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Topic :
Common Structural Forms for High-rise Buildings in Hong Kong
Prepared by Raymond Wong
wind
Building bends or deflects under lateral force
The more rigid of a building structure, the less it deflects
Deflection is a comfort consideration for building users. Building regulation has a basic criteria on deflection.
The structure of a building should be so designed to have a deflection less than 1/500 of its height
The problems of tall and slim building
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Various deflection modes under wind tunnel test
Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK1. Column and beam (framed) structure in RC
sometimes called framed buildings which are structures formed by the framed elements usually in the form of columns and beams, as well as further strengthened as necessary by the introduction of rigid floor membranes and external walls. - Simple formwork is required- lower cost of construction- easy to satisfy various spatial arrangement and shapes- may not be very able to cater for the structural needs of
tall and slim buildings- more suitable to construction low-rise or horizontal-
spread buildings such as schools, podium or carparkstructures
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Example of layout design evolution from a 5 x 3 grid system
Example of In-situ RC frame building
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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK
2. Load bearing wall (shear wall) structure in RC- More complicated formwork is required- cost of construction may increase especially for
building with more internal walls or in complicated shape
- the load bearing walls can strengthen the rigidity of the building and able to resist building against deflection
- building examples: public buildings such as theHarmony Blocks
Example of load-bearing wall structures
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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK3. Load bearing wall plus core wall structure
- Complicated formwork is often required especially in forming the core
- cost of construction is higher, especially for buildings with complicated shape (e.g. lots of set-back or light wells
- has very strong rigidity to resist deflection- this is the most common structural form for use in HK’s
residential buildings due to:. walls between residential flats can be best used as a
load bearing wall (fire resistance is one reason). To fulfill building regulation for prescribed window
areas. To satisfy the rigidity of high-rise buildings
Example of load-bearing wall structures with building area below 500 sq m
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Example of load-bearing wall structures of building area around 800 – 1000 sq m
Example of load-bearing wall structures with several blocks linked together to form a connected structure
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Structures inload-bearing wall with a RC core
Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK4. RC Centre core plus a RC frame structure
- Confine to more regularly shaped or building with simpler layout, such as usual tower type buildings- fair rigidity performance but may not be sufficient for building higher than, say 50 storeys.- rigidity can be improved by the adding in of other stiffening members- plenty of window areas (it is only a frame in the external face the building)- The internal core may have difficulty in getting natural ventilation or sunlight.
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Example of cored structure with an external frame for tower-type office building
Various layout arrangement for building using core and outer frame structure
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Various layout arrangement for building using core and outer frame structure
Example of cored structure with an external frame –Central Plaza in Wanchai
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Example of cored structure with an external frame –Langham Place in Mong Kok
It is sometimes quite difficult and costly to construct the RC core
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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK
5. Center core plus a outer core structure (tube in tube)- Formwork usually very complicated with the floor
added in at a second stage- building shape confined to tubular forms- area of windows limited due to the provision of a
structurally strong external tube (wall)- quite strong in rigidity and be able to construct to
very tall structure- building examples – Hopewell Center (HK) or the
previous World Trade Center in New York
Examples of tube-in-tube structures – Jardin House in Central
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Hopewell Centre in Wanchai
Examples of a framing plan showing the location/layout of walls, columns and beams
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Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK6. Steel frame structure
- building is lighter than usual RC structure due to the relative higher weight/strength ration of steel
- construction cost is lower especially for buildings adopting high level of standardization
- building is weak in rigidity due to steel is a more flexible (elastic) material when compare to RC
- additional stiffening elements in the form of internal/external trusses, out-rigger or bracing members are often required to make the building structure more rigid
- addition work is required to fire-protect the steel structure
- building examples: The Center, China Bank Building
Examples of building constructed in pure structural steel frame
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Construction of Structural steel frame building
Structural forms suitable for buildings in HKStructural forms suitable for buildings in HK
7. Composite structure (RC Core plus steel frame, hybrid structure)- building can be lighter than usual RC structure but
with a more acceptable rigidity than pure steel buildings
- construction cost is higher for the adding in of a RC core which requires a complicated formwork system
- it is time consuming and more complicated to make connections between the RC and steel elements
- It is even more difficult and costly if stiffening members are introduced into the building in order to make it more rigid to resist deflection
- Building examples: Time square, Manual Life Tower, Cheung Kong Center, IFC 1 and 2
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Examples of composite structures
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More examples of composite structures
More examples of composite structures
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Complicated stiffening elements incorporated in steel or composite building to improve the rigidity of the structure
The IFC 2
Outrigger system used in Cheung Kong Center
Cheung Kong Center
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Complicated stiffening elements incorporated in steel or composite building to improve the rigidity of the structure
The Cheung Kong Center
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Complicated stiffening elements incorporated in steel or composite building to improve the rigidity of the structure
Cost idea of using RC, Steel and composite method in constructing tall buildings
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How to construct various forms of BuildingsHow to construct various forms of Buildings
Buildings can be constructed or formed in a number of ways, such as:
1. In-situ manner using formwork – for all reinforced concrete buildings
2. Prefabricated manner – for using part or all in precast concrete elements
3. Prefabricated manner – using structural steel elements
4. Hybrid manner – making combination of any of the above systems
Construction of in-situ RC buildings
Forming the wall structure using aluminum moulds
Forming the wall structure using manual-type timber formwork
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Construction of in-situ RC buildings
Forming the structure using large panel-type forms for walls or columns
Construction of in-situ RC buildings
Forming the wall structure using mechanical-operated formwork systems
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Construction of in-situ RC buildings
Forming the floor structure using timber formwork systems
Construction of in-situ RC buildings
Forming the floor structure using table formwork – most suitable for office buildings
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Construction of in-situ RC buildings
Forming the floor structure using table formwork – floor being strengthened by tensioning technique
Construction of prefabricated frame building
Headquarters building of Hong Kong Jockey Club
Podium – KCR Kowloon Station
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Construction of prefabricated frame building
Using precast elements as part of the external walls as well as the permanent formwork for load-bearing walls
An external view of building –majority of external walls are constructed in precast manner
Advantageous features of framed structureAdvantageous features of framed structure1. Speedy construction due to simplicity in geometry –
consist of only columns and beams (or partially by the floor slab) as the main structural elements
2. Very rigid and stable – able to resist tremendous vertical (dead load) and lateral loads (wind)
3. Reduced dead load – absent of thick shear wall etc.
4. Roofed over at an earlier stage – every floor slab being finished becomes an cover to protect the lower floors from sun and rain
5. Offer large unobstructed floor areas – without obstacle between columns
6. Flexible utilization of space
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AdvanAdvan. features of framed structure (continued). features of framed structure (continued)7. Adaptable to almost any shape8. Easily altered within limits of frame
– regular or non-regular grid system is very adaptable in spatial arrangement
9. Offsite preparation possible – especially for prefabricated construction using precast concrete or structural steel elements
10. May be designed to accommodate movement11. Acceptable distribution of natural light – window openings
can be provided easily on eternal walls12. Easy to design structurally including computer design – again,
due to simple geometry
Principle factors affecting choice of framePrinciple factors affecting choice of frame
Production considerationAvailability of materials, labour and plantSpeed of constructionAvailability of mechanical plants
Architectural Design considerationSize and shape of siteConditions of siteIntegration of mechanical elementsArchitectural or aesthetic requirements
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Principle factors affecting choice of framePrinciple factors affecting choice of frame
Structural Design considerationFoundation considerationStandardization of members or designSpan and floor loadsFire resistance requirementMaintenance considerationIntegration of architectural & structural elements
Features of InFeatures of In--situ concrete frame constructionsitu concrete frame construction
Construction aspects1. Insitu concrete is inconsistent in quality in performance –
mixing, delivery, placing and compacting of concrete require very tight quality control
2. Overlapping formwork, steel fixing and concreting process make site operations more difficult – these works are to be done almost at the same time at the same location
3. Formwork erection is often timely, expensive, environmental unfriendly and labour intensive
4. Increase a lot of wet-work – difficult to maintain site in a clean and tidy environment
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Features of InFeatures of In--situ concrete frame constructionsitu concrete frame constructionConstruction aspects – examples of problem
Improper placing and compaction will serious lower the strength of concrete
Features of InFeatures of In--situ concrete frame constructionsitu concrete frame constructionConstruction aspects – examples of problem
Finishing the concrete surface after placing – improper finish will affect the size and dimension of member
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Features of InFeatures of In--situ concrete frame constructionsitu concrete frame constructionConstruction aspects – examples of problem
It is difficult to maintain a clean and tidy site using in-situ concrete structure for the casting process is wet and dirty
Exterior environment Interior environment
Features of InFeatures of In--situ RC frame constructionsitu RC frame constructionConstruction aspects (continue)5. Easier to allow for dimensional discrepancy – formwork
can relatively easy to provide any ready dimension and shape
6. Concrete is cheap, easy available and can be cast into complicated shape
7. Frame erection affected seriously by climatic condition – in windy day it is difficult to erect formwork nor to place concrete
8. Durability affect by heat, moisture or environmental factors – concrete is not so durable as most person think
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Features of inFeatures of in--situ RC frame construction (cont.)situ RC frame construction (cont.)
Structural characteristics and design aspects1. Concrete design more flexible and accurate than steel
because of non dependence on standard sections2. Concrete frame easily damaged by building movements3. Problems of creep & shrinkage (cause damage to finishes)4. Higher dead load and bigger structural elements5. Better fire resistance6. Durability sensitive to workmanship7. Overloading cause irreversible structural damages8. Flexible in layout and shape
Typical case using traditional timber formwork for frame structure in RC with load-bearing walls
The CCCU Building of CityU
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Features of structural steel construction Features of structural steel construction
Structural characteristics1. Steel has lower dead load (unless encased in concrete)2. Steel frame can easily to have the layout changed to suit
new design than concrete, especially requiring alteration after completion of the building.
3. Easily accommodate building movements for steel is a relatively flexible material and have greater adaptability to take up strain and deformation
4. However, it is weaker in fire resistance for steel will lose strength and deform serious at higher temperature (at 600oC or above). This can be improved by applying fire resistant plaster
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Features of structural steel construction Features of structural steel construction
Structural characteristics (continue)5. Beams usually shallower in size than for concrete Beams6. Sections in various convenient type and size thus
economical in design and uses – refer to standard steel sections
7. Produce larger deflection & deformation (Bend) under wind – this will cause uncomfort to users of building
8. Steel has higher thermal expansion value9. Rusting or corrosion problems – very strict anti-corrosion
treatment has to be applied
Features of structural steel construction (cont.)Features of structural steel construction (cont.)
Construction aspects1. Quicker to erect and can be prepared offsite – in
workshop/factory environment with good production and quality control
2. Erection on site less affected by climatic conditions –without placing of concrete
3. Longer and highly coordinated planning – require long time to make structural design, fabrication and delivery
4. Higher requirement in the control of dimensional accuracy before and during construction (in fabrication and in erection
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Features of structural steel construction (cont.)Features of structural steel construction (cont.)
Construction aspects5. Demand greater transportation or cranages provision6. Complicated quality assurance procedures – especially in
the control of welding connection7. Difficult to make connection with rigid structures –
especially in composite structure in which RC core structure is involved
8. More complex when building become more gigantic and taller – due to the huge number of structural members, some may be of very heavy section
9. Induce more works at higher altitude
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Delivery of structural steel member by ship
Large member delivery to site waiting to hoisting up for erection
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Hoisting of the structural steel member to the upper floor
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Connecting steel members with RC element – an anchor frame may be required for making strong connection
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
To connect floor to core wall –starter bars are to be provided within the core structure
Constructing the composite floor in steel/RC composite structure
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Very large component often in complicated shape
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Huge amount of structural members make erection very complicated
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Very complex and gigantic framework as stiffening members to the overall structure – Belt truss system, the IFC II
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Very complex and gigantic framework as stiffening members to the overall structure –Outrigger, Cheung Kong Center
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
The existence of very complicated jointing in steel structure
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Required to perform works at very high altitude
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Workers work at high altitude
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Connecting large and complicate shaped components can be very difficult
Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Examples of location where unmatched dimension causing problem
Concrete has to be trimmed to allow steel to pass through
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Features of structural steel constructionFeatures of structural steel constructionConstruction aspects – highlight of some problems
Examples of location where unmatched dimension causing problem
Roof truss and the decking not on the same level