Reliability of nailed timber connections with gusset plates

Abstract

First order second moment (FOSM) analysis techniques, recently employed in the development of limit states design codes allow the engineer/designer to take into account the variations and random nature of the material properties and load effects present in the design of structural timber. A generated non-linear equation is used in conjunction with basic design mechanics to model the moment–rotation behaviour of dowel type (nailed) timber connections. The connections examined incorporated a series of nailed gusset beam to column joints with varying number of nails, subjected to a series of permanent and variable loading conditions. Joint reliability is evaluated by imposing an end rotation and calculating the reliability index under imposed deformation levels. The parameters of the equation considered as random variables were nail diameter, timber density, connection geometry and the applied loading condition. The statistics of the random variables considered are modelled using the normal, lognormal and extreme value type-1 (Gumbel) distributions. Results show that irrespective of the magnitude of variation of the other parameters, nail diameter significantly influences the moment-capacity of the connection, especially for smaller diameters. Use of probabilistic analysis techniques in design is intended to provide improved insight into system behaviour, the influence of different random variables on system performance and the interaction between different system components. This paper demonstrates how the incorporation of FOSM analysis with a non-linear moment–rotation model provides a more rational description of connection behaviour without the need to resort to more traditional Monte Carlo simulation, which can be both costly and time consuming.