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Improved Column-Beam Joint in Glulam Semi-Rigid Portal Frame

Kohei KomatsuProfessor, Research Institute for Sustainable Humanosphere, Kyoto University

Uji, Japan

Mitsushi AkagiFormer Engineer, Yamasa Mokuzai Co., Ltd.

Kagoshima, Japan

Chiori KawaiFormer Engineer, D.fact Co., Ltd.

Nagoya, Japan

Takuro MoriAssistant Professor, Research Institute for Sustainable Humanosphere, Kyoto University

Uji, Japan

Shingo HattoriPresident, D.fact Co., Ltd.,

Nagoya, Japan

Kiyoshi HosokawaPresident, Mokkozo Giken Ltd.,

Hamamatsu, Japan

Summary

Previous column joint was composed of pass-through bolts to connect steel gusset with column.

The joint, however, tended to bring larger deformation due to embedment of bearing plate to sidegrain of column. To prevent this deformation, LagscrewboltRwas introduced, and evaluation tests

were done using three different kinds of specimens (120 x 300, 120 x 360, and 120 x 450 mm in

cross section of column member). Experimental results showed that at maximum about 40%

increase of maximum moment and stiffness, while same percentage of decrease of ductility. The

decrease of ductility was caused by a simple mistake in preparing test specimen. Thus, it can be

possible to expect that the new type of column-beam joint give excellent total performance by

executing careful further development on joints details.

1. Introduction

In WCTE2006 [1] held at Portland, we presented performance of glulam portal frames of 4m and6m span, which were composed of specially designed column-beam as well as column-base joints.

In our presentation, we emphasized that the glulam portal frame developed had an excellent

performance especially on the ductility that kept increasing bending moment even if the portal

frames were deformed over 1/10 radian. As previous column joint, however, was composed of

pass-though bolts to connect special shaped steel gusset with column member as shown in Fig.1,

it was a disadvantage point that embedment due to bolt nuts made initial stiffness weakened. In this

research, therefore, in order to prevent this initial deformation due to embedment by bearing plate,

LagscrewboltR, which was developed by the first author, was used instead of using pass-through-

bolt, and some evaluation tests were performed by employing full-scale column-beam joint

specimens. In this article, details of theoretical analysis as well as comparisons between

experimental results and theoretical results are to be reported.

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2. Mechanical Model for Column-Beam Joint

2.1 Beam Side Model

As the theoretical derivation of mechanical model on

the beam side joint shown in Fig.1 was reported in

details in the previous proceedings [1], only the finalexpressions for the rotational rigidity of the beam side

joint are shown in this part. The rotational rigidity of

the beam side joint is expressed in equations (1) and

(2).

( )200

390

3

312bez

ebfef

BJCB gkAkbkHb

R

+

+

=

(1)

+=

f

z

f

z

f

z

b b

A

gb

A

b

A

2

(2)

where,

ZA : Area of bearing plate of M12 bolt at centre of steel gusset plate (mm2)

fb : Width of double sided flange (mm)

: Distance from most outer compression side to the line of tension side bolt (mm)

H: Longitudinal length of steel gusset having double sided flanges (mm)

( )2

00

/H

Ek we = : Embedment constant of glulam parallel to the grain (N/mm

3) (3)

0wE : Modulus of elasticity of glulam parallel to the grain (kN/mm2)

143

090

.

kk ee = : Embedment constant of glulam perpendicular to the grain, which is assumed that the

same relationship used in AIJ design standard [2] can by applied. (N/mm3) (4)

2.2 Rotational Rigidity of Column Side Joint in Previous Type Assembly

Figure 2 indicates a mechanical model on the

previous type of beam-column joint in whichpass-through-bolts were used for connecting

steel gusset plate with glulam column. When

the pass-through-bolt is subjected to the tensile

force T, the bearing plate is bent as shown in

Fig.2. Resistance force T1acting at constant

embedment stress region is expressed in

equation (5).

( )zcTe bakT 2901 = (5)

While, resistance force T2, which is defined asa resultant force of lineally distributed

Glulam Column

Glulam-Beam

Fixed with Nuts

M12 Bolt

Flange

Bearing

Plate

hb

y

Cg

a

H

T

g

b

bg

x

H/2

Cw

2/3H/2

b3/2

b

M

x

2/3H/2Cw

Fig.1 Beam side mechanical model for

the previous joint.

Fig.2 Mechanical model for column-beam joint.

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embedment stress, is expressed in equation (6).

2

1 1

2190z

02

1

exz kbdybT == (6)

Considering relationships of )(and11 == gTT , and equilibrium between tensile resultant

force and compression force, following relationship is obtained.

zc

Sc

ceScezcezc

b)g(

b

kb)g(kb)g(kbaCTTT

=+

=+=+=

22a

2

2

1

2

12

2

c1

2901909021

(7)

From geometrical relationship in Fig.2,

cc ag += 1 (8)

From equations (7) and (8), following equation for the neutral potion of column-side is obtained.

( ) ( ) ( ) 0323 22 =+++ gbgbagbbabb zzcczzccsz (9)

where, zb is width of bearing plate of column side, and Sb is contact width of beam end to the side

face of column. As the difference between zb and Sb is usually small, it will be reasonable to

neglect the difference, hence the location of neutral potion of column-side is obtained as equation

(10).

+

+=

ga

gag

c

cc

23

3 (10)

From equilibrium of external momentMand moments due to tensile force Tas well as compression f

orce C, relationship between moment and rotational angle is derived as equation (11).

32(2a

3

23

21c90

++=+=c

czecc )g)(bkT)g(CM (11)

Considering equation (7), the rotational rigidity for column-side joint of previous type joint is derive

d as equation (12).

=

32

1 290

ccezCJCB gkbR

(12)

As the column-side joint and beam-side joint is connected in series with shearing approximately the

same moment, apparent rotational rigidity for beam-column joint of previous type assembly is

expressed as equation (13).

CJCBBJCB

CJCBBJCBBoltJCB

RR

RRR

+

= (13)

2.3 Yield Moment of Column-Beam Joint in Previous Type Assembly

It is assumed that the yielding of column-beam joint occurs when the embedment stress x reaches

to the partial compression strength 90cf perpendicular to the grain of glulam column. The force

embedment relationship is,

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cec kf 9090 = (14)

Relationship between embedment and rotational angle at yielding level is,

ccc = (15)

Relationship between rotational angle and moment at yielding level is,

cBoltJCBy RM = (16)

Hence, substituting equations (14) and (15) into equation (16), equation for predicting yield

moment at column-beam joint is obtained as equation (17).

ce

BoltJCBcy

k

RfM

90

90 = (17)

2.4 Rotational Rigidity of Column-Side Joint in New Type Assembly

Figure 3 shows a mechanical model for new type column-beam joint in which LagscrewboltRis

used instead of using pass-through-bolts for

connecting steel gusset plate with glulam column.

In this model, number of LSB for width direction

was assumed to be m for making mechanical

model has generalization. Relationship between

load and elongation at tensile side of LSB is

expressed in equation (18).

TLSBmKT = 90 (18)

Relationship between load and deformation at

compression side of LSB is expressed in equation(19).

CLSBL mKC = 90 (19)

where,

90LSBK : Slip modulus of LSB and it was assumed

that for both tension and compression

load, same value could be given by the following equations.

( )

( )9090909090909090

90 cosh

sinh

wwss

ssww

LSB AElkAEk

lkAEAERK

+

+=

(kN/mm) (20)

+=

ssww AEAERk

11

9090

9090 (21)

90 : Shear stiffness of LSB defined as stiffness between shear stress and displacement measured on

the specimen in which LSB inserted into thin plate. (N/mm3)

90wE : Modulus of elasticity of glulam perpendicular to the grain (=Ew0/25). ( kN/mm2)

90wA : Effective area defined as hatched part surrounded by 4.0R in width directiontimes nRin fibre

direction as shown in Fig.4, and can be evaluated by equation (22) [3] (mm2)

T

Cw

hb

g

T

hc

x

Column

M

0

3

2x

y

bs

g

ac

C

CL ac

m-LSB

m-LSB

m

m

Lag-Screw-Bolt=LSB

Fig.3 Mechanical model for new type

column-beam joint.

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( )( ) ( )

=

=

c

w

h

l.exp.n

R.RnRA

59436832

5042

90

(22)

where,

R : Peak diameter of LSB (mm)

l : Effective insert length of LSB (mm)

ch : Height of column (mm)

sE : Modulus of elasticity of steel. (kN/mm2)

sA : Cross sectional area of LSB based on the bottom diameter (mm2)

Relationship between elongation and rotational angle at tensile LSB is,

( ) = gT (23)

Relationship between deformation and rotational angle at compression LSB is,

( )cC a= (24)

Resultant compression force by embedment stress due to contact of end flange of steel gusset plate

to side grain of glulam column is,

2

290

0

==es

xsw

kbdybC (25)

From equations (18) and (23),

( ) =

gmKT LSB 90 (26)

From equations (19) and (24),

( ) = cLSBL amKC 90 (27)

Equilibrium of T, CLand Cwis,

Lw CCT += (28)

Substituting equations (25),(26), and (27) into equation (28), following equation for determining

is obtained.

022

290

90

90

902=

+

b

es

LSB

es

LSB hkb

mK

kb

mK (29)

Solving equation (29), is expressed as,

+

=

90

90

90

90

90

90 222

es

LSBb

es

LSB

es

LSB

kb

mKh

kb

mK

kb

mK (30)

Equilibrium of external moment and those due to tensile force and compression force is

Fig.4 Effective area Aw90for LSB inserted

erpendicular to the grain.

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( ) ( ) ( ) ( ){ }

++=++=

390

2290

3

1

3

2escLSBLcw kbagmKCaCTgM (31)

Therefore, the rotational rigidity for column-side joint is,

( ) ( ){ }3

90

22

90 3

1

++= escLSBLSBJc kbagmKR (32)

Finally, apparent rotational rigidity for beam-column joint of new type assembly is expressed as

equation (33).

LSBJCBJCB

LSBJCBJCBLSBJCB

RR

RRR

+

= (33)

2.5 Yield Moment of Column-Beam Joint in New Type Assembly

It is assumed that apparent yielding of column-beam joint occurs when the tensile force Ton LSB

reaches to its maximum strength 90maxP perpendicular to the grain of glulam column. Hence,

apparent yielding moment is expressed as,

( )

=

gmK

RPM

LSB

LSBJCBmaxy

90

90 (34)

where,

( )( )90909090

9090909090

cosh

sinh

wwss

sswwvmax

AElkAEk

lkAEAERfP

+

+=

(35)

90vf : Shear strength perpendicular to the grain obtained from thin plate specimen with penetrating

LSB[3]. (kN/mm2

)

3. Experiments

Table 1 shows

specification of test

specimens used in this

experiment. In each

specification, three

replications were

prepared. For column andbeam members, glulam

having a grade of

JASE105-f300 (fb=30MPa,

MOE=10.5 GPa) mixed species glulam, which is the same as those used in the previous

experiments [1], were used. Figure 5 shows a test set-up of beam-column joint. This configuration

represents the upper half and lateral half portion of portal frame subjected to a horizontal load. In

this experiment, lengthL was 2500mm and heightHwas 1480mm, thus moment at beam column

joint was estimated asM=HP=1.48P(kNm). While the rotational angle at beam-column joint was

defined as ( ) 3434 h/## = . Loading protocol applied was1/300,1/200,1/120,1/60,

1/30 rad. and finallyPmaxthen returns back to zero. In this experiment, only one cycle repeat wasadopted within each peak deformation.

Specimen

Code Name

Common

Width

b (mm)

Height of

Column

h c(mm)

Height of

Beam

hb(mm)

Joint Between Column-Steel

Gusset

B300-1,2,3 120 300 360 4-M12 Bolts Previous Type



L300-1,2,3 120 300 360 LSB2-30New Type

L360-1,2,3 120 360 420 LSB2-30New Type

L450-1,2,3 120 450 540 LSB2-30New Type

Table Specification of Test Specimens Used for Experiments

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4. Results and Discussion

Figures 6 to 8 show comparisons

between observed envelope curve

and predicted stiffness and yield

moment calculated using equations

derived in clause 2 in this paper.

From these comparisons, it is clear

that the equations for predicting

initial stiffness as well as yielding

moment of both previous and new

type joint specimen had fairly good

applicability on the real beam-

column joints.

Previous TypeB300)

-40

-30

-20

-10

0

10

20

30

40

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10

Rotational Angle (rad.)

MomentM(k

Nm)

B300-1

B300-2

B300-3

Stiffness M-cal

Yield My-cal

New TypeL300)

-40

-30

-20

-10

0

10

20

30

40

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10


MomentM(k

Nm)

L300-1

L300-2

L300-3

Stiffness M-cal

Yield My-cal

Fig.6 Comparisons between observed values and predicted ones in case of B300 and L300.

Previous TypeB360)

-50

-40

-30

-20

-10

0

10

20

30

40

50

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10


MomentM(kNm)

B360-1

B360-2

B360-3

Stiffness M-cal

Yield My-cal

New TypeL360)

-50

-40

-30

-20

-10

0

10

20

30

40

50

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10


MomentM(kNm)

L360-1

L360-2

L360-3

Stiffness M-cal

Yield My-cal


H

P

#3

#1

500 kN Oil Jack

300kN Load Cell

#4

L

Pined Support#2

h34

Beam

Column

Fig.5 Test set-up for beam-column joint specimen.

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Previous Type B450)

-80

-60

-40

-20

0

20

40

60

80

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08


MomentM(k

Nm)

B450-1

B450-2

B450-3

Stiffness M-cal

Yield My-cal

New TypeL450)

-80

-60

-40

-20

0

20

40

60

80

-0.06 -0.04 -0.02 0.00 0.02 0.04 0.06 0.08


MomentM(kNm)

L40-1

L40-2

L40-3

Stiffness M-cal

Yield My-cal


Photo 1 shows typical ultimate situations in different type of test specimens.

Photo1 Left: Large deformation at bearing plate in previous type. Middle: Pull-out of LSB in new

type (L300). Right: Tear off of high-tension bolt in new type (L450).

5. Conclusions

Experimental results showed that at maximum about 40% increase of maximum moment and

stiffness, while same percentage of decrease of ductility due to simple mistake in preparing test

specimen occurred. Equations derived in this research showed excellent applicability, hence,

consequently column-beam joint proposed in this research was proved to express enough structuralperformance both in experimentally and theoretically.

6. References

[1] Komatsu K., Hosokawa K., Hattori S., Matsuoka H., Yanaga K. and Mori T.: Developmentof Ductile and High-Strength Semi-Rigid Portal Frame Composed of Mixed-Species Glulamsand H-shaped Steel Gusset Joints,Proceedings of the World Conference on Timber

Engineering 2006, (CD-ROM only), Portland, Aug. 2006.

[2] Architectural Institute of Japan (edited): Design of Joints, Standard for Structural Design ofTimber Structures, Maruzen, Tokyo, 2006, pp.200-320. (in Japanese)

[3] Japan Lagscrewbolt Society (edited): Design and Construction Guideline on Glulam Joints byLagscrewbolt, Kyoto, 2007, p.13. (in Japanese)

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