The year before last year, Beijing West West 4 plots due to the collapse of the template led to 8 people died; last April, Dalian and the collapse of the template caused six people were killed. Mold support the accident has become a difficult problem, and aroused national attention. Mold accident is not just a business or a responsible person, is the construction workers need to think deeply about the problem. Analysis of mold accident can not be eyebrows and beard a grasp, otherwise we will be transferred to the line of sight on the issue and ignore the accident the real "culprit", and ignore the control of the key issues. For example, the current supply of steel pipe on the market are almost less than the standard, the error of up to 10%; fastener may be worse. Xinhua News Agency published the "three red head of the file could not manage a killer of the fastener," the comments, in fact, steel pipe fasteners are not we can see, easy to grasp, and steel pipe fasteners caused by the error may only be a percentage Of the dozens of theoretical mistakes will likely bring more serious mistakes, which is more worthy of attention. I believe that people can easily be ignored by the theoretical error is the mold collapse of the "culprit".
"Theoretical environment" is seriously polluted
National standard "construction of fasteners steel scaffold safety technical specifications" (JGJ130-2001) promulgated time-consuming 18 years, the national standard taking into account the template stent calculation theory and construction methods. In the past twenty years, the application of fastener steel pipe calculation theory can be described as flourishing: many scholars in accordance with their own understanding put forward different computing theory and methods, which for the future national standard unified theory has brought great difficulties, GB preparation process in many intense debate delayed the time of the national standard and the master of the energy. After the promulgation of the national standard, some comrades compiled the "construction construction calculation manual" did not adjust the contents of the new specification, but claimed that "this manual all according to the national new promulgation of norms, standards", the resulting errors will inevitably lead to risk The In addition, the national standard JGJ130-2001 also exist in negligence. GB standard "construction fastener steel scaffolding safety technical specifications" in addition to the norms for the scaffolding and set aside for the template bracket, although the relevant provisions of only five (template bracket calculation of three, two structures), but still in the calculation Played a standard control role in the construction of the provisions of a quantitative control. Mold construction measures are an important means of ensuring the theory and safety of the calculation, and it is regrettable that the provisions of the mandatory enforcement clause have not been adopted. On the other hand, the omission of the key words in the narrative of the text poses a threat to the safety of the mold.
From the local procedure to the future mold frame construction direction
(DG / TJ08-016-2004): This procedure is in principle similar to the national standard JGJ130-2001 (calculation theory and construction method); and put forward the " "Induced load", "safe load" and "installation deviation load" several important words. The emergence of these vocabulary is not accidental: the United Kingdom has tasted the bitter fruit induced load; the Japanese have also been due to the inexplicable force to make the template collapsed, had to add 2.5% of the horizontal safety load. So these two additional load will be the future of mold design theory of important issues, as to how the value can be further discussed. Shanghai regulations in the general clearly stated: "In addition to compliance with these procedures, but also to comply with other relevant national and Shanghai standards and regulations." Shanghai regulations on a variety of scissors do not have a specific quantification, not on the national standard Omission is noticeable. The Shanghai procedure also provides examples of stress generated from the pole in the lateral force (wind, 1% erection of the error load and 2.5% of the safety load), but there are still some clerical errors.
The problem of dynamic impact and induced load is an important problem in mold design. All the structural failure process is not a dynamic process, but the world's structural engineers and structural norms are based on static mechanics, power shock effect at best to make up the dynamic load factor. As structural engineers are impaired by impetus for dynamic students, the lack of valuations. The dynamic impact effect is often up to several tens of times the static effect. For example, we use less than ten kilograms of hammer can easily cut off a ten tons of shear can withstand the round bar. In the construction practice, we also suffered a variety of dynamic impact of the bitterness. The stencil brackets should also be considered in the construction process in addition to the rigorous requirements of the above construction, such as the vertical splashing of concrete and the level of vibration of the fabric or cloth pipe are important issues of concern. This is particularly to beware of the instability caused by a rod and the rapid rise of the stress of the adjacent bar by a little collapse and the overall situation, although this process only a few seconds. To this end in the security strategy to strengthen the top layer: whether in the horizontal or vertical direction, but also to avoid the weak joints placed in the top directly to withstand the impact of power (deep buried at the bottom of the impact of the impact of the joints).
The 2.5% level of safe load in Shanghai is actually a static and difficult level of impact load from a static point of view, but its value remains to be discussed. Horizontal impact load is external energy, not necessarily directly linked with the plate weight - depending on the actual situation, which must rely on the actual test, the problem is China's mold and even countries should be concerned about and unavoidable problems. Shanghai regulations also provides 1% erection of the level of error load, this figure based on the shelves erection to meet the erection of the quality can be reduced to 3 ‰, because the requirements of the vertical bar ≤ 3 ‰, from the statistical law of deviation Can not be one-way, the value is safe.
As for the calculation of wind load, there is no need to pay too much attention in the calculation of the structure, and people will not carry out the construction of the wind at the extreme value of the wind (calculated for several decades of wind theory), so there is no need to combine with the construction load. On the one hand, if we have considered 2.5% of the level of safety load is generally greater than the role of the wind, and the two are not at the same time, so do not have to consider the wind load calculation, special circumstances another matter.
In the future direction of the mold structure, we should pay attention to the national standard or local rules in the mold design theory with ambiguity and even the structure of the less rigorous problem. In the preparation of the "bowl button steel pipe scaffolding safety technical specifications" trying to build the framework for the geometric invariant system to change the current state, but there are many worthy of study and further improve the problem. Even in the design of the mold when the language is correct, the stereotype of the mold is difficult to imagine only language can be expressed very precise, if not fully use the drawings (flat, vertical, cross-section and even the axis of the projection), there may be accidents: The specification should be used as the main engineering language.
Template stent accident is controllable, which requires us to carefully study the mold theory and construction methods and objective facts. At present, in the process of development and reform, due to economic interests and ignore the phenomenon of basic theoretical research need to be concerned about the industry should be based on basic theory of "support" model, to guard against the collapse of the template collapse. Xiong Yaoying