Improved Seismic Performance of Braced Frame Connections

Yao Cui

Dalian University of Technology

Braced frames are widely used for steel constructions in seismic regions. Gusset plates are used to connect the ends of the brace to the framing elements, Fig.1. The forces or rotations in the brace must be accommodated by the gusset plate. Failure of the gusset plate connection will result in considerable loss of strength of the brace and compromise the seismic performance of the braced frame. Among the failure modes of the gusset plate connections, the fracture of the interface weld between the gusset plate and the beam and column (Fig. 2) is one of the most undesirable failure modes [1, 2]. Recent experiments [3-5] have demonstrated that welds joining the gusset plate to beams and columns are important to the ductility and deformation capacity of the system. An extensive review of braced frame gusset plate research was conducted by Chambers and Ernst [6]. It pointed out the necessary to understand the interface weld behavior of gusset plate connections.

Experimental study was conducted to investigate the ultimate strength of the gusset plate connection governed by the interface weld fracture under the tensile axial brace load. The 12 mm thick gusset plate was connected to the endplates using a fillet weld on both sides. The brace angle was 30 degree. Two pieces of plate with the thickness of 19 mm were connected with the gusset plate using three high tension bolts (F10T) with the nominal diameter of 22 mm to transfer the axial brace force, as shown in Fig. 3. The test parameters are the weld length of beam and column side (Lb, Lc). The gusset plate dimensions could be found in Fig. 3.

(a)

Fig. 1 Braced frame gusset plate connections Fig. 2 Weld fracture

- 15 -

(b)

Fig. 3 (a) Test setup (b) specimens Load-displacement curves of all specimens are shown in Fig. 4. Specimen

“B135-C45” lost the resistance immediately after the interface weld fracture. The other three specimens reached the maximum strength when the vertical gusset plate displacement is around 15 mm, while Specimen “B135-C45” reached the maximum strength when the vertical displacement is around 11 mm.

Fig. 4 Test results

A comprehensive series of nonlinear, inelastic FE analyses were performed to simulate the response of the test specimens using the ABAQUS 6.9. The experimental and analytical relations between the axial load and the displacement for the two specimens are shown in Fig. 5. The FEM model closely approximated all aspects of the measured response. The difference between experimental and analytical maximum strength is 3% and 14% for specimens B135-C45 and B90-C90, respectively.

(b)

Fig. 5 Analysis results: (a) load-displacement relationship; (b) failure mode

90 64 135

B90-C90 B60-C120 B135-C45

B90-C90 B135-C45

- 16 -

The finite element models verified with the experimental study were adopted for the further parametric study to investigate the effect of the gusset plate size, brace angle, and eccentricity of the brace on the resistance strength of the interface weld. Based on the parametric study, the following were observed. The interface weld within the extension Whitmore effective region transfers almost all the brace force from the gusset plate to the beams and columns. The effective interface length is affected by the gusset plate size, brace angle, and eccentricity of the brace. The resistance force of the interface weld is generally aligned to the brace.

Based on the pre-mentioned observations, the extension Whitmore effective length was modified by considering the geometrical effect of the gusset plate (such as, the gusset plate size, brace angle, and eccentricity of brace). Further study should be conducted to develop the evaluation of the effective length. Further experimental study is required to verify the proposed evaluation. In addition, more parameters should be considered, such as the connection between the brace and the gusset plate, the yield of gusset plate, and cyclic loading condition.

References

[1] Astaneh-Asl H. Seismic behavior and design of gusset plates. Steel Tips. Moraga Calif.: Structural Steel Education Council; 1998.

[2] Roeder C, Lehman D, Yoo, JH. Improved design of steel frame connections. International Journal of Steel Structures 2005;141-53.

[3] Johson S. Improved seismic performance of special concentrically braced frames, a thesis submitted in partial fulfillment of the MS degree. Seattle: University of Washington, 2005.

[4] Herman D. Further improvements on and understanding of SCBF systems, a thesis submitted in partial fulfillment of the MS degree. Seattle: University of Washington, 2006.

[5] Kotulka B.A. Analysis for a design guide on gusset plates in special concentrically braced frames, a thesis submitted in partial fulfillment of the MS degree. Seattle: University of Washington; 2007.

[6] Chambers, J. Brace frame gusset plate research – Phase 1 literature review, University of Utah, Salt Lake City, 2005.

- 17 -

Polar Oxide Interfaces

Project Coordinator Name: Vlado K. Lazarov Affiliation: University of York

１ Introduction

Recently polar oxides have gain significant attention due to discovery of 2D electron gas at perovskite type of interfaces (e.g SrTiO3 /LaAlO3). While the origin of the 2D electron gas at this interface is still somehow debatable, polar nature of LaAlO3 was proposed as an explanation for the nature of this interface. In general, due to abrupt change of electrostatic potential across the polar interfaces one can expect strong electronic reconstruction; this could provide means for new interface stabilized electronic phases.

２ Aims of Research

Aim of the project is to create, characterise and obtain fundamental knowledge on strong polar oxide interfaces and surfaces (beyond perovskite systems) on atomic level; with ultimate goal to utilise these artificial hetero-interfaces as a platform for electronic and spintronic devices.

We focus on the polarity of simple binary oxides including MgO(111) (insulator), NiO(111) ( AFM insulator), Fe3O4 (111) ( ferrimagnet) and will establish a new platform for device application with a variety of functionalities.

３ Results

During the one year period of our research project we realised two visits to TIT from staff from York Dr Leonardo Lari, for one week and a PhD student (Daniel Gilks, research stay for 4 weeks). During this period we have managed to grow a number of specimens as initially planned, with focus on NiO(111)/MgO(111) and Fe3O4(111)/STO and Fe3O4(111)/MgO(111).

a) NiO/MgO

In order to understand the electronic structure of the NiO/MgO interface we have prepared cross-sectional electron microscopy specimens, and utilise atomic resolution STEM and EELS. Fig. 1a and 1b show cross sectional images of the interface region of NiO(111)/MgO(111) and NiO(100)/MgO(100). Films morphology is perfect, with surface structure atomically sharp. In contrast to surface interface structure show much richer structure. Intensity profiles along both interfaces show that interface are gradually mixed. In other words there is inter-diffusion of Ni and Mg, creating a stepped (111) interface, which is rather unique since it is independent of the crystallographic orientation of the film and substrate. Based on these results we created atomistic models and investigate the electronic and magnetic structure of the interfaces. First principle calculations confirm the experimental finding showing that gradually mixed interface is energetically the most stable (Fig.2). The electronic calculations show that we have two distinctive regions. One is near the NiO/NixMg1-xO and NixMg1-x/MgO interface. Of importance is the uppermost interface since it is predicted to carry half-metalic states and contribute the most to the overall net magnetic moment that is associated with this interface. Finally we would like to note that difusion of the Ni and Mg is along the 111 plane as demontsrated with the prismatic mixing profile of NiO(100)/MgO(100) in Fig. 1b.

- 18 -

Fig.1. STEM-HAADF image from interface region of NiO(111)/MgO(111) and NiO(100)/Mgo(100) interface region show atomic mixing and formation (111) stepped interfaces. Intensity profiles show that interface mixing is constrained to eight atomic planes.

Fig. 2. Total energy calculation performed on various atomic models clearly favour gradually mizxed interface as best atomic structure of NiO/MgO. The values shown under each model interface are compared to the energy of the sharp interface.

- 19 -

Fig.3 STEM cross-sectional image of Fe3O4(111) on STO(111).

B) Fe3O4(111)/STO(111)

Fig. 3 shows a cross-ectional STEM-HAADF of magnetite on STO(111) substrate. The film is showing a bulk atomic ordering in the magnetite film starting from the interface region onwards. Detailed studies of the film structure reveals a small amount of the extended defects such as antiphase domain boundary that govern the film behaviour in thin films. The most interesting finding is the sharpness of the film substrate interface which is on atomic level. Interfacial layer is determined by TiO2/Fe_octahedral bonds. Due to the lattice mismatch misfit dislocation network originates from the interface and localy changes the bond angles as seen from the central region of the interface shown in Fig. 2. Ability to form sharp interfaces, in principle can be used to engineer at least several Fe3O4/STO interfaces, in order to investigate the effect of several atomic interface structure on the spin injection in STO, when STO is used either as a semiconductor ( e.g. Nb doped STO) or as an insulating tunnel barrier.

４ Conclusion / Summary

We have successfully undertaking the growth of polar NiO(111), MgO(111) , and Fe3O4(111) heterojunctions. Atomic structures of these junctions were determined by high resolution STEM-HAADF. We used experimentally derived structure to perform first principle calculations and predict electronic structure of the MgO(111)/NiO(111) interface. We have propsed neutron scattering experiment to confirm our theoretical predictions of magnetic structure of NiO/MgO interface. We also show that Fe3O4/STO interface can be atomically engineered, and we are planning near future experiment to determine the spin injections in Nb doped STO as a function of different interface structure.

5 Team Members

(Name) Vlado Lazarov (Affiliation) York

(Name) Daniel Gilks (Affiliation) York

(Name) Leonardo Lari (Affiliation) York

(Name) Kosuke Matsuzaki (Affiliation) TIT

Name) Tomofumi Susaki (Affiliation) TIT

- 20 -

コンクリート躯体の高耐久化を目指した建築仕上材の保護機能評価

忠南大学校 宮内博之

１ はじめに

コンクリート躯体に建築仕上材を施工することは建築物の高耐久化を図るために有効であると報告

されている。例えば，建築物の塩害抵抗性に関して，建築仕上材の施工により塩化物イオンの浸透抑

制効果を期待することができる。しかし，コンクリート下地等にひび割れが発生した場合，仕上材の

塩害抵抗性については多くの検討が未だなされていない。そこで，本研究では下地モルタルに施工し

た塗膜防水材の塩害抵抗性の評価を目的とし実験を行った。

2. 建築仕上材の塩害抵抗性試験概要

2.1 使用材料

モルタル下地ひび割れ幅は，ひび割れなし，0.3，0.5，1mm の 4 水準とした。防水材はウレタン系

およびアクリル系塗膜防水材の 2 種類とし，厚さは 2mm とした。なお，無塗布コンクリート試験体も

同時に作製した。

2.2 実験方法

(1) 塩化物イオン浸透深さ測定

モルタル試験体の養生条件は材齢 4 週まで水中養生，その後材齢 8週まで恒温恒湿条件（温度 20±

2℃，R.H.:60±5％）とした。その後，NaCl 5％水溶液に浸漬した塩水浸漬試験を実施し，材齢 1，4，

8，13 週毎に KS F 2737"指示薬によるコンクリートの塩化物浸透深さの測定方法"に準じて，AgNO3 溶

液を噴霧し正色反応した部分より塩化物イオン浸透深さを測定した。

(2) 塩化物イオン拡散実験

防水材の有無，及び下地ひび割れ発生時の防水材厚さ変化を考慮した膜厚さの影響を評価するため

に，φ100×50mm のモルタル試験体を用いて塩化物イオン拡散実験を実施した。実験方法について，

各促進材齢で NT BUILD 492(非定常状態電気泳動試験)に準じて実施し，試験体に AgNO3 溶液を噴霧し

て変色域により浸透深さを求めた。また，塩化物イオンの拡散係数は，Tang＆Nilsson が提案した式

を用いて求めた。

3. 結果および考察

3.1 モルタル下地の塩化物イオン浸透深さ

モルタル下地の塩化物イオン浸透深さの測定結果を表 1 と図 1 に示す。また，塩化物イオン浸透深

さの予測式を表 2 に示す。無塗布試験体の場合，試験期間 1 週間で下地に塩化物イオンが浸透し，13

週後の浸透深さは 22.2mm となった。無塗布試験体の場合，ひび割れ部での浸透深さは，ひび割れ無

しの試験体に比べて 3〜5 倍以上大きくなった。一方，ウレタン系防水試験体はひび割れ幅 0〜0.5mm，

アクリル系ではひび割れ幅 0〜0.3mm の範囲で，試験期間 13週まで塩化物イオンの浸透を抑制した。

3.2 モルタル下地の塩化物イオン拡散係数

各試験体の塩化物イオン拡散係数の結果を表 3 と図 2 に示す。無塗布試験体はウレタン系及びアク

- 21 -

リル系防水試験体に比べて，下地の塩化物イオン拡散係数が高くなり，3.95×10-12 m2/sec となった。

また，防水材膜厚さが厚くなることで，下地の塩化物イオン拡散係数は低下した。

3.3 塩化物イオン浸透深さ速度係数と拡散係数の関係

表 2 の結果により得られた塩化物イオンの浸透深さ速度係数と，拡散実験により得られた塩化物イ

オン拡散係数の関係を図 3 に示す。本研究の範囲では，両者は相関性があり，塩化物イオンの拡散係

数が約 0.5×10-12 m2/sec 以下の条件では，塩害を抑制することができると考える。また，下地にひび

割れが 1mm 以下の条件で発生しても，防水材塗布により，無塗布・下地ひび割れの無いモルタル下地

より高い塩害抵抗性を示すことがわかった。

4. まとめ

本研究の結果を要約すると次の通りである。

1) 無塗布試験体は塩化物イオンが早期に浸透したが，本研究で用いたウレタン系およびアクリル系

防水材を塗布した場合は，試験期間 13 週間までひび割れの有無に関係なく，高い塩害抵抗性を示

した。

2) 防水材を施工し，膜厚さを十分に確保することで，モルタル下地にひび割れが発生した場合でも，

塩化物イオンの浸透を低く抑えることが可能であることを示した。これより，下地への防水材の施

工は塩害抵抗性の有効であると判断された。

図1 下地ひび割れ部における塩化物イオン浸透深さ測定結果

図2 防水材厚さと下地の塩化物イオン拡散係数の関係

図3 塩化物イオンの浸透深さ速度係数と拡散係数との関係

塩化

物イ

オン

拡散

係数

(×10

-12 m

2 /se

c.)

防水材の膜厚さ(mm)

모르타르 (Plain)

우레탄계

아크릴계

ひび割れ幅1mm

ひび割れ幅0.5mm

ひび割れ幅0.3mm

ひび割れ無し

材齢（週）

塩化

物イ

オン

浸透

深さ(m

m)

0 1 4 8 130

20

40

60

80

100

ひび割れ幅1mm

表1 塩水浸漬試験結果（材齢13週）

区分試験体断面の

浸透状況

平均浸透深さ

(mm)

塩化物イオン拡散係数

(×10-12m2/sec.)防水材 厚さ（mm)

無塗布 0.0 35.3 3.95

ウレタン系

2.0 5.2 0.26

1.6 11.3 1.20

アクリル系

2.0 5.9 0.30

0.8 15.7 1.68

ひび割れ幅 無塗布 ウレタン系 アクリル系

なし 1.5+2.2√t - -

0.3 ｍｍ 3.5+6.5√t - -

0.5 ｍｍ 4+10√t - 0.2+0.2√t

1.0 ｍｍ 6+14√t 0.1+0.11√t 0.2+0.53√t

区分無塗布 アクリル系 ウレタン系

ひび割れなし ひび割れ幅1.0mm

断面

表2 塩化物イオンの浸透深さの予測式 (X = A + B√t)

表3 モルタル下地の塩化物イオン拡散係数の測定結果

塩化物イオン拡散係数(×10-12m2/sec.)

塩化

物イ

オン

浸透

深さ

速度

係数

(B)

R2 = 0.9906

塩害の抑制領域

ひび割れ幅0.5～1mm防水材塗布試験体

基準モルタル（ひび割れ無し、無塗布）

Y=0.12x2+0.1XR2=0.99

無塗布アクリル系ウレタン系

～

y=4.7e-

1.3xR2=0.89

無塗布アクリル系ウレタン系

0

1

2

3

4

0 0.5 1.0 1.5 2.52.00

0.5

1.5

2.0

2.5

1.0

0 1 2 3 54

X:塩化物イオン浸透深さ(mm), t:塩水浸漬期間（day),A,B:塩化物イオン浸透速度係数

- 22 -

Study of collective behavior of electrons

in the vicinity of quantum phase transitions

University of Crete and Nanyang Technological University

Christos Panagopoulos

1. Introduction & Activity Report

There is growing experimental evidence for the emergence of spatial inhomogeneities at the

nanoscale in many strongly correlated electron systems. In addition to charge, other degrees of

freedom, such as spin and lattice, typically also play an important role in these materials, leading to

the competition of several ground states and the resulting nanoscale phase separation. Such

nanophases have been variously described as bubbles, stripes, clumps, clusters, or domains,

depending on system details. Other

investigations have discussed the emergence

of inhomogeneous charge-ordered phases in

analogy with the smectic and nematic states in

liquid crystals. In general, many different

configurations of such nanoscopic ordered

regions often have comparable (free) energies,

such that these metastable states are separated

by barriers with a wide distribution of heights

and, thus, relaxation times. This leads to the

slow dynamics typical of glassy or

out-of-equilibrium systems.

The resistance noise spectroscopy employed

at very low temperature (T) and on very long

time (t) scales is clearly a technique that is

well suited for probing the charge dynamics. It

has already been used successfully in charge

(Coulomb) glasses in nonmagnetic systems.

The analysis of the noise statistics can provide

evidence for the presence of a large number of

metastable states, which are an essential

prerequisite for well-known dynamical

features of glassiness, such as aging, memory,

and breaking of ergodicity.

FIG. 1 (a) Noise R(t)/<R> vs time at T =

0.118 K for several B // ab. All traces are shifted

vertically for clarity. (b) the probability density

function (PDF) vs R(t)/<R> in different fields

for 12-hour observation periods; T = 0.118 K.

- 23 -

Therefore, we investigated the noise in the in-plane resistance Rab of La1.97Sr0.03CuO4 (LSCO) at

very low temperature far below the spin-glass transition temperature and with magnetic fields

parallel to the CuO2 planes (B // ab), as shown in Fig. 1. Just like what was observed for the c-axis

transport and a different field orientation (B // c), the fluctuations of the in-plane resistance Rab with

time provided evidence for the increasingly slow, correlated dynamics as T → 0. Here, however,

the magnitude of the resistance noise was significantly smaller and the emergence of charge

glassiness took place at even lower T than for the out-of-plane transport. Also, the data did not seem

to show any effect of the magnetic field on either the amplitude or the character of the noise. In

spite of these quantitative differences, the overall data strongly support earlier conclusions and

provide evidence that doped holes in lightly doped LSCO form a collective, glassy state of charge

domains or clusters located in the CuO2 planes.

Further work is needed to examine the evolution of this dynamically inhomogeneous state with

doping and its possible coexistence with high temperature superconductivity.

2. Team Members

University of Crete and FORTH: Christos Panagopoulos, Zacharias Viskadourakis

Nanyang Technological University: Sai Swaroop Sunku

National High Magnetic Field Laboratory:

Dragana Popović, I. Raičević, J. Jaroszyński, E. S. Choi

University of Cambridge: Glenton Jelbert, Jiwon Seo, Leszek Spalek, Sridhar Saxena

Tokyo Institute of Technology: Takao Sasagawa, Takao Katagiri, Manabu Kanou

3. Papers

[1] “Memory Effects in the Charge Response of Lightly Doped La2-xSrxCuO4” I. Raičević, D.

Popović, C. Panagopoulos, and T. Sasagawa, J. Supercond. Nov. Magn. 25, 1239 (2012).

[2] “Evidence for Quantum Skyrmions in a Doped Antiferromagnet” I. Raičević, D. Popović, C.

Panagopoulos, L. Benfatto, M.B. Silva Neto, E. S. Choi, and T. Sasagawa, Phys. Rev. Lett. 106,

227206 (2011).

[3] “Non-Gaussian Noise in the In-Plane Transport of Lightly Doped La2-xSrxCuO4: Evidence for

a Collective State of Charge Clusters” I. Raičević, D. Popović, C. Panagopoulos, and T.

Sasagawa, Phys. Rev. B 83, 195133 (2011).

[4] “Large Positive Magnetoresistance of the Lightly Doped La2CuO4 Mott Insulator” I. Raičević,

Dragana Popović, C. Panagopoulos, and T. Sasagawa, Phys. Rev. B 81, 235104 (2010).

[5] “Evidence for Charge Glassiness at Low Temperatures in La1.97Sr0.03CuO4” I. Raičević, J.

Jaroszyński, D. Popović, C. Panagopoulos, and T. Sasagawa, Phys. Rev. Lett. 101, 177004

(2008).

[6] “Measurement of Low Energy Charge Correlations in Underdoped Spin-glass La-based

Cuprates using Impedance Spectroscopy” G. R. Jelbert, T. Sasagawa, J.D. Fletcher, T. Park, J.

D. Thompson, C. Panagopoulos, Phys. Rev. B 78, 182513 (2008).

- 24 -

地震観測に基づいた高層建築物の耐震性能に関する研究 武漢理工大学 蒲武川

１ はじめに

この度、東京工業大学応用セラミックス研究所の共同利用研究費（国際 B）を受け、本研究を展開す

ることができた。東京工業大学地震工学に関する研究資料及び研究施設を利用することができて、大変

感謝している。特に連絡教員の笠井和彦教授に長くそして深く研究指導を受け、誠に感謝の意を表する。

本研究は東北大地震を背景に、高層建築の耐震・制振技術の性能及び対策を対象に展開した。様々の面

から高層建築の耐震性を評価し、有意義な結果が得られた。

２ 研究目的

東北大地震によりエレベーターで閉じ込め事故や地震の揺れによって非構造部材の損傷など高層建

築物の被害が発生した。このような顕在化されなかった問題は今回の地震で注目を集めるようになった。

一方、新しい形式の構造物、制振・免震構造を含め様々な耐震技術が近年開発そして普及されている。

これらの構造物の実地震時の性能を知ることはできなかった。多くの高層建物に地震計が配置されてお

り、地震時の応答が取られた。取られたデータを有効活用することによって、地震時高層建物の動的挙

動の解明、現行設計法の問題の提出および対策などの検討ができ、今後の構造安全性を高めることに繋

がり、非常に大きな意義を持っている。地震後、笠井和彦教授は様々な学術活動によって、精力的に建

物観測データを集めてきた。本研究では、笠井教授に実測データを共有して頂き、そして共同研究を行

うことにより、高層建築物の地震時挙動を解明し、解析手法の提案そして今後の構造設計への提言を行

う。

３ 研究成果

2011 年 3 月に起きた東北大地震で計測された高層建築の地震時応答データを用いて、統計的分析を

行った。対象建物は耐震、制振及び免震建物などがある。モード同定手法を用いて、各対象建物のモー

ド周期、減衰定数などの動的特性値を同定した。まず、建物の加速度応答の増幅倍率は、耐震建物では

2－3倍になり、制振建物は 1－2倍ほどに止まった。耐震建物のモード減衰は１％～２％に対し、制振

建物では３％～４％に増加した。減衰定数の差は僅か1％～２％位だが、建物特に高層建物の地震時応

答への影響は大きい。建物応答の計測値に基づき、同定手法を用いて建物のモード減衰、周期及び刺激

関数を同定できた（弾性応答と仮定）。また、その同定値に基づき、モード解析を行い、建物の地震時

応答を再現できた。これにより、詳細な解析モデルを作らなくても、建物地震時応答を大まかに把握す

ることができる。解析により以下の結果が示された。高層建物の応答は各次モードの応答の総和であり、

応答開始時高次モードの寄与が大きくて、その後は 1次モードの寄与が大きくなる。図１は 54 階建物

の 41階の変位の各次モードの寄与を示し、前記の傾向が見られる。

耐震構造は制振構造と比べ、地震時大きくそして長く揺れたことがわかった。建物モード解析に基づ

き、建物に制振ディバイスの付加を模擬し、建物のモード減衰を変えて時刻歴解析を試した。減衰を僅

か（1％～２％）増加することで、高層建築の振動の振幅が大きく低減し、そして建物振動の継続時間

が短縮した（図２）。これは地震時高層建物構造材の疲労破壊の軽減に繋がり、減衰を増加することで

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大きな効果が期待できる。勿論、高層建築では、僅かの減衰定数を増加するには、大量なダンパーが必

要でもある。実設計時に減衰定数目標値の設定には、設計者と業者の判断が必要である。

今回同定された東京地区の高層耐震建築構造の減衰定数は平均的に 2％以下となっている。日本では

高層建物の減衰定数は鋼構造では２％、鉄筋コンクリート造は 3％が多く用いられる。これは高層建築

の減衰定数を過大評価する可能性がある。減衰定数は構造振動の振幅によって変わるが、より安全な設

計に導くため、高層建築の減衰定数の設定が非常に重要であり、深く検討する必要がある。

東北大地震では高層建築の室内設備の被害が多かった。室内設備への振動入力は建築の構造の床加速

度である。そのため、高層建築の床スペクトルを検討した。図３はある耐震構造の床応答スペクトルで

あり、これにより床応答スペクトルに顕著な構造特性が見られる。室内設備などの周期が建物周期と一

致する場合、大きな振動または被害が予測される。ゆえに、建築非構造材または設備の振動周期を建物

周期から離れることで、非構造材または設備の被害を大きく回避することができる。また、建築構造ま

たは設備自体の減衰定数を高くすることも被害を収まることができる。

図 1 高層建物１次，２次と３次モードの変位応答の比較

図２ 制振構造の減衰定数を変えた場合の応答

図３ 床応答スペクトル

４ ま と め

本研究は東北大地震に高層建物の計測データに基づき、高層耐震・制振構造の地震時性能を評価した。

建物のモードを精度よく同定できて、建物の地震時性能を再現することができた。高層建築の減衰定数

を僅か増加することで、応答の振幅そして継続時間を大きく短縮できる。耐震構造に減衰を増加する制

振技術の応用が必要である。

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Passive controlled RC building structures with novel configurations

of buckling restrained braces

Institute of Engineering Mechanics, China Earthquake Administration Qu Zhe

１ はじめに

Buckling restrained braces (BRBs), which exhibit stable hysteretic behavior and provide superior

energy dissipation capacity to building structures, have been extensively studied and applied

to various types of steel braced frames since 1980s. In contrast, however, the applications of

BRBs in reinforced concrete (RC) structures are quite limited, and are mostly confined to the

retrofit of existing buildings. A major limitation comes from the troublesome connection between

steel braces and concrete member, which are usually incapable of accommodating large concentrated

tensile force. Innovative solutions are needed for the local connection of BRBs and concrete

members in order to promote the applications of BRBs in the seismic protection of RC buildings. ２ 研究目的

The present study proposed a continuously buckling restrained braced frame system (CBRBF) for

RC constructions, in which the BRBs are arranged continuously along the height of the braced

span and the two BRBs in adjacent stories share the same gusset plate, which is attached to the

surface of the concrete beam-to-column joint. It is expected that the local tensile force on

the shared gusset plate could be minimized by the force equilibrium of the neighboring BRBs,

and the normal and tangent force resistance of the local connection could be separated in order

to simply the load condition to make it more reliable.

３ 研究成果

Large scale experimental tests on CBRBF subassemblies are conducted to validate the proposed

system with special focus on the local connection behavior. The performance of the proposed

connection and the BRBs themselves in the new system was confirmed by the test results. The limited

damage to the RC part of subassemblage was also carefully examined. In addition, nonlinear time

history analysis of CBRBF as compared to bare RC frames were conducted to show the response

reduction effect of the bracing and to understand the behavior of the local connection and its

influence on the global response under dynamic loading.

４ ま と め

A novel CBRBF system for RC constructions is proposed and tested. The BRBs generally yield at

about 1/600~1/500 story drift ratio in the proposed system. The end rotations of BRBs are

comparable to those in conventional V-brace system. The deformation in the proposed connection

is negligibly small and the damage to the RC parts is well under control.

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System and Damage Identification of a Full-Scale Steel Moment-Resisting

Frame Structure using Ambient and Hysteretic Vibration Data

Project Coordinator Name: Ertugrul Taciroglu Affiliation: University of California, Los Angeles

１ Introduction

This report summarizes the outcomes of the efforts that were aimed at meeting the objectives of the collaborative research project titled “System and Damage Identification of a Full-Scale Steel Moment-Resisting Frame Structure using Ambient and Hysteretic Vibration Data.”

Two time-domain system identification algorithms were proposed for utilizing Takatori and white-noise excitation shake table test data from the E-Defense full-scale four story steel moment resisting frame structure.

The collaborative research project provided the UCLA team the opportunity to access and procure test data. In what follows, the original goals of the project are recited and the results of applying system identification methods to the test data are briefly discussed. Plans for future efforts are outlined, accordingly.

２ Aims of Research

The main objective of the proposed collaborative effort has been to investigate the capabilities of two—recently developed—parameter estimation algorithms for system identification of torsionally coupled multi-story framed buildings through the analysis of experimental vibration data.

One of the said methods utilizes linear (ambient, forced, and strong motion) vibration data of a structure to estimate the stiffness and damping properties of structure's individual stories. For a permanently instrumented building, the comparison of stiffness values extracted from data sets, which are collected before and after an event, would reveal if the structure has experienced any permanent loss of stiffness.

The second method aims to identify the nonlinear behavior of lateral load resisting systems—e.g., moment-resisting frames—during strong motion excitation. This allows the characterization of the force deformation behavior and energy dissipation capacity of such systems under actual boundary conditions.

Both methods work in the time-domain, as such, need a relatively dense instrumentation array which can characterize translational and torsional acceleration response history at each floor level.

The proposed collaborative project aimed to validate the aforementioned methods by using experimental data from shake table testing of the E-Defense full scale four-story steel moment resisting frame structure. The dense instrumentation of the test structure provides adequate amount of data to be employed with the aforementioned identification techniques and for validation of the system identification results.

３ Results

Acceleration data from the 20% Takatori shake table excitation (during which the structure remains linear) have been used with the first method for identifying stiffness and damping matrices of individual stories of the building. The original method utilizes a non-iterative least-squares-based algorithm for identifying stiffness and damping properties. Therefore, no initial estimate of the these properties is needed. Although the algorithm yielded reasonable values for the lateral and torsional story stiffness and damping, the identified stiffness and damping matrices were not symmetric, as such, violated the

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Maxwell-Betti Reciprocal theorem. In order to circumvent such outcome, an iterative constrained optimization algorithm was employed, in which the stiffness and damping matrices are constrained to be symmetric and positive definite. The identified stiffness and damping matrices estimated by the least-squares-based approach were subsequently used as an initial guess to the constrained optimization problem. The obtained story stiffness values are larger than stiffness properties which are evaluated based on the story shear calculated from measured strains in the columns of the story. This is a reasonable observation, since the identified stiffness properties reflect the lateral load resistance capacity contributed by not only the structural members, but also the non-structural components such as partition walls. The updated symmetric story stiffness and damping matrices were assembled to form the global stiffness and damping matrices of the test structure. These were subsequently used to simulate the response of a shear building model of the structure subjected to the 20% Takatori base excitation. Comparison of simulation and measured response show that the identified stiffness and damping matrices generate a low-passed filter version of the response of the structure (as depicted in Fig. 1 for one lateral direction), i.e., the higher modes of response are filtered from the simulation. As a diagnostic task, an eigenvalue analysis (modal decomposition) was conducted with the identified stiffness and damping matrices, to extract natural periods and damping ratios. The results of eigenvalue and spectral analyses corresponding to one lateral direction are listed in Table 1 for comparison. The damping ratios which correspond to the fourth (and possibly third) mode of vibration are spuriously large, and almost an order of magnitude larger than the damping ratios that are identified through frequency-domain spectral analysis. Such large ratios significantly damp out the contribution of higher modes of vibration. This phenomenon is more prominent in the simulated response of lower floors compared to higher floors, since the contribution from the higher modes is more substantial at the lower floors of shear-type buildings.

-4

-2

0

2

4

-4

-2

0

2

4

Abs

olut

e A

ccel

erat

ion

(m/s

2 )

-4

-2

0

2

4

0 2.5 5 7.5 10 12.5 15-4

-2

0

2

4

Time (s)

MeasurementSimulation

a)

d)

c)

b)

Figure 1. Comparison of Simulated and Measured Lateral Response in y Direction: a) Roof, b) 3rd

Floor, c)2nd Floor, and d) 1st Floor.

Table 1. Natural Periods and Damping Ratios of the Idealized Shear Building Model

Mode

Eigenvalue and Mode Decomposition Analysis

with Estimated Stiffness and Damping

Matrices

Spectral Analysis

T (s) (%) T (s) (%)

y1 0.776 2.7 0.776 4.0 y2 0.267 6.6 0.246 6.9 y3 0.171 12.0 - - y4 0.139 18.9 0.130 1.3

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It is suspected that the numerical aspects of the solution algorithm is leading to identification of the abovementioned large damping ratios. Outcome of this study were submitted as a conference paper and have been accepted for oral presentation at the 15th European Conference on Earthquake Engineering (August 24-29, Istanbul, Turkey).

An extension of the algorithm for linear response data may be used to distribute the lateral stiffness of each story among the individual planes of lateral load resistance within the story. However, this extension requires that the torsional response is present in the vibration signature of the structure. One aspect of the strong motion response of the test structure is the subtlety of torsional modes of vibration, which is confirmed by comparing the lateral motion of the rigid floor slabs with the lateral motion due to rotation at a coordinate at the farthest distance from center of rotation at any given floor. The latter is almost ignorable compared to the former. The small contribution of torsional modes of vibration to the dynamic response is mainly due to closeness of centers of rigidity and mass, which result in very small amount of eccentricity in each floor. The same issue (lack of enough torsional motion), has hindered the second algorithm from identifying force-deformation characteristics of individual lateral load resisting frames from the nonlinear response during higher levels of shake table excitation.

Considering the above outcomes, two tasks have been foreseen to be addressed during the extended period of the project: Improvement of the numerical attributes of the solution algorithm with the goal of achieving meaningful damping ratios for higher modes of vibration; Application of the nonlinear system identification algorithm for identifying lateral force-deformation properties of individual stories of the structure (rather than individual frames) from its nonlinear strong motion response.

Data from several white-noise excitation tests were procured during a visit to the Structural Engineering Research Center at Tokyo Instituted of Technology in March 2014. Availability of white-noise excitation data from time intervals in between various levels of Takatori base excitation allows assessing the performance of the algorithm in detecting loss of stiffness from one testing configuration to another. This task will be attended during the extended period of the project, as well.

４ Conclusion / Summary

The results that have been obtained so far demonstrate the capability of the proposed time-domain system identification methodology in identifying stiffness and damping properties pertinent to the first two dominant modes of vibration of the E-Defense full scale four-story test structure. The identified damping matrix overly damps out higher modes of vibration from the response. This encourages improving the numerical attributes of the solution algorithm in order to identify story damping matrices which are consistent with the actual damping characteristics of the higher modes. Since the identification algorithm is not based on any assumption regarding the normality of modes of vibration, it has potentials to be used for identification of structural systems whose damping mechanisms are pertinent to non-classical damping models. Lack of adequate torsional motion in the strong motion response of the building has hindered the identification of nonlinear force-deformation relationship of individual planes of lateral load resistance. Thus, the efforts will be directed towards identification of nonlinear force-deformation response in each lateral direction.

5 Team Members

(Name) Ertugrul Taciroglu (Affiliation) University of California, Los Angeles

(Name) Roshanak Omrani (Affiliation) University of California, Los Angeles

(Name) Ralph E. Hudson (Affiliation) University of California, Los Angeles

(Name) Kazuhiko Kasai (Affiliation) Tokyo Institute of Technology

(Name) Tuan Nam Tran (Affiliation) Tokyo Institute of Technology

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Development of damage controlled structural systems for seismic applications

Project Coordinator Name: Prof. Tony T.Y. Yang

Affiliation: University of British Columbia, Vancouver １ Introduction

Recent earthquakes in Japan, Chile and New Zealand have shown that structures designed through conventional design approach suffer significant damages. These lead to hefty financial losses which have crippled the city’s and the nation’s ability to recover from the earthquakes. Designing resilient structures is becoming the highest priority in earthquake engineering for metropolitan cities such as Tokyo, Taipei and San Francisco. ２ Aims of Research

The aim of the collaborative research is to develop a high-performance structural system which has controlled structural damages during earthquake shakings. This will allow the structure to be repaired economically and efficiently and to be immediately functional after an earthquake. The collaborative research was carried out in the following phases: l) detailed literature review of innovative components and systems that have been developed for seismic applications; 2) a novel and innovative structural system, named the buckling restraint knee braced truss moment frame (BRKBTMF), was developed; 3) robust finite element model of the BRKBTMF was developed; 4) nonlinear time history analyses were conducted to verify the robustness of the system under different earthquake shaking intensities; 5) a new energy-balanced design procedure was developed for the BRKBTMF. ３ Results

Figure 1 shows a newly proposed structural system named buckling restrained knee braced truss moment frame (BRKBTMF). This system combines open web steel trusses and buckling restrained braces. The combination results in large clear spans and a well-defined energy dissipation mechanism. Bucking restrained braces dissipate earthquake energy during strong shakings and can be easily replaced after the earthquake.

Figure 1: Buckling restrained knee braced truss moment frame (BRKBTMF) A practical and non-iterative energy-balanced design procedure for BRKBTMF was developed to promote the implementation of the new system in design offices. The energy-balanced equation uses the plastic mechanism shown in Figure 2b and energy-balanced concept to identify the sizes of bucking restrained braces. The sizes of open web steel trusses and columns were designed to remain elastic under the expected forces in the braces using the capacity design principal shown in Figures 2c and 2d.

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Figure 2: Plastic design procedure for BRKBTMF Preliminary parametric studies have been conducted to identify the seismic performances of BRKBTMF. Figure 3 shows the performances under three seismic hazard levels namely 50%, 10% and 2% probability of exceedance in 50 years. The results show that BRKBTMF has controlled maximum inter-story drifts and floor accelerations that do not amplified at higher stories.

Figure 3: BRKBTMF responses under different earthquake shaking intensities The seismic performances of BRKBTMF were also studied using the next-generation performance-based assessment procedure. Figure 4 shows BRKBTMF has excellent performances with low to no damages observed at the 50% in 50 years hazard level. The median and mean annualized repair costs at the 2% in 50 years hazard level were limited to $2.5 million and 8 thousand dollars, respectively.

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Figure 4: Performance assessment of BRKBTMF ４ Conclusion / Summary

The collaborative research provided the unique opportunity for the researchers at Tokyo Institute of Technology (TIT) and University of British Columbia (UBC) to develop novel structural systems for seismic applications in Japan and Canada. The newly proposed system shows promising performances with controlled drifts and accelerations. In addition, low to limited repair costs at low seismic hazard and moderate repair cost at high earthquake shaking intensities have been achieved.

5 Team Members

(Name) Prof. Susumu Kono (Affiliation) Tokyo Institute of Technology

(Name) Prof. Tony Yang (Affiliation) University of British Columbia

(Name) Mr. Dorian Tung (Affiliation) University of British Columbia

(Name) Mr. Yuanjie Li (Affiliation) University of British Columbia

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Exploration for new multiferroic material under high pressure

Junye Yang , Youwen Long*

Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China

*Corresponding Email: ywlong@iphy.ac.cn

1 Introduction

Multiferroics is a kind of very important multifunctional materials. It exhibits many intriguing physical properties and also provides potential applications in date-storage media, spintronic devices and multiple-stage memories etc. Unfortunately, however, the amount of multiferroic materials is still extremely limited, and the magnetoelectric coupling temperatures found in the present multiferroic materials are rather low (usually much less than room temperature), which is unfavorable for practical applications in the future. It is, therefore, greatly significant to explore new multiferroic materials with high performance above room temperature.

Recently, Inaguma et al made a success for preparing a new compound PbNiO3 under high pressure with the charge combination of Pb4+Ni2+O3. Through a heat treatment, this antiferromagnetic compound (TN≈205 K) was found to transform to a polar LiNbO3-type structure with space group R3c, and a very large ferroelectric polarization was predicted by a first-principle theoretical calculation to occur at room temperature. These results open up a way to search new multiferroic materials in Pb-M-O (M: transition metal) systems by using high-pressure technique.

2 Aims of Research

To synthesize a potential multiferroic material Pb-M-O by using high-pressure and high-temperature conditions, and study the crystal structure, magentic, electronic, dielectronic and ferroelectric properties, and find the possible coupling and interaction between magnetism and ferroelectricity (i.e. the so-called multiferroic property).

3 Results

During the CRP-B in 2013, we focused on the high-pressure synthesis of Pb-Co-O system and successfully obtain an oxygen deficient Pb2Co2O7-δ for the first time.

X-ray diffraction (XRD) was used to study the crystal structure. The powder XRD pattern can be well indexed based on a cubic pyrocholre structure with lattice constant a = 9.9692 Å. The temperature dependence of the dc magnetic susceptibility shows that there is a considerable divergence between field-cooling and zero-field-cooling curves below 20 K, suggesting a probable spin glass ground state. The susceptibity data between 400 K and 170 K can be well fitted based on the Curie–Weiss law with the formula χ= C/(T-θ), giving the Curie constant C = 4.7 emu K mol-1 and the Weiss constant θ= -170.1 K. According to the fitted Curie constant, the effective moment was calculated to be 6.13 μB. In addition, ac magnetic susceptibility and specific heat measurements also confirm the spin glass ground state in this compound. X-ray absorption spectral measurements show mixed valence states for both Co and Pb ions. Although the Co is a mixed valance state, the temperature dependence of the electrical resistivity for Pb2Co2O7-δexhibits insulating behavior and the resistivity-temperature (RT) relationship follows a Mott 3D variable-range hopping (VRH) model between 40-80 K.

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4 Conclusion / Summary

The new cubic pyrocholre Pb2Co2O7-δwas synthesized under 8 GPa and 1380℃ in an oxidizing atmosphere for the first time. This material is the first compound in Pb-Co-O ternary system in the best of our knowledge. At low temperature, spin glass was observed due to the geometric frustration in pyrocholre structure. Although the B-site Co ion is a mixed valence state, the compound exhibits insulating behavior and the RT relationship follows a Mott 3D VRH model at low temperature, implying the possibility of Co2+ and Co3+ order.

5 Team Members

(Name) Junye Yang (Affiliation) Institute of Physics, Chinese Academy of Sciences

(Name) Youwen Long (Affiliation) Institute of Physics, Chinese Academy of Sciences

(Name) Masaki Azuma (Affiliation) Tokyo Institute of Technology

(Name) Runze Yu (Affiliation) Tokyo Institute of Technology

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Magnetic Vortices in High Temperature Superconductors

Weizmann Institute of Science Eli Zeldov

1. Introduction

The magnetic field penetrates into the superconductors in the form of quantum magnetic

flux lines (vortices). Due to their repulsive interactions, the vortices form a lattice which

serves as a unique model system that allows investigation of a wide range of general

phenomena in condensed matter physics. In addition, the static and dynamic behaviour of

vortex matter determines the electrical and magnetic properties of superconductors,

comprehension of which is essential for technological applications.

The comprehension of the vortex matter properties in high temperature superconductor

is based to a large extent on magnetization studies. Most of the investigations rely on

global measurements in which an integrated magnetic response of the entire sample is

measured. In recent years we have developed several local techniques. The local studies

are particularly important since the distribution of the magnetic field within a

superconductor can be highly non-uniform due to disorder, metastability, and geometrical

effects. In this study, the magneto-optical (MO) system with cooled digital CCD camera

was used for direct imaging and investigation of vortex dynamics and phase transitions.

2. Activity Report

The local magnetization loop measured in a thin Bi2Sr2CaCu2O8+δ (BSCCO) crystal

using conventional MO imaging is shown in Fig. 1(a). It is found that application of an

in-plane field (Hx) significantly reduces the hysteresis on the ascending and descending

branches, showing that Hx facilitates both vortex entry and exit. In highly anisotropic

layered superconductor BSCCO, the in-plane field Hx results in the formation of stacks of

Josephson vortices (JV’s). The addition of Hz causes the formation of crossing lattices in

which stacks of pancake vortices (PV’s) form chains along the Josephson vortices.

In order to visualize the field distribution with enhanced sensitivity, we carried out a

differential magneto-optical (DMO) with either current modulation or field modulation. In

the latter case, for example, B(x,y) images taken at Hz = H0 − dH were subtracted from

images taken at Hz = H0 + dH and few tens of such differential images were averaged

resulting in the differential image δB(x,y).

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Figs 1(b)-(c) show DMO images using current modulation at Hz = 3 Oe. In the absence

of an in-plane field (Hx = 0), the behavior was consistent with the geometrical barrier

model. We found that, by adjusting the modulation parameters, we were able to resolve the

PV chains along the JV’s. In the presence of Hx = 30 Oe, as shown in Fig. 1(c), the vortex

chains are clearly visible as bright, slightly tilted horizontal lines that are aligned along the

direction of the in-plane field Hx. We verified that these lines are indeed vortex chains

decorating the stacks of JV’s by rotating the in-plane field and by varying Hx.

3. Team Members

Weizmann Institute of Science: Y. Segev, I. Gutman, Y. Myasoedov, E. Zeldov,

Duke University: S. Goldberg

Max-Planck-Institut für Metallforschung: E. H. Brandt, G. P. Mikitik

Tokyo Institute of Technology: T. Katagiri, K. Okawa, S. Yamaichi, T. Sasagawa

4. Papers

[1] “Suppression of geometrical barrier in Bi2Sr2CaCu2O8+δ crystals by Josephson vortex

stacks” Y. Segev, I. Gutman, S. Goldberg, Y. Myasoedov, E. Zeldov, E. H. Brandt, G.

P. Mikitik, T. Katagiri, and T. Sasagawa, Phys. Rev. B 83, 104520 (2011).

FIG. 1 (a) The measured B−H in the center of a BSCCO crystal at Hx = 0, 40 Oe and T = 79 K.

Current modulated DMO images at Hz = 3 Oe (dI = 10 mA, T = 75 K) for Hx = 0 (b) and Hx = 30

Oe. The slightly tilted horizontal stripes in (c) and (d) are PV chains. The gray scale is about 2.5

G in (b) and 1.5 G in (c). The images are 0.4 mm wide. (top inset) The experimental schematics

showing the BSCCO crystal with gold contacts glued onto a substrate.

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