Progressive collapse: norms, calculation and recommendations

The theme of progressive collapse today is relevant and mentioned. Until now, people have been horrified by the famous catastrophe of this kind, which occurred on September 11, 2011 in New York. Millions of people watched these tragic events from the video, which claimed the lives of 2977 people.

At 8 hours 46 minutes 40 seconds from the north between the 93rd and 95th floors of the north tower of the World Trade Center, a Boeing 767 led by terrorists crashed (flight 11). At 9 hours 3 minutes 11 seconds between 78 and 85 floors in the direction from the south, the South Tower of the World Trade Center at a speed of 959 km / h was pierced through by a Boeing 767 (flight 175).

The progressive collapse (PO) of the WTC South Tower occurred after 55 minutes and 51 seconds, at 9 hours 58 minutes, and the North Tower - after 1 hour 41 minutes 51 seconds, at 10 hours 28 minutes. In both skyscrapers, the structural elements holding floor floors, floor trusses of the impact area were destroyed.

Unfortunately, most software happens due to inadequate control of building maintenance. Thanks to the press, we learn about the facts of the collapse of residential entrances, which, unfortunately, are the most frequent.

Note that in the American example, the destruction occurred due to an extraordinary case, and the design of the twin towers met the technical requirements. Accordingly, neither the builders nor the designers had the opportunity to anticipate these types of directional impacts that caused local damage that led to critical chain destruction and, as a result, the collapse of buildings. However, according to statistics, in most cases, software occurs under the influence of factors that can be calculated. In addition, scientists and engineers have developed effective methods for calculating the construction of buildings that are little susceptible to such critical damage.

The history of the category of "progressive collapse"

This term itself appeared in 1968 after the work of the construction commission, which studied the complete destruction of the 22-story London Ronan Point building by the explosion of domestic gas. British designers took this tragedy as a challenge to their professionalism. The scale of the tragedy, which caused dozens of civilian casualties in peacetime, found a response in society. As a result of engineering surveys in 1970, legislative amendments were proposed for parliamentary consideration - a new edition of building codes. The basis of the changes was the principle of proportionality of the accident to the local impact, leading to collapse.

For this, the designers were charged with calculating the progressive collapse. Its necessity since 1970 was regulated by law and, accordingly, since then it has been strictly implemented in Britain. Thus, it was normatively established:

1. Even at the project stage, the possibility of dangerous local destruction should be considered.
2. The number of articulated joints is reduced as much as possible, and the degree of continuity for the structure increases.
3. Building materials characterized by plastic deformations are selected.
4. The design includes elements that are not load-bearing during normal operation, but that carry out (in whole or in part) load-bearing functions during local damage.

Buildings are protected from progressive collapse in a comprehensive manner, taking into account all these factors. A year ago, a Russian code of rules was developed that regulates compliance with the survivability of buildings and structures at the stages of their design, reconstruction and overhaul.

The relevance of the problem. Causes

According to software statistics, such global destruction occurs due to corrosive, force, or deformation effects. Options for such technological events can be:

1. Groundwater flooding.
2. Blurring of the foundation due to accidents on water mains.
3. Destruction of structural elements due to their overload or due to explosion, collision.
4. Weakening of the structure of materials due to corrosion.
5. Errors in the design when calculating fasteners and load-bearing elements.
6. Gas explosion go fire.

Often there is a progressive collapse due to brittle fracture with an increase in the number of microcracks. Obviously, the first case of such destruction that occurred in 23 BC e. with the amphitheater of Fiden, described by the historian of Ancient Rome Cornelius Tacitus. The software that arose on the day of gladiatorial structures in a crowded building, according to this chronicler, took as many lives as the war would have done. We are talking about several tens of thousands of people.

We give a later historical example. Progressive collapse with an increase in the number of microcracks caused the collapse of the arch bridge over the Wye River in 1786 (Great Britain, Herefordshire). Another arched bridge called Lsen-Beneese over the Rhone river (France), built in the XII century, collapsed so many times due to the adverse effects of the environment and internal degradation so often that it stopped being restored in the XVII century (different bridge spans collapsed 1 time - in 1603, 3 times - in 1605, 1 time - in 1633 and in 1669 - finally).

It should be noted that modern urban development technologies, unfortunately, did not deactivate the progressive collapse of buildings and structures. Sad statistics continue into the 21st century:

1. 09/08/1999 - terrorist attack - an explosion of 350 kg in TNT equivalent, which brought down two porches of a nine-story building on the street. Guryanova (Moscow) and resulting in the death of 106 people.
2. 07/02/2002 - a household gas explosion with an epicenter on the 7th floor of the staircase of a nine-story building on Dvinskaya Street (St. Petersburg), which led to the death of two people.
3. 02/14/2004 - the collapse of the roof of the Transvaal Park with an area of ​​about 5 thousand m2, which led to the death of 28 people.
4. 10/13/2007 - a household gas explosion in a house on the street. Mandrykovskaya (Dnepropetrovsk) destroyed the third entrance of a residential building and led to the deaths of 23 people.
5. 02/27/2012 - a gas explosion initiated by a suicide brought down a staircase in a house along N. Ostrovsky Street, ten people died.
6. 12/20/2015 - a gas explosion in the house on the street. Cosmonauts (Volgograd), 3 apartments were destroyed, one person was killed.

Normative regulation

Before considering the problem, it would be logical to familiarize yourself with the regulatory documents that examine it and organize the corresponding prevention. The protection of buildings and structures from progressive collapse in the Russian Federation is regulated by regulatory documents, a list of which is presented below:

1. Manual for the design of residential buildings. Vol. 3. Designs of residential buildings (to SNiP 2.08.01-85). - TsNIIEP homes. - M. - 1986.

2. GOST 27751-88 Reliability of building structures and foundations. The main provisions for the calculation. - 1988

3. GOST 27.002-89 “Reliability in technology. Basic concepts. Terms and Definitions". - 1989

4. Recommendations for the prevention of progressive collapse of large-panel buildings. - M .: GUP NIAC. - 1999

5. MGSN 3.01-01 "Residential buildings", - 2001, paragraphs 3.3, 3.6, 3.24.

6. NP-031-01 Design standards for earthquake-resistant nuclear power plants, - 2001

7. Recommendations for the protection of residential frame buildings in emergency situations. - M .: GUP NIAC. - 2002

8. Recommendations for the protection of buildings with load-bearing brick walls in emergency situations. - M .: GUP NIAC. - 2002

9. Recommendations for the protection of monolithic residential buildings from progressive collapse. - M .: GUP NIAC. - 2005

10. MGSN 4.19-05 Multifunctional high-rise buildings and complexes. - 2005, paragraphs 6.25, 14.28, Appendix 6.1.

Recently, the software problem has found fuller coverage in the latest domestic regulatory sources. Any construction documentation of buildings with a normal and increased level of responsibility must necessarily take into account the requirements of the code of rules (SP) 385.1325800.2018, which regulates the protection of buildings from progressive destruction.

Software and building capacity

According to paragraph 4.1 of these rules, the customer has the right to initially require the inclusion of additional elements in the design of the building (structure) under construction that will increase the load-bearing capacity of the structure.

The same JV “Calculation of progressive collapse” is most fully represented in two design options for protection against software during overhaul. The first - in the case of overhaul of buildings and structures of an increased level of responsibility and the second - for the same objects of a normal level of responsibility. In the first case, the bearing capacity is increased by a multiple of the second.

The main condition for compliance with the requirements of protection against software is compliance with the condition that the bearing capacity of structural elements and their joints exceeds the forces leading to local collapses in these structural elements and joints. If any design does not satisfy this requirement, then it should either be strengthened or replaced.

If we are talking about the reconstruction of buildings (structures), then first they must be technically inspected in accordance with GOST 31937, and then the reconstruction itself is carried out as a whole, or within the boundaries of the expansion joints (depending on the chosen reconstruction strategy).

Local Destruction Sector

When diagnosing the survivability of buildings with respect to software, planners at the project stage detail their possible sources - local destruction points. Each such destruction is considered by them separately and spatially. In particular, the joint venture we are considering for progressive collapse begins with a forecast of local fracture sectors in the design of load-bearing structures:

• for buildings and structures up to 75 m high they are limited by a circle of diameter not less than 6 m;
• for buildings and structures from 75 m to 200 m high - with a circle of diameter not less than 10 m;
• for buildings and structures over 200 m high - with a circle of diameter not less than 11.5 m.

For multi-story, large-span buildings, local damage in the form of damage to any of the supporting structures is considered. In this case, the zone of local destruction should be localized by the structure and in no case should develop into software.

The joint venture “Protecting buildings from progressive collapse” provides as preventive measures that prevent global destruction of this kind:

• accounting for the maximum number of probable local damage;
• the use of materials and structures prone to plastic deformation,
• increase in static indeterminacy (SN) of a structure (increase in its level of indeterminacy, decrease in the number of articulated elements).

Forcedly using a special term, we explain it. CH-systems are a complex characteristic of the interaction of the building structure and the applied forces to it. In other words, in CH systems, in contrast to statically determined, the distribution of forces depends not only on external forces applied to buildings (structures), but also on the distribution of these forces on structural elements, which, in turn, are characterized by elastic moduli .

It is the acting load-bearing structural elements (the so-called bonds) that, under local influences, prevent the transformation of a whole statically indefinite system into a geometrically variable system (the latter assumes the possibility of software). Thus, it is connections that make progressive collapse impossible. Building standards - this is what should take into account and regulate software prevention.

Regulatory Summary

You are obviously interested in what regulatory documentation regarding software is the most advanced in the world. It should be recognized that despite the domestic developments of recent years, accounting for software counteraction is presented in more detail today (relevance - 2016) in the American standards UFC 4-023-03 and GSA.

The fact is that they take into account the latest building materials, as well as various building designs. At the same time, the Russian compilation E TKP 45-3.02-108-2008 was compiled on the basis of recommendations written in the 2000s regarding reinforced concrete structures.

We note the clear progress of Russian regulatory documents in recent years and the obvious efforts to streamline the existing disparate and numerous sources of norms. However, it is fair to say about the shortcomings. Take at least regulatory documentation. Experts note that today various sources of domestic regulatory documentation are often contradictory, and also contain flaws. Here are just a few examples:

1. In GOST 27751-88, paragraph 1.10, “Regulation” is at the level of “any structural element”. (Excuse me, concretization is needed, because we are talking about human lives!)
2. STO 36554501-024-2010 "Ensuring the safety of large-span structures ..." (Clause D.3 erroneously states that the choice of software calculation should be determined by special technical conditions. This logic is absurd).
3. SNiP 31-06-2009 “Public Buildings and Structures” in paragraph 5.40 mentions that design should “consider design situations of a terrorist nature”. (But this is a dead end. For example, suppose the designers check the local destruction of the convoy on the same floor, but the terrorists put explosives under the two convoys. In the same place, clause 9.8, again the regulation is at the level of “some structural element.)
4. STO-008-02495342-2009 "Prevention of reinforced concrete buildings". (The document is criticized. In principle, neither software dynamics nor plastic deformations are considered.)

Obviously, the list goes on. The progress of the construction industry, which has significantly accelerated in recent years, has led to the obsolescence of most of the existing regulatory documents governing the software industry. Obviously, the effective prevention of progressive collapse will soon require adaptation to domestic realities of already generalized foreign experience. This refers to US standards UFC 4-023-03 and GSA, which contain not vague, but very clearly formulated requirements for the structures and materials of specific types of buildings.

Unfortunately, many domestic experts consider the joint venture “Protecting buildings from software ...” and the joint venture “Buildings and constructions. Special Impacts ”).

Features recommendations for high-rise building software

In particular, the JV under consideration is regulated by the progressive collapse for high-rise buildings. The peculiarity of calculating software for high-rise buildings is determined by a wider step in the location of walls or columns. In this case, the general design, in the event of an accidental impact, allows local collapse of the bearing elements, but only within one floor, without further chain continuation of this destruction. The collection of rules contains recommendations regarding the design and construction of new ones, as well as the verification and reconstruction of already constructed high-rise buildings and structures. (For reference, the height criterion is a height mark of more than 75 m, which is equivalent to a 25-story building.)

Equilibrium Calculation

The calculation of the design of a high-rise building is carried out on the basis of the assumption that it, under the influence of local destruction, is transformed into a state conventionally called the "limiting states of the first group." Let us explain this term. The limiting condition is such a state of a structure when it ceases to counteract destruction or is damaged (undergoes deformation). In total, two groups of limit states are distinguished. The first conditionally called the state of complete operational unsuitability. The second is called the state of damage, which allows partial operation.

Technically, the calculation is performed by modeling the system of differential equations of nonlinear stiffness characteristics of the structure of a high-rise building. The calculation of a high-rise building is carried out on the basis of building a spatial model, which takes into account non-load-bearing elements, but capable of taking over the redistribution of forces under local influences. In this case, the stiffness characteristics of structural elements adjacent to the fracture site are taken into account. The computational model itself is calculated many times, each time taking into account a specific local fracture. This method allows you to achieve the most reliable results. Moreover, in the model being built, the factor of reducing excessive material costs is considered.

How is the spatial model analyzed? On the one hand, efforts in structural elements are equated to the maximum possible, which can be sustained by them. It is believed that the progressive collapse of high-rise buildings becomes impossible when the efforts are less than the bearing capacity of the structure. , .

: .

, , . :

1. , , . ( — , .)
2. , , .
3. — , , . , . .

, , , .

:

1. , .
2. , . , .
3. , , .
4. .

« » .

- () . , . , , , . , .

- . , . , - .

- , . , . , , , .

, . , .

. . ( ) , .

, .

, , , . ( ), , .

, , , , .

:

• ( , , , , );
• , , , .;
• , ;
• , : , , ;
• , .

, :

• :
• ;
• ;
• ;

(). , . , .

, « », , «» - № 184- № 384-, . :

• () ;
• () ;
• () .

:

• ;
• ();
• ;
• .

, . , , ANSYS, SCAD, Nastran. , .

, .

:

• , ;
• ;
• ;
• , ;
• , .

Conclusion

. . , : « ?» , . , .

:

• ;
• , ;
• ().

, - -, . , , . . , , — , , .

, . , .

, , .

, , 31.12.2018 . , 39 . , , , . , , , . .