“Sun Tower” 26-Storey Seismo-Safe Skopje Symbol Building: Inventive Project With New GVCS System Nominated To Represent R. Macedonia At The Millennium EXPO of Inventions

Danilo Ristic Prof. D-r, Institute of Earthquake Engineering and Engineering Seismology, University "Ss Cyril and Methodius", P.O. Box 101, 1000 Skopje, Republic of Macedonia, Phone: +389 2 3177 015, Fax. +389 2 3112 163, ABSTRACT: The GVCS seismo-resistant building system represent qualitatively new strategy for construction of buildings providing simultaneously: (1) Full seismic safety of high-rise buildings, (2) Reduction of actual construction time, and (3) Profitable construction in seismic and non-seismic areas achieved with special system characteristics. Promotion of the first application of the patent is created by the author through inventive design of attractive 26-storey multi-purpose "SUN TOWER" symbol building which will be constructed in Skopje as unique land-mark and symbol of successful construction of new generation of seismically safe buildings in areas with the highest seismicity.The paper presents the original experimental and theoretical proof of the advantages of the patented "GVCS" system for construction of this attractive prototype structure. Included are basic proof results from: (1) Analysis of non-linear seismic response of the integral structure using originally developed computer software by the author and (2) Experimental results from conducted forced-vibration dynamic tests of constructed large-scale model 1:10, (tested in IZIIS), as part of 3-year scientific project financed by the Ministry of science and various other sources. KEYWORDS: Nonlinear systems, seismic response, passive structural control, GVCS system, vibration isolation devices, added damping devices, seismic vulnerability

Patron of the integral project:

Mr. Branko Crvenkovski President of Government of Republic of Macedonia

1. INVENTIVE CONCEPT OF "GVCS" SEISMO-RESISTANT SYSTEM

The patented "GVCS" seismo-resistant building system actually represents adoption of new industrialized building technology for construction of vibro-isolated and seismo-resistant tall buildings in regions characterized with the highest seismicity. Through implementation of incorporated new global vibro-compensating system (GVCS-System) based on efficiently combined seismic energy balance (CSEB) of adaptive building module, created is conceptually advanced system of tall buildings, favorable for satisfying optimal multi-objective construction requirements. The GVCS system is patented under the original title: "Global vibro-compensating structural system (GVCS) for industrialized construction of vibro - isolated and seismo - resistant buildings", by three authors (D. Ristic, et all), (12).

Using approved support by the Macedonian Ministry of Science and support from other institutions, (see acknowledgements) realized is specific three-year scientific research project including large-model test of a designed the first representative GVCS building prototype structure. To create an attractive prototype structure for this specific scientific and development study, the author of this paper created and promoted the original "Sun Tower" project, which is briefly described in this paper.

The disclosed new building construction technology is actually based on the incorporated global vibro-compensating system (GVCS) integrating an optimal combination of: (a) An effective base

vibration isolation system (BVIS) for the lower building part, (b) A specific hanging vibration isolation system (HVIS) for the upper building part and (c) An adjusted interactive vibration isolation system (IVIS) between two globally separated building perimeter segments, in which case the transmitted energy to the structure or building excitation intensity can be rapidly reduced including convenient change of response frequency for the case of actual ground excitation originated by strong earthquakes or any other artificial sources. In the adopted globally separated structure, vibration response of the lower building part is basically controlled by the base vibration isolation system (BVIS) possessing advantageous capability for vibration control of stiff low-rise structures. The vibration response of the upper building part is dominantly controlled by the advantageous hanging vibration isolation system (HVIS), while the interactive vibration isolation system (IVIS) serves as a compensation device to transmit positive effects between the two out-of-phase activated isolation systems into the remaining building part, achieving in general vibration reduction of the integral building as well as required safety level under strong earthquakes by effective elimination of unacceptable building oscillations under generated strong ground vibrations.

The significant advantage of this building system is expressed through the possibility of dominant application of the industrialized building construction technology based on in situ assembling of modular prefabricated elements. The main advantages are disposed in the following: (1) Simplification of structural design process, (2) Reduction of building construction time, (3) Achievement of high construction quality, (4) Implementation of new materials with advanced performances, (5) Elimination of some specific and costly construction phases, (6) Simplification of building finalization phases, and (7) Reduction of the total building construction and maintenance cost during long serviceability period in seismically active regions.

Finally, by adopting the developed unified building modules (units) it is made possible to create flexible architectural building compositions in both, building plane and building elevation.

2. "SUN TOWER" SYMBOL BUILDING: FIRST PROMOTION OF NEW GVCS-SYSTEM

To promote the first application of the invented GVCS seismo-resistant system, specific research project has been originated by the author. Namely, the author of this paper and principal investigator of the integral development project paid particular attention to the selection and conceptualization of representative and attractive prototype structure which, according to its usage and other specificieites, shall represent important structural engineering challenge. Respecting this initial idea, Prof. Dr. Danilo Ristic, the principal investigator of the development project and co-author of the patent, originally conceptualized and proposed the fundamental concept of the adopted symbol "Sun Tower" prototype structure. With its specific purpose, appearance, grandeur and specific integral structural system, this prototype structure bears the characteristics of uniqueness in a wider and general sense.

During the initial creation of general concept of the prototype structure, the following primary characteristics were basically promoted and applied: (1) Created is a prototype structure which is characterized by unique, atractive and representative structural system, expressing the main positive seismic performances of the patent itself and (2) In addition to the above, the created prototype structure efficiently exhibits a specific and attractive multi-purpose use, promoting therefore important contents of wider commercial and other specific interests.

The general architectonic appearance of the created "Sun Tower" prototype structure successfully integrates in itself a pronounced symbolics, since the structure of the tower ends with a polyhedron sphere symbolizing the Sun, while the eight cantilever girders of the upper segment symbolize the rays of the Macedonian flag. The structure is therefore called the "Sun Tower".

The final and extended goal is focused on construction of "Sun Tower" structure in Skopje, as a structure representing "symbol of our time and world solidarity". Skopje has particular and noble reasons for this, particularly having in mind the great international assistance and the shown wide world solidarity in mitigation of the consequences of the catastrophic earthquake that struck this town in 1963.

Fig.1. Typical Section of "Sun Tower" Structure

Fig.2 Typical Car Parking Floor

Respecting the above stated characteristics, design and construction of this prototype structure represents a great professional challenge for inventive engagement of creative experts of the integral research team. Considering the main concept of a unique prototype structure - symbol in the form of

"Sun Tower", various steps were taken toward its final elaboration. Consequently, this original concept of the defined representative "Sun Tower" prototype structure became subject of further investigations within the frames of the considered development project.

The main geometrical characteristics of the designed prototype structure are presented in Fig. 1 showing a characteristic cross-section of the designed prototype structure with application of the new "GVCS" structural system. Presented in Fig. 2 is a plan of (the first four floors are planned to function as garages), while Fig. 3 displays the characteristic photograph of the constructed large scale experimental model of "Sun Tower" structure. It clearly demonstrates general appearance of the promoted prototype structure designed by application of the new "GVCS" structural system.

Fig.2a. Alternative View of Created Inventive "Sun Tower" Skopje Symbol Building

The polyhedron sphere, the "symbol of the Sun" is planned to consist of four floors. The lowest floor shall be organized as a space for the restaurant needs and other services. The other two stories are planned for special open-view restaurants, while the topmost storey shall be organized as a place where one could have an exceptional beautiful view of the entire town. Due to limitation of space, the other important and unique specificities of "Sun Tower" structure have not been explained in this paper.

3. EXPERIMENTAL DYNAMIC TESTING OF 26-STOREY "SUN TOWER" MODEL

In designing the experimental model of the "Sun Tower" prototype structure (Figure 5), special attention was paid to enable a realistic simulation of the dynamic behaviour of the integral "GVCS” structural system. Since the dynamic behaviour of this system is dominantly controlled by the stiffness and strength characteristics of base isolators and hysteretic absorbers, these elements have been designed to satisfy ideal similaruty by application the principle of "true replica model". The designed aseismic devices were ordered from the ALGA S.p.a Company from Milano. This company has patent and attesting rights to these devices and has produced them for engineering practice for a longer period of time. In this particular case, this company expressed an interest in supporting this project by elaboration of base isolators and hysteretic absorbes with exactly the required characteristics, reduced to the scale necessary for their incorporation into the experimental model. Principal investigator of this project, Prof. Dr. Danilo Ristic, is expresing his personal the most sincere gratitude to Dr. Agostino Marioni, President of ALGA S.p.a., from Milano (Italy), for his great support of this project and highly valuable and creative advices for the benefit of this original development and research activities.

Considering the fact that the "GVCS" structural system is based on the principle of construction of the structure segment by segment, the experimental model itself has been designed and constructed by integration of structural elements which realistically represent the individual structural elements of the prototype structure.

Fig.3. Experimental "Sun Tower" Model

Fig. 4. Model Construction in IZIIS Lab

Applying this principle, the experimental model has been composed of a total number of seven segments. A typical view of the "Sun Tower" experimental model under construction is presented in Fig. 6. The completed design of experimental model (separate Report) contained a number of detailed drawings based on which the construction of each element was completed. The main segments of the model are the following:

(1) POS-100: Central RC core (segment 1) with a steel base structure. The central core was constructed according to the final drawing applying as material the reinforced micro concrete of Class 30. An adequate steel device was anticipated for the fixation of the central core in its lower end. The upper part of the central core ends with a sheet metal ring with anchors for fixation of segment 4. Along height, the central core is equipped with steel plates on four sides at appropriate levels for the purpose of enabling fixation of hysteretic absorbers, where needed; (2) POS-200: Base isolated stories (steel + reinforced concrete) that compose the lower ring structure (Segment 2). Segment 2 represents a lower ring structure around the central core which is base isolated by adequate seismic isolators and extends over a total of ten storey heights. In the experimental model, the structure over the base isolators is elaborated from steel profiles with an appropriate disposition of structural elements adapted to the disposition of the anticipated eight base isolators. The bearing structure of the stories is constructed from steel profiles 40x40x3 mm. It is designed to satisfy the conditions of assemblage storey by storey. The floor slabs are placed in the special areas formed between the steel profiles and they are also prefabricated. The floor slabs are designed to have a weight that realistically simulates (according to the similitude theory) the weight of the base isolated stories from the base isolated segment 2. Hysteretic absorbers are installed between the central core and the base isolated segment 2. The fixation of the hysteretic absorbers is planned to be simple for the purpose of making possible the variation of their number and distribution, if necessary; (3) POS-300: Suspended stories, or the so called upper ring structure (segment 3). Segment 3 represents an upper ring structure around the central core which is suspended from a cantilever structure (Segment 4) and extends over a total of ten storey heights. It is also constructed from steel profiles with a cross-section of 40*40*3 mm and using

the same principle of mounting as that used for segment 2. The floor slabs are designed such that their weight realistically simulates the weight of the suspended stories of the prototype structure. Adequately distributed hysteretic absorbers of adequate stiffness and deformability characteristics are also installed between the central core and the floor structures of the suspended stories. The suspended segment is also equipped with adequate seismic isolators on the corresponding top cantilevers; (4) POS-400: cantilever steel structure for suspending the upper 10 stories (segment 4). Segment 4 represents a steel truss cantilever structure with eight cantilever girders which are connected in the centre of the central core by welding to a vertical steel pipe φ 200 mm with a thickness of 10 mm and length appropriate to support the spherical structure (segment 6). The cantilever structure of segment 4 is prefabricated and is fixed to the central core by bolts; (5) POS-500: Steel structure for supporting of the spherical structure (segment 5). Segment 5 represents a bearing structure of the designed sphere. It is constructed from steel profiles and is mounted over the steel structure of segment 4; (6) POS-600: Spherical 4-storey structure (steel + RC floor slabs) (segment 6). Segment 6 represents a four-storey spherical structure. It is constructed from precast steel segments made of steel profiles 40x40x3 mm according to the principal drawings. The floor structures for simulation of weights are constructed analogous to those in the case of segment 2 and segment 3; (7) POS-700: Steel structure of antenna (segment 7). The antenna structure is constructed from steel tubes of a variable diameter. For a thorough insight into the completion of the experimental model, it is necessary to provide a brief description of additional items as follows: a) POS-800 - structure of floor slabs. The structure of the floor slabs has been adapted to satisfy the criteria of easy assemblage and dismantling as well as the condition for realistic simulation of storey weights; b) POS-900: facade structure. The facade structure is constructed as transparent, light structure composed of prefabricated segments that realistically present the outward appearance of the designed prototype structure. To simulate glass, colored Plexiglas plates were incorporated; c) POS-1001: base isolators. The base isolators in the model correspond to the required stiffness and deformability characteristics by which the structure of the base isolation of the designed prototype structure is realistically simulated. These base isolators were manufactured by the Italian company ALGA S.p.a. from Milano which is successfully participating in this development project; d) POS-1002: hysteretic absorbers. The structure of the hysteretic absorbers corresponds to the required stiffness and deformability characteristics by which the structure of the hysteretic absorbers of the designed prototype structure is realistically simulated. These are also manufactured by ALGA S.p.a. from Milan.

Fig.4a. Mr. Zagar (left), Dr. A. Marioni (middle), President of ALGA, Milan and Prof. D. Ristic (right), Author of "Sun Tower" Symbol Building

The experimental model was constructed in the Institute of Earthquake Engineering and Engineering Seismology, at the University "St. Cyril and Methodius", Skopje. The model was constructed by "Saga Engineering" company from Skopje. The first phase (Phase 1) of model testing was realized in the second half of September 1998.

Presented in this paper are the results obtained from these tests. However, the complete experimental results shall be published immediately after the realization of the integral programme of experimental testing. Within the frames of the mentioned experimental Phase-1, the anticipated dynamic tests of the experimental model were realized by application of the forced vibration test method. By these tests,

the main dynamic characteristics of the model, as well as the specific characteristics of its nonlinear dynamic behavior were defined.

Table 1. Dynamic Characteristics of GVCS 26-Storey "Sun Tower" Model (1:10) Defined by Conducted Forced Vibration Tests

Test conditions Dynamic characteristics

No

Segment Loading Seismic isolators

SI

Hysteretic Dampers

HD

Excitation Source

f (Hz)

T (sec)

β (%)

1 Central

Core DL - - EX-50 13.00 0.077 4.9

2 Hanged

(10 stories) DL 8 24 EX-50 8.80 0.113 4.8

3 Base-Isolated

(10 stories)

DL 8 24 GSV-101 3.04 0.329 2.4

Within the frames of the experimental Phase-2, it is anticipated that numerous dynamic tests of the "GVCS" model will be performed in compliance with the elaborated detailed experimental programme. Generally, within the frames of this experimental phase, it is planned that the characteristics of the dynamic response of the model under different types and intensities of real earthquake excitations will be investigated. It is planned that the following ranges of earthquakes will be used: relatively slight earthquakes (earthquake intensity EQI = 0.05 - 0.20 g), moderately strong earthquakes (earthquake intensity EQI = 0.20 - 0.40 g) and very strong earthquakes (earthquake intensity EQI = 0.40 - 0.60 g and greater than 0.60 g). By the planned gradual increase of input intensity for the same dynamic excitation (by a relatively small step of 0.05 g), minimum 10 - 12 dynamic tests shall be realized for each excitation on the average, which means that for 6-10 excitations a large number of experimental tests are expected to be done within the integral experimental programme. Such an ample experimental programme is planned for the purpose of getting as better as possible insight into all the important characteristics of dynamic behavior of the tested model. For the purpose of enabling recording of the time histories of all the relevant parameters (relative displacements, total displacements, accelerations and other parameters), it is anticipated to perform an adequate instrumentation of the tested model. The concept of the instrumentation, the necessary measuring equipment and the contents of instrumentation of the model shall be optimized in the previously prepared programme of instrumentation of the model. In this way, considering the planned ample tests, creation of a large data base relevant for final evaluation of all the essential seismic performances of the tested "GVCS" model of the prototype "Sun Tower" structure shall be enabled.

Taking into account the obtained integral results from the experimental investigations realized in the mentioned Phase-1, the following most essential conclusions can be drawn: (1) The dynamic response of the experimental model is in complete compliance with the expected dynamic behaviour; (2) The "GVCS" structural system has a vast capacity of seismic energy absorption; (3) The frequency characteristics of the different segments are different whereby the main assumptions of the patent have been confirmed; (4) By adequate interventions in the domain of antiseismic devices, it is possible to efficiently control the effective dynamic characteristics of individual segments providing thereby an optimal seismic energy balance; (5) It has been proved that the patented GVCS seismically-resistant system offers great qualitative improvement of the seismic safety of high rice building structures, and can be implemented in practice for efficient seismic protection of buildings.

To demonstrate the fulfilled condition regarding dictated fully controlled and different dynamic characteristics of different segments, some selected characteristic results are presented in Table 1 in

this paper. The table contains the test conditions and experimentally obtained dynamic characteristics of different segments. The indications used are: DL - dead load, SI - seismic isolators, HD - hysteretic dampers, f - resonant frequency, T - resonant period and β - damping coefficient.

4.00 8.00 12.00 16.00 20.00frequency (Hz)

0.00

0.40

0.80

1.20

1.60

norm

aliz

ed d

ispl

acem

ent (

mm

)

f=8.8 Hzβ=4.8 %

f=13.0 Hzβ=4.9 %

Fig.5. Frequency Curve of Central Core and Hinged Segment Under-DL, See Tab. 1

2.00 2.50 3.00 3.50 4.00frequency (Hz)

0.00

0.40

0.80

1.20

1.60

2.00

norm

aliz

ed d

ispl

acem

ent (

mm

)

f=3.04 Hzβ=2.4 %

Fig. 6. Frequency Curve of Base-Isolated Segment with 10 Stories Under-DL, See Tab. 1

In relation with the results presented in Table 1, presented in Fig. 5 and Fig. 6 are the corresponding frequency curves for the central core, the suspended segment and the base isolated segment. These figures provide a very clear insight into the real resonant frequencies of different segments which are very clearly expressed and perfectly separated. Based on knowledge and evidence that has been gained so far from the performed forced vibration dynamic tests (Phase-1), it is expected that the experimental model shall exert a very favorable dynamic behavior under simulated effect of real earthquakes (Tests will be completed as Phase-2).

4. NONLINEAR SEISMIC RESPONSE ANALYSIS OF 26 STOREYS "SUN TOWER"

One of the greatest achievements of the research carried out within the frames of this specific development project has been made in the domain of theoretical treatment of this specific dynamic problem. To that effect, presented briefly in this paper are the first original results obtained from the theoretical simulation of the dynamic nonlinear behavior of the integral structure under the effect of strong actual recorded earthquakes. For these investigations, implemented was the new original computer software NORA-SEB, i.e. computer program developed by the author of this paper on the basis of the previously formulated advanced original theoretical procedure and total nonlinear mathematical model of the integral structure incorporating all specific anti-seismic devices. Due to lack of space, discussed in this paper are only the most essential elements of the applied analytical model and the specific knowledge gained from the performed nonlinear seismic response analyses of the modeled integral "Sun Tower" prototype structure.

The formulated detailed 2D mathematical model of the integral "Sun Tower" prototype structure is presented in Fig. 7 along with indication of nodal points, finite elements and global coordinate system. The mathematical model itself is composed of elements of the individual structural segments as well as special elements of the corresponding "aseismic devices". The mathematical model contains: (1) NNEL - 384 - total number of nonlinear finite elements; (2) NP = 197 - total number of nodal points; (3) NF - 9 - total number of fixed points at the base; (4) NP* = 188 - total number of movable points; (5) NDOF - 3 - number of degrees of freedom of a nodal point; (6) NS = NP* x NDOF = 564 - total number of degrees-of-freedom of motion; (7) EIE = 5 - number of interface elements for each beam

element; (8) NBEAM = 308 - total number of beam finite elements; NASU = 76 - total number of elements of the aseismic devices; (10) NIE = NBEAM x EIE x 2 = 3080 - total number of nonlinear relationships for beam finite elements; (11) NNR = NNR + NASU = 3156 - total number of nonlinear relationships in the mathematical model of the "Sun Tower" structure.

The modeling of the corresponding structural elements and aseismic devices has been done by using individual group of elements as follows: (1) NE = 5, EL = 1-5 - beam elements of the antenna structure (M-ϕ) non-linear modeling concept; (2) NE = 29, El = 6-14 - beam elements of the central core (M-ϕ); (3) NE = 14, EL = 35-48 - columns of the spherical structure (M-ϕ); (4) NE = 20, EL = 49-68 - other elements of the spherical structure (M-ϕ); (5) NE = 8, EL = 69-76 - upper part of the cantilever structure (M-ϕ); (6) NE = 8, EL = 77-84 - lower part of the cantilever structure (M-ϕ); (7) NE = 8, EL = 85-92 - verticals of the cantilever structure (M-ϕ); (8) NE = 8, EL = 93-100 - diagonals of the cantilever structure (M-ϕ); (9) NE = 28, EL = 101-128 - external columns of the suspended stories (M-ϕ); (10) NE = 43, EL = 129-171 - beams of the suspended stories (M-ϕ); (11) NE = 20, EL = 172-191 - inner columns of the suspended stories (M-ϕ); (12) NE = 4, EL = 192-195 - vertical springs - seismic isolators of the suspended stories (Kv); (13) NE = 4, EL = 196-199 - horizontal springs - seismic isolators for the suspended stories (Kh); (14) NE = 12, EL = 200-211 - hysteretic absorbers for the suspended stories (HD); (15) NE = 4, EL = 212-215 - interactive absorbers between suspended and isolated segment (HD); (16) NE = 60, EL = 216-275 - columns of base-isolated stories (M-ϕ); (17) NE = 57, EL = 276-332 - beam elements of the base-isolated stories (M-ϕ); (18) NE = 12, EL = 333-344 - hysteretic absorbers for base-isolated stories (HD); (19) NE = 8, EL = 345-352 - vertical springs - seismic isolators for base-isolated stories (Kv); (20) NE = 8, EL = 353-360 - horizontal springs - seismic isolators for base-isolated stories (Kh); (21) NE = 24, EL = 361-384 - rubber buffers (stoppers) between the central core and the ring segments (Kh);

From the above review, it is evident that the mathematical model contains a total of 308 non-linear beam finite elements modeled by nonlinear relationships M - ϕ and 76 special nonlinear elements modeled by specific and corresponding nonlinear relationships P - δ.

Such formulated completely nonlinear mathematical model of "Sun Tower" prototype structure contains a total of 3156 nonlinear theoretical relationships (Number of Nonlinear Relations, NNR = 3156). To achieve adequate accuracy of nonlinear analyses, a very small time step of ∆t = 0.001 sec. has been applied in solving the nonlinear dynamic equations of motion. This means that a total number of 1000 analyses of the type of classical static analyses have to be performed in order to make analysis of the dynamic behavior of the structure for a time of only one second (1 sec.). Since an earthquake time duration of T = 10 sec (encompassing the most intensive part of the record) has been applied in all the analyses, it means a single dynamic analysis contains in itself a total of 10 000 classical static analyses (NSTA = 10 sec. x 1000 = 10 000 classical static analyses). This parameter clearly indicates the existing extremely large complexity of conducting the non-linear earthquake response analysis of this specific (GVCS) structural system.

Fig. 7. Non-Linear Mathematical Model of "Sun Tower" Structure So far, a series of nonlinear dynamic analyses have been performed by applying different frequency contents and intensities of actual recorded earthquakes. A typical example of time response of point 110 under the effect of El Centro earthquake with a very strong intensity of a = 0.5 g is presented in Fig. 8.

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0Time t [s]

-0.30

-0.20

-0.10

0.00

0.10

0.20

0.30

Dis

plac

emen

t D

[m]

Prototype: "SUN TOWER" El - Centro 0.5 g, T-110, Displacement

Max. displacement

EL Centro 0,5 g

D max = - 0.0985 m

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0Time t [s]

-1.50

-1.00

-0.50

0.00

0.50

1.00

1.50

Vel

ocity

V [m

/s]

Prototype: "SUN TOWER" El - Centro 0.5 g, T-110, Velocity

Max. Velocity

EL Centro 0,5 g

V max = - 0.4500 m/s

0.0 1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0 9.0 10.0Time t [s]

-12.00

-8.00

-4.00

0.00

4.00

8.00

12.00

Acc

eler

atio

n A

[m/s

**2]

Prototype: "SUN TOWER" El - Centro 0.5 g, T-110, Acceleration

Max. Acceleration

EL Centro 0,5 g

A max = 6.1953 m/s**2

Fig.8 Node – 105: Typical Time-History Response of Displacement (a), Velocity

(b) and Acceleration (c) under El-Centro Earthquake ap=0.5g A unique insight into the main seismic performances and characteristics of non-linear dynamic behavior of the applied GVCS seismically resistant system has been obtained on the basis of the results from the performed analytical investigations. Due to limitation of space, attention in this paper shall be focused only on the following most essential observations:

(1) Due to the large energy input reduction and great seismic energy dissipation in the system, the inertial forces affecting the central core have been greatly reduced. This positive effect is manifested such that the stability of the central core is not endangered even under the strongest earthquake intensities;

(2) The suspending segment is characterized by dynamic vibration dominantly in the horizontal direction, as a rigid body motion, which has an extremely positive effect since relative deformations in it are completely eliminated which means that both the structural and nonstructural elements remain undamaged;

(3) The base-isolated segment is also characterized by a dynamic vibration dominantly in horizontal direction as a rigid body motion, which also has an extremely positive effect as to absence of relative deformations which makes possible that also the structural and nonstructural elements remain undamaged:

(4) Aseismic devices, i.e., seismic energy dissipaters which are installed in the form of hysteretic dampers between the central core and the two ring segments (the suspended and the base-isolated one) behave in the nonlinear range during the dynamic vibration which contributes to great seismic energy dissipation. This assertion is evident from the obtained values of plastic deformations pointing directly to the large dissipation of the seismic energy by the installed seismic devices:

(5) Analyzing the computed maximum response accelerations of characteristic nodal points denoted in formulated analytical model, it may be concluded that the GVCS system possess highly favorable effects upon reduction of dynamic amplification. Unlike the classical systems where the dynamic amplification factors DAF may reach the value of 4, 5 or even more, in this case, DAF = 1.3 - 1.6 under the earthquake of the greatest intensity of ap = 0.5g = 4.905 m/sec2, which is an enormous advantage from the application of the invented GVCS system.

5 CONCLUSIONS

The conducted long-term, complex and unique research activities should be generally viewed as part of the specific project entitled "From Patent to Application" originated and promoted by the author of this paper. Up to date, particular efforts have been made in order to complete not only the original creation and the development of the invented GVCS system, but also to successfully complete the realization of many other very important parallel activities and developments including: (1) Patent protection, (2) International promotion of the GVCS system (3) Preparation of consistent and optimized research programme for realization of further development activities, (4) Inventive creation and design of "Sun Tower" prototype structure, (5) Design, construction and testing of experimental model, (6) Realization of unique theoretical developments, including development of special purpose software, (7) Establishment of cooperative national and international contacts crucial for successful continuation of the overall work, (8) Establishment of important contacts with potential cooperation partners in various technical and application domains of interest including promotion of new construction materials, special vibration control devices, advanced construction technologies, etc. Based on the overall engagement of the author with research team and extensive work done up to date, it is clear that this original and creative development will actually result in a valuable contribution to achievement of drastic reduction of severe earthquake catastrophes through construction of high-rise buildings with highly increased seismic safety. Consequently, this study indicates that consistent practical application of the invented GVCS system may be in practice accepted as "a new era in construction of seismo-resistant buildings", particularly because it may simultaneously satisfy the three most important construction conditions: (1) Safe construction; (2) Cheaper construction and (3) Faster construction. Of course, it is a great challenge to confirm these three "target" conditions in the case of planned construction of the designed "Sun Tower" prototype structure in Skopje. In fact, construction of "Sun Tower" prototype structure remains as one of the principal goals of the general project "From Patent to Application".

6 ACKNOWLEDGEMENT

To successfully realize the creative and complex research activities in the area of development of this specific invention, great and highly appreciated support was extended by many experts, individuals and institutions, both domestic and from abroad. I am pleased to mention particularly the Macedonian Ministry of Education and Science, the Institute of Earthquake Engineering and Engineering Seismology at the University "Ss Cyril and Methodius", Skopje, Republic of Macedonia, the Ministry of Development, Industrial Property Protection Office - Skopje, Ministry of Construction, Alga S.p.a. - Milano (Italy), Daris Invent –Skopje, Liting - Skopje, Mavrovo - Skopje, Saga Inzenering - Skopje, Granit - Skopje, Fadom - Strumica, Pelagonija-Skopje, EIC Management GmbH - Oberhausen (Germany) and many other project collaborators, institutions and individuals suppoorting these long-term activities in various ways. The most sincere gratitude is also extended to the members of research team engaged in realization of three year scientific project realized in IZIIS, and particularly to Prof. Dr. Ljubomir Taskov, Prof. Dr. Nikola Nocevski, Dr. Lidija Krstevska, Assoc. Prof. Dr. Snezana Stamatovska, Dr. Viktor Hristovski, Dr. Vlado Micov, M. SC. Nikola Zisi, M. Sc. Nikola Sesov, Prof. Dr. Dragan Hadzievski, Prof. Dr. Milan Arsovski, and others. My acknowledgement is also extended to Prof. Dr. Kosta Talaganov and Prof. Dr. Mihail Garevski, for extended support for realization of experimental part of the project. My sincere gratitude is extended to Prof. Dr. Jakim Petrovski and Prof. Dr. Boris Simeonov for permanent support and encouragement. Finally, my deep acknowledgement is extended to the Macedonian Association of Structural Engineers (MASE) and to the Macedonian Association for Engineering Mechanic, for extended continuous interest in this research and permanent support.

7. AWARDS RECEIVED

The originality and high potential of this specific invention are very well recognized up to date. This is directly confirmed by received the highest awards in the area of inventions:

• First, this invention was awarded with gold medal in the field of civil engineering at the 23-rd International exhibition of inventions held in Geneva, Switzerland from 31.03. to 09.04 1995.

• Second, in 1996 the invention was awarded with distinguished unique national award "Patent of the Year" in the Republic of Macedonia.

• Thierd, in February, 1998 the invention was awarded with "Gold metal with mark" at the International exhibition of inventions held in Casablanca, Maroco.

• Forth, on September 1999 the invented "GVCS" was awarded with the highest national award "Patent of the Decade" by the Government of the Republic of Macedonia.

• Finally, this project is promoted at EXPO-2000, the greatest world exhibition of inventions and new technologies for the 21st century, held in Hanover, Germany, (June 1 to October 31, 2000). The project was officially nominated by the Government of the Republic of Macedonia to represent new and advanced national achievements in the field of INVENTIONS AND SCIENCE. At present related research activities are continued and will be more concentrated to practical application, particularly to construction of “Sun Tower Symbol Building” in Skopje.

8. ACKNOVLEDGEMENT TO PATRON OF THE INVENTIVE PROJECT It is my great honor to express sincere personal gratitude to Mr. Branko Crvenkovski, President of Government of Republic of Macedonia, for his appreciated comments expressing strong encouragement to continue with further project phases up to complete realization of this unique long-term but very significant project for Republic of Macedonia. Particularly, I am expressing my gratitude for his acceptance to be patron of the integral project started with promoting the project

during visiting IZIIS and by attending initial laboratory tests, as well as for extended permanent support. The extended support is highly appreciated and next phases will be continued in order to reach the point when Sun Tower in Skopje will be reality.

9. REFERENCES

Ristic, D. 1998. Concept of New Combined Seismic Energy Balanced System Efficient for Earthquake Protection and Seismic Vulnerability Control of Buildings, Proceedings 11ECEE, Paris, France.

Ristic, D. 1998. Toward Practical Application of the New GVCS - System of Seismo-Resistant Buildings (Patent of the Year of the Republic of Macedonia), Project: Symbol Building "Sun Tower", 6-th Symp. for Engineering Mechanics, Ohrid, Republic of Macedonia.

Ristic, D., M. Popovski, V. Hristovski, N. Zisi, N. Nocevski, 1994. Seismic Vulnerability Reduction of Reinforced Concrete Buildings and Industrial Halls Using Base-Isolation and Vibration Control Devices, Proceedings 10ECEE (1): 755-760, Vienna, Austria. Rotterdam: Balkema.

Ristic, D. 1994. New Methodological Concept for Structural Diagnosis and Seismic Vulnerability Analysis of Classical and Base-Isolated Structures (in Macedonian), Proc. 5th Symp. for Theoretical and Applied Mechanics, Ohrid, Republic of Macedonia.

Ristic, D. 1992. Vulnerability Assessment of Existing Buildings and Development of Analytical Vulnerability Functions, Part-2 of Vol. IV, Guidelines for Earthquake Damage Evaluation and Vulnerability Assessment of Buildings, Earthquake Protection of Engineered Buildings, United Nation Centre for Human Settlements (HABITAT), UNDP-UNCHS (HABITAT), Project IRA/90/004, Tehran 1992.

Ristic, D. 1988. Nonlinear Behavior and Stress-Strain Based Modeling of Reinforced Concrete Structures under Earthquake Induced Bending and Varying Axial Loads. Ph.D. Dissertation, School of Civil Engineering, Kyoto University, Kyoto, Japan.

Oncevska, S., Gugulovski M. and Ristic, D., 1994. Verification of MF-NONMIFE analytical model based on results of quasi-static experimental tests of RC columns. Proc. 5th Symp. for Theoretical and Applied Mechanics, Ohrid, Republic of Macedonia.

Micov, V., Ristic, D., et al. 1994. Hysteretic Characteristics of Laminated Rubber Bearings and Modeling of Inelastic Earthquake Response of Integral Bridges. Proceedings 10ECEE (3): 2001 – 2106 Vienna, Austria. Rotterdam: Balkema

Hristovski, V. and Ristic, D. 1994. Algorithm for Moment-Curvature and Moment-Axial Force Diagrams for Random Traditionally Reinforced and Prestressed Concrete Cross-Sections (in Compliance with European Standards) and Their Application in Nonlinear Analysis of Structures. Third National Conference on Reinforced Concrete Structures, Sofia, Bulgaria.

Zisi, N. 1995. Formulation of non-linear micro-analytical model for prediction of earthquake induced damage degree of traditionally RC buildings, Master thesis, IZIIS, Skopje, June 1995.

Petrovski, J., D. Ristic and N. Nocevski. 1992. Evaluation of Vulnerability and Potential Seismic Risk Level of Buildings. Proceedings 10WCEE (1): 509 - 514, Madrid, Spain, July 1992. Rotterdam: Balkema

Ristic, D., et. all., “GVCS-Structural System: New Technology For Construction of Seismo-Resistant Buildings for Actions of Very Strong Earthquakes”, Journal of Structural Engineers of Macedonia, Volume-1, No. 2, October 1995, (Invited Paper).

Ristic, D., Principal Investigator (Scientific Project-1, Duration: 3-Years), “Formulation of Nonlinear Models and Energy-Based Criteria for Earthquake Damage Degree Prediction and Its Application for Seismic Risk Control of Classical and Base Isolated Buildings”, Period of Realization 1993-1995, Ministry of Science of the Republic of Macedonia, (Final Report).

Ristic, D., Principal Investigator (Scientific Project-2, Duration: 3-Years), “Development of Vibration Control Systems for Seismic Risk Reduction of Bridge Structures”, Period of Realization 1993-1995, Ministry of Science of the Republic of Macedonia (Final Report).

Ristic, D., Principal Investigator (Scientific Project-3, Duration: 3-Years), “Experimental Testing of GVCS-System for Construction of Seismo-Resistant Buildings Based on Model Testing of Real Building on Seismic Shaking Table”, Ministry of Science of the Republic of Macedonia (Final Report).

Ristic, D., Principal Investigator (Scientific Project-4, Duration: 3-Years), “Systems for Seismic Isolation Applicable For Seismic Protection of New and Seismic Revitalization of Existing Bridges”, Period of Realization 1997-2000, United States-Macedonian Science and Technology Cooperation Programme (Final Report).

Ristic, D., “Sun Tower – Symbol Building”, 26-Story Seismo-Resistant Prototype Symbol Euro-Port Building in Skopje, (Invention:GVCS Seismo-Resistant Buildings Taller of 8 Stories). Nationally Nominated Inventive Project and Author, Representing Republic of Macedonia In The Field of “INVENTIONS AND SCIENCE, World Exhibition, EXPO-2000, Hannover, Germany, June 01–October 31, 2000.

Ristic, D., “Seismically Safe Cities of The Future”, (Invention:GOSEB Seismo-Resistant System, Buildings Up-To 8 Stories and Other Types of Structures).). Nationally Nominated Inventive Project and Author, Representing Republic of Macedonia In The Field of “INVENTIONS AND SCIENCE, World Exhibition, EXPO-2000, Hannover, Germany, June 01–October 31, 2000.

Ristic, D., European Project-5: INCO COPERNICUS–"EUROQUAKE", “Towards European Integration in Seismic Design and Upgrading of Building Structures”, Leader of Task-2: “Refined Non-Linear Numerical Simulation of R/C Iinfilled Frames”; (Participating European Centers: University of Bristol-England, European Joint Research Center(JRC)-Ispra-Italy, ISMES-Italy, University of Ljubljana-Slovenia, Academy of Science-Slovakia, ECOLAND-Romania, and IZIIS-Republic of Macedonia), Financed by RTD Fund, Brussels, Duration: 3-Years (Final Report).