The angle, radius, and curvature of an arch dam determine its classification. Constant radius arch dams, variable radius arch dams, constant angle arch dams, and double curvature arch dams are the four types of arch dams. An arch dam is a solid wall with a curved shape that is usually made of cement concrete. Where river valleys form, it is desired.The operation of an arch dam is similar to that of a cantilever retaining wall with some arch action. The entire curved wall stands on a wide base and uses horizontal thrust to transfer loads to the dam’s two ends. Another crucial factor to remember is that the load-bearing capacity of an arch dam is proportional to its curvature; the greater the curvature, the greater the load resistance.
Table of Contents
Arch Dams of Various Types Construction
Arch dams can be divided into four different types: Dam with a constant radius arch Dam with a variable radius arch Dam with a constant angle arch Dam with a double curvature arch Dam with a Constant Radius Arch The outer side curve of the arch is designed with constant radii at all heights in a Constant Radius Arch Dam. Simultaneously, the inner curve of the arch is built with a decreasing radius from the top to the bottom of the dam.Extrodos refers to the arch’s outside side curve, whereas introdos refers to the arch’s inside curve. Extrados always looks upstream, while intrados always faces downstream.
The dam’s thickness is greater at the bottom to withstand hydrostatic pressure from water, and it is thinnest at the top. The cross section of a constant radius arch dam resembles a right angled triangle, with extrados represented by the vertical line and intrados represented by the hypotenuse. In this form of arch dam, the centres of all circular curves of intrados are on the same line, and the centres of extrados are also on the same line. As a result, this dam is also known as a constant centre arch dam. The building of constant radius arch dams necessitates a considerable volume of concrete. These are the most popular types of arch dams, and they’re best for valleys with a U shape.
Arch Dam with Variable Radius
The central angles of a constant radius arch dam do not remain constant throughout time. At varying elevations, the angle formed by each arch ring at its centre varies. At the top of the dam, the central angle is greatest, and at the bottom, it is smallest. However, according to certain suggestions, the safest angle for an arch dam is 133o 34′. However, because of its design, it is impossible to maintain a consistent angle across the dam.As a result, the middle arch ring has the safest angle. The angle will grow towards the top and decrease at the base of the dam as you progress from the middle ring. However, the angle at the top of the dam should not exceed 150o, as determined during its design.
The radii of both extrados (outer side) and intrados (inner side) curves are altered with relation to elevation in a variable radius arch dam, as the name implies. The radius is greatest at the top of the dam and smallest at the bottom. Because the central angles of the arch rings vary at different heights in this scenario, it is also known as a variable centre arch dam.From the top view, the centre line or crown line on the downstream face appears to be a vertical line, and both sides of this line appear battered. A vertical line appears at the abutments, and the upstream side appears to be vertical as well. As a result, we can create overhangs at both the crown and the base.
Constant Angle Arch Dam
Variable radius arch dams are generally more cost effective than constant radius arch dams. Only 58 percent of the concrete used in a constant radius arch dam is used in this structure. V-shaped valleys are better suited to this style of arch dam.Arch Dam with Variable Radius Dam with a Constant Angle Arch A constant angle arch dam is one in which the centre angle of each arch ring remains constant throughout its height. It’s made possible by modifying a variable radius arch dam. In this example, the central angle is 1330 34′, which is the safest and optimal angle. It is important to provide overhangs at the crown and abutments for this sort of arch dam. When it comes to overhangs, there are a few things to keep in mind.
This form of arch dam is less expensive than the other two, requiring only 43% of the concrete used to construct a constant radius arch dam. For V-shaped valleys, a constant angle arch dam is better. Dam with a Constant Angle Arch Dam with a Double Curvature Arch Curvature is provided not only in the horizontal but also in the vertical direction in a double curvature arch dam. It signifies that the cross section of a twofold curvature resembles a curve as well. Because the entire dam resembles a shell, it is also known as the shell arch dam. The thickness of the arch wall is lowered due to the double curve. Non-vertical dams, on the other hand, are more difficult to build than the other three varieties. They also necessitate more solid foundations.
Dam with a Constant Angle Arch
The extrados radius is smaller in this type of dam (i.e. outside the curved surface of the arch is kept fixed at any elevations, from the top of the dams towards its base). However, because the depth below the crest will increase in larger dams, the radius of the Intrados, i.e. the radius of the downstream face, gradually increases with decreasing radius to increase the thickness. Extrados, intrados, and the horizontal line’s midline are all at a standard level. The continuous centre arch dam is a vertical line that depicts the arrangement of the centres at completely various heights. The U-shaped face is vertical on this type, and the arch thickness is proportional to the peak.
The constant angle arches are a type of dam in which the centre angles of the arches remain constant and radial at various heights. The central angle of the arch rings at all elevations in such dams is the same magnitude from the dam’s height to its base.Based on the thin cylinder principle, the central angle of constant angle arch dams should be between 133° and 134° for cost-effective design. However, depending on the size of the valley, the centre angle can range from 100 to 150 degrees in actual construction. The greatest arch action is established in the arch rings at all elevations in such dams, and the thickness of a constant-angle arch dam is less than that of a constant radius or constant length arch dam.
Because it resembles a rock structure and is curved in elevation along the plan, this style of dam is also known as cupola dams or shell arch dams. In comparison to a single curvature arch dam, this dam has a small thickness. It is more cost-effective in India because of its reduced thickness; the Idukki dam in Kerala is an example of a double curvature arch dam. ARCH-GRAVITY DAM: When the arch thickness is greater, these dams are referred to as arch-gravity dams, and they are built in conjunction with gravity dams. Extrados of arch rings with gradually increasing radius in the lower half of the valley can be found in such dams. At the base of the waterfall, there is batter on the upstream face.
The arch dam is designed so that the force of the water against it, known as hydrostatic pressure, presses against the arc.
A variable radius arch uses about 58% of the concrete required in constant radius arch dams.
Arch dams are made from concrete. They are curved in the shape of an arch, with the top of the arch pointing back into the water.