Testing steel lattice towers with a hybrid (numerical/ experimental) method
Loignon, Alex; Langlois, Sébastien; Lamarche, Charles-Philippe; Légeron, Frédéric
Abstract : The analysis of transmission line steel lattice towers is usually performed with linear numerical methods. However, the actual behaviour of bolted lattice towers is complex and may be highly affected by different factors such as rotational stiffness of connections, bolt slipping, eccentricities in the connections, initial out-of-straightness, etc. For this reason, most power utilities perform full-scale tests for the qualification of novel steel lattice transmission tower designs. These tests are expensive and add delays in the planning of the construction of new transmission lines. Over the past years, advanced numerical methods were developed and they may effectively provide more insight into the force distribution found in lattice structures. However, the actual capacity and failure modes remain difficult to identify numerically and experimental tests are often required. On the other hand, over the last decades, the civil engineering field has seen the development of a completely new testing technique called hybrid testing that combines both experimental and numerical methods. This testing technique involves the experimental testing of a substructure and the interaction during the test with a numerical model of the remainder of the structure. This technique was mostly used for the dynamic analyses of buildings and bridges under the action of seismic loads. To adapt hybrid techniques to lattice towers, a methodology needs to be put in place to identify the substructure of interests to be tested experimentally. The work presented here aims at developing a hybrid testing technique for the evaluation of the failure modes and structural capacity of lattice towers. The long term objective of this research program is to provide a new testing technique that would be an advantageous alternative to advanced numerical methods and reduce the need for full-scale tests. This paper presents hybrid tests that were performed on reduced-scale lattice tower sections. Firstly, an existing 32 m lattice tower was adapted to be able to build a reduced 1:4 scale model. Secondly, a numerical model was developed to identify load cases and substructures that could allow to obtain similar capacities and failure modes to those obtained for the complete structure model. Then, experimental tests on complete 1:4 reduced scale towers were performed to serve as references. Finally, hybrid tests were performed on a 1:4 reduced scale substructure corresponding to a critical section of the tower. The hybrid tests yielded results that were in agreement with the complete tower experimental tests. The test results were also coherent with the numerical model’s results.
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