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Structural test hinge support test

In architectural experiments, a large number of data and theories are obtained through a large number of experiments. In the process of doing the experiment, it is inevitable to consider a series of problems such as the experimental environment, the fixation of the device, the condition simulation of the field environment and so on. When it comes to the fixed test device, people usually design the support of the test device according to different purposes and different ideas of structural test. One idea is hinge support for structural testing.

Bearing in structural test is the equipment that supports the structure, correctly transmits the force and simulates the actual load mode, and usually bears the vibration and earthquake load in operation.

Articulated bracket refers to the bracket whose connection between the object and the required fixed position is articulated. In structural design, the common bearings or boundary conditions are simply supported boundary conditions realized by articulated bearings, which generally have the following forms.

1. living hinge bracket

Movable hinge supports allow members standing on the supports to rotate freely and move in one direction. It provides a vertical bearing reaction force, which can't transfer bending moment or horizontal force, can't prevent the object from moving along the bearing surface, can't restrict the object from rotating around the pin, but can restrict the object from moving along the negative normal direction of the bearing surface. It is more accurate than the fixed hinge bearing to be introduced below, because when the simple roller bearing rolls in the horizontal direction, the contact position with the specimen changes all the time, which leads to the change of the supporting position of the specimen, that is, the reaction point of the bearing changes.

The bearing reaction force of the living hinge bearing passes through the center of the pin and is perpendicular to the supporting surface. However, because the force on it cannot be determined, the specific direction is still uncertain, and it is necessary to analyze it in detail. The following figure is a schematic diagram of the living hinge bracket.

2. Fix the hinge bracket

Bearings that allow members standing on the supports to rotate freely but cannot move are called fixed hinge supports. Theoretically, the fixed hinge bearing should be able to bear horizontal force, but in the test of beam members, as long as one bearing is a movable hinge bearing, the horizontal force of the other bearing is usually very small and can be ignored. However, in practice, it provides a vertical bearing reaction, which cannot transmit bending moment or horizontal force. In the static load test of continuous beam, only one bearing is fixed hinge bearing, and the others are movable hinge bearings. In order to avoid the initial settlement caused by the manufacturing error of the specimen and the installation error of the bearing, the height of the hinged bearing of the continuous beam should be adjustable.

The force supported by the fixed hinge passes through the center of the pin, but the direction of the force cannot be determined. So in general, we are used to replacing this force with two orthogonal forces (usually horizontal and vertical forces).

3. Hinge support of beam-column specimen

In addition to the above-mentioned two forms of movable hinged support and fixed hinged support, there is also an external hinged support, that is, the hinged support of column specimens. Bearings used for test columns or walls also belong to fixed hinge bearings. In the column compression experiment, there is a high demand for the position of pressure point. Eccentricity is one of the main control factors for static load test under eccentric compression on long column testing machine. The circular-arc bearing with large radius of curvature is used in the platen of testing machine, which can not meet the requirement that the platen of cylindrical testing machine should be equipped with hinge bearings.

There are still many classifications of hinge bearings, and different classification methods will get different structural forms. For example, there are rolling hinge support, fixed hinge support, ball hinge support and knife-edge support (a specific form of fixed hinge support) in different ways. Steel is generally used.

4. Simply supported members and continuous beam supports

Usually, one end of such a member is a fixed hinge bearing and the other end is a rolling bearing. During installation, the axes of each bracket should be parallel to each other.

And the distance between the brackets is taken as the calculated span of the member. In order to reduce rolling friction

Force, the diameter of the steel roller should be selected according to the load according to the following table. But under no circumstances should the diameter of the roller be very small.

At 50 mm.

The top and bottom of the steel roller should be provided with pads, which can not only prevent the local compression damage of the specimen and the support area, but also reduce the damage.

Rolling friction. The width of the cushion block is generally not less than the vertical bearing width of the specimen, and the length of the cushion block is calculated according to the compressive strength of the component.

The calculation is not less than the actual supporting length of the member. The thickness h of the backing plate can accept the cantilever beam meter with triangular distributed load.

Calculation and not less than 6 mm, when it is necessary to simulate the embedded end support of the beam, the test pedestal can be anchored with a pull rod in the laboratory. As long as the embedding length between the bracket and the pull rod is ensured, the test requirements can be met.

5. Bearings for four-corner bearing plates and four-side bearing plates

Fixed balls should be placed when configuring the four-corner bearing plate, and the ball spacing of the four-corner bearing plate should not be too large.

It should be 3-5 times the thickness of the bracket. In addition, attention should be paid to the treatment of the four corners of the simply supported support. When the four-sided bearing plate has no cross beam, the four corners will tilt up after loading. So the bearing that can be pulled should be placed in the corner. The arrangement of plate and shell supports is shown in the figure.

6. Bearings at both ends of torsion member

For the beam torsion member test, in order to ensure the free rotation of the specimen in the torsion plane, the support form can be shown in the figure. The two ends of the specimen are erected on two freely rotating supports, and the rotation centers of the supports should coincide with the rotation centers of the specimen, and the rotation planes of the two supports should be balanced with each other and perpendicular to the torsion axis of the specimen.

7. Bearings at both ends of compression members

When testing columns and compression bars, spherical bearings or double-layer orthogonal knife-edge bearings should be set at both ends of the component respectively. The center of the spherical hinge should coincide with the loading point, and the intersection point of the double-layer knife edge should fall on the loading point. At present, there are two kinds of centering methods for test columns: geometric centering and physical centering. In theory, physics is better for China and France, but in fact, it is impossible to be in a state of physical alignment forever during the whole experiment. Therefore, it is more practical to take the centroid line at the control section of the column (generally, the equal section is the midpoint of the column height) as the center line, or to calculate the eccentricity during the test and center it according to the eccentricity line. When the column or compression bar is subjected to eccentric compression test, the distance between the knife edge and the geometric center line of the specimen can be adjusted by adjusting the screw to meet the requirements of different eccentric moments.

When testing the compressive bearing capacity of short columns on the testing machine, because the short columns do not bend longitudinally when damaged, the two ends are short-drawn.

No relative rotation occurs; Therefore, when one of the upper platen and the lower platen of the testing machine has a ball hinge, there is no need to add another knife edge at the short end.

This treatment is reasonable and can be consistent with the strength test method of concrete prism.