**Experimental Investigations of Timber Beams with Stop-Splayed Scarf Carpentry Joints**

#### **Anna Karolak \*, Jerzy Jasie ´nko, Tomasz Nowak and Krzysztof Raszczuk**

Faculty of Civil Engineering, Wroclaw University of Science and Technology, Wybrzeze Wyspianskiego 27, 50-370 Wrocław, Poland; jerzy.jasienko@pwr.edu.pl (J.J.); tomasz.nowak@pwr.edu.pl (T.N.); krzysztof.raszczuk@pwr.edu.pl (K.R.)

**\*** Correspondence: anna.karolak@pwr.edu.pl; Tel.: +48-71-3203879

Received: 4 February 2020; Accepted: 17 March 2020; Published: 21 March 2020

**Abstract:** The paper presents the results of an experimental investigation of stop-splayed scarf joints, which was carried out as part of a research programme at the Wroclaw University of Science and Technology. A brief description and the characteristics of scarf and splice joints appearing in historical buildings are provided, with special reference to stop-splayed scarf joints (so-called 'Bolt of lightning') which were widely used, for example, in Italian renaissance architecture. Analyses and studies of scarf and splice joints in bent elements presented in the literature are reviewed, along with selected examples of analyses and research on tensile joints. It is worth noting that the authors in practically all the cited literature draw attention to the need for further research in this area. Next, the results of the authors' own research on beams with stop-splayed scarf joints, strengthened using various methods, e.g., by means of drawbolts (metal screws), steel clamps and steel clamps with wooden pegs, which were subjected to four-point bending tests are presented. Load-deflection plots were obtained for load-bearing to bending of each beam in relation to the load-bearing of a continuous reference beam. A comparative analysis of the results obtained for each beam series is presented, along with conclusions and directions for further research.

**Keywords:** carpentry joints; scarf and splice joints; stop-splayed scarf joints ('bolt of lightning'); static behaviour; experimental research
