**Tapered Members **

A built up plate member consisting of flanges welded to a variable depth web.

**Tapered Tread Wheels **

End truck wheels with treads which are tapered, the large diameter being toward the center of the span.

**Tensile Strength **

The longitudinal pulling stress a material can bear without tearing apart.

**Tension Forces **

Forces acting on a member tending to elongate it.

**Thermal Block **

A spacer of low thermal conductance material.

**Thermal Conductance, (C-factor) **

The time rate of heat flow through unit area of a body induced by unit temperature difference between the body surfaces. Units are Btu / (hour x feet squared x Fahrenheit)

[Imperial system] or Watts / (mass squared x “Celsius) [SI system]. See “Thermal resistance”.

**Thermal Conductivity, (k-factor) **

The time rate of heat flow through unit thickness of a flat slab of a homogenous material in the perpendicular direction to the slab surfaces induced by unit temperature gradient. Units for k are (Btu x in) / (hour x feet squared x Fahrenheit) or Btu / (hour x feet x Fahrenheit)

[Imperial system] and Watts / (m x Celsius) [SI system]. See “Thermal resistivity”.

**Thermal Resistance (R-value) **

Under steady conditions, the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through unit area. Note: Thermal resistance and thermal conductance are reciprocals. Thermal resistances are R-values; to obtain the U-factor, overall thermal transmittance, the R-value for either materials or constructions must first be evaluated because, by definition, the U-factor is the reciprocal of the sum of the individual R-values.

**Thermal Resistivity **

Under steady conditions, the temperature difference between parallel surfaces of a slab (large enough so there is no lateral heat flow) of unit thickness that induces unit heat flow through unit area. Note: Thermal resistivity and thermal conductivity are reciprocals.

Thermal resistivity is the R-value of a material of unit thickness.

**Thermal Transmittance (U-factor) **

The time rate of heat flow per unit area under steady conditions from the fluid on the warm side of a barrier to the fluid on the cold side, per unit temperature difference between the two fluids. It is evaluated by first evaluating the R-value and then computing its reciprocal.

**Through Ties **

Reinforcing steel, usually in the concrete, extending from one column pier to the other column pier, tying the two columns of a rigid frame together to resist thrust.

**Through-Fastened Roof System **

A through-fastened roof system is one in which the roof panels are attached directly to the roof substructure with fasteners which penetrate through the roof sheets and into the substructure.

**Thrust **

The horizontal component of a reaction usually at the column base.

**Tie **

A structural member that is loaded in tension.

**Ton **

2000 pounds.

**Track **

A metal way for wheeled components; specifically, one or more lines of ways, with fastenings, ties, etc., for a craneway, monorail or slide door.

**Translucent Light Panels **

Panels used to admit light.

**Transverse **

The direction parallel to the main frames.

**Tributary Area **

The area directly supported by the structural member between contiguous supports.

**Trim **

The light gauge metal used in the finish of a building, especially around openings and at intersections of surfaces. Often referred to as flashing.

**Trolley (Crane) **

The unit carrying the hoisting mechanism.

**Trolley Frame (Crane) **

The basic structure of the trolley on which are mounted the hoisting and traversing mechanisms.

**Truss **

A structure made up of three or more members, with each member designed to carry a tension or compression force. The entire structure in turn acts as a beam.

**Turn-of-the-Nut Method **

A method for pre-tensioning high strength bolts. The nut is turned from the “Snug tight” position, corresponding to a few blows of an impact wrench or the full effort of a man using an ordinary spud wrench, the amount of rotation required being a function of the bolt diameter and length.

**Turnout **

See “Kick-Out”.

**Twist Off Bolts **

Bolts with a segment which shears off at a predetermined torque during bolt tightening.

These bolts utilize a specially designed wrench for proper installation.