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Superiority and comprehensive economic benefit of steel structure

No matter from the structural performance, use function or economic benefits, steel structure has certain advantages.

The tensile, compressive and shear strength of steel is relatively high, and the structural section of steel structure members is small and light. In general, the dead weight of high-rise reinforced concrete buildings is about 1.5~2.0t/m2, and the dead weight of steel structures in high-rise buildings is mostly below 1.0t/m2, and even some offices are only 0.5~0.6t/m2. Light weight of the structure can reduce the transportation and hoisting costs, and the load of the foundation can also be reduced accordingly, which can reduce the foundation cost, especially in areas with poor geological conditions, such as Shanghai and Tianjin, and its advantages are more prominent.

In high-intensity earthquake areas, if the weight of high-rise buildings with fortification requirements is reduced by half, it is equivalent to reducing the seismic fortification intensity by one degree. Taking the seismic fortification intensity of Beijing No.8 as an example, the adoption of steel structure for medium-height buildings can reduce the structural weight by about 1/3, the earthquake action can be reduced by 30-40%, and the load area per unit area on the foundation can be reduced by more than 25%.

According to foreign data, the technical and economic indicators of super high-rise buildings are shown in the following table:

Steel reinforced concrete structure

Dead weight 1 1.22 1.72

Structural area 0.28 0.37 1

Construction period 1.33 1.6

Steel consumption 1.45 1.23 1

Steel structure has good ductility and seismic performance, especially in high-intensity earthquake areas, it has more advantages. The guarantee of ductility of reinforced concrete structure lies in that the stress of the structure is not too high, while the ductility of steel structure lies in plasticizing some members.

The occupied area of the structure (or the plane density of the structure) is small, which actually increases the usable area. The structural occupation area of steel structure in high-rise buildings is only 28% of that of similar reinforced concrete structures. The use of steel structure can increase the use area by about 4%, which actually increases the use value and economic benefits of buildings. For example, the Changfugong Center in Beijing (a 26-story pure frame system with steel structure) has a steel column section of only 450×450mm, reinforced concrete structure, similar floors and column network, and a column section of about 900× 900 mm If the use area is increased by 4%, it is equivalent to an increase of about 2,000 square meters for a 50,000-square-meter building, and its value is considerable.

The construction speed is fast. The adoption of steel structure can provide more space and more spacious working face for construction. The columns of steel structure engineering generally take 3 ~ 4 floors as a construction section, and are hoisted at one time on site. Moreover, parallel three-dimensional crossing operation can be implemented in the lifting of columns, the installation of steel frames, the pouring of reinforced concrete core tubes and the construction of composite floors. Sometimes when installing columns and frames on the upper part, indoor decoration and decoration works can be carried out on the lower part. Therefore, it can be put into use in advance under the condition of ensuring technology, supply and management. See attached table for the construction period of some high-rise steel structures in China. It can be seen that the 30 ~ 50-story steel structure project can shorten the construction period by about 8 ~ 12 months compared with the reinforced concrete structure. With the development, application and accumulation of experience of high-rise steel structures, the construction speed can be accelerated.

Comparison of construction period of several high-rise buildings in China;

Project name Shanghai Ruijin Building Beijing Shangri-La Hotel Shanghai Jing 'an Hilton Hotel Beijing Changfu Palace Center Beijing International Hotel Beijing International Building

Number of floors (above ground/underground) 29/126/243/125/3 27/3 29/3

Total construction area (m2) 36167 56710 52000 50516 97000 47700.

Structural form reinforced concrete

Construction period (month) 20 24 30 30 43 36

(Note: S- steel structure, SRC-steel reinforced concrete structure and RC-reinforced concrete structure)

The quality of steel structure is easy to ensure. Steel structure members are generally manufactured and processed in factories with high precision. It is only installed in the construction site, which saves labor and makes the site more civilized. It reduces the stacking places of sand, stone and cement, and also reduces the wet operation of formwork storage and transportation, field component prefabrication and cast-in-place reinforced concrete structure, which has great advantages in downtown areas or densely populated areas.

The steel structure building is easy to be reformed in the process of use, such as strengthening, heightening and expanding floors, and the replacement is relatively easy and flexible. Some developed countries believe that steel structures are environmentally friendly and can be reused to reduce the exploitation of mineral resources.

Steel structures can be made into large spans and large spaces. Large-scale open office has been greatly developed since 1960s, and some countries call it "garden office". This kind of office needs a larger column network layout, and the smaller the column section, the more suitable it is. It is very common to use 12 ~ 15m column net. Steel structure is just suitable for this requirement, because it can form a spacious column-free space and facilitate flexible internal layout.

Of course, in order to form an open space, truss beams, lattice beams and suspended structures are commonly used and effective methods.

The pipeline layout is convenient. In the structural space of steel structure, there are many holes and cavities, which also allow the web of steel beam to pass through the pipeline with a certain diameter, which makes the layout of the pipeline more convenient, increases the clear height of the building and facilitates the replacement and maintenance of the pipeline.

Although the steel structure of high-rise building has the above advantages, it also has some disadvantages. The problem of high cost of steel structure needs to be comprehensively and correctly analyzed with comprehensive benefits. The steel structure has poor fire resistance, so it must be treated with fire prevention and rust prevention, which increases the cost. See the following table for the cost composition of high-rise steel structures:

Optimal composition of project theory (%) Actual average composition (%)

Fire protection 16 30

Rust prevention 12 10

Transportation and installation 8 7

Manufacturing costs 28 23

The value of steel 32 27

Design cost 4 3

The cost of steel structure is related to many factors, such as steel production, processing level, steel varieties, specifications, design technology level, cost calculation method and so on. , so it is necessary to analyze it in detail.

Capital construction investment = construction cost+equipment purchase and installation cost+relocation cost+land purchase cost+others.

Civil engineering cost = superstructure cost+decoration cost+foundation (underground part)

As can be seen from the table, the superstructure only accounts for about 30% of the civil construction cost and 7~ 10% of the total investment. According to analysis, the price difference between steel structure and concrete structure only accounts for less than 4% of the total investment, and at present, various miscellaneous fees account for an increasing proportion, such as land acquisition fees and relocation fees, and the more prosperous the lot, the higher it is; However, the decoration and equipment costs of some projects often exceed the structural costs. With the development of technology, the application of lightweight materials and the improvement of design methods, the cost of steel structure will also be reduced, and the problem of higher cost than reinforced concrete will not be obvious.