structural performance of cold-formed steel framed rok-on

Structural Performance of Cold-Formed Steel Framed ROK-ON Walls

Report No. UNT-ST919 By

Cheng Yu, PhD Professor

May 15, 2017

Department of Engineering Technology

University of North Texas

Denton, Texas 76207

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Table of Contents 1 Introduction .................................................................................................................... 1

2. Research Personnel ....................................................................................................... 1

3 Shear Wall Tests ............................................................................................................ 1

3.1 Test Setup ................................................................................................................. 1

3.2 Test Procedure .......................................................................................................... 4

3.3 Test Specimens ......................................................................................................... 4

3.4 Test Results ............................................................................................................... 5

3.4.1 Monotonic Shear Wall Tests .............................................................................. 5

3.4.2 Cyclic Shear Wall Tests ..................................................................................... 7

3.4.3 Material Properties ........................................................................................... 10

3.5 Recommended Nominal Shear Strength ................................................................. 11

4 Transverse Load Tests ................................................................................................. 12

4.1 Test Setup and Test Procedures .............................................................................. 12

4.2 Test Specimens ....................................................................................................... 13

4.3 Test Results ............................................................................................................. 14

4.3.1 Transverse Load Tests ..................................................................................... 14

4.3.2 Material Properties ........................................................................................... 21

4.4 Recommended Nominal Flexural Strength ............................................................. 22

5 Conclusions ................................................................................................................... 23

6 References ..................................................................................................................... 24

Appendix .......................................................................................................................... 25

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1 INTRODUCTION The objective of this project was to investigate the behavior and performance of cold-formed steel framed ROK-ON walls subjected to either shear or transverse loads. ASTM standard test methods were used in the test program. Nominal strength was established from the test results and the analysis procedure followed the North American Specification and Standard for cold-formed steel structures.

2. RESEARCH PERSONNEL Director of Testing - Cheng Yu

Research Assistants - Xing Lan, Nathan Derrick, Nick O’Connor

3 SHEAR WALL TESTS The shear wall test program was carried out during the time period from February 8, 2017 to February 24, 2017 in the Structural Testing Laboratory at the Discovery Park of the University of North Texas, Denton, Texas. A total of 4 monotonic and 2 cyclic shear wall tests were conducted. The following sections provide the details of test setup, testing procedure, test specimens, and test results.

3.1 Test Setup The monotonic tests and the cyclic tests were performed on a 16-ft. span, 12-ft. high adaptable structural steel testing frame. Figure 1 shows the front view of the testing frame with a 6-ft. 9-in. u 8-ft. ROK-ON wall installed. Figure 2 shows the back view of the test setup. The wall specimen was bolted to the base beam and loaded horizontally at the top. A “T” shape hot-rolled steel load beam was used to apply horizontal forces to the top track of wall. The “T” shape was attached to the top track of the wall by 2 - No. 12 u 1-1/2-in. hex washer head (HWH) self-drilling self-tapping screws placed every 3-in. on center. The out-of-plane displacement of the wall was prevented by a series of steel rollers placed on both sides of the “T” shape load beam.

The wall specimen was anchored to the hot-rolled steel base beam by seven 3/8-in. ASTM A325 bolts with standard cut washers, as shown in Figure 3. Two anchor bolts were used in each section for the two end sections, and single anchor bolt was used in each interior section. The base beam was 10-in. u 4-in. u ½-in. structural steel tubing. The web of the structural steel base beam was cut-out in several locations on one side to provide access to anchor bolts.

All the wall specimens were assembled in a horizontal position with backside panel uninstalled. The wall was then installed vertically to the testing frame. After the anchor bolts were installed to the bottom track, drywalls were finally installed to the backside of the wall.

The testing frame was equipped with one MTS 35-kip hydraulic actuator with r5-in. stroke. A Shore Western SC6000 controller and one 20-Gpm MTS hydraulic power unit were employed to support the loading system. A 30-kip TRANSDUCER TECHNIQUES SWO universal compression/tension load cell was placed to connect the hydraulic actuator to the “T” shape for force measurement. Five NOVOTECHNIC position transducers were employed to measure the

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horizontal displacement at the top of wall, the vertical displacements of the two boundary studs, and the horizontal displacements of the bottom of the two boundary studs. The data acquisition system consisted of a National Instruments unit (including a PCI6225 DAQ card, a SCXI1100 chassis with SCXI1520 load cell sensor module and SCXI1540 LVDT input module) and a desktop PC. The applied force and the five displacements were measured and recorded instantaneously during the test.

Figure 1 Front View of Test Setup

Out-of-plane support

Load cell

Load beam Position transducer

Position transducerPosition transducer

Hydraulic actuator

Base beam

3

Figure 2 Back View of Test Setup

Figure 3 Anchor Bolts on Bottom Track

Position transducer

Position transducer

Out-of-plane support

Load cell

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3.2 Test Procedure Both the monotonic and the cyclic tests were conducted in a displacement control mode. The procedure of the monotonic tests was in accordance with ASTM E564-06 “Standard Practice for Static Load Test for Shear Resistance of Framed Walls for Buildings.”

The cyclic tests used the CUREE protocol specified in ASTM E2126-11 “Stand Test Methods for Cyclic (Reversed) Load Test for Shear Resistance of Vertical Elements of the Lateral Force Resisting Systems for Buildings.” A constant cycling frequency of 0.2-Hz (5 seconds per cycle) was adopted for the CUREE protocol for all the cyclic tests. The maximum displacement for all cyclic tests were set to +-4.5 in. Figure 4 shows the CUREE loading history used in this project.

Figure 4 CUREE Basic Loading History (0.2 Hz, 40 cycles)

3.3 Test Specimens

All shear wall specimens were cold-formed steel framed with ROK-ON panel on one side and drywall on the other side. The overall dimensions of all walls were 6-ft. 9 ½-in. wide and 8 ft. high. The drywall sheathing consisted of two Sheetrock Ultralight 1/2-in. thick 8-ft. high gypsum boards. One gypsum board was 4-ft. wide and the other gypsum board was 33-in.wide. The ROK-ON sheathing consisted of two 40 ½-in. wide 8-ft. high panels. The ROK-ON panel was ½-in. + ¼-in. the ¼-in. side was in contact with the steel frame. The additional wall configurations are listed in Table 1.

0 20 40 60 80 100 120 140 160 180 200-150

-100

-50

0

50

100

150

Time (s)

Spe

cim

en D

ispl

acem

ent (

%'

)

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Table 1 Detailed Wall Configurations Test

Label Test

Protocol Stud Track Framing

Connection Drywall Screw

ROK-ON Screw

M1 Monotonic

50 ksi

350S162-33

50 ksi

350T150-43

Rivet

#6×1 5/8” drywall screws

spaced 12” o.c.

#12×3-1/2” flat head screws spaced 6” on tracks, 12” on studs

M2 Monotonic

Rivet + #10×3/4” modified truss head

screws

#12×3-1/2” flat head screws spaced 4” on tracks, 12” on studs

M3 Monotonic

M4 Monotonic

C1 Cyclic

C2 Cyclic

3.4 Test Results

3.4.1 Monotonic Shear Wall Tests The test results of monotonic shear wall tests are summarized in Table 2. The peak loads in pound per liner foot (plf), the lateral displacement of the top of the wall at peak load, and observed failure modes are provided in Table 2.

The wall M1 failed due to the broken screws on the bottom track, as shown in Figure 5. To improve the connection strength, more screws were installed on walls M2, M3 and M4. In addition to the original rivets, #10×3/4” modified truss head screws were added to the stud and track connections. The screw spacing on the tracks for ROK-ON panels were changed to 4 in. for M2 to M4 walls. Walls M2 to M4 yielded consistently higher shear strength than M1 and the failure mode was the bearing and tilting of the screws on the bottom track. The ROK-ON panels behaved as a rigid board as shown in Figure 6 and rotation of the screws on tracks were observed and it became the failure mode. Figure 7 shows the load vs. displacement curves for all monotonic shear wall tests.

Table 2 Monotonic Test Results

Test Label Peak Load (plf) Disp. @ Peak (in.) Failure Mode

M1 583 1.714 Screw broken on bottom track

M2 782 1.608 Screw bearing and tilting failure on bottom track



6

Figure 5 Failure Mode of Test M1

Figure 6 Typical Failure Mode of Tests M2 to M4 (@ peak load)

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Figure 7 Load vs. Displacement Curves of Monotonic Tests

3.4.2 Cyclic Shear Wall Tests The results of cyclic shear wall tests are summarized in Table 3 which includes the peak loads in pound per liner foot (plf), the lateral displacement of the top of the wall at peak load, and observed failure modes. The peak load and lateral displacement are the average results of the positive and negative directions of the loading for each test. Both cyclic tests failed by screw’s bearing and titling behaviors at the bottom tracks. Figure 8 shows the wall C1 at its peak load. The two RON-ON panels behaved as rigid boards, and the movement of the panels caused bearing and tilting failures of the screws on the bottom tracks. Pull-out failures of rivets and screws at the wall corners were also observed in both walls. Figures 9 and 10 respectively show the bottom track of the walls after the testing. The shear wall hysteresis curves are shown in Figures 11 and 12.

Table 3 Cyclic Test Results Test Label Peak Load (plf) Disp. @ Peak

(in.) Failure Mode

C1 913 2.054 Screw bearing and tilting on bottom track, bending of bottom track

C2 972 1.883 Screw bearing and tilting failure on bottom track

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Figure 8 Wall C1 at Peak Load

Figure 9 Failure of Test C1

9

Figure 10 Failure of Test C2

Figure 11 Hysteresis Curve of Test C1

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Figure 12 Hysteresis Curve of Test C2

3.4.3 Material Properties Coupon tests were conducted according to the ASTM A370-14 “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”. The test results are summarized in Table 4. The coating on the steel was removed by hydrochloric acid prior to the coupon tests. The coupons tests were conducted on the INSTRON 4480 universal testing machine. An INSTRON 2630-106 extensometer was employed to measure the tensile strain.

Table 4 Coupon Test Results

Member Uncoated Thickness

(in.)

Yield Stress

Fy (ksi)

Tensile Strength

Fu

(ksi)

Fu/Fy Ratio

Elongation for 2 in.

Gage Length (%)

33 mil 350 stud 0.0337 52.0 64.3 1.24 15.2%

43 mil 350 track 0.0453 62.4 75.7 1.22 18.2%

The test results indicate that the measured uncoated thicknesses of 33 mil and 43 mil materials were greater than the minimum base steel thickness specified in AISI S201-12 “North American Standard for Cold-Formed Steel Framing – Product Data” (2012) (0.0329 in. for 33 mil and 0.0451

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in. for 43 mil). The measured uncoated thickness of 33 mil steel was less than the design value specified in AISI S201 (2012) (0.0346 in.). The measured uncoated thickness of 43 mil steel was greater than the design value specified in AISI S201 (2012) (0.0451 in.).

All materials had both tensile strength and yield strength greater than the specified values. All the materials met the minimum ductility requirement by AISI S100 North American Specification for Design of Cold-Formed Steel Structural Members 2016 Edition (AISI 2016), which requires the tensile strength to yield strength ratio greater than 1.08, and the elongation on a 2-in. gage length higher than 10%.

3.5 Recommended Nominal Shear Strength The nominal shear strength is determined as the average peak load of all the identical tests (minimum 2 tests). The nominal shear strength for wind loads is based on monotonic test results and the nominal shear strength for seismic loads is obtained from the cyclic tests. The nominal strength of the cyclic tests is taken as the average of the peak loads from the positive and negative quadrants of the hysteresis curve.

Per the AISI S100 (2016) Chapter K, the tested nominal loads shall be adjusted by the variations in material’s strength and thickness. Only downward adjustment is permitted. The coupon tests indicate that the measured base metal (i.e., uncoated) thickness for 33 mil stud was greater than the design thickness (0.0337 in. vs. 0.0329 in.) and the tensile strength is less than the specified value (64.3 ksi vs. 65 ksi), no adjustment is needed. However the measured base metal (i.e., uncoated) thickness for 43 mil track was greater than the design thicknesses (0.0453 in. vs. 0.0451 in.), therefore adjustment due to variation in thickness was needed. The tensile strength for 43 mil track (75.7 ksi) was greater than the specified value (65 ksi), therefore the nominal strengths need to be adjusted due to the variation in material strength. Overall the tested nominal loads shall be adjusted by a factor of (65/75.7)(0.0451/0.0453) = 0.855.

All shear walls reached their peak load at a lateral displacement less than the drift limit of 2.5% as specified in AISI S213 North American Standard for Cold-Formed steel Framing – Lateral Design (2012). No adjustment to the test results is needed with regard to the lateral drift requirement.

Based on the results, the adjusted nominal shear strengths are summarized in Table 5. For the monotonic tests, since M1 has different configuration than the remaining specimens, the nominal strength for wind load design was based on tests M2, M3 and M4.

Table 5 Recommended Nominal Shear Strength

Design Wall Specimen Average Peak Load

(plf)

Nominal Shear Strength

(plf)

Wind M2, M3, M4 831 711

Seismic C1, C2 943 806

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4 TRANSVERSE LOAD TESTS The transverse load tests on ROK-ON wall specimens were conducted during the time period from March 27, 2017 to April 7, 2017 in the Structural Testing Laboratory at the Discovery Park of the University of North Texas, Denton, Texas. A total of 4 specimen configurations and 12 tests were conducted. The following sections provide the details of test setup, testing procedure, test specimens and test results.

4.1 Test Setup and Test Procedures The test setup and procedure for the transverse load tests followed the ASTM E72-15 “Standard Test Methods of Conducting Strength Tests of Panels for Building Construction.” The wall specimen was simply supported at both ends and loaded transversely at two points/lines. Figure 13 shows the overall test setup and Figure 14 illustrates the section view. The supports were two steel rollers with a 4-in. wide steel plate between each supporting roller and the specimen. At the two loading locations, there were two steel rollers with a 4-in. wide steel plate between each loading rollers and the specimen. A hot-rolled steel load beam was used to apply two equal loads to the loading rollers.

Figure 13 Test Setup for Transverse Load Test

Load cell

Position transducer

Load beam

Roller support

Roller support

Position transducer

Hydraulic cylinder

13

Figure 14 Section View of Test Setup

The testing frame was equipped with one 30-kip hydraulic cylinder with 8-in. stroke. A Shore Western SC6000 controller and one 20-Gpm MTS hydraulic power unit were employed to support the loading system. A 30-kip TRANSDUCER TECHNIQUES SWO universal compression/tension load cell was placed to connect the hydraulic cylinder to the load beam. Three NOVOTECHNIC position transducers were employed to measure the vertical displacement of the center of the wall specimen and the vertical displacement of load beam. The data acquisition system consisted of a National Instruments unit (including a PCI6225 DAQ card, a SCXI1100 chassis with SCXI1520 load cell sensor module and SCXI1540 LVDT input module) and a desktop PC. The applied force and the displacements were measured and recorded instantaneously during the test.

4.2 Test Specimens The wall specimens were in four configuration groups and three identical tests were performed in each group. All walls were 4-ft. wide and 8-ft. high. All walls used the same drywall which was Sheetrock Ultralight 1/2-in. thick 4-ft. × 8-ft. gypsum board. Table 6 lists additional configurations of the test specimens. The framing details can be found in the drawings provided in the Appendix.

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Table 6 Test Matrix for Transverse Load Tests Test

Label Stud Track ROK-ON

Panel ROK-ON Screw Drywall Screw

A1 350S150-33 350T150-33 ½” + ¼” Panel on

compression side of frame

Flat Head #12x3 ½”

6” spacing on tracks

12” spacing on studs

Flat Head #6x1 5/8”

12” spacing on studs and tracks A2

A3

B1 350S150-43 350T150-43 ½” + ¼” Panel on






12” spacing on studs and tracks B2

B3

C1 350S150-43 350T150-43 ½” + ¼” Panel on

tension side of frame





12” spacing on studs and tracks C2

C3

D1 550S150-43 550T150-43 ½” + ½” Panel on






12” spacing on studs and tracks D2

D3

4.3 Test Results

4.3.1 Transverse Load Tests The results of transverse load tests are summarized in Table 7, where the maximum applied equivalent uniform pressure and the corresponding vertical deflection of the center of the specimen, as well as the observed failure mode are provided. The equivalent uniform pressure was calculated according to a two-point loading setup with the point loads being applied at two quarter points of the span. Figures15 through 22 show the typical failure modes. Figures 23 through 26 illustrate the applied load vs. deflection curves for the tests in each specimen group. The tests indicated that the flexural strength of the ROK-ON walls were dominated by the flexural strength of the cold-formed steel framing members. 43 mil framed wall assemblies yielded higher flexural strength than the 33 mil framed wall assemblies. The walls with ROK-ON panel on the compression side gave higher flexural strength than the walls with ROK-ON panel on the tension side. It shall be noted that Tests D1 and D2 failed by webcrippling of stud at support while D3 failed by flexural buckling of stud at the loading point. Those three tests had similar peak load which indicated that the two limit states had a similar ultimate strength.

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Table 7 Test Results for Transverse Load Tests Test

Label Maximum Equivalent Uniform Pressure (lbf/ft2)

Vertical Deflection

at Peak (in.)

Average Equivalent Uniform Pressure (lbf/ft2)

Average Deflection

at Peak (in.)

Failure Mode

A1 175.3 1.589 64,576 1.578 Buckling of stud and cracking of ROK-ON panel at the loading point

A2 190.0 1.631

A3 184.0 1.513

B1 268.2 1.918 92,121 1.736 Buckling of stud and cracking of ROK-ON panel at the loading point

B2 253.1 1.624

B3 262.3 1.665

C1 139.1 0.708 47,019 0.780 Buckling of stud and cracking of ROK-ON panel at the loading point

C2 140.6 0.878

C3 120.3 0.755

D1 477.5 0.825 182,385 0.985 D1 & D2:Webcrippling of stud at support.

D3: buckling of stud at the loading point.

D2 539.8 1.347

D3 534.2 0.783

Figure 15 Failure Mode of Test A1

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Figure 16 Failure Mode of Test A1 (drywall removed)

Figure 17 Failure Mode of Test B2

17

Figure 18 Failure Mode of Test B2 (drywall removed)

Figure 19 Failure Mode of Test C1

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Figure 20 Failure Mode of Test C2 (drywall removed)

Figure 21 Failure Mode of Test D2

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Figure 22 Failure Mode of Test D3

Figure 23 Test Results of Walls A1, A2, A3

20

Figure 24 Test Results of Walls B1, B2, B3

Figure 25 Test Results of Walls C1, C2, C3

21

Figure 26 Test Results of Walls D1, D2, D3

4.3.2 Material Properties Coupon tests were conducted according to the ASTM A370-14 “Standard Test Methods and Definitions for Mechanical Testing of Steel Products”. The test results are summarized in Table 8. The coating on the steel was removed by hydrochloric acid prior to the coupon tests. The coupon tests were conducted on the INSTRON 4480 universal testing machine. An INSTRON 2630-106 extensometer was employed to measure the tensile strain.

Table 8 Coupon Test Results

Steel Member Uncoated Thickness

(in.)

Yield Stress

Fy (ksi)

Tensile Strength

Fu

(ksi)

Fu/Fy Ratio

Elongation for 2 in.

Gage Length (%)

33 mil 350 0.0337 52.0 64.3 1.24 15.2%

43 mil 350 0.0453 62.4 75.7 1.22 18.2%

43 mil 550 0.0465 50.2 66.5 1.33 17.8%

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The test results indicate that the measured uncoated thicknesses of 33 mil and 43 mil materials were greater than the minimum base steel thickness specified in AISI S201-12 “North American Standard for Cold-Formed Steel Framing – Product Data” (2012) (0.0329 in. for 33 mil and 0.0451 in. for 43 mil). The measured uncoated thickness of 33 mil steel was less than the design value specified in AISI S201 (2012) (0.0346 in.). The measured uncoated thickness of 43 mil steels were greater than the design value specified in AISI S201 (2012) (0.0451 in.).

All materials had both tensile strength and yield strength greater than the specified values. All the materials met the minimum ductility requirement by AISI S100 North American Specification for Design of Cold-Formed Steel Structural Members 2016 Edition (AISI 2016), which requires the tensile strength to yield strength ratio greater than 1.08, and the elongation on a 2-in. gage length higher than 10%.

4.4 Recommended Nominal Flexural Strength The nominal flexural strength is determined as the average maximum equivalent uniform pressure of all the identical tests. Per the AISI S100 (2016) Chapter K, the tested nominal loads shall be adjusted by the variations in material’s strength and thickness. Only downward adjustment is permitted.

The coupon tests indicate that the measured base metal (i.e., uncoated) thickness for 33 mil steel was greater than the design thickness (0.0337 in. vs. 0.0329 in.) and the tensile strength is less than the specified value (64.3 ksi vs. 65 ksi), no adjustment is needed for 33 mil specimens.

For 43 mil 350 members, the measured base metal (i.e., uncoated) thickness was greater than the design thicknesses (0.0453 in. vs. 0.0451 in.), therefore adjustment due to variation in thickness was needed. The tensile strength for 43 mil 350 members (75.7 ksi) was greater than the specified value (65 ksi), therefore the nominal strengths need to be also adjusted due to the variation in material strength. Overall the tested nominal loads for specimens with 43 mil 350 members shall be adjusted by a factor of (65/75.7)(0.0451/0.0453) = 0.855.

For 43 mil 550 members, the measured base metal (i.e., uncoated) thickness was greater than the design thicknesses (0.0465 in. vs. 0.0451 in.), therefore adjustment due to variation in thickness was needed. The tensile strength for 43 mil 550 members (66.5 ksi) was greater than the specified value (65 ksi), therefore the nominal strengths need to be adjusted due to the variation in material strength. Overall the tested nominal loads for specimens with 43 mil 350 members shall be adjusted by a factor of (65/66.5)(0.0451/0.0465) = 0.948.

Based on the results, the adjusted nominal flexural strengths in terms of equivalent uniform pressure are summarized in Table 9.

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Table 9 Recommended Nominal Flexural Strength

Wall Specimen Average Maximum Equivalent Uniform

Pressure

(lbf/ft2)

Nominal Flexural Strength in Terms of Equivalent

Uniform Pressure

(lbf/ft2)

A1, A2, A3 183.1 183

B1, B2, B3 261.2 223

C1, C2, C3 133.3 114

D1, D2, D3 517.2 490

5 CONCLUSIONS

A series of shear wall tests were conducted on a cold-formed steel framed wall assemblies using ROK-ON panels and drywall boards. Both monotonic and cyclic tests were performed. Based on the test results, nominal strength for both wind and seismic design were established. The nominal shear strength was adjusted according to variations of material properties between actual and specified values.

A series of transverse load tests were also performed on four different cold-formed steel framed wall assemblies using ROK-ON panels and drywall boards. Nominal flexural strength of the tested wall assemblies were established based on the test results. The nominal flexural strength was adjusted accordingly based on the variations in the material properties between actual and specified values. The flexural strength was reported as the equivalent uniform pressure in this research.

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6 REFERENCES

AISI S100 (2016). “North American Specification for the Design of Cold-Formed Steel Structural Members, 2016 Edition,” American Iron and Steel Institute, Washington, DC.

AISI S201-12 (2012) “North American Standard for Cold-Formed Steel Framing – Product Data, 2012 Edition,” American Iron and Steel Institute, Washington, DC.

AISI S213 (2012). “North American Standard for Cold-Formed Steel Framing – Lateral Design 2007 Edition with Supplement 1/Reaffirmed 2012,” American Iron and Steel Institute, Washington, DC.

ASTM A370 (2014). “Standard Test Methods and Definitions for Mechanical Testing of Steel Products,” American Society for Testing and Materials, West Conshohocken, PA.

ASTM E2126-11 (2011). “Standard Test Methods for Cyclic (Reversed) Load Test for Shear Resistance of Vertical Elements of the Lateral Force Resisting Systems for Buildings,” ASTM International, West Conshohocken, PA.

ASTM E564-06 (2012) “Standard Practice for Static Load Test for Shear Resistance of Framed Walls for Buildings,” ASTM International, West Conshohocken, PA.

ASTM E72-15 (2015) “Standard Test Methods of Conducting Strength Tests of Panels for Building Construction,” ASTM International, West Conshohocken, PA.

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APPENDIX

Details for Walls A, B, C

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Details for Wall D

structural performance of cold-formed steel framed rok-on

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