Engineering Structures 29 (2007) 3475–3484 www.elsevier.com/locate/engstruct Application of neural networks for the structural health monitoring in curtain-wall systems Ch. Efstathiades a , C.C. Baniotopoulos a , P. Nazarko b,∗ , L. Ziemianski b , G.E. Stavroulakis c,d a Institute of Steel Structures, Faculty of Engineering, Aristotle University of Thessaloniki, GR-54124, Greece b Department of Structural Mechanic, Rzeszow University of Technology, W. Pola 2, 35-959 Rzeszow, Poland c Department of Production Engineering and Management, Technical University of Crete, GR-73132 Chania, Greece d Department of Civil Engineering, Carolo Wilhelmina Technical University, D–38106 Braunschweig, Germany Received 3 August 2006; received in revised form 21 August 2007; accepted 21 August 2007 Available online 25 September 2007 Abstract In a curtain-wall system, the main and the most possible cause of failures, is the total or partial destruction of its connections with the bearing structure. The present paper deals with the respective health monitoring problem and proposes an Artificial Neural Network (ANN) in order to identify possible imperfections in a typical curtain-wall system. Several Finite Element (FE) models of the curtain-wall system were developed and a parametric analysis was carried out dealing with the loss of rigidity in the aforementioned connections. During the numerical investigations, datasets containing the deflections of the columns of the curtain-wall structure were computed. The obtained results were used to create the Patterns Database, which, in turn, was used as the input for the training of the ANNs. Due to the relatively small number of training patterns, the regularization technique was also employed in order to improve the network generalization. The number of sensors and their optimal placement for appropriate network training were investigated. A wide variety of network architectures was studied and their influence on the network training was analyzed. The obtained results showed that ANNs can be an efficient method for the identification and localization of imperfections in curtain-wall systems. c  2007 Elsevier Ltd. All rights reserved. Keywords: Curtain-wall system; Structural health monitoring; Artificial neural networks; Finite elements method; Damage detection; Regularization techniques 1. Introduction Curtain-wall systems are becoming one of the most important parts of modern structures, since they greatly improve both their serviceability and their appearance. This is due to the fact that curtain-wall systems recently began to be designed as a part of the principal load-bearing structure. In consequence, a wide research effort on the structural behavior of such fac ¸ades is nowadays in progress having as final target the improvement of the response of such systems and the optimum design (from the financial and safety point of view) since in certain cases the cost of the fac ¸ade exceeds the fifteen percent of the total cost of a structure [1]. Currently the curtain-wall systems are being used in various shapes and types, not only in new buildings but also during the ∗ Corresponding author. Tel.: +48 17 865 1535; fax: +48 17 865 1173. E-mail address: pnazarko@prz.edu.pl (P. Nazarko). renovation of existing structures, mainly in order to improve the physical properties of buildings (Fig. 1(a)). The early detection of damages in a curtain-wall system, by means of Structural Health Monitoring (SHM), is an important factor since it supports early decisions about necessary repair and helps the engineers to avoid unfortunate accidents. One of the most possible positions for a fault in a curtain-wall system is the connection of the fac ¸ade with its bearing structure. In most cases, these connections are easily accessible during the construction of the fac ¸ade (Fig. 1(b)), but they are not accessible during the operation life of the building. The curtain-wall system is suspended from the main structure through point connections in certain distances over the whole area. The bolted connections used in curtain-walls cannot be assumed to be either completely rigid or pinned, but in most cases they are semi-rigid. For the generation of the Patterns Database (PD), damage in these connections can be represented by introducing a different (much lower) stiffness 0141-0296/$ - see front matter c  2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.engstruct.2007.08.017