RU2012749C1 - Trussed beam - Google Patents

Abstract

FIELD: construction. SUBSTANCE: beam made of steel, or aluminium, or plied wood, etc. , has a steel tie rod made of two tension members and one compressed post. The beam is prestressed by a load constant during temperature and other displacements, by means of a tie. This tie acts as a compressed post. The main sizes of the beam and the tie rod are determined from a system of two differential equations presented in the description. EFFECT: increased strength of the construction. 2 cl, 2 dwg

Description

 The invention relates to building and bridge structures. It can be used to cover spans of industrial and civil buildings and bridge spans, as well as to strengthen exploited structures.

 Known truss beam, truss which has a stretched element and one, two or more compressed racks.

 A disadvantage of the known truss beam, pre-stressed by constant force using a special connection included in the stretched element of the truss, is that the prestressing force is not used fully enough to create negative bending moments in the beam (negative in sign).

 The aim of the present invention is to provide such a trussed beam, pre-stressed by constant force using a special connection, in which the constant pre-stress force would be used more fully to create negative bending moments in the beam. In other words, in which he would have the same prestressing force created by a special bond, and ceteris paribus, the negative bending moments in the beam would have a large value.

 This goal is achieved by setting the connection, which creates a constant force pre-stressing the truss in a compressed rack and due to the new ratio of the main dimensions of the beam and truss.

 In FIG. 1 schematically shows a truss beam; in FIG. Figure 2 shows the forces with which the elements of the spreel are applied to the beam, which are prestressed by a constant force by means of a special connection.

 The elements of the truss 0-3 and 2-3 (see Fig. 1) are stretched, the strut 1-3 is compressed. The stretched elements of the truss are inclined to the lower belt of the beam at an angle γ and at an angle α to the strut 1-3.

 Negative bending moment in the beam arise from the force Nс and from the horizontal forces Нш. The negative moment from the forces Нш is equal to the product Нш · Z, where Z is the shoulder of the forces Нш relative to the neutral axis 0-0.

 The proposed beam differs from the prototype in that the connection, which creates a constant pre-stress force in the stretched elements of the truss, is rearranged from the stretched element of the truss 0-3 or 3-3 in a compressed rack 1-3, as well as a new ratio of the main dimensions of the beam and truss.

= const (2).In the strut, the bond creates a compressive stress force Nc, and in the stretched elements of the spreel, a constant stress force S. These forces are found by the formulas
N _c = 2Scosα = 2S sinγ, (1)
S =

= const (2).

 A change in the angle γ at temperatures of elongations and contractions of the stretched elements of the truss and the beam will not affect the force S, if you put in the rack a link that creates the force Nc, which is in the same functional dependence on the angle γ as in formula (2).

Suppose that the connection in the prototype and the connection in the proposed beam creates the same absolute value of the force equal to P (this means that the cost of the bonds is approximately the same). The rearrangement of the bond from the extended element of the truss to the compressed strut leads to an increase in the force Nc from Nc '= 2Pcos α = 2Psin γ to Nc''= P and to an increase in the strength Hsh from Hsh1 = Pcos γ to Hsh' = 0.5сtg γ · P. In this case, the negative bending moment in the middle of the beam increases by
ΔM = P [0.5l (0.5-sinγ) + Z (0.5ctgγ-cosγ)]
The increase in negative bending moments reduces the positive bending moments that occur in the beam from the action of the load on it. This leads to an increase in the bearing capacity of the beam.

(3) где Х1 - усилие в растянутых элементах шпренгеля, возникающее от действия на балку нагрузки.The new ratio of the main dimensions of the beam and the truss is determined by a system of two differential equations

(3) where X1 is the force in the stretched elements of the spreel arising from the action on the load beam.

 In a trussed beam having γ and Z obtained from equations (3), from the same load and ceteris paribus, the force X1 will be maximum and the beam mass will be minimal.

.In the stretched elements of the truss, the connection can create a pre-stress S, greater than the force X1. Denote the degree of prestressing of the sprengel by ν. It is equal to ν =

.

x₁Δ_1p+ηνx₁Δ $\genfrac{}{}{0ex}{}{\text{н}}{\text{1}}$ _p (4) где Uо - потенциальная энергия основной системы;
Δ $\genfrac{}{}{0ex}{}{\text{н}}{\text{1}}$ _p - перемещение силы Х1 по ее направлению, возникающее от действия на балку нагрузки;
Δ $\genfrac{}{}{0ex}{}{\text{н}}{\text{1}}$ _p - перемещение силы Х1 по ее направлению, условно названное перемещением теневой геометрической нелинейности;
η - коэффициент полноты диаграммы P= f(Δ) при теневой геометрической нелинейности.The potential energy of the trussed beam pre-stressed by constant force during temperature and other movements is determined by the formula
U = U _o -

x ₁ Δ _1p + ηνx ₁ Δ $\genfrac{}{}{0ex}{}{\text{n}}{\text{1}}$ _p (4) where Uо is the potential energy of the main system;
Δ $\genfrac{}{}{0ex}{}{\text{n}}{\text{1}}$ _p is the movement of the force X1 in its direction, arising from the action on the load beam;
Δ $\genfrac{}{}{0ex}{}{\text{n}}{\text{1}}$ _p is the movement of the force X1 in its direction, conventionally called the movement of the shadow geometric nonlinearity;
η is the coefficient of completeness of the diagram P = f (Δ) with shadow geometric nonlinearity.

 The bond, which maintains a constant force X1 during temperature displacements, keeps it constant during displacements of shadow geometric nonlinearity. Based on this, equation (4) is written.

As γ and Z increase from zero to the values obtained from equations (3), the force X1 increases and the displacement Δ _1p increases. Since the displacement of the shadow geometric nonlinearity Δ $\genfrac{}{}{0ex}{}{\text{n}}{\text{1}}$ _p decreases, then the potential energy of the truss beam, as shown by equation (4), decreases. Equation (4) also shows that with an increase in the degree of prestressing of the truss beam, its potential energy from the same load and ceteris paribus decreases. Reducing potential energy, as you know, makes it possible to increase the efficiency of the design.

 Rearrangement of the connection, which creates a constant pre-stress force, from the stretched element of the truss to the compressed strut gives a new result. Only due to such a permutation (other conditions are equal) does the negative bending moment in the beam increase. And this makes it possible to increase the economy of the beam, while maintaining its strength and rigidity. In addition, permutation of the connection leads to a simplification of the design. The inclusion of a link that creates a constant pre-stress force in a compressed rack practically means replacing the rack with a link. There is no need to do a stand. Sprengel is more economical and simpler. As for the new ratio of the main dimensions of the beam and the truss, it provides additional material savings.

Claims (2)

 1. SPRINGEL BEAM, comprising a compressed strut, characterized in that it is equipped with a link included in the strut to create a constant pre-stress force in the stretched elements of the truss during temperature and other movements. 2. The beam according to claim 1, characterized in that the ratio of the main dimensions of the beam and the truss is determined by a system of two differential equations

,
where x _i is the force in the stretched elements of the truss arising from the action on the load beam;
γ is the angle of inclination of the stretched elements of the truss to the horizontal;
Z - shoulder horizontal forces compressing the beam relative to the neutral axis of the beam.

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