Effect of Vertical Load under Cyclic Lateral Load Test for Evaluating Sugi CLT Wall Panel

Transcription

1 Effect of Vertical Load under Cyclic Lateral Load Test for Evaluating Sugi CLT Wall Panel Minoru OKABE 1, Motoi YASUMURA 2, Kenji KOBAYASHI 3, Takeshi HARAMIISHI 4, Yo NAKASHIMA 5, Kazuhiko FUJITA ABSTRACT: Structural performance of shear walls to resist against wind and seismic loading is evaluated by applying static or cyclic load testing. ISO21581 specifies the static and cyclic lateral load test for shear wall. ISO defines two method of lateral load test. Method 1 shows the boundary conditions are designed to produce mainly the shear response of the wall. Method 2 shows the boundary conditions are designed to produce mainly the rocking (rigid body rotation of the wall) or combined shear-rocking response of the wall reflecting the intended actual construction details of joints connecting the wall to bottom and top boundaries. Cross Laminated Timber panels (also known as CLT or X-LAM) are relatively new building material and high rigidity and strength compared to sheathing materials. It is possible to apply to low-rise residential buildings from the multi-story timber buildings. In Japan manufacturer has been already trying to produce Sugi CLT. Sugi (Cryptomeria japonica)is most popular softwood in Japan. In this report shows effect of vertical load based on ISO21581 method 2 under cyclic lateral load test of Sugi CLT. Vertical load applied three condition, 15kN/m, 3kN/m and without vertical load. Stiffness of CLT wall panel against horizontal load shows higher on vertical load. However maximum strength increase due to vertical load was smaller than the stiffness. KEYWORDS: Vertical load, Cyclic lateral load test, Sugi CLT 1 Introduction 123 Structural performance of shear walls to resist against wind and seismic loading is evaluated by applying static or cyclic load testing. ISO21581 specifies the static and cyclic lateral load test for shear wall. ISO defines two method of lateral load test. Method 1 shows the boundary conditions are designed to produce mainly the shear response of the wall. Method 2 shows the boundary conditions are designed to produce mainly the rocking (rigid body rotation of the wall) or combined 1 Minoru OKABE, Center for Better Living Tsukuba Building Research and Test Laboratory, 2 Tatehara Tsukuba Ibaraki, Japan & The United Graduate School of Agricultural Science, Gifu University okabe@tbtl.org 2 Motoi YASUMURA, Professor, Faculty of Agriculture Shizuoka University, 83 Ohya Suruga Shizuoka, JAPAN afmyasu@agr.shizuoka.ac.jp 3 Kenji KOBAYASHI, Assistant Professor, Faculty of Agriculture Shizuoka University, 83 Ohya Suruga Shizuoka, JAPAN kobayashi-k@agr.shizuoka.ac.jp 4 Takeshi HARAMIISHI, MEIKEN Lamwood Corporation. LTD. 129 Katsuyama Maniwa Okayama JAPAN t.haramiishi@meikenkogyo.com 5 Yo NAKASHIMA, MEIKEN Lamwood Corporation. LTD. 129 Katsuyama Maniwa Okayama JAPAN yo.nakashima@meikenkogyo.com Kazuhiko FUJITA, Hiroshima prefectural Technology Reserch Institute Forestry Research Center,-1 4 Toukaitihigashi Miyoshi Hiroshima JAPAN k- fujita83939@pref.hiroshima.lg.jp shear-rocking response of the wall reflecting the intended actual construction details of joints connecting the wall to bottom and top boundaries. Cross Laminated Timber panels (also known as CLT or X-LAM) are relatively new building material and high rigidity and strength compared to sheathing materials. They have been used to build everything from houses to multi-story apartment buildings. In Japan manufacturer has been already trying to produce Sugi CLT. Sugi (Cryptomeria japonica)is most popular softwood in Japan. In this report shows effect of vertical load based on ISO21581 method 2 under cyclic lateral load test of Sugi CLT. 2 Manufactured Sugi CLT MEIKEN Lamwood Corporation. LTD. has stated the prototype Sugi CLT panel. Sugi lumber used CLT panel was screened by machine grading based on glued laminated timber provided Japanese Agricultural Standard (JAS). Figure 1 shows the distribution of lumber MOE used CLT panel by machine grading. MOE of CLT lumber was used as the MOE of less 8.kN/mm 2 over 3.5kN/mm 2. Average MOE of lumber shows 5.kN/mm 2. Dimensions of the CLT wall panel manufactured, 1m wide, 3m long and 9mm thickness. And the test specimen of CLT was prepared three types of cross-sectional configuration. Layer arrangement of prototype CLT was provided 3 layers, 4 layers and 5 layers on 9 mm thickness. Adhesive bonding is used water based polymer- isocyanine adhesive which formaldehyde emission F4star certificated by Japan

2 Adhesive Industry Association (JAIA). And this adhesive was generally used on structural glue laminated timber in Japan. Adhesive is used only lamination without edge glue of lumber. Measured average density of Sugi CLT was 439 kg/m 3 and coefficient of variation shows 1.2%. And measured average moisture content was 12% used wood moisture tester by dielectric constant. Manufactured prototype Sugi CLT is shown in Photo 1 includes thickness 12mm and 15mm floor panel and m length. Frequency G1-G3 Ave.=5. STD.=1.27 AVE.=5.83 STD.=1.5 G1 G2 G MOE(kN/mm 2 ) Figure 1 Distribution of lumber MOE by machine grading necessary to confirm the shear performance using spline material. Vertical displacement Horizontal displacement Horizontal displacement Horizontal displacement W W Rocking mode Bending mode Shear mode Figure 2 Comparison of deformation mode of CLT shear wall 3.1 Tension Performance of Hold-down Fastener Test specimen Test specimen of CLT is consisted of 24mm width, 1mm maximum length and 9mm thickness. 2 types of Hold-down fastener were prepared which allowable tension strength shows 2kN and 25kN. And 2 types of Hold-down fastener which connected CLT and holddown are used ZN9 (diameter 4.11mm length 9mm JIS) nail type and M12 (diameter 12mm JIS) bolt type. Hold-down fasteners tested every type used M1 (diameter 1mm JIS) bolt to connect steel basement. Those hold-downs called Z mark fastener which were certificated for post and beam timber construction by Japan Housing and Wood Technology Center. Test specimen is shown in Figure 3. Caption of Hold-down fastener, N is meaning ZN5 nailed and 2kN used 2 nails and 25kN used 2 nails. B is meaning M12 bolted and 2kN used 4 bolts and 25kN used 5 bolts. W H HD-N25 HD-B Photo 1 Prototype Sugi CLT panel which is 9mm, 12mm and 15mm thickness 3 Structural Design of CLT Shear Wall CLT panel has rigid-body for using shear wall. Main criteria deformation mode shows rocking than bending deformation mode and shear deformation mode. Figure 2 shows the comparison of deformation mode of CLT shear wall. In order to predict load-displacement performance of CLT wall, it is necessary to confirm the tension performance of hold-down fastener against uplift load of CLT shear wall. And shear performance between bottom of CLT wall and sill or between top of CLT wall and floor CLT panel is important against horizontal load. If 1m width CLT wall panel placed continuously, 2m width or 3m width shear wall to wall connection is HD-N Figure 3 Tension test specimen of Hold-down fastener Test method Tension test was carried out based on ISO 17:23, Timber structures - Joints made with mechanical fasteners - Quasi-static reversed-cyclic test method. Based on monotonic loading test, cyclic loading protocol HD-B

3 was determined. However hold-down fastener worked on tension load did not work on compression load. So reversed cyclic test was carried out on only tension side. Figure 4 shows loading protocol of reverse cyclic test for hold-down fastener on CLT. Ultimate displacement decided 4mm based on monotonic loading test result and loading rate was provided approximately 1mm/sec. Figure 5 shows the hold-down tension test specimen set up the loading apparatus using slider. Number of cyclic loading test specimen is. And HD-B2 was tested only monotonic loading. Final failure mode of HD-25N, HD-25B and HD-2B is rapture of M1 bolt to connect the steel base. Rapture on M1 bolt was shown at the part of screw.hd-b2 failure mode shows not only rapture of M1 bolt but the embedding of M12 bolt at the CLT. Final failure mode of HD-2N is embedding of ZN9 nail at the Hold-down fastener connected of CLT. Photo 2 shows the general failure mode of HD-N25 and HD-N2. CLT9 HD-N25 1 CLT9 HD-N Figure Comparison of monotonic and cyclic loading of HD-N25 and HD-N2 HD-25N 1 HD-25B 1 8 M1 bolt Rapture 8 M1 bolt Rapture Figure 4 Loading protocol of reverse cyclic test for hold-down fastener on CLT 4 4 Jack 1kN (Tension side) Jack 1kN (Tension side) Displacement transducer Load Cell1kN Steel base Displacement transducer Load Cell 1kN HD-2N ZN5 nail CLT Failure HD-2B M1 bolt Rapture 2 2 Steel base Slider Figure 5 Hold-down test specimen set up the loading apparatus Figure 7 Envelop load-displacement curve on 4 types of Hold-down fastener Test results Figure shows the comparison of monotonic and cyclic loading of HN-N25 and HD-N2 hold-down fastener. Envelop load-displacement curve on 4 types of holddown fastener shows in Figure 7. HD-N25 and HD-B25 hold-down fastener shows approximately 8kN maximum load and rapidly tension load was reduced. HD-2N hold-down shows approximately kn maximum load. Beyond the maximum load, tension load was reduced gradually. HD-B2 shows approximately 8kN maximum load and rapidly tension load was reduced. However load-displace curve is different from HD-N25 and HD-B25. HD-N25 Photo 2 Failure mode of HD-N25 and HD-N2 HD-N2

4 3.2 Shear performance between bottom of CLT wall and sill Test specimen Test specimen of CLT is consisted of 5mm width, 25mm height and 12mm thickness. Sill plate is consisted of 12mm by 12mm section, 98mm long of glue laminated timber and made of Hinoki (Chamaecyparis obtuse). Average density of sill plate made of Hinoki was measured 482 kg/m 3 and average moisture content was measured 15.9%. At the center of the sill plate, CLT is set up. Face and back Layers of CLT are arranged vertical in the longitudinal direction and perpendicular to the sill plate grain. Connected fastener of CLT and sill plate was used wood screw manufactured Rothoblaas HBS D8-L18 in Italy. Connection between CLT wall panel and sill plate was toe screw connection from the CLT wall to sill plate. One test specimen was consisted four wood screws and screw spaced at 1mm. Number of monotonic loading test specimen is 2 and cyclic loading is. Test spacemen is shown in Figure 8. M1 Bolt CLT t=12mm 5 layer Figure 8 Test specimen of CLT wall and sill plate Test method Horizontal shear test was carried out based on ISO 17:23, Timber structures - Joints made with mechanical fasteners - Quasi-static reversed-cyclic test method. Based on monotonic loading test, cyclic loading protocol was determined. In this test, ultimate displacement was measured 8mm based on monotonic loading test result and loading rate was provided approximately 1mm/sec. load was measured in the load cell attached at the tip of oil jack and relative displacement from sill plate to CLT wall was measured displacement transducer. Measuring load was divided by the number of wood screws. Shear test apparatus of bottom of CLT wall and sill plate is shown in Figure Test results Envelop load-displacement curve for horizontal shear force between CLT wall panel and sill plate is shown in Figure 1. Red line shows monotonic loading and blue line shows envelop curve of cyclic loading. And the vertical axis shows the load per screw. Monotonic loading results show high ductility. Initial curve of cyclic loading was consistent with the monotonic loading. However when relative displacement between CLT wall and sill plate shows over 3mm, cyclic loading force were reduced but monotonic loading force were continually. Failure mode of GlueLam t=12mm 4lamina 12 CLT t=12mm 5 layer 8 4-Wood Screw Rothblass HBS 8-18 GlueLam t=12mm 4lamina monotonic loading shows embedding screw to the CLT wall and sill plate. Failure mode of cyclic loading shows breakage for bending wood screw. Photo 3 shows the typical failure mode. Jack st=3mm kN 荷重計 1kN Load cell Flat roller Figure 9 Shear test apparatus of bottom of CLT wall and sill plate Load (kn/screw) Jack st=3mm Figure 1 Envelop load-displacement curve for horizontal shear load between CLT Wall and sill plate (red line: monotonic loading, blue line: cyclic loading) Photo 3 Failure mode of monotonic and cyclic loading test for shear force between CLT wall and sill plate 25 Disp. transducer Disp. transducer Monotonic loading Cyclic loading 4-Wood Screw Rothblass HBS 8-18

5 3.3 Vertical shear performance between CLT wall to wall connection Test specimen Shear performance of wall to wall connection used spline is necessary to evaluate consecutive shear wall performance. Test specimen of spline is laminated veneer lumber made of larch provided JAS structural LVL 12E-385F. LVL spline is consisted of 27mm thickness and 149mm width. Wood screw of connected fastener is manufactured by rothoblaas HBS in Italy. CLT is cut off the surface and make single surface spline type and CLT cut off internal and arrange LVL as double shear connection. Test specimen shows Figure 11. Four types of test were carried out D18 キリ Test results Envelop load-displacement curves on four types of spline connection between CLT wall and wall were shown in Figure 13. Red line shows monotonic loading and blue line shows envelop curve of cyclic loading. And the vertical axis of graph shows the load per screw. Comparison of single shear and double shear at CLT thickness 9mm shows upper graph and comparison of CLT thickness 12mm and 15mm connected internal spline shows lower graph. Monotonic loading results show high ductility. Initial curve of cyclic loading was consistent with the monotonic loading. However when relative displacement between CLT wall and LVL spline shows over 2mm, cyclic loading force were reduced but monotonic loading force were continually. Failure mode of monotonic loading shows embedding screw to the CLT wall and LVL spline. Failure mode of cyclic loading shows breakage for bending wood screw and embedding wood screw to the LVL spline shows long hole at LVL spline by cyclic loading. Photo 4 shows typical failure mode of wall to wall LVL spline. Rothoblaas Wood Screw HBS CLT 9mm Surface spline 12 CLT 9mm Internal Spline CLT 9mm 3ply 15 LVL t=27 w= CLT 9mm 3ply 28 LVL t=27 w= CLT 12mm 5ply LVL t=27 w= CLT 15mm 5ply LVL t=27 w= Load(kN/Screw) Load(kN/Screw) 8 Rothblass HBS Rothblass HBS Rothblass HBS Rothblass HBS Figure 11 Test specimen of CLT wall to wall connection Test method Shear test was carried out based on ISO 17:23, Timber structures - Joints made with mechanical fasteners - Quasi-static reversed-cyclic test method. Based on monotonic loading test, cyclic loading protocol was determined. In this test, ultimate displacement was decided 8mm based on monotonic loading test result and loading rate was provided approximately 1mm/sec. load was measured in the load cell attached at the tip of oil jack and relative displacement from LVL splinel plate to CLT wall was measured displacement transducer. Measuring load was divided by the number of wood screws. Shear test apparatus of bottom of CLT wall and spline is shown in Figure 12. Load(kN/Screw) CLT 12mml Internal Spline Figure 13 Envelop load-displacement curve of four types of connection between CLT Wall to wall spline (Red line: monotonic loading, Blue line: cyclic loading) Load(kN/Screw) CLT 15mm Internal Spline Transducer Lateral Gaide Roller Load Cell 5kN Oil Jack st=3mm Figure 12 Shear test apparatus of CLT wall to wall spline Photo 4 Typical failure of wall to wall connection of internal LVL spline on 12mm CLT

6 3.4 Evaluation on strength of fastener Envelope curve is determined using load-displacement test data of cyclic loading. Yield strength (Py) is obtained by cross point of 1% maximum load (Pmax) to 4% Pmax line and tangent to the envelope curve of 4% Pmax to 9% Pmax line. Stiffness (K) is obtained by the yield strength divided yield displacement (Dy). Ultimate displacement determined envelope curve reduced 8% Pmax after maximum load. Ultimate strength (Pu) is obtained by the area of trapezoid equal to surround area using envelope curve from zero to ultimate displacement. Py, K, Pu are obtained as shown in Figure 14. Yield strength and ultimate strength of hold-down fastener, toe screw of bottom CLT wall to sill plate and wall to wall spline shows Table Structural Design of CLT shear wall based on the strength of fastener CLT panel has rigid-body for using shear wall. Main criteria deformation mode shows rocking as shown in Figure 2. And Figure 15 shows the horizontal and vertical load distribution of CLT shear wall. Shear wall test specimen was selected doubled hold-down fastener HD-N2 at the bottom of wall. Hold-down HD-N2 shows 33.7kN yield strength and 3.47mm yield displacement in Table 1. Double arrangement of holddown at the bottom of wall calculated 7.4kN and aspect ratio of wall shows 3, so horizontal yield load calculated 22.5kN/m and horizontal ultimate load calculated 37.2kN. Against horizontal load, bottom of wall and sill plate should be connected rigidly. 1 wood screws per 1m connected and screw spaced 1mm, so horizontal yield strength calculated over 35kN for cyclic loading. Wall to wall connection was selected single surface spline because of easy setup. Wall to wall connection decided 3 wood screws per 3m for each CLT wall connected and screw spaced 1mm. Calculated yield shear strength of 3 wood screws shows 89.4kN. Embedding deformation of sill plate assumed same of uplift deformation of hold-down fastener. Figure 1 shows design load-displacement of shear wall used hold-down fastener s structural performance. Figure 14 Evaluation methods on yield strength and ultimate strength of fastener F 2F Table 1 Yield strength and ultimate strength of holddown fastener, toe screw of bottom CLT wall to sill plate and wall to wall spline Type of fastener Num ber Average Py(kN) Dy(mm) Pu(kN) Du(mm) HD-N HD-B HD-N HD-B Wall to sill plate per screw Wall to wall spline per screw (1) (2) (3) (4) Note: wall to wall spline Symbol (1) shows CLT9mm single surface spline. Symbol (2) shows CLT9mm internal spline. Symbol (3) shows CLT12mm internal spline. Symbol (4) shows CLT15mm internal spline. 1 2 Figure 15 Horizontal and vertical load distribution of CLT shear wall Figure 1 Design load displacement curve used holddown fastener structural performance 3

7 2-ZN Horizontal Loading Test of CLT Shear Wall 4.1 Shear wall test specimen Basic dimension of Sugi CLT wall panel was 1mm width, 3mm height and 9mm thickness. Three types of CLT shear wall were setting up and test condition of wall is 1P, 2P and 3P. Bottom sill plate of wall assembly was firmly attached to 15mm square Hinoki (Chamaecyparis obtuse) glue lam and bottom timber secured steel basement of test apparatus. Top plate of wall was attached 3mm width and 9mm thickness Sugi CLT panel. Connection of CLT wall and top and bottom plate was used wood screw HBS 8mm diameter and 18mm length and pitched 1mm. doubled holddown fasteners HD-N2 were arranged at the corner of CLT wall panel. Wall to wall connection is 15mm width and 27mm thickness LVL attached and screwed D8 and L1mm pitched 1mm angle is provided horizontal displacement divide height of test specimen. And the three times cyclic test at the each deformation of 1/45, 1/3, 1/2, 1/15, 1/1, 1/75, 1/5, 1/37.5, 1/3, 1/24, 1/2, 1/17, and 1/15. Counter Weight Slider 1Lateral guide Oil Jack 2 2 Actuater Load 3kN st=}25mm Stopper Strong beam H Load cell Steel Base Wood Screw HBS D8 L18 spaced 1mm CLT wall Panel 2-Hold-down fastener HD-N2 M1 bolt 35 3 CLT wall Panel CLT wall Panel CLT wall Panel Figure 17: Test specimen of CLT shear wall Hold-down fastener HD-N2 M1 bolt LVL Spline Wood Screw HBS D8 L1 spaced 1mm Wood Screw HBS D8 L18 spaced 1mm CLT wall Panel Wood Screw HBS D8 L18 spaced 1mm CLT wall Panel 2-Hold-down fastener HD-N2 M1 bolt LVL Spline Wood Screw HBS D8 L1 spaced 1mm 4.2 Shear wall test method Test apparatus of 3P CLT wall panel is shown in Figure 18. Appling lateral load on test shear wall was used actuator loading jack and vertical load on test shear wall was used oil jack with feedback controlled using load cell arranged on the top of shear wall. Position of vertical load to test specimen is the center of CLT wall panel. Vertical loading system of shear wall was shown in Figure 19. Cyclic test procedure of shear wall under 1/5 radian was according to the building minister certification method on Performance Evaluation Organization in Japan. After 1/5 radian cyclic procedure was simulated to ISO method of three time s cyclic test. Deformation Slider 1guide 2Lateral Oil Jack Figure 18: Test Apparatus of 3P CLT wall panel Ball Bearing Load Cell Figure 19: Vertical loading system Strong Beam H Test Results Load-Displacement curve of 1P CLT wall applied vertical load shows in Figure 2. Load-Displacement curve shows over 3kN strength and high ductility. Bilinear line of shear wall based on hold-down strength and deformation shows circle line. Ductility shows similarity to the test results; however stiffness of wall shows higher than the test results. Failure mode was nail yield (CN9) of hold down fastener connected Sugi CLT wall. CLT Wall 1P Load (kn) V Load: kn V Load: 15kN/m V Load: 3kN/m

8 Figure 2: Load-Displacement curve of 1P CLT wall Load-Displacement curve of 2P CLT wall applied vertical load is shown in Figure 21. And 3P CLT wall is shown in Figure 22. Ductility of test results is reduced than the calculation value. Because before hold-down fastener failed, LVL spline of wall to wall connection is failed splitting. Load (kn) CLT Wall 2P V Load: kn V Load: 15kN/m V Load: 3kN/m Figure 21: Load-Displacement curve of 2P CLT wall However in 2P shear wall and 3P shear wall, strength of.2 Pu multiplied by square root of (2u-1) shows lower value than the strength of yield Py. Because before holddown fastener failed, LVL spline of wall to wall connection is failed splitting as shown in Photo 5. Strength(kN/m) kn/m 15kN/m 3kN/m kn/m Figure 23: Comparison of each strength and effect of vertical load 15kN/m 3kN/m kn/m 15kN/m 1P 2P 3P Py.2Pu (2μ-1) 2/3Pmax P1/12 3kN/m 1 CLT Wall 3P 12 8 Load (kn) V Load: kn V Load: 15kN/m V Load: 3kN/m Figure 22: Load-Displacement curve of 3P CLT wall Envelope curve is determined using load-displacement data of shear wall. Yield strength (Py), maximum load (Pmax), stiffness (K), yield displacement (Dy), ultimate strength (Pu) and ultimate displacement (Du) shows in Figure 14. Allowable strength of shear wall of post and beam timber structure in Japan is usually determined using four criteria; First one is yield strength Py, second is 2 % ultimate strength.2 Pu multiplied by square root of (2u-1) that u means yield ratio calculated Du divided Dy multiplied by Pu/Py, third is 2/3 maximum strength Pmax and fourth is 1/12 radian deformation strength P1/12. Figure 23 shows the comparison of strength on four criteria due to applying the vertical load. Y axis shows the strength per meter meaning divided test wall length. Strength of the four criteria determined on the allowable strength was increased by applying vertical load. Strength of.2 Pu multiplied by square root of (2u-1) shows the ductility shear performance. In 1P shear wall, strength of yield Py and Strength of.2 Pu multiplied by square root of (2u-1) shows almost the same value. Photo 5: Failure mode of 3P CLT shear wall applying 3kN/m vertical load. 5 Conclusion On the basis of the experimental data obtained from cyclic loading test of shear walls and strength and stiffness of hold-down fastener, wood screw and spline connection, following could be concluded. 1. Regardless of the length of the wall, strength of the four criteria determined on the allowable strength was increased by applying vertical load in Sugi CLT shear wall. 2. Main deformation mode of Sugi CLT shear wall was shown rocking mode. Strength and deformation at the bottom corner of CLT shear wall was determined the strength and deformation of shear wall. 3. 2P and 3P CLT shear walls were shown in the splitting failure of wall to wall connected by LVL spline. Acknowlegement This study was conducted based on subsidy by the Ministry of Land, Infrastructure and Transport that MEIKEN Lamwood Corporation has been adopted.