Thermal movement

Free and restrained thermal strain, movement and force of a member or a building segment, the movement an expansion joint must take, and the length between expansion joints against your criterion. Use it for long roof and floor framing, exposed members, rails and pipes, parking structures and masonry or concrete walls.

Inputs of the thermal movement #

• Material: structural steel (α = 6.5 × 10⁻⁶ /°F), stainless steel (9.6), aluminum (13), normalweight concrete (5.5, the middle of the ACI 209R range, which depends on the aggregate), clay masonry (4.0) and concrete masonry (4.5, TMS 402-22 4.2.4, to confirm against the code text), wood along the grain (2.0); or Entered with your own α.
• Length between joints L: the member, or the building segment between expansion joints.
• Design temperature change ΔT: your value. Federal Construction Council Technical Report No. 65 (1974) takes the larger of the summer temperature exceeded 1 % of the time less the mean temperature during construction, and that mean less the winter temperature exceeded 99 % of the time. Metric: °C (a change converts by 5/9, without offset).
• Restrained force: degree of restraint r (100 % between rigid supports, the upper bound; your estimate where the supports flex), E, A, and the member's available axial strength from its own calculation (φPn or Pn/Ω).
• Expansion joints: the joint's rated movement; the allowable length for ΔT that you read from TR-65 Fig. 1 (heated building, hinged column bases) or your own criterion; heating and cooling (air-conditioned +15 %, unheated −33 %), fixed column bases (−15 %) and a building much stiffer at one end (−25 %), the report's adjustments as the AISC and NRC guidance quote them (to confirm against the report).

Each of the three checks can be turned off. There is no auto-design: nothing here is a member size.

Checks performed #

Limitations #

• Axial movement only: no thermal gradient through the depth (bowing), no frame analysis of the columns that restrain a roof, no creep or shrinkage of concrete and masonry (add them to the movement where they matter).
• The restraint is one number; the force in a real frame depends on the column and connection stiffness.
• The TR-65 chart is not built in: you read the allowable length from it.

Verification examples #

Verification status: 7 values compared in 5 examples (5 published, 0 hand calculations from the cited equations): 7 within tolerance, 0 recorded deviations. Code basis: written without the code document on hand, and confirmed only in part through published examples.

Hand values of the formulas (tests/test_verify_thermal_movement.py); no published worked example is on disk: