1. INTRODUCTION 2 PASSIVE SYSTEMS FOR DISSIPATING SEISMIC ENERGY

▪ DAMPERS ▪ TUNED MASS DAMPERS 3. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS "NON DESTRUCTIVE" METHOD « PARSANT » 4. SEISMIC ISOLATION OF BUILDINGS 5. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS USING SEISMIC ISOLATING DEVICES

▪ CONCRETE BUILDINGS ▪ MASONRY WALL BUILDINGS

6. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS USING CONVENTIONAL METHODS 7. WHO WE ARE

1. INTRODUCTION

This leaflet includes part of the material of my presentation during an Engineering Conference, which took place in June 2013.

The purpose is to inform the active Architects and Engineers of some very recent methods, which can be applied to everyday projects providing new improved design tools, such us: ▪“Dampers” can be applied to new buildings, improving their structural behavior and making their structural system more elegant. As an example the numerous and large shear walls, required by the Codes of Practice, can be drastically reduced or even eliminated. This can be very useful in cases that shear walls are difficult to be extended to the basements, due to their use as parking areas etc. They can also very useful in case of extended use of flat slabs systems, due to reduction of the bending moments due to horizontal forces at the joints of columns and plates.

▪BRUB (Buckling Restrained Unbonded Braces) are very modern type of dampers, in the form of the usual double diagonal braces, used in steel structures. They can easy to be produced and are inexpensive, solving that way the problem of relatively high cost of dampers in general. They can be used in every steel structure by replacing part of their diagonal bracing system, in which case the latter act simultaneously as bracing element and damper, making the whole structure more economical.

▪Using independently or in combination the “non destructive” PARSANT method and the “passive systems for dissipating seismic energy” (like dampers and tuned mass dampers), practically all buildings can be strengthened / retrofitted, in a very economic non-destructive way, without intervening in their inside, without damages and without interrupting their use.

▪The above does not apply to “masonry buildings”, but even for them the use of dampers incorporated to their floor and roof system can greatly improve their structural behavior.

▪TMD (Tuned Mass Dampers) can be used in flexible high rise buildings, improving drastically their dynamic behavior against earthquakes and wind forces.

▪The use of base isolation for buildings using elastic bearings underneath the ground floor columns is the best anti-seismic method, which can guarantee absolutely no damage at all, not only to the structural elements, but also to the non structural ones, like the partitions etc. The cost of this method is only 5.0-7.5% higher than that of the conventional buildings, covering the total cost of the buildings. The reason of the relatively limited application of this great method is not the higher cost, but the lack of experience of the engineers and architects, regarding the relatively complex calculations and special detailing, a fact that can easily be changed.

▪ The base isolation system can be applied also in precast buildings, due to the dramatic reduction of forces of the building above ground (about 20% of forces applied to conventional buildings). These way parts of each floor of the buildings, extending between columns, can be prepared in factory with all architectural and electromechanical items fixed in place. They will be prepared during the construction of the basement and the seismic isolation system and on site, they will be connected to each other in a very simple way.

2. PASSIVE SYSTEMS FOR DISSIPATING SEISMIC ENERGY 2.1 DAMPERS Dampers are very sophisticated devices belonging to “cutting edge” technologies, which are included in the structural system of new or existing buildings, usually through steel diagonal braces. During an earthquake they are pressed and stretched sequentially and these movements activate the absorption of seismic energy, which is eventually converted to heat.

This way, a percentage of 40% or more of seismic energy can be absorbed, relieving at the same time the structural system of the building in a proportional manner. As the Eurocodes do not cover this subject, we use the American ones (FEMA 450 for new buildings and FEMA 356 for existing ones). A “non linear” analysis is required, using seismographs, rather than seismic spectra, a fact that makes calculations complex and time consuming, whereas reliable and sophisticated international software is required. For some simpler cases the Codes allow the use of “equivalent linear analysis”, using spectra of reduced magnitude (“shrinked” spectra), by increasing accordingly the “damping factor” of the buildings. The dampers can be used in new buildings, thus ensuring a more economical and much lighter structural system. It is emphasized that in this way the numerous large shear walls, required by the Codes in conventional buildings, can drastically be reduced or even eliminated, solving that way a lot of architectural problems, like shear walls that is difficult to be extended in the basement, due to the parking areas provided in there. They can also very useful in case of extended use of flat slabs systems, due to reduction of the bending moments due to horizontal forces at the joints of columns and plates. Dampers can also be used in existing buildings, achieving a great improvement of their behavior against earthquakes, due to significantly reduced seismic forces, which are finally applied to the structures.

On the left, the “fluid viscous” dampers are included on the upper two floors of an existing building – On the center, the deflected shape of the building before the “strengthening” (retrofitting) with dampers – On the right, the deflected shape of the building before after the “strengthening” (retrofitting) with dampers…analysis models

On the left, “fluid viscous” dampers are included to a new building - On the right, “friction” dampers are used to a new building

There are two main categories of dampers: ▪ “Deflection dependent” dampers, like “metallic yielding” or “friction” type devices. ▪ “Velocity dependent” dampers, like “fluid viscous” and “viscoelastic” type devices.

A type of “metallic yielding” damper, very modern and efficient and very much used lately especially in Japan, is the “Buckling Restrained Unbonded Braces” (BRUB) system, see photo on the right. In a hollow steel diagonal bracing member, a steel plate is inserted, and the gap is filled with concrete mortar. The plate is appropriately coated in order to have no, or very little, friction affinity to the mortar, so that it will be able to slide freely, when stressed in tension or compression. The plate is designed in such a way so that to yield in axial force, tension or compression, during the design earthquake, creating that way an enlarged hysteresis loop, which leads to significant absorption of seismic energy. Two are the main innovations of this system: ▪ the “encasement” of the steel plate was crucial for the overall development of the system, since it made possible to reach yielding of the steel plate, without arising the phenomenon of buckling. ▪ the transition to plastic region was not limited to certain points (plastic hinges), as it is common in flexural members, which has the disadvantage to reach failure due to material “fatigue”. In the case of BURB system the creation of plastic hinges is continuous along the whole length of the plate, a fact that creates no fatigue failure and also guarantees greater efficiency. This simple and less expensive method can be used in every steel structure by replacing part of their diagonal bracings by BRUB, in which case these bracing elements will act simultaneously as dampers, absorbing seismic energy and making the while structure more economic.

The dampers can properly be inserted to the floor system (steel or wooden) of existing masonry buildings, as a retrofitting method of this kind of structures.

2.2 TUNED MASS DAMPERS (TMD)

TMD is placed in the upper part of a skyscraper

TMD is placed on the terrace of a building

The mass of TMD, which can be a reservoir of water, is surrounded and supported by dampers and springs

Tuned mass dampers are independent oscillators, which are placed in the upper part of flexible, high rise buildings. They consist of a mass and some springs and dampers, attached to the main vibrating system i.e. the building.

TMD improves the dynamic behavior of the flexible high rise buildings for two reasons: ▪ By “tuning” (arranging in a fine way) the mass and the frequency of a TMD, we can achieve them to oscillate during an earthquake, to the opposite direction of the buildings, therefore reducing their corresponding displacements and forces. This usually does not apply to the critical first mode of vibration, corresponding to the lowest frequency, but to the 2nd or 3rd mode, for which the modal mass participation is still reasonably high (35-50%). ▪ The horizontal movements of the mass activate the dampers, usually fluid viscous, and this has as effect the absorption of a large amount of the seismic energy, reducing proportionally the seismic forces acting on the buildings. In some cases the deflections of a TMD during oscillation become too big, and this poses some limitations to the “ideal” tuning of the mass and frequency. But even then the system remains efficient, due to the contribution of the dampers connected to the mass, which absorb seismic energy.

Same as for the dampers, the structural analysis of the TMD systems requires very sophisticated software and “non linear” or “2nd order” analysis, together with the use of accelerograms, instead of seismic spectra.

During an earthquake the TMD oscillates to the opposite direction of the building.

3. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS USING THE "NON DESTRUCTIVE" METHOD « PARSANT »

This method of retrofitting / strengthening of existing concrete buildings, patented in the writer’s name, is applied at their perimeter facades, without causing damages and without interrupting their use. On the basis of this method, additional panels made of strong steel frames with diagonal members and their own foundations, are placed on the perimeter of buildings (one at each side or at least one at three sides), pin connected to their framing system. The panels consist of tubular steel sections filled with small aggregate concrete (composite construction)

The pin-connection is achieved using steel rods, which go through existing and new beams and are bolted at both sides. The existing beams sides in contact with the new ones, are previously reinforced using steel plates attached to them by epoxy glue and steel anchors (beton plaque)…see detail right

During an earthquake the major part of horizontal forces are transferred to the rigid additional panels, relieving the existing columns, which that way have sufficient strength for the reduced forces they receive. The same applies for the rest of the structural elements avoiding that way their strengthening with conventional destructive methods, like concrete mantles etc, while it makes it possible to add one or more additional floors even if this was not foreseen in the original design.

Pin connection (section)

On the left, the PARSANT panels are placed outside the perimeter of the existing building - In the center, "fluid viscous" dampers are included in the diagonals of the two upper floors in order to absorb seismic energy – On the right, the PARSANT panels are covered

with cement board (at the right side of the building) and with decorative steel panels (at the left side)

The method often is applied in combination with high technology systems of absorbing seismic energy (dampers), installed directly to the buildings framing system or inserted to the diagonal members of the PARSANT additional panels. They are very sophisticated devices, usually “fluid viscous” or “friction” type, that can absorb about 40% of the seismic energy, relieving that way proportionally the existing structure. The structural analysis of such structures requires non linear methods and needs special software. Lately we use the most advanced and less expensive damper named “buckling restrained braces” which are “metallic yielding” devices” replacing the total diagonal bracing system of the upper floors (see top photo on the right. For more information see Chapter 2.1.

The foundation The PARSANT panels have their own foundation system, which and can be: ▪ Conventional long footings, made by cast in place concrete, which usually extend over two consecutive footings of the existing building. The new footings cover the existing ones, acting like concrete mantles with steel dowels at the common surface. ▪ Piles of small diameter 0.25-0.30m with a slab on top, at the level of ground floor, which contains the anchors for the positioning of the PARSANT panels. The length of the piles comes out of soil /structural calculations and guarantees the full fixity of the panels. That way no excavation at all is required, whereas the small diameter piles machinery is quite small and versatile, being able to approach the building closely and work even under balconies. The structural analysis considers a model of two separate structures (the existing building and the PARSANT panels) very close to each other, connected by steel members, which represent the connecting rods. Each rod is described in the model as a structural element and its adequacy is checked by the program, taking into account a higher safety factor.

The PARSANT method can be applied to ground floor “soft floors”, like pilotis (see bottom photo on the left)

The cost of application of the PARSANT method, as expected, varies from case to case. As a rule of thumb, we can say that a statistically reliable average cost is about 60-80 €/m2, applied to the total area of the strengthened floors above ground. This price includes also the very few damages of the non structural elements. The cost of the method becomes more favourable for large buildings, where the PARSANT panels take better advantage.

The applicability of this practical, economical and short in construction time method is as follows: ▪ Buildings already damaged by earthquakes. ▪ Buildings needing upgrading of their anti-seismic behaviour, according to the latest Codes of practice. ▪ Buildings expecting additional floors, when their framing system has not adequate strength. ▪ Buildings with new higher live loads than the initial ones, due to change of their use.

For more information please visit the "link": www.marneris.gr

"buckling restrained braces” used as dampers

The PARSANT method applied to a "soft" ground floor (pilotis)

PARSANT was presented during “The 14th World Conference on Earthquake Engineering”, in Beijing China on October 2008, and during the “3rd Greek Conference of anti-seismic mechanics and technical seismology” in Athens, Greece on November 2008.

The method is included in the “Greek Code for Repairing and Strengthening of Existing Buildings (KANEΠE) In conclusion the application of the PARSANT method in combination, or not, with passive systems for absorbing seismic energy (dampers and tuned mass dampers), guarantees the retrofitting of buildings, without intervention in their inside and without interrupting their use.

From left to right: Office building “before the strengthening”, “after the strengthening”, and “after the covering of the additional steel frames with perforated decorative metal panels”

From left to right: deformation of a building “before the strengthening”, after the “strengthening” with PARSANT panels without dampers, and after the “strengthening” with PARSANT panels with dampers at the two upper floors.

During and after the strengthening of a building using the PARSANT method

(in this case the PARSANT panels were also used for the addition of balconies of about 3.5m long)

During and after the strengthening of a building using the PARSANT method (PARSANT panels can easily adjusted in case of existing balconies)

On the left the placement of a PARSANT panel by a crane – On the centre, the connection of the panels to the beams of an existing super market - On the right, the addition of one floor (made of steel members) was achieved by strengthening of the existing building with the PARSANT method.

On the left and centre, the PARSANT panels are placed and connected by bolting to their foundations – On the right, addition of 3 floors made of steel in a 2 storey building, which is strengthened using the PASANT method. The front left additional panel was not allowed to be continued in the ground floor, due to urban regulations and so the PARSANT panel is seated on a short cantilever extended from a shear wall, which is constructed in the ground floor.

4. SEISMIC ISOLATION OF BUILDINGS

4.1

all, not only to structural members, but also to the non structural ones, like the partitions, the glazing system, the mechanical

The occupants of the building do not suffer any inconvenience, during the earthquake.

General description of the system The “base isolation” system of buildings is the most advanced anti-seismic one, and the only which can guarantee the following:

▪ No damage at installations etc. ▪ The buildings remain operational even after a very strong earthquake. ▪

The conventional buildings s isolation base show a large horizontal deflection at the base and the part above remains practically vertical.

(On the left, conventional building / On the right building on isolation base) (On the left, conventional building / On the right building on isolation base)

how a “bending type” deflection throughout their height, whereas the buildings on

Schematic deflection of a building during an earthquake. Deflection of a building during a seismic experiment on a vibrating table

4.2 The isolation bearings The most used isolation bearings are the following :

▪ The HDRB (High Damping Rubber Bearings), are made of a series of vulcanized rubber layers, separated by steel reinforcing steel plates, thus providing a device with high vertical and low horizontal stiffness. The rubber has the ability to dissipate energy (damping capacity) in the range of 10%. ▪ The LRB (Lead Rubber Bearings), are made like the HDRB, but contain also one or more lead cores. The later can absorb large amount of energy, so that the total damping capacity of the bearing is increased to about 30%. Our Company is in close cooperation with the largest producers of seismic isolation bearings, like "ROBINSON Seismic Protection" of New Zealand, their structural consulting office “HOLMES”, also from the New Zealand, and finally the "MIN Industries" of Malaysia, with the greatest overall activity in this area.

Seismic isolators support the whole superstructure of the building

On the left, hospital on seismic isolators, of LRB type – In the center, section of a LRB isolator – On the right, the hysteresis loops of

isolators, representing the seismic energy absorbed by them.

The application of the seismic isolation greatly improves the dynamic behavior of the buildings against earthquakes for two reasons: ▪ The dynamic characteristics of buildings become more favorable because the main period of oscillation 'T' increases from 0.7-1.0 sec for conventional buildings, to 2.5-3.0 sec for the same buildings on isolated foundations. As one can see from diagram “Period-Acceleration” on the right hand side photo, this “shift of the period” leads to a remarkable decrease of accelerations and consequently seismic forces, of the range of 60%. ▪ The damping produced by the isolators, provides an additional reduction of forces and displacements up to 10% to 30% (see diagram “Period – displacement” on the right hand side photo) This significant reduction of forces and displacements, in the range of 70%, compared to conventional buildings, has among else as effect: ▪The remarkable reduction of the shear walls required, concerning their size and number ▪The even more remarkable reduction of the steel reinforcement required.

On the other hand the system presents the following inconveniences regarding the architectural and mechanical design: ▪ The need to create a “moat” around the building, like a “cour anglaise”, for the unlikely event that the horizontal deflections of the seismic isolators will become greater than the ones, taken into account in the design (earthquake of a magnitude greater the one considered in the design) ▪ The need to provide a greater height of the upper basement, on top of which the seismic isolators are installed. This is because a mezzanine level is created, which is necessary for the inspection of the isolators.

▪The bearings have to be regularly inspected and some of them changed after a strong earthquake or after many decades of use.

▪ Special attention is needed in the connection of elevators and mechanical piping up and down of the seismic isolators, where large horizontal deflections occur. ▪ If expansion joint are provided between seismically isolated buildings, the connection between them should be in the form of steel platforms, hinged at one side and free to move in all direction at the other side.

For better understanding of the above see sections of a hospital designed by our Company.

The base isolation system can be applied also in precast buildings, due to the dramatic reduction of forces of the building above ground (about 20% of forces applied to conventional buildings). These way parts of each floor of the buildings, extending between columns, can be prepared in factory with all architectural and electromechanical items fixed in place. They will be prepared during the construction of the basement and the seismic isolation system and on site, they will be connected to each other in a very simple way.

4.3 The cost of seismically isolated buildings

As a result of a broad international statistic information, the cost of these buildings is higher in comparison to conventional ones, about 10% concerning cost of the structural system and about 5.0 -7.5% concerning the total cost of the building.

To my opinion the lightly higher cost is not the main reason for the limited application of this great method, but rather the lack of experience of the engineers worldwide, regarding the relatively complex calculations, as well as the special detailing regarding all disciplines involved, architects, engineers, contractors.

Section of a seismically isolated hospital building

Blow up of previous section around basement floor

Detail of the connection of buildings in case of expansion joints

5. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS USING SEISMIC ISOLATING DEVICES

5.1 CONCRETE BUILDINGS

Photo 1 Photo 2

Photo 3 Photo 4 Photo 5

Photo 1: The area around each concrete column is supported provisionally by steel poles. Photo 2: A part of the column is cut slightly just above the ground floor slab, using special non destructive machinery. Photo 3: The cut portion of the column is moved away. Photo 4: The seismic isolating bearing is ready to be inserted in the column’s gap. Photo 5: The isolating bearing is positioned and fixed in place. The provisional steel poles are removed and the force of the column above is transferred to the bearing. This procedure gradually applies to all concrete columns It is recommended to connect the bottom parts of all reinforced concrete columns, just above the isolating bearings, with a grid of steel beams , creating that way a a new diaphragm, acting as an “elevated ground floor”, although this will result in the reduction of the available ground floor height. A “moat” around the building, like a “cour anglaise”, should be provided.

5.2 MASONRY WALL BUILDINGS

Photo 1 Photo 2 Photo 3

Photo 4

Photo 1: The basement walls and their foundations are strengthened using concrete mantles at both sides. Then holes are drilled in the walls close to another and the seismic isolating bearings are inserted in them. Photo 2: The isolating bearings are filled with epoxy mortar at their base and in this way they swell and they are under pressure Anchor bolts are inserted to connect them with the bearings with the walls up and down. Photo 3: The parts of walls between the isolating bearings holes are cut, using special non destructive machinery. This way the loads of the building above ground are transferred to the seismic bearings. Photo 4: General elevation of the building after the retrofitting. A “moat” around the building, like a “cour anglaise”, should be provided.

6. RETROFITTING / STRENGTHENING OF EXISTING BUILDINGS USING CONVENTIONAL METHODS 6.1. DIAGNOSIS AND EVALUATION OF THE EXISTING BUILDINGS BEARING CAPACITY Our Company is exclusively specialized to this type of projects, which include the following main phases. 1) Preparation of the survey drawings 2) Recording and evaluation of the structural damages like cracks, soil deformations, deterioration of concrete or other materials, rebar oxidation etc 3) Laboratory and other tests in order to determine the materials strength and quality. 4) Structural calculations 5) Identification of the structural damages causes. 6) Evaluation of the overall buildings strength. 7) Strengthening / retrofitting design of buildings. 6.2. CONVENTIONAL METHODS Apart from the application of the “non destructive” methods for strengthening / retrofitting of existing buildings, as discussed in previous chapters, our Company is specialized in all other conventional methods, such, as: 1. Concrete mantles (shot crete or cast in place) 2. Steel plates attached to concrete (beton plaque) 3. Carbon reinforced plastics (FRP) in the form of tissues, or plates. 4. Homogenizing grout for stone masonry walls etc FRP materials in the form of tissues or plates are attached to the concrete using strong epoxy glues and function as additional reinforcement of the concrete member. Note that the tensile strength of FRP is 3.500 MPa, which is about seven times greater of the steel strength.

Reinforcing of a concrete slab with FRP materials (tissues and plates), around the area where a large hole is opened

Reinforcing of concrete slabs and beams with FRP materials (tissues and plates)

6.3. GALVANIC PROTECTION OF CONCRETE STRUCTURES REINFORCEMENT, USING ZINC ANODE DEVIES INSERTED IN THE CONCRETE MASS. In cases of highly oxidized steel reinforcement, oxidation continues even after the careful cleaning of the steel bars and painting them with antioxidant, showing the usual cracks in the direction of the reinforcing bars. Quite often this has as a result the “destruction” of concrete mantles, which were positioned to the members, after the cleaning of the reinforcing bars. The only effective solution to this is the application of the galvanic protection, according to which “zinc anodes” are inserted in the concrete mass and their metal wires are connected to the reinforcing bars. This way an electrolysis phenomenon takes place, which has as result the oxidation to be transferred to the “zinc anodes”, which are “sacrificed” after many years.

Coupe d’une plaque de béton, - une

anode de zinc est placée. Le ferraillage est nettoyé, etc.

Anode de zinc avec ses fils,

entourée de mortier de ciment de haute alcalinité.

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EN ISO 9001 : 2008 TUV HELLAS

PHOTOS OF SELECTED PROJECTS