In recent years, wood has been increasingly used in the field of civil engineering from the viewpoint of contributing to the environment. Recently, it has been reported that the water absorption effect of wood piles promotes the effect of ground improvement. The authors conducted sounding tests, water content ratio and saturation measurements, pull-out tests, and wood moisture content measurements at the beginning and one year after the start of the tests. The results indicated that the ground below the water table approached saturation due to capillary action, resulting in a decrease in frictional resistance. The results also indicated that the lateral roughness of piles buried in ground with similar compaction and saturation affected the pullout load. In addition, the moisture content of wood that has absorbed groundwater by capillary action and the soil saturation showed similar trends at different depths, suggesting the possibility of approaching an equilibrium state while interacting with each other.

 The authors are developing a timber truss bridge as an emergency bridge for life saving and transportation of daily necessities. It is possible that the assembling the bridge by hands and quickly is executed. Long term durability is not necessary because this bridge will be used temporarily for only recovery time. In the Warren truss bridge developed as emergency bridge in 2010, there was a problem of heat strain by welding in the steel connection plates. In another Warren truss bridge developed in 2019, the problem was removed without welding, however, deformation and vibration for the direction perpendicular to bridge axis occurred easily. To improve these problems, this study develops the bridge with the following characteristics ; (1) Using two steel plates with 3.2mm thickness for the connection, (2) Attaching the portal members to the intermediate part of the bridge as well as the end part of the bridge. (3) Using connection plates with folding processing, not welding processing.As the results, the bridge developed here became light and simple, and the construction time was only 3 hours and 8 minutes.

 In recent years, CLT has been utilized in road bridge decks. The mechanical characteristics of CLT are complicated because of the difference in properties depending on the direction of fibers in timber. The numerical analysis of CLT's mechanical characteristics was studied. However, it was necessary to verify the results of the numerical analysis. In this study, the bending test of CLT and the numerical analysis that reproduced the bending test were conducted. The experimental and numerical results were compared to verify the numerical method. As a result of comparison, it was established that Young's modulus of the timber in the direction of the fibers and the linear limit stress of the laminar are necessary for the analysis.

 This study aims to clarify the stiffness and serviceability of a large section glued laminated timber girder bridge (Fukazawa Bridge) that has been in service for 26 years, natural frequency were measured using a tablet device. To confirm the reduction in bending stiffness due to aging, the natural frequencies were compared with those of a deemed newly constructed bridge calculated using a numerical analysis model. The vibration serviceability of the bridge was investigated by measuring the vibration response of the bridge during both solo and group walking(five person). The results confirmed that the bending stiffness of the entire bridge, calculated from the natural frequency, was reduced by approximately 10%. While the main girder deflection calculated by numerical analysis met the design specifications. In addition, no vibration response that would be uncomfortable for pedestrians was detected in terms of vibration serviceability. There was therefore confirmed that the modern timber bridge, which has been in service for 26 years, has a certain degree of usability.

 In the inspection of existing bridges, the measurement of natural frequencies by vibration testing is relatively safe and easy. The natural frequencies can also be determined from analysis using a numerical model. In this study, the effect of partial decay on the natural frequencies of the deck arch bridge (Kajika Bridge) was investigated by subjecting arches and longitudinal girder joints to partial decay on a wooden upper arch carriageway bridge. As a result, it was confirmed that the natural frequency decreased with a reduction in Young’s modulus, such that it could be regressed as a second-order polynomial or logarithm. Sensitivity analysis using the slope of the regression line of the reduction curve revealed that the antinode of the vibration in each vibration mode has high sensitivity, while the nodes have low sensitivity. It was also found that the sensitivity of the combination of decay points is almost equal to the sum of the magnitudes of the sensitivities of the decay at one point.

 Cross Laminated Timber (CLT), a building material, has been proposed to be used for soft ground improvement to promote the use of wood in the civil engineering field. In this method, CLT is placed horizontally or vertically in the ground, and the shear properties of the ground are necessary to evaluate its stability against slips. In this study, direct shear tests were conducted on a simulated dry sandy soil with CLTs installed in it. The results showed that the shear resistance between sand and wood was smaller than that sand only. Furthermore, the surface of the dry and saturated wood was observed using an electron microscope, and it was found that the height difference between the surfaces increases as the wood become saturated.