seismic performance of novel spring based piston bracing

The 1st China-Canada Symposium on Structural and Earthquake Engineering August 20-24 2017, Vancouver, Canada

SEISMIC PERFORMANCE OF NOVEL SPRING BASED PISTON BRACING

Anas Issa Research Assistant, University of British Columbia, Canada

[email protected]

Shahria Alam Associate Professor, University of British Columbia, Canada

[email protected]

Keywords: Bracing, Seismic resistance, Spring, Piston, Hysteresis.

Earthquakes are considered as one of the most devastating phenomena that cause huge human and economic losses.

Concentric Braced Frames (CBFs) have been developed and used in many places all over the world to resist these

forces. Buckling, however, is a major concern for CBFs where they lose their strength and stiffness when subjected

to severe earthquakes. To solve this issue, many bracing systems have been developed by researchers in the past few

decades. These systems exhibit fat hysteresis loops which contribute to the higher amount of damping and thus can

reduce velocity and acceleration of the system but they do not have the self-centering property. To solve this issue, a

novel Spring Based Piston Bracing (SBPB) system is developed. In this system, a brace member can carry a large

magnitude of tension and compression forces where a special spring is employed in the piston cylinder. Stable and

self-centering hysteresis behavior is achieved when the system is subjected to qualifying quasi-static loading. The

developed system is easy to fabricate and low cost compared to the available systems.

The idea for the SBPB device can be summarized as follows. The system is anticipated to work mainly in a

Chevron/V/X configuration bracing in buildings. This system can be employed for new and existing both steel and

concrete structures. Other applications include a single configuration as bridge restrainer, or parallel to the beam and

attached to the beam and bracing which works like a shear panel device. Also, a parallel configuration attached to top

and bottom flange of beams at the beam-column joints in buildings. The proposed system is employed using a device

commonly seen in mechanical systems, which is a cylinder-piston assembly. The tensile and compressive strength of

a brace should be almost equal. Using this assembly, a brace member can carry large magnitude of tensile and

compression forces where a ring spring, also known as friction spring, is employed in the piston cylinder. There are

mainly five different parts which assemble the specimen, namely Encasing Cylinder, RingFeder Spring, Piston,

Locking Cylinder, and bolts. For fabrication purposes, plan drawing, as well as sections, have been generated as shown

in Figure 1. The piston head is located between two friction spring where the locking cylinder is applied and fixed by

means of high strength bolts. A high strength steel rod will be employed as the piston body. The piston rod is only

used for compressing the springs in both directions. The two employed springs are the means for carrying the

tension/compression cycles.

Figure 1: SBPB configuration (Left), Friction spring hysteresis behaviour (Right)

of 2

The initial loading tests were run in displacement control in accordance with SAC Protocol load history (Venture,

1997). This load history is based on the interstorey drift angle which is the beam tip displacement divided by the beam

length in a frame structure equipped with the brace. The fixed displacements were applied to the grip of the brace

specimen using the MTS hydraulic actuator at a rate of (25.4 mm/min.) as shown in Figure 2. The test specimen was

subjected to symmetric reversed-cyclic loading to characterize its performance. Loading imposed by the MTS actuator

was done at a sufficiently slow rate to prevent the development of any dynamic effects. Loading was applied

continuously without intermittent stops to reduce any strain-rate effects. The objective of the experimental program

was to investigate the cyclic behaviour of bracing members in concentrically braced frames by means of cyclic axial

tests. Quasi-static tests were carried out at the High Head Laboratory for Structural Engineering of the University of

British Columbia Okanagan (UBCO). The specimen was tested using the MTS universal testing machine with a

capacity of 500 kN. Taking into consideration the machine dimensional limits and characteristics, together with ease

of specimen handling, the experimental set-up described in Figure 2 was adopted.

Figure 2: Used loading protocol (Left), test setup (Right)

The proposed bracing system has been modeled in a 3D environment in the structural analysis software SAP2000

(SAP, 2011). The loading protocol discussed in the previous section was implemented and Fast Nonlinear Analysis

(FNA) was conducted. To accurately simulate the hysteresis response of the spring, forces, stiffness, and

displacements have to be defined properly. Table 1shows the different parameters used in the numerical simulation as

per the values provided by the spring manufacturer.

Table 1: Friction spring define parameter

This study presented and discussed the seismic performance evaluation of a novel Spring Based Piston Bracing for

the civil engineering structures. Such bracing will not only be cost effective and efficient technique for new buildings

but also for retrofitting older deficient structures. Design drawings were generated, and the test specimen was

fabricated and tested under quasi-static loading protocol using the MTS machine. Finite element model was generated

and fast nonlinear analysis was conducted using the same loading protocol. Excellent agreement in the seismic

response of the proposed system for the experimental and numerical results was achieved. Based on the results

obtained from the experimental test and the numerical simulation, it was concluded that the force-displacement

hysteresis loops of the spring are repeatable, stable, and identical in tension and compression. The employed spring

had no residual deformation throughout the 32 loading cycles. The proposed system overcome the other available self-

centering systems in its simplicity and constructability. The used friction-spring dissipate energy efficiently even with

high loading amplitudes and can sustain large deformations by means of increasing the number of rings.

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Parameter Description Value

Effective Stiffness Input Spring Slope during the Loading Cycle

(spring rate). E=1.35kN/mm

Effective Damping Input Damping = 66 for standard F-S1 grease. 66

Initial (Non-

slipping) Stiffness

Input Spring Slope during the Loading Cycle

(spring rate). E=1.35kN/mm

Slipping Stiffness

(Loading)

Input Spring Slope During the Unloading

Cycle. F=0.46kN/mm

Slipping Stiffness

(Unloading)

Input Spring Slope During the Unloading

Cycle. F=0.46kN/mm

Pre-compression

Displacement Input Preload Travel. 0

Stop Displacement Input Total Spring Travel minus Preload Travel. 253.2mm

The 1st China-Canada Symposium on Structural and Earthquake EngineeringAugust 20-24 2017, Vancouver, Canada

INFLUENCE OF VELOCITY PULSE ON LONGITUDINAL SEISMICRESPONSE OF SEISMIC ISOLATED CONTINUOUS BEAM BRIDGE

Junya YuGraduate student, Tongji University, [email protected]

Wancheng YuanProfessor, Tongji University, [email protected]

Xinzhi DangPhD, Tongji University, [email protected]

Keywords: near-fault ground motions; velocity pulse-like effect; seismic isolated continuous beam bridge; cable-sliding friction aseismic bearing

1 ObjectivesThree pulse-like and three non-pulse-like near-fault ground motions used as input waves are selected from

Taiwan Chi-Chi and Imperial Valley earthquake records. A continuous beam bridge is selected as background tobuild finite element models. Compared with non-seismic isolation bridge consisting of pot rubber bearing (PRB),leader rubber bearing (LRB) and cable-sliding friction aseismic bearing (CSFAB) are selected as research objects tocomprehensively inspect the seismic responses of seismic-isolated bridge using the two bearings.

3 cases have been discussed. Case 1 is the layout of pot rubber bearing, case 2 is the layout of leader rubberbearing, and case 3 is the layout of CSFAB.2 Relevant Results

The average seismic responses are listed in table 1.Table 1 Longitudinal seismic response of bridge under near-fault pulse-like

and non-pulse-like ground motions

Case Non-pulse-likeEarthquake

pulse-likeEarthquake

Pulse-like/Non-pulse-like

Maximum Shear/kN

Case 1 3011 5450 1.81Case 2 1048 2322 2.21Case 3 970 2447 2.52

seismic-reductionrate

Case 2 65.2% 57.4% -Case 3 67.8% 55.1% -

Maximum BendingMoment/ kN m

Case 1 41205 76229 1.85Case 2 14545 32550 2.24Case 3 13845 36209 2.61

seismic-reductionrate

Case 2 64.7% 57.3% -Case 3 66.4% 52.5% -

MaximumDisplacement of

Bearing/m

PRB - - -LRB 0.131 0.397 3.03

CSFAB 0.208 0.220 1.06

of 2

In order to analyze the influence of pulse effect on the seismic response of the bridge more intuitively, theTime-history charts of bending moment and displacement of bearing of P2 pier have been displayed as below.

(a) Under wave RSN1494 (b) Under wave RSN1494(Non-pulse-like Earthquake) (Pulse-like Earthquake)

Fig.1 Time history chart of bending moment

(a) Under wave RSN1494 (b) Under wave RSN1494(Non-pulse-like Earthquake) (Pulse-like Earthquake)

Fig.2 Time history chart of displacement of bearing3 Conclusions

(1)Under the effect of velocity pulse, the ratio of isolated bearing damping is reduced, and the amplificationeffect of velocity pulse on displacement of leader rubber bearing is particularly outstanding, but cable-slidingfriction aseismic bearing still has a good limit ability.

(2)Compared with other seismic isolated system, the earthquake response of bridge structure thatadopts cable-sliding friction aseismic bearing tends to be stable quickly after the velocity pulse.

(3)cable-sliding friction aseismic bearing still shows great performance in displacement’s limitation,making a balance between the reduction of the seismic internal force response of bridge structure and thelimitation of the large displacement of bearing, which is applicable in seismic-isolated continuous beambridge structure controlled by displacement in design.


SEISMIC DESIGN OF GUSSET PLATE CONNECTIONS IN CONCENTRICALLY BRACED FRAMES

Wei ZHANG Master Student, Dalian University of Technology, China

[email protected]

Yao CUI Associate Professor, Dalian University of Technology, China

[email protected]

Qi TANG Doctor Student, Dalian University of Technology, China

[email protected]

Keywords: Concentrically braced frame; gusset plate; seismic design; finite element analysis

Objectives

In concentrically braced frames (CBF), gusset plates as the connected members are subjected to forces not only from

brace but also from frame action. When the braced frame is deformed, the beam-column connection will deform, and

the deformation of beam-column connection either “open” or “close” as the brace under “compression” or “tension”. Therefore, the design of gusset plate should consider the effect of such frame action, in addition of the brace axial load.

The objectives of this study are to provide the force distribution on the gusset-to-beam and gusset-to-column interfaces

based on a series of numerical analysis. According to the analytical results, the stress distribution along the interface

between gusset plate and frames induced from brace and frame actions will be discussed in details. A method

combining the two actions to predict to stress distributions for concentrically braced frames (CBF) will be proposed.

(a) Combined action model(EC/LC) (b)Frame action model(EC-F/LC-F) (c) Brace action model(EC-B/LC-B)

Fig.1 Separation model

Six FEM models were developed using ABAQUS to investigate the force distribution of gusset plate under the two

actions. As shown in Fig.1, specimen EC and LC were decomposed into specimen EC-F/LC-F (F stand for frame) and

specimen EC-B/LC-B (B stand for brace) to discuss the relations of the braced frame with frame and brace actions.

Results

According to the backbone curve, as shown in Fig.2, the lateral resistance in positive loading of combination curve are

5% and 7% larger than that of the braced frame for specimen EC and LC, respectively. In conclusion, the lateral force-

story drift ratio relationship of braced frame could be decomposed into frame action and brace action.

The stress distribution observed from the braced frame (specimen EC) and the sum of the stress distribution observed

from brace action (specimen EC-B) and frame action (specimen EC-F) are compared in Fig.4 (The same situation is

in LC series and the stress distributions of LC series are omitted). It is noted that the normal stress and shear stress

distributions along gusset plate-frame interface could be decomposed into frame action and brace action well.

of 2

(a) EC series (b) LC series Fig.3 Normal and shear stress distribution on the gusset

plate interfaces Fig.2 Lateral force-drift curve

As shown in Fig.4, the normal stress induced by brace action and frame action are in opposite direction; while the

shear stress induced by brace action and frame action are in the same direction. The normal and shear stresses of gusset

plate-frame interface under the brace and frame action can be assumed to be distributed linearly in triangular as shown

in Fig.3. After the composition, the normal stress is still distributed in triangular shape with the maximum value y at

gusset tips. However, the shear stress is distributed in a right-angled trapezoid shape with the maximum value is y.

Moreover, it should be noticed that the contribution of frame action could be neglected when brace in compression.

(a) Brace in tension (b) Brace in compression

Fig.4 Stress distribution along the gusset plate-frame interface of specimen EC series

Conclusions

1. The interface force between gusset plate and frames can be divided into brace action and frame action. For

normal stress, the interface force induced by brace action and frame action are in the opposite directions, and two

action effect is decreased. While for shear stress, the interface force induced by both actions are in the same direction,

and combined action is increased.

2. When only brace action is considered, the normal stress distributions along the gusset plate-frame interface can

be assumed triangular with the peak stresses occurring at the gusset tips and zero at the beam-to-column corner. The

shear stress distribution along the gusset plate-frame interface can also be assumed triangular, but the peak stresses

occurring at the beam-to-column corner.

3. When only frame action is considered, both normal and shear stress distributions along the gusset plate-frame

interface can be assumed triangular with the peak stresses developing at the gusset tips.

4. The gusset plate is subjected to the forces from both the brace axial force and frame action effects when brace

is in tension. However, the gusset plate is subjected to the brace axial force only when brace is in compression, since

the deformation of frame is relatively small when brace reached the maximum compressive strength.

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Frame action Combined action


SEISMIC ANALYSIS OF STEEL FRAME HERITAGE ARCHITECTURE

Liangjie Qi Ph.D. candidate, Xi’an University of Architecture and Technology, China

[email protected]

Jianyang Xue Professor, Xi’an University of Architecture and Technology, China

[email protected]

Keywords: heritage architecture; quasi static test; plastic hinge; mechanical behaviors

To analyze the seismic performance of heritage architecture, the quasistatic test of a two-bay-one-storey building

was conducted. The combined constant axial load and reversed lateral cyclic loading was applied to the building.

The mechanical behaviors of the steel frame were analyzed. Based on previous experimental studies, three

dimensional finite element models were used to investigate the behavior of the heritage architecture subjected to

monotonous load. The load-displacement backbone curves of the structure were calculated and analyzed.Research

results showed that the majority horizontal load was borne by the Dou-Gong component (a special construct in

heritage architecture) in elastic stage, the plastic hinges at the beam end developed sufficiently. The finite element

analysis results are in good agreement with those of the experiments, which verified the finite element models built in this paper. The conclusion provides valuable references for the design and engineering application of this kind of

structure.


SEISMIC VULNERABILITY OF A CABLE-STAYED BRIDGE EQUIPPED WITH WIRES-BASED LEAD RUBBER BEARING

Shuai Li1, Hedayati Dezfuli Farshad2, Jing-quan Wang1 and M. Shahria Alam2 1 Ph.D. candidate, School of Civil Engineering, Southeast University, Nanjing, Jiangsu, 210096, P.R. China Email:

[email protected] 2 Ph.D., School of Engineering, University of British Columbia, Kelowna, BC, V1V1V7, Canada. Email:[email protected] 3 Professor, School of Civil Engineering, Southeast University, Nanjing, Jiangsu, 210096, P.R. China Email:

[email protected] 3 Associate Professor, School of Engineering, University of British Columbia, Kelowna, BC, V1V1V7, Canada.

Email:[email protected]

Keywords: seismic fragility assessment; shape memory alloy; lead rubber bearing; cable-stayed bridge; near fault

ground motion

Shape memory alloy wire-based lead rubber bearings (SMA-LRBs) possess superior damping capacity and re-

centering property compared to conventional LRBs. However, their efficiency in isolating long-span bridge systems

has not been thoroughly investigated. The objective of this study is to numerically assess the seismic fragility of cable-

stayed bridge system isolated by SMA-LRBs. This type of bridge is highly vulnerable to damage subjected to severe

near fault ground motions, as evidenced during past earthquakes. The Sutong Cable-stayed bridge in China is

considered here as a case study. A new constitutive model, which has been recently developed to simulate the

hysteretic behavior of SMA-LRBs, is implemented in OpenSees. Vulnerability of two non-isolated bridges, i.e. the

floating system (FS) and rigid system (RS), and two isolated bridges, i.e. the bridges equipped with LRBs (LRBS)

and SMA-LRBs (SMA-LRBS) are compared under 20 near fault ground motions. The applicability of three commonly

used intensity measures (IMs), i.e. peak ground acceleration (PGA), peak ground velocity (PGV), and spectral

acceleration at fundamental period (Sa(T1)), are evaluated and PGV turns out to be the optimal IM for long-span cable-

stayed bridge system. Results show that incorporating SMA wires in LRB can enhance the dynamic stability of

conventional bearings and consequently, reduce the failure probabilities of the bearing. The bridge piers and towers

with isolation bearings lead to lower seismic fragility over the non-isolated towers and piers. The non-isolated bridges

are more susceptible to damage than the LRBS and SMA-LRBS. RS is the most vulnerable bridge and SMA-LRBS

is the least one. Compared to LRBS, SMA-LRBs can significantly increase the performance of the bridge system at

the extensive and collapse damage states. The SMA-LRBs are an efficient solution for aseismic design of cable-stayed

bridges in near-fault zones.

mailto:[email protected]


SHEAR CONNECTIONS WITH SELF-TAPPING-SCREWS FOR CROSS-LAMINATED-TIMBER PANELS

Afrin HOSSAIN PhD Candidate, Wood Science, University of British Columbia, Vancouver, Canada

[email protected]

Thomas TANNERT Assistant Professor, Wood Science and Civil Engineering, University of British Columbia, Vancouver, Canada

[email protected]

Keywords: Cross-laminated-timber; Self-tapping-screws; Shear connections; and Cyclic loading.

1. OBJECTIVES

The objective of this research is to examine the performance of 3-ply and 5-ply cross-laminated-timber (CLT) panel

assemblies connected with self-tapping-screws (STS). Different traditional joint types (surface spline with STS in

shear and half-lap joints with STS in either shear or withdrawal) along with two innovative solutions were tested in

189 quasi-static and 21 cyclic tests performed at University of British Columbia Vancouver. The first novel assembly

used STS with double inclination of fasteners (butt joints) and the second a combination of STS in withdrawal and

shear. The performance of the connections was evaluated in terms of i) Capacity; ii) Yield strength; iii) Stiffness; and

iv) Ductility.

2. QUASI-STATIC TESTS

Two different assemblies featuring single and double shear planes (Figure 1) were considered. Sixty CLT test

specimens (1200mm wide, 400mm high and 105mm (3-ply) / 175mm (5-ply) thick) were tested with two shear planes.

For this, each test specimen consisted of three CLT panels of 400mm wide exhibiting two joint planes. For the second

setup, one hundred and twenty nine CLT test specimens (290mm wide, 700mm high and 105mm (3-ply) / 175mm (5-

ply) thick) were tested. Each test specimen consisted of two CLT panels of 145mm wide exhibiting one joint plane.

a. Double shear plane b. Single shear plane

Figure 1: Quasi-static test specimens (all measurements are in mm)

3. CYCLIC TESTS

Twenty-one CLT test specimens (600mm wide, 1600mm high and 105mm thick were tested. Each test specimen

consisted of two CLT panels of 300mm wide exhibiting one joint plane.

of 2

Figure 2: Cyclic Test specimens (all measurements are in mm)

4. RESULTS

The results confirmed that using STS in shear could lead to a ductile connection, which can reach large relative

displacements. Changing the connector layout allows to achieve a target capacity and target stiffness: with closer

spacing leading to lower capacities (per STS) but higher stiffness. Using STS in withdrawal leads to much stronger

and stiffer joints, however, such joints fail at small displacements. The innovative connector assembly with double

inclination of STS provided high capacity and stiffness and adequate ductility for seismic applications. Finally, the

combination of STS in withdrawal and shear seems to allow for joints that exhibit high capacity, high stiffness and

high ductility. Average test results for 3ply is shown in Figure 3.

Figure 3: Average test results

5. CONCLUSIONS

The data obtained allows engineers to specify innovative low cost connection assemblies for lateral load resisting

systems of CLT structures. The findings will be shared with the designers and code officials in an effort to introduce

design values for STS in the next edition of Canadian Standard for Engineering Design in Wood.

The 1st China-Canada Symposium on Structural and Earthquake EngineeringAugust 20-24 2017, Vancouver, Canada

FREQUENCY ANALYSIS ON SEISMIC RESPONSES OF A SEVEN-STORY CHINESE TRADITIONAL TIMBER PAGODA

Yajie WU Ph.D. candidate, Tongji University, China

[email protected]

Xiaobin SONG Associate professor, Tongji University, China

[email protected]

Keywords: timber pagoda; shaking table test; seismic responses; frequency analysis

1 Objectives

To consider the fabrication fidelity of wood-to-

wood connections and reflect their mechanical

influences on the seismic performance of the entire

structure, a one-fifth scaled seven-story Chinese

traditional pavilion-style timber pagoda was

elaborately built following traditional construction

techniques, as presented in Fig.1. The pagoda was

tested on a shaking table in the Multi-Function

Vibration Test Center of Tongji University.

Fig.1 A seven-story Chinese traditional timber

pagoda

One artificial wave specified in local design code,

SHW2 wave, and two natural earthquake records,

Kobe and ChiChi waves, were scaled in time durations

and acceleration amplitudes and input to excite the

model. Three seismic hazard levels, including

frequent-met 7-degree level, fortification 7-degree

level and rare-met 7-degree level specified in Chinese

seismic code were considered. In this test, the three

seismic hazard levels corresponded to the input PGAs

of 0.07 g, 0.2 g and 0.44 g, respectively. The main test

scenarios are listed in Table 1.

Table 1 Main test scenarios

Intensity level Test ID Input wave

Frequent-met

7-degree

1 WN1

2 SHW2

3 Kobe

4 ChiChi

5 WN2

Fortification

7-degree

6 SHW2

7 Kobe

8 ChiChi

9 WN3

Rare-met

7-degree

10 SHW2

11 WN4

12 Kobe

13 WN5

14 ChiChi

15 WN6

Dynamic responses along the height of the

pagoda were obtained. The shaking table test

demonstrated that such kind of timber pagodas would

survive under high-intensity seismic inputs with no

substantial damages in main structural members. To

understand the seismic responses of the timber pagoda,

a frequency was calculated by use of equivalent

stiffness of each story for every seismic wave input.

The calculated frequencies were compared with the

frequencies identified from white noise excitations.

2 Frequency analysis results

2.1 Frequencies identified from white noise

excitations

Frequency is a commonly used index of stiffness

in shaking table tests. The shift in natural frequency

reflects a stiffness change and indicates a damage

degree of a structure after earthquake shocks. Table 2

lists the fundamental frequencies identified from each

of 2

white noise excitation. Compare the frequencies

obtained from WN2 to WN5 excitations, as their

excitation intensity remained the same, it was found

that the identified frequency shifted minor even the

pagoda had suffered high intensity seismic inputs such

as SHW2 and Kobe waves with a PGA of 0.44 g,

which indicated that there was little damage in the

pagoda.

Table 2 Fundamental frequencies identified from

white noise excitations

Test ID White noise

Identified

fundamental

frequency/Hz

1 WN1(0.03 g) 0.94

5 WN2(0.02 g) 0.99

9 WN3(0.02 g) 0.96

11 WN4(0.02 g) 0.92

13 WN5(0.02 g) 0.92

15 WN6(0.02 g) 0.84

2.2 Frequencies calculated by using equivalent

interstory stiffnesses

The timber pagoda could be idealized as a

lumped mass model. The hysteretic intetstory shear

force-drift curve of each story for every seismic wave

input was obtained. As the hysteretic curves were

narrow and long in shapes, as shown in Fig. 2, the

slope of the linear fitting linear through the origin

could be approximately regarded as the equivalent

interstory stiffness.

Fig.2 Hysteretic curve of a typical story

As the deformation of the pagoda was dominant

with the first mode shape, substitute the equivalent

stiffness of each story to the lumped mass model and

do the eigenvalue analysis. The frequency calculated

by eigenvalue analysis was a frequency that the

pagoda experienced before it reached its peak

displacement in one seismic input. Table 3 lists the

calculated frequencies for all the seismic wave inputs.

Table 3 Frequencies calculated using equivalent

interstory stiffnesses

Test ID Input wave

Calculated

frequency

/Hz

2 SHW2(0.07 g) 0.874

3 Kobe(0.07 g) 0.917

4 ChiChi(0.07 g) 0.815

6 SHW2(0.2 g) 0.754

7 Kobe(0.2 g) 0.744

8 ChiChi(0.2 g) 0.668

10 SHW2(0.44 g) 0.6036

12 Kobe(0.44 g) 0.625

14 ChiChi(0.44 g) 0.554

The comparison of the identified frequencies and

calculated frequencies is shown in Fig.3. It can be

found that with the increase with the input PGA, the

frequency of the pagoda decreased dramatically, while

the white noise excitations indicated that the damage

of the structure did not evolved so much. That implies

most of the stiffness degradation happened during the

translational motions could be restored when the

structure returned to the initial position.

Fig.3 Comparison of the identified frequencies

and calculated frequencies

3 Conclusions

A one-fifth scaled seven-story Chinese traditional

timber pagoda was fabricated and conducted with the

shaking table test. Frequency analysis was carried out

for white noise excitations and input seismic waves. It

was found that the pagoda could experience great

stiffness degradation during translation motions, but

most of the stiffness degradation could be restored

when the structure returned to the initial position.

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EXPERIMENTAL RESEARCH ON THE RESISTANCE OF UNDERGROUND CIVIL DEFENSE STRUCTURES TO EARTHQUAKE

Cuizhou YUE Ph.D, Tongji University,China

[email protected]

Yonglai ZHENG Professor, Tongji University, China

[email protected]

Sheng DAI Assistant Professor, Georgia Institute of Technology, USA

[email protected]

Keywords: civil defense structure; shaking table test; strain; seismic resistance

The seismic performance of large underground structures buried in soils, e.g., subway and highway tunnels and so

on, has been an important topic focusing on the damages of such buried structures in large earthquakes. One focus of

the topic is on how to mitigate these damages of the underground structures. The general prototype underground

structure, as well as the other two with their central columns reformed, are modeled to compare the functions and

differences of different column forms in releasing the earthquake damages. It is found that as to the seismic

resistance properties, structure with steel pipe concrete center columns behaves well, following by that with

laminated rubber vibration isolater central columns, while the typical prototype underground structure shows last.



The 1st China-Canada Symposium on Structural and Earthquake Engineering August 20-24 2017, Vancouver, Canada BIDIRECTIONAL SEISMIC SITE RESPONSE ANALYSIS FOR SELECTED MOTIONS IN THE CASCADIA SUBDUCTION ZONE Andrés REYES MSc. Candidate, Department of Civil Engineering, The University of British Columbia, Canada [email protected] James ADINATA MSc. Candidate, Department of Civil Engineering, The University of British Columbia, Canada [email protected] Mahdi TAIEBAT Associate Professor, Department of Civil Engineering, The University of British Columbia, Canada [email protected] Keywords: Bi-directional loading, scaling factors, seismic site response The frequency content, duration, and intensity are essential characteristics of different types of earthquakes that are necessary to be considered in conducting seismic site response analysis. However, one important feature of earthquakes commonly neglected in geotechnical engineering practice is the multidirectional nature of ground motions. In certain occasions, the horizontal component of earthquakes has no dominant shaking direction, in which case it is important to consider both directions simultaneously in a seismic site response analysis. Presented in this paper is seismic site response analysis of a medium dense profile of saturated soil with a set of selected input motions consisting of crustal, sub-crustal and subduction earthquakes recorded in the Cascadia subduction zone. The analyses for each pair of earthquake motions are carried out both for one loading direction considering either one of the horizontal components, and for two perpendicular loading directions, using a coupled three-dimensional finite difference framework. The ground motions are applied without any scaling and then linearly scaling then to a single uniform hazard spectrum. The differences between scaling procedures to account for the combined response of pair of ground motions, and changes of the acceleration response, and strains obtained from the unidirectional and bidirectional analyses are closely examined in order to develop an insight on the effects of diverse characteristics of earthquake motions in seismic site response analysis. File Upload: The Extended Abstract must be submitted in PDF format, so please click on “File -> Save as -> .pdf” once you are done editing. The file name of the Extended Abstract should be: “FirstName_LastName_AbstractTitle.pdf”. At the end, upload the PDF through the conference website: http://smartstructures.civil.ubc.ca/CCSSEE17/abstract


PULL-OUT OF BASALT TEXTILE REINFORCEMENT IN ECC

Xiangxiang DOU Graduate student, Tongji University, China

[email protected]

Jiafei JIANG Assistant Professor, Tongji University, China

[email protected]

Keywords: textile reinforced concrete(TRC);engineered cementitious composites(ECC); pull-out test; bond strength

Textile reinforced concrete (TRC) has advantages in corrosion resistance and both thinner and light-weight structures,

but the brittle fracture of the cementitious matrix makes great influences on the bond strength transfer between matrix

and fiber and subsequently causes a significant decreases on the effectiveness of fibers/textiles. Therefore a new

composite system, textile reinforced engineered cementitious composites (TR-ECC), which uses engineered

cementitious composites (ECC) to replace cementitious matrix, was proposed and expected to an attractive foreground

of engineering applications for the strain-hardening behavior and multiple creak behavior of ECC. The transfer of

force from textile to ECC is accomplished through the bond properties which mainly affect the mechanical properties

of TR-ECC. The aim of this paper was to extract local-bond behaviour and propose appropriate embedded length from

pull-out tests of basalt and ECC.


DISPROPORTIONATE COLLAPSE FOR MID-RISE MASS-TIMBER BUILDINGS

Hercend Mpidi Bita University of British Columbia, Canada

[email protected]

Thomas Tannert University of Northern British Columbia, Canada

[email protected]

Keywords: Disproportionate Collapse, Progressive Collapse, Robustness, Structural Integrity, Flat-Plate System

Damage to individual structural elements after extreme loading events, such as an earthquake, is acceptable.

However, major concerns arise when this element failure triggers the impairment of connected elements and,

ultimately, the collapse of a large part of the structure. This phenomenon is also known as disproportionate collapse.

Numerous collapses of this nature have been recorded during the past decades; the World Trade Centre incident is

the most prominent one. These types of failure have brought scepticisms on the design and construction of multi-

storey buildings and, therefore, the design against disproportionate collapse is indirectly embodied in the building

regulations. For the case of mid-rise timber structures, however, using the current guidance could results to

unrealistic and expensive designs. As a consequence, design to avoid disproportionate collapse is often left solely to

engineering judgements. The general understanding is that, with adequate provisions for structural integrity, the

building can develop a new equilibrium state to redistribute the loads to the undamaged parts, and ultimately stop

the initial failure from spreading beyond the acceptable collapse thresholds. The ability to develop resistance

mechanisms that signal impending failure is also defined as structural robustness.

Alternative Load Path Analysis (ALPA) is generally considered as the preferred approach for evaluating the

robustness of structures, a strategy for disproportionate collapse prevention. Currently there are developed

guidelines, along with example analyses on how to perform the ALPA, to help designing structures that can bridge

over damages caused by abnormal loads without propagation. However, as a new method of construction, mid-rise

mass-timber buildings are not included in those guidelines, and few studies are available on this topic.

Acknowledging the growing interest in the use of timber in mid- and high-rise constructions, practical guidance and

design provisions shall be established to evaluate and improve the structural robustness. This paper presents ALPA

of a nine-storey timber building with a flat-plate system. The building has Glulam columns and Cross-Laminated

Timber designed as gravity and lateral force resistance systems for ultimate and serviceability limits states.

Nonlinear dynamic analysis is the preferred method to capture a realistic approximation of the load distribution, and

hence estimate the performance of the building following the initial damage. The study comprises different

scenarios of sudden removal of ground floor columns and investigates the subsequent structural performance.

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The reliability analysis for the considered building resulted in probability of failure of 37% for all considered

column removal scenarios. Figure 1- left and right show the vertical deformed shape of the building following the

removal of a corner and penultimate columns, respectively. The results have shown that punching shear, resulting

from rolling shear on the CLT floor panels, is the main failure mechanism for the considered structural system. The

building failure is dictated by violating the deformation capability rather than the load capacity of the CLT floor

panel, especially for corner column loss. Here, the column-to-floor connection detailing should consider a hanging

action as a resistance mechanism which allows the floor panels to be suspended on the column above. For the

penultimate column removal, although double- or triple-span panels are good for load distribution, they impose

limits on the maximum allowable deformations. For this case, a robust configuration shall account for the formation

of plastic hinges at the location of maximum bending moments in order to enable large deformations by means of

catenary action.

Figure 1: Deformation after removal of corner column (right) and penultimate column (left)

This study serves as an example to help design professionals and code developers in the analysis for

disproportionate collapse prevention for mid-rise timber buildings. In addition, it highlights safety concerns for this

emerging construction type. Focus must be on connection detailing that enables the formation of resistance

mechanisms such as hanging and catenary actions to improve structural robustness, hence meeting requirements for

disproportionate collapse prevention.


NUMERICAL STUDY ON AN INNOVATIVE WOOD-CONCRETE HYBRID TALL BUILDING STRUCTURAL SYSTEM

Jiawei CHEN Graduate student, Tongji University, China

[email protected]

Haibei XIONG Professor, Tongji University, China

[email protected]

Keywords: Timber-concrete hybrid structure; Seismic performance; Tall building

An innovative assembly-type wood-concrete hybrid structural system was proposed, which consisted of concrete

frame-tube structure as a main structure, and prefabricated light wood frame construction as substructures stacked in

the main structure. Three numerical models based on different characteristics of connections between main structure

and substructures were carried out to study the feasibility and their seismic performance. In Gravity Model, no

connections or weak connections between main structure and substructures were adopted, hence the lateral stiffness

of substructures was ignored. In Rigidity Model, effective bolt connections were employed. In Isolation Model,

substructures were connected to main structure through rubber bearings. Based on the finite element analysis, the

Gravity Model verified the reasonability of the main structure. The Rigidity Model validated that the lateral stiffness

contribution of substructures to the whole building accounted for 35%. The Isolation Model indicated that the seismic

responses of the whole structure distinctly decreased because of the isolated substructure.


EXPERIMENTAL STUDY ON THE SEISMIC PERFORMANCE OF REINFORCED CONCRETE GRID MOMENT RESISTING FRAME

Jiajun Fan Ph.D Canditate, Southeast University, China

[email protected]

Gang Wu Professor, Southeast University, China

[email protected]

Aolin Xu Master, Southeast University, China

[email protected]

Keywords: grid moment resisting frame; seismic tests; ductility; prefabricated construction; energy dissipation.

A novel grid moment resisting frame (GMRF) has been proposed and applied in high-rise buildings in the seismic area in China. It shows good seismic performance with reducing the construction material, while it is convenient to construct in the prefabricated construction method. There are just two basic elements of the grid moment resisting frame when it is built in the prefabricated construction method, as shown in Fig.1. This paper conducted an experimental study on the seismic performance of precast and monolithic grid moment resisting frames and the advantages were compared with traditional moment resisting frame and discussed in detail.

(a) Grid moment resisting frame (RC-GMRF) (b) Moment resisting frame (RC-MRF)

(c) Prefabricated grid moment resisting frame (PC-GMRF) (d) Basic elements of PC-GMRF

Fig. 1 Design and configurations of the test specimens

Three half-scale specimens were prepared and tested under lateral cyclic loading. Tests on the novel precast and monolithic grid moment resisting frames were conducted to investigate their seismic performance, and the test results were compared with the moment resisting frame (MRF) which is the control specimen. Fig.2 shows the schematic representation and photograph of the experimental test setup. All the three specimens were designed in the principle of the same amount of material, however the grid moment resisting frame had four columns and three beams because the size of these beams and columns were smaller compared with the moment resisting frame.

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(a) Schematic representation of the test setup (b) Picture of the test setup

Fig.2 Schematic representation and photograph of the experimental test setup

Fig. 3 shows the concrete cracking and failure modes of the three specimens at the end of the test. In the later stage of the test, for RC-GMRF and PC-GMRF specimens, a large amount of tiny cracks were observed at the beam and the diagonal cracks at the joint symmetrically. Ultimately, concrete crushing failure occurred at the bottom of the column with the yielding of bars in the same section in the GMRF. The lateral load-displacement hysteresis curves and the envelope curves of the test specimens are shown in Fig. 4. For PC-GMRF, the maximum strength of the specimen occurred at 30 mm displacement and the maximum displacement was 55 mm. For RC-MRF, the maximum strength of the specimen occurred at 28 mm displacement and the maximum displacement was 42 mm. PC-GMRF showed slightly larger energy dissipation in comparison with RC-GRMF. The hysteresis loops of PC-GRMF and RC-GRMF were almost the same, showing better performance than RC-MRF. The slight difference of seismic performance between PC-GMRF and RC-GMRF, including the stiffness, load-carrying capacity and ductility, is considered to be satisfactory.

`

(a) RC-GMRF (b) RC-MRF

Fig.3 Concrete crack and failure models of test specimens

(a) Load-displacement hysteresis curves (b) the envelope curves

Fig. 4 Load-displacement hysteresis curves and envelope curves of test specimens

The experimental results indicated that PC-GMRF exhibited good seismic performance, which was comparable to that of the conventional grid moment resisting frame. The reason is that the connections were in the middle zone of the beams, where the shear strength and moment are small and the reinforced bars keep elastic until the end of the test. According to the test results, the load-carrying capacity, ductility and energy dissipation capacity were improved by 44%, 29% and 30% compared with the moment resisting frame in average, respectively. This means that GMRF is a good alternative for RC-MRF in the seismic area.

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DEFORMATION LIMIT ANALYSIS OF STEEL REINFORCED CONCRETE COUPLING BEAMS

Yinghui Li PhD student, Tongji University, China

[email protected]

Huanjun Jiang Professor, Tongji University, China

[email protected]

Keywords: coupling beam; deformation limits; steel concrete composite structures.

The seismic design approach for the steel reinforced concrete (SRC) coupling beams in China is slightly different

from the North American approach. In the Chinese design approach it is required that the longitudinal rebar should be

fully embedded into the wall, while such requirement is not strictly enforced in North America. Seven full-scale

flexure-dominating SRC coupling beams designed according to Chinese specification were tested under cyclic loads.

The primary test variables were aspect ratio (span-to-depth ratio), steel ratio, and flange-web area ratio of encased

steel. One typical specimen reinforcement and test setup are shown in Figure1. The principal damage states were

investigated throughout the entire testing process. One typical specimen force-displacement hysteretic curve is shown

in Figure2 and with the damage states marked on the backbone curve.

Figure 1. Steel reinforcement details of one typical specimen (unit: mm)

Figure 2. Force-displacement hysteretic curves of one typical specimen

Based on the test results, the approach for determining seismic deformation limits of different performance levels

were established, as shown in table 1. By using ABAQUS, three dimensional finite element models for SRC coupling

beams were calibrated based on the force-displacement backbone curve and damage displacements in different

performance level. Large number of SRC coupling beam models designed according to Chinese specification were

analyzed to obtain the limit of chord rotations for each performance levels, and corresponding parametric analysis

1 1 22 3001-1500 2C20C12@752C122-2 8C28 6C20C12@6051 81859091858581 51 860700 51140 80 85 148 85 80 14051 C12@606C25L 500700 Lateral load

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were also conducted. The formulas for calculating the rotation limit of SRC coupling beams were obtained by

regression analysis. The research results can be utilized for the performance-based seismic design and seismic

performance evaluation of steel-concrete composite structures.

Table 1. Criteria for classifying performance levels of flexure-dominating SRC coupling beams.

Performance

levels Damage description Repair method

Classified criteria

Steel

tensile

strain

Concrete

compress

ion strain

Load

capacity

Almost intact

The member retains

elastic. No yielding

occurs.

Repair is not needed. fy/Es

0.0018

(cover

edge)

--

Light damage

Yielding is possible. No

crushing occurs.

(ωres<1mm)

Minor repairs may be

appropriate for structures in

extreme environment.

0.015

0.004

(cover

edge)

--

Moderate

damage

Spalling of cover concrete

occurs. (1mm<ωres<2mm)

A certain amount of repair is

acceptable. 0.03

0.005

(confined

edge)

95%Pmax

Severe

damage

The range of concrete

spalling extends. No

collapse occurs.

Repair becomes no longer

feasible. 0.072

ɛcu

(confined

edge)

85%Pmax

1. ωres is the maximum residual crack width2. εcu is the ultimate compressive strain of concrete, and Pmax is the

maximum load-carrying capacity of the member.


BUCKLING RESTRAINED ENERGY DISSIPATION DEVICES FOR ROCKING SYSTEMS

Ahmad Rahmzadeh PhD student, The University of British Columbia, Canada

[email protected]

M. Shahria Alam Associate professor, The University of British Columbia, Canada

[email protected]

Keywords: Energy dissipation; Rocking systems; Buckling restrained bars.

Recent earthquakes have shown that although structural systems designed in accordance with conventional seismic

codes were successful in securing life safety, they failed from an economic point of view due to losses and downtime.

In such structures, some components (fuses) along a load path are chosen to yield in an earthquake and detailed to

undergo large inelastic deformations before the onset of fracture or instability. Based on capacity design principles all

other components must be strong enough to ensure the full usage of the fuse capacity. In other words, the aim in the

conventional seismic codes is to confine damage in a pre-known location along primary members. However, this leads

to the permanent deformations of the structural components followed by residual drifts in the structure. Even if the

structural damages can be repaired, it is often more economic to demolish rather than to repair a building with large

residual drifts. When exposed to strong ground motions, ductile structures are highly resistant to collapse, but, there

is a significant probability of being demolished after an earthquake due to the residual drifts.

With the development of performance-based seismic design codes attention was attracted toward reducing the damage

in addition to life safety. As a response to the concerns of new seismic codes, self-centering structures were introduced

in which post tensioning tendons are incorporated to provide them with re-centering feature. In such systems, gap

opening provides ductility without damage to the primary members under lateral load. Post-tensioning forces close

the gap after load removal and the system goes back to its original position. Since these systems have almost no

inherent energy dissipation, additional elements are utilized to dissipate energy. This study is focused on a buckling

restrained bar as the energy dissipator for the self-centering structures. The energy dissipator comprises of a steel bar

dogbonned in the middle and a buckling resistant system including filler and steel tube to provide the bar with the

ability to yield in compression as well as tension. Previous research has shown that the strength of the outer tube has

a significant effect on the failure mechanism of this dissipator. In this study, finite element (FE) analyses of previously

tested specimens are done to validate the model. Then, various parameters are investigated to achieve proper insight

on its cyclic behavior and avoid undesirable failure modes.

(a)

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(b)

Figure 1. a) components of the dissipator, b) FE mesh

Figure 1 illustrates the configuration and mesh of the model. A combined material model including the Chaboche

nonlinear kinematic hardening model and bilinear isotropic model were used for the inside bar. The filler and tube

materials were modeled by an elastic-perfectly plastic model and a trilinear kinematic model, respectively. The results

of the FE analysis shows that the model is capable of capturing the cyclic behavior with satisfactory agreement as

illustrated in Figure 2.

Figure 2. The comparison between test and FE results.

seismic performance of novel spring based piston bracing

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