DEVELOPMENT OF DUCTILE MOMENT-RESISTING JOINT BASED ONA NEW IDEA FOR GLULAM PORTAL FRAME STRUCTURES.

Kohei Komatsu1, Shouichi Nakashima2 and Akihisa Kitamori3

ABSTRACT: A new ductile glulam moment-resitting joint system was developed by making use of friction resistanceof steel splice joint for before-yielding revel and for post-yielding level embedment resistance of steel bolted joint wasused. The basic idea has been recognized by the author through past experiments on glulam splice joints using drift-pinsand this time the same idea was extended to glulam moment resisting joint system using Lagscrewbolt (LSB). At thismoment, only limited number and type of experiments have been conducted but good coincident between predictionand experiment was obtained, therefore using this limited results, we would like to introduce a concept of new ductileglulam moment-resisting system which will be usable for low-rise glulam semi-rigid portal frame structures.

KEYWORDS: Friction Joint, Post-Yielding Embedment of Steel, Lagscrewbolt, Glulam, Ductility

1 INTRODUCTION 123

On May in 2010, a law called as “Promoting TimberStructures for Public Low-Rise Buildings” wasproclaimed in Japan. This law led good wind blowtowards timber structures. So as to meet this law, weneed to develop a new moment-resisting joint systemwhich should satisfy the following requirements.

1) High initial stiffness2) Clear yielding point3) Controllable ultimate strength4) High energy absorption performance (Ductility)5) Easy repair after suffering devastating earthquake6) Low cost7) Versatility of existing technologies

In order to satisfy the above mentioned criteria, wedeveloped a new method as shown below.

2 BASIC CONCEPT

2.1 Conventional glulam LSB joint

Figure 1 shows a schematic explanation of conventionalLSB glulam joint with steel splice joint connected by

1 Kohei Komatsu, Research Institute for SustainableHumanosphere, Kyoto University, Gokasyou, Uji, Japan,Email: kkomatsu@rish.kyoto-u.ac.jp2 Shouichi Nakashima, Research Institute for SustainableHumanosphere, Kyoto University, Gokasyou, Uji, Japan,Email: s-nakashima@rish.kyoto-u.ac.jp3 Akihisa Kitamori, Research Institute for SustainableHumanosphere, Kyoto University, Gokasyou, Uji, Japan,Email: kitamori@rish.kyoto-u.ac.jp

high tension bolts (HTB). In this joint, as HTB joint isalmost rigid, only elastic deformation between LSB andglulam affects on the initial stiffness but its quantity isvery small thus the apparent initial stiffness of the wholeserial joint is very high. Once tensile force reaches toPslip, which indicates load at HTB starts to slip, loaddrops suddenly with big sound. After then load onceagain rise up steeply because HTB contacts with steelplate. If the ultimate tensile strength of LSB PLSB islower than the ultimate strength of HTB PHTB, wholejoint will lose its performance due to pull-out failure ofLSB from glulam. This type of rather brittle failure modewas observed in previous LSB joint actually.

Fig.1 Load-deformation behaviour of conventional LSBjoint connected with steel splice HTB joint. .

2.2 Improved glulam LSB joint

To avoid steep rise-up of tensile force due to contact(embedment) of HTB with steel plate after initial slip ofHTB, we provided artificial slotted-hole whose shortdiameter “d” is adjusted to be slightly smaller than thelead hole “D” of HTB, hence HTB will be able toprogress with expanding narrow pass by consuming a lotof energy. If this scenario could be realized, the apparentload-deformation curve of modified LSB joint willbehave like solid-line in Fig.2, subjected to the conditionthat ultimate tensile strength of LSB PLSB should behigher enough than the ultimate strength of HTB PHTB.

Fig.2 Load-deformation behaviour of modified LSB jointconnected with steel splice HTB joint with special slotted-hole [1].

3 EXPERIMENT

3.1 COLUMN LEG JOINT

Fig.3 Column leg joint and test specimen [1]

In order to verify the above mentioned hypothesis,column leg joint test specimens were fabricated usingEuropean red-pine glulam (JAS-E110F330), 30 x 360mm LSB and M16-F10T HTB. In this experiment, the

lead hall of HTB “D” was 17 mm, while short diameterof slotted-hole “d” was 14 mm as shown in Fig.3.

3.2 RESULT

Figure 4 shows an example of moment-rotation anglerelationship of column leg joint. A lot of zigzag up &down curves indicate load-drops due to slip of HTB. Inspite of these up-and-down, consequently envelopecurve of the test specimens showed constant up-wordtendency as shown in Fig.5. A simple prediction basedon the design value on HTB also gave fairy goodprediction for the initial stiffness and yielding moment.

Fig.4 Moment-rotation relationship

Fig.5 Envelope curves and prediction by mechanicalmodel.

4 CONCLUSIONS

As can be seen from the preliminary experimental result,the moment-resitting joint based on a new idea let usexpect to explore new possibilities for glulam portalframe structures. We will finish further experimentalstudies for applying this joint system to beam-columnjoint and actual portal frame structure before end of 2011.

ACKNOWLEDGEMENTThis work was supported by Grants-in-Aid for ScientificResearch (B) 22380095 provided by Japan Society forPromoting Science (JSPS). Authors would like toexpress their sincere thanks to JSPS.

REFERENCES[1] Japanese Patent Application : No. 2011-148503,

Inventor : Kohei Komatsu, Applicant : KyotoUniversity, 4th July 2011.

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