CAESAR_II_减震弹簧

CAESAR II - Applications Guide Sway Brace Assemblies Restraints 3-49 Sway Brace Assemblies The sway brace is commonly used to allow unrestrained thermal movements while “tun- ing” the system dynamically to eliminate vibration. In this respect sway brace resembles a spring: it may be pre-loaded in the cold (installed) position, so that after thermal pipe growth it reaches the neutral position and the load on the system in the operating condition is zero or negligible. The sway brace is composed of a single compression spring enclosed between two mov- able plates. The spring is pre-compressed a full inch providing an initial force that instan- taneously opposes vibration. Any movement from the sway brace neutral position is opposed by a load equal to the pre-load plus travel from neutral position times the sway brace spring constant. Once maximum allowed travel (usually 3-in. in either direction) is reached the sway brace locks preventing additional movement. Manufacturers typically recommend a specific size sway brace for a given pipe nominal diameter. A more specific sway brace selection is possible when the exact restraining force required to control the piping vibration is known. The energy necessary to control the piping is pro- portional to the mass, amplitude of movement, and the force causing the vibration. From this relation the exact restraining force required to control the piping vibration may be cal- culated and an appropriate sway brace size selected. Once selected, the sway brace may be modeled in CAESAR II using a combination of a bi-linear restraint and a translational restraint: Sway Brace Assemblies CAESAR II - Applications Guide 3-50 Restraints In the event that the sway brace is to be installed in the operating condition (or the neutral position is to be adjusted in the operating position), the modeling is CAESAR II is a little more complex. In this case, before modeling the sway brace, you must analyze the piping system without the sway brace to obtain displacements from the cold to neutral operating position: Run analysis on the system without the sway brace to obtain the displacements from cold to operating condition. For the sake of this example, let’s assume the CAESAR II calcu- lated displacement from cold to operating position is 0.5 in. In the SUS case the displacement D2 (vector 2) represents the pre-load in cold position. Under shutdown conditions, the pipe returns to its cold position and the brace exerts a force as previously described. Sustained case restraint loads on sway brace = Pre-Load + Hot Deflection * Spring Rate In OPE the displacement allows thermal expansion and the sway assumes neutral position exerting zero or negligible load on the pipe. Operating case restraint loads on sway brace =~ 0.0 (does not restrain thermal expansion) Example: Sway Brace Installed in the Cold Position Sway Brace Installed in neutral position as shipped Spring rate: 150 lb./in. Initial loading: 150 lb. Allowed movement: 3 in. CAESAR II - Applications Guide Sway Brace Assemblies Restraints 3-51 Example: Sway Brace Installed in Operating Condition Sway Brace opposing compression force (movement occurs after pre-load is overcome) Spring rate: 150 lb./in. Initial loading: 150 lb. Allowed movement: 3.0 in. Calculated displacement: .5 in. Note Be sure to include D2 in the sus- tained and operating cases.