EXPERIMENTAL BEHAVIOUR OF FRICTION T-STUB
BEAM-TO-COLUMN JOINTS UNDER CYCLIC LOADS
Massimo Latour; Vincenzo Piluso; Gianvittorio Rizzano
DICIV - Department of Civil Engineering, University of Salerno, Italy
[email protected]; [email protected]; [email protected]
ABSTRACT
Eurocode 8 has introduced the possibility of adopting partial strength joints in
case of seismic-resistant MR-Frames, provided that connections are demonstrated
to perform adequately under cyclic loads. An experimental program devoted to the
investigation of the cyclic behaviour of traditional joint details has been recently carried out by the Authors. Within this experimental program, the analysis of the obtained results has evidenced that, even though connections designed to dissipate
the seismic energy in bolted components can provide significant advantages because easy to repair after a destructive seismic event, they possess reduced dissipation capacity when compared to RBS connections and traditional full-strength connections. In this work, an advanced approach aimed to enhance the hysteretic behaviour of double split tee (DST) joints and to the ambitious goal of joint damage
prevention is presented. The proposed system is based on the idea of using friction
dampers within the components of beam-to-column joints. A preliminary set of prototypes has been experimentally tested and the joints performances under cyclic loading conditions have been compared to those of classical joint details. The experimental work has been carried out at the Materials and Structures Laboratory of
Salerno University.
1. INTRODUCTION
According to the most recent seismic codes (CEN, 2005a; ANSI/AISC 341-10)
moment resisting steel frames can be designed either according to the full-strength
criterion and the partial-strength criterion. The first one is based on the dissipation of
the seismic input energy at the beam ends, the second one concentrates damage in
the connecting elements and/or the panel zone. In the former case, aiming to promote the yielding of the beam ends, the beam-to-column joint is designed to possess
an adequate overstrength with respect to the connected beam to account for strainhardening and random material variability effects which affect the flexural resistance
actually developed by the beam end. In the latter case, the beam yielding is prevented as the joints are designed to develop a bending resistance less than the
beam plastic moment, so that dissipation occurs in the connecting elements. In addition, as a consequence, regarding the column design, the hierarchy criterion has to
be applied by making reference to the maximum moment that connections are able
to transmit. This design philosophy, as demonstrated by Faella et al. (1998), is particularly cost/effective in cases where the beam size is mainly governed by vertical
loads rather than lateral loads, i.e. low-rise/long span MRFs.
The traditional design of MRFs (Mazzolani & Piluso, 1996), based on the use
of full-strength beam-to-column joints, requires only the prediction of the monotonic
response of connections (CEN, 2005b; CEN, 2005c). In particular, in order to characterize the behaviour of such joints, only the prediction of the initial stiffness and of
the plastic resistance is needed, whereas the cyclic behaviour is governed by the
width-to-thickness ratios of the plate elements of the connected beam. Conversely,
as the energy dissipation supply of semi-continuous MRFs relies on the ability of
connections to withstand a number of excursions in plastic range without losing their
capacity to sustain vertical loads, it is evident that, in order to successfully apply partial-strength joints, it is necessary to properly characterize and predict the response
of connections under cyclic loading conditions (Astaneh-Asl, 1987; Bernuzzi et al.,
1996; Faella et al., 1999; Piluso & Rizzano, 2008; Latour et al., 2011a). For this reason, the use of partial-strength joints is allowed, both in AISC and Eurocode 8 provided that a “conformance demonstration” of the cyclic behaviour of connections
adopted in the seismic load resisting system is shown by the designer. As a result,
joints have to be pre-qualified accordingly with the ductility class of MRFs. For this
reason a set of pre-qualified connections with the corresponding design criteria is
suggested (ANSI/AISC 358-10), whose cyclic behaviour has been experimentally
investigated demonstrating the development of plastic rotation supplies compatible
with the corresponding ductility class.
Unfortunately, pre-qualified connections are not suggested in Eurocode 8,
therefore, aiming to provide engineers with the tools needed to predict the cyclic behaviour of joints, new efforts for the developments of analytical approaches are
needed, unless specific experimental tests are carried out.
To this scope, in last two decades a number of experimental programs dealing with the characterization of the cyclic behaviour of beam-to-column connections
has been carried out. In a recent work of the Authors research group (Iannone et al.,
2011), the behaviour of bolted joints designed to possess the same strength, but detailed to involve in plastic range different components, has been experimentally investigated pointing out the hysteretic behaviour. In particular, it has been pointed out
that the energy dissipation provided by the whole joint can be obtained as the sum of
the energy dissipations due to the single joint components, provided that the joint
components are properly identified and their cyclic response is properly measured.
This result is very important, because it testifies the applicability of the component
approach also to the prediction of the joint behaviour under cyclic loads (Latour et
al., 2011a). Within the above research program, due to the significant advantages
which are able to provide under the reparability point of view, Double Split Tee (DST)
connections have been recognized as an interesting solution to be applied in dissipative semi-continuous MRFs. In fact, DST connections can be easily repaired after
destructive seismic events and allow to govern the joint rotational behaviour (i.e. the
rotational stiffness, strength and plastic rotation supply) by properly fixing the bolt diameter and by simply calibrating three geometrical parameters: the width and the
thickness of the T-stub flange plate and the distance between the bolts and the plastic hinge arising at the stem-to-flange connection (Piluso et al., 2001a; 2001b). On
the other hand, joints involving bolted components in plastic range provide also several disadvantages. First of all, even though experimental studies demonstrate that
bolted components are able to dissipate significant amounts of energy, it has to be
recognized that their hysteretic behaviour is less dissipative compared to other joint
typologies or to the cyclic response of steel H-shaped sections. This is mainly due to
contact and pinching phenomena which usually lead to the quick degradation of
strength and stiffness of the tee elements.
For this reason, on one hand, the use of hourglass shaped T-stub flanges has
been recently proposed (Latour & Rizzano, 2012) where, in other words, the dissipative capacity of classical tee elements has been improved by applying to the T-stub
flanges the same concepts usually developed to design hysteretic metallic dampers,
such as ADAS devices (Aiken et al., 1993a; Whittaker et al., 1989; Christopoulos &
Filiatrault, 2000; Soong & Spencer Jr, 2002). On the other hand, an innovative approach aimed to enhance the dissipation capacity of classical rectangular T-stubs by
using friction pads has also been proposed (Latour et al., 2011b) with the primary
aim of joint damage prevention.
This last approach, which can be considered an innovative application of the
seismic protection strategy based on supplementary energy dissipation, is herein
presented. The main scope of the work is to investigate the possibility of governing
the dissipative capacities of DST connections by exploiting the cyclic behaviour of
friction materials by contemporaneously preventing the joint damage. In particular,
as shown in the following, two innovative DST joints are detailed aiming to dissipate
the seismic input energy by means of the slippage of the stems of the tees on a friction pad, which is interposed between the tee stems and the beam flanges. In this
way, under seismic loading conditions, structural elements do not undergo to any
damage provided that rigorous design procedures for failure mode control are applied (Mazzolani & Piluso, 1997; Longo et al., 2012), but energy dissipation is provided by the alternate movement of the tee stems on the friction pads, which are preloaded by means of high strength bolts. Therefore, in the present paper a new type
of dissipative beam-to-column joints, namely dissipative DST connections with friction pads, to be adopted in the seismic design of semi-continuous MRFs is proposed
and its behaviour is investigated by means of experimental tests under displacement
control in cyclic loading conditions.
2. EXPERIMENTAL TESTS ON FRICTION MATERIALS
Preliminarily, in order to investigate the frictional properties of different interfaces to be used in Double Split Tee friction joints, a sub-assemblage constituted by
two layers of friction material or metal located between three steel plates made of
S275JR steel has been realised at Materials and Structures Laboratory of Salerno
University (Fig.1). In order to allow the relative movement of the steel plates on the
interposed friction material, one of the inner plates has been realised with slotted
holes.
Fig. 1. Scheme of the tested sub-assemblage
Conversely, the other inner plate and the two outer plates have been realized with
circular holes. The clamping force has been applied by means of 16 preloaded bolts
M20 10.9 class, and the holes have been drilled with a 21 mm drill bit. Aiming to
evaluate the magnitude of the friction coefficient, several different layouts of the sub-
assemblage have been considered varying three parameters: the interface, the
tightening torque, the number of tightened bolts and the type of bolt washers. The
frictional properties of the following five different interfaces have been evaluated (Fig.
2):
 Steel on steel;
 Brass on steel;
 Friction material M0 on steel;
 Friction material M1 on steel;
 Friction material M2 on steel.
Brass on Steel 8 Bolts Ts=200Nm f=0.25Hz
Steel on Steel 4 Bolts Ts=200Nm f=0.25Hz
200
300
150
250
200
100
150
50
100
-40
-30
-20
-10
0
10
20
30
F [kN]
F [kN]
0
40
-50
50
0
-20
-15
-10
-5
0
5
10
15
20
-50
-100
-100
-150
-150
-200
-200
-250
-250
d [mm]
d [mm]
Steel on Steel Cycles 1-10 (Ts=200 Nm)
Brass on Steel Cycles 1-60 (Ts=200 Nm)
M0 on Steel 4 Bolts Ts=200Nm f=0.25Hz
M1 on Steel 8 Bolts Ts=200Nm f=0.25Hz
150
100
50
50
F [kN]
100
0
-20
-15
-10
-5
0
5
10
15
20
0
-15
-10
-5
0
-50
-50
-100
-100
-150
-150
d [mm]
5
10
d [mm]
M0 on Steel Cycles 1-20 (Ts=200 Nm)
M1 on Steel Cycles 1-10 (Ts=200 Nm)
M2 on Steel 8 Bolts Ts=200Nm f=0.25Hz
200
150
100
50
F [kN]
F [kN]
150
-20
0
-15
-10
-5
0
5
10
15
20
-50
-100
-150
-200
d [mm]
M2 on Steel Cycles 1-10 (Ts=200 Nm)
Fig. 2. Force-Displacement Curves of interfaces
15
20
In particular, two different types of washers have been employed. In the first
part of the experimental program, circular flat steel washers have been used, while in
the second part of the campaign a packet of steel disc springs has been interposed
between the bolt head and the steel plate (Fig. 3). In addition, the experimental
analysis has been carried out by varying the bolt tightening level in the range between 200 Nm and 500 Nm, obtaining different values of the clamping force acting
on the sliding surfaces. The main goal of the experimental program is to obtain the
friction coefficients of the investigated materials, both static and kinetic, for values of
the normal force varying in a range leading to sliding forces suitable for structural
applications and for values of the velocity compatible with seismic engineering applications. In addition, the experimental analysis is also devoted to evaluate the variation of the sliding force as far as the number of cycles of the applied loading history
increase. In fact, as already demonstrated by Pall & Marsh (1981), the response of
an interface subjected to cyclic loading conditions can substantially be of two types.
The first type of response provides a monotonically softening behaviour. In this case,
the maximum sliding load is reached during the first cycle whereas in all the subsequent cycles only degradation behaviour is expected. The second type of response
is characterized by three phases: first a hardening response, then a steady state
phase and finally a load degradation phase.
The tests have been carried out by means of a universal testing machine
Schenck Hydropuls S56. The testing apparatus is constituted by an hydraulic piston
with loading capacity equal to +/- 630 kN, maximum stroke equal to +/- 125 mm and
a self-balanced steel frame used to counteract the axial loadings. In order to measure the axial displacements the testing device is equipped with an LVDT, while the
tension/compression loads are measured by means of a load cell. The cyclic tests
have been carried out under displacement control for different displacement amplitudes at a frequency equal to 0.25 Hz (Figs. 2-3).
For all the tests the average values of the static and kinetic coefficient of friction have been determined considering the following expression:
=
(1)
where m is the number of surfaces in contact, n is the number of bolts,
is the bolt
preloading force and is the sliding force. The obtained values are delivered in Table 1.
Table 1. Values of the friction coefficient
Interface
static
dynamic
Steel on Steel
Brass on Steel
M0 on Steel
M1 on Steel
M2 on Steel
0.173
0.097
0.254
0.201
0.158
0.351
0.200
0.254
0.201
0.180
Concerning the behaviour exhibited by the five materials under cyclic loads,
the main results of the experimental program can be summarized as follows:





Steel on steel interface exhibited an high coefficient of friction, but with an unstable behaviour which is initially characterized by a significantly hardening behaviour and successively by a quickly softening behaviour;
Brass on steel interface showed a significant hardening behaviour with a low
static friction coefficient;
Material M0, which is a rubber based material developed for automotive applications exhibited a very stable behaviour and high energy dissipation capacity also
under high values of the preloading level;
Material M1, which is a rubber based material developed for electrical machines,
exhibited a cyclic behaviour with some pinching and with low friction coefficient
and a quickly degrading behaviour;
Material M2, which is an hard rubber based material developed for applications
where low wearing is needed, developed a quite low value of the friction coefficient, but a very stable behaviour and high dissipation capacity.
Fig. 3. Tested Specimen
3. EXPERIMENTAL TESTS ON DST JOINTS WITH FRICTION PADS
Starting from the component behaviour, i.e. the testing results of the subassemblage with friction pads presented in the previous section, the design of dissipative DST connections with friction pads, i.e. with interposed layers of friction material between the beam flanges and the stems of the tee elements, has been performed. The cyclic behaviour of the proposed innovative DST connections with friction pads can also be compared with the energy dissipation capacity of a traditional
double split tee connection tested in a previous work (Iannone et al., 2011), namely
TS-CYC 04. Experimental tests have been carried out at Materials and Structures
Laboratory of Salerno University. The testing equipment is that already adopted to
test traditional beam-to-column connections (Iannone et al., 2011).
Two steel hinges, designed to resist shear actions up to 2000 kN and bolted
to the base sleigh have been used to connect the specimens to the reacting system.
The specimen is assembled with the column (HEB 200) in the horizontal position,
connected to the hinges, and the beam (IPE 270) in the vertical position (Fig.4). The
loads have been applied by means of two different hydraulic actuators. The first one
is a MTS 243.60 actuator with a load capacity equal to 1000 kN in compression and
650 kN in tension with a piston stroke equal to +/- 125 mm which has been used to
apply, under force control, the axial load in the column equal to 630 kN. The second
actuator is a MTS 243.35 with a load capacity equal to 250 kN both in tension and in
compression and a piston stroke equal to +/- 500 mm which has been used to apply,
under displacement control, the desired displacement history at the beam end. The
loading history has been defined according to ANSI-AISC 341-10. During the tests
many parameters have been monitored and acquired, in order to get the test machine history imposed by the top actuator and the displacements of the different joint
components.
Vertical frame
IPE270
L=170cm
Horizontal frame
Hydraulic Actuator
max load: +/- 250 kN
max disp.: +/-500mm
JOINT
Hydraulic Actuator
Left hinge
max load: +/- 1000 kN
max disp.: +/-125mm
Right hinge
HE200B
L=200cm
Sleigh base
Concrete floor
Fig. 4. Experimental testing equipment
Aiming at the evaluation of the beam end displacements due to the beam-to-column
joint rotation only, the displacements measured by means of the LVDT equipping
MTS 243.35 actuator have been corrected by subtracting the elastic contribution due
to the beam and column flexural deformability according to the following relationship
(Iannone et al., 2011):
2
FL3b FLc L2b  Lc 
6a 
 


 j  T 3 

(2)
3EI b 12EI c  Lc  2a  Lc  2a 


where Ib and Ic are the beam and column inertia moments, Lc is the column length, Lb
is the beam length and a is the length of the rigid parts due to the steel hinges. The
experimental tests carried out up to now concern four specimens (Fig. 5):
 TSJ-M1-460-CYC08, TSJ-M2-460-CYC09 and TSJ-B-460-CYC11, which are three
double split tee connections. The first two are equipped with layers of friction material, namely M1 and M2, and the third one with a brass plate interposed between
the Tee stems and the beam flanges. The slipping interfaces have been clamped
by means of eight M20 class 10.9 bolts tightened with a torque equal to 460 Nm.
In order to allow the relative movement between the stems of the T-stubs and
beam flanges, two slotted holes have been realized on the tee stems. The slots
have been designed in order to allow a maximum rotation of 70 mrad. The flanges
of the T-stubs are fastened to the column flanges by means of eight M27 class
10.9 bolts located into holes drilled with a 30 mm drill bit.;
 TSJ-M2-DS-460-CYC010, which is a double split tee connection with the same
characteristics of the other tested joints, but with a couple of disc springs interposed between the bolt nut and the beam flange.
171
t=30 mm
Bolts M27 class 10.9
45
81
45
81
45
45
400
45
132
173
15
263
116
45
t=10 mm
173
15
263
132
IPE 270
116
Friction Material
45
Slotted plate (t=15 mm)
Bolts M20 class 10.9
45
171
HEB 200
Fig. 5. Geometrical detail and picture of tested joints
The identity tag of the tested specimens uniquely identifies the connection detail.
In particular, the meaning of the letters is: 1 - Joint typology, i.e. Tee Stub Joint
(TSJ); 2 – Friction interface, i.e. friction material M1 (M1), friction material M2 and
Brass (B); 3 – Washer typology if different from the classical flat washer, i.e. Disc
Spring (DS); 4 – Bolt tightening level; 5 -Test number, i.e. CYCnumber.
4. CYCLIC BEHAVIOUR OF SPECIMENS
As aforementioned, the main goal of the work herein presented is to provide an innovative approach to prevent structural damage in dissipative zones of MRFs where
the main source of energy dissipation is due to the beam end damage in case of fullstrength connections and to the damage of connecting plate elements in case of partial-strength connections. To this scope, the proposed beam-to-column joint typology
is detailed in order to dissipate the seismic input energy through the slippage of the
friction material interposed between the T-stub stem and the beam flange. In particular, hierarchy criteria at the level of joint components can be established to assure
the desired connection behaviour. Therefore, starting from the design bending moment, equal to 100 kNm, established with the aim of developing the same degree of
flexural strength of the traditional joints already tested in a previous research work
(Iannone et al., 2011), all the remaining joint components (i.e. the T-stub flanges, the
bolts and the column panel zone) have been designed to assure an adequate overstrength with respect to the friction resistance. In particular, the friction interface has
been designed according to Eq. (1) considering that the force to be transmitted is
simply obtained as the ratio between the design bending moment and the lever arm.
Therefore, the desired friction resistance at the sliding interface has been obtained
by properly fixing the number of bolts and the tightening force of the bolts fastening
the tee stems to the beam flanges.
In perfect agreement with the adopted design criteria, all the experimental tests
have not shown any damage of the joint components, pointing out only the involve-
ment of the friction pads. Therefore, the most important result of the experimental
program is that the proposed connection typology can be subjected to repeated cyclic rotation histories, i.e. to repeated earthquakes, by only substituting the friction
pads and by tightening again the bolts to reach the desired preloading level. In addition, the rotation capacity can be easily calibrated by simply governing the length of
the slots where the bolts are located. The results of the experimental program on
DST connections with friction pads are in line with the results found by testing the
friction component outlining that, as expected, the cyclic the behaviour of the joint is
mainly governed by the cyclic behaviour of the weakest joint component (i.e. the friction component in the examined cases).
In fact, as verified during the test TSJ-M1-460-CYC08, where material M1 was
adopted, the response of the joint has been very similar to that evidenced during the
uniaxial tests investigating the friction interface behaviour. A significant pinching and
strength degradation behaviour was exhibited, after that the design resistance of 100
kNm was reached (Fig.6). This was also due to the premature fracture of the friction
pad, which was not observed in component testing. For this reason, this material will
be excluded from the forthcoming developments of this research activity.
In case of friction material M2 (TSJ-M2-460-CYC09), a stable cyclic response with
a hardening behaviour due to the increase of local stresses caused by the beam rotation and by the rotational stiffness due to the bending of the tee stems has been
pointed out (Fig.6). In addition, the results show that a slight strength and stiffness
degradation begins at high rotation amplitudes probably due to the consumption of
the friction pads during the sliding motion.
The test on brass friction pads, TSJ-B-460-CYC11, also exhibited a good behaviour in terms of shape of the cyclic response. In fact, the obtained cycles are very
stable also at high values of the plastic rotation. Nevertheless a value of the bending
moment lower than the design value of 100 kNm was obtained, because of poor friction resistance. This result can be justified on the base of the results obtained by
component testing. In fact, in case of brass on steel interface (Table 1) the value of
the static friction coefficient is much lower than the dynamic one and, as a consequence, a bending moment lower than the expected one has been obtained (Fig.6).
For this reason and considering the high cost of this material, the use of brass for
friction pads will be excluded in the forthcoming research developments.
Finally, in order to reduce the problems related to the consumption of the friction
material observed during the test TSJ-M2-460-CYC09, another test, namely TSJM2-DS-460-CYC10, with the same layout but adopting disc springs interposed between the bolt head and the tee web plate has been carried out. Such a type of
washer is a high resistance cone shaped annular steel disc spring which flattens
when compressed and returns to its original shape if compression loading is released. In this way, the wearing of the friction material, which would lead to the partial loss of bolt preload, is compensated by the action of the disc spring which restores the force by maintaining the bolt shaft in tension. In fact, the results of test
TSJ-M2-460-CYC10 have demonstrated the effectiveness of the adopted disc
springs. Therefore, higher dissipation capacity and lower strength and stiffness degradation was obtained (Fig.6).
In addition, in order to compare the cyclic behaviour of DST connections with friction pads with that of a traditional DST partial strength joint dissipating in the bolted
components and characterized by same resistance, reference has been made to the
test TS-CYC04 (Fig. 6) (Iannone et al., 2011). In particular, the envelopes of the cy-
clic moment-rotation curves are reported in Fig. 7 for all the tested specimens, both
innovative and traditional.
It can be observed that the bending moment corresponding to the knee of the
curves, corresponding to the design value of the joint resistance, is similar for all the
tests adopting friction materials, but the obtained post-elastic behaviours are quite
different with respect to traditional DST connections. In fact, compared to the case of
joint TS-CYC04, friction DST joints do not exhibit significant hardening behaviour
whose magnitude is limited to the effects coming from the bending of the T-stub
stems.
Hysteretic Curve M-q
Hysteretic Curve M-q
TS-CYC 04
250
M ma x = 186.3 kNm
M min = -197.5 kNm
200
TS-M1-460-CYC 08
150
Mmax = 116.6 kNm
Mmin = -132.5 kNm
100
150
50
Moment [kNm]
Moment [kNm]
100
50
-0,100
-0,075
-0,050
0
0,000
-50
-0,025
0,025
0,050
0,075
0
-0,060
0,100
-0,035
-0,010
0,015
0,040
-50
-100
-150
-100
-200
Envelope
-150
-250
Joint Rotation [rad]
Joint Rotation [rad]
Hysteretic Curve M-q
-0,060
TS-M2-460-CYC 09
Hysteretic Curve M-θ
150
100
100
50
50
0
-0,035
-0,010
0,015
0,040
-50
TS-M2-DS-460-CYC 10
150
Mmax = 100,7 kNm
Mmin = -126,13 kNm
Moment [kNm]
Moment [kNm]
Mmax = 116.6 kNm
Mmin = -124.6 kNm
0
-0,060
-0,035
-0,010
0,015
0,040
-50
-100
-100
-150
Joint Rotation [rad]
-150
Joint Rotation [rad]
Hysteretic Curve M-θ - TS-B-460-CYC11
80
60
Moment [kNm]
40
-0,08
20
0
-0,06
-0,04
-0,02
0,00
0,02
0,04
0,06
0,08
-20
-40
-60
-80
Rotation [rad]
Fig. 6. Hysteretic curves of tested joints
With reference to TS-M2-460-CYC09 and TS-M2-DS-460-CYC10 tests, it is worth
to note that the hysteresis cycles are wide and stable with no pinching. This is the
reason why the joints, in spite of the less hardening behaviour, are able to dissipate
more energy than connection TS-CYC04 (Fig. 7).
5. CONCLUSIONS
In this paper the possibility to enhance the cyclic behaviour of traditional DST joints
dissipating the seismic input energy in bolted components has been analysed. In
particular, the cyclic rotational response of four Double Split Friction Tee Stub beamto-column joints adopting different friction materials has been investigated. The response in terms of energy dissipation and shape of the hysteresis loops of the pro-
posed connection structural details has been compared to that of a traditional DST
joint tested in a recent experimental program. The presented results are very encouraging confirming the goodness of the proposed approach.
Hysteretic Curve M-q
Energy dissipation
200
250
180
200
140
120
50
Energy [kNm]
Moment [kNm]
100
-0,100
TS-M2-460-CYC 09
TS-CYC 04
TS-M1-CYC 08
TS-B-CYC 11
TS-M2-DS-460-CYC 10
160
150
100
-0,075
-0,050
-0,025
0
0,000
-50
0,025
0,050
0,075
Envelope TS-CYC04
-100
80
60
TS-M1-460-CYC 08
TS-M2-460-CYC 09
-150
0,100
40
TS-M2-DS-460-CYC10
TS-B-460-CYC11
20
-200
0
-250
1
6
Joint Rotation [rad]
11
16
21
26
31
36
41
46
n° cycles
Figure 7. Cyclic envelopes and energy dissipation of tested DST connections
In particular, all the experimental tests have confirmed that the strategy of adopting
friction pads within the components of bolted connections can be effective for the
ambitious goal of damage prevention, because the proposed DST connection is able
to withstand repeated cyclic rotation histories, i.e. repeated earthquakes, by simply
substituting the friction pads and by restoring the tightening of the connecting bolts.
ACKNOWLEDGEMENTS
This work has been partially supported with research grant DPC-RELUIS 2010-2013.
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