Xfx

Apl where V is the design shear force on the element and Apl is the effective shear area of the element. Where clip angles are used to transfer shear at the beam web in beam-to-column connections, the shear stress is typically calculated at the ''heel'' of the angle and is taken as the length of the angle multiplied by the angle thickness.

Combinations of shear and tensile stresses in parts of the connection or the connected members must be checked to prevent''block-shear'' failure of the pultruded material through the fastener holes. Where flanges of beams are coped to detail the connection, this is often a governing failure mode.

Even in shear-type connections, tensile loads (due to prying action) may develop in the members and the parts of a connection due to eccentricities in the connection. Such eccentricities are neglected in the design of steel shear connections. However, in pultruded structures these eccentricities should be considered. The local tensile stress on the member or the element should be determined since such loads typically are applied transverse to the longitudinal direction of the pultruded material. The appropriate tensile load and the effective area are difficult to determine precisely due to complex stress states in the connecting elements, and simple approximations based on the geometry of the connection are usually made for design calculations.

16.1.5.3.2 Critical Connection Limit States

Bearing failure in the base pultruded material is the recommended failure mode for pultruded connections. This failure mode is generally ductile and leads to a progressive shear-out failure of the material when loads are in the longitudinal direction of the pultruded material and sufficient transverse reinforcement is provided (in the form of mats and fabrics). (In the transverse direction bearing failure may not be ductile and may lead to brittle net-tension transverse failure of the base material.) The bearing strength provided by pultrusion manufacturers can be used in calculations. If bearing strength is not available from test data, it can be conservatively approximated as the material compressive strength (for bearing in the longitudinal direction) and the transverse tensile strength (for bearing in the transverse direction). Either the longitudinal bearing strength or the transverse bearing strength is used depending on the direction of the member or element relative to the load.

Tensile failure in the elements of the connection is a function of the tensile strength of the pultruded material either in the longitudinal or in the transverse direction. For tensile stress on the gross area

For tensile stress on the net area a reduced ultimate strength is recommended to account for stress concentrations (as with members in tension):

Shear failure (and shear-out failure) of the elements of the connection is a function of the in-plane shear strength for the pultruded material:

Shear failure of the fasteners is a function of the shear strength of the fasteners. For steel fasteners this is typically not a likely ULS. For FRP fasteners shear in the fasteners can govern the design of the connection:

where tut is the ultimate shear strength of the fastener.

Where FRP threaded rods or bolts are used in connections, the threads of the bolt can shear off longitudinally. This limit state is a function of the longitudinal shear strength of the rods or bolts used. It should be checked when FRP bolts and nuts are used. Ultimate thread shear strength is given in manufacturers' design guides.

In semirigid connections in which top and bottom seats made of pultruded angles are used, extreme caution must be used to ensure that the angles do not fail locally in through-the-thickness radial tension or compression in either an ''opening'' or a ''closing mode'' (Bass and Mottram 1994; Smith et al. 1999).

In addition, the flange-web junction behind the flange in the column section to which the top and bottom angles are connected must be checked for transverse tensile local failure (Bank et al. 1994a). As noted previously, semirigid connection design should only be used where test data are available for a full-sized connection as detailed in the structure.

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