PERFORMANCE OF ROTATIONAL FRICTION DAMPER (RFD) IN STEEL FRAMES

Transcription

1 The 4 th World Conerence on Earthquake Engineering PERFORMANCE OF ROTATIONAL FRICTION DAMPER (RFD) IN STEEL FRAMES J.Vaseghi Amiri, M.Naghipoor and S.G.Jalali 3, Associate Proessor, Dept. o Civil Engineering, Noshirvaniy University o Technology, Babol. Iran ABSTRACT : 3 PHD candidate, Dept. o Civil Engineering, Noshirvaniy University o Technology, Babol. Iran, vaseghi@nit.ac.ir, m-naghi@nit.ac.ir and jalali_sgj@yahoo.com Rotational riction damper (RFD) was introduced in. Primary experimental and numerical studies were done in Denmark. Optimal slip load has the most importance in perormance o riction damper. Optimal slip load can be obtained rom the minimum o perormance indexes. There are two perormance indexes, seismic perormance index (SPI) and relative perormance index (RPI). In this paper three rames equipped with rotational riction damper, are modeled. These rames are studied with dierent slip loads, acceleration records and PGAs and 54 nonlinear dynamic time history analyses were done to speciy the optimal slip loads. The results show that dierent perormance indexes can give similar slip load. Perormance o RFD is improved by increasing the heights o the rame. Damage index signiicantly decreases in optimal slip load.. KEYWORDS: Rotational Fiction Damper, Seismic Perormance Index, Relative Perormance Index, Damage Index

2 The 4 th World Conerence on Earthquake Engineering. INTRODUCTION Energy dissipation o riction damper is or the slip o rictional component. Rotational riction damper (RFD) was introduced by Mualla in. This damper is applied or new construction and rehabilitation o existing buildings. Primary tests were done in Denmark [], and it was tested by using a shaking table in Taiwan []. All tests expressed good perormance o RFD in seismic events. Also a good agreement between numerical simulation and the results o tests were acquired [, ]. Friction damper are displacement-dependent devices, and NEHRP Guidelines presents some rules to use displacement-dependent devices [3]. Factors such as the reduction o displacement, base shear, elastic energy and the increase o energy dissipation o structure are eective on perormance o riction dampers. The actors are deined in two indexes that which are: relative perormance index (RPI) and seismic perormance index (SPI). Optimal slip load can be gained rom these perormance indexes [, 4]. In previous studies o RFD, eects o this damper are not investigated in real buildings. At irst, in this paper RFD is modeled in SAP. To study the heights and period o buildings on perormance o RFD, three rames with three, ive and eight storeys equipped with RFD are investigated. For studying the intensity o earthquake, dierent PGAs are used.. INTRODUCE OF (RFD) All components o RFD are seen in igure (). The main elements o RFD are a vertical and two horizontal plates. Circular riction pad discs are between the plates. Vertical plate is jointed to the above beam. Energy dissipating is produced by rotating horizontal plates beside the vertical plate [5]. Figure Component o rotational riction damper Figure A single storey equipped with RFD Figure () shows a single storey rame equipped with riction damper. Frictional hinge is located in C. The real behavior o RFD in rictional hinge is seen in igure (3), which is the same as Coulomb rictional behavior. In igure (3), F h is the slip load. This orce eects on RFD by the beam o rame, and rictional moment (M ) on C.

3 The 4 th World Conerence on Earthquake Engineering Figure 3 Behavior o rictional hinge M produces tension and compression orces in braces. I the elastic deormation o moment rame and braces are negligible, the behavior in igure(3) can be true or the rame equipped with riction damper, and the rotational o rictional hinge can be related to the drit o rame. On the other hand, i the elastic deormation o braces is important, they should be checked to conine to the perormance o riction damper. Tension and compression loads are: M F = a (.) h a cos( v) Where M is rictional moment, v is the angle o brace and ha is the height o vertical plate. The tension orce in brace increases when the rame excited, thereore the braces are designed or this orce. A b M = (.) σ h cos(v) y a Where, σ y is yielding stress o the material o braces [6]. The main step in designing o riction damper is to speciy the optimal slip load. Factors and indexes are usually between and. Value o means that, the slip load is zero or is very high, that riction damper cannot slip. Value o is idealistic value, and it cannot be gained, thereore it s minimum value is selected. Seismic perormance index is introduced by Mualla: SPI = + R + (.3) R d R e Where, R is response reduction actor, R is base shear reduction actor and R is remaining energy actor. d D R d = (.4) D p e V R = (.5) V p R e ( E E ) = i h E (.6) i Where, D, V and E are, respectively displacement, base shear and hysteresis energy dissipating o structure h

4 The 4 th World Conerence on Earthquake Engineering equipped with riction damper. D, V and E are, respectively displacement, base shear and total input energy o p p i primary moment rame. These ormulas are normalized that the member o rame will be elastic []. Relative perormance index is: SEA U max RPI = + SEA (.7) ( o) U max( o) Where SEA and U max are, respectively the area under the elastic strain-energy time history and the maximum strain energy or a riction damped structure; SEA (o) and U max(o ) are the response values o the primary moment rame. Both o the indexes have a concept that structure reaches the elastic mode. Thereore the minimum nonlinear hinges should be occurred in minimum o perormance indexes, and damage index should be studied. Damage index is deined as the relative o members, which nonlinear hinges occur in them to total member o rame [7]. 3. MODELLING OF RFD The real behavior o rictional hinge is seen in igure (3). The value o rictional moment is acquired by a multiple o shear orce to the height o damper. SAP is utilized to model the rotational riction damper. Wan plastic is used to model this behavior o rictional hinge. This element can behave such as igure (4). It is similar to Coulomb rictional behavior. To show the accuracy o simulation, veriication with the previous numerical study is achieved. Figure (5) and (6) show the comparison between Mualla, s numerical simulation and simulation o this study. Dimension o moment rame is m and column cross sections are wide lange with moment o inertia mm and the beam is a rigid element. For the assumed weight o 45kN, the period o vibration is s. The EL Centro NS acceleration history with PGA = 3.47 m and s duration is used. Dimensions o damper are s r =. 65m and ha =.m. The section area o brace is mm and the brace pre-stressing is according to the maximum orce in earthquake duration []. Figure 4 Behavior o rictional hinge by SAP In this study, rame with RFD and mentained characteristics is modeled in SAP. But the brace prestressing is assumed to be zero.

5 The 4 th World Conerence on Earthquake Engineering Figure 5 Response o rame with and without riction damper by Drain-DX.5 Drit(m) without RFD with RFD tim(sec) Figure 6 Response o rame with and without riction damper by SAP Maximum responses in igure (6) by SAP have a good agreement with igure (5) by Drain-DX. But the discrepancy in low response is inluenced by the zero brace pre-stressing in SAP modeling. It shows that the brace pre-stressing dose not have a high inluence on the response o rames equipped with RFD [8]. 4. STUDDING OF RFD IN STEEL FRAMES In order to study the inluence o RFD in steel rames, three rames with 3, 5 and 8 storey rames are studied. Sum o slip load is increased rom zero to the twenty percent o total rame weight (.W ), and the perormance indexes are acquired [8]. Weights o three, ive and eight storey rames are, respectively 55, 8 and 46 tons. Shear slip load divides to the number o the riction dampers. The section area o braces is 98mm. Dimension o damper (h and r) are equaled 5 percent o rame dimensions. 54 nonlinear dynamic time history analyses were done or rames with three acceleration records (, and ) and our PGAs (.g,.5g,.3g and.35g). A ew o perormance indexes are seen in igure (7) to (9). For instance the values o optimal slip loads or ive storey rame present in table 4.. The values o average optimal slip loads or all rames present in table 4.. RPI.3g slip load (percent o total weight) SPI.3g slip load (percent o total weight) Figure 7 Let- relative perormance index, Right- seismic perormance index o 3 storey rame and PGA=.3g

6 The 4 th World Conerence on Earthquake Engineering SPI.3g RPI.3g slip load (percent o total weight) slip load (percent o total weight) Figure 8 Let- relative perormance index, Right- seismic perormance index o 5 storey rame and PGA=.3g SPI.3g slip load (percent o total weight) RPI.3g )slip load (percent o total weight) Figure 9 Let- relative perormance index, Right- seismic perormance index o 8 storey rame and PGA=.3g Table 4. The values o optimal slip loads ore ive storey rame earthquake Perormance Optimal slip loads (percent o total weight) index.g.5g.3g.35g (SPI) (RPI) (SPI) (RPI) (SPI) (RPI) (SPI) 6 7 8

7 The 4 th World Conerence on Earthquake Engineering Frames (story) Table 4. The values o average optimal slip loads or all rames optimal slip loads (percent o total Perormance weight) index.g.5g.3g.35g (SPI) (RPI) (SPI) (RPI) (SPI) (RPI) For the calculation o the perormance indexes, reduction o displacement, base shear and remain energy actor should be obtained. Each o the actors can mean the reduction o orce in structure and lead to the decrease o damage index. But nor o them can give a slip load that is in agreement to others. Using the reduction actors to calculate the seismic perormance index (SPI) can give a slip load in agreement with relative perormance index (RPI). Equation.3 and.7 have a concept to reduce the damage index, thereore in the minimum o perormance indexes; the yielding elements should be minimized. Except or the 5 storey rame in earthquake with PGA=.35g, in all o rames, PGAs and acceleration records, the damage indexes are zero. The perormance o the damper is improved by increasing the height o rame, and need to less brace pre-stressing, because the period o higher rame equipped with RFD is relatively near to primary moment rame. This rationalizes the using o cable braces in RFDs. According to the table 4., the average values o optimal slip loads or 3, 5 and 8 storey rames, or PGA=.35g are, respectively 5, and 7.5 percent o total weight. According to igure (7), (8) and (9), the slip load is not sensitive in limit o 5 to percent o optimal slip load. It can neutralize the manuacturing, installation and environment condition errors. Maybe using one acceleration record is not suitable or the evaluation o perormance indexes, and optimal slip load. But the average results o 3 acceleration records are reliable. There is no solicitude to unsuitable perormance o RFD in lower PGAs. When RFDs are adjusted to higher PGAs, more than 4 percent o input energy is dissipated at least in lower PGAs. RPI and SPI result a similar slip load, thereore SPI can mean to minimize the elastic energy o structure such as RPI. The weight o RFD may be less than.5 percent o total structure weight, but it signiicantly decreases the damage index in structure. This is important or rehabilitation o existing building and construction o new building [8]. 5. CONCLUSIONS RFD is modeled in SAP and veriication with previous numerical analysis is acquired. Slip loads are obtained rom perormance indexes. Nonlinear dynamic time history analyses indicate that: - Using the RFD signiicantly decreases the damage o structure in seismic events. - According to the table 4. the value o slip load or 8 story rame has 5% decrease relative to 3 storey rame, that indicates using o RFD in higher rame is more suitable than shorter rame. 3- optimal slip load o dierent acceleration records is reliable. 4- SPI and RPI can give similar slip loads. REFERENCES - Mualla, I. And Bellev, B. (). Perormance o steel rames with a new riction damper device under earthquake excitation. Journal o Engineering Structures 4, Liao, W. Mualla, I And Loh,C. (4). Shaking table test o a riction damped rame structure. Journal o Struct.

8 The 4 th World Conerence on Earthquake Engineering 3- FEMA. NEHRP guidelines or the seismic rehabilitation o buildings. FEMA Report 73, Washington, DC, Chaidez, S. ( 3) Contributation to the assessment o the eiciency o riction dissipaters or Seismic o building. MS thesis. Barcelona, Spain 5- Mualla, I. () Parameters inluencing the behavior o a new riction damper device. technical university o denmark, 8 Lyngby, Denmark 6- Nielsen, L. Mualla, I. () A riction damping system low order behavior and design. Report BYG DTU, R-3, ISSN 6-97, ISBN Moreschi, L. () Seismic design o energy dissipation systems or optimal structural perormance. PHd thesis. Blacksburg, Virginia 8- Jalali, S.G. (7) Parametric study o rotational riction damper in steel rame with eccentric braced rame. MS thesis, University o Mazandaran, Iran Author name/s. (year). Paper title. Journal title Journal volume: issue, pages. Murakawa, H., Ueda, Y. and Xiang, D. (995). Eect o luid orce acting on colliding body upon damage given to oshore structures. Journal o Constructional Steel Research 33:3, For books the ormat is: Author name/s. (year), Book title, Publisher Oehlers, D.J. and Bradord, M.A. (995). Composite Steel and Concrete Structural Members, Pergamon, Oxord, U.K.