Industry Promoting advanced structural engineering technology In modern steel construction Collaborators Imperial College London, Institution of Structural Engineering, the Steel Construction Institute Tsinghua University, Tongji University, University of Science and Technology Beijing 9

10 CNERC for Steel Construction (Hong Kong Branch) 10

11 Modular Housing System integration of Structural systems Architectural systems Fire protection Corrosion protective coatings for improved cost-effectiveness. Weather resistant fire resistant steel strips Advanced joints for quick assembly between units and frames 11

12 Modular Housing System integration of pre-fabrication in factories pre-installation in shops new construction procedures and skills on sites for new types of living environments. There is no major problem on structural forms for 20 to 30 storeys while experience is needed before construction is streamlined and costs can be reduced. A new housing product in a highly competitive and regulated construction industry! 12

13 THANK YOU! Professor K.F. Chung

14 Fire Resistance Design for Transitional Pre-fabricated Modular Housing Professor Asif S Usmani Department of Building Services Engineering Hong Kong Polytechnic University

15 Fire resistance in buildings Fire safety requirements are usually expressed as Insulation Integrity Stability For general building fire safety Compartmentation: maintaining structural and thermal barriers to prevent spread for a sufficient length of time to enable safe exit of all occupants For structure/structural members Fire resistance: length of time a structural component withstands exposure to a standard fire while retaining adequate capacity to resist fire limit state load 15

16 Traditional Prescriptive approach for fire resistance design Temperature [oc] ? Fire (BS-476-Part 8) time [minutes] Standard fires specify a fixed temperature-time curve (developed over 100 years ago in USA in a 2.9mx2.9mx4.4m compartment to reach 926 Celcius in 30 mins) 16

17 Performance-based approach general principles No universally agreed framework currently exists, a relatively ad-hoc process is: Determine Hazard scenario(s) against which resistance is to be provided Set performance criteria against each hazard scenario Determine structural response to hazard scenario(s) by one or more of - thermal and structural analyses for agreed set of hazard scenarios - computational simulations of thermo-mechanical response - full-scale testing Determine if performance criteria are met against each hazard scenario If not, improve design and iterate until performance criteria are met 17

18 Modular construction using light steel framing (LSF) Greenwich Millennium Village, London An LSF panel cross-section with mineral fibre insulation 18

19 Thermal bridging across steel studs 19

20 Dalmarnock fire tests (Glasgow, July 2006) 20

21 Heat flux distribution on LSF wall in a real fire 21

22 Aftermath 22

23 Conclusions and recommendations Dalmarnock may be the only documented research on fire resistance of LSF panels in the context of prefab modular construction. It was useful but limited as it was restricted to heat transfer across the LSF panel (with no structural testing under load, no connection tests and no system level response) A radiant panel based testing rig (see figure) should be set up to test panels chosen and connections for HK prefab modular housing (such as rig allows much greater flexibility than a furnace for imposing desired heat flux histories based on, idealized or realistic fire hazard scenarios (internal or external) A validated simulation approach should be used to obtain system level response 23

24 THANK YOU! Professor Asif S Usmani Department of Building Services Engineering Hong Kong Polytechnic University

25 Foundation design for Transitional Pre-fabricated Modular Housing Andy Y.F. Leung Department of Civil and Environmental Engineering 25

26 Weight of steel modular housing much lighter than traditional concrete structures. e.g. comparing weight of container versus unit with concrete slabs and walls. For 5-10 storeys, simple foundations (e.g. concrete pad) would suffice in many areas of Hong Kong *. Efficient site formation and foundation construction can be achieved. The simple system also involves minimal disturbance to the ground. (Source: Ganti + Associates) *Following bearing capacity recommendations in the Code of Practice for Foundations 2017 (Buildings Department), assuming standard weight of container, typical refurbishment and live loads 26

27 Concrete pad footing represents the simplest foundation solution for 5-10 storey modular housing. For taller modular structure, small diameter mini-piles may be suitable depending on the site conditions. Mini-piles require relatively small installation equipment, which is quick to mobilize. Raking piles can resist horizontal load from wind loads. (Source: 27

28 Considering the potential redevelopment of the site, long-term monitoring of foundation elements can be implemented. Monitoring data provides information about the integrity of foundation elements and suitability of ground for potential reuse in the future. Analyzer Such technology has been implemented by PolyU team on soil nails (similar element compared to mini-piles). (Source: Dept. of Electrical Eng., PolyU) 28

29 The key advantages of steel modular housing, from the foundation perspective, is the lightweight structure and fast construction. These features make them suitable for traditionally difficult sites. Reclaimed sites often involve waiting time before the ground settlements have stabilized for construction of permanent structures. At some sites, the waiting time can be utilized for transitional modular housing projects. Reclamation sites under study Pre-longlisted reclamation sites (Source: CEDD/Arup Enhancing Land Supply Strategy Reclamation outside Victoria Harbour and Rock Cavern Development) 29

30 Difficult geologic conditions are encountered in a number of areas in Hong Kong: Scheduled Area No. 2: Northwest New Territories Scheduled Area No. 4: Ma On Shan Reclamation Designated Area in Northshore Lantau Two cases of abandonment of planned residential tower blocks at the Tung Chung New Town due to difficult ground conditions. The lightweight modular housing can be suitable for these sites. (Source: ETWB(W) 505/83/03, HKSAR Government) 30

31 Andy Y.F. Leung Department of Civil and Environmental Engineering