DYNAMIC BEHAVIOR OF TIMBER FOOTBRIDGES WITH UNCERTAIN MECHANICAL PROPERTIES AND STOCHASTIC WALKING LOADS

D. A. GARCIA; M.B. ROSALES; R. SAMPAIO

São Sebastião

Simposio; XVII International Symposium on Dynamic Problems of Mechanics - DINAME 2017; 2017

Brazilian Society of Mechanical Sciences and Engineering ABCM

A dynamic study of timber footbridges with uncertain mechanical properties under the action of stochastic walking loads is presented in this paper. These structural systems made of timber are increasingly employed due to the high relation stiffness/weight that wood exhibits in relation to others structural materials. More, the development andimplementationoflaminatedbeamspermitslargerspans. Thesefeaturescanleadtolightweightstructuralsystems in which the acceleration levels can exceed the human comfort limits. The sources of uncertainty of this structural model are the timber mechanical and physical properties, Modulus of Elasticity (MOE) and mass density. Also, the geometrical design of the boards that compose the laminated timber beams supporting the floor involves variability in the distances between finger joints. Probability Density Functions (PDFs) of the timber properties are formulated from the Principle of Maximum Entropy (PME). The finger joints distance generates the lengthwise variability of the MOE and mass density functions in each board of the laminated beams. The influence of these stochastic variables in the structural response on a forced vibration problem that includes a stochastic model of the load induced by the human walking is assessed. Pedestrians arrive to the footbridge under a Poisson distribution. The arrival velocity is such that a medium/low transit density is achieved in accordance with the footbridge dimension. The PDFs of the natural frequencies of the structure, the mode shapes and the structural response are numerically obtained through the Finite Element Method (FEM) and Monte Carlo Simulations (MCS). Values of peak accelerations produced at the mean span of the footbridge are evaluated in relation to the footbridge occupancy at each instant. The present stochastic model contributes to obtain a more realistic description of the response of this type of structures