Development of wooden portal frame structures with improved columns
ABSTRACT In Japan, the lifetime cycle of most housing lasts around 20–30 years. A governing factor in this respect is poor durability
due to old-fashioned use of the house. As a solution of this problem, houses can be built with a skeleton structure that allows
free partition of spaces by future owners. To develop the skeleton structure effectively, multistory frames with spans of
6 to 10 m are required. For this reason, attention has been focused on the behavior of multistory timber frame structures.
In this article, two types of wooden portal frame structures are proposed. Both structures have improved vertical columns
with short horizontal members glued in. The aim of this study was to investigate structurally effective solutions with these
types of columns. The first type of the new structure changed the location of the moment-transmitting ductile connection with
the improved columns. The second type of structure used an extended panel zone. Nine portal frame specimens were tested. The
stiffness values were improved by around 1.7 and 3.5 times when compared with the control, and the strength was improved by
around 1.25 and 1.45 times.
Key wordsImproved column-Timber-Portal frame-Multi-story-Semirigid
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ABSTRACT: Bolted cross-lapped joints (BCLJs) are one of the basic jointing methods used in Japan and European countries. There are, however, some problems in the design of BCLJs. With increasing use of large-scale wooden frame structures in Japan, it is necessary to establish proper estimating methods for predicting actual characteristics. A new approach was developed, using Saint Venant torsion theory, to estimate the performance of bolted timber joints in a more practical manner than using computer simulations. The calculated values were compared with the experimental results, indicating that the rotational stiffness and yield moment of BCLJs would be precisely predicted using the proposed theory. It was also found that the rotational stiffness calculated using the design method rooted on Coulombs torsion theory is about two times higher than the experimental results in the case of a rectangular arrangement of bolts.Journal of Wood Science 09/2004; 50(5):391-399. · 0.77 Impact Factor
Development of Wooden Portal Frame Structures
with Improved Columns
Dr. Masahiro Noguchi
Post Doctoral Fellow
Tokyo Institute of Technology, Yokohama, Kanagawa, Japan
Prof. dr. Kohei Komatsu
Research Institute for Sustainable Humanoshere, Kyoto University, Uji, Kyoto, Japan
This paper proposes two semi-rigid timber frames with a more effective structural
performance are compared and a structural design method is derived. Usually the joints are
located at the intersection of the beam and the column. The first frame type applies two types
of joints. A high strength capacity rigid glued joint is used to replace the traditional
beam-to-column joint while a second ductile semi-rigid joint is positioned at the area with low
bending moments.. The beam pieces that run between the column and the semi-rigd joints are
so well fixed to the column that they form one integral part. In the second frame type the
horizontal beam between the columns is extended beyond the location of the semi-rigid joints
of the first frame. This creates a large overlapping area where mechanical fasteners such as
bolts are generously spaced. Due to the large fastener spacing the stiffness is enhanced as well
as the strength.
In Japan, the lifetime cycles of most housing are around 20-30 years. This might be
considered as wastes of resources and energies from the global environment perspective. Most
governing factor is durability due to old fashioned use of the house. As a solution of this
problem, it is thought to build houses with skeleton structures which allow free partition of
spaces by future owners. To develop the skeleton structure effectively, multi-story frame with
span of 6 to 10m are required. For this reason, we pay our attentions on the multi-story
wooden portal frame structures.
The approaches of many researches in the past 1-8 were that the structural performances were
improved by improving only the moment transmitting connections. However, it can be
thought that more parameter influences: as example, location of the moment connection,
member, and so on.
In this article, two types of wooden portal frame structures were proposed. Both having
vertical columns added a short horizontal member with glue joints as shown the shadow area
in Fig. 1 (a) and (b). These vertical members were defined as “improved columns”. The aim
of this article was to show the structural advantages of this type of improved columns.
Material and methods
First type is the structures changed the location of moment transmitting ductile connection
with improved columns (Type E), in Fig. 1 (a). There is no ideal rigid beam to column joint
having stronger than member, regarded as rigid, ductile. Thus, in order to improving the
structural performance of semi-rigid structure, it could be thought better to make the position
move to where bending moment is small.
Second type is the structure whose panel zones were extended with the improved column
(Type S), in Fig 1 (b). The panel zone, in this article, was defined as the overlapping area
where column and beam met. The structural performances of moment resisting joints were
always limited in the height of both members geometrically. If the height at joint part is
increased, the larger moment resisting joint can be made. In bolted cross lapped joint,
mechanical properties were governed by the mechanical property of single bolted joint and
the adjacent bolt space. This result in that beam to column moment resisting joint having
higher capacity on stiffness and strength could be expected, extending the panel zone.
Finally, the portal frame with traditional bolted cross lapped joints is shown in Fig. 1 (c) as the
control type (Type C).
Nine portal frame specimens were built, three types × three replications. Each column
member was 3000 × 200 × 120 mm, pairs of beam members were 3000 × 200 × 60 mm. All
specimens were made of Sugi (Japanese Cedar, Cryptomeria japonica) glulam having JAS
(Japanese Agricultural Standard) strength grade of E65 – f 220 (MOE = 6500 MPa and
MOR= 22 MPa). The average moisture content was 11 %. All specimens were two story
miniature semi-rigid frame structures. Each leg joint was shown in Fig. 2 (a).
(a) Type E (b) Type S (c) Type C
Fig 1 Specimen
(a) Leg joint (b) Knee joint of Type C (c) Knee joint of Type S
Fig 2 J oint detail
Preparation of the improved columns
Two rectangle holes were made in each column and drilled eight circular holes as shown in
Fig. 3 (a). Each rectangle hole was cross-section of 200 ×30 mm, depth of 160 mm. Each
circular hole have diameter of 18 mm, length of 100 mm. Tenon member was also made, as
shown in Fig. 3 (b). Central tenon was the width of 29.5 mm, the depth of 200 mm, and the
tenon length of 155 mm. Similar to the mortise, each tenon have eight circular hole having
diameter of 18 mm, length of 100 mm were drilled in longitudinal direction.
The tenon and the slender steel rods of diameter 16 mm were driven into the rectangle holes
and circular holes respectively, and they were fixed with epoxy resin adhesive using
sledgehammer. They finally they were formed a F-shaped assemblage were completed. We
confirmed the adhesive injection by observing overflow of adhesive from holes.
The insert length of the steel rod in each member was set to 100 mm. The time to cure was set
at least two weeks.
(a) Mortise (b) Tenon
Fig 3 Construction of T-shaped member for the improved column
Assemble of portal frame specimens
Three types of portal frame specimens were assembled with improved columns, pairs of
beams and short bases using bolts as shown in Fig. 1. The clearance between bolts and
pre-drilled holes were 1.5 mm, hole diameter was 12 mm and bolt diameter was 10.5 mm.
Figures. 2 (b) and (c) show the bolt arrangement. Bolt arrangement of Type E was
geometrically the same as that of Type C.
Measurements and test procedure
The portal frame specimens were subjected to cyclic loading by applying a horizontal lateral
force at the top of the specimens, as illustrated in Fig. 1, (c). Cyclic loading tests were carried
out based on the protocol shown in Table 1. Story drift θdrift was calculated by the Eq. (1).
where δa : Displacement at roof beam (mm)
δb : Displacement at column base (mm), h : Distance between device for δa and that forδb.
Table 1 Load protocol
Displacement Angle R (rad)
The number of cycles
Results and Discussions
In Type C, failure did not occurred up to the end of the stroke length of hydraulic actuater.
Bolted moment transmitting joints were yielded and then worked as the plastic hinges, which
made collapse mechanism of the structures. Similarly, Type E specimens gave no failure up to
the end of stroke. However collapse mechanism was different from Type C. Fig. 4 shows the
typical failure mode of Type E specimens. As can be seen in Fig. 4, the failure was occurred
not at the regions where vertical and horizontal member met, but the regions where the bolted
moment transmitting joints were located. Keep this failure mode in mind to the latter
discussions. In Type S, the sprit failure occurred at the outer bolt hole in moment joint as
illustrated in Fig. 2 (c). But final fatal reduction of load was due to the sprit of bolt hole in
timber beam (see Fig. 2 (c)).
Fig. 4 Failure mode of Type E
Shear force - story drift curve
Typical shear force - story drift curves for the three different types of portal frames specimens
are shown in Fig. 5. From Fig. 5, it is obvious that type E and S specimens have remarkable
advantages on structural performance to the control type, especially stiffness. Therefore, the
portal frames proposed in this article obviously have high possibility for rational wooden
portal frame structures. In latter chapters, the detail features were discussed.
Fig 5 Shear force-story drift relationship
Story drift (rad)
Shear force (kN)