Rotation capacity

It is important that connections for blast loaded members have sufficient rotation capacity, A connection may have sufficient strength to resist the applied load however, when significant deformation of the member occurs this capacity may be reduced due to buckling of stiffeners, flanges, etc. Figure 10.1 is an example of a connection design for large rotation capacity. 

Wherever possible, joints should he located away from critical sections. If this is not possible, the deformation or rotation capacity of the joint should be assessed. 

It can readily be shown (reference 10,) that the support rotation capacity of a uniformly loaded simply supported beam needs to be 13 mrad to meet the serviceability limit state of a maximum deflection l/250th of the beam span. Note that this rotation assumes the beam is attached to rigid columns and that it is therefore not necessarily the situation at external connections or at internal connections subjected to non symmetric deformation. 

A rotation of 13 mrad was not obtained, without adhesive failure, with the MMFG recommended connection Wmj bt+bd. However, bond failure was restricted to the top of the web cleats by the restraining effect of the top bolt row and thus this connection has adequate performance to meet the serviceability limit state. Both bolted connections Wmj bt and Wmj bt.2 achieved the required of 13 mrad, but, along with connection WmJ bt+bd, all provided insufficient rotation capacity (32.5 mrad) for the design to be considered safe if the MMFG maximum deflection limit of 1/lOOth of the beam span is used (reference 1]). 

The situation is further complicated because the data here is for shortterm loading and do not provide information on a Joint s creep behaviour. Both members (references 11,12) and the connections (reference 10) are known to creep, such that in time there will be increased beam deflection and therefore an increase in the required rotation capacity of the connection. Rigorous procedures to account for creep in the design process are not available. Designers are advised to use creep moduli (i.e. reduced values from short term values) when determining deflections of beam members in a braced frame (reference 1). It may be assumed that the a web cleat connection does not adversely affect this design approach. 

Increasing the rotational capacity of potential plastic hinges without changing their position... 

Class 1 - For plastic global analysis the usage of cross-sections with large rotation capacity, at least at the plastic hinge location. The b/t ratios are efficiently stocky to permit the necessary substantial deformations without... 

Class 2 - Most rolled sections have b/t values of sufficiently stocky for the cross-section to reach Mpi and they are termed Qass-2 or compact sections. Here some strain hardening occurs and some limited rotation is possible before falling part of the curve drops (rotation capacity) below Mpi. 

In the third step, the plastic rotation capacities of the structural members are determined. It is then eventually corrected if the shear failure occurs before the limits to the flexural plastic rotation capacity are reached. The story inelastic drift capacity is estimated from the plastic rotation capacities. 

European code for the assessment of RC elements (CEN 2005) provides, as collapse prevention acceptance criteria for RC members, the value of the ultimate rotation capacity according to Biskinis and Fardis (2010b) as life safety acceptance criteria, 75 % of the ultimate rotation capacity according to Biskinis and Fardis (2010b) and, as immediate occupancy acceptance criteria, the value of yielding rotation... 

Further analytical research on the same connection complement this work, as design model and guidelines have been recommended. A target plastic rotation capacity of 0.02 rad was selected. In 2004, Engelhardt recommended (Bruneau 2004) the following as potential positive solutions ... 

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