ORIGINAL Stress-laminated-timber decks: state of the art and design based on Swedish practice Roberto Crocetti 1 • Kristoffer Ekholm 2 • Robert Kliger 2 Received: 16 February 2015 / Published online: 23 September 2015 Ó Springer-Verlag Berlin Heidelberg 2015 Abstract Stress-laminated-timber (SLT) bridge decks are a valid alternative to conventional short- and medium-span bridges in terms of cost and performance. SLT decks are made from a number of planks or glulam beams positioned side by side and stressed together using high-strength steel bars. A concentrated load can therefore be distributed from the loaded beams onto adjacent beams due to the resisting friction caused by the pre-stressing of all beams in the deck. This paper describes the state of the art of SLT bridge decks, with special emphasis on Swedish practice. The effect of butt joints on deck deflection and solution applied to accommodate the loss of pre-stress are shown. Simple design tools for the preliminary design of road bridges are illustrated. Best practice with regard to some detailing, water protection and durability is also discussed. Finally, possible developments of SLT bridges are discussed. 1 Introduction Stress lamination for timber bridges began when engineers began to reinforce existing nail-laminated bridge decks using bars over and under the deck to prevent the beams separating from one another. The post-tensioning of nail- laminated timber decks not only restored the original capacity, it also increased the load distribution between the beams. Many researchers have studied the suitability of timber bridges as a part of modern infrastructure. In the 1980s and early 1990s, comprehensive experimental and theoretical investigations on SLT bridge decks were performed in North America (Batchelor et al. 1981; Ritter 1990; Davalos et al. 1996; Oliva and Dimakis 1988). Ritter’s work (Ritter 1990) contributed to the first guidelines which included all the aspects relating to timber bridges. It contains information about basic timber knowledge, general bridge concepts and detailed descriptions of how different types of timber bridges can be designed and maintained. In the early 1990s, extensive research work was conducted in Australia (Crews and Walter 1996). Crews (2001, 2002) developed techniques for SLT decks and stress-laminated cellular timber bridge decks which were adapted for Australian materials and conditions. Crews and Walter (1996) presented a review of timber bridge devel- opment in Australia. In the late 1990s and 2000s, significant research on SLT decks—made primarily of glulam beam laminations (rather than laminations made of planks)—was performed in Sweden. Several reports which covered aspects such as climate influence, loss of force in pre-stressing bars, field measurements, design values, numerical modelling and so on were produced (Marklund 1997a, b; Pousette 1997, 2001; Pousette et al. 2002). In Norway, Dahl et al. (2006) performed a full-scale test on a stress-laminated-timber bridge deck sub- jected to failure loads. They concluded that slip occurred between laminations at moderate loads, which made linear models insufficient to predict the failure load of the deck. 2 Stress-laminated-timber bridge decks The principle of SLT bridge decks is shown schematically in Fig. 1. Timber laminations (planks of structural timber or glulam beams) are stacked side by side across the width & Roberto Crocetti Roberto.Crocetti@kstr.lth.se 1 Division of Structural Engineering, Lund University, Lund, Sweden 2 Division of Structural Engineering, Chalmers University of Technology, Gothenburg, Sweden 123 Eur. J. Wood Prod. (2016) 74:453–461 DOI 10.1007/s00107-015-0966-1