Fastener Pull-Out & Torque Behavior

Fastener pull–out and torque behavior is an important factor to consider when constructing a building as it plays a significant role in the overall stability of the structure. Fastener pull–out refers to the amount of force required to remove the fastener from the material it is secured to. While torque behavior is the amount of force required to secure the fastener in place. As the type of building material used affects the pull–out and torque behavior, it is important to consider the material when selecting fasteners.

Unlike steel, composite properties like modulus of elasticity and tensile strength can vastly differ lengthwise and crosswise, leading to issues if not all directional properties are known or considered.

Because reinforced plastic thermosets are being used, operational temperatures and strength performance must be examined (see chart to the left). Heat affects fastener pull-out properties. It’s crucial that sub-framing materials are tested for the high end of the operational temperature range to verify suitable strength.

Structural Properties of the Sub-Framing Materials

*Average for multiple FRP

When designing with composite sub-framing, building envelope service temperatures must be taken into account. The temperature within the building envelope can differ significantly from exterior or interior temperatures. Therefore, testing must be provided and considered at elevated temperatures for fastener pull-out, tensile strength (crosswise and lengthwise), and modulus of elasticity (crosswise and lengthwise).

Several generic FRP materials were tested along with CMH for fastener pull-out strength at various service temperatures ranging from room temperature (70 degrees Fahrenheit) to 190 degrees Fahrenheit.

According to the data shown to the left, the fastener pull-out strength of composite sub-framing can drop greatly when the service temperature rises. Although CMH and FRP both saw a decrease in strength with an increase in temperature, CMH remains stronger than steel even at elevated temperatures. However, we can conclude that although some FRP started above the strength of steel at room temperature, they all fell below the strength of steel at elevated temperatures.