SU1527370A1 - Concrete gravity dam for seismic regions - Google Patents

Abstract

FIELD OF THE INVENTION The invention relates to hydraulic engineering. The purpose of the invention is to simplify the design of the seismic resistance of the dam and the production technology, as well as to increase its reliability in operation. Each section of the dam is made of upper and lower blocks 1 and 2 and a seismic isolation layer 3 separating them. Layer 3 is made of a material whose acoustic rigidity differs from the acoustic rigidity of concrete, for example sandy gravel soil. The upper unit 1 and layer 3 are supported on the base, with the layer 3 being perpendicular to the resultant static and seismic forces acting on the dam. With this arrangement, the seismic insulating layer is always compressed and does not perceive a shear load. In addition, since the seismic insulating layer does not have access to the pressure face, there is no need for special waterproof seals. 5 il.

Description

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Figg

The invention relates to the field of hydraulic engineering.

The purpose of the invention is to simplify the design of an earthquake-resistant dam and the production technology, as well as to increase its reliability in operation.

FIG. 1 shows a concrete gravity dam of the proposed construction, a cross-section; FIG. 2 is a graph showing the effect of the seismic layer on the distribution of seismic accelerations over the height of the dam; FIG. 3 - the system of forces acting on the dam; in fig. 4 is a diagram for determining the angle of the grapho-analytical method; FIG. 5 - values of vertical stresses at the pressure face of the dam in sections A-A and B-B (Fig. 1).

The dam consists of sections (not shown) in length, each of which is from- (Complete from upper block 1, lower block 2, seismic insulating layer 3, for example, from sand and gravel soil. In the upper block, lost 4 for arranging the grout curtain 5. The upper block and the layer are supported on the base. Layer 3 is oriented perpendicular to the static and seismic loads (Fig. 3 and 4). The angle of inclination to the horizontal is determined by the formula:

tgoi

with t to

1 + K

J

Jy

H

de C - coefficient characterizing

the geometry of the structure of the structure, whose value increases with a decrease in the laying of the lower edge of the dam; At about - volumetric weight of concrete dam,

t / ZT / m, 50

H - the height of the dam, m; B - dam width along the base, m; K is the mean horizontal seismic acceleration acting on the dam, in series, gi K is the same for vertical acceleration;

g acceleration of free fall, m / s.

about 5 0

5 0 5

0

five

0

Layer 3 is located in the lower part of the shaft; 1 m distance b from the pressure face, which allows separation between them is lost 4.

The presence of a seismoisolation layer oriented and located as indicated above leads to the division of the dam sections into two block layers interacting through the material: upper and lower, each of which rests on the base. Since the large mass of the structure is enclosed in the upper block, and its area of bearing on the base is less than that of the lower block, the upper block transfers to the base a large specific load (per unit contact surface), which leads to a favorable redistribution of static compressive stresses at the base, nx increase at the base under the top block compared to that under the base block.

Studies show that compressive stresses in the basement under. the upper unit when tilting the seismic insulating element at an angle about the AO is 3 times higher than under the lower unit (Fig. 5). The increased level of compressive static stresses at the base below the ridge prevents the formation of cracks in the cementing curtain during earthquake. The orientation of the layer perpendicular to the resultant of all forces ensures a constant compression of the material of the layer and the transfer of only compressive forces to the lower block of the dam.

Work designs.

Under seismic impact, the construction, due to the seismic insulating layer of the material greater than concrete, makes complex vibrations: the upper block of the dam oscillates in the same way as the tambourine, rocking on a small area support, and its vibrations are limited by a very damping 1M insulating layer material. Due to these two factors: oscillations. A large mass with a small footprint and the presence of a damper significantly changes the spectrum of free oscillations of the dam - periods of oscillations increase significantly (as shown by studies for a 100 m dam with В / Н 0.7 this increase is about four times), which leads to a sharp

five

reduce seismic load on the structure. In this case, the lower block of the dam plays the role of a thrust array, which is perceived by the inertial load transmitted through the upper block through the material of the insulating layer. The significant difference in the deformability of the concrete and the material of the seismic insulating layer makes it possible for the oscillation phases of the two blocks to differ, significant (almost) differences in the amplitudes of their oscillations, which leads to a decrease in the shear seismic load, i.e. to increase the stability of the structure during earthquake.

Claims (1)

Invention Formula Concrete gravity dam for seismic areas, each section of which is made of blocks separated by a seismic insulating layer of material inclined towards the headwater, whose acoustic rigidity differs from acoustic 273706 the rigidity of concrete, characterized in that, in order to simplify the design and production technology and increase its reliability in operation, the upper unit and the layer separating it from the lower unit are interfaced with the base, while the angle of inclination of the layer to the horizon by formula ten tgo С ± К  IF five 0 five 1 ± TF IT where C is a coefficient characterizing the geometry of the structure of the structure; K is the same for vertical acceleration; H - height ppotin, m, B - width of the dam along the base, m g - volume weight of the concrete of the dam, g t / m; K is the mean horizontal seismic acceleration acting on the dam, in fractions gj g is the acceleration of free fall, m / s. W srig.Z Recognition fi-tudpocmamu4ecKoe pressure on the dam 0.5N G-weight of the dam 0.5gl GdN ./T/.// .O.Z5 K-rs-m-H Accepted for 9 points Iff.n 9  Gdep, .- 2., 7 we get dt anason angle ,, o when rozli n. on top PC FIG.