Recently, ”reduction of CO2 emission” has been raised as a most important topic needed to be solved immediately all over the world and each country has declared its reduction target. It is known that construction industry shared the highly CO2 emissions. Thus the new sustainable materials and/or construction methods must be developed as soon as possible. In this research, it is a final target to develop a new timbersteel hybrid beam as a new sustainable material. It is expected to use timbers for the construction site to reduce CO2 emissions than the ordinal materials such as concrete and steel, so that timbers are now one of the most recognized as a sustainable material. In order to replace the concrete to timbers, the timber beam should have the same or even stronger strength than concrete. Thus, in this research timber and steel are combined to improve the beam engineering characteristics.

 In this paper, as a first step to develop such a sustainable beam, knots are presented in the timber beam, because it is found that knots on the beam showed significant reduction of the strength of the beam according to experimental researches. It is shown that knots on the beam have unique material properties and linearly analyzed using FEM. The results of beams are presented in this paper.

 The natural frequency of wood by the longitudinal vibration method is effective as an index to evaluate the Young's modulus of wood and can be applied to quality control of structural materials, so it has been adopted as a method to estimate or evaluate mechanical properties in factory production lines and construction site. To measure the natural frequency, measurement sensors such as microphones and accelerometers are used, but the measurement at the construction site depends largely on the characteristics of the measurement sensors, and differences in the sensors affect the accuracy and workability of the measurement. Furthermore, when accelerometers are used, there are several ways to fix them, and it is difficult to determine which method is appropriate.

 The purpose of this study was to clarify how to accurately and efficiently measure the natural frequency of wood at a construction site using the longitudinal vibration method. Microphones, laser displacement meters, and accelerometers were used as different measurement sensors, and contact methods via adhesive tape, rubber bands, and screws were used as different methods of fixing the accelerometers, and the effects of these methods on the measurement of the natural frequency of cedar cylinder wood were investigated.

 Nowadays, construction of buildings with wood structure is gaining momentum since the Diet introduced a policy to promote the use of wood for public buildings in 2010, and the demand for long wooden beams with a large cross section is increasing. In this study, we tested hybrid composite beams made up of square timbers of Sakhalin fir that were put together with laterally glued CFRP sheets and their bending performance was evaluated. A series of bending tests on hybrid composite beams is reported, of which the test parameters are arrangement of CFRP sheets, presence of butt joint of composing timbers, and that of lateral adhesion between timbers. For the type in which the CFRP sheet was arranged vertically in the cross section of the beams, absence of lateral adhesion between timbers did not lower the bending strength. The type in which two CFRP sheets were arranged vertically in the cross section and externally glued on the tension side of the beams and composing timbers had butt joints exhibited 95% higher bending strength than that without CFRP sheets. These results exhibited potential of hybrid composite beam of timber and CFRP sheet on the production of wooden beams with a large cross section for lengthening of products and labor saving.

 A timber Warren truss bridge was developed by the authors in 2010 as the emergency bridge which can be assembled within a short time in disaster. It was obtained that the construction time was within half an hour with human power assembling the bridge. However, processing the end of truss member was necessary to insert the steel connection plate. Removing the distortion of welding in processing the steel connection plate was also necessary as the problem. Therefore, this study presents connecting method without special processes of timber member except for bolt holes. Also, the connection system without welding is applied in this bridge. As for the material, the market size of 2×8 timber which can be bought easily is adopted in this presented truss bridge. The results of construction tests in the gym and in the field are shown in this paper. The results of loading tests are also reported to confirm the structural performance.

 Small model test is conducted to verify the shear effect of composite ground reinforced with logs. In this test, following contents are verified. the improvement effect of ground with or without logs, the interval of logs and the effect of confining pressure are verified. As the result, As the number of log increases and driven interval narrows, the displacement is not large with surcharge. It is clarified from the photo at the experiment that the displacement is small as driven interval narrows. The final load increases due to the reinforce of the log. It is considered that the ground strength is strong under shear deformation due to the reinforce of the log.

 Long-term massive use of wood is effective to mitigate climate change. For this reason, liquefaction countermeasures using logs have been developed and commercialized.The design of this method is based on the design chart of “Method A” of the sand compaction pile method. The design chart seems to include the ground uplift, which may be over-designed because it has not ovserved in the liquefaction countermeasures using logs. The purpose of this study is to clarify the characteristics of vertical displacement caused by log insertion as a first step to rationalize the design method. In this study, it was clarified by the model experiments that the vertical displacement at the ground surface caused by log insertion was not only dilatation but also contraction, and those changes were related to the initial relative density.

 In the history of glued timber bridges in Japan 34 years passed since the first bridge was built in 1987, which is much shorter than that of Europe and the United States. Data about stiffness and strength for glue-laminated timber bridges, which have been in service for more than 20 years and then replaced, have not been enough accumulated. In this study, we measure stiffness and strength for the members of Meoto Bridge replaced in 2020 by static/dynamic methods. As a result, the stiffness of the main structural members, such as arch ribs and stiffeners, was generally reduced by about 10%, while design stresses for the arch members and the floor girders are within the allowable stresses. Thus it is suggested that timber members, which have been in service for more than 20 years, have enough stiffness and strength.

 While CLT(Cross-Laminated-Timber), which is lightweight and is resistant to fatigue, is expected to apply to bridge deck, it is needed to joint commercially available railing on it. It is important to confirm the safety and to investigate the load bearing performance of the joint part between the railing post and the CLT deck. We show relatively simple modeling of the joint part using general-purpose 3D FEM tool and illustrate the numerical results. The modeling considering elasto-plasticity for both steel and CLT members seems to well simulate the sink deformation behavior of CLT.

 Cross laminated Timber (CLT) is made by orthogonal gluing plates to each other. In addition, CLT slab is lightweight compared to a reinforced concrete deck and a steel deck. CLT can be expected to apply for bridge deck. There are several cases that CLT is applied to bridge deck. The deflection and stress are reduced by changing the layer composition of CLT, and it is possible to rational design of CLT. In this study, we consider the mechanical characteristics of 4 CLT slabs with different laminar composition. As a result, it is more advantageous to glue the side surface of the plate for load transfer of the width direction of the road. And, deflection and stress can be reduced by increasing the area of high grade parallel layers.

 To promote the widespread use of timber as ground improvement material, it is necessary to show that timber has the effect of ground improvement semi-permanently without biological degradation. In this study, we investigated on changes in wood properties in the early stage burying log piles of practical size under the ground below groundwater for one month. In this result, we confirmed to be maintained soundness and not biological degradation for one month, suggested that the water absorption changed depending on the density and heartwood ratio, and that the ground components flowed into the wood due to the water absorption. These results are expected to be used as a new perspective in discussing long-term durability of log piles.

 The ultimate bearing capacity of a timber pile in clay is evaluated by the circumferential resistance of a cylindrical body whose diameter is the end diameter. Since timber piles are originally tapered, the taper angle and the shape of the joint may affect the bearing capacity. In this study, four types of single piles and two types of jointed timber piles with the same end diameter and different taper angles were used for vertical loading tests of timber piles in clay ground to investigate the effects of timber pile shape on the vertical bearing capacity and changes in the surrounding ground conditions. It was found that the vertical bearing capacity of the timber pile in clay increased with taper, and that the vertical bearing capacity of a jointed pile decreased as the area of non-contact between the pile and the surrounding clay increased at the joint. Furthermore, it was confirmed that the timber pile had the effect of reducing the water content of the clay around the pile.

 The 1948 Fukui earthquake caused extensive damage to casualties and structures in the Fukui plain region, which is a soft alluvial ground. This study focused on bridges and buildings supported by wood pile foundation that existed in the earthquake-stricken area, and investigated the design method of wood piles, effects of seismic motion and liquefaction on the wood piles and soundness of the excavated wood piles. As a result, it was clarified that the structures supported by wood pile foundation that experienced the Fukui earthquake had very minor damage to the superstructure due to seismic motion and liquefaction, and the wood piles used as the foundation were also sound.