Motoi Yasumura’s research while affiliated with Shizuoka University and other places

In order to provide the mechanical properties and seismic performance of CLT shear walls to which tensile bolted joints and screwed steel joints were applied for vertical restraint, cyclic lateral loading tests and pseudo-dynamic tests were conducted on 3-ply sugi CLT shear walls. Moreover, the analytical model was validated by comparing the time-history earthquake response analysis and pseudo-dynamic test results for these types of shear walls. The relation between the magnitude of input ground motion and the horizontal displacement response was investigated by conducting time-history earthquake response analysis on several earthquake records and artificial waves with variable magnitude of input ground motion. Also, the possibility of replacing the tensile bolted joints by screwed steel joints was discussed. The yield strength and the maximum strength of shear walls with screwed joints were 20% higher than those with tensile bolts in the cyclic lateral loading tests. With the same seismic wave input in the pseudo-dynamic tests, the maximum response displacements of screwed joint specimens were smaller than those of tensile bolt specimens. Furthermore, the response displacement of earthquake response analysis showed good agreement with pseudo-dynamic test results. It is suggested that CLT shear walls with screwed steel joints give enough performance compared to shear walls with tensile bolt joints.

The performance of plywood-sheathed shear walls is determined at the plywood-to-timber joints. In joints with dowel-type fasteners, such as nails and screws, the fastener is fractured under reversed cyclic loading (e.g., seismic force), reducing the ductility of the joint. The fracture is caused by low-cycle fatigue due to the reversed cyclic bending of the fastener. Therefore, evaluating the fatigue life is important for estimating the ultimate displacement. The main objective of this study is to estimate the ultimate displacement of the joints and to enable load–displacement calculation of single shear joints under reversed cyclic displacement when bending fatigue failure of the fastener occurs. Single shear tests were conducted under different loading protocols, and the damage performances of the fasteners were determined by subjecting them to reversed cyclic bending tests. Based on the results, the failure lifetimes of joints with dowel-type fasteners were estimated. In addition, the fracture mechanism of these dowel-type fasteners was elucidated. CN50-type nails and wood screws with dimensions of 4.1 × 38 and 4.5 × 50 mm were used as fasteners. The single shear tests showed that the smaller the displacements per cycle, the lower are the ultimate displacement and ductilities of the joints. Moreover, load–displacement relationship up to fastener failure can be approximately estimated by combining the yield model and failure lifetime.

This study examines the mechanical performance of large and small cross-laminated timber (CLT) wall panels with different applications. Two CLT structures were subjected to reversed cyclic lateral loads. One structure consisted of 90-mm-thick, large CLT wall panels (6×2.7 m), and the other consisted of 90-mm-thick, small CLT wall panels (1×2.7 m). A weight was installed on the roof of two-story structures to simulate the weight of three-story structures, designed by elastic calculations with a base shear coefficient of 1.0. The number of screws for each joint was determined by a linear finite-element method (FEM) analysis. The experimental results showed that the ultimate capacity of these structures is 60-80% higher than the design load, indicating high structural performance. A three-dimensional, nonlinear analysis was conducted via the FEM, which accurately predicted the mechanical performance of the CLT structures. This design procedure, based on linear analysis, resulted in a conservative design, and simulation using the nonlinear FEM provided an effective tool for design optimization.

Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. CLT panels are excellently applicable for timber buildings as slabs for horizontal structural members. Live load and dead load on CLT panels cause internal shear stress. Distribution of internal shear stress in CLT panels is affected by the modulus of elasticity of parallel layers. Rolling shear stress occurs in cross layers under shear force applied to CLT panels. Generally rolling shear strength is lower than the shear strength parallel to the grain. Few data of rolling shear strength of lumber exist. Internal shear capacity of several types of CLT panels was predicted by calculating the distribution of internal shear stress from the experimental rolling shear strength of sugi lumber. To verify the calculated shear capacity of several types of CLT cross sections, asymmetric four-point bending tests were carried out. The experimental shear capacity was found to be 12% lower than the average value of the rolling shear strength model for the lumber of the shear zone and was 16% higher than the minimum value of rolling shear strength model.

Cross-laminated timber (CLT) panels consist of several layers of lumber stacked crosswise and glued together on their faces. Prototype sugi CLT floor panels were manufactured and bending tests were carried out under the different parameters of lumber modulus of elasticity (MOE), number of layers, thickness of lumber and thickness of CLT panels. On the basis of above tests, bending stiffness and moment carrying capacity were predicted by Monte Carlo method. MOE of lumber was measured by using grading machine and tensile strength of lumber was assumed to be 60 % of bending strength based on the obtained bending test. Bending stiffness EI of CLT panels could be estimated by adopting composite theory and equivalent section area. Experimental moment carrying capacity showed 12 % higher value than the calculated moment carrying capacity by average lumber failure method, and also showed 45 % higher value than the calculated moment carrying capacity by minimum lumber failure method due to the reinforcement of the outer layer by the neighboring cross layer.

Multi-storey buildings made of cross-laminated timber panels (X-lam) are becoming a stronger and economically valid alternative in Europe compared with traditional masonry or concrete buildings. During the design process of these multi-storey buildings, also their earthquake behaviour has to be addressed, especially in seismic-prone areas such as Italy. However, limited knowledge on the seismic performance is available for this innovative massive timber product. On the basis of extensive testing series comprising monotonic and reversed cyclic tests on X-lam panels, a pseudodynamic test on a one-storey X-lam specimen and 1D shaking table tests on a full-scale three-storey specimen, a full-scale seven-storey building was designed according to the European seismic standard Eurocode 8 and subjected to earthquake loading on a 3D shaking table. The building was designed with a preliminary action reduction factor of three that had been derived from the experimental results on the three-storey building. The outcomes of this comprehensive research project called ‘SOFIE – Sistema Costruttivo Fiemme’ proved the suitability of multi-storey X-lam structures for earthquake-prone regions. The buildings demonstrated self-centring capabilities and high stiffness combined with sufficient ductility to avoid brittle failures. The tests provided useful information for the seismic design with force-based methods as defined in Eurocode 8, that is, a preliminary experimentally based action reduction factor of three was confirmed. Valid, ductile joint assemblies were developed, and their importance for the energy dissipation in buildings with rigid X-lam panels became evident. The seven-storey building showed relatively high accelerations in the upper storeys, which could lead to secondary damage and which have to be addressed in future research. Copyright

We conducted pseudo-dynamic tests and earthquake response analysis on half scaled three-dimensional models of conventional wooden structures, by changing horizontal diaphragms stiffness, vertical walls stiffness and ground acceleration ratio in the perpendicular direction on the specimens. Displacement response of simulation agreed well with pseudo-dynamic tests. The lumped mass 3D-model is suitable for predicting earthquake response of this structure. We conducted also additional simulation on the specimens. The maximum displacement in the parallel direction of specimens was more affected by the eccentricity in the perpendicular direction than by floor stiffness. When the eccentricity ratio is under 0.3 in both directions of specimens, the ground acceleration ratios in the perpendicular direction and floor stiffness little effect on the maximum displacement response parallel to the specimens.

Pseudodynamic (PSD) tests were conducted on plywood-sheathed conventional Japanese three-dimensional (3D) wooden structures. Lateral load was applied to the edge beam of specimen structures to generate eccentricity loading. Specimens were based on a combination of shear walls with openings in the loading direction and horizontal diaphragms with different shear stiffness. The principle deformation of the horizontal diaphragm was torsion for rigid diaphragms and shear deformation for flexible diaphragms. Lumped-mass time-history earthquake response analysis was conducted on the tested structures, and additional calculations were conducted on structures with different eccentricity rates. Dynamic analyses were conducted by varying the masses and the resistance of the walls in the loading direction. The simulated peak displacement response in the loading plane agreed comparatively well with the PSD test results. The maximum displacement response on changing the wall resistant ratio showed almost the same tendency as that obtained by changing the mass ratio up to an eccentricity rate of 0.3; however, the maximum displacement response increased markedly beyond an eccentricity rate of 0.4. It was proved that the lumped-mass D model proposed in this study was appropriate for conducting a parameter study on the 3D dynamic behavior of timber structures.

Time-history response analysis could be obtained good information of seismic performance of timber structure building. Modelling that used of time history analysis usually based on the static test results of fasteners, walls and frames. Shaking table test is one of the effective methods to verify the reliability of model on dynamic behaviour. To verify the model's reliability, shaking table test should be carried out in consideration of the weight of test building, acceleration of each layer and internal story drift of displacement. To measure internal story drift is rather difficult and important factor, because the rigid tower for measuring displacement within the table as ordinary static loading test. CNR-IVALSA have been established SOFIE project on sustainable buildings used cross-laminated panels(X-LAM) and shaking table test on 7 story X-LAM building was carried out E-Defense in MIKI city on cooperation research with NIED, Shizuoka University and BRI in Japan. In this tested we could try two methods for measuring the internal story drift. One is displacement transducer setting in the building for measuring relative displacement between floor and ceiling, the other is optical displacement measuring system that optical transmitter is attached to the building and optical receiver is placed out of the table. In this report, internal story drift was compared with accumulated displacement measuring transducer in the building and difference displacement of table and optical transmitter. Optical displacement system is necessary to compensate the angle of roll, pitch and yaw on the table. Comparison with test results, long direction of building that mainly shear deformation shows good agreement of two measuring results, but short direction of building that include bending deformation shows optical displacement is larger than the accumulated displacement in the building.

Ten types of single shear screwed joints and nailed joints with different diameters, lengths, and side members were subjected to the monotonic and reversed cyclic loading. Test results were compared with the yield capacity and load-carrying capacity calculated by Yield Theory using the embedding test results of main and side members and the bending tests results of nails and screws. The calculated yield capacity and load-carrying capacity by Yield Theory showed good agreement with the experimental results. It was proved that Yield Theory is applicable to determining the allowable strength of screwed joints.