How to judge the direction of shear force! Concrete!

In the mechanics of materials, it is stipulated that the element body is positive from the top left and the bottom right, and then the others are inferred according to the theorem of shear stress equality. The relationship between shear stress and normal stress depends on whether it is tensile or torsional.

Calculation formula. 1. Average shear stress.

v - calculate the shear force on the cross-section;

a - calculate the cross-sectional area;

b - cross-sectional width; h - high cross-section.

2. Shear force calculation formula based on shear flow.

v - calculate the shear force of the plane acting along the plane of the web;

s - calculate the area moment (static moment) of the neutralization axis of the section above or below the shear stress;

i – moment of inertia of the cross-section;

t - web thickness.

Causes the subject to be studied to produce clockwise.

Rotational shear force.

Shear force is a force that cannot be used to build a house, just as it cannot be used to build a house with water pressure. Shear is a force, but it is not necessarily a destructive force. When there is an action perpendicular to the cross-section, the harm depends on how much the shear resistance of the component itself is, and when the shear force is greater than the shear resistance, the component will crack or even break.

The shear force plot is drawn on either side of the member, but it must be marked plus or minus. If the question is how to determine the direction of the shear force, it is to take the micro section to consider, the left section shear force (arrow) is positive upward, and the right section shear force (arrow) is positive downward.

If the left isolator moves upward relative to the right isolator, the shear force in the rod is positive, that is, the upper left and lower right are positive; Conversely, the lower left and the upper right are negative. In fact, it is the same as 'Ye Ruofeng's heart'.

It is stipulated that the establishment of a positive direction is positive when the rod segment under study has a clockwise rotational tendency, and vice versa.

1. Judgment of positive and negative shear direction: the direction of shear force is perpendicular to the action surface and points to the opposite transverse external force. The force that causes a material to shear deformation is known as shear or shear force.

The positive or negative of the shear force can be judged according to the positive and residual direction selected in the application. The section in which shear deformation occurs is called a shear plane. The key to determining whether the material is "sheared" is whether the cross-section of the material is relatively dislocated.

2. Judgment of the direction of the bending moment: Generally speaking, the positive and negative of the bending moment have different regulations in different disciplines. If the positive and negative of the bending moment is specified, the bending moment can be calculated algebraically.

In the calculation of column bending moments, the discrimination method of "positive for upper left and lower right, negative for lower left and upper right" is applied. Where the moment of the external force on the beam on the left side of the section is clockwise turning, or the moment of the external force on the right side of the section is counterclockwise turning, a positive bending moment will be generated, so the positive sign is taken; Otherwise, it is negative, that is, the left is backward and the right is reversed, and the bending moment is positive.

For a beam (referring to a horizontal component) in a civil engineering structure, when the lower side of the component section is under tension, we call the bending moment of this section as a positive bending moment; When the upper side of a component segment is under tension, we call the bending moment on this segment a negative moment.

It is stipulated that when the rod section under study has a clockwise rotation trend, it is in the positive direction, and vice versa, and the left isolator moves upward relative to the right isolator, then the shear force in the rod is positive, that is, the upper left and lower right are positive; Conversely, bottom left.

This is the equilibrium state of the beam under vertical loads. The vertical load is in the direction of the plumb, of course, the support reaction force is also in the direction of the plumb, and the load effects generated in the beam are bending moment m and shear force q, and of course the shear force is also in the direction of the plumb. As for the upward and downward movements, there is a downward and an upward shear force of equal magnitude on each section of the beam in order to maintain equilibrium, the downward is the load generated, the upward is the support reaction is generated, and the distance between the downward and upward is zero.

Static planar equations x 0, y 0, m 0. There are no horizontal loads here, so the internal forces are only in the plumb direction.

Since the self-weight of the beam is downward in the straight direction of the lead, the direction of counteracting this force should be upward (the opposite direction of the magnitude is equal), and we call this force in the direction of counteracting the self-weight force shear force.

Regulation of shear force: With the micro-section study, the shear force of the left section is positive upward, and the shear force of the right section is positive downward. The micro-section balance is in the vertical direction, which is the balance between the shear force at both ends and the vertical load of the micro-section.

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