Steel Tips-Slotted Bolted Connection Energy Dissipaters-Grigorian

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REPORTNO.

UCB/EERC-92/10

JULY 1992 EARTHQUAKE ENGINEERINGRESEARCHCENTER

SLOTTEDBOLTEDCONNECTION

ENERGYDISSIPATERS

(WITHANAPRIL,1993ADDENDUMOFSOMERECENTRESULTS)

by

CARLE. GRIGORIAN

TZONG-SHUOHYANGEGORP. POPOV

Reportto National ScienceFoundation



Abstract

Slotted Bolted Connections (SBCs) are modified bolted connections designed t o dissipate

energy through friction during rectilinear tension and compression loading cycles. Exper-

imental results on two types of SBCs are reported. In one type, friction occurs between

clean mill scale steel surfaces; in the other, friction is between clean mil1 scale steel and

brass surfaces. The behavior of connections with brass on steel frictional surfaces is found

to be more uniform and simpler to model analytically than tha t with steel on steel surfaces.

These connections maintain essentially constant slip force, and unlike those with steel on

steel surfaces, require minimal overstrength of the system in design. The frictional mecha-

nisms giving rise to the observed behavior are explained. As an example of application a one

story diagonally braced frame was designed and its behavior determined for four different

earthquakes. Experimental results are presented for the fabricated SBC for this frame sub-

jected consecutively to the four displacement histories derived from these earthquakes. Theagreement between the analytical and experimental results is found to be excellent. Because

of the intrinsic simplicity of the SBCs and their very low cost, their use in seismic design

and retrofit applications appears to be very promising.

This 7ps publication is a re-print of a Univ. of California, Berkeley,Earthquake Engineering Research Center Report No. UCB/EERC-92/10

and includes an April 1993 addendum.



Introduction

Various types of energy dissipating devices, utilizing friction as means of energy dissipation,have been tested and studied by researchers [4, 6, 7]. Two of the common features of these

devices have been that their manufacture requires precision work or exotic materials and

that their installation demands specialized training. Consequently, the additional expense

in using such devices has prevented their wide acceptance in engineering practice. The

development of the Slotted Bolted Connections (SBCs) as energy dissipators represents an

at tempt to overcome the abovementioned shortcomings of these systems. SBCs, as presented

in this paper, require only slight modification of standard construction practice, and require

materials that are widely available commercially.

In this paper a Slotted Bolted Connection (SBC), see Figure 1, refers to a bol ted connec-

tion where the elongated holes or slots in the main connecting plate, in which the bolts are

seated, are parallel to the line of loading. In addition a Belleville washer [8] is placed underthe nut. Two types of SBC specimen are discussed in this paper, one with brass insert plates

and one without. Upon tightening of the bolts, the main plate is "sandwiched" directly

between either the brass insert plates or the outer steel plates. The holes in the brass insert

plates and in the steel outer plates are of standard size. When the tensile or compressive

force applied to the connection exceeds the frictional forces developed between the frictional

surfaces, the main plate slips relative to either the brass insert plates in the case of the first

type specimen or the outer steel plates in the case of the second. This process is repeated

with slip in the opposite direction upon reversal of the direction of force application. Energy

is dissipated by means of friction between the sliding surfaces. Application of cyclic loads of

magnitude greater than the slip force results in approximately rectangular hysteresis loops.

The earliest investigations of SBCs as energy dissipators date back to 1976 when a series of

experiments were carried out at San Jose State University (SJSU) [1] on specimens similar

in concept to those presented here. The term SBC used here is adopted from the report

by T. F. Fitzgerald, et al. [3]. A number of other researchers have also investigated similar

devices [2, 5].

Specimens and Experimental Results

To date, over forty SBC specimens of various bolt sizes, configurations and surface conditions

have been tested at the University of California at Berkeley (UCB). Experimental results

for specimens presented in this paper are representative of the salient SBC characteristics

encountered throughout testing. Presented here are two specimens which are identical inevery aspect with the exception that one includes shim like brass insert plates with a hole

pattern matching tha t of the outer steel plates. Figures 1 and 2 show, respectively, the

details of an SBC connection and the overall view of a typical assembled test specimen.



3

Both specimens are of A36 steel. The steel surfaces were cleaned to clean mill scale

condition. The brass plates were of the widely available half hard cartridge brass variety(UNS-260). The test specimens were prepared by a local structural steel fabricator so as

to simulate industry standards. Holes and slots in the steel plates were punched, and t he

edges were deburred. The two specimens described in this section are two bolt specimens.

The bolts used were inch diameter, 3 inches long A325 bolts. The Belleville washers used

were 8-EH-112 Solon compression washers. One such washer with a hardened washer on top

was placed under each nut. Belleville washers are initially cone shaped annular disk springs

which flatten when compressed. Earlier studies of SBCs [1] have shown that without the

use of Belleville washers, and under large cyclic displacements, there is an almost immediate

loss of bolt tension resulting in quick degeneration of the slip force. With the inclusion of

Belleville washers, both turn of the nut and torque wrench methods of developing minimum

bolt tension (70% of minimum tensile strength [llD become inapplicable. To achieve thedesired initial bolt tension, Direct Tension Indicator (DTI) washers were placed under each

bolt head. DTIs are specially produced washers with protrusions pressed out of th e flat

surface. As the bolt is tightened, the compressive force exerted on the DTI flattens the

protrusions and reduces the gaps between the flat portions of the DTI and the head of the

bolt. Th e gaps can easily be measured with a supplied feeler gage. When the feeler gage

fails to enter a specified number of gaps, the desired load in the bolt has been reached. DTIs

used here were designed to indicate a bolt tension in the range of 12 to 14 kips.

The specimens, described above, were placed within an MTS loading frame as shown

in Figure 3. The ram was capable of applying forces of 300 kips statically and 250 kips

dynamically, with a maximum displacement stroke of 6 inches. Both displacement and

force control were possible through a controller unit, and a function generator enabled theservorarn to produce preprogrammed load or displacement histories. All testing was done

under displacement control. Axial load and displacements in the specimen were measured

through a load cell built into the MTS loading frame and a Linearly Variable Displacement

Transducer (LVDT) built into the servoram. Axial force and displacement were monitored

and recorded using a Data Acquisition System in conjunction with an IBM PC-AT computer.

In addition, an X-Y plotter recorded load-displacement curves on paper for immediate visual

observation of results.

Figures 4 and 5 show the applied displacement histories, force responses and the resulting

hysteresis loops for the two selected tests. Figure 4, representing the case of friction between

like clean mill scale steel surfaces, shows the main shortcoming of SBCs with friction between

steel surfaces. As seen in the force response diagram, there is an almost immediate increase

in t he slip force followed by a quick drop to a magnitude several times less than the peak

slip force. Although this behavior has not been observed in all tests of SBCs with friction

between like steel surfaces, it has been present, to various extents, in the majori ty of cases.

In tests with specimens where the mill scale steel surfaces were polished by wire brushing

and those in which the surfaces were roughened and the mill scale removed by sand blasting,



this behavior not only did not disappear but was actually intensified. The occurrence of this

behavior in SBCs where friction occurs between steel surfaces renders such SBCs inefficient,at best, and impractical, at worst, as energy dissipators. Figure 5 represents the case of a

SBC test with friction between clean mill scale steel and brass surfaces. As seen in Figure

5, the use of brass insert plates significantly reduces the variations in slip force magnitude

observed in SBCs where friction occurs between steel plates, almost completely eliminating

this undesirable behavior.

Discussion of Experimental Results

A discussion of experimental results involving friction must necessarily involve concepts

of Tribology. Tribology is the body of science dealing specifically with friction, wear and

lubrication. Terminology is a matter controversy in this field. The Tribological terminologyused here is adopted from E. Rabinowicz's classic book "Friction and Wear of Materials"

[9]. Friction is defined as "resistance to motion which exists when a solid object is moved

tangentially with respect to the surface of another which it touches." Wear is defined as the

"removal of material from solid surfaces as a result of mechanical action." Of the several types

of wear discussed in Tribology literature, the two most relevant to the present discussion are

adhesive wear and abrasive wear. Adhesive wear occurs when "two smooth bodies are slid

over each other, and fragments are pulled off one surface to the other." These fragments

may later return to the original surface or form into loose wear particles. Abrasive wear

occurs when "a rough hard surface, or a soft surface containing hard particles, slides on

a softer surface and ploughs a series of grooves in it." The material from the grooves

generally forms into loose wear particles. Adhesive wear is almost universally present in allfrictional phenomena, and it is the authors' belief tha t it, in conjunction with some abrasive

wear, is the main mechanism of wear in the SBCs tested. In general, no one explanation

can satisfactorily account for observed frictional behavior as many different mechanisms

are involved in friction and wear processes, some simultaneous, some sequential and often

interacting with each other. Presented here is a qualitative explanation of the experimentally

observed SBC behavior based on the above mentioned Tribological notions and experimental

observations. The explanation given here applies to both SBCs where friction occurs between

like steels and where friction occurs between steel and brass. It is believed that as sliding

is begun, wear particles are formed due to adhesive wear between the sliding surfaces. This

results in outward displacement of the outer plates in the direction of the bolt axes. This in

turn results in an increase in the bolt tension force and therefore an increase in the normal

force between the sliding surfaces. As frictional force is directly proportional to normal

force, this increase in the normal force is observed as an increase in the slip force. With

continued sliding, a portion of the loose wear particles fall out of the connection, as observed

experimentally, while the rest are either reabsorbed or act as abrasive particles contributing



5

to abrasive wear. In Tribological terminology, the phenomenon that occurs here can be,

simplistically, described as adhesive wear giving rise to wear particles which then causeadditional abrasive wear. That abrasive wear occurs despite the smoothness of the original

surfaces is evidenced by the appearance of sliding surfaces observed after the completion of

experiments and upon the dismantling of the specimens. In the case of friction between like

clean mill scale steel surfaces, both surfaces can be described as severely scratched. While

in the case of friction between clean mill scale steel on brass, only the brass surface appears

as scratched while the steel surface appears undamaged but with smears of brass. Scratched

surfaces are a typical consequence of abrasive wear. The fall out and reabsorption of wear

particles has the effect of reducing the bolt tension force as the outer plates now displace

inward. This results in a reduction of normal force and is observed as a drop in the slip

force. That the outer plates displace outward and then inward simultaneous with rise and

drop in the slip force has been confirmed by measurements of the displacements of the outerplates along the axes of the bolts.

The above mentioned behavior, i.e. initial increase in slip force followed by a drop,

observed in bo th Figures 4 and 5, although clearly far more poignantly evident in Figure 4,

is directly attributed to the wear mechanisms mentioned above. The difference in behavior

between the two types of specimens is solely due to the choice of the use of brass as a

frictional surface, as the other two parameters known to influence adhesive wear, namely

initial normal force and total travel distance, were identical for the two presented specimens.

This choice was made precisely with the reduction of wear in mind. Brass is a common

choice as a material frictionally compatible with low and medium carbon steels, and is often

used in moderate cost applications where it is desired to reduce adhesive wear [9].

Application and Verification of Assumptions

As an illus tration of the uti lity of SBCs as energy dissipators, consider the example structure

shown in Figure 6. A SBC with a slip force of 60 kips connects the diagonal brace to the main

structure. Analysis of the structure was performed using the DANS [10] computer program.

Newmark's step-by-step integration method was used. The structure was assumed to behave

as a shear structure, and the SBC was assumed to behave as an elastic-perfectly-plastic

connection. Viscous damping was assumed to be 2%. Responses due to four acceleration

histories were calculated. The acceleration histories were as follows: the 1971 Pacoima Dam

earthquake S16E, the 1952 Taft earthquake N21E with magnification factor of 5, the 1940

E1 Centro earthquake S00E with magnification factor of 2 and the 1987 Whittier earthquakeN00E, at Sylmar, with magnification factor of 40. Figures 7, 8, 9 and 10 show ground

acceleration histories, structure displacement responses and energy diagrams for each applied

history. The columns remain elastic at all times and the SBC prevents the buckling or

yielding of the diagonal brace. An examination of the energy diagrams reveals tha t on the



6

average close to 85% of the total input energy is dissipated by the SBC.

To verify the validity of the assumption of elastic-perfectly-plastic behavior for SBCs withbrass insert plates and to observe the response of such an SBC to displacement histories more

realistically representing response to actual earthquakes, an SBC specimen was designed to

slip at 60 kips. Based on previous results from tests of specimens with two inch diameter

A325 bolts, a test specimen with eight inch A325 bolts was fabricated. The specimen was

subjected to SBC slip displacement responses derived from the above mentioned analyses.

The four SBC slip displacement response histories were applied consecutively, in the order

of acceleration histories mentioned above, to this specimen. Figures 11, 12, 13 and 14

show SBC sup displacement response histories and analytical and experimental hysteresis

diagrams for each acceleration history. It is seen that the target slip force of 60 kips is

attained almost perfectly in response to the first displacement history. As expected, the slip

force drops, although not significantly, for the next three applied displacement histories. The

rectangular shape of the hysteresis loops, coupled with the reasonably constant slip force,

indicates that the assumption of elastic-perfectly-plastic behavior for SBCs with brass insert

plates is a valid one.

Concluding Remarks

Both SBC types have been shown capable of dissipating significant quantities of energy as

judged by the areas enclosed by the experimentally arrived at hysteresis loops. Slip force in

SBCs where friction occurs between like steel plates has been shown to vary significantly.

The peak slip force for such SBCs occurs almost immediately and may be several times

the magnitude of the mean slip force. As such, for this type of SBC to dissipate energythroughout the course of ground excitation, either the members supporting the SBC must

be designed with excessively large safety factors or the SBC itself must be under-designed.

On the other hand, in SBCs where because of the brass insert plates friction occurs between

brass and steel, slip force has been shown to remain relatively constant over the range of

interest. It has also been shown that such SBCs behave in nearly perfect elastic-perfectly-

plastic manner. In view of these results, it is evident that SBCs with steel on brass frictional

surfaces possess significant advantages in terms of efficiency as energy dissipators and ease

of modelling. As such, and with low material and fabrication cost, these SBCs exhibit great

potential as an alternative choice for energy dissipation in seismic design and retrofit of

structures.



Acknowledgements

The authors are grateful for the support of the National Science Foundation under Grant

BCS-9016781 enabling the pursuit of the described research. The continued encouragements

of Henry Lagorio and S. C. Liu of NSF are particularly appreciated.

Thanks are also due to Bill MacCracken our electronics engineer who has been involved in

every phase of testing over three years and whose assistance with testing and da ta acquisition

equipment operation has been invaluable.

Machine shop specialists Mark Troxler, Jeff Higginbotham and Doug Zulaica are also thanked

for their assistance.

The opinions expressed in this paper are those of the writers and do not necessarily reflect

the views of the sponsor.



References

[1]

[2]

Venuti, W.J., "Energy Absorption of High Strength Bolted Connections,"Test Report,Structural Steel Educational Council, California, May, 1976.

Pall, A.S. and Marsh, C., "Energy Dissipation in Panelized Buildings Using LimitedSlip Bolted Joints," Proceedings, AICAP-CED conference,Vol. 3, Rome, Italy, May,1979.

[3]

[4 ]

[6]

[7]

Fitzgerald, T.F., Anagnos, T., Goodson, M., Zsutti, T., "Slotted Bolted Connectionsin Aseismic Design of Concentrically Braced Connections,"Earthquake Spectra,Vol. 5,No. 2, 1989.

Pall, A.S., Verganalakis, V. and Marsh, C., "Response of Friction Damped Braced

Frames," J. Struct. Div., ASCE, 108(6), 1313-1323, 1987.

Roik, K., Dorka, U. and Dechent, P., "Vibration Control of Structures Under Earth-quake Loading by Three Stage Friction Grip Elements," Earthquake Engineering andStructural Dynamics,Vol. 16, 501-521, 1988.

Constantinou, M.C., Reinhorn, A.M., Mokha, A. and Watson, R., "Displacement Con-trol Devices for Base Isolated Bridges," Earthquake Spectra,Vol. 7, No. 2, 1991.

Aiken, I.D. and Kelly, J.M., "Earthquake Simulator Testing and Analytical Studies ofTwo Energy Absorbing Systems for Multistory Structures," Report No. UCB/EERC-90/03, University of California, Berkeley, October, 1990.

[8] Timoshenko, S., Strength of Mate rial s, Vol. 2, Van Nostrand Co., New York, NY,1934.

[9 ]

[10]

[11]

Rabinowicz, E., Friction and Wear of Materials , John Wiley and Sons, Inc., NewYork, NY, 1965.

Yang, T.S., "DANS, A Computer Program for the Dynamic Analysis of Nonlinear ShearBuildings," CE99 Project,University of California, Berkeley, 1991.

Kulak, L.K., Fisher J.W. and Struik, J.H.A., Guide to Design Criteria for Bolt edand Riveted Joi nts , 2nd. Ed. John Wiley and Sons, Inc., New York, 1987.



9

1/8" TH. BRASS PU

MAIN PLATE...............

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,.HARDENED FLAT WASHER

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NUT

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UNDER HEAD

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11

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ANAJ.,Y33CAJ., HYSTERESIS D IAGR AM

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17

Addendum

April, 1993

Shake Table Experiments

Within six months of the publication of the original body of this document, a test structure

incorporating twelve SBCs was tested on the shake table at UCBs Earthquake Simulator

Laboratory. For sake of completeness, a sampling of the experimental results gained from

this testing program is presented in this addendum.

The three story one bay steel test structure, depicted in Figure lA, supported 30,000

lbs. per floor and stood over 20 ft. high. The lateral force resisting system of the structure

consisted of two moment resisting frames and Chevron braces connected with SBCs at each

level and on each of the two frames of the structure. The design slip loads for the SBCs were

determined by computer simulation of the structure's response to various seismic inputs. The

design called for slip forces of 15 kips for SBCs a t the first level and 7.5 kips at the second

and third levels. This requirement was accommodated by using two bolt SBCs identical

to that shown in Figures 1 and 2 of this report and leaving one of the two bolts loose in

the second and third levels. This arrangement was chosen so tha t slip loads in the second

level could be doubled by tightening of the second bolt midway through the testing program

to experiment with an altogether different design with a different structural response. The

entire bracing system, including the SBCs, was fabricated commercially using standard shop

tolerances and practice at a local steel fabrication shop.

Figure 2A shows th e shake table acceleration history for one of the tests conducted on

the structure. Figures 3A and 4A show hysteresis diagrams for the six SBCs on each of

the two frames in the structure in response to the above table acceleration history. The

diagrams are arranged such that they represent hysteresis diagrams for SBCs at the first,

second and third levels at the bottom, middle and top of the figures respectively. The data

presented in these figures is raw, unfiltered with no adjustment to account for zero shifts

in instrumentation. It is seen that the curves are similar in character to those obtained

for SBCs tested in the MTS testing frame. The slip loads are within reasonable range ofthe design requirements. It must be noted that as the second and third level SBCs were

effectively single bolt connections, variations in slip loads axe expected to be greater than

those in the two bolt connections at the first level. With a larger number of bolts, as would

be th e case in a real structure, th e degree of variation between slip loads for SBCs with same



18

number and size of bolts is expected to be smaller due to averaging of errors. It is also noted

the these curves verify again the validity of the elastic-perfectly-plastic characterization ofthe behavior of SBCs. A sense for the effectiveness of SBC may be gained from Figure

5A. In this figure, the top curve represents the absolute input energy of the structure based

on integration of the measured base shear force of the structure with respect to the table

displacements. The curve immediately below this curve represents the sum of the total energy

dissipated by the SBCs, based on calculation of areas enclosed by the hysteresis curves, and

strain and kinetic energies. It is seen that at the end of the record, where kinetic and strain

energies vanish, nearly 75 % of the input energy is dissipated by the SBCs. The figure also

indicates the relative magnitude of energy dissipated at each story and the magnitude of

energy dissipated by each individual SBC, each layer below the "Total Dissipated" curve

representing the contribution of one SBC.

In summary, the results obtained from the shake table testing of the structure with

SBCs, a glimpse of which has been presented above, appear to verify at once the practicality

of implementation of SBCs into realistic structures and their effectiveness. A tremendous

wealth of data has been generated from these experiments and the process of data reduction

is currently in progress. Furthermore, analytical studies complementing and motivated by

the experimental efforts are being conducted by the authors with the aim of establishing

design guidelines for use of SBCs in real structures.



19

Figure IA

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Figure 2A

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-0.2 -0.1 0 0.1 0.2 0.3r r ( m a r e s )

HYSTERF_SlS OF BRACE NE1A

20 20

15 .........................i ...................................................................................... 'i ................................................ 15 ...................-' ....................... i ............................ = .. .. .. .. ..:....... --- . . . . . . . .

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OF BRAC SW3A

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; .....:i.................1 0 .............................

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0 .. . . . . .i............

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DISPLACE (n,i)

21

HYSTERESIS OF BRACE NW3A

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15 - - . 4 . . . . .'...................-:.................................................... i . . . . . . .

1 0 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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Figure 5A



EARTHQUAKE ENGINEERING RESEARCH CENTER REPORT SERIES

EERC reports are available from the National Information Service for Earthquake En$ineerinNISEE) and from the National Technical InformationService(NTIS}. Numbers in parentheses are Accession Numbers assigned by the National Technical Information Service:. these are followed by a iiee code.Contact NTIS. 5285 Port Royal Road, Springfield Virginia. 22161 for more information. Reports without Accession Numbers not available from NTISat the time of printing. For a current complete list of EERC reports (from EERC 67-1) and availablity information, please contacl University o f Califonmt,

EERC, NISEE. 1301 South 46th Street. Richmond, California 94804.

UCB/EERC-90/16 'Sensitivity of Long-Period Response Spectra to System Initial Conditions,' by Bla.uez. R., Ventunt, C. and Kelly, J'.M., 1990.

UCB/EERC-90/17 ' Behavior of Peak Values and Spectral Ordinates o f Near-Source Strong Ground-Motion over a Dense Array,' by Niazi, M., June 1990.

UCB/EERC-90/18 'Material of Elastomers used in Earthquake Base Isolation,' by Papoulia, K.D. and Kelly, J.M., 1990.

UCB/EERC-90/19 'Cyclic Behavior o f Steel Top-and-Bottom Plate Moment Connections,' by HarrioR, J.D. and Astaneh-Asl. A.. August 1990, (PB9 ! 229260/AS)A05.

UCB/EERC-90/20 'Seismic Response Evaluation of an Instrumented Six Story Steel Building,' by Shem J.-H. and Astaneh-Asl, A., December 1990, (PB91229 294/AS)A04.

UCB/EERC-90/21 'Observations and Implications of Tests on the Cypress Street Viaduct Test Structure,' by BolIo, M., Mahin, S.A.. Moehle, J.P.,Stephen. R.M. and Qi, X.. December 1990.

UCB/EERC-91/01 'Experimental Evaluation of Nitinol for Eneri Dissipation in Structures,' by Nims, D.K., Sasaki, fl=K. and Kelly, J.M., 1991.

UCB/EERC.91/02 'Displacement Design Approach for Reinforced Concrete Structures Subjected to Earthquakes,' by Qi, X. and Moehle, J.P., January1991.

UCB/EERC-91/03 'A Lons-Period Isolation System Using Low-Modulus Hijh-Damping Isolators for Nuclear Facilities at Soft-Soil Sites,' by Kelly, J.M.,March 1991.

UCB/EERC-g[/04 'Dynamic and Failure Characteristics o f Bridgestone Isolation Bear ing, ' by Kelly, J.M., April 1991.

UCB/EERC-91/05 'Base Sliding Response of Concrete Gravity Dams to Earthquakes.' by Chopra, A.K. and Zhan$, L., May 1991.

UCn/EERCo91/06 'Computation of Spatially Varying Groun d Motion and Foundation-Rock Impedance Matrices for Seismic Analysis of Arch Dams," byZhang, L. and Chopra, A.K., May 1991.

UCB/EERC-91/07 'Estimation o f Seismic Source Processes Using Strong Motion Array Data,' by Chiou, S.-J., July 1991.

UCB/EERC-91/08 'A Response Spectrum Method for Multiple-Support Seismic EJtcitations,' by Der A. and Neuenhofer, A., AulPiSt 1991.

UCB/EERC-91/09 'A Preliminary Study on Energy Dissipating Cladding-to-Frame Connection,' by Cohen, J.M. and PoweU, O.H.. September 1991.

UCB/EERC-91/10 'Evaluation of Seismic Performance of a Ten-Story RC Building During the Whittier Narrows Earthquake,' by Miranda, E. and Bergtero, V.V., October 1991.

UCB/EERC-91/I 1 'Seismic Performance o f an Instrumented Six Story Steel Building.' by Anderson, J.C. amd Bertero, V. V, November 1991.

UCB/EERC-91/12 'Performance of Improved Ground During the Loma Prieta Earthquake,' by Mitchell, J.K. and Wentz, Jr., F.J., October 1991.

UCB/EERC-91/13 'Shaking Table - Structure Interaction,' by Rinawi, A.M. and Clouf, R.W , October 1991.

UCB/ERC-91/14 'Cyclic Response of RC Beam-Column Knee Joints: Test and Retrofit,' by Mazzoni, S.. Moehle, J.P. and Thewalt, C.R., October 1991.

UCB/EERC-91/I$ 'Design Guidelines for Ductility and Drift Limits: Review of State-of-the-Practice and State-of-the-Art isa Ductility and Drift-BasedEarthquake-Resistant Design of Buildings,' by Bertero. V,V., Anderson, J.C., K.rawin.kler, H., Miranda, E. and The CUREa and TheKajima Research Teams,, July 1991.

UCB/EERC-91/16 'Evaluation of the Seismic Performance or a Thirty-Story RC Buildinl,' by Anderson. J.C., Miranda, E., Bertero. V.V. and The KajimaProject Research Team., July 1991.

UCB/EERC-91/17 'A Fiber Beam-Column Element for Seismic Response Analysis of Reinforced Concrete Structures,' by Taucer, F., Spacone, E. and

Filippou, F.C.. December 1991.

UCB/EERC-91/18 'Investition of the Seismic Response of a Lightly-Damped Torsionally-Coupled Building.' by Boroschek. R. and Mahin, S.A.,December 1991.

'Studies o fa49-Story Instrumented Steel Structure Shaken dui'inS the l.oma Prieta Earthquake,' by Bonowitz, D., Chert. C.-C. andAstaneh-AsL A., February 1992.

UCB/EERC-92/02 'Response of the Dumbarton Bridge in the Loma Prieta Earthquake,' by Fenves, G.L.. Filippou. F.C. and Sze. D.T., January 1992.

UCEERC-92/03 'Models for Nonlinear Earthquake Analysis of Brick Masonry Buildinls,' by Menili, Y.,'McNiven, H.D. and Tanrikulu, A.K., March1992.

UCB/EERC-92/04 'Shear StreniBh and Deformability of RC Bridge Columns Subjected to Inelastic Cyclic Displacements,' by Aschheim. M. and Moehle.J.P., March 1992.

UCB/EERC-92/05 'Parameter Study of Joint Openin$ Effects on Earthquake Response of Arch Dams,' by Fenves, G. L, Mojitahedi, S. and Reimer, R.,April 1992.

UCB/EERC,92/06 "Seismic Behavior and lsign of Semi-Rigid Steel FTamcs,' by Nadet, M.N., and Astancb-Asl, A., May 1992.

UCB/EERC-g2/07 "A Beam Element for Seismic Damage Analysis,' by Spacone, E., Ciampi, V. and FUippou, F.C., August 1 .

UCIEERC-2/O8 'Nonlinear Static and Dynamic Analysis of Reinforced Concrete Subasscmblages," by Filippou, F.C., D'Ambrisi, and lsan, ,it.,

August 1992

UCB/EERC-92/10 "Slotled Bolted Connection Energy Dissipators," by Grigorian, C.E., Yang, T.-S. and Popov, E.P., July 1)2.



UCB/EERC-88/14

UCB/EERC-88/15

UCB/EERC-88/16

UCB/EERC-88/17

UCB/EERC-88/18

UCB/EERC-88/19

UCB/EERC-88/20

UCB/EERC-89/0 I

UCB/EERC-89/02

UCB/EERC-89/03

UCB/EERC-89/04

UCB/EERC-89/05

UCB/EERC-89/06

UCB/EERC-$9/07

UCB/EERC-89/08

UCB/EERC-89/09

UCB/EERC-89/10

UCB/EERC-89/I I

UCB/EERC-89/12

UCIFEERC.89/l3

UCB/EERC-89/14

UCB/EERC-89/15

UCB/EERC-89/16

UCB/EERC-90/01

UCB/EERC-90/02

UCB/EERC-90/03

UCB/EERC.90/04

UCB/EERC-90/0$

UCB/EERC-90/06

UCB/EERC-90/0?

UCB/EERC-90/08

UCB/EERC-90/09

UCB/EERC-90/I 0

UCB/EERC-90/i 1

UCB/EERC-90/i 2

'An Experimental Study of' the Behavior of Dual Steel Systems.' by Whittaker. A.S., UanlL C.-M. and Berteto. V.V,, September 1918.(PB91 212 712)AI6.

'Dynamic Moduli and Damping Ratios for Cohesive Soils,' by Sun, J.g.. Golesorkhi. R. and Seed, H.B., August 1918, (PB91 210922)A04.

'Reinforced Concrete Flat Plates Under Lateral Load: An Experimental Study Including Biaxial Effects,' by Pan, ,aL and Moehle, J.P.,October 1988, (PB91 210856)AI3,

'Earthquake Engineering Research at Berkeley - 1988.' by EERC, November 1988, (PB91 210 864)A!0 .

'Us e o f Energy as a Design Criterion in Earthquake-Resistant Design,' by Uanlg C.-M. and Benero, V.V., November 19811, (PB91 210906/AS)A04.

'Steel Beam-Column Joints in Seismic Moment Resisting Frames,' by Tsai, K.-C. and Popov, E.P., November19118, (PBgl 21798a/AS)A20.

'Base Isolation in Japan, 1988,' by Kelly, J.M., December 1988, (PB91 212 449)A08.

'Behavior of Long Links in Eccentrically Braced Frames,' by Enlelhardt, M.D. and Popov, E.P., January 1989, (PB92 143 OS6)Aig.

'Earthquake Simulator Testing of Steel Plate Added Damping and Stiffness Elements,' by Whittaker, A., Bertero, V.V., Alonso, J. amdThompson, C., January 1989, (PB91 229 252/AS)Al0.

'Implications of Site Effects in the Mexico City Earthquake of Sept. 19, 1985 for Earthquake-Resistant Design Criteria in the San Fran-cisco Bay Area of California,' by Seed, II.B. and Sun, J.l.. March 1989, (PBgl 229 369/AS)A07.

'Earthquake Analysis and Response of Intake-Outlet Towers,' by GoyaL A. and Chopra, A.IC. July 1989, (PB91 229 286/AS)AIg.

'The 1985 Chile Earthquake: An Evaluation of Structural Requirements for Bearing Wall Buildin p,' by Wallace, J.W. and Moehle,J.P., July 1989, (PB91 218 O08/AS)AI3.

'Effects of Spatial Variation of Ground Motions on Large Multiply-Supported Structures,' by HaG, H., July 1989, (PB91 22916 l/AS)A08.

'EADAP - Enhanced Arch Dam Analysis Program: Users's Manual.' by Ghanaat, Y. and Clough. R.W., AulluSt 1989, CPB91 212$22)A06.

'Seismic Performance of Steel Moment Frames Plastically Designed by Least Squares Stress Fields,' by Obi. lC, and Mahin, SA.,August 1989, (P Bgl 212 597)A05.

'Feasibility and Performance Studies on [mprovin8 the Earthquake Resistance of New and Existing Buildin8s Using the Frict ion Pendu-lum System,' by Zayas. V., Low. S.. Mahin, S.A. and Bozzo, L , July 1989, {PB92 143 064)A!4.

'Measurement and Elimination of Membrane Compliance Effects in Undrained Triaxial TestinlL' by Nicholson. P.O., Seed, R.B. andAnwar. II.. September 1989. (PB92 139 641/AS)Al3 .

'Static Tilt Behavior of Unanchored Cylindrical Tanks,' by Lau, D.T. and Clough, R.W., September 1989, (PB92 143 049)AI0.

'ADAP-88: A Computer Proip=am for Nonlinear Earthquake Analysis of Concrete Ah Dams,' by Fenves, G.L, Mojtahedi, S. and Rei-ruer, R.B., September 1989, (PB92 139 674/AS)A07.

'Mechanics of Low Shape Factor Elastomeric Seismic Isolation Bearings,' by Aiken, I.D., Kelly, $.M. and Tajirian, F.F., November1989, (PB92 139 732/AS)A09.

'Preliminary Report on the Seismological and Engineering Aspects of the October 17, 1989 Santa Cruz oma Prieta) Earthquake,' byEERC, October 1989, (PB92 139 682/AS)AC)4.

'Experimental Studies of a Single Story Steel Structure Tested with Fixed, Semi-Ri8id and Flexible Connections,' by Nader, M.N. andAstaneh.Asl, A, August 1989, (PB91 229 21 I/AS)Al0.

'Collapse of the Cypress Street Viaduct as a Result of the l,oma Prieta Earthquake,' by Nims, D.IC, Miranda, ., Aiken, I.D., Whit-taker, A.S. and Bertero. V.V., November 1989, (PB91 217 93S/AS)A05.

'Mechanics of High-Shape Factor Elastomeric Seismic Isolation Bearings,' by Kelly, J.M., Aiken, I.D. and Tajirian, F .F , March 1990.

'Javid 's Paradox: The Influence of Preform on the Modes of Vibrating Beams,' by Kelly, J.M., Sackman, J.L. and Javid, A., May 1990,(PB91 217943/AS)A03.

'Earthquake Simulator Testing and Analytical Studies of Two Energy-Absorbing Systems for Muit istor y S t r u , a u ' by Aiken, I.D. andKelly, J.M., October 1990.

'Damage to the San Francisco-Oakland Bay Bridle Durinl the October 17, 1989 Earthquake,' by Astaneh-Asl, A., June 1990.

'Preliminary Report on the Principal Geotechnieal Aspecu of the October IT, 1989 l.oma Prieta Earthquake,' by Seed, ]LB., Dicken-son. S.E., Riemer, M.F., Bray, J.D., Sitar, N., Mitchell, J.IC, Idriss, I.M., Kyen, R.E., Kropp, A., Harder, Jr. and Power, M.S.,April 1990.

'Models o f Critical Regions in Reinforced Concrete Frames Under Seismic Excitations,' by Zul6qar, N. and Filippou, F.C., May 1990.

'A Unified Earthquake-Resistant Design Method for Steel Frames Using ARMA Models,' by I, Conte, J.P., Mahhng S.A. andPister, K.S,, June 1990.

'Soil Conditions and Earthquake Hazard Mitiltion in the Marina District of San Francisco,' by Mitchell J.IC, Masood, T Kayen,R.E. and Seed, R.B., May 1990.

'Influence of the Earthquake Ground Motion Process and Structural Properties on Response Characteristics of Simple S 'byConic, J.P., Pister, K.S. and Mahin, S.A., July 1990.

'Experimental Testing of the Resi lient-Friction Base Isolation System,' by ClarlL P.W. and Kelly, J.M., July 1990, (PB92 143 OT2)A011.

'Seismic Hazard Analysis: Improved Models, Uncertainties and Sensitivities,' by Araya, R. and Der Kiureghiam A., Mat 1988.

'Effects of Torsion on the Linear and Nonlinear Seismic Response of Structures," by Sedarat, H. and Berteto, V.V., September 19119.



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Steel Tips-Slotted Bolted Connection Energy Dissipaters-Grigorian

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