CALCULATION OF THE INTERMEDIATE SUPPORT OF A THREE-SPAN OVERPASS

ABSTRACT

In the article, calculations were carried out taking into account the relationship between the supporting and foundation structures of bridge structures deformed by external forces and various soils around them. The practical method of modeling structural deformations and internal stresses formed in the “support-ground” system under the influence of load, their numerical indicators are determined.

АННОТАЦИЯ

В статье были проведены расчеты, учитывающие взаимосвязь опорных и фундаментных конструкций мостовых конструкций, деформируемых под действием внешних сил, и различных грунтов вокруг них. Определен практический способ моделирования деформаций конструкций и внутренних напряжений, образующихся в системе “опора-грунт” под действием нагрузки, их численные показатели.

Keywords: Deformation, soil, foundation, structure, foundation, impact of load, bridge structure.

Ключевые слова: Деформация, грунт, основание, конструкция, фундамент, воздействие нагрузки, мостовая сооружение.

Calculate the intermediate support of a three-span overpass with a massive foundation. Overpass 18+24+24m, superstructures consist of  24m ribbed beams of  6 T-shaped prestressed beams with a frame in cross section and 14m hollow plates between them.G-10m.The width of the sidewalks is 1m, the intermediate supports are columnar and have a thickness of 1m.

The roadway consists of the following layers: asphalt concrete - 7cm; protective layer of concrete - 4cm; waterproofing - 1cm; leveling layer - 3cm.

The use of columnar supports with a shallow foundation involves the use of structures of the same type in size, which reduces the number of mechanisms and, of course, reduces construction costs [1-3]. We make calculations in the direction of the longitudinal and transverse axes of the overpass. When calculating reinforced concrete supports and foundations, as well as the own weight of superstructures, we enter the volumetric weight: γ=2,5kN/m². The program also introduces soil parameters. In the developed method, we mainly include a horizontal load falling from the brake, for a structure on a category III-highway, the temporary load is assumed to be equal to the calculated value of the braking load falling from A-14 equal to 102kN, and the value of these temporary loads in the horizontal direction is assumed. We also include the vertical effect of time loads [4-6]. The standard vertical load, determined by the loads A-14 and NK-100 for the support, is determined for the longitudinal and transverse axes of the overpass as follows:

R_A14=R(1+u)(1+μ)n + vω(1+μ)[1+0,6(n-1)]                            (1)

R_ol=g_tω²                                                        (2)

R_NK-100= g_ekvω(1+μ)                                             (3)

where: n - number of movable strips for cargo A-14; R - truck axle weight;  g_ekv - equivalent load for NK-100; g_t - the intensity of the regulatory load on pedestrians; ω - the line of action of the superstructure; v - the value of the load A-14, evenly distributed over the strip.

The maximum value of the found loads is selected for calculation. The impact lines of the superstructure are built in two versions and loaded with A-14 and  NK-100 loads. We calculate the external seismic forces by the formula:

                                           (4)

where: K_i - a coefficient that takes into account possible breakdowns of a bridge or overpass, K_i=0.25; Kψ - a coefficient that takes into account the vibration of the structure, Kψ=1; for seismic points A-7,8,9 the seismic coefficient is assumed to be equal to -0,1; 0,2; 0,4;  Q_k,red- the mass of the structure, given at the point k; β_i, η_ik - dynamic coefficient and shape of oscillations.

The dynamic coefficient is defined as:

                                                        (5)

where: T_i– a particular oscillating contour of a bridge or overpass in tone, the coefficient of the oscillating contour cannot be less than 0,8 and more than 2,5.

It is allowed to take the coefficient η_ik equal to 1.

The estimated cost of vertical permanent loads falling from the superstructure and the roadway is equal to: R_oq,qq=2321,25 kN.

The normative vertical load on the base,determined by formulas (1)and(3),is equal to:

R_A14=1005,19 kN, R_NK-100=745,42 kN

The estimated value of the load falling from A-14 in the transverse direction relative to the axis of the bridge is equal to: =96 kN.

The calculated value of the braking load falling from A-14 in the longitudinal direction relative to the axis of the bridge is equal to:  =102 kN.

Calculated resistance of the ground under the foundation: R = 0,5353MPa.

a)

b)

Figure 1. Transverse direction of the intermediate support a) design scheme; b) deformation from its own weight

It follows that the deformations and deformations of the structure from its own weight are insignificant [7-9]. The deformation of the intermediate support from its own weight in the transverse direction, the mass of the superstructure of vertical temporary loads and seismic forces is shown in Figure 2.

Figure 2. Deformation of the intermediate support from its own weight in the transverse direction, the mass of the superstructure of vertical temporary loads and seismic forces

Consequently, the values of stresses and displacements of the soil at the base of the foundation from this combination of loads increased significantly and did not exceed the calculated resistances, namely:

σ_u = 0,485,3 MPaR=0,6353 Mpa;  S =

Consequently, the deformation of the base relative to overturning was ensured, and the tension of the ground of the foundation base did not exceed its normative design resistance. The assessment of the strength of the ground rocks around the foundation of the foundation and the analysis of the priority of internal processes are carried out using the developed algorithm for calculating the sequential cycle.

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