Strap joints

Thermosetting resin pipe can be joined with mechanical joints or adhesive-bonded Joints. Mechanical joints are generally a variation of gasketed bell-and-spigot joints and may be either nonrestrained or self-restrained. Adhesive-bonded joints are typically bell-and-spigot or butt-and-strap. Butt-and-strap joints join piping components with multiple layers of resin-saturated glass reinforcement. 

Nguyen, T.C., Bai, Y., Zhao, X.L., and Al-Mahaidi, R. (2011) Mechanical characterization of steel/CFRP double strap joints at elevated temperatures. Compos. Struct., 93, 1604-1612. 

Single and joggle lap joints (Figure 7.2) are more likely to cause delamina-tion than scarf or beveled lap joints. Strap joints may be used to support bending loads. ... 

In-plane shear loading—kAherenA shear loads that produce shear stresses to the bondline in lap and strap joints. 

P(l) This section covers the design of mechanical joints where at least one of the primary components to be joined is made of glass FRP. Such joining techniques include fastener connections, friction joints (shear loads), contact joints (direct loads), threaded joints, strap joints and joints incorporating embedded fasteners (see 5.i.4 P(2)). 

Double-lap joint outer adherends, or double-strap joint straps... 

Single-lap joint adherends 1 and 2 single-strap joint adherend and strap... 

Single- and double-lap and single- and double-strap joints have stress concentrations at the ends of the overlap when loaded with in-plane loads. These are the most probable locations for the failure initiation. A t3rpical shear stress distribution is shown in Figure 5.27. 

The effects of the eccentricity are the greatest in lap and strap joints, particularly in a single-lap joint. 

Owing to the fact that the joint failure is triggered by the practically constant peel stresses induced by the eccentricity and by shear stress peaks at the ends of the overlap, the static load-bearing capacity of a bonded lap or strap joint cannot be increased significantly by increasing the lap length beyond a certain minimum. 

P(l) Two design methods are given for the design of lap and strap Joints a simplified procedure and a rigorous procedure (5.3.5.4 and 5.3.5.5 resnertiveivl In both nmcediires Ian and stran inints are treated... 

The models used in the rigorous procedure have been developed for lap Joints. The use of the same models for the corresponding strap Joints brings added conservatism to the design. 

P(l) This design procedure shall be applied only to tensile shear loaded single-and double-lap and single- and double-strap joints. 

For single-lap and single-strap joints calculate the maximum adhesive shear stress ... 

P(3) The theoretical temporary maximum joint resistance for douhle-lap and douhle-strap joints with long overlaps shall he specified hy the lesser of the values given hy the following pair of equations ... 

P(2) Compressively loaded double lap, double strap, supported single-lap, and supported single-strap joints shall be designed as the corresponding tensile loaded joint in respect of adhesive shear stresses. The load shall be taken as negative. 

P(2) In-plane loaded single-lap and single-strap joints shall be designed using the corresponding equations for tensile shear loaded Joints and using the parameter conversions indicated in Table 5.6. 

P(l) When lap and strap joints are loaded simultaneously by more than one of the above listed loadings, the joint resistance shall be determined using the maximum strain failure criterion applied to the resultant shear strain vector in the adhesive. 

Although stress concentrations are a problem mainly with lap and strap joints, it should be noted that stress concentrations are present also in scarf and step-lap joints. However, in scarf joints the stress concentrations are irrelevant when the scarf angle is low, typically less than 20°. in step-lap joints the stress concentrations generally have to be taken into account only at the ends of the outermost steps. 

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