Structural, Fire Resistance and Foundation Designs

Prof. K F Chung, Prof. Asif Usmani & Dr. Andy Leung

The Hong Kong Polytechnic University

3 November 2017

Seminar on Transitional Pre-fabricated Modular Housing

Structural Designfor Transitional Pre-fabricated Modular Housing

Professor K.F. Chung

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/mm2

(Structural steel: 275 and 355 N/mm2)

• Jointing: Bolts, screws, and fire pins

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Cold-formed Steel Technology

Structural instability in thin gauge sections

Material strengths / Cross-section capacities / Member resistances / Connections and joints / System behaviour

Codes of Practice for

cold-formed steel structures:

• Structural Eurocode

EN 1993-1-3

• Hong Kong Steel Code

• BS5950: Part 5

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Cold-formed Steel Technology

Joints

Bolts, screws and fire pins Different joint details

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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 .

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The Steel Construction Institute Professional Publications

SCI P276 Building Design Using Cold Formed Steel SectionsStructural Design to BS 5950-5:1998 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.

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On 6th 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.

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CNERC for Steel Construction (Hong Kong Branch)

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

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

CollaboratorsImperial College London, Institution of Structural Engineering, the Steel Construction InstituteTsinghua University, Tongji University, University of Science and Technology Beijing

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CNERC for Steel Construction (Hong Kong Branch)

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Modular Housing System –

integration of

Structural systemsArchitectural systemsFire protectionCorrosion protective coatings

for improved cost-effectiveness.

Weather resistant fire

resistant steel strips

Advanced joints for quick

assembly

between units and frames

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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 !

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THANK YOU!

Professor K.F. Chung

Professor Asif S UsmaniDepartment of Building Services EngineeringHong Kong Polytechnic University

Fire Resistance Design for Transitional Pre-fabricated Modular Housing

Fire resistance in buildings

♦ Insulation

♦ Integrity

♦ Stability

Fire safety requirements are usually expressed as

Fire resistance:

length of time a structural component

withstands exposure to a standard

fire while retaining adequate capacity

to resist fire limit state load

For structure/structural members

Compartmentation:

maintaining structural and thermal

barriers to prevent spread for a

sufficient length of time to enable safe

exit of all occupants

For general building fire safety

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0

250

500

750

1000

1250

0 30 60 90 120 150 180time [minutes]

Tem

pera

ture

[o

C]

Fire (BS-476-Part 8)

Traditional Prescriptive approach for fire resistance design

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)

?

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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

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Modular construction using light steel framing (LSF)

Greenwich Millennium Village, LondonAn LSF panel cross-section with mineral fibre insulation

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Thermal bridging across steel studs

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Dalmarnock fire tests (Glasgow, July 2006)

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Heat flux distribution on LSF wall in a real fire

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Aftermath

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Conclusions and recommendationsDalmarnock 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

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THANK YOU!

Professor Asif S UsmaniDepartment of Building Services EngineeringHong Kong Polytechnic University

Foundation design for Transitional Pre-fabricated Modular Housing

Andy Y.F. LeungDepartment of Civil and Environmental Engineering

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• 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

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(Source: www.containerhomeplans.org)

• 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.

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• 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.

• Such technology has been implemented by PolyU team on soil nails (similar element compared to mini-piles).

(Source: Dept. of Electrical Eng., PolyU)

Analyzer

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• 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.

(Source: CEDD/Arup 2014 - Enhancing Land Supply Strategy Reclamation outside Victoria Harbour and Rock Cavern Development)

Pre-longlisted reclamation sites

Reclamation sites under study

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• 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)

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Andy Y.F. Leung

Department of Civil and Environmental Engineering