Civil Notes Logo AboutCivil Logo Residual Stresses, Definition, Properties, Effect on Behavior of Tension Members

Residual Stresses - Definition, Properties and Effect on Behavior of Tension Members

Advertisements

They have more surface exposure per unit volume, the flange tips tend to cool faster than flange-to-web junctures.

  • Tension members response to load is much similar to that of tensile-test coupon .
  • Member behavior may differ from coupon behavior because of:
  • Slip in bolted & riveted connections
  • Non-linear behavior of connections
  • Residual stresses in member
  • Residual stresses result principally from non-uniform cooling of hot rolled or welded shapes and from cold straightening of bent members.
  • They have more surface exposure per unit volume, the flange tips tend to cool faster than flange-to-web junctures.
  • Similarly, Central portion of web tends to cool faster than junctures
  • As a result, metal at junctures continues to contract as it cools after flange tips and web interior have cooled to temperature of surroundings.
  • This contraction is partially restrained by cooler metal.
  • Developing tensile stresses in regions of junctures & compressive stresses in remainder.
  • These are called residual Stresses
  • Magnitude and distribution of thermal residual stresses are influenced to considerable degree by geometry of x-section
  • 20 W's were investigated
  • An investigation on W's Revealed that flange tip stress varied from 4.1 to 18.7 Ksi
  • Residual stresses in web varied from 41Ksi comp; to 18.2Ksi tension.
  • Showing some W's develop residual tension over entire web, instead the pattern shown.
  • Only one out of 20 sections was thicker than 1 in.
  • Residual stresses tend to increase in magnitude with increase in thickness
  • Because of high concentration of heat, tensile residual stresses at the weld in welded members usually equal the yield strength of the weld metal itself.
  • Residual stresses in welded shapes are determined by section geometry and method of preparation of components.
  • Example H may be fabricated from Universal-mill plates or from plates flame-cut to width.
  • Because they are quenched and tempered, A514 rolled steel shapes are partially stress-relieved, so residual stresses are small
  • Quenching is the act of rapidly cooling the hot steel to harden the steel.
  • Quenched steel is hard and brittle. Often it is just too brittle and must be made more malleable, This is achieved by a process known as tempering.
  • The quenched steel is heated again but this time to a temperature between 200C and 300C.
  • When the metal reaches the tempering temperature, it is quenched again in cold water or oil. The result is a steel that is still hard but is more malleable and ductile
  • Fabricating operations such as cambering and straightening by cold bending also induce residual stresses.
  • These stresses are superimposed on the thermal residual stresses.
  • If member is straightened by rotorizing, which is a continuous procedure, the residual stress distribution will be changed along entire length of member.

Effect on Behavior of tension Members

Effect of Residual Stresses on Behavior of Tension Members

SJ Logo About Us | Site Map | Privacy Policy | Contact Us | © 2014 WebTechTix