Steel Structures 6 (2006) 209-213 www.kssc.or.kr

Development of a New Steel Connection

Jong-Won Park1,* and In-Kyu Hwang2

1Associate Professor, Architectural Engineering Department, Hong Ik University, Chochiwon, Chungnam, 339-701, Korea2Graduate Student, Architectural Engineering Department, Hong Ik University, Chochiwon, Chungnam, 339-701, Korea

Abstract

A new connection method of steel members is currently under development. The concept of the new connection is basedon using wedges instead of high strength bolts. When a force is applied to the connected member, the face of the wedge exertsa lateral force and the friction force between the steel member and the wedge resists the applied force. As the applied forceis increased, the friction force increases proportionally. Therefore, pretensioning is not necessary as for bolts. Several methodsto secure the contact between the steel member and the wedge were proposed and verified using uniaxial tension tests.Application of the new connection to beam splices was investigated using beam strength tests. Test results showed that thebeams could develop their strength at the splice locations without the failure of the new connection.

Keywords: Wedge, Connection, Steel, Friction force, Beam splice

1. Introduction

Bolted connection has been widely used as the means

of structural connection in civil and architectural construction

fields such as column splices, beam-to-column connections,

beam splices and brace connections (Salmon and Johnson,

1996). Bolted connection requires bolt holes to be drilled

in the connected structural members and the splice plates

or bracket that are placed at one or both sides of the

connected structural members. However, the bolt holes

cause problems such as reduced section, stress concentration,

reduction in the energy absorption capacity. Moreover,

slip between the connected members may occur under

tension or compression force, because the diameter of

bolts is always smaller than that of holes. To prevent slip

and stress concentration, friction-type connection has

been used, in which high clamping force is induced for

the friction force at the connected surface to resist the

applied force. For the friction-type connection, full

pretensioning of bolts is necessary. However, full

pretensioning procedure increases the installation time

and cost, and it is not easy to check if required pretension

is obtained.

To solve the problems of bolted connections, a new

connection method based on using wedges is under

development. This is a study to verify the feasibility of

the new connection. The new connection consists of a

coupling case, a pair of wedges that touch the connected

member, and a pair of fillers that are inserted into the

space between the coupling case and the wedge as shown

in Fig. 1.

When the external force acted on the connected member

is increased, the vertical force that is induced to the

member by wedge action increases proportionally. As the

vertical force is increased, the friction force between the

wedge and the connected member increases proportionally

and the connected member does not come out of the

*Corresponding authorTel: +82-41-860-2607, Fax: +82-41-865-9434E-mail: jwp@wow.hongik.ac.kr

Figure 1. Illustration of the new connection.

Figure 2. Free-body diagram of the wedge.

210 Jong-Won Park and In-Kyu Hwang

coupling case, unless the coupling case fails. Figure 2

shows the free-body diagram of the wedge.

The slope of the wedge is determined from the

equilibrium of force as follows.

(1)

where µ and µ' are the coefficients of friction of the

slope side and the bottom side of the wedge, respectively.

2. Connection Types

To prevent the connected member from slipping out of

the coupling case before wedging action starts, it is

critically important to ensure firm contact between the

wedge and the member. Four different methods to put the

wedge and the member in close contact were proposed.

To verify the structural performance of each connection

type, simple connection specimens were made and tested

in uniaxial tension as shown in Fig. 3.

The sizes and material properties of the coupling case

and the connected member used in the tests are listed in

Table 1. The size of the coupling case was designed for

the maximum stress in the coupling case to be less than

its yield stress when the connected member reached its

tensile strength. A finite element program - ANSYS was

used for the analysis of the coupling case (ANSYS,

1992). Figure 4 shows the stress distributions in the

coupling case. Instead of a design equation, sizing in

practical use will be provided by design aids to be

developed later on.

2.1. Longitudinally-divided wedge connection

Figure 5(a) shows a longitudinally divided wedge

connection (Type I), in which the wedges are divided in

half longitudinally. Elastic devices such as springs are

placed between the divided parts to spread them inducing

close contact between the wedge and the connected

member. Figure 5(b) shows that premature failure in the

connection occurred, before the tensile strength of the

connected member was reached.

2.2. Laterally-divided wedge connection

Figure 6(a) shows a laterally divided wedge connection

(Type II), in which a screw-type space adjuster is used to

ensure close contact between the wedge and the

connected member by spreading the divided wedges.

Figure 6(b) shows the necking failure of the connected

member. No failure occurred in the connection. The

indentations made on the surface shows that a large

tightening force was induced to the member by wedge

action.

θtanµ' µ–

1 µ µ'⋅+-----------------⎝ ⎠⎛ ⎞≤

Figure 3. Simple connection specimen in the uniaxial testingmachine.

Table 1. Material properties

Yield strength of coupling case 833 MPa

Tensile strength of coupling case 980 MPa

Size of coupling case Φ 165 mm

Material property of coupling SCM440

Size of connected members 75 × 17 mm

Yield strength of connected members 235.2 MPa

Tensile strength of connected members 401.8 MPa

Figure 4. Stress distribution in the coupling case.

Development of a New Steel Connection 211

2.3. Tapered filler type connection

Figure 7(a) shows a tapered filler type connection

(Type III). In this connection type, the fillers are formed

to be tapered inwards as shown in the figure. As the filler

was pushed into the space between the coupling case and

the wedge, the wedge and the connected member come

into firm contact due to the spreading force of the tapered

filler. Necking failure of the connected member occurred.

Figure 7(b) shows the load-displacement curve.

2.4. Stud type connection

Figure 8(a) shows a stud type connection (Type IV) in

which a shear stud is attached to the surface of the

connected member and a hole which is corresponding to

the stud is formed in the wedge. This connection type can

secure the wedge action by the bearing of the stud against

the side of the hole, if slip occurs due to insufficient

initial contact between the wedge and the connected

member. Three specimens of different stud diameters (3

mm, 5 mm, and 10 mm) were tested. In all three

specimens, necking failure of the connected member

occurred. Figure 8(b) shows the load-displacement curve.

The shear strength of the 10 mm stud was just 3.14 tf

(30.8 kN). It means that once the stud induces the wedge

action, the external force is resisted by the friction force

between the wedge and the connected member.

Figure 5. Longitudinally divided wedge connection.

Figure 6. Laterally divided wedge connection.

Figure 7. Tapered filler type connection.

212 Jong-Won Park and In-Kyu Hwang

3. Beam Splice Tests

3.1. Test specimens

Beam tests were performed to study the feasibility of

the application of the new connection for beam splices.

Three beam specimens spliced with the new connection

were tested (NC, NCR & NCD). The flanges were

connected using the new connection while the webs were

connected using high strength bolts as in the conventional

beam splices. One specimen with a conventional bolted

beam splice was tested as a reference one (BC). Figure 9

shows the test set-up.

A wide flange section of 600 mm (beam depth) × 200

mm (beam width) × 11 mm (web thickness) × 17 mm

(flange thickness) was used for the beam. The beam was

of SS 400 material (equivalent to A36 steel). The size and

the material properties of the coupling case were same as

those listed in Table 1. Laterally divided wedges (Type II

connections) were used in all three specimens. Shear

studs (Type IV connection) were attached to the surfaces

of the beam flanges in all three specimens for more

reliable performance. The cost of the flange splicing with

the new connection was about 3/4 of that with bolted

connection. Moreover, the installation time of the new

connection was just 1/6 of that of the bolted connection.

3.2. Test results

Figure 10 shows the load-displacement curves of the

test specimens. The ultimate strength of Specimen NC,

which used the new connection for beam flanges, was 8%

less than that of Specimen BC, which had the conventional

bolt splice.

Figure 11 shows the surface of the beam flange of

Specimen NC after the test. The indentations made on the

surface shows that full wedge action occurred. Figure 12

shows the local buckling of the beam compression flange

of Specimen NC.

Specimen NCR was same as Specimen NC except that

the load was applied repeatedly to investigate the performance

of the new connection under repeated loading (JSCE,

1982). The loading was repeated 30 times up to the point

at which 95% of the beam yield strength was reached at

the splice. No slip was observed throughout the test.

In conventional bolted connections, fill plates are

necessary to take up any variation in depth at the

connections. In Specimen NCD, the beam sections that

were connected at the splice were fabricated to have

different depths. The difference in depth was the largest

one of the tolerances allowed for wide-flange shapes by

the Specification (MOCT, 1994). The load-displacement

curve of Specimen NCD shows that the new connection

can take up any variation in depth at the connections

within the allowed tolerances without any reduction in

strength.

4. Summary and Conclusions

A new connection method of steel members based on

using wedges is currently under development. Four

different methods to put the wedge and the member in

close contact were proposed and tested to verify their

structural performance. All three methods except the

longitudinally divided wedge connection showed good

performance. Beam splice tests were performed to study

the feasibility of the application of the new connection for

beam splices. The beam specimens could reach their

plastic moments without failure at the splices. The cost

and the installation time of the flange splicing with the

Figure 8. Stud type connection.

Figure 9. Test set-up.

Development of a New Steel Connection 213

new connection were about 3/4 and 1/6 of those with

conventional bolted connection respectively.

The number of tests conducted in this program is

limited and insufficient to develop general design guidelines.

However, based on performance evaluations and economic

study, it is believed that the new connection method is

feasible for application in actual structures. Full-scale

beam-to-column connection specimens will be tested to

evaluate the structural performance of the new connection

when subjected to cyclic loading.

References

Salmon C.G. and Johnson E.J. (1996). Steel Structures,

Fourth Edition, Harper Collins, New York, NY.

ANSYS-user’s manual (1992), Swanson Analysis, Houston,

PA.

JSCE (1982). Technical recommendations for splicing of

reinforcement, Japanese Society of Civil Engineers, Japan.

MOCT (1994), Korean Architectural Standard Specification,

Ministry of Construction and Transportation, Korea.

Figure 10. Load-displacement curves.

Figure 11. Beam flange after test. Figure 12. Local buckling of compression flange.