Multi-storey structural Steel Structures

Multi-storey structural Steel Structures

Background Steel has been used for constructing buildings in the western world for more than 150 years. With the introduction of standard sections by the end of 19 th Century, steel structures were getting much more popular as a choice of construction for high-rise buildings. The use of structural steel to construct started only in the 70 s in HK, below is some of the projects being completed: 1. Park Lane Hotel (Causeway Bay, 1972) 2. Grand Hyatt & Harbor View Hotel (HKCEC Phase I, 1990) 3. Bank of China Tower (Central, 1991) 4. Time Square (Causeway Bay, 1992) 5. Lee Garden Redevelopment (Manu-life Tower, 1997) 6. The Center (Central, 1999) 7. Cheung Kong Center (Central, 2000)

Properties of steel - Steel has the following properties, that makes it one of the most efficient materials for use in building construction. Favorable properties - Strong: has a high strength/weight ratio - Versatility: adaptable and ductile - Cheap and plentiful - Easy to cut, connect and fabricate Some drawbacks - Heavy and lengthy, not easy to handle - Loss strength under higher temperature - Easily get rust if not properly treated - Deflect under loads

The use of structural steel sections The availability of steel sections in a variety of dimensional ranges provides the designers with a wide variety of design options. These sections are manufactured in convenient shapes, sizes and thickness. They can be readily fabricated, combined and connected to form unlimited possibility of designs

Standard structural steel sections

Typical jointing details for structural frame Column connects to base

Typical jointing details for structural frame Using splice plate Using welded joint Connecting H-column H to form continual column

Typical jointing details for structural frame Connecting beam to column Connecting beam to beam

Typical layout of structural frame Simple cage frame cantilever frame

Typical layout of structural frame Propped cantilever frame

Typical layout of structural frame Wind-braced structures

Typical layout of structural frame Core structure

Characteristic of various kinds of structural steel framed structures In general, the performance of steel frame structure may be affected by the following factors a) Length of span b) Composition/continuity of span c) Methods of jointing the members d) Movement and deflection allowed When using in lowhas very good and efficient. Favorable properties of steel - Strong: has a high strength/weight ratioentiful - Easy to cut, connect and fabricateget rust if not properly treated

Principle factors affecting choice of frame Structural Design consideration n n n n n n Foundation consideration Standardization of members or design Span and floor loads Fire resistance requirement Maintenance consideration Integration of architectural & structural elements

Features of structural steel construction Structural characteristics 1. 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 600 o C or above). This can be improved by applying fire resistant plaster

Features of structural steel construction Structural characteristics (continue) 5. Beams usually shallower in size than for concrete Beams 6. 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 value 9. Rusting or corrosion problems very strict anti- corrosion treatment has to be applied

Features of structural steel construction (cont.) Construction aspects 1. 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

Features of structural steel construction (cont.) Construction aspects 5. Demand greater transportation or cranages provision 6. Complicated quality assurance procedures especially in the control of welding connection 7. 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 (e.g. those stiffening members) 9. Induce more works at higher altitude

Stiffening members in the form of outrigger, belt truss or transfer truss is very difficult to install during the construction process Outrigger tying up the core wall and the outer frame

Detail of the outrigger and transfer truss system used in Cheung Kong Center

The actual process in installing the transfer truss a temporary support frame erected for the purpose

The completion of the belt/transfer truss and outrigger at various stages

Features of structural steel construction Construction aspects highlight of some problems Delivery of structural steel member by ship Large member delivery to site waiting to hoisting up for erection

Features of structural steel construction Construction aspects Hoisting of the structural steel member to the upper floor

Features of structural steel construction Construction aspects Connecting steel members with RC element an anchor frame may be required for making strong connection

Features of structural steel construction Construction aspects Constructing the composite floor in steel/rc composite structure To connect floor to core wall starter bars are to be provided within the core structure

Features of structural steel construction Construction aspects Very large component often in complicated shape

Features of structural steel construction Construction aspects Huge amount of structural members make erection very complicated

Features of structural steel construction Construction aspects The existence of very complicated jointing in steel structure

Features of structural steel construction Construction aspects highlight of some problems Required to perform works at very high altitude

Features of structural steel construction Construction aspects Workers work at high altitude

Features of structural steel construction Construction aspects Connecting large and complicate shaped components can be very difficult

Features of structural steel construction Construction aspects Concrete has to be trimmed to allow steel to pass through Examples of location where unmatched dimension causing problem

Features of structural steel construction Construction aspects Roof truss and the decking not on the same level Examples of location where unmatched dimension causing problem

Future development of using structural steel or composite structures in Hong Kong Instead of building very large and complex building using composite manner, which resulted to very high cost in construction, the following ways may be adopted in order to achieve more cost effective application of technology in future. 1. Use more simple and straight forward design like regular steel frame structure in grid layout 2. Use more standardized components such as universal sections, lattice trusses or prefabricated standard sections in the design 3. Apply more to other types of building structure/construction as in many developed country like Japan, USA, or even Korea and Taiwan 4. Forming hybrid structure with other prefabricated elements

The use of standard structural steel members in construction

Convenient products in market allowing the use of very cheap and effective ready-install structural steel members to form various building systems

A hybrid structure in Melbourne, Australia with the mixed use of Precast concrete, cast-in-situ concrete and steel composite

Detail of the hybrid elements

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