4.3 Fiber concrete: Benefits: 1. Due to the high tensile strength and high elongation of the fiber, the tensile, flexural, impact strength, elongation and toughness of the concrete are improved. 2. Fiber can control the further development of cracks in the base concrete to improve crack resistance (Ahmed, 2016). Drawbacks: 1. The cost is high due to its control problems (production problems) and high raw material costs. 2. Maintenance is difficult (Doshi, 2016).
4.4 Reinforced concrete: Benefits: 1. Reinforced concrete has high compressive strength and good tensile stress. 2. Has good durability and fire resistance. 3. The structure is flexible and widely used in prefabricated structural members (Din, 2016). Drawbacks: 1. Corrosion of steel bars and freeze-thaw cycles of concrete can cause damage to the structure of concrete, which will result in loss of bonding force. 2. The casting cost is relatively high. 3. Shrinkage can cause cracking of the component and loss of strength (Din, 2016).
4.5 Cross laminated timber: Benefits: 1. cross laminated timber has a very high strength to replace concrete materials and has good seismic performance. 2. It is natural, green and has its own fire protection function. 3. It has the advantages of high efficiency and high-speed construction, and has low weather requirements, which can greatly improve the construction progress. 4. Has a flexible design (TIMBERFIRST, 2012). Drawbacks: 1. The design needs to be completed before the start of the project to allow off-site manufacturing. 2. External cladding is required to provide weatherproof materials (Andy Sutton and Daniel Black, BRE Pete Walker, University of Bath, 2011).
4.6 Oriented strand board: Benefits: 1. The oriented strand board has high physical and mechanical properties, compact structure and high strength. 2. It has strong anti-corrosion, anti-mite, anti-deformation and flame-retardant ability. 3. It has excellent heat insulation and sound insulation effect and has good paint performance (DO IT YOURSELF, n.d.). Drawbacks: 1. The density is heavier, so the furniture made with it is heavier. 2. The edges are rough and easy to absorb moisture.
5. Sustainability credentials of engineered products
5.1 Cold-formed steel: 1. Because it shrinks and expands easily with the weather, it is more durable than wood. 2. It meets the requirements of fire code, because of its resistance to insect damage and fire. 3. According to LEED certification, all truss materials and accessories are manufactured from 90% recycled steel. (ENGINEERED STEEL PRODUCTS, 2018)
5.2 Cast steel: The material properties of cast steel have a wide range of properties. 1. Due to the high hardness of the cast steel, the wear resistance is enhanced. 2. The corrosion resistance of cast steel increases the range in which it can be used. 3. Because of the effective thermal conductivity, cast steel can withstand stress and load without being affected by temperature (RELIANCE FOUNDRY, 2017).
5.3 Fiber concrete: Under static and dynamic loads, the fiber not only enhances crack resistance, but also has a strong repair interface, stronger water tightness and better control of corrosion in the repaired structure (Nemkumar Banthia, Cristina Zanotti and Manote Sappakittipakorn, 2014).
5.4 Reinforced concrete: First, reinforced concrete building systems are more durable than any other building system. Second, the maintenance cost of reinforced concrete is very low. It is the most economical building material when building some large buildings (Din, 2016).
5.5 Cross laminated timber: Cross laminated timber is a renewable building material that is one of the least energies consuming in the life of all building materials and can save costs. In addition, it also absorbs carbon dioxide from the atmosphere, releases oxygen, and seals the carbon in the wood (TIMBERFIRST, 2012).
5.6 Oriented strand board: The oriented strand board has a very low formaldehyde emission and is a truly green product.
6. The typical construction process of building using engineered products
6.1 Cold-formed steel: Cold rolled steels take hot rolled steels as raw materials. After pickling and removing the oxide scale, they are cold-rolled. The finished product is hard rolled, in which the shape of steel can be changed by cold water (STEEL FRAMING INDUSTRY ASSOCIATION, n.d.).
6.2 Cast steel: 1. Mould preparing: the mould is designed and produced according to the specific shape of the product. 2. Wax mode & tree assembly. 3. Sand shell making and dewaxing. 4. Pouring: pour molten steel into dewaxed sand shell. When the liquid steel is cooled and solidified, the solid steel is obtained by breaking the outer sand shell. 5. Testing (Admin, 2018).
6.3 Fiber concrete: 1. Preparing Portlan cement. Calculate the total amount of materials such as fiber, cement and anti-cracking waterproof agent in advance, and make corresponding plans and quantities. 2. Mixing. Mix all materials such as aggregates, cement, fibers and water in mixers. 3. Transport to work site. 4. Placing and compacting. 5. Curing (How Products are Made, n.d.).
6.4 Reinforced concrete: The preliminary work is the same as the concrete. The most obvious difference is that steel bars need to be placed before concrete is poured.
6.5 Cross laminated timber: 1. Species selection. 2. Drying. 3. Strength grading. 4. Visual grading. 5. Removing defects. 6. ‘Endless’ lamellae. 7. Panel assembly. 8. Completion (greenspec, 2018).
6.6 Oriented strand board: OSB production of the main process: logs ? peeling ? flake ? drying ? screening ? sizing ? pavement ? hot pressing ? plate treatment (Quality Control In China, 2016).
7. One existing timber structure and an existing concrete structure.
7.1 Timber structure: The Forbidden City palace is the imperial palace of the Ming and qing dynasties, located in the center of the central axis of Beijing, is the essence of ancient Chinese palace architecture. The imperial palace in Beijing centers on three main halls, covering an area of 720,000 square meters and a building area of about 150,000 square meters. It is one of the largest and best preserved ancient wooden structures in the world (Travel China Guide, n.d.).
7.2 Steel structure: As one of the ten contemporary buildings, Beijing national stadium is composed of reinforced concrete frame shear structure and bending and torsion member steel structure. The main steel structure forms a “bird’s nest” structure with a building area of 258,000 square meters and a total project cost of 3.3 billion yuan (eulor2008, 2018).
8. The principal structural system and the reason why the system would have been adopted
8.1 The Forbidden City: Bucket arch, as a unique component in Chinese traditional wooden structure architecture, is a kind of small and short wood intersection built up layer by layer. It is located between the column and the beam, plays the role of transfer load. As the main combination mode of ancient wooden buildings in China, it can greatly reduce the seismic load and play an anti-seismic role (China Fact Tours, 2008).
8.2 Beijing national stadium: In the design of the main truss of bird’s nest, triangular stable structure support is used. The reinforced concrete wall board is used to replace the beam and column in the frame structure to bear all kinds of loads. Its innovative look and energy efficiency make it one of the big “green buildings” (BAIDU WENKU, 2018).
9. Live loads and the factors considered by wind speed in The Forbidden City and Beijing national stadium
9.1 The Forbidden City: The most obvious live load is come from people. Because Beijing is snowy in winter and prone to earthquakes, snow and earthquake loads should be taken into account. The height and height to width ratio of buildings should be considered when calculating wind load. Due to limited conditions, the wind tunnel test cannot be carried out, so the surface wind load system coefficient is adopted (GAN ZHOU, WEIMING YAN and HONGZHI GUAN, 2013).
9.2 Beijing national stadium: The live load is same with The Forbidden City. This structure is similar to the horizontal structure to resist the lateral loads. Wind loads are decomposed through steel grids, while being dissipated to provide natural ventilation in buildings (Monika Mickute, Sam Pomager, and Lemond Brown, 2010).
10. The load paths for permanent (dead), imposed (live) loads and wind loads in the two structures
10.1 The Forbidden City: the most important elements in the Forbidden City are beams and columns which are support the whole building dead loads. The load passed down from the roof and upper frame is passed to the column through the bucket arch and from the column to the foundation (Travel China Guide, n.d.).
10.2 Beijing national stadium (Monika Mickute, Sam Pomager, and Lemond Brown, 2010): The core of the building carries dead loads of all the structures, and these loads will be transmitted directly to the plinth foundation.