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20ASSESSMENT OF RESISTANCE TO THE PROGRESSIVE COLLAPSE EVIDENCE FROM REAL HIGH-RISE BUILDINGS IN
DUSHANBE CITY
Gafurov S.S. Kholikov M.A.
Ministry of Education and Science of the Republic of Tajikistan M. S. Osimi Tajik Technical University Faculty of Construction and Architecture Department: «Industrial civil engineering» Undergraduate of the 2nd course Rahmonov A.J.
Scientific Supervisor: candidate of engineering sciences
ABSTRACT
This article presents several ways to engineering real buildings with protective measures from the progressing collapse. Modeling of the progressing collapse is necessary for a research of survivability of structures, opportunity and the mechanism of her adaption at an emergency exit out of operation separate structural elements. In this regard obviously to need of development of numerical methods of calculation of buildings on the progressing collapse of the bearing structural elements in case of emergency. An actual example of realization of calculation on the progressing collapse of structures of a high-rise housing estate with underground parking taking into account on staging of installation, check of the building on capsizing is executed.
Keywords. The progressing collapse, life cycle, computer modeling, structural elements, the reinforced floors, dynamic analysis.
Introduction. Analysis of several large collapse in construction, that occurred last 30 years has shown, that the main cause of accidents is the poor quality of the engineering and the imperfection of modern construction norms. A significant number of collapses was due to non-fulfillment of technological installation requirements, understatement of concrete brand, etc. Often to accidents and collapses resulted the wrong design decisions, that have been taken from the wrong accounting of loads, wrong computer modeling complex constructions. In practice of construction there are also accidents because of not thorough geotechnical testing, inadequate for groundwater and many other factors.
Modern means of computer-aided design (CAD) software allows to move from the concept previously adopted for calculating (structural design - SSS) to modern - modeling of processes of lifecycle (the construction process, loading and other process.). In particular, modeling of the operational period of construction, where besides such factors, as the accounting of rheological properties of material (creep), changes in the structural scheme in connection with the reconstruction etc., includes the simulation of progressive collapse. In this article is offered the technique of modeling and calculation on the progressing collapse of the high-rise building in the LIRA-SAPR program complex on the example of Dushanbe-Plaza.
Review of the literature on the subject of research. In recent years, significantly increased interest in the issue of survivability (vitality) of constructions in emergency situations.
In regulating documents the term «survivability» is used, generally in relation to objects of mechanical engineering and a row of engineering systems (for examples, the system of heating, gas and electric power
supply). At the same time «under the survivability understand an object property, consisting in his ability to resist to development of critical failures from defects and damages at the installed system of maintenance and repair, or an object property to store a limited working capacity at impacts, not foreseen operating conditions, or an object property to store a limited operation in the presence of defects or damages to certain species, and also at the failure of some components».
In London, May 16 1968 there was an explosion of household gas in 22-storey building Ronan-Point, built by Larson-Nielsen system. In the explosion the carrier end wall and curtain wall outside of corner apartment on the 18th floor was destroyed. The end walls and the overlap of overlying floors, losing support, collapsed, and the weight of the impact and the kick of falling components caused the destruction of the walls and overlaps of building angle to the ground floor [1].
The destruction of this kind came to be called progressive collapse.
Issues of development of methods of preventing progressive collapse devoted to the works Almazov V.O. (2006, 2007, 2009), Rastarguev B.S. (2003), employees work Plotnikov A.I. et al. (2004), foreign scientists Powell (2005), Kaewkulchai and Williamson (2003), Pretlove et al. (1991), Gilmour and Virdi (1998), Izzudin et al. (2008), Vlassis et al. (2008) and other scientists. The works shows the influence of dynamic effect in progressive collapse, which decreases with increasing plastic deformation [2,3].
Today, there are a number of documents that define the design rules for preventing progressive collapse, for example the «Recommendations for the Protection of monolithic apartment buildings from the progressive collapse», developed DBN-V.2.2.-24:2009 et
al. (MGSN 4.19-2005, STO 008-02495342-2009, TSN 31 -332 -2006) requirements to solve the problem as follows:
- The supporting construction system of residential buildings must be resistant to progressive (avalanche, chain) collapse in case of the local destruction of individual structures during emergency actions (gas explosion, fire, etc.).
- Allowed local destruction of the individual load-bearing structures, but these initial destruction should not lead to the collapse of neighboring structures, which are transmitted to the load, is perceived earlier elements, damaged by accidental impact.
- The structural system of the building must ensure its strength and stability, at least for time, necessary to evacuate people. Displacement structures and cracks in the disclosure are not limited to them.
Consider a real example of the calculation on the progressive collapse of structures of high-rise residential complex with underground parking on Rudaki Avenue, Bukhara Street in Dushanbe city. The total height of the building H = +87.95m, Hbasement= -7.70 m, foundation slab 1.50 m, drilling injection piles diameter 80 and 100 cm length 15.50 m. The calculation is made based on the staged construction and taking into account nonlinear operation materials in software complex LIRA-SAPR. General view of the building and the finite element scheme is shown in Fig.3. To obtain reliable data on the stress-strain state (SSS) of high-rise buildings, the calculation is performed based on the staged installation (see. Fig. 4).To assess the sustaina-bility of buildings against progressive collapse are considered a variant destruction of one of the columns section 60^60 cm in the middle of the building with a maximum span.
Calculated seismic loads are taken in accordance with the requirements of Rules of civil engineering 2207-2007 «Earthquake resistant construction. Design Standards».
Calculated seismicity of the site taken 9 points. The type of soil on seismic properties taken Il-nd category.
When determining seismic loads keeping static loads formed using the following coefficients:
- permanent - K=0.9
- long temporary load - K=0.8,
- short temporary load - K=0.5.
The direction of action of seismic loads taken in three orthogonal directions along the axes of the building (X, Y, Z) and at 45° to the main horizontal axis. The number of forms of natural oscillations was accepted KF=30, at which the size of modal weight participating in work in the horizontal direction, has exceeded 96,0%. In general, in the calculation model of a building adopted 9 loadings:
Uploading 1 - static uploading from the action of its own weight;
Uploading 2 - static uploading from the action of permanent loads (the weight of partition walls structure and filling of brick and lateral pressure of soil on the foundation wall);
Uploading 3 - static uploading from the action of permanent loads (The weight of the floor structure);
Uploading 4 - static uploading of temporary long-acting loads on SNIP 2.01.07-85*;
Uploading 5 - static uploading of temporary short-acting loads on SNIP 2.01.07-85*;
Uploading 6 - dynamic action of seismic loading on X axis;
Uploading 7 - dynamic action of seismic loading on Y axis;
Uploading 8 - dynamic action of seismic loading on Xy 450
Uploading 9 - dynamic action of seismic loading on Z axis
In determining calculated reinforcement of structural elements of building into account the provisions of sections SNIP 2.03.01-84* «Concrete and reinforced concrete structures» and Rules of civil engineering 2207-2007 «Earthquake resistant construction. Design Standards». The short description of modules of reinforcing is given in the appendix. The thickness of the protective layer of concrete adopted in accordance with the design data:
for foundation slab - 50mm, for frame of columns - 30mm,
for frame collar beams - 25mm (in the lower zone) and 40mm (in the upper zone), 50mm to the side
for floor slabs - 20mm.
Basic data on the model and the results of the calculations presented below.
The results of calculations of the building and settlement reinforcing of the basic reinforced concrete elements are presented in graphic form.
Fig.1. Spatial scheme of building
Fig.2. The mosaic of displacements without removing the columns of the middle row (№element=218865)
Fig.4. The mosaic of displacements after removing the column of middle row (№element=218865)
Fig. 5. Removing the column of marginal row (№el=156867;156866;156864;156865;156854;156919;156920;156862;156868; 156925)
Fig. 6. The mosaic of displacements after removing the column of marginal row (№el=156867;156866;156864;156865;156854;156919; 156920;156862;156868; 156925)
Table 1.
№ The name of Without re- After removing A, After removing A,
uploading moving col- column №218865, % column №156867, %
umn, mm mm mm
1 Seismic X 23.90 22.00 7.95 25.70 7.53
2 Seismic Y 26.50 28.30 6.79 26.20 1.13
3 Seismic Z 32.50 33.00 1.54 33.30 2.46
4 SeismicXY 35.60 35.60 - 36.80 3.37
After removing the columns of the buildings, check is made on rollover. The tasks of sustainability is closely linked to the geometrically nonlinear problems. Realized in software complex LIRA-SAPR the method of sustainability presupposes, study of the stability of the building on the deformed scheme [6].
After imposition to the building of wind load, the calculation performed on all the calculation load combinations (CLC) and analysis of displacement and maximum acceleration of the upper floors (no more 8 cm/s2). At the same time integrally counted understated the stiffness of the vertical elements and floor slabs based on the engineering of non-linearity. For system stability Kreserve should be more than 2,0.
Conclusion. In the engineering of high-rise buildings is necessary to create structural preconditions for
adaptability of constructions to different situations, including force majeure. To solve these problems it is necessary to calculate the structure in the nonlinear formulation. Step method for solving nonlinear problems are most appropriate in these cases. In accounting for the safety criteria and maximum prevention of emergencies is necessary to strive to solve these questions in the most economical way.
Realized in software complex LIRA-SAPR, the method physically-nonlinear analysis of structures with cracks allows to perform assessment of sustainability and sustainable strength of the frame in progressive collapse.
References
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