Stress Isobar or Pressure Bulb Concept
The isobar, also known as a pressure bulb, is a line that connects all points below the ground surface where the vertical pressure is the same. This line takes the form of a curved surface, resembling a bulb in shape. It is called the pressure bulb because the vertical pressure at all points in a horizontal plane, at equal radial distances from the load, is equal. The pressure at points inside the bulb is greater than that at a point on the surface of the bulb, while pressures at points outside the bulb are smaller.
A pressure bulb may be drawn for any applied load, and any number of pressure bulbs may be created, each corresponding to a specific value of stress. A system of isobars can be used to indicate the decrease in stress intensity from the inner to the outer ones, similar to the layers of an onion. An isobar diagram is a system of isobars that shows the distribution of stress intensity.
Fig.1: Pressure bulb for point loads
Fig. 2: Pressure isobar for footing
Procedure for plotting pressure bulb
To plot an isobar, a specific procedure must be followed. First, you need to determine the value of the constant pressure that the isobar represents. Once you have this value, you can proceed with the plotting process.
To start the plotting process, draw a horizontal line on a graph paper to represent the constant pressure level. Then, locate the data points that correspond to the given pressure value along the vertical axis of the graph paper. Connect these data points using a smooth curve, which will represent the isobar.
It is important to note that isobars are used to represent the distribution of pressure in a system, such as in weather maps or in the study of thermodynamics. By plotting isobars, scientists and researchers can better understand the pressure patterns and relationships within a system.
The context given is related to the stress distribution formula for a specific situation. The formula describes how stress is distributed over a certain area, specifically the 10% isobar. The isobar refers to a line on a map or graph that connects points with equal pressure values. In this case, the 10% isobar is a line that connects points with equal pressure values that are at 10% of the maximum value.
The stress distribution formula provides information on how much stress is present in a specific area, which is important in various fields, including engineering and physics. The formula may be used to determine the amount of stress that a structure can withstand or the amount of stress that is placed on a particular material under certain conditions.
Overall, the given context provides information on a specific mathematical formula used to understand the distribution of stress over a particular area. This formula can be applied in various fields to help make important calculations and decisions related to stress management and material properties.
where,
The given context describes a process of calculating the r-values for different values of z, based on the corresponding KB-values. The first step is to assume various values for z, and then compute the corresponding KB-values. Next, the r/z-values are obtained for each computed KB-value. Finally, for the assumed values of z, the corresponding r-values can be calculated.
The context also mentions that for the same value of r on any side of the z-axis or line of action of the point load, the value of something is affected. However, the specific value being referred to is not clear from this context alone. More information or context would be needed to understand the meaning of this statement.
The given context discusses the construction of an isobar, which is a graphical representation of the distribution of stresses in a body. The isobar is symmetrical with respect to a certain axis, which means that one half can be drawn and the other half can be obtained through symmetry.
At the point where r=0, the value of KB is 0.4775. This point is significant because it marks the intersection of the isobar with the line of action of the load. The depth of this intersection point can be calculated using the information provided in the context.
The calculations are best performed in the form of a table as given below:
Table 1: Data for isobar ofper unit area.
| Depth z (units) | Influence coefficients KB | r/z | r (units) |  |
| 0.5 | 0.0250 | 1.501 | 0.750 | 0.1Q |
| 1.0 | 0.1000 | 0.932 | 0.932 | 0.1Q |
| 1.5 | 0.2550 | 0.593 | 0.890 | 0.1Q |
| 2.0 | 0.4000 | 0.271 | 0.542 | 0.1Q |
| 2.185 | 0.4775 | 0 | 0 | 0.1Q |