Thrust Block
Thrust block, abbreviated as TB, is a structural component used in plumbing and pipeline systems to resist the axial forces or thrust generated by the fluid pressure within the pipes. These forces can occur when the fluid inside the pipe changes direction, such as when there are bends, tees, or other fittings in the pipeline. Thrust blocks are commonly used in underground water and sewer systems, as well as in other fluid transport systems. The primary purpose of a thrust block is to prevent the pipes from moving or separating due to the internal pressure forces.
Thrust Block Index
- Thrust Block Advantages and Disadvantages
- Here's How a Thrust Block Works
- Step 1 - Resultant Thrust Formulas
- Step 2 - Thrust Block Volume Formulas
- Thrust Block Drawings
Here's how a thrust block works
- Counteracting Forces - When fluid flows through a pipe and encounters a change in direction, it exerts a force in the direction opposite to the change. This force is known as thrust. For example, if a pipe makes a 90-degree turn, there will be a thrust force trying to push the pipe straight ahead.
- Thrust Block Construction - A thrust block is typically a mass of concrete or other strong and stable material that is placed around the pipe at points where thrust forces are expected to occur. It is designed to distribute and absorb these forces.
- Resistance to Movement - The thrust block's weight and structural strength resist the axial forces by preventing the pipe from moving or shifting. It essentially anchors the pipe in place and ensures that it remains stable under pressure.
- Preventing Damage - Without a thrust block, the thrust forces could potentially cause damage to the pipe joints, fittings, or even lead to pipe separation, which could result in leaks or a pipeline failure.
The size and design of a thrust block depend on various factors, including the pipe diameter, material, the angle of the bend, and the fluid pressure. Engineers and plumbers calculate the necessary dimensions and reinforcement of thrust blocks to ensure they can effectively counteract the thrust forces and provide stability to the pipeline system.
Step 1 - Resultant thrust
Resultant thrust FormulasResultant thrust is the overall thrust force acting on a pipeline at a change in direction or slope. It is the combined effect of the horizontal and vertical components of the thrust force. When a pipeline changes direction or slope, there is a tendency for the pipe to exert a force on the surrounding soil. The resultant thrust (R) is the vector sum of these horizontal and vertical components and is calculated using the Pythagorean theorem. |
||
\( R = \sqrt{ T_h^2 + T_v^2 } \) (Resultant Thrust) \( T_a = p \; A_c \) (Axial Thrust) \( T_h = T_a \; tan \left(\theta\right) \) (Horizontal Thrust) \( T_v = T_a \; tan \left(m\right) \) (Vertical Thrust) |
||
Symbol | English | Metric |
\( R \) = resultant thrust | \( lbf \) | \( N \) |
\( T_h \) = horizontal thrust (axial thrust caused by changes in slope) | \( lbf \) | \( N \) |
\( T_v \) = vertical thrust (axial thrust caused by changes in slope) | \( lbf \) | \( N \) |
\( T_a \) = axial thrust (force acting along the pipe due to changes in direction or slope) | \( lbf \) | \( N \) |
\( p \) = internal pressure of the pipeline | \(lbf \;/\; in^2\) | \( Pa \) |
\( A_c \) = area cross-section of the pipeline | \( in^3 \) | \( mm^3 \) |
\( \theta \) = angle of the bend | \( deg \) | \( rad \) |
\( m \) = slope of the pipeline | \( ft \) | \( m \) |
Step 2 - thrust Block Volume
thrust block Volume FormulasThrust block volume is the amount of concrete or material needed to construct a thrust block, which is a stabilizing structure used in the design of pipelines at changes in direction or slope. The purpose of a thrust block is to resist the forces generated by changes in the direction or slope of a pipeline and prevent movement or displacement. It's important for the thrust block to extend below the frost line and provide sufficient resistance against the horizontal and vertical components of the thrust forces. |
||
\( V_{tb} = M_b \;FS \;/\; S \; h \; FS_s \) (Thrust Block Volume) \( M_a = D \;/\; 2 \) (Moment Arm) \( M_b = R \; M_a \) (Bending Moment) |
||
Symbol | English | Metric |
\( V_{tb} \) = thrust block volume | \( in^3 \) | \( mm^3 \) |
\( M_b \) = bending moment | \(lbf \;/\; sec\) | \(kg-m \;/\;s\) |
\( FS \) = factor of safety | \(dimensionless\) | |
\( S \) = allowable stress in the concrete | \(lbf \;/\; in^2\) | \(Pa\) |
\( h \) = depth of the thrust block (how deep the block extends into the ground) | \( ft \) | \( m \) |
\( FS_s \) = factor of safety of soil bearing capacity | \(dimensionless\) | |
\( M_a \) = moment arm | \(lbf \;/\; sec\) | \(kg-m \;/\; s\) |
\( D \) = OD of pipe | \( in \) | \( mm \) |
\( R \) = resultant thrust (see step 1) | \( lbf \) | \( N \) |
Thrust Block Drawings
Tags: Force Pipe Support Pipeline