RU2652008C2 - Plant for testing stability of centrally compressed rods - Google Patents

Abstract

FIELD: testing equipment.

SUBSTANCE: invention consists of a base, a vertical rack welded to the base, at the top of which there is an opening for the hinged connection of a loading lever with the rack. At one (larger) end of the loading lever, a weight-holder is suspended; on the other (smaller), a lever-counterweight in the form of a rod with a thread and a nut-weight, or in the form of a telescopic-type lever, is provided to compensate the own weight of the loading lever with the weight holder. To fix the rods at the bottom under different test patterns, a special device consisting of two corners is provided, between the vertical flanges of which it is possible to clamp either the ends of the rods to be tested, or an insert simulating the lower hinge. Wherein one corner is welded to the base, and the second one can be pressed to the base with a bolt. For the upper hingedly fixed ends of the rods in the loading lever, from the lower side, at a certain distance, a small recess in the form of a groove is provided, into which the rods to be tested rest and which prevents the movement of their ends in the horizontal direction. In addition, a special weight-holder and a retaining frame for the deflections of the rods to be tested are provided.

EFFECT: increasing the carrying capacity of the rods.

4 dwg

Description

When some rods are in compression, their destruction does not occur because internal forces exceed the allowable tensile strength, but because the rods lose their stability, i.e. the straightforwardness of its form provided by the designer.

A device is known for testing the stability of a centrally compressed vertically mounted rod with a rigidly fixed end at the bottom and a free end at the top (Scheme 1). In this case, the vertical load on the free end is transmitted using the so-called rocker arm with two plates suspended at the ends of the latter, loaded simultaneously with weights of the same mass. The disadvantage of this device is that in construction such compressible rods are practically not used. However, to confirm the theoretical conclusions in laboratories, the “resistance of materials” is used.

Such a device is available at the Department of Material Resistance at St. Petersburg University and at the Department of Structural Mechanics at Voronezh State University of Architecture and Civil Engineering.

The purpose of the invention is to conduct research with two more rods with both ends that are differently fixed and most often encountered in construction practice, namely: rods with both ends pivotally attached (Scheme 3) and rods with one end rigidly fixed and the other pivotally fixed ( Scheme 2).

In FIG. 1 shows a General view of a device consisting of a base 1, a stand 2, welded to the base, the main lever of the load 4 with a counterweight lever 3, ending with a threaded rod and a load with the same thread to balance the weight of the lever of the load holder with the device for weights, suspended at the end of the main lever, and when examining the rods with a free upper end fixed directly to its end.

On the base 1 of the device, fixture 5 is shown, shown separately in FIG. 2. This device consists of two corners. One is welded to the base at a certain distance from the axis of the rack, corresponding to the length of the small shoulder of the lever-loader. The second corner is used for rigid pinching (fixing) the lower ends of the investigated rods in the first and second research schemes.

In the study of rods with rigid fastening at the bottom, they are clamped with bolts between the fixed and movable corners, and then with the help of bolts are pressed to the base through the existing slot. This provides a rigid (pinched) fastening.

To fix the upper ends of the test rods from horizontal movement when examining the second and third conditions for fixing the ends, a small recess ("groove") 6 is provided on the lower side of the load arm, which is also located at a distance from the axis of rotation of the load arm, equal to small shoulder. This recess also serves as a “hinge”, since there is no rigid fastening.

When examining rods with articulated ends, the lower end of the rod rests on the “hinge” shown in FIG. 2. This hinge is provided by the insert between the vertical shelves of the corners.

In all studies, a hoop holder is used (Fig. 3), consisting of a vertical rod with a small hole at the end, perpendicular to the plate being welded to the rod, two more plates are also welded at right angles to the lower side of the plate, between which the upper free end of the test rod is clamped. In this case, the lever-loader is removed. In studies with a lever-loader, the hoist is suspended at its end.

Since the deflections of the rods (deviations from the vertical) are different in different schemes, a special frame of FIG. 4, also installed in different places in height in 2 holes drilled in the rack 8. Installation sites (half height, two-thirds of the height and above) are marked with dots. The installed deflection lock frame is secured to the stand on both sides by nuts.

The experiments are carried out in the following sequence. At the desired height, a deflection frame of the deflection of FIG. 4, a test rod is inserted into it, the ends of which are fixed in accordance with the studied circuit. If a lever-loader is used to load a sample, then its own weight with a hoop is balanced by a compensator lever. After that, the locking frame is installed taking into account possible deflection and is fixed on both sides with nuts. Next, the rod is loaded. Upon reaching a fixed deflection, the load is calculated. The rods are studied in a similar manner under other conditions for securing the ends.

When examining a rod with a free upper end, the lever-loader is removed. At the upper end of the shaft, a hoop is mounted and secured with a bolt, FIG. 3.

According to the theoretical dependence (Euler-Yasinsky formula), the stability of a rod with pivotally fixed ends is provided, for example, by the load P. The stability of a rod with a rigidly fixed lower end and pivotally fixed upper can be ensured with twice as much external load than in the first case. And the stability of the rod with a free upper end and a rigidly fixed lower end can be ensured by four times less load than in the first case.

When examining other rods, the hoist is suspended at the end of the load arm using the slots there.

Claims (1)

A device for carrying out studies of centrally compressed rods for stability for three cases of fixing the ends of the rods, containing a base, a vertical stand welded to it, at the upper end of which there is a loading lever with a compensating lever for balancing the dead weight of the loading lever with a hoop at the end, serving at the same time with a loader of the upper ends of the test rods and their lock from horizontal movement, using the groove-recess from the bottom s of the loading arm, into which the upper ends of the test rods abut, fixtures for three cases of fixing the lower ends of the test rods, consisting of two angles, one of which is welded to the base, and the second, after pinching the ends of the rods or the hinge insert, is screwed to the base through a slot in the lower flange of the second corner, a hoop holder, suspended at the end of the loading arm or mounted on the free end of the rod without a loading lever, and a deflection fixation frame with erzhney fixed on the vertical stand depending on the study design.

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