Recently, the "Unified Standard for Reliability Design of Building structures" GB50068-2018 has been released, the most remarkable change is that the constant load sub-coefficient is adjusted from 1.2 to 1.3! The partial coefficient of live load is adjusted from 1.4 to 1.5, and the partial coefficient of prestress is adjusted from 1.2 to 1.3, which will be implemented from April 1, 2019. The implementation of the new standard not only enhances the safety factor of the project, but also lays the foundation for the consistency of the reliability setting level between the building structure of our country and the international mainstream code. In the medium and long term, the new standard is also helpful to improve the steel demand of the construction industry.
First, the new standard will be applied to all types of buildings, but because the mechanical characteristics and code requirements of different components in the building structure are different, the influence of the increase of load partial coefficient on the amount of steel will vary with the form of building structure and the type of components. According to whether it belongs to structural stress members or not, building steel can be divided into structural steel (60%) and non-structural steel (40%). Because non-structural steel is not directly involved in the force, it is not affected by the new standard.
Second, from a sub-industry point of view, construction projects are divided into infrastructure, real estate and manufacturing industries. The design of infrastructure projects generally exceeds the lower limit of the national standard, while the design of real estate projects generally follows the lower limit of the national standard. As a result, most of the boost to demand for construction steel from the new standards has been focused on property projects. However, the area of new real estate construction continued to grow high in 2018, with a cumulative total of 17.2% for the whole year compared with the same period last year, and the new construction area reached the highest level in nearly five years, while the completed area was relatively low, and a large number of construction work was carried out in 2019. At the same time, the low growth rate of sales will affect the growth rate of new construction, which in turn will affect the volume of follow-up real estate construction. According to the Bureau of Statistics, the sales area of commercial housing and the area newly started in February 2019 increased by-3.6% and 6.0% respectively compared with the same period last year.
Third, the new standard was issued at the end of January 2018, and the landing time of the policy is April 2019, and the new construction of the design drawings approved before April 1 will not be affected. The normal process is the structural modeling and calculation of the design institute-the first draft of the design is submitted for review-the final draft-the examination permit-the construction license. Therefore, in order to reduce the increase of the cost of steel used by construction units, it is common for various architectural design units to rush to work in the early stage. According to SMM, most of the drawings submitted for review at the end of March are affected by the new standard, and most of them have been revised and calculated.