Lessloss Report 3 Text

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LESSLOSS RISK MITIGATION FOR EARTHQUAKES AND LANDSLIDES

LESSLOSS Report No. 2007/03

Innovative Anti-Seismic Systems Users Manual

Editor

Massimo Forni

Reviewer

Polat Glkan

July, 2007


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prodotto e distribuito da:produced and distributed by:

IUSS Press

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Tel.: (+39) 0382.516911 - fax: (+39) 0382.529131Email: [email protected] - web: www.iusspress.it

ISBN: 978-88-6198-007-5


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FOREWORD

Earthquake and landslide risk is a public safety issue that requires appropriate mitigationmeasures and means to protect citizens, property, infrastructure and the built culturalheritage. Mitigating this risk requires integrated and coordinated action that embraces a

wide range of organisations and disciplines. For this reason, the LESSLOSS IntegratedProject, funded by the European Commission under the auspices of its Sixth FrameworkProgramme, is formulated by a large number of European Centres of excellence inearthquake and geotechnical engineering integrating in the traditional fields of engineersand earth scientists some expertise of social scientists, economists, urban planners andinformation technologists.

The LESSLOSS project addresses natural disasters, risk and impact assessment, naturalhazard monitoring, mapping and management strategies, improved disaster preparednessand mitigation, development of advanced methods for risk assessment, methods ofappraising environmental quality and relevant pre-normative research.

A major objective of the project is to describe current best practice and advanceknowledge in each area investigated. Thus, LESSLOSS has produced, under thecoordination of the Joint Research Centre, a series of Technical reports addressed totechnical and scientific communities, national, regional and local public administrations,design offices, and civil protection agencies with the following titles:

Lessloss-2007/01: Landslides: Mapping, Monitoring, Modelling and Stabilization

Lessloss-2007/02: European Manual for in-situ Assessment of Important ExistingStructures

Lessloss-2007/03: Innovative Anti-Seismic Systems Users Manual

Lessloss-2007/04: Guidelines for Seismic Vulnerability Reduction in the UrbanEnvironment

Lessloss-2007/05: Guidelines for Displacement-based Design of Buildings and Bridges

Lessloss-2007/06: Probabilistic Methods to Seismic Assessment of Existing Structures

Lessloss-2007/07: Earthquake Disaster Scenario Predictions and Loss Modelling forUrban Areas

Lessloss-2007/08: Prediction of Ground Motion and Loss Scenarios for SelectedInfrastructure Systems in European Urban Environments


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ABSTRACT

This report contains the Innovative Anti-Seismic Systems User Manual, which was

prepared by all partners of Sub-Project 6 at the conclusion of the LESSLOSS Project.

The aim of this User Manual is to provide potential Designers and End users of theantiseismic devices developed within Sub-Project 6 of the LESSLOSS project withpractical tools to design structures incorporating such devices. The document contains adescription of the main features and performance of the devices and instructions for theirdesign, installation and maintenance. Comparisons among different types are alsoprovided, so as to help the User to choose the most suitable device. The antiseismicdevices developed in the framework of Sub-Project 6 are:

1.

Low Stiffness Isolators (LSIs), particularly addressed to the seismic isolation of lightstructures like family houses;

2. Electroinductive Dampers (DECS), energy dissipators suitable for the seismicprotection of large structures like bridges;

3. Steel Hysteretic elements coupled with flat sliders, addressed to the isolation ofviaducts and bridges;

4. Sliding Isolation Pendulum, curved surface sliders for the protection of buildings andother structures.

Devices 1 and 2 are developed by ALGA, Italy. Devices 3 and 4 are developed byMAURER Shne, Germany. All the devices have been subjected to severe qualificationtests. Moreover, all of them have been tested on the ENEA shaking table in real seismicconditions using natural and synthetic acceleration time-histories implemented by ENEA.STAP and VINCI, design and construction companies, contributed to the optimizationof the devices and the preparation of this document.


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TABLE OF CONTENTS

FOREWORD................................................................................................................................................. i

ABSTRACT..................................................................................................................................................i ii

TABLE OF CONTENTS...........................................................................................................................v

1. INTRODUCTION..................................................................................................................................1

1.1 INTRODUCTION..................................................................................................................................1

2. LOW STIFFNESS ISOLATORS ..........................................................................................................3

2.1 DESCRIPTION .....................................................................................................................................3

2.2 MATERIALS AND DIMENSIONS ........................................................................................................5

2.3 SPECIFICATIONS.................................................................................................................................5

2.4 CALCULATION EXAMPLES ................................................................................................................6

2.5 TESTING AND QUALITY CONTROLS ...............................................................................................8

2.5.1 Testing.....................................................................................................................................8

2.5.2 Quality controls......................................................................................................................8

2.6 INSTALLATION,INSPECTION AND MAINTENANCE ......................................................................9

2.6.1 General....................................................................................................................................9

2.6.2 Installation ............................................................................................................................10

2.6.3 Maintenance..........................................................................................................................15

3. ELECTROINDUCTIVE DEVICES..................................................................................................19

3.1 DESCRIPTION ...................................................................................................................................19


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LESSLOSS Risk Mitigation for Earthquakes and Landslidesvi

3.2 MATERIALS AND DIMENSIONS...................................................................................................... 20

3.3 SPECIFICATIONS .............................................................................................................................. 20

3.4 CALCULATION EXAMPLES.............................................................................................................. 20

3.5 TESTING AND QUALITY CONTROLS............................................................................................. 21

3.5.1 Testing .................................................................................................................................. 21

3.5.2 Quality controls ................................................................................................................... 21

3.6 INSTALLATION,INSPECTION AND MAINTENANCE .................................................................... 22

3.6.1 Installation............................................................................................................................ 22

3.6.2 Maintenance......................................................................................................................... 24

4. STEEL HYSTERETIC SYSTEMS..................................................................................................... 27

4.1 DESCRIPTION................................................................................................................................... 27

4.2 MATERIALS AND DIMENSIONS...................................................................................................... 31

4.3 SPECIFICATIONS .............................................................................................................................. 32

4.4 CALCULATION EXAMPLES.............................................................................................................. 33

4.5 TESTING AND QUALITY CONTROLS............................................................................................. 39

4.5.1 Testing .................................................................................................................................. 39

4.5.2 Quality controls ................................................................................................................... 40

4.6 INSTALLATION,INSPECTION AND MAINTENANCE .................................................................... 41

4.6.1 General ................................................................................................................................. 41

4.6.2 Type Designation Plate on each Bearing ......................................................................... 41

4.6.3 Unloading, Transportation and Storage........................................................................... 41

4.6.4 Installation............................................................................................................................ 42

4.6.5 Maintenance......................................................................................................................... 43


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Innovative Anti-Seismic Systems Users Manual vii

5. SLIDING ISOLATION PENDULUM .............................................................................................45

5.1 DESCRIPTION ...................................................................................................................................45

5.2 MATERIALS AND DIMENSIONS ......................................................................................................49

5.2.1 Concave Plates, Housing and Lens ...................................................................................49

5.2.2 Concave Sliding Surface......................................................................................................50

5.2.3 Bearing Liner ........................................................................................................................505.2.4 Other Materials ....................................................................................................................51

5.3 SPECIFICATIONS...............................................................................................................................51

5.4 CALCULATION EXAMPLES ..............................................................................................................51

5.5 TESTING AND QUALITY CONTROLS .............................................................................................58

5.5.1 Testing...................................................................................................................................58

5.5.2 Quality controls....................................................................................................................58

5.6 INSTALLATION,INSPECTION AND MAINTENANCE ....................................................................59

5.6.1 Type Designation Plate on each Bearing..........................................................................59

5.6.2 Unloading, Transportation and Storage............................................................................60

5.6.3 Installation of SIP bearings ................................................................................................61

5.6.4 Maintenance..........................................................................................................................65

REFERENCES...........................................................................................................................................67


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1.INTRODUCTION

1.1 INTRODUCTIONThe current earthquake codes for conventionally protected structures, though theyprevent collapse, allow even severe damage under strong earthquakes. In fact, the seismicresistance of the conventionally protected structures relies on their capacity to undergosignificant inelastic deformations in strong earthquakes, namely on their ductility.Moreover, the conventional techniques provide no protection to the contents of abuilding or to secondary structural features. The prevention of earthquake damage tocontents such as sensitive equipment is vital for hospitals and other critical facilities likemuseums [Pinho, 2004].

Passive control systems of seismic vibrations are innovative techniques which areworldwide considered to be already fully mature for providing mitigation of seismicdamage for civil structures and components or equipment and have proven to be reliableand cost-effective for bridges and viaducts, civil buildings, cultural heritage and criticalfacilities.

This Manual presents the most common passive control systems, which are the seismicisolation and the energy dissipation.

Seismic isolation (SI) provides a method for protecting not only the structures but alsothe non-structural members and the structure contents, by means of a considerablereduction of the seismic loads transmitted through the foundations into thesuperstructure.

The horizontal stiffness of the SI system has to be sufficiently low as to make thefundamental response frequency of the structure well below the frequency range of theground motion; the SI systems must also possess sufficient damping capability, in orderto limit the horizontal displacement to an acceptable value. For buildings the SI system isusually installed at the base or at the first floor, while for bridges and viaducts it is usuallyinstalled at pier top.

Energy dissipation (ED) consists in the use of special devices, which attract onthemselves and dissipate there a large amount of the seismic energy: for buildings they are


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LESSLOSS Risk Mitigation for Earthquakes and Landslides2

installed at the base (usually in conjunction with SI devices) or, more frequently, insidethem between positions subjected to significant relative displacements; for bridges and

viaducts they are installed (similar to the isolators) at pier top or, more frequently,between deck and abutments.

ED systems may be used in most cases where SI is not applicable, e.g. for retrofits ofbuildings that are not provided with sufficiently large gaps, construction of high risebuildings, components which require small lateral displacements, soft soils, etc.

Several types of seismic isolators and energy dissipators have been developed, both insideand outside Europe.

As regard isolators, the High Damping Rubber Bearings (HDRBs) can very often providea simple and economical isolation system, as they combine the required low stiffness anddisplacement capacity with a sufficiently large level of damping. The high-to-mediumstiffness HDRBs presently available on the European and non-European markets areexcellent for a wide variety of applications, but there exist several circumstances wheretheir use is technically difficult, if not impossible. These circumstances include, forinstance, light structures, like small buildings or electrical equipment, which are quite

important potential markets for SI.

Furthermore, the performance of presently available ED devices may be considerablyimproved from both the technical and economical points of view. Finally, otherinnovative ED devices, based on different physical phenomena, can be developed. Hencethe main objectives of Sub-Project 6 were:

- the development of innovative low stiffness isolators (LSIs) to be used in civilapplications characterized by light structures (residential houses) or for light industrialequipment;

- the development of innovative electro-inductive devices (DECS) to be used in civilapplications characterized by heavy structures (bridges and viaducts);

- the evaluation of the benefits, as well as ascertaining the limitations, of two importanttypes of devices actually available on the market: sliders coupled with hystereticelements and Sliding Isolation Pendulum (SIP) systems.


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2. LOW STIFFNESS ISOLATORS

2.1 DESCRIPTIONRegular High Damping Rubber Bearings (HDRBs) are formed by alternate vulcanizedrubber layers and steel plates, bonded together by use of chemical compounds. They areusually placed between the structure and its foundations. Their features provide highstiffness in the vertical direction (to support the dead load) and low stiffness in thetransverse direction (which minimizes amplification of ground acceleration, by leading,however, to large horizontal displacements during strong earthquakes).

During the seismic attack, the isolated structure oscillates at the isolation frequency f(usually chosen close to 0,5 Hz), which is given by Equation (2.1),

MKf h /2/1 = (2.1)

where Khis the total horizontal stiffness of the isolation system andMis the total mass ofthe isolated structure.

The horizontal stiffness (Kh) of a single HDRB is given by the following correlation:

tGAKh /= (2.2)

where Gis the shear modulus of the rubber,Ais the cross-section of the isolator and tisthe total thickness of the rubber.

The cross-section of the HDRB is proportional to the dead load to be supported whilethe total height of the rubber is proportional to the design displacement, which stronglydepends on the seismicity of the site. Heavy structures are equipped, in general, withisolators with large cross-sections: they are stable under the design vertical load, even atlarge deformations (Figure 2.1). On the contrary, light structures need low cross-sections;in this case the isolator could be much too slender and could become instable in thedeformation range of interest (Figure 2.2). Paradoxically, the seismic isolation of a lightstructure like a small house is more difficult than that of a heavy one like a nuclearreactor, referring to the same seismicity of the site.


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Figure 2.1. View of a HDRB 250 mm diameter and 72 mm rubber height which supports 800 kNvertical load up to 300% shear strain. A seismic isolator with high cross-section isstable and can support the dead load up to very high horizontal deformations.

Figure 2.2. A light structure like a statue requires a low cross-section isolator which could becameinstable. To avoid the roll-over of the isolator, a particular configuration called MULTI-STAGE is necessary. In Italy, several statues, like the Riace Bronzes, are isolated usingthis system.


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Innovative Anti-Seismic Systems Users Manual 5

One of the aims of the LESSLOSS Project was the development of a seismic isolatorcharacterized by a very low horizontal stiffness to be used for the isolation of lightstructures like family houses. This goal was reached with the development of a regularHDRB with a huge central hole (Figure 2.3). This geometrical solution reduces the cross-section area and consequently the horizontal stiffness of the isolator, providing at thesame time sufficient stability at large deformations.

Figure 2.3. Finite element model of a Low Stiffness Isolator.

2.2 MATERIALS AND DIMENSIONSThe low stiffness isolators are usually made with regular soft rubber compounds, with aG modulus equal to 0.4-0.5 MPa. Dimensions and sizes are those of the regular HDRBs,typically 500 mm diameter and 150 mm rubber height.

2.3 SPECIFICATIONSThe low stiffness isolators are similar to the high damping rubber isolators so the designrules given by international design codes have to be applied. The codes describe the wayto design, verify and test the isolators and how to design the structures where the devices

are to be installed.

The principal standards for the design of base isolated structures are:

AASHTO - Guide Specifications for Seismic Isolation Design;

EN 1998-1 - Eurocode 8: Design of structures for earthquake resistance;

prEN 15129 - Anti-seismic devices, CEN;


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Only for Italy: Ordinanza 3274 - Primi elementi in materia di criteri generali per laclassificazione sismica del territorio nazionale e di normative tecniche per lecostruzioni in zona sismica.

2.4 CALCULATION EXAMPLESThe design of the low stiffness isolators follows the same rules and procedures of aregular isolator.

In the following an example of the calculation of a low stiffness isolator system is shown.The design data are taken from the small building design example shown in LessLossDeliverable Report D33 [2006] where a single floor isolated family house has beenconsidered. The main data for the isolation system design are the following:

- total mass of the structure in seismic load condition = 472 ton;

- target isolation period = 2.58 sec;

- total isolation system stiffness = 2796 kN/m;

- number of isolators = 16;

- single isolator stiffness = 174,8 kN/m;

- single isolator vertical load in seismic condition = 300 kN;- isolator device equivalent damping = 10%;

- isolation system design displacement = 160 mm.

Using the previous design data the calculation checks of a suitable isolators system areshown in Table 2.1. In this example the checks are done using the new Italian code forthe design of structures subjected to earthquakes. According to the code the isolatorsdisplacement must be amplified by the factor 1.2 for the checks so in this example theisolator is checked for a displacement equal to 192 mm.


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Table 2.1. Calculation checks of a low stiffness isolators system


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2.5TESTING AND QUALITY CONTROLS2.5.1 Testing

The low stiffness isolators work as the well known rubber isolators, each test programfollows the international standard applied for the design or can be eventually defined forthe specific project. In any case the types of test are the following:

1. compression test in order to evaluate the capacity of the low stiffness isolator to

sustain the design static maximum vertical load. The test is performed applying the designvertical load by defined load steps and the vertical displacement is measured in order toevaluate the device vertical stiffness;

2. horizontal test performed by applying the vertical load in the seismic load conditionand applying the horizontal displacement by defined displacement steps in order tocalculate the horizontal stiffness; the load is applying at least for three cycles;

3. rubber-steel adherence test where the isolator horizontal displacement is amplified inorder to reach the rubber deformation tan = 2.5 to verify the capacity of the isolator tosustain a very heavy horizontal displacement with no rubber cracks or failure in theconnection between rubber and steel plates;

4. dynamic test applying the horizontal displacement in order to evaluate the damping

of the low stiffness isolators.

2.5.2 Quality controlsThe quality production control is applied to the raw materials of the low stiffnessisolators and to the final product.

For the raw materials the quality control is applied by using ad hoc ALGA internalprocedure to check conformity of the materials to the reference standards. For the steelparts the following checks are performed:

- chemical analysis;

- yield strength;- tensile strength;

- elongation at break.

For the rubber compound the main checks are:

- hardness;

- tensile strength;

- elongation at break;


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- density;

- compression set;

- hardness changes due to accelerated ageing;

- tensile change after accelerated ageing;

- elongation at break after accelerated ageing;

- ozone resistance test;

- bond test;

- G modulus test.

On the manufactured low stiffness isolators the main final checks are:

- dimensional checks;

- visual inspection of corrosion protection and thickness check;

- functional tests such as vertical stiffness test, horizontal stiffness test (G modulus),bonding steel-rubber test.

2.6 INSTALLATION,INSPECTION AND MAINTENANCE2.6.1 General

The philosophy of the recent design codes requires that the design and construction of anew structure must consider as a primary target the efficiency and the maintenance of theconstruction along its life time; in order to satisfy the previous requirements eachstructural component must have a maintenance plan.

For the structure where seismic isolators can be used (buildings, infrastructures) the mostsuitable criteria for maintaining the functionality is the planned maintenance that followsthe structure behaviour during its life in order to detect the factors that can cause primarydamages and to plan with an adequate time the retrofit tools to obtain the maximumbenefit with the minimum financial costs.

To prepare in advance a general retrofit plan can be very difficult due to the need ofconsidering the variation of the structure conditions during its life. The maintenance plan,in fact, must be managed as a consequence of the inspection results considering also the

velocity of degradation. For the previous reason it seems not significant to makeinspection plans with a time prevision longer that 20 years.

Due to the fact that the control inspections start with the service functioning, the firstinspection is required during the final construction inspection. In the first inspection onemust analyze the structure recording photo, comments to define a clear initial status of


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the structure and of the seismic isolation system; it represents the reference status for thefuture inspection controls. These will be characterized by a detailed analysis and acomparison with the initial status to detect possible changes that could affect the seismicisolation system response.

The present section defines the criteria and the procedures to censure an adequatecontrol and maintenance of the high damping rubber isolators manufactured by AlgaS.p.A.

2.6.2 InstallationDelivery and temporary storage. All the bearings are dispatched assembled and readyfor installation, with the main characteristics marked on an aluminium label. If thebearings are not installed immediately after their arrival on site, the final user has to makesure that they are properly stored, i.e., protected against dirt, humidity and any otherdamage whatsoever.

Inspection before installation. In order to preclude any mix-up of the bearings all thedata written on the aluminium label shall be checked and compared with the ones showed

in the shop drawings. Furthermore, before installation, parallelism of bearings plates hasalso to be checked.

Casting of the substructures. Substructures shall reach the exact level to suit thethickness of the bearing so that the superstructure will be at the specified level aftercompletion. An advisable procedure is to cast substructures leaving void spaces in theconcrete substructure in the positions foreseen for the anchors. These void spaces shouldallow suitable tolerance for positioning of the bearing. Advised to create these voidspaces are for instance some pieces of corrugated steel sheathing, the same used for post-tensioning tendons with a 10 to 15 cm diameter.


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substructure void to place theanchor bar

isolatorwith loweranchor bars

Figure 2.4. Schematic view of casting of substructure in view of positioning a Low Stiffness Isolator.

Bearing positioning. Exact level will be reached by means of three or more steel (orwood, or concrete) wedge-shaped spacers. Care shall be taken so that the maximum

deviation from the horizontal plan does not exceed 0.001 radians. A wood formworksurrounding the bearings base plate and with top level higher than plate bottom by 10mm at least, shall be made.

A wood formwork, surrounding the bearings base plate and with top level higher thanplate bottom by 10 mm at least, shall be made. At this point, the bearing may be groutedon the substructure; to this end, advised material is a non-shrink, quick setting cementmortar. If the wedges used to hold the bearing in its correct position are made ofdifferent material from concrete, they shall be removed after sufficient hardening of themortar and then voids shall be filled by the same mortar pad.

If the thickness of the quick setting cement mortar exceeds 40 mm, a suitablereinforcement shall be provided.

Note that top level of cement mortar shall not exceed bottom level of the bearing, inorder to avoid bearings embedding, with consequent problems for future removal.


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Figure 2.5. Schematic view of bearing positioning to place a Low Stiffness Isolator.

Figure 2.6. View of a Low Stiffness Isolator installed on the substructure.

isolator placed at the final level

mortar to grout theisolator and anchor bars


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Casting of the superstructure - cast in situ superstructure

Superstructure formwork shall be tightly arranged around the top plate perimeter andscaled with adhesive tape to prevent leakage of concrete during casting. Formwork willalso be arranged in such a way that the bearing will not protrude into superstructure(taking into account also the estimated settlement of scaffolding during pouring), as this

would make the bearing replacement very difficult or even impossible.

Be sure that the total height of the bearing is kept equal to that shown on the shop

drawing during the superstructure casting.

Any welding work as well as mounting and cutting-off of auxiliary structures for bearings,are not admissible except when carried out by Alga S.p.A. erectors or by any otherspecialist working on Alga S.p.A. instructions.

Upon completion of such works, the bearings must be cleaned of dirt and the coat ofpaint is to be repaired, where necessary.

Figure 2.7. LSI installed on the substructure with the formwork and reinforcement for casting thesuperstructure already placed


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Casting of the superstructure - prefabricated superstructure

As the bearings have top anchorages, the prefabricated structure shall have void roomssuitable for those ones, the beam shall be supported on the bearings or by other methodsagreed by the Engineer.

At this point, a rubber seal (with its injection and leakage pipes) shall be placed all aroundthe upper plate of the bearing, to cover the air gap between the same bearing and the

superstructure; then high strength mortar shall be cast filling up the gap and the voidrooms in the superstructure. When the mortar has achieved sufficient strength totransmit the weight of the bearings, the temporary supports shall then be removed.

In case of steel superstructure a suitable counter plate with threaded holes to fix theisolators anchor bolts must be provided and once the steel beams have been placed onthe bearings the anchor bolts must be screwed.

Upon completion of such works, the bearings must be cleaned of dirt and the coat ofpaint is to be repaired, where necessary.

Figure 2.8. Example of a LSI installed on the top of a column of a steel superstructure


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2.6.3 MaintenanceGeneral requirements and control frequency. The state of functioning andconservation of the isolators should be checked by a visual inspection made by a qualifiedinspector with adequate experience on these devices, with a frequency at least equal to theone to be done on the principal structure. It is recommended, in any case, to perform thefirst inspection within the first year after installation and to repeat every five years Table2.2.

Should the inspector verify some critical condition that he/she is not able to completely

evaluate or recommend suitable repairs, the assistance of an expert before completing theinspection must be required. In this case contact the Alga S.p.A. Technical Director of

Technical Design Office Manager.

Table 2.2. Frequency of inspections of isolators

Normal inspection. It is strongly recommended to do a normal inspection each fiveyears; the checks to be performed for a normal maintenance plan are shown in Table 2.2.In any case the normal inspection procedure is here shown and the following propertiesmust be checked:

a) sufficient capacity of moving into the structure near the isolation devices to reach eachdevice;

b) absence of macroscopic and visible defects: rubber external cracking; positions,parallelism and planarity not correct; unexpected movements and/or deformation;

c) condition of conservation and cleanness of the area surrounding the devices and inparticular of the fixing tools to the structure;

d) conservation of the anti-corrosion protection system;

e) absence of visible defects of the structural parts around the device.

INSPECTION FREQUENCY

MAINTEINANCE INSPECTION Frequency of the inspection [years]0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Principal inspection X X

Normal inspection X * X


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The results of the inspection must be registered and stored. The inspection report will beeventually completed with drawings and photos of the inspected parts. In case of visibledefects or damages that could affect the functionality of the isolators, further checks willbe performed as described in the next paragraph.

Principal inspection. The principal inspections will be performed at time intervals lessfrequent that the normal ones and normally substitute one of the normal. It is suggestedto perform a principal inspection after a seismic event or each ten years after installation.

The normal inspection has the aim of obtaining a detailed documentation of the status ofthe isolators in order to ensure that the devices are continuing to guarantee their responseaccording to the design requirements. The first inspection must be performed within thefirst year of installation of the devices and the construction must be analysed in detail todescribe the initial condition by comments, drawings and photos in order to define areference document that will be the base for the future inspections.

The principal inspection will include all the items required in the normal inspection but itmust be performed with a more detailed control. The items of particular importance thatfor each device must be checked are the following. The recovered measurementscalculated for the same load condition will be compared with the design values as a

function of the age of the structure. In case the devices show significant rotations anddisplacements they must be calculated in order to check the device functioning. Theregularity of the vertical deformation of the rubber layers will be checked according to thescheme shown in Figure 2.9.

Figure 2.9. Schematic view of vertical deformation of the rubber layers


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The absence of macroscopic cracking of the rubber will be checked and the ones that gointo the rubber cover layers of 5 mm must be carefully investigated.

For each principal inspection it is suggested to remove one isolator and test it in alaboratory to acquire the variation in time of the main properties under service loads.

Control results. According to the inspection results one of the following proceduresshould be adopted:

A) positive result: no action to be taken.

B) irregular displacement and/or rotations, or small rubber cracks with dept lower than 5mm, or damages to the corrosion protection of the steel parts: additional checks andmeasurements to be performed and repair of the corrosion protection. In case after theadditional inspection the damages are worse than before, it is recommended to contact

Alga S.p.A. before starting the procedure described in the item C.

C) structural damages to the device or to its components: repair and/or replacement ofthe device or parts of it, local or general repair of the corrosion protection, etc. It isrecommended in any case to contact immediately the Technical Direction of Alga S.p.A.before starting any device repair or substitution.

Control frequency plan

In case that during the periodic control inspections the inspector notice damages thatneed exceptional maintenance contact the Technical Director of Alga S.p.A. TechnicalDesign Office Manager before starting any operation on the devices.

The exceptional maintenance and eventual substitution of the devices is required in casethat important damages that affect the device functioning are noticed. Due to thedifferent situations that could occur for an exceptional maintenance it is not possible todevelop a general procedure but each situation must be carefully studied by the structuralengineer and Alga S.p.A. technicians in order to guarantee the functioning of the isolationsystem and also to avoid any significant damages to the structure.


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3. ELECTROINDUCTIVE DEVICES

3.1 DESCRIPTIONThe principle of operation of the Electro-Inductive Devices (DECS) is based on thegeneration of electrical power from vibration power, using the motion caused by externalexcitations due to earthquakes as primary energy source at the device mechanical input, inorder to limit and damp the motion.

The devices, in fact, must be located on structures and connected between two points inrelative movement during the earthquake excitation. Due to these movements, theapparatus develops electric energy (as in the electrical generators), subsequently dissipatedinto heat.

The basic device scheme of a non-active device includes a part equipped with permanent

magnets, in order to create a magnetic field, and another part, in relative motion withrespect to the previous one, containing the induced electric circuit and, in case, connectedto an external circuit: the selection of which parts are fixed or moveable depends ondesign choices, nature of the device, level of power to be dissipated. The use ofpermanent magnets, instead of a current excitation system, is preferable because of itssimplicity, security and ready availability of the magnetic field and the consequent higherreliability features.

The dissipation level depends on the relative velocity of the electric circuit as regards tothe magnetic field. Being the response of devices related to the operating linear velocityv, the electro-inductive dissipators can be compared with the viscous dampers; for boththe devices the response law can be expressed by the following equation:

F = C v (3.1)

where: Frepresents the response force, C and suitable constants to model the devicebehaviour.

When the velocity is small, the reaction force of the devices is negligible: this isfundamental to allow the slow movements of the structures (for example, thermal


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expansion or contraction); on the contrary, when the motion is fast, the responseincreases and the dissipation effect is required.

Compared to standard dampers, the electro-inductive devices require very lowmaintenance (limited to the anchorage to the structure), no ageing effects, no limitationon cycle life and low scattering on the response.

The operating velocity range definition is the basic requirement for the electro-inductive

devices design; for seismic applications, a reasonable average reference value for theearthquake velocity is approximately equal to vref= 0.5 m/s.

3.2 MATERIALS AND DIMENSIONSThe materials used for the DECS manufacturing are:

- hot rolled structural steel type S355JR according to EN10025;

- steel 100Cr6 for roller bearing;

- permanent ferrous magnets.

3.3 SPECIFICATIONSThe DECS devices are designed to meet the international design codes. The principalstandard for the design of structures are:



prEN 15129 - Anti-seismic devices, CEN;

Only for Italy: Ordinanza 3274 - Primi elementi in materia di criteri generali per laclassificazione sismica del territorio nazionale e di normative tecniche per lecostruzioni in zona sismica.

The codes describe the way to design, verify and test the devices and how to design thestructures where the devices are placed.

3.4 CALCULATION EXAMPLESThe calculation of the DECS device has to be performed by a non linear dynamic analysisthat can be summarized in the following steps:

- model the device as a damper in a finite element code;


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- functional tests such as checking of the allowable stroke and slow motion checking inorder to verify the DECS functioning.

3.6 INSTALLATION,INSPECTION AND MAINTENANCE3.6.1 InstallationDelivery and temporary storage. All the bearings are dispatched assembled and ready

for installation, with the main characteristics marked on an aluminium label. If thebearings are not installed immediately after their arrival on site, the final user has to makesure that they are properly stored, i.e. protected against dirt, humidity and any otherdamage whatsoever.

Inspection before installation. In order to preclude any mix-up of the bearings all thedata written on the aluminium label shall be checked and compared with the ones showedin the shop drawings. Furthermore, before installation, parallelism of bearings plates hasalso to be checked.

DECS installation. The DECS device is normally located between two parts of thestructure where relative motion can occur such as: deck and abutment wall and/or piercap and deck. In order to install the DECS, suitable anchorages must be inserted in thestructure. If a steel deck is used, the DECS anchorages are bolted to the steel beam at oneside and fixed to the pier cap or abutment by anchorages into concrete. If a concrete deckis used, the DECS anchorages are provided by anchorages to be grouted into concrete. Ifthe concrete deck is cast in situ, the DECS anchorages are directly grouted during deckpouring. If the deck is precasted, the anchorages must be inserted in the beam deckformwork.

Once the anchorages are fixed to the structure, the DECS device must be installed byinserting the connection pins that fix the DECS to its anchorages. The pin connectionguarantees the future replacement and allows the DECS to react as a truss (only axis

force) with no negative bending effects.

The DECS installation phases for a device placed between abutment and deck is shownbelow.


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Phase 1 Device positioning near the final position

Phase 2 Device positioning in the final position

Phase 3 Insertion of the connections


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Phase 4 Device final position

For future replacement the sequence starts from the last phase to the first.

3.6.2 MaintenanceGeneral requirements and control frequency. The DECS state of functioning andconservation will be checked by a visual inspection made by a qualified inspector withadequate experience on these devices with a frequency at least equal to the one principalstructure. It is recommended in any case to perform the first inspection within the firstyear after installation and to repeat every five years Table 3.1.

If the inspector verifies some critical condition that he/she is not able to completelyevaluate or recommend suitable repairs, the assistance of an expert before completing theinspection must be required. In this case contact the Alga S.p.A. Technical Director of

Technical Design Office Manager.

Table 3.1. Frequency of inspections of devices

INSPECTION FREQUENCY

MAINTEINANCE INSPECTION Frequency of the inspection [years]0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Principal inspection X X

Normal inspection X * X


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Normal inspection. It is strongly recommended to do a normal inspection each fiveyears; the following properties must be checked:

a) sufficient capacity of moving into the structure near the devices to reach each device;

b) absence of macroscopic and visible defects: unexpected movements and/ordeformation;

c) condition of conservation and cleanness of the area surrounding the devices and in

particular of the fixing tools to the structure;d) conservation of the anti corrosion protection system;

e) absence of visible defects of the structural parts around the device.

The results of the inspection must be registered and stored. The inspection report will beeventually completed with drawings and photos of the inspected parts. In case of visibledefects or damages that could affect the functionality of the DECS, further checks shouldbe performed by Alga S.p.A. Technician.

Control results. According to the inspection results, one of the following proceduresshould be adopted:

A) positive result: no action to be taken.B) irregular displacement and/or rotations or limited corrosion of the steel parts:

additional checks and measurements to be performed and repair of the corrosionprotection. In case after the additional inspection the damages are worse thanbefore, it is recommended to contact Alga S.p.A. before starting the proceduredescribed in the item C.

C) structural damages to the device or to its components: repair and/or replacementof the device or parts of it, local or general repair of the corrosion protection, etc.It is recommended in any case to contact immediately the Technical Direction of

Alga S.p.A. before starting any device repair or substitution.

Control frequency plan

The exceptional maintenance and eventual substitution of the devices is required in casethat important damages that affect the device functioning are noticed. Due to thedifferent situations that could occur for an exceptional maintenance, it is not possible todevelop a general procedure but each situation must be studied carefully by the structuralengineer and Alga S.p.A. technicians in order to guarantee the functioning of isolationsystem and also to avoid any significant damages to the structure.


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4. STEEL HYSTERETIC SYSTEMS

4.1 DESCRIPTIONSteel Hysteretic Dampers (SHD) preferably serve as base isolation in bridge construction.

They are installed in the bridge bearings area as devices independent from the bearingitself, which means they do not participate in the damping of loads from thesuperstructure. The dampers are arranged in a way that if necessary they can possiblybe replaced with a new unit after an earthquake.

Due to the steel hysteretic dampers, the total bridge bearing becomes a fixed one. Hence,the dissipation device has to be designed considering the degrees of freedom of thebearing. During a severe earthquake the steel elements undergo a plastic deformation.

The superstructure shifts on the sliding bearings activating the sliding friction. The plasticdeformation of the coupling elements produces the necessary energy dissipation.

The different damper forms are shown as examples in Figure 4.1.

Figure 4.1 Steel-hysteretic dampers with crescent moon/pin/U-clamps


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The chosen coupling elements are predominantly those forms that are subjected tobending and/or shear strain, so that the entire volume extensively and uniformlyplasticises. All other parts including joints and fastenings must not plastically deform,stresses must remain in the elastic region.

The coupled arrangement shown in the sketch in Figure 4.2 consists of parallel triangularplates with constant thicknesses that are exposed to a bending force F. The bendingmomentM(x)is linearly variable, while the shear forceQis constant:

=

l

xFlxM 1)( (4.1)

constFQ == (4.2)

The triangular shape results in a constant curvature over theheight of each plate, since the bending stress is constant andthereby an extensively uniform plasticisation occurs. It has tobe considered that the short plate stumps at the top aresubjected to large shear stress. The material has to possess

distinctive stable flow behaviour.

Figure 4.2. Bending/shear stress in a triangular element

A precise dynamic seismic analysis of a complex structure, e.g. a bridge includingsuperstructure, piers, abutments, different forms of bearings and integrated steel


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hysteretic dampers with high grade non-linear behaviour, can be executed only by meansof sophisticated design software, which, however, might be too expensive.

In this case an assessment based on the secant stiffness procedure is recommended, inparticular because it provides a quick overview. The supporting frame is assumed as anelastic structure. The curved hysteretic gradient of the steel hysteretic dampers is replacedby a bilinear gradient.

The gradient depends on the type of element as schematically shown in the force

displacement diagrams as illustrated in Figure 4.3.

Figure 4.3. Different plastic hysteretic loops (schematic)

Figure 4.4 shows the hysteretic loops of a triangular element with linear growingdisplacement amplitudes from one cycle to the next cycle.

Figure 4.4. Hysteresis of a plasticizing steel-hysteretic element

The parameters ke, kp, Fp and yp characterise the bilinear behaviour. The values can bedrawn from measurements, as it is demonstrated in Figure 4.4 (b,c,d). It can be seen thatthe dissipated energy is somewhat overestimated, which should be adjusted by correctionfactors depending on the solidity of the material.


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Satisfactory plastic ductility particularly during the violent phase of an earthquake is themain requirement for the functionality of a steel hysteretic damper. Alternatingplasticisation must not lead to short-time fatigue and thereof to brittle failure. Asindicated in Figure 4.5, mild steel is able to withstand high plastic energy dissipation for acertain period of time. The number of acceptable cycles strongly depends on thedeformation amplitude.

Figure 4.5. Resistant energy dissipation amplitude at low cycle fatigue

It is therefore essential to know the dissipation amplitudes particularly at critical locationsof the device to check functionality and reliability. Time history analyses with severalnatural or artificial acceleration diagrams are necessary for a realistic determination offunctionality and reliability.

One of the main objectives of the Lessloss Project was to evaluate the benefits and todetermine the limits of sliders coupled with steel-hysteretic elements. The specificobjective of sub-task 2.2a_2.1 was to study the effects of different types of steel hystereticelements on the response of the structure. The influence of the elastic/post-elasticstiffness ratio, which is the most representative parameter of this class of devices, wasparticularly examined.

For the calibration of the model developed by ENEA, the characterization tests with theSHD devices were carried out at the University of Armed Forces in Munich.


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4.2 MATERIALS AND DIMENSIONSThe steel-hysteretic dampers are designed for a high fatigue resistance and for operationat high levels of plastic strain. This is achieved by using high-ductility mild steels.

In the scope of the LessLoss Project different types of steel were tested. The steel-hysteretic devices and the bearing parts were composed of structural steel gradeS355J2G3 acc. 10025 with minimum tensile strength as specified in Table 4.1.Material certification is according to EN 10204, 3.1. B.

Table 4.1 Nominal values of yield and tensile strength in MPa (according to Table 3.1, EC3 1-1,conform to EN 10025)

Thickness (mm)

t 40mm 40mm < t 100mmSteel

fy(MPa) fu(MPa) fy(MPa) fu(MPa)

Fe 510 345 490 315 490

Maurer Shne designed and manufactured 37 steelhysteretic elements forcharacterisation tests at the University of Armed Forces and shake table tests at ENEA.Figure 4.6 shows the shape of the devices and the dimensions are listed in Table 4.2.

Figure 4.6. Model of a triangular plate device - geometric definition and element deformation


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Table 4.2 Geometrical data of triangular plate elements

Figure 4.7 shows an example of the so-called TR-element no. 7 (triangular plate with halfmoon head).

Figure 4.7. TR-Element 7 with half moon head

4.3 SPECIFICATIONSThe standards for the design of base isolated structures are:



prEN 15129 - Anti-seismic devices, CEN.

Element L b c t smax

# [mm] [mm] [mm] [mm] [mm]

7 250 70 50 40 60

13 190 100 50 14 96

17 190 70 70 35 36


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Standards for the design of sliding bearings and isolators:

ETA-06/0131 Maurer MSMSpherical Bearing;

EN 1337-2:2004;

EN 1337-7:2004.

The codes describe the way to design, verify and test the devices and how to design thestructures, in which the devices shall be placed.

4.4 CALCULATION EXAMPLESThe effect of a base isolation with SHD is shown with a simple example. The calculationmodel of the structures with solid foundation is shown in Figure 4.8. a), while in Figure4.8. b) it is enlarged by a base isolation. The model presents a realistic building. Mass mGand spring constant kG are kinetically equivalent to the real properties of the building.Self-damping capacity exists and corresponds (with =0.025) to the behaviour ofcommon structures. The structure is analysed without and with base isolation.

Figure 4.8. Example a) SDOF with rigid clamping b) DDOF with interconnected base isolation

The system is analysed according to the response spectrum procedure. The responsespectrum Seshown in Figure 4.9 (following Eurocode 8) is taken as excitation input. Thespectrum is not a reference spectrum Sdand the behaviour value qis not included.

Steel Hystereticdevices SHD


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Figure 4.9. Elastic acceleration response spectrum

Structure without base isolation

Starting from the following system parameters:

kgmG6104,1 = and mNkG /1085

6= ,

the natural vibration behaviour is then determined:

179,7 == sm

k

G

GG ,

Hzf GG 24,12

==

,

sf

TG

G 81,01 == .

The damping coefficient follows:

)//(105,52 5 smNmd GGGG ==

The acceleration value is taken from the spectrum for the natural vibration periodT = 0,81 s:


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/685,481,0

795,3)81,0( smsTSe ===

Multiplied by mass mGthe appertaining inertia force results as follows:

kNNF 655910559,6685,4104,1 66 ===

The lateral elastic deflection with kGis:

mu 077,01085

10559,6 6

6

= =

Structure with base isolation

A base plate with mass mBsupported on the base isolation is added. Figure 4.8. b) appliesfor the base isolation:

mNkkgm GG /1085;104,166 == quiBB kkkgm == ;101,0

6

The system in question is dual, which means that two natural mode shapes exist:

5. Self generated form 1 (Mode shape): both masses swing in the same direction with anatural period T1.

6. Self generated form 2 (Mode shape): the masses swing in opposite direction with anatural period T2.

Natural oscillation form 1 is dominant and therefore normative.

25 pieces of steel hysteretic devices type 7 with the following properties are used:

mmmu

NkNFmN100,154N/mm154,5k

mN105,226N/mm5226k

p

p

6

p

6e

0098,08,9

513003,51/

/

==

====

==


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Figure 4.10. Bilinear Hysteretic definition SHD

kquiis calculated for selected -values:

y

y

y

yykFk

ppp

qui

)0098,0(10154,051300

)( 6 +=

+=

The damping ratio qui is calculated using the assumed -values and the elasticdisplacement up:

22

)0098,0()49790(2

)()(2

uk

u

uk

uuukF

quiqui

pppp

qui

=

=

The conversion factor is calculated:

qui

qui

+

=05,0

10,0

and finally the spectral acceleration Seas well as the displacement Su:

)05,0,(),( quiequiquiquie TSTS = ,

),(2

),(

2

quiquie

qui

quiquiu TST

TS

= .


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The results for five different -values are listed in Table 4.3. It becomes apparent that thesought result lies between 0,060 and 0,090m. An additional iteration delivers the solutionu = 0,084 m.

Table 4.3 Values from iteration calculation

Figure 4.11. Elastic acceleration response spectrum with spectral values from the calculation

1 2 3 4 5 6 7

T1 T2 1 2 qui qui

0,03 1,39 0,17 1,51 -0,047 0,39 0,48

0,06 1,74 0,19 1,27 -0,056 0,45 0,45

0,09 1,99 0,19 1,20 -0,060 0,44 0,450,12 2,19 0,19 1,16 -0,062 0,43 0,46

0,15 2,34 0,20 1,13 -0,063 0,41 0,47

0,084 1,95 0,19 1,21 -0,059 0,45 0,45

m s s - - - -

8 9 10 11

Se qui x Se Su Su/

2,73 1,30 0,0635 2,12

2,18 0,98 0,0748 1,25

1,91 0,86 0,0861 0,96

3,47 1,59 0,1925 1,60

3,24 1,52 0,2108 1,41

1,95 0,88 0,0840 1,00

m/s m/s m -


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The total structure is loaded with an inertial force of:

NFFB666 1032,188,0)101,0104,1( =+== (1.1)

The structure without base plate (mG) carries a force of:

NFG66 10232,11032,1

5,1

4,1==

The associated displacement is:

muG 0145,01085

10232,16

6

=

=

This static value is scaled with 1= 1,21 (Table 4.3):

muG 0175,00145,021,1 ==

The total displacement of the structure mGis:

myG 102,00175,0084,0 =+=

The comparison of the different systems for this example is shown in Figure 4.12.

Figure 4.12. Max. oscillation without and with base isolation

0,017

0,102m

0,084


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The displacement of the SHD isolator can be calculated additionally using the followingformula:

mk

Fu

qui

BB 071,0

1087,1

1032,17

6

=

==

The calculated displacement value Su delivers a conservative result of 0,084 m. It isreasonable to calculate with the iteration of FB /kqui.

The oscillation with a period of T= 1,95 s corresponds to an Eigen angular frequency of=3,222 rad/s. The initial force is determined as follows:

NF

my

G

G

626 10243,1086,0222,3104,1

086,00145,0071,0

==

=+=

The example shows that the uG-values (movement of the structure) of the differentconcept lead to different results.

uGwithout base isolation: 0,077 m

uGwith base isolation: 0,0175 m (= 0,23 = 23%)

The relative displacement of the structure is reduced by the base isolation to 1/5. Hence,the stress due to an earthquake is negligible.


Tests shall be carried out with the steel-hysteretic devices and samples of sliding elementsto demonstrate the satisfying properties of the following general performancecharacteristics:

1.

Load bearing capacity2. Horizontal displacement capacity

3. Rotation capacity

4. Isolation characteristics / Energy dissipation

5. Wear resistance / Fatigue capacity

Each test program is according/complies with international standards applied for thedesign or, alternatively, should be defined for the specific project.


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4.5.2 Quality controlsThe quality production control is performed with the raw materials and the final product.MAURER bearings are designed according to European Technical Approval ETA-06/0131 or EN 1337. MAURER is supervised by an independent third party theMaterial Testing Institute of University of Stuttgart.

The internal quality control is supervised by control cards with details about dimensions,tolerances, design issues, applied materials and the numbers of the material certificates.

The prototype testing is executed at independent Universities to prove the performanceof the devices.

Figure 4.13 shows an example of the hysteretic loops of the dynamic test of the SHelement no. 17 with the material 1.0570 and the finite element model analysis of elementno. 17 with the same material. Basically, it seems that the yielding stress of the devicematerial is higher than the ones obtained in the tests of the material.

Figure 4.13. Dynamic test TR 250 1.0570 with 60 mm displacement

Device #17 - W0570

-70

-60

-50

-40

-30

-20

-10

0

10

20

30

40

50

60

70

-40 -30 -20 -10 0 10 20 30 40

Displacement (mm)

Force

(kN)

Test new

Spring

Spring mat. updated


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4.6 INSTALLATION,INSPECTION AND MAINTENANCE4.6.1 GeneralDetailed information is available in the European Standard EN 1337-11: Transport,storage and installation.

4.6.2 Type Designation Plate on each BearingAll important data of the bearing are shown on the plate in Figure 4.14, which is located

at the bearing top part edges.

Figure 4.14. Type data plate

Description of the short cuts on the designation plate: Type = Type of bearing or isolator (SHS = Steel Hysteretic Slider),

O-NO = Order number and date of order,

C-NO = internal sheet number and bearing number,

LOC = Axis resp. location of bearing within the building structure,

vx = Plus/minus movement in longitudinal direction,

evx = Pre-adjustment in longitudinal direction,

vy = Plus/minus movement in transversal direction,

evy = Pre-adjustment in transversal direction.

4.6.3 Unloading, Transportation and StorageThe delivered steel-hysteretic sliders are precision-made components. Therefore,functionality can only be guaranteed if the devices are carefully treated. Sliding plate resp.bearing top part and lower bearing part are assembled parallel to each other in the

workshop and safely fixed for transportation by means of assembly brackets. Theassembly brackets are red marked and must be kept until the bearing is completelyinstalled. This means the bolts of the brackets must not be loosened until the bearing is

SHS ... KN

66**** / 05-2007

no. 1

1400140 0


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located at the final position and is safely grouted to the superstructure or substructurerespectively.

Immediately upon receipt of the bearings at site, the bearings must be examined fortransportation damages. In case of any damage, Maurer Shne shall be informedimmediately in written form and the damage must be indicated in the shippingdocuments, too.

Bearings, which cannot be installed in the structure immediately, should be stored in asuitable place, covered with well-ventilated tarpaulins, to protect them from damage andfouling with dirt.

4.6.4 InstallationThe steel-hysteretic elements are located between two parts of the structure, whererelative motion occur, e.g. between deck and abutment, or pier cap and deck. In order toinstall the steel-hysteretic elements suitable anchorage must be inserted in the structure.

The steel-hysteretic elements shall be fixed to the structure by bolts to allow replacement

in case of damage or fatigue.

The anchorages are fixed to the structure with bolts. The bolt connection enables a futurereplacement.

Figure 4.15. Location of Steel-hysteretic devices in a structure


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4.6.5 MaintenanceIt is recommended to perform the first inspection after installation and to repeat theinspection every five years. Functionality and conservation of the steel-hystereticelements shall be checked visually by a qualified, adequately experienced inspector.

If the inspector finds a critical situation or a situation difficult to judge, it isrecommended to require the assistance of an expert before completing the inspection. Inthis case contact Maurer Shne Munich.

The five-yearly inspection shall be included in the maintenance program for the structureand shall check the following questions:

a. Is there sufficient space left between the isolated structure and the abutment after anearthquake or other movements?

b. Has the device itself sufficient capacity of movement?

c. Has the device any macroscopic and visible defects resulting from unexpectedmovements, deformation, fatigue or corrosion?

d. Is the conservation in good condition and are the device and its surrounding clean?

e. Is the fixation to structure, e.g. bolts OK?

The results of the inspection must be reported in a written form. The inspection reportshall be eventually completed by drawings and photos of the inspected parts. In case of

visible defects or damages that influence the functionality of the steel-hysteretic devices, afurther inspection shall be performed by Maurer Shne.

An exceptional maintenance and eventual substitution of the device is required ifdamages affecting the functionality of the device occur. Each situation must be studiedcarefully by a structural engineer and Maurer Shne technicians in order to guarantee thereliability of the isolation system and to avoid damages to the structure.


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5. SLIDING ISOLATION PENDULUM

5.1 DESCRIPTIONThe Sliding Isolation Pendulum Bearing (SIP) consists of a pivoting solid steel lens with aslider, which slides along a stainless steel spherically curved sliding surface (the concaveplate) in bridge bearing quality. This lens is a double spherically shaped solid steel part,

which matches the stainless steel concave curved sliding surface, and an opposing convexspherical surface, which allows its containment in a load bearing housing (the housingplate) while its free rotation (pivoting) is allowed. A self-lubricating bearing liner materialcalled MSMis fixed to the sliding surface of the lens and to the housing. A environmentrubber apron is provided around the bearing. The housing and concave plates are lockedin with suitable temporary shipping and transportation restraints at the edges of thehousing plates.

Radius

housing

Lens

MSM

Concave sliding plate withstainless steel sheet

Figure 5.1 Principle sketch of SIP

The Isolator Slider Material is MSM. The tolerance definition of the inner bearingcomponents and detailed inner isolator geometry were developed by the supplier and areproprietary information protected by applicable law for the protection of intellectualproperty and patents. Therefore any information provided about these issues must betreated strictly confidentially.


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Theoretical and mathematical description

The bearing types SIP are designed for friction values of = 3 up to 12%, acting at thespecified design force level of the bearing. The design force level is the load duringservice and design limit state.

The MAURER sliding isolation pendulum bearings are modeled according to theequations below.

Figure 5.2. Characteristic hysteretic loop of a spherical sliding isolator

Figure 5.3. Principle sketch of a spherical sliding isolator of SIP type


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Effects of damping produced by friction between the sliding couple (stainlesssteel against sliding liner material) can be taken into account by means of thedamping ratio eff ,which is defined as:

rectanglebedcircumscriofarea

loophysteresisofarea2=

eff [5.6]

where area of the hystereticloop= DW4 [5.7]

area of the circumscribed rectangle= 24 DKeff [5.8]

effis obtained by introducing [5.7], [5.8] and [5.4]:

)(

22

RD

R

RDeff

+

=

+

=

[5.9]

2eff for D/R .

Radius relation to period: R = 22

2

25,0)2(

TTg

[5.10]

Upward displacement depending on displacement 22 DRRV = [5.11]

Static re-centring criterion:D/R>must be fulfilled [5.12]

Dynamic Self-centring capabilitymust be fulfilled

ss EE 25,0 [5.13]


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-ESis the reversible stored energy (elastic strain energy, potential energy andkinetic energy)

)cos1( ds RWE = ; dthe design angular displacement [5.14]

- EHis the energy dissipated by hysteretic deformation

dh RWdRWEd

sincos0

== [5.15]

5.2MATERIALS AND DIMENSIONS

The materials shall conform to the standards specified herein.

5.2.1 Concave Plates, Housing and LensAll bearing parts except bolts, liner and stainless steel sheets are composed of structuralsteel grade S355J2G3 acc. 10025 with minimum tensile strength as specified in Table5.1.

Table 5.1 Nominal values of yield and tensile strength in MPa (according Table 3.1, EC3 1-1,conform to EN 10025)

Thickness (mm)

t 40mm 40mm < t 100mmSteel

fy(MPa) fu(MPa) fy(MPa) fu(MPa)

Fe 510 S355 345 490 315 490

All parts shall conform to the dimensions of the drawings within the acceptable tolerancecriteria set herein:

Flatness requirement for the mechanical machining (lathing) of the concave andconvex surfaces: the tolerance of flatness over the plan dimension (diameter D ofconcave or convex surface) must be equal or less than 0,0008 x D,

Flatness requirement for the mechanical machining (milling) of the flat upper andlower bearing surface: the tolerance of flatness over the plan dimension (diagonal Dof upper or lower bearing surface) must be equal or less than 0,0007 x D.

Steel plates certification and test certificate is according to EN 10204:3.1.B


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5.2.4 Other MaterialsPerimeter protective seal: EPDM (Ethylene Propylene) or any other suitable material.

Assembly brackets: S235JRG2, S355J2G3 according to EN 10025.

Restraining Plates Connection Bolts: 8.8 quality according to ISO 898.

5.3 SPECIFICATIONSDesign rules given by international design codes have to be applied.

The principal standards for the design of structure base isolation are:



prEN 15129 - Anti-seismic devices, CEN.

The principal standards for the design of bearings and isolators are:

- ETA-06/0131 Maurer MSMSpherical Bearing,

- EN 1337-2:2004 and EN 1337-7:2004.

The codes describe the way to design, verify and test the isolators and how to design thestructures, in which the devices are placed.

5.4 CALCULATION EXAMPLESThe effect of a base isolation is shown with a simple example. Figure 5.4a) shows themodel of a structure with solid foundation and Figure 5.4b) a structure with baseisolation. The model presents a real building. Mass mG and spring constant kG arecoordinated that way as to kinetically equivalent replace it. Self-damping capacity existsand corresponds (with =0.025) to the behaviour of common structures. First of all the

structure will be analysed without and with base isolation thereafter.


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Figure 5.4. Example a) SDOF with rigid clamping b) DDOF with interconnected base isolation

The system is analysed according to the response spectrum procedure. The responsespectrum Seshown in Figure 5.5 (following Eurocode 8) is taken as excitation input. Thespectrum is not a reference spectrum Sd and the behaviour value q is not included.

Figure 5.5 Elastic acceleration response spectrum

Structure without base isolation

Starting from the following system parameters:

Sliding Isolation


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mNkkgm GG /1085;104,166 ==

The natural vibration behaviour is determined:

sf

THzfsm

k

G

GG

G

G

GG 81,0

1;24,1

2;79,7 1 ======

The damping coefficient follows:

)//(105,52

5

smNmd GGGG ==

Take the acceleration value from the spectrum for the natural vibration period T=0.81s:

/685,481,0

795,3)81,0( smsTSe ===

Multiplied by mass mGthe appertaining mass force results as follows:

kNNF 655910559,6685,4104,1 66 ===

The lateral elastic deflection with kGis:

mu 077,01085

10559,66

6=

=

Structure with base isolation

A base plate with mass mBsupported on the base isolation will be arranged. Figure 5.4b)applies for the base isolation:

mNkkgm GG /1085;104,166 == quiBB kkkgm == ;101,0

6

The system in question is dual, which means there are two natural oscillation forms:

1. Self generated form 1, where both masses swing in one direction, self oscillation timeT1.

2. Self generated form 2, where the masses swing in opposite direction, self oscillationtime T2.

Natural oscillation of form 1 is dominant and therefore normative.


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The radius of curvature of the Sliding Isolation Pendulum bearings is chosen as r = 2500mm = 2,5 m and the friction value = 0.06. kqui is calculated for selected -values,

where

gmmG BG += )(

is the total load transmitted via the isolation system:

81,9)101,0104,1(06,0

5,21

1 66 +

+=

+==

uG

urkk quiB

Table 5.2 shows the computation result for five u-values: =0,050; 0,075; 0,100; 0,125;0,150 m. T1and T2are the natural periods of 1st and 2nd natural mode. 1and 2 are theappertaining amplitudes, i.e. conditions of the amplitudes of m1mG to theamplitude of m2mBin the respective natural mode. A positive means a movement inthe same direction of mGand mB, a negative means an opposite-one. The second naturalmode is suppressed, i.e. T is set = T1.

The spectral acceleration value Seis taken from the elastic response spectrum (Figure 5.6).

Table 5.2 Values from iteration calculation

Iteration


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Figure 5.6. Elastic acceleration response spectrum with spectral values from the

calculation

The damping ratio quiis calculated for the assumed - values:

+

=

+=

06,05,2

06,02

2

u

r

uqui

The conversion factor is calculated:

qui

qui

+

=05,0

10,0

and finally the spectral acceleration Se as well as the displacement Su

)05,0,(),( quiequiquiquie TSTS =

),(2

),(

2

quiquie

qui

quiquiu TST

TS

=


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The calculation for five -values is shown in table 4.2. The sought result is between 0,075and 0,100m. A additional iteration deliver the solution u = 0,091 m.

The total structure is loaded with an inertial force of:

NFFB666 10224,1814,0)101,0104,1( =+==

The structure without base plate (mG) carries a force of:

NFG66 10140,110221,1

5,1

4,1==

The associated displacement is:

muG 0134,01085

10140,16

6

=

=

This static value is scaled with 1= 1,171 (table 4.2):

muG 0154,00134,0171,1 ==

The total displacement of the structure mGis:

myG 107,00154,0091,0 =+=

The following comparison of the different systems is shown in Figure 5.7.


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Figure 5.7. Max. Oscillation without and with base isolation

Alternatively, the displacement of the SIP isolator can be calculated using the followingformula:

mk

Fuqui

BB 078,0

1059,1510221,1

6

6=

==

The calculated displacement value Su delivers a conservative result of 0,091m. It isreasonable to calculate with the iteration of FB/kqui.

The oscillation with a period of T = 2,10s complies with result to an Eigen angularfrequency of =2,992 rad /s. The initial force is determined to:

NF

my

G

G

626 10146,10914,0992,2104,1

0914,00134,0078,0

==

=+=

The example shows that the uG-values (movement of the structure) according to differentconcept lead to different results.

uGwithout base isolation: 0,077m

uGwith base isolation: 0,0154m (= 0,2 = 20%)


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The relative displacement of the structure is reduced by the base isolation to 1/5. Hence,the stress due to an earthquake is negligible.


Tests shall be carried out on the Sliding Pendulum Isolator and samples of sliding

elements to demonstrate the satisfying properties of the following general performancecharacteristics:

1. Load bearing capacity;

2. Horizontal displacement capacity;

3. Rotation capacity;

4. Maximum frictional resistance to service movements;

5. Isolation characteristics;

6. Wear resistance of the friction material.

Each test program is according to international standards applied for the design or can be

alternatively defined for the specific project.

5.5.2 Quality controlsThe quality production control is performed with the raw materials and the final product.MAURER bearings are designed according to European Technical Approval ETA-06/0131 or EN 1337. MAURER is supervised by an independent third party Material

Testing Institute of University Stuttgart.

The internal quality control is supervised by control cards with details about dimensions,tolerances, design issues, applied materials and the numbers of the material certificates.

The prototype testing is executed at independent Universities to check the performanceof the devices.


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Figure 5.8. MAURER quality control

5.6 INSTALLATION,INSPECTION AND MAINTENANCEDetailed information is available at the European Standard EN 1337-11 Transport,storage and installation.

5.6.1Type Designation Plate on each BearingAll important data of the bearing is shown on this plate, which is located at the bearingtop part edges.

Description of the short cuts on the designation plate:

SIP ... KN

66**** / 05-2007

no. 1

1400140 0


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Type = Type of bearing and service load,

O-NO = Order number and date of order,

C-NO = internal sheet number and bearing number,

LOC = Axis resp. location of bearing within the building structure,

vx = Plus/minus movement in longitudinal direction,

evx = Pre-adjustment in longitudinal direction,

vy = Plus/minus movement in transversal direction,

e vy = Pre-adjustment in transversal direction.

5.6.2 Unloading, Transportation and StorageThe delivered SIP bearings are precision-made components. Functioning can only beguaranteed if they are carefully treated. Sliding plate resp. bearing top part and lowerbearing part are assembled parallel to each other in the workshop and are safely fixed fortransportation by means of securing assembly brackets. By all means position of thebearing parts must be kept until the bearing is completely installed. This means, the boltsof the securing devices must not be loosened until the bearings will be located in the finalposition and be safely grouted to the superstructure or substructure respectively.

Immediately upon receipt of the bearings at site, they must be examined fortransportation damages. In case of any damage being found, immediate notice should begiven to MAURER in written form and must be indicated in the shipping documentsrespectively.

Bearings, which cannot be installed in the structure immediately, should be stored in asuitable place, covered with well-ventilated tarpaulins, to protect them from damage andfouling with dirt.


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5.6.3 Installation of SIP bearingsa) Preparation of bearing plinth

b) Setting and levelling of lower bearing anchor plate (flatness tolerance according to SIPdesign drawings) and inserting two 10-15mm diameter steel chains into the joint


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c) Grouting of anchor plate within the curing time of the resin! See also additionallyenclosed information about grouting procedure of bearing bottom plates. A suitablegrout is e.g. PAGEL V1 (Company PAGEL; www.pagel.com). The grout joint has tobe free of air bubbles!

d) After grout/resin has gained 50% of service hardness the bearing is placed by craneand bolted to the lower anchor plate by bolts of high strength grade 10.9.


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e) Placing of upper anchor plate onto the bearing and bolting it to upper bearing plate

f) IMPORTANT: Protection of bearing against dirt and concrete before superstructure iscast onto the upper anchor plate

8/13/2019 Lessloss Repor

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