2019 CSCE Annual Conference - Laval (Greater Montreal)

2019 CSCE Annual Conference - Laval (Greater Montreal) Conference


Title
Substructuring strategy for pseudo-dynamic testing of steel lattice towers.


Author(s)
Mr. Rajab Kammouh (Presenter)
Dr. Kahina Sad Saoud, Université de Sherbrooke
Dr. Charles-Philippe Lamarche, Université de Sherbrooke
Mr. Sébastien Langlois, Université de Sherbrooke
Mr. Alex Loignon, Université de Sherbrooke
Abstract

Lattice towers are the most commonly used structures in the field of overhead power transmission lines.In the design process of transmission lines, there are several methods for the evaluation of the carrying-capacity of lattice towers. The most common method involves the use of three-dimensional linear elastic truss analyses to evaluate the axial forces in the pin-ended members. The resulting design is normally validated by full-scale experimental tests. These tests are very expensive and time consuming. Moreover, the rarity of the testing facilities adds an additional difficulty. Hence the interest of using substructured pseudo-dynamic testing methods in which the experimental substructure, tested in a laboratory environment, interact with a numerical model to emulate the structural behaviour of a complete structure. During a substructured pseudo-dynamic test, the critical substructure that usually exhibits a highly complex  behaviour is tested experimentally, while the remainder of the structure is modeled numerically. Recently, a substructured pseudo-dynamic testing method was developed at Université de Sherbrooke to evaluate the strength of a reduced-scale lattice tower. This testing method allows the analysis of the behaviour of the whole structure with an experimental test on the critical parts only.  Thus, the substructuring pseudo-dynamic method reduces the preparation tasks and the associated costs. This method has several advantages but requires several preliminary analyses and planning for defining the critical substructure, dynamic parameters, and the setup’s flexibility. This work aims to develop a completely numerical substructuring tool using the finite element software Code_Aster to ensure relevance and simplify the preparation and planning of pseudo-dynamic tests on lattice towers. Full-scale lattice towers are analyzed under quasi-static and dynamic load cases. The developed numerical model employs beam elements to represent the angle members and discrete elements for the bolted connections. Both the eccentricity and the rotational stiffness of connections are modeled.  The highly nonlinear behaviour of the critical substructure is solved in an incrementally way considering both geometric and material nonlinearities. An example of a lattice tower, under quasi-static and dynamic loads, is presented and compared with reference numerical results. The relevance of the use of a full-scale substructured pseudo-dynamic test is discussed. The effect of dynamic parameters (time step, damping ratio and load rate) on the emulated structure’s behaviour is analyzed in details. Finally, the effect of the flexibility of a full-scale experimental setup on the accuracy of the test results is studied.