Материал: Russian Journal of Building Construction and Architecture

It is an easy task to see from the presented analytical dependences that survivability parameterdepends of the continuity and location of the structural elements of the system defining the quantitative redistribution of loads in the structurally non-linear system, the parameters of the diagram of static-dynamic deformation of the sections of system elements and consequently, the reinforcement pattern and intensity of reinforced concrete elements.

Numerical analysis

Let us perform as an example a numerical analysis of the parameter of survivability of a twice redundant model of a reinforced concrete frame with the span l = 1.200 mm, H = 700 mm, cross section h = 120 m, b = 40 mm (Fig. 3). The girder is reinforced with symmetrical reinforcement, the diameter of 5 mm, grade А-400, area of compression and tensile reinforcement is Аs = Аs = 0.196 * 104 m2. Frame pole and girder are designed of B35 concrete. The frame is

the middle of the girder span, varying with parameter

Two variants of the system topology were analyzed. In the first variant (Fig. 3), the left pole of the frame is hinged and rigidly connected to the girder. In the second variant, this pole is hinged to the girder but it has an additional intersect at the point of connection.

Fig. 3. Structural (a) and design (b) diagrams for two variants of bounding conditions

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Russian journal of building construction and architecture

Calculated for the specified dimensions of the section and girder reinforcement limit value of the ultimate moment in its span and support sections is 0.6 kN * m. The reduced flexural rigidity of the girder is Bred. = 0.169 Mn * m2. Since the girder section for the specified reinforcement pattern fractured brittly due to the compressive concrete deterioration as an overreinforced section, the coefficient of the excess of the failure moment over the design ultimate moment (C) is taken as 1.4 and correspondingly, the value of estimated failure moment in the span (1––1) and support (2––2) sections is Mult = 0.84 kN * m.

Having chosen the basic system in the specified variant of the mixed-mode method and having calculated coefficients of canonical equations and solved simultaneous equations (1) in

MathCAD, we find the values of the unknown M and z . Using the formula (6), we determine the minimum value of the parameter λ, at which in the sections С1…., С6 limit value of failure moment is reached. From the calculation for the 1st variant frame, the following values of λm are obtained: λ1 = 1.657, λ2 = 1.652, λ3 = 1.852, λ4 = 2.851, λ5 = 2.851, λ6 = 2.083.

For the 2nd variant frame survivability parameter values are λ1 = 2.359, λ3 = 2.795, λ4 = 3.144, λ5=3.154, λ6=1.991 respectively.

According to the specified data that in the 1st variant frame section С2 fails first and in the 2nd variant frame section С6 fails first. The 2nd variant frame is much more survivable as all values for this frame are more than λm values for the 1st variant frame. During further calculation for frames of the 1st and 2nd variants correspondingly, after cutoff of the moment tie in С2 section or С6 section and decrease of redundancy of each of the frames per unit, the λm parameter values change. Redistribution of loads in the structural system takes place and position of hazardous weak sections changes. Therefore, it can be concluded that as far as ties in the structural system fail and thus system topography changes, the coefficient of dynamic loading in the sections of structural system elements (relation Mnd 1 / Mnc ) and system destruction resistance change.

Conclusions

The proposed method of survivability parameter analysis for redundant framed structurally and physically non-linear systems of buildings and facilities provides opportunity to perform in a fairly simple way and in compliance with the physical meaning of the issue under consideration the analysis of load and dynamic loading changes in structure elements as well as the sequence of structural transformations and collapses of the sections of structural elements in case of abrupt failure of one of the bearing elements (ties).

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The applied diagram of static-dynamic deformation of a reinforced element section makes it possible to determine dynamic loading in the loaded and dynamically loaded sections of the structural system in case of its sudden structural transformation, considering elastic-plastic properties of materials and the time of dynamic loading of the section without involvement of the body of structural dynamics.

Quantitative analysis of the reinforced redundant system (frame with different bounding conditions) found that the sequence of element sections failure, value of survivability parameter of the structural system (λ) and the coefficient of dynamic loading in the sections of structural system elements depend on the system topology and characteristics of static-dynamic deformation of the sections of its elements.

References

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HEAT AND GAS SUPPLY,VENTILATION,AIR CONDITIONING,

GAS SUPPLY AND ILLUMINATION

UDC 644.1

S. N. Kuznetsov1

A SELECTION OF VENTILATION MODE IN PREMISES WITH MOVING

SOURCES OF HARMFUL SUBSTANCES

Voronezh State Technical University

Russia, Voronezh, tel.: +7 (4732) 71-53-21, e-mail: kuznetvrn@mail.ru

1 D. Sc. in Engineering, Prof. of the Dept. of Heat and Gas Supply and Oil and Gas Business

Statement of the problem. When designing the ventilation systems of industrial premises with moving sources of harmful substances, it is necessary to choose an effective scheme of ventilation. Results. Based on the turbulent exchange of non-stationary equation, a mathematical model of transport of harmful substances in the room with the moving source was developed. The model is implemented as a computer software in MatLab and Simulink package.

When driving hazardous substance sources in the longest room in one direction most effective air exchange scheme is a scheme with the air flow towards the source. When moving sources of harmful substances in different directions is the most effective air exchange scheme with a uniform supply and removal of air along the length of the room.

Conclusions. The proposed approach allows one to select a scheme and the amount of air to areas with moving sources of harmful substances more effectively utilizing the fresh air and increase the effectiveness of ventilation.

Keywords: ventilation, moving source, mathematical model.

Introduction

Designing of ventilation systems of industrial premises with moving sources of hazardous substances (car tonnels, industrial containers, etc.) involves a challenging selection of an effective scheme of air exchange due to non-stationary concentration field of hazardous substances. A study of concentration fields of hazardous substances in industrial premises in natural conditions or the air and heat model is commonly associated with a large amount of experiments. This paper sets forth a mathematical model of concentration fields for choosing an effective scheme of air exchange [3, 9, 11, 17, 18, 20].

© Kuznetsov S. N., 2017

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