Akihisa kitamori

Prestressing in wood connection, due to frictional forces, improves mechanical properties of the connection. This paper presents novel friction-based connectors, and corresponding tests at the connection and system levels. The friction-base connector is composed of a softwood or hardwood dowels inserted into the wood-based material and tightened to generate frictional force. Long-term performance was evaluated by stress relaxation tests and time-dependent connection tests. To evaluate dynamic performance of shear walls with friction-based connectors, shake table tests were conducted. The shake table tests showed that the restoring force characteristics of the wood friction shear walls were bilinear reflecting the behaviors of the friction-based connectors. The strength degradation of the wood friction shear walls due to cyclic input was small that more seismic inputs could be applied before any significant damage to the wood friction shear wall. Results of stress relaxation tests, for periods of 1 to 3 years, showed that the stresses were maintained at 70–90% under uncontrolled environment. On the other hand, the results of time-dependent connection tests, for 1 to 6 years, showed high initial clamping stresses caused large performance loss, but high performance could be maintained when tightened below the allowable stress for sustained loading.

<title>Abstract</title>In this study, the columns with interior notches in traditional Japanese timber frames were selected as the research object, and static bending tests were performed to investigate the effect of interior notches on the flexural properties of columns. First, the bending behaviors of columns under three-point and four-point load configurations were compared to obtain a suitable referenced strength of a column without notches. The reduction in the load-bearing capacity of columns with different types of interior notches in traditional Japanese timber structures was determined through experimental tests and statistical analysis. The results indicated that the mean bending strength of columns with three different notch types was consistent with those without notches, the continuous timber on both sides of the notch had a beneficial effect on maintaining a higher strength and reducing the stress intensity around the notch. The fracture position and the standard deviation of the bending strength were affected not only by the notch depth, but also by the notch width on the tensile side of the column.

<title>Abstract</title>The pretensioning force in bolted joints enhances the lateral strength of the connections, and causes the embedment of metal washers into wood. Despite the significance of embedment behavior in the design of bolted joints, its mechanism has yet to be fully understood. In this study, the mechanism of the embedment of a metal washer into wood along the radial direction was examined through three-dimensional nonlinear finite-element analysis (FEA). The FEA results were validated by comparing them with experimental results for nine metal washers with different geometries. Moreover, the sensitivity of embedment stiffness and yield load to wooden material constants was also investigated. The numerical results showed good qualitative and quantitative agreement with the experimental results. In addition, the embedment stiffness and yield load were sensitive to the yield stress and Young’s modulus of wood in the radial and tangential directions. The determination of these mechanical properties of wood through material testing is important for reproducing the behavior of the embedment of a metal washer into wood and accurately estimating the yield load and initial stiffness using FEA. This will play a significant role in designing bolted joints.

We have developed the new hybrid structure of CLT infill and steel frame for middle-rise and high-rise buildings. This structural system can achieve the high structural potential of the CLT panel by holding around the CLT panel with steel frame. Steel frame can support sustained load of a high-rise building without CLT panels and can build long-span beams reasonably. Compression stress of CLT seismic panel can be transmitted to the upper and bottom steel beams through high strength mortal layer, and the steel beams can secure high shear strength as boundary beams. Shear of the CLT panel is transmitted by drift pined joints with insert-steel gusset plate. And tension stress balanced with compression stress of CLT is supported by steel tie bar. To clarify the performance of this structural system, we have conducted the structural experiment series with seven test frames in 1/2 scale. The result of the structural experiment series provided the following findings. Firstly, all of the CLT specimens reached compressive or shear failure, and performed to their full structural potential. Because of that, it has been found that it is possible to perform structural design that takes advantage of full CLT performance. The structural performance has increased up to max. 3.48 times for the horizontal stiffness and up to max. 2.67 times for the horizontal bearing capacity, by inserting CLT panels into the streel frames. All CLT panel showed slip type restoring force characteristic. In case of shear failure, the decreases in shear force were caused at story deformation angle greater than 1/71 radian. In case of compression failure, the decreases of shear force were gradual, and their deformation performances were excellent. It has been found by the experiment series that these failure modes of CLT depend on aspect ratio (H/L) of CLT, and in case of low H/L, shear failure tends to occur. The shear strength and elastic shear modulus of test frame CLTs in shear failure could be reduced to about 70% of the material shear test. When the story deformations of the CLTs are separated into the deformation components of shear deformation, slip displacement of the joints, and rotational deformation of the CLTs, the rotational deformations of the CLTs are the largest. And the rotational deformation ratio of story deformation tends to increase by H/L of CLT Based on the above findings, a subsequent paper will show the detail study on compressive stress transfer in the upper and bottom surfaces of CLT with analytical studies, and propose structural design and stress analysis method of the structural system.

The study deals with the damage control system of wooden houses using wood friction-based dampers subjected to earthquake motion. In this study, wood friction joints were developed to introduce damping into wood shear walls. Shaking table tests were also conducted to investigate the seismic performance of two-story timber structures composed of plywood shear walls, plasterboards and timber shear walls using high damping devices. The purpose of this study is to propose an estimation method of the required quantity of the friction damper to satisfy the restriction value of the story drift angle for the continued use after earthquake motion.

To investigate the effects of tightening speed on the torque coefficient in lag screw timber joints with steel side plates, tightening tests were conducted on main timber members made from Cryptomeria japonica, Chamaecyparis obtusa and Pseudotsuga menziesii, under four tightening speed conditions (1, 4, 10, and 20 rpm). Major stick-slip behavior was observed in C. obtusa based on the relationship of tightening angle with clamp force, tightening torque, and thread torque at tightening speeds of 1 and 4 rpm. In addition, tightening speed’s effects on the torque coefficient (K) varied depending on the wood species of the main member. In P. menziesii, K was not affected by the tightening speed: the ratio of torque expended on tightening was 25% on average, and the ratio of torque expended on bearing surface friction was higher than the ratio of torque expended on thread friction.

An occurrence of brittle failure at the corner notch when large size CLT plane is subjected to the inner shear force has been pointed out as a problem. In this research, in-plane shear tests of L shape CLT corner elements were carried out to investigate their failure mode and moment carrying capacity. The maximum moment showed smaller value than bending strength of straight CLT. Maximum moment in pullover loading was lower than pushover condition, and cyclic loading showed the smallest strength. It was thought the rolling shear failure caused a reduction of maxim moment in pushover loading condition, and stress concentration at in-corner notch also became at reason of low moment carrying capacity of L shape CLT members.

Taking the Dou-gong bracket complex on the column of Tianwang palace in Baosheng temple, Ming dynasty as the research object, the lateral rigidity of Dou-gong bracket complex with the utilization of Glulam on Chinese traditional architectural components were studied based on the cyclic loading tests conducted on the full-scale specimen. To compare the relationship of lateral rigidity with initial vertical load, 3 initial roof loads of 0.8t, 1.6t, and 2.4t were applicable to the specimen. Results have shown that the lateral rigidity of Dou-gong specimen showed positive correlation with the increase of vertical load, and the rotation of Lu-dou component plays a major role in the whole deformation of Dou-gong bracket complex. In contrast with sawn timber, the specimen made of Glulam has stable working and energy dissipating conditions under lateral load, but when Glulam applied on the smaller components or tenon and mortise connections, the different adhesive strength and fiber directions will increase the instability of their performance.

Laminated Veneer Lumber (LVL) is a kind of engineered wood product that could be used as joists in a timber building. Holes in joists are many times necessary to allow piping system to pass through, such as water plumbing, for the purpose of avoiding additional space requirement. Introducing a hole in the shear dominant area of a joist significantly changes the distribution of stresses in the vicinity of the hole. Tensile stresses perpendicular to grain appear and the bearing capacity of the member can accordingly be decreased. Therefore, the failure mechanism of joists with holes should be concerned seriously. This paper presented the result of tests on LVL joists with round holes of different diameters, two kinds of LVL specimens that made by Douglas fir and Chinese poplar respectively were tested. The failure mechanism was analysed, and two existing design methods were compared. The result showed significant reduction of bearing capacity along with the increase of hole's diameter, and some differences between two design methods.

This research aims to figure out the performance of Cross Laminated Timber (CLT) shear wall infilled in steel frame as a seismic reinforcement. Firstly, to make the most of the shear capacity of CLT panels, the steel plate inserted drift-pin joint as end connection of CLT panel was investigated to find out the best drift-pins arrangement. Then as a case study, unit frame with this system was analysed by FE model. Results suggested that the system have enough shear capacity by virtue of CLT panel. In addition to the case study, shear wall test was conducted to investigate the actual behaviour of CLT shear wall. Joint tensile test was also conducted in the condition of different arrangement of drift-pin. The results suggest that CLT shear wall have enough strength of shear, but estimation of failure mode and yield load is remained to be discussed.

This study empirically examines the relationship between clamp force and pull-out strength in lag screw joints of timber members, using data obtained in tightening tests and pull-out tests. Maximum clamp force per unit screw length as determined from the tightening tests was lower than the lower bound for the 95% tolerance range for pull-out strength per unit screw length as determined from the pull-out tests. Moreover, X-ray CT (computed tomography) observations of anchor members from both tests revealed that failure behavior clearly differed between the tightening test and the pull-out test: tightening caused damage to the wooden, female thread in addition to major splitting damage in the wood perpendicular to the grain near the tip of the lag screw.

A method for calculating plastic clamp force from tightening torque was presented by considering a bi-linear model obtained from experimental tightening torque-clamp force relationships. The practical applicability of the calculation method was verified by tightening tests of Cryptomeria japonica bolted joints using metal washers of various sizes. Results were as follows : It was found that a ratio of side length (diameter) to thickness of metal washers ranging from 7.8 to 16.0 did not affect the torque coefficient. In addition, the ratio of maximum plastic torque coefficient to maximum elastic torque coefficient, gamma(max) and the ratio of minimum plastic torque coefficient to minimum elastic torque coefficient, gamma(max), which are elements of the calculation method, tended to increase depending on embedment into timber of metal washers in side-length (diameter) to thickness ratios of 10.0 (washer size : 32 x t 3.2 mm), 10.9 (washer size : 35 x t 3.2 mm) and 7.8 (washer size : 35 x t 4.5 mm). Furthermore, calculated tightening torque values were verified by tightening tests using a digital torque wrench. As a result, plastic clamp force values obtained by experiment agreed with calculated values ranging from minimum clamp force F-min to maximum clamp force F-max. However, the method of reducing variation in gamma(max) and y(min) remained to be investigated.

The new type of seismic retrofit method using CLT panels as shear walls is proposed. In this method, setting small CLT panels in RC frame and bonding each panel and panel to RC frame with epoxy resin, panels compose shear walls in dry construction method. This paper reports the shear tests of 1/3 scale specimens for 5 reinforced types. Element tests of materials and joints used in these specimens were also conducted. A ductile load-slip behavior was observed even after failure of bonding joint in every specimen. The stress analysis showed that the bond strength between CLT and RC and shear modulus of CLT in these specimens match the result of element tests. This indicates the specimen strength could be divided into the RC frame strength and the CLT strength at the initial stage. As the bond strength between CLT and RC was smaller than the shear strength of CLT, the specimens can be stronger by increasing the adhesive area.

Shear wall tests of single CLT wall of which size is 1 x 3m were conducted to evaluate the shear performance and 4m width shear wall with opening tests consisting of double 1x3m of CLT panels and hanging panels were also conducted. Tensile bolts were used as connection between the shear wall and foundation, shear wall and hanging wall, and top-bottom of shear walls. Simple tensile tests for every bolt joint, compression, shear and bending tests for CLT panel were conducted to calculate the load-displacement relationship and to derive structural design procedure of the shear wall. As results of these static loading tests, the following conclusions are drawn 1. Each CLT panel remained elastic and shear deformation of CLT panel is less than the connections deformation. This highlighted seismic performance of CLT construction is controlled by the design and detailing of the connections. 2. Equations to calculate load-displacement relationship of CLT shear walls are computed from the equilibrium of internal and external forces. The equations are validated with the experimental results.

Due to major recent major earthquake, many traditional Joglo buildings have been damaged. In order to preserve Javanese wooden house against earthquake attack, as tangible culture, an evaluation and improvement of timber structures is indispensable. Joglo is the most complicated and sophisticated roof type in terms of the construction and techniques of Javanese wooden houses. The Joglo use teak wood as the primary construction material for both the building's structure and the ornaments. The house is use a knock down construction method, using mortise and tenon. Joglo-style for high-class society e.g., sultan place. The Joglo structure consists core and side structure. In term vertical and horizontal direction, they have different proportion and performance against lateral force. Structural proportion has role with seismic vulnerability. Here, investigation of the structural proportions of Javanese wooden house was carried out associated with earthquake structural damages. It shows the level of vulnerability of Joglo buildings against earthquake attack. A total of 29 Joglo buildings were estimated; the estimation can be used for earthquake mitigation in the future. In this paper, we report the results of investigation and objective to verify the contribution of structural proportion to the damage level of Joglo. (C) 2015 The Authors. Published by Elsevier B.V.

Six scaled-specimens of glued-acacia beam were tested in bending and effectiveness of non-metal repair of damaged beam by epoxy adhesive-vacuumed method was investigated. Two failure modes of glued-acacia beams by bending test were crack in bottom center and split from edge. Different covering method was used for them. MOE of type A showed fairly good recovery after repair. However in comparisons both specimens between bending strength before and after repair remarkable degradation. The epoxy adhesive-vacuumed method in full cover condition was thought to be appropriate and bending strength has possibility to increase more. The reason is adhesive is difficult to permeate the crack inside of the beam, they can permeate mostly from the surface. (C) 2015 The Authors. Published by Elsevier B.V.

A post-earthquake survey was performed on Joglo Javanese wooden houses, seriously affected by the May 27, 2006, Yogyakarta earthquake in Java, Indonesia. Investigations on 20 damaged Joglo buildings reveal that the structure's damage can be classified into three categories: slip between columns and stone foundation, broken joints between outer ring beam and column, and collapse of core structure. Four damage levels were defined: I) damage on the base joint of side structure, II) fatal damage on the side-structure, III) destroyed core structure, and IV) totally collapsed core structure. The side structure turns out to be relatively weak, while the core structure is able to secure the structural performance of Joglo buildings. A distinct relationship was identified between the levels of structural damage and the area ratio of core structure and the main column projection. It was verified that structural proportion significantly contributes to the assessment of damage. The joint failure represents a significant point in terms of maximum retention for conservation. Based on a damage level approach, an assessment methodology to optimize reinforcing strategies. This study gives recommendations for the preservation of such precious structures from future earthquakes, while avoiding inappropriate interventions.

本研究では、インドネシアジャワ島の代表的伝統木造建築物である、Joglo形式の建物の地震被害について論じた。2006年の地震被害調査結果と関連づけ、Jogloの規模および構成する部材の寸法比率と、被害規模に明確な関連性を見出した。これにより特定比率以下の建物の耐震補強の必要性を提言した。

The tensile performance of Japanese traditional wood-to-wood joint connected by inclined shear key was studied. Firstly series of full scale joint tests were carried out to grasp load carrying capacity and deformation phenomena. Then mechanical model was proposed especially focusing on the equilibrium of load and moment around shear key. The reaction forces which caused the split failure at both tip and bottom of the slit for spline were calculated based on elemental beam theory. Finally equations to estimate the stiffness and strength of the joint were introduced. The calculated bi-linear curves of load-displacement relationship satisfactory evaluated the test results by the safe side.

Many Javanese traditional timber structures have been destroyed by major earthquake. A lot of them tend to be dismantled due to a high cost of reconstruction and a demand for more reliable structures. In order to preserve this disappearing building as valuable and tangible culture, a deeper understanding on these traditional timber structures is necessary. Especially the restoring force of the traditional joints, which are the major earthquake-resisting elements has to be investigated. The static characteristic of these structural components has been investigated experimentally. A total of 12 full-scale specimens of 2 types made from glued Acacia-mangium were tested. The specimen simulated joint at middle part, which is a joint of column-tie beams interlocked each other. The horizontal cyclic load was applied on the specimen placed in pin joint frame from two mutually perpendicular directions. The cyclic loading protocol consists of 7 increasing target deformations from 1/200 radian to 1/15 radian, and finally until failure. As the test result, failures were caused by embedment, crack, and split in beams parallel to the load direction. All crack of beam started from corner of beam mortise and resulted in the split. From the curve of load and rotational relationship, occurrence of initial slip leaded to the larger deformation. It revealed the importance of joint tightness against future earthquake. (C) 2014 The Authors. Published by Elsevier B.V.

In order to evaluate the dependence of angular orientation of Cross Laminated Timber (CLT) in terms of embedment and shear strengths, we derived a prediction formula and compared it with experimental results. The assumptions used in the formula based on independence of each layer are: (a) For embedment of circular steel bar against the CLT, the total embedment strength is the average strength of each layer. (b) Embedment strength of a layer inclined to the loading direction is expressed by Hankinson's formula. (c) For shear strength of CLT, either vertical compression or shear failure along the grain occurs in each layer. (d) The total shear strength is also the average of the strength of each layer. Evaluated strength to angle relationship tended to correspond with test results, although estimated values were lower than actual test results.

The tensile performance of Japanese traditional wood-to-wood joint connected by inclined shear key was studied. Firstly series of full scale joint tests were carried out to grasp load carrying capacity and deformation phenomena. Then mechanical model was proposed especially focusing on the equilibrium of load and moment around shear key. The reaction forces which caused the split failure at both tip and bottom of the slit for spline were calculated based on elemental beam theory. Finally equations to estimate the stiffness and strength of the joint were introduced. The calculated bi-linear curves of load-displacement relationship satisfactory evaluated the test results by the safe side.

Prefabricated mud-shear wall is a mud-shear wall in a compact modular size manufactured in factory work. At construction sites it is constructed simply by being fitted into a wooden frame. It keeps the quality stable even if there is no skilled craftsmen, and it significantly shortens the construction period. In this paper we evaluated structural performance of prefabricated mud-shear wall conducted using static loading test and dynamic shaking table test. It is confirmed that the shear wall has a simple structural mechanism that depends on the single unit, and so its structural performance can be analyzed by a simple model. It is also confirmed that ultrasonic measurement method applied to the prefabricated mud-shear wall is effective for damage evaluation estimation.

A shear wall composed by prefabricated mud wall units (PMWU) was studied. Mud panels reinforced by bamboo laths are enclosed in wooden frame, combining mud material's high energy absorption and stiffness of wooden frame. Among the advantages are workability and quality control before and after assembly. The PMWU's performance related to the number of frames’ connectors was analyzed. Digital speckle photography (DSP) was used to measure strains and finite element method (FEM) to validate the results. The shear stiffness of PMWU varied due to rotation of the panels. The stress transmission was influenced by the number of connectors via shear and contact between frames.