A newly developed hybrid pin (HP), composed of a compressed wooden dowel inserted into a stainless steel pipe is suggested in this research. This configuration is expected to grant high stiffness by bending performance of the metal pipe and rich ductility through shear deformation of compressed wooden dowel without brittle split of the joint member. Experimental tests were performed in order to verify your assumptions and pursue an optimum design. Double shear test perpendicular to the grain of HP was conducted with parameter of thickness and loading direction for base member for pin’s diameter. Rotational test for mortise and tenon joint inserted with HP was performed in order to evaluate the moment resisting performance. Consequently, the hybrid pin showed satisfactory performance as shear type fastener by virtues of not only relatively high stiffness but also rich ductility originated from the properties of each component, stain less steel pipe and compressed wood.
In order to resist the destructive forces of earthquakes in Japanese small scale timber structures, structural performance (as eismic performance) is demanded. Timber structures have relatively low joint-performance compared to that of RC (reinforced concrete) or steel structures, and focus needs to be set not only stiffness but also on their ductility.
Consequently, various types of joints and a lot of effort have been put into improving the joint performance of a traditional wood-to-wood joint in order to apply it in modern joints using steel fasteners.
Recently, the new types of timber joint with less steel usage, and more newly developed materials have been vigorously introduced as improvement based on environmental points of view.
Hence, this research is focused on a shear-key type of joint. The shear-key type of joint has been widely used in traditional as well as in modern joinery until now due to its ease of assembly and relatively high performance as a mechanical joint method [
Aiming to improve the key-joint’s performance, a hybrid pin (HP), composed of a compressed wooden dowel [
Firstly, double shear perpendicular to the grain of HP was studied; focusing on the balance between shear performance and the ratio of base member’ thickness for dowel’s diameter [
In this research, the hybrid pin is composed of a 12 mm inner-diameter stainless steel pipe (SUS304) with a thickness of 1 mm, and a 12 mm diameter dowel of Japanese cedar (Cryptomeria japonica D. Don) compressed until 70% of its original radial dimension. The appearance of the hybrid pin is shown in
The bending property for HP was obtained using the 3_Point bending test with 200 mm span as shown in
This section deals with the evaluation of double shear properties of HP focusing on the balance between strength, loading direction, and dimensions of the base member. The experimental results are then compared with the values calculated by European yield theory.
Bending properties | ||
---|---|---|
MOR (MPa) | MOE (GPa) | |
SC0 | 405 | 1352 |
SC90 | 412 | 1462 |
Double shear test of HP-joint with the loading direction parallel to the grain was performed in order to evaluate
the performance of HP as shear-key fastener and verify its optimum design.
Four types of base members were prepared, with thicknesses of 1d (13 mm), 2d (26 mm), 3d (39 mm) and 4d (52 mm) for dowel diameter. Joints for double shear test were assembled to m2s1, m3s2, m4s3 as shown in
An axial load was applied by a testing machine (TCM10000: shinkoh) to each specimen to produce shear deformation between the main member and two side members of the test specimen, as shown in
Average relative shear deformation between the main and the side members was measured while the load was applied at a speed of 2 mm/min.
All the parameters show rich ductility after yielding. Yield and maximum strength increased with the thickness of the base member, although no considerable difference was found in the stiffness with variation of the
Base member | L (mm) | W (mm) | T (mm) | ||
---|---|---|---|---|---|
Main member | 200 | 100 | m2 | m3 | m4 |
26 | 39 | 52 | |||
Side member | 200 | 100 | S1 | S2 | S3 |
12 | 26 | 39 |
base member’s thickness. Double shear performances improved with the thickness of the base member. But there is no big difference was observed regarding the inserting direction of the dowel.
m2s1, and mode-II for setup 2 for m3s2 and m4s3 by European yield theory [
Double shear test of HP-joint with loading direction perpendicular to the grain of the base member was per- formed in order to evaluate the performance of HP as shear-key fastener, as shown in
The test specimen’s thickness was cut to 3d (39 mm) for the main member and 2d (26 mm) for the side member. A 13 mm HP was used, as shown in
No. | Stiffness | Yield strength | Maximum strength | |
---|---|---|---|---|
K (kgf/mm) | Py (kgf) | Pmax (kgf) | ||
SC0m2s1 | 1 | 849 | 741 | 911 |
2 | 1068 | 543 | 794 | |
3 | 1065 | 527 | 928 | |
Ave. | 994 | 604 | 878 | |
SC0m3s2 | 1 | 1059 | 1161 | 1334 |
2 | 1071 | 928 | 1271 | |
3 | 1150 | 1003 | 1304 | |
Ave. | 1093 | 1031 | 1303 | |
SC0m4s3 | 1 | 1061 | 894 | 1415 |
2 | 875 | 1054 | 1396 | |
3 | 984 | 1145 | 1589 | |
Ave. | 973 | 1031 | 1467 | |
SC90m2s1 | 1 | 1210 | 789 | 871 |
2 | 1667 | 594 | 928 | |
3 | 1703 | 577 | 911 | |
Ave. | 1527 | 653 | 904 | |
SC90m3s2 | 1 | 1470 | 953 | 1237 |
2 | 1966 | 853 | 1329 | |
3 | 1413 | 978 | 1329 | |
Ave. | 1616 | 928 | 1299 | |
SC90m4s3 | 1 | 1121 | 897 | 1394 |
2 | 1092 | 1079 | 1405 | |
3 | 1444 | 1137 | 1488 | |
Ave. | 1219 | 1038 | 1429 |
No. | Experimental | EYT |
---|---|---|
Py-exp (kgf) | Py-cal (kgf) | |
SC0m2s1 | 604 | 878 |
SC0m3s2 | 1031 | 1015 |
SC0m4s3 | 1031 | 1522 |
SC90m2s1 | 653 | 878 |
SC90m3s2 | 928 | 1015 |
SC90m4s3 | 1038 | 1522 |
The test setup was placed on a 3-point bending test device with a 400 mm-span in order to load the side members. Axial load was then applied to the main member at its center point. Shear deformation between main
and side members was measured by displacement meter.
One specimen was tested by constant loading. Then yield strength was defined at 800 kgf. Thus the cyclic loading schedule was set to 100, 200, 400 and 800 kgf for the other three specimens. After reaching the target load, the loading was decreased to 0 kgf then next target load was then followed. The cyclic loading test was finished once the last target load of 800 kgf was reached. Subsequently, a constant load was applied until the specimen’s failure or drop of load to an 80% of the maximum load. The loading speed was 0.5 mm/min for cyclic loading test and 3 mm/min for the constant loading test.
Even though a joint with a steel pin resulted in a 2.5 times higher stiffness, and 1.4 times higher maximum strength than a HP-joint but brittlely failed soon after reaching maximum strength.
However, HP-joint showed idealistic performance that it had long plastic zone maintaining almost same level of maximum strength after yielding from 3 mm to 20 mm in displacement. HP-joint showed 3 times than steel pin joint in energy consumption.
No significant differences between constant loading and repeated loading were revealed from the double shear test performed on HP-joint.
Shear performance of loading direction perpendicular to the grain of the base member in side member is lower than that of parallel in chapter 2.3.1. It is due to bearing strength of perpendicular to the grain of the base member is relatively lower than that of parallel direction.
Moment resisting joint using HP was suggested.
Constant loading | Repeated loading | |||||
---|---|---|---|---|---|---|
XHP | Steel pin | XHPR1 | XHPR2 | XHPR3 | Ave. | |
K (kN/mm) | 3.94 | 15.74 | 4.60 | 6.89 | 8.39 | 6.63 |
Py (kN) | 7.78 | 9.59 | 8.60 | 8.19 | 7.87 | 8.22 |
Pmax (kN) | 10.49 | 13.85 | 10.98 | 10.73 | 10.73 | 10.82 |
E (kNmm) | 223 | 76 | 220 | 310 | 211 | 247 |
Note: K: initial stiffness, Py: yield strength, Pmax: maximum strength, E: energy.
ration for the dowel’s insertion. The specimen was made of spruce (Piceaabies) glue-lam. The jointing process, involved the manufacturing of mortise-and-tenon on each specimen, their assembling, drilling of holes, and insertion of HP. Each specimen was placed on a frame with hydraulically-operated jack, as shown in
Horizontal load was applied by hydraulically controlled Jack at the top of the column. The applied load, and horizontal displacement were simultaneously measured.
A cyclic loading schedule was applied as follows: ±1/300, 1/150, 1/75, 1/50, 1/25, 1/10 (Rad) at a first step, afterwards a constant loading was applied until to the specimen’s failure or limited displacement at test machine.
Stiffness | Yield moment | Maximum moment | Energy | |
---|---|---|---|---|
K (kN/rad) | Py (kNm) | Pmax (kNm) | E (kNm∙rad) | |
HPJ1 | 129 | 4.54 | 7.35 | 761 |
HPJ2 | 184 | 4.54 | 9.08 | 914 |
HPJ3 | 256 | 7.41 | 12.26 | 1055 |
number of HP, HPJ2 shows 1.42 times higher initial stiffness than HPJ1. It is thought that additional length of mortise in HPJ2 give influence on rotational performance. Compression strength on the flat edge in mortise of HPJ1 is relatively lower than that of additional edge in HPJ2 on the imbedding behavior between mortise and tenon originated from rotational moment [
Comparing specimens with different number of dowels, HPJ3 shows 1.39 times higher initial stiffness, 1.35
times higher maximum moment, and 1.63 times higher yield moment than that exhibit by specimen type HPJ2.
Specimen HPJ3 with 4 pins inserted exhibit a stiffness of 255.94 kNm, a yield moment of 7.41 kNm, and a maximum moment equal to 12.26 kNm.
In this research, the performance for the newly developed hybrid pin (HP) joint was evaluated.
The results from the double shear test loaded in direction parallel to the grain of the base member, specimen type m3s2 exhibit stiffness equal to 1400 kgf/mm, and yield strength of about 922 kgf. On the shear test with loading direction perpendicular to the grain of the base member, the specimen type m3s2 showed a stiffness of about 680 kgf/mm, and a yield strength of about 840 kgf.
Mortise-tenon joint with inserted hybrid pin showed high moment-resisting-performance from the rotational tests results. These values resulted in a stiffness of 255.94 kNm, and a yield moment of 7.41 kNm in the specimen type that includes 4 pins.
Consequently, the hybrid pin showed satisfactory performance as shear-type fastener by virtues of not only relatively high stiffness but also rich ductility originated from each different property of steel pipe and compressed wooden material.