The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes of wood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellas and knowledge of relationships between lamella and CLT properties. In the present study the relationship between dynamic axial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. By means of four-point bending test it is shown that the effective quasi-static MoE of lamellas in CLT is only 2­–6 % lower than the average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict and control the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shear stiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection to four-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2 the average apparent or effective rolling shear modulus was determined to 159 MPa. The average rolling shear modulus of the same material was determined to 56 MPa.

The use of cross laminated timber (CLT) for construction has increased greatly in recent years and the large volumes of wood used for CLT means that it is important to optimize the use of the material. This requires relevant grading of lamellas and knowledge of relationships between lamella and CLT properties. In the present study, the relationship between dynamic axial modulus of elasticity (MoE) of lamellas and the quasi-static out of plane bending stiffness of CLT is investigated. By means of four-point bending test, it is shown that the effective quasi-static MoE of lamellas in CLT is only 2–6% lower than the average axial dynamic MoE of the individual lamellas. With this knowledge, producers of CLT can easily predict and control the important out of plane bending stiffness of the produced CLT. Moreover, it is shown that effective rolling shear stiffness of layers in CLT can be accurately determined by means of digital image correlation performed in connection to four-point bending of CLT, even for long test spans. For layers of lamellas of Scots pine of size 40 × 190 mm2 the average apparent or effective rolling shear modulus was determined to be 159 MPa. The average rolling shear modulus of the same material was determined to be 56 MPa.

The dynamic action of footbridge users in different forms of activity (especially during walking and running) may cause an excessive vibration of the footbridge deck and may disturb the comfort of use of the structure. The dynamic susceptibility of the footbridges varies depending on the construction material used to build the footbridge and the typical construction solutions (construction details) resulting from the construction material used. The paper presents the basic dynamic characteristics of timber footbridges of various structural solutions, collected during dynamic field tests of these structures. The obtained results indicate relatively high dynamic resistance of timber footbridges to the dynamic loads generated by users under normal conditions of use. In addition, the results show that in the case of timber footbridges, it is possible to consider changing the requirements of international standards defining the range of natural frequencies sensitive to the dynamic impact of users. In the case of timber footbridges, characterized by a relatively high self-weight (compared to steel footbridges), high stiffness and high damping, it is possible to consider changing the requirements for performing forced vibration analyses only for structures with fundamental vertical vibration frequency 𝑓 3.0 Hz instead of the currently defined 𝑓 5.0 Hz.