MAURER Seismic Protection

7/29/2019 MAURER Seismic Protection

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MAURER Seismic Protection



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Contents

1. Introduction1.1. General1.2. General aspects of seismic protection1.2.1. Protection by energy distribution1.2.2. Protection by basis isolation and dissipation

2. Bearing elements for basis isolation2.1. Rubber Bearings2.1.1. Low damping rubber bearings (LDRB)2.1.2. High damping rubber bearings (HDRB)2.1.3. Rubber bearings with lead core

2.2. Sliding bearings2.2.1. Sliding bearings without recentering (SI)

2.2.2. Sliding isolation pendulum (SIP) - recentering2.2.3. Double sliding isolation pendulum type D - recentering

3. Hydraulic coupling and damping elements3.1. Shock transmitter (MSTU)3.2. Shock transmitter with overload protection (MSTL)3.3. Hydraulic Damper (MHD)

4. Expansion joints for seismic movements(type DS / DS-F)

5. Non-linear structural analysis

Maurer Söhne Head Offi ceFrankfurter Ring 193, 80807 München / GermanyPhone ++49 - 89 - 3 23 94-0Fax ++49 – 89 - 3 23 94-3 [email protected]

Seite

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1. Introduct ion

Today’s state of art allows to adopt all kind of

structures to the different loads due to traffic,wind, seismic events etc.. Thus the tensionsare proportionally distributed to the wholestructure or they are reduced from thebeginning by isolation technique andadditional damping.

As each structure shows individualcharacteristics, no general concepts do existfor seismic protection. Project relevant choiceof the mechanical components is required toindividually calculate and design the structurefor seismic events.

A specially adapted seismic protection systemavoids personal injuries and guarantees fulloperational reliability after a seismic event.Besides, structural damages are avoided.Thus the structure is always in service andcan counteract aftershocks without anydamages. No repair of components or structure is required, which proofs that such aprotection systems is not only technically butalso economically highly efficient.

The mechanical MAURER components for

seismic protection listed below have beensuccessfully installed in numerousconstructions. Dependent on the requirementsfor individual components, different standardsas EURO NORM, AASHTO, BRITISHSTANDARD, DIN or others can be based.

Despite the fact, that some fundamentalapprovals for seismic engineering have beenintroduced in the passed years, each projectshows must be designed individually. Thisautomatically creates custom-made seismicprotection components such as isolators and

dampers.

Fig.1 :Tejo-Bridge Lisboa with slidingbearings and swivel-joist expansion

joints type DS

Fig.2 :New Akropolis Museum, Athens,with SIP basis isolation

Fig.3 : Rion-Antirion Bridge / Greecewith swivel-joist expansion joints type DSand Fuse Box



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1.2.General aspects of seismic protection

1.2.1 Protection by energy distribution

Energy distribution means, that the seismicenergy proceeding from the subsoil isdistributed to different structural componentsand thus significant energy accumulation isavoided.

For this, special components, so-called ShockTransmission Units are used, which allowrelative movements due to temperaturedifferences and shrinking/creeping duringnormal service load (fig. 4). Only with seismiceffects or other suddenly arising effects due totraffic or similar, MAURER ShockTransmission Units (MSTUs) act as securingdevices (fig. 5). The horizontally acting seismicforces due to earthquake or traffic aretransmitted to several structural parts, whichincreases the structural capability to storeelastic and also kinetic energy. Simultaneouslythe structural movements decrease comparedto the design without MSTUs. The horizontalforces are thus distributed more or lessconstantly to the whole construction and evennon-uniform structural loads with tensionpeaks are avoided.

Contrary to above mentioned assumption,seismic loads and deformations are not thecause rather the effect of the short dynamicappearance of huge stored energy from thesubsoil. For a more efficient effect of theprotection system, it must obey the seismiccharacter. The pure distribution of seismicenergy to different structural parts is usuallynot sufficient to adequately protect thestructure. The seismic energy still reaches andgoes through the structure without being

weakened, as each axis provided with aMSTU becomes a fixed axis in case of seismicevent (fig. 6), so that the complete structure isaccelerated.

Fig. 4: Bearing system with MSTUs

Longitudinal direction of bridge

Fig. 5: Bridge during service loadwith inactive MSTU`s

MSTU

Fig. 6: Bridge with active MSTU´s duringseismic event

structuraldeformation

seismic stimulation



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1.2.2. Protection by basis isolation anddissipation

Basis isolation and dissipation result indecreasing the energy applied to the systemand the transformation from energy to heat.This is also designated as “energy approach”,which especially takes into account the energycharacter of a seismic event. Applying thissystems means prevention of cost-intensivestructural stiffening and attainment of maximum protection of persons and structure.

Two statements are applied at the same time:

Seismic isolation:The superstructure respectively the structureis separated from the subsoil. This method,also called seismic isolation, automaticallylimits the energy effecting the structurerespectively reduces the same considerably. As a result the natural structural period(periodical displacement) is increased, whichcauses a considerable reduction of thestructural acceleration during seismic event(fig. 7). Depending on the installed type of isolator, the isolators do not only guaranteethe vertical load transmission but also the

restoring capacity during and after a seismicevent. Restoring means, that thesuperstructure, which has been displaced fromneutral position during the seismic event, isautomatically recentered. Thus, accumulatedstructural displacements in one direction areavoided!

Energy dissipation:By means of passive energy dissipation(transformation of energy into heat) theremaining energy, which effects the structuredue to isolators, is effectively dissipated by

additional damping elements. Thus thealready dissipated energy does no more effectthe complete structure (fig. 8).

This energy reducing method, which combinesseismic isolation with energy dissipation,produces the best possible seismic protection.

Summarized the following demands on basisisolation have to be applied:

●vertical load transmission●free movement in all directions●damping of structural vibrations●recentering in neutral position

period [s]

acceleration [a]

2

1

acceleration of a non-isolated structure

accelerationof isolatedstructure

Fig. 7: Characteristic response spectrumof a bridge

periodical displacement

reduction of a

Fig.9: possible arrangement of dampers

no damages

seismic stimulation

nostructuraldeformations

damper

isolators

Fig. 8: possible arrangement of isolators with damping effect

= multidirectional seismic isolator withrestoring force

= damper



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If flexible piles do exist – e.g. high piles in themiddle of a bridge – the restoring force for theseismic protection system and the

superstructure is guaranteed by the flexibilityof the piles, which act as rod-shaped springs.In that case, longitudinally fixed bearings areinstalled on the flexible piles (fig. 10). Fixedand longitudinally fixed bearings do not allowany relative movements between pile andsuperstructure. Flexible piles are bending on aseismic event, thus creating restoring forces. At the same time, this system isolates thesuperstructure at least mostly from the subsoil. A slight disadvantage of this system is themissing isolation in lateral bridge direction, sothat the resulting lateral forces have to be

transmitted by the bridge bearings.

Particularly with huge structures (bridges witha length exceeding 1500m) a completeisolation often is not practicable. Thus, thissolution does not offer the full seismicisolation, however guarantees a significantenergy reduction and a pleasing forcedistribution within the structure.

Moreover, this solution is highly qualifiedretrofit of existing bridges.

The method of energy reduction makes use of isolation advantages and energy dissipation,so that it is the technically most effectivesolution with high safety reserves at extremelyhigh efficiency.

With this concept the building is protectedsuch that also in case of aftershocks theprotection system is still operational.

To adjust movements of the superstructure atthe abutments and to bridge the gap,earthquake-fit expansion joints are installed

(fig. 12). These expansion joints must adjustquickly arising, alternating relative movementsin all directions (x, y and z) without beingdamaged or damaging the structure.

Fig.12: Movements at the expansion joint

Fig. 10: Bearing system with dampers andflexible piles

Fig 11: Bridge with protection systembased on fig. 10

seismic stimulation

slidingbearing

flexible piles withfixed bearings

Dehnfuge

DeckWider-lager

Lager



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2. Bearing elements for basisisolation

2.1. Elastomeric bearings

2.1.1. Elastomeric bearings

Elastomeric isolators consist of severalsuperposed steel sheets, which are connectedby a special elastomer (fig. 13). The isolatorstransmit the vertical loads from the structureby simultaneous rotation and automaticl re-centering, which is dependent on the height of the elastomer and its shear force. Last-mentioned is between 0.6 and 1.0 N/mm².Damping of the elastomeric isolators totals to6 – 15 %, dependent on demands, and canthus individually be adjusted to each structure.However in many cases no sufficient structuralprotection and energy dissipation can beobtained in case of a seismic event, using onlythis type of isolator. A combination withviscous dampers is technically andeconomically required.Depending on the system demands as e.g.floating bearing system, partially floatingbearing system or securing by flexible piles,besides isolators movable on all sides alsofixed bearings are used to obtain a specialfunction for service and seismic loads.Thus the choice of the appropriate type of bearing resp. isolator depends on thestructural demands, the loads, the horizontalstiffness criterion and the required energydissipation.

2.1.2. High damping elastomeric bearings

High damping elastomeric bearings include anelastomer with high damping characteristics.These “High Damping Rubber (HDR)” show

an improved contact area betweenelastomeric molecule and filling material,

which leads to higher damping rates ζ = 0.10to 0.20, compared with “Low Damping Rubber

(LDR)” ζ= 0.04 to 0.06 and thus results in amore complete hysteresis.

Fig.13: Elastomeric bearing with lead core

Fig.14: Elastomeric bearingwithout lead core

OhneBleikern

Mit Bleikern:

Fig.15: Hysteresis of an elastomericbearing with/without lead core



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2.1.3. Rubber isolatores with lead core

Similar to conventional rubber bearings the

vertical load of a lead rubber bearing (LRB)with lead core is accommodated by therubber. To increase the damping up to 40 %,additionally one ore more lead cores arevertically inserted into the rubber (fig. 14 &16). In case of horizontal displacements, adistinctly higher resistance force is activateddue to the lead core, that way providing amore complete hysteresis with higher dampingeffect (fig. 15).

2.2. Sliding isolators

Sliding bearings consist of an upper and lower bearing plate and an interposed sphericalMSM

®sliding part. This type of bearing

transmits vertical loads to the sliding surface,obtaining the horizontal displacement. Thefriction coefficient between sliding part andbearing plate determines the dissipation,which results from the relative displacementsof the structure to the subsoil (Fig. 17, 18 and19).Depending on the demands, the damping of the sliding isolators is 5 to 35 %. To achieve a

higher damping rate without increasing thefriction and thus to put at risk the isolatingcapacity, the isolators may additionally becombined with viscous dampers.

To serve the individual demands to dissipationof different kinds of structures, the frictioncoefficients are individually adapted to thesestructures.

Test and controls of independent institutes(e.g.: University of California at SanDiego/U.S.A., the University of the German

Armed Forces at Munich/Germany amongothers) confirm the efficiency and thefunctional characteristics.

Generally there are to different types of slidingisolators:

type SI: isolator without recenteringcapacity

type SIP and SIP-D: isolator withrecentering capacity

Fig.16: Rubber isolators with lead core (LRB)

Fig.17: Sliding isolator pendulum (SIP)with recentering capacity

Fig.18: Sliding isolator (SI) withoutrecentering capacity

Fig. 19: Sliding isolation pendulum (SIP)installed in a building



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2.2.1 Sliding isolators without recenteringcapacity (SI)

Sliding isolators type SI (= sliding isolator)without recentering capacity consist of ahorizontal sliding surface, allowing adisplacement and thus dissipating energy bymeans of defined friction between both slidingcomponents MSM

®and stainless steel (fig. 20

& 21).

The hysteresis curve of fig. 22 shows thetypical course of friction force in dependenceon the displacement direction, compared witha sliding isolation pendulum with recentering

capacity. As, apparent from the hysteresis curve, noelastic energy is created, thus no restoringforce exists within the system. To yet achieveresetting, elastic components must beinstalled, which produce the relevantcounteracting force for the respectivedisplacement, which is necessary for recentering. Depending on the design of thesuper- and substructure, also an arrangementof an isolator turned about 180° (“upsidedown”) is possible.

Fig.20 : Sliding isolator type SI

Fig.22 : Hysteresis curves of sliding isolatorsand sliding isolation pendula

Fig.21 : SI - sliding isolator for 130,000 kNload (SLS)

s

F

SI

SIP undSIP-D



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2.2.2 Sliding isolation pendulum withrecentering capacity (SIP)

Compared with sliding isolators, slidingisolation pendula (SIPs) with recenteringcapacity have a concave sliding plate (fig. 24).Due to geometry, each horizontaldisplacement results in a vertical movement of the isolator. Thus a part of kinetic energy istransformed into potential energy. Thepotential energy, stored by the superstructure,which has been pushed to the top,automatically results in recentering thebearing into neutral position This restoringforce can also be taken from the hysteresis

curve for types SIP and SIP-D (fig. 23.).

The sliding isolation pendula are excellentlysuited to isolate the structure from the subsoil.They remain horizontally flexible, dissipateenergy and recenter the superstructure intoneutral position.

2.2.3 Double sliding isolation pendula type Dwith recentering capacity (SIP-D)

In case of a type D sliding isolation pendulawith recentering capacity the sliding partmoves between two symmetrical concavebearing plates (fig. 23).With the same diameter, the type D bearings

perform double the displacement as simplesliding isolation pendula. Thus the type Disolators with movements +/-300mmfrequently guarantee a more efficient solution. Also the outline of this type of isolator becomes smaller, as well as the eccentricitiesare shared to super- and substructure.

Fig. 23 :Characteristic hysteresis curve of asliding isolation pendulum (SIP)

Fig.22 : Sketch of a sliding isolationpendulum (SIP)

Fig.23 : Double sliding isolation pendulum(SIP-D)

Keff = effektive

Verschiebung

Kraft

KSI = Isolatorsteifigkeitµ W = Reibkraft

Ki = initiale Steifigkeit

D

F

Keff = effektive

Verschiebun

g

Kraft

KSI = Isolatorsteifigkeitµ W = Reibkraft

Ki = initiale Steifigkeit

D

F



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3. Hydraulic coupling and dampingelements

3.1 Shock Transmitter

MAURER Shock Transmission Units (MSTUs)are maintenance-free, hydraulic devices, torigidly connect structures, which are moveablerelatively to one another, in case of suddenlyarising dynamical shocks as e.g. earthquakes,brake forces etc.. MSTUs are installedseparately into the structure or combined withbridge bearings. In specialist literature alsoterms like Lock-Up Device (LUD), RigidConnection Device (RCD), SeismicConnectors, Buffers or similar can be found for these mechanical devices.

Dependent on the motion speed, the shocktransmitter reacts with a corresponding force(fig. 26).Very slow movements e.g. from temperature,shrinkage/creeping etc. do not result insignificant forces. With these forces the fluidmoves within the hydraulic cylinder withoutcreating worth mentioning forces.

If sudden acceleration between the connectedstructural elements result e.g. due to seismicor brake forces, which lead to motion speedswith more than 0.1 mm/s, the shocktransmitter reacts with a force(fig. 26), thatmeans, no movements between theconnected structural elements are allowed. Arigid connection between the structuralelements is thus created. With this quickrespectively sudden movements, the hydralicfluid cannot move from one side of the cylinder to the other, so that the MSTU blocksmovements.

Both functional characteristics are:

No worth mentioning force (max. 10 % of thedesign force) resulting from movements due toshrinkage/creeping and changes intemperature.

Sudden blockade respectively formation of resisting force (= design force = Fn) for suddenly arising movements due to traffic,earthquake or similar.

Fig.25: Shock-Transmitter

Fig. 24: Shock-Transmitter (MSTU)

Seal-systemFluid chamber Orifice

piston

[F]

[v]

A) Service- B) Erdbebenlastfall

0,1 mm/s

Fig. 26: force [F] - speed [v] –graph for MSTU

Fn

[F]

[s]

[F]

[s]

A) Servicelastfall B) Erdbeben

Fn

Fig. 27: force [F] - direction [s] –graph for MSTU



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3.2. Shock Transmitter withoverload protection (MSTL)

Shock transmitter can additionally beequipped with a force limiter, which reducesthe maximum limit force (Fl) to an individuallydeterminable maximum value. Usually thisvalue is calculated insignificantly above thenominal shock force (Fn) or can be stipulatedindividually.

If the maximum value of the force is obtaineddue to excessive energy supply, an„intelligent“ control mechanism allows amovement of the MSTL (fig. 28 & 29). The

response force is always kept constantly at thein advance determined maximum level,whereby the motion speed does not play part.If the energy supply falls below a certain level,the movement almost stops.

This load limiting function is of greatadvantage for the planner, as the maximumforce of the shock transmitter is exactlyknown. Thus the structure can exactly bedesigned as to this force, resulting inconsiderably lower constructional costs andsignificantly increased structural safety.

The MSTL guarantees that, compared with theMSTU, all shock transmitters are stressedevenly and simultaneously, or rather thatneither the structure nor the component isdamaged due to different operationalbehaviour of the shock transmitters at differentparts of the structure.

During the „overload“ above maximum load,,the MSTL moves and thus dissipates energy.This energy quantity however turns out lessthan in case of pure dampers (MHD), as the

MSTL is not designed for energy dissipation,but primarily for force limiting.

So, if moreover an optimum energy dissipationis required, dampers of type MHD must beinstalled.

The three functional characteristics are:

A) No worth mentioning response force (max.10 % of the design force) resulting frommovements due to shrinkage/creeping andchanges in temperature.

B) Sudden blockade respectively formation of resisting force (= design force = Fn) for suddenly arising movements due to traffic,earthquake or similar.C) Limitation of the maximum response force(= limitation force = Fl) in case of to muchenergy input, which would cause an undefinedgreat response force.

Fig. 28 :force [F] - speed [v] - graph

Fig. 29 :force [F]- distance [s]- graph

[v]

[F]

A) Service- B) C) Erdbebenlastfall

0,1 mm/s 1 mm/s

Fl

Fn

A) Servicelastfall B+C) Erdbeben

[F]

[s]

[F]

[s]

FlFn

FlFn

Fig. 30: Shock Transmitter with force limiter

(MSTL)



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3.3 Hydraulic dampers (MHD)

Additionally to the isolators resp. the bridge

bearings it is often required to use MAURERHydraulic Dampers (MHDs) for effectiveenergy dissipation. The MHDs guarantee themaximum possible damping resp. energydissipation at the corresponding parts of thestructure.MHDs are components (fig. 31), which permitmovements (due to changes in temperature,creeping, shrinkage etc.) under quiescentcondition of the structure, without producingsignificant response forces. If however suddenmovement do arise, maximum energy quantityis dissipated, i. e., motion energy is

transformed into heath within the damper.

Very slow movements from temperaturedifferences or similar do not result insignificant response forces within the MHD.The hydraulic fluid can move from one side of the piston to the other.

During loads due to earthquake, traffic or similar, an intelligent control systemguarantees relative movements between theconnected structural parts, which results in aconstant level of the response force. This

unique mechanism ensures that the responseforce is independent on the energy input, i.e.,independent on the motion speed (fig. 32).The response force is always held at constantlevel.

On the one hand, the planner can thus beassured that a maximum of the energy input isdissipated, and on the other hand, themaximum response force of the MHD effectingthe structure is exactly known, independent onseismic loads or similar energy inputs.

The three functional characteristics are: A) No worth mentioning response force (max.10 % of the design force) resulting frommovements due to shrinkage/creeping andchanges in temperature.

B) Sudden blockade respectively formation of resisting force (= design force = Fn) for suddenly arising movements due to traffic,

earthquake or similar.C) Limitation of the maximum response force(= limitation force = Fl) in case of to muchenergy input, which would cause an undefinedgreat response force.

Fig.32: force – speed graph

Fig.33: force – displacement graph

[F]

A) Service- B) C) Erdbeben

lastfall

0,1 mm/s 1 mm/s

Fl

Fn

[F]

[s]

[F]

[s]

Fl

Fl

A) Servicelastfall C+B) Erdbeben

FN

FN

Fig. 31: Dampers (MHD) installed in a brdige



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4. Seismic expansion joints

Earthquakes can generate structuralmovements which are considerably larger,many times quicker and much more complexin their direction than those under normaloperational conditions. That is whyapplications of that kind require a specialdesign of the expansion joint. Swivel joistexpansion joints type DS (fig. 34) areespecially designed for use in seismic regions.

The conventional requirements set to theoperating conditions are irrelevant during

seismic action. Of particular importance,however are as follows:

maintenance of serviceability of thestructure after the earthquake, at least for emergency vehicles,

protection of the structure from impactdamages caused by closing movementsduring the earthquake as well as

prevention of an open gap due to too largeopening movements.

Employing a long and superior performance

history in normal service conditions, theSwivel-Joist Expansion Joint had been further enhanced such as to also fulfil theaforementioned seismic requirements. Whenthe expansion joint or the structural gapcloses, there might result damages or evenbreakdown of the structure. For better protection of the bridge structure, a so-called"fuse box" has been developed (fig. 35). If theexpansion joint should close in case of aquake, the breaking point will be activated.The anchorage system disengages alongsidea ramp according to a defined failure load and

will return to its original position as soon as thequake is over. The breaking point is repairablewith less effort.

Fig. 34: DS – Swivel joist expansion joint

Fig. 35: functional principle of a Fuse boxat a swivel joist expansion joint



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5. Non-linear structural analysis

At request, MAURER offers a non-linear structural analysis for each kind of structureand suggests the most suited protectionsystem, which meets all requirementsregarding protection and economy.

For this we need the following data:

• structural drawings

• significant cross sections (deck, abutment,piles)

• moment of inertia, constant of torsion,stiffness of lateral displacement )

• materials (Young modulus, shear modulus,density)

• foundation (dimensions and Winkler modulus, longitudinal and rotational stiffnesof the exchange springs.

• Seismic data: response spectra andrepresentative acceleration graphs

• loads (permanent loads, max. traffic loads,traffic loads during earthquake

• Allowable forces at the most importantstructural parts e.g. piles, abutments etc.(allowable transverse moments, allowable

displacement and axial forces, andmovements)

• Other demands of the designer

Advantages of a non-linear structural analysis:

● Precise determination of the structuralmovements

• Precise calculation of the response forcesacting on the structural components andthe building

• Optimized adjustment of the seismicprotection system to efficiency factor and

economy• Proof of seismic protection

• Precise determination of the really existingstructural safety factors

• The designer can compare his calculationswith those of MAURER to confirm hisresults

• less reinforcement or similar result inconsiderable savings of structural costs

Fig. 36: Steps of a non-linear Structural analysis

Lineare Bauwerksanalyse

Ermittlung der Bauerksmodi und derenzugehörige Frequenzen

FE-Modellierung der Bauwerkstruktur mitSchutzsystem

Zeitverlaufanalyse

Ermittlung des Bauwerkverhaltens unter Berücksichtigung des nicht-linearen Verhaltens

der Schutzkomponenten

Bauwerksantwort

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MAURER Seismic Protection

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