- Email: [email protected]
The non-linear behavior of composite joints
J. Construct. Steel Research 21 (1992) 59-70
The Non-linear Behavior of Composite Joints Ferdinand Tschemmernegg Institute of Steel and Timber Construction, University of Innsbruck, TechnikerstraBe 13, 6020 Innsbruck, Austria
ABSTRACT This paper describes the tests used to examine the non-linear behavior of composite joints. Extensive test series were performed at the Institute of Steel and Timber Construction, University of 1nnsbruck. As bases of the test, the macromechanical model of steel joints--developed at the Institute--was used. At present, only hinges are used in composite construction to connect the slabs and beams to the column. New possibilities for rigid or semi-rigid, full or partial strength composite joints are shown, which can be used in non-sway composite frames.
1 INTRODUCTION Elements of buildings are slabs (S) and beams (B), columns (C) which are connected by joints (J). The frames of the buildings consist of the elements in steel reinforced concrete or composite. Also, mixed structures of steel, reinforced concrete and composite elements have become of greater interest (see Fig. 1). The overall frame costs are mainly determined by the layout of the joints. Reference 1 focuses on the non-linear behavior of steel joints. This paper reports on the non-linear behavior of composite joints; to study this the spring model according to Ref. 1, Fig. 10 for steel joints is used with the load introduction, shear, connection and overall springs. A composite joint can also be classified according to EC 3 in view of stiffness strength and rotation capacity (see Fig. 2). Until now only hinges were used in composite non-sway frames (solution 9, according Fig. 2). All other solutions (1-8) have not been studied. Thus, the aim of 59 J. Construct. Steel Research 0143-974X/92/$05.00 © 1992 Elsevier Science Publishers Ltd,
England. Printed in Malta
60
F.
~
DESIGN
ELEMENT~\
Tschemmernegg
1
2
STEEL
COMPOSIT
3 R.-CONCRETE
o 7
N
2
i
Z
I
~J. ://'/:
3 O
i
.'*;h74
I
i
[-.
4 ¸
z
imm .
\ .
.
.
,:S
\I
'
i 5
i
STEEL-SHEETS
SANDWICHELEMENTS
R.-CONCRETEELEMENTS
Fig. 1. Elements of frames in structures. the research program was to find solutions for rigid and semi-rigid partial or full strength joints and the corresponding m o m e n t - r o t a t i o n curves. 2
2 DEFINITIONS
AND BACKGROUND
The background of the research was to find simple solutions for composite joints. As an example, the composite joint for a frame with composite slabs connected to a composite beam by stud connectors with a composite column is shown in Fig. 3. The beam is supported hinged by a small steel-block welded to the column flange. By concreting the slabs the joint becomes, rigid or semi-rigid. Only a tension reinforcement on both sides of the columns in the slab is necessary. The compression forces go through
The non-linear behavior of composite joints
M ~
61
(~)FULLRIGSTRENGTHID @
MOMENT CAPACITY OF THE BEAM PARTIAL STRENGTH-
SEMIRIGID
@NO STRENGTHROTATION
STRENGTH FULL pARTIAL NO g3 Z f.~ [.r.,
F-
RIGID 6)
©
®
.(!) @
®
UNTILNOW
Fig. 2. Classificationof joints. the column in the region of the lower flanges of the beams. Thus, the construction can be erected with hinges, which is a very simple process, and by concreting the slab; so the joint is obtained without bolting or rigid or semi-rigid welding. The dimensions of a composite joint depend on the depth of the beam plus the slab, and respectively the depth of the columns. Shear forces and load introduction compression forces are acting in the panel zone of the joint, while the tension forces in the tension reinforcement in the slabs on both sides of the column belong to the connection.
3 TESTS The test program was developed in view of the spring model according to Ref. 1, chapter 4.
3.1 Load introduetiou compression The load introduction in rectangular and circular composite columns were tested in comparison to steel columns 3'4 (see Fig. 4). It was found that the stiffness of the load introduction spring is not much influenced by the concrete, but the strength and deformation capacity is much improved (Fig. 5). At low load levels, the strength is positively influenced by the
62
F. Tschemmernegg
i i i i ' i ~ !¸¸¸¸)i!~ h J
Fig. 3. Compositejoint ~photo}. normal force in the composite columns, because the cracks are closed by compression from the normal forces in the columns (see Fig. 6). 3.2 Shear The shear behavior in composite rectangular and circular composite columns were tested in comparison to steel columns according to Refs 5 and 6 (see Fig. 7). Again, the result was that the stiffness of the shear spring is not much influenced by the concrete, but the strength and deformation capacity is improved (see Fig. 8). Also, the positive influence of compression out of normal forces in the column can be seen (see Fig. 9). 3.3 Connection--tension
The problem of introducing the tension forces in the slab out of the moment differences AM in the beams is illustrated in Fig. 10.
The non-linear behavior of composite joints
63
LOAD INTRODUCTION ~- ~
~;
II
//
(b) Fig. 4. Load introduction from bottom flange of beam to composite column: (a) theory; (b) test (photo). LOAD INTRODUCTION SPRING
MA~
MApCtOMPOSTIE ONLS YTEEL
Fig. 5. Load introduction rotaton spring for steel and composite columns.
In another paper 7 the problem will be studied through 18 full-scale tests (see Section 3.4) on composite joints with rectangular and circular columns. The problem is equal to a bolted connection. The bolt corresponds to the column, the steel sheet to the slab. The main problem here is the compression between the slab and column (Fig. 11) and the design of the reinforcement in the slab for the tension forces.
64
F. Tschemmernegg M- N - INTERACTION
NO,I 1,0~ . ~
1,0 MA m
Fig. 6. M-N interaction. (MA, N moment and normal force in the column). SHEAR
--F
Z =
M~ - M A h
(a)
(b) Fig. 7. Shear in the column: (a) theory; (b) test (photo).
3.4 Full-scale test F i g u r e 12(a) shows the m o m e n t distribuUon in a frame for different cases. W i t h a test a r r a n g e m e n t a c c o r d i n g Fig. 12(b) it is possible to simulate all these cases.
The non-linear behavior of composite joints SHEAR
65
SPRING ,~.Mpl
COMPOSITE
ONLY STEEL
Fig. 8. Shear rotation in the column.
M - N - INTERACTION N Np~
1,0
1,0
~M"~Mpl
Fig. 9. M-N interaction. (AM, N moment and normal force in the column).
CONNECTION (TENSION SIDE)
•
®
Fig. 10. Connection. Slab-column.
Figure 13(a) shows details of the test arrangement and Fig. 13(b) a view of the test of a composite joint. Table 1 shows the main parameters of the 18 different composite joints which have been tested: columns rectangular and circular; beams steel or composite; slabs solid or composite, connected to the beams being stud- or angle-connectors. The measurements taken from the test are shown in Fig. 14. The measurements allow us to obtain separately the load introduction, shear and connection spring in relation to the test load. For a control, the reactions for the test specimens were also measured. The first studies show very good agreement with the measurements according to Sections 3.1-3.3. Thus, it is possible to obtain the main parameters for load- introduction, shear and connection separately.
66
F. Tschemrnerneyo
(a)
(b) Fig. I 1. Connection: (a) rectangular column (photo); (b) circular column (photo}. The test results of the full-scale test are at present being analyzed using the finite element methods 7-9 in order to obtain a model and simplified methods for the design, and consequently the moment rotation behaviour.
N
g+p
Ul!l
It ,,r
/g
k Y ~
'N+.~.N
~+z~N
CASE(~)
CASE@
(a)
CASE(~
N~ CASE(~)F CASE®
CASE@
N~
I
(b)
Fig. 12. Moment distribution in a frame: (a) theory; (b) testing equipment.
E
i
(a) Fig. 13. Full-scale tests: (a) theory; (b) test arrangement (photo).
68
F. Tschemmernegg
(b) Fig. 13.-contd. TABLE 1 Tests of Composite Joints
iE~qT1 >;YSTEM
]-
~l...\II
"
BEAM
(()I,~]MN - , O k k E ( ' T O t , ~
[
t
_
I I
69
The non-linear behavior of composite joints |
i
ooooooo °1i
~ _
_
_
:
.
.
.
.
.
.
.
.
.
.
.
.
~_
L
_
19®
I
39o~
I
Fig. 14. Measurements.
4 CONCLUSIONS Different possibilities of composite joints have been tested to obtain the non-linear moment-rotation behavior of composite joints. Using the computer program for frames, and using the moment-rotation curves, it is also possible to design composite frames.
REFERENCES 1. Tschemmernegg, F. & Humer, C., The design of structural steel frames under consideration of the nonlinear behavior of joints. J. Construct. Steel Res., 11 (1988) 73-103. 2. Tschemmernegg, F., The moment rotation behavior of composite joints. I AB S E Symposium Brussels, 60 (1990) 83-8. 3. Grimus, W., Die Krafteinleitung in Verbundstiitzen. Institute fiir Stahlbau und Holzbau, Universit~it Innsbruck, Diplomarbeit, 1989. 4. Dornetshuber, J., Zur Krafteinleitung in Verbundknoten mit Rohrprofilen. Institut fiir Stahlbau und Holzbau, Universit~it Innsbruck, Diplomarbeit, 1990.
70
F. Tschemmernegg
5. Leitner, H., Die Querkraftdeformation bei Verbundknoten. lnstitut fiir Stahlbau und Holzbau, Universit~t Innsbruck, Diplomarbeit, 1989. 6. Stoiberer, H., Zur Querkraftdeformation yon Verbundknoten mit Rohrprofilen. Institut fiir Stahlbau und Holzbau, Universitfit Innsbruck, Diplomarbeit, 1990. 7. Hittenberger, R., Zur Durchdringung yon Stfitzen- und Deckenplatten bei Verbundknoten. Institut ffir Stahlbau und Holzbau, Universitfit Innsbruck, Dissertation (in Arbeit). 8. Wiesholzer, J., Zur Krafteinleitung bei Verbundknoten. Institut f/Jr Stahlbau und Holzbau, Universitfit lnnsbruck, Dissertation (in Arbeit). 9. Brugger, R., Zur Schubtragf~ihigkeit bei Verbundknoten. lnstitut fiJr Stahibau und Holzbau, Universit~it Innsbruck, Dissertaton (in Arbeit).
The Non-linear Behavior of Composite Joints Ferdinand Tschemmernegg Institute of Steel and Timber Construction, University of Innsbruck, TechnikerstraBe 13, 6020 Innsbruck, Austria
ABSTRACT This paper describes the tests used to examine the non-linear behavior of composite joints. Extensive test series were performed at the Institute of Steel and Timber Construction, University of 1nnsbruck. As bases of the test, the macromechanical model of steel joints--developed at the Institute--was used. At present, only hinges are used in composite construction to connect the slabs and beams to the column. New possibilities for rigid or semi-rigid, full or partial strength composite joints are shown, which can be used in non-sway composite frames.
1 INTRODUCTION Elements of buildings are slabs (S) and beams (B), columns (C) which are connected by joints (J). The frames of the buildings consist of the elements in steel reinforced concrete or composite. Also, mixed structures of steel, reinforced concrete and composite elements have become of greater interest (see Fig. 1). The overall frame costs are mainly determined by the layout of the joints. Reference 1 focuses on the non-linear behavior of steel joints. This paper reports on the non-linear behavior of composite joints; to study this the spring model according to Ref. 1, Fig. 10 for steel joints is used with the load introduction, shear, connection and overall springs. A composite joint can also be classified according to EC 3 in view of stiffness strength and rotation capacity (see Fig. 2). Until now only hinges were used in composite non-sway frames (solution 9, according Fig. 2). All other solutions (1-8) have not been studied. Thus, the aim of 59 J. Construct. Steel Research 0143-974X/92/$05.00 © 1992 Elsevier Science Publishers Ltd,
England. Printed in Malta
60
F.
~
DESIGN
ELEMENT~\
Tschemmernegg
1
2
STEEL
COMPOSIT
3 R.-CONCRETE
o 7
N
2
i
Z
I
~J. ://'/:
3 O
i
.'*;h74
I
i
[-.
4 ¸
z
imm .
\ .
.
.
,:S
\I
'
i 5
i
STEEL-SHEETS
SANDWICHELEMENTS
R.-CONCRETEELEMENTS
Fig. 1. Elements of frames in structures. the research program was to find solutions for rigid and semi-rigid partial or full strength joints and the corresponding m o m e n t - r o t a t i o n curves. 2
2 DEFINITIONS
AND BACKGROUND
The background of the research was to find simple solutions for composite joints. As an example, the composite joint for a frame with composite slabs connected to a composite beam by stud connectors with a composite column is shown in Fig. 3. The beam is supported hinged by a small steel-block welded to the column flange. By concreting the slabs the joint becomes, rigid or semi-rigid. Only a tension reinforcement on both sides of the columns in the slab is necessary. The compression forces go through
The non-linear behavior of composite joints
M ~
61
(~)FULLRIGSTRENGTHID @
MOMENT CAPACITY OF THE BEAM PARTIAL STRENGTH-
SEMIRIGID
@NO STRENGTHROTATION
STRENGTH FULL pARTIAL NO g3 Z f.~ [.r.,
F-
RIGID 6)
©
®
.(!) @
®
UNTILNOW
Fig. 2. Classificationof joints. the column in the region of the lower flanges of the beams. Thus, the construction can be erected with hinges, which is a very simple process, and by concreting the slab; so the joint is obtained without bolting or rigid or semi-rigid welding. The dimensions of a composite joint depend on the depth of the beam plus the slab, and respectively the depth of the columns. Shear forces and load introduction compression forces are acting in the panel zone of the joint, while the tension forces in the tension reinforcement in the slabs on both sides of the column belong to the connection.
3 TESTS The test program was developed in view of the spring model according to Ref. 1, chapter 4.
3.1 Load introduetiou compression The load introduction in rectangular and circular composite columns were tested in comparison to steel columns 3'4 (see Fig. 4). It was found that the stiffness of the load introduction spring is not much influenced by the concrete, but the strength and deformation capacity is much improved (Fig. 5). At low load levels, the strength is positively influenced by the
62
F. Tschemmernegg
i i i i ' i ~ !¸¸¸¸)i!~ h J
Fig. 3. Compositejoint ~photo}. normal force in the composite columns, because the cracks are closed by compression from the normal forces in the columns (see Fig. 6). 3.2 Shear The shear behavior in composite rectangular and circular composite columns were tested in comparison to steel columns according to Refs 5 and 6 (see Fig. 7). Again, the result was that the stiffness of the shear spring is not much influenced by the concrete, but the strength and deformation capacity is improved (see Fig. 8). Also, the positive influence of compression out of normal forces in the column can be seen (see Fig. 9). 3.3 Connection--tension
The problem of introducing the tension forces in the slab out of the moment differences AM in the beams is illustrated in Fig. 10.
The non-linear behavior of composite joints
63
LOAD INTRODUCTION ~- ~
~;
II
//
(b) Fig. 4. Load introduction from bottom flange of beam to composite column: (a) theory; (b) test (photo). LOAD INTRODUCTION SPRING
MA~
MApCtOMPOSTIE ONLS YTEEL
Fig. 5. Load introduction rotaton spring for steel and composite columns.
In another paper 7 the problem will be studied through 18 full-scale tests (see Section 3.4) on composite joints with rectangular and circular columns. The problem is equal to a bolted connection. The bolt corresponds to the column, the steel sheet to the slab. The main problem here is the compression between the slab and column (Fig. 11) and the design of the reinforcement in the slab for the tension forces.
64
F. Tschemmernegg M- N - INTERACTION
NO,I 1,0~ . ~
1,0 MA m
Fig. 6. M-N interaction. (MA, N moment and normal force in the column). SHEAR
--F
Z =
M~ - M A h
(a)
(b) Fig. 7. Shear in the column: (a) theory; (b) test (photo).
3.4 Full-scale test F i g u r e 12(a) shows the m o m e n t distribuUon in a frame for different cases. W i t h a test a r r a n g e m e n t a c c o r d i n g Fig. 12(b) it is possible to simulate all these cases.
The non-linear behavior of composite joints SHEAR
65
SPRING ,~.Mpl
COMPOSITE
ONLY STEEL
Fig. 8. Shear rotation in the column.
M - N - INTERACTION N Np~
1,0
1,0
~M"~Mpl
Fig. 9. M-N interaction. (AM, N moment and normal force in the column).
CONNECTION (TENSION SIDE)
•
®
Fig. 10. Connection. Slab-column.
Figure 13(a) shows details of the test arrangement and Fig. 13(b) a view of the test of a composite joint. Table 1 shows the main parameters of the 18 different composite joints which have been tested: columns rectangular and circular; beams steel or composite; slabs solid or composite, connected to the beams being stud- or angle-connectors. The measurements taken from the test are shown in Fig. 14. The measurements allow us to obtain separately the load introduction, shear and connection spring in relation to the test load. For a control, the reactions for the test specimens were also measured. The first studies show very good agreement with the measurements according to Sections 3.1-3.3. Thus, it is possible to obtain the main parameters for load- introduction, shear and connection separately.
66
F. Tschemrnerneyo
(a)
(b) Fig. I 1. Connection: (a) rectangular column (photo); (b) circular column (photo}. The test results of the full-scale test are at present being analyzed using the finite element methods 7-9 in order to obtain a model and simplified methods for the design, and consequently the moment rotation behaviour.
N
g+p
Ul!l
It ,,r
/g
k Y ~
'N+.~.N
~+z~N
CASE(~)
CASE@
(a)
CASE(~
N~ CASE(~)F CASE®
CASE@
N~
I
(b)
Fig. 12. Moment distribution in a frame: (a) theory; (b) testing equipment.
E
i
(a) Fig. 13. Full-scale tests: (a) theory; (b) test arrangement (photo).
68
F. Tschemmernegg
(b) Fig. 13.-contd. TABLE 1 Tests of Composite Joints
iE~qT1 >;YSTEM
]-
~l...\II
"
BEAM
(()I,~]MN - , O k k E ( ' T O t , ~
[
t
_
I I
69
The non-linear behavior of composite joints |
i
ooooooo °1i
~ _
_
_
:
.
.
.
.
.
.
.
.
.
.
.
.
~_
L
_
19®
I
39o~
I
Fig. 14. Measurements.
4 CONCLUSIONS Different possibilities of composite joints have been tested to obtain the non-linear moment-rotation behavior of composite joints. Using the computer program for frames, and using the moment-rotation curves, it is also possible to design composite frames.
REFERENCES 1. Tschemmernegg, F. & Humer, C., The design of structural steel frames under consideration of the nonlinear behavior of joints. J. Construct. Steel Res., 11 (1988) 73-103. 2. Tschemmernegg, F., The moment rotation behavior of composite joints. I AB S E Symposium Brussels, 60 (1990) 83-8. 3. Grimus, W., Die Krafteinleitung in Verbundstiitzen. Institute fiir Stahlbau und Holzbau, Universit~it Innsbruck, Diplomarbeit, 1989. 4. Dornetshuber, J., Zur Krafteinleitung in Verbundknoten mit Rohrprofilen. Institut fiir Stahlbau und Holzbau, Universit~it Innsbruck, Diplomarbeit, 1990.
70
F. Tschemmernegg
5. Leitner, H., Die Querkraftdeformation bei Verbundknoten. lnstitut fiir Stahlbau und Holzbau, Universit~t Innsbruck, Diplomarbeit, 1989. 6. Stoiberer, H., Zur Querkraftdeformation yon Verbundknoten mit Rohrprofilen. Institut fiir Stahlbau und Holzbau, Universitfit Innsbruck, Diplomarbeit, 1990. 7. Hittenberger, R., Zur Durchdringung yon Stfitzen- und Deckenplatten bei Verbundknoten. Institut ffir Stahlbau und Holzbau, Universitfit Innsbruck, Dissertation (in Arbeit). 8. Wiesholzer, J., Zur Krafteinleitung bei Verbundknoten. Institut f/Jr Stahlbau und Holzbau, Universitfit lnnsbruck, Dissertation (in Arbeit). 9. Brugger, R., Zur Schubtragf~ihigkeit bei Verbundknoten. lnstitut fiJr Stahibau und Holzbau, Universit~it Innsbruck, Dissertaton (in Arbeit).