WO2001073212A1

WO2001073212A1 - Aseismic supporting structure

Info

Publication number: WO2001073212A1
Application number: PCT/MK2001/000001
Authority: WO
Inventors: Antim Antimovski; Ljubomir TAŠKOV; Mirče KOKALEVSKI
Original assignee: Antim Antimovski; Ljubomir Taskov; Mirce Kokalevski
Priority date: 2000-03-31
Filing date: 2001-03-23
Publication date: 2001-10-04
Also published as: AU2001239583A1

Abstract

Aseismic Almost Lifted Structure ('AALS') is a specific solution of problems related to earthquake and similar disturbances, which belongs to the well known 'sliding concept', where the main structure (MS) is split from the supporting structure (SS) by a low friction material (LFM), thus allowing the main structure to slide, when forced. The sliding force is controlled by means of system for lifting of the main structure (LS). Because of large lifting force, the 'AALS' system has a very small friction force i.e. very small seismic force could be transmitted to the main structure during an earthquake. The 'AALS' is defined by the following simple formulas: G = L + N, L >> N, N > or = 0, Fr = mu N, 'Fr' is the horizontal force (friction force) which is transmitted to the MS, 'G' is the total weight of the main structure, 'L' is lifting force, 'N' is compression force at the dry contact(s), 'mu' is the friction coefficient.

Description

ASE1SMIC SUPPORTING STRUCTURE

(Almost) Lifted Structure Concept ("ALSC") is a specific solution of problems related to earthquake and similar disturbances, which belongs to the well known "sliding concept", where the main structure(MS) is split from the supporting structure(SS) by a low friction material(LFM). thus allowing the main structure to slide, when forced, characterized by that, a system for lifting the main structure(LS), as well as, when necessary, a number of horizontal displacement limiters (DL) are provided, in addition.

The man made structures, even in th most developed countries, have suffered heavy damages with catastrophic consequences in the resent past earthquakes. Most of them have been designed in correspondence with the actual official codes. It is a very clear message for earthquake engineering scientists, that a new approach in aseismic design of the structures should be developed. The "ALSC" system belongs to above mentioned new approach, offering an opportunity for reduction of earthquake effects on a simplest, cheapest and most effective way. A. Description of the ALSC system In Fig. l the principal concept of the claimed system is presented:

SS is the Supporting Structure (sometimes the terrain itself, covered with sheet/s of plastics, for example for low cost housing). In most cases the SS will be a rigid supporting structure, grounded.

MS is the Main Structure, for example: a house, or a building, or a sports stadium, or a liquid storage tank(LST) etc.

LS is a Lifting System, for example consisting of channel/s, or dish/es, or combined, filled with pure liquid, or with liquid with additives and put under pressure "p", this pressure being such, as to keep the MS in the status of (almost) lifted. - LFM is representing the remaining contact surface between the main and the supporting structure, which should be any flat, smooth and low friction support. - "G" is the total weight of the MS

"L" is the total lifting force of the lifting system. (LS) "N" is the difference between the total weight of the main structure and lifting force (G-L), i.e. the compression force acting at the contact between the two structures (MS and SS) where there is no liquid. Theoretical considerations related to "ALSC" system The claimed ALSC system is defined by the following simple equations:

G = L+N B.l.

L » N B.2.

N > 0 B.3.

Fr = μN B.4. - "Fr" is the horizontal force(friction force) which is transmitted to the MS. Stronger seismic forces than Fr are neglected by the MS. The structure responds than with sliding. The ground displacement during an earthquake is a random and oscillatory process, so it is difficult to say how much the structure will be displaced if sliding happens. Normally, few centimeters. In extreme cases much more. There are two alternatives to solve this problem: a. Neglect this residual displacement. This is applicable in case of low cost housing and favorable position of the structure. Eventually, in the regions with low earthquake intensity. b. Provide adequate protection against unacceptable displacement of the main structure by implementing a number of displacement limiters (DL)

Concerning the possibility for centering of displaced structure, the ALSC system is the more convenient in comparison to any other existing systems, "μ" is the friction coefficient. For better earthquake protection, "μ" should be very small. The classical "sliding systems" developed up to day, have succeeded to " drop" the value of "μ" to 0.15 only. That means that the friction force( at which the

MS starts sliding) will be 15% of the total weight of the MS. This is still quite a strong force which require complicated and expensive " centering system". The displacement limiters (DL) of the "ALSC" system are very small, simple and cheep because the " Fr" is very small as a result of considerable reduction of the compression force (N) at the contact surface (according to the formulas B.3. and

B.4.) The reliability of the "ALSC" is better than of any other known system, by far, if adequate attention is paid to the following: a. There is always a vertical acceleration "av" present in the oscillatory movement of the ground during the earthquake events. Consequently, the total weight of a structure is not constant:

G = m( g +/- av) B.5. where: "m" is the total mass of the structure

"g" is the ground acceleration(9.81m/sec2)

N=G-L B.6. where: "N" is the total compression force at the contact

"L" is the total lifting force This means that the total lifting force for high value of "av" could exceed the "G" and structure could be lifted. Consequently, considerable loss of the liquid will appear. That's why, lifting system with constant liquid pressure (independent of "av") should be used only in regions with low earthquake intensities or when a large quantity of the pressurized liquid is available. For example the ALSC for protection of large liquid storage tanks(LST). b. This problem does not exist for lifting systems where the total lifting force

"L" is dependent of the said vertical acceleration "av". One solution is, for example the ALSC system in which the pressure in the lifting liquid is produced by a vertical tube, filled with liquid. If "h" is the height of the liquid in the tube, the pressure at the bottom of the tube and at the contact surface between the supporting and the main structure is: P = pgh B.7. where: "p" is the specific density of the liquid in the tube p = ph(g+/- av) (for av ≠ O) B.8.

L = pS = phS(g+/-av) B.9. where "S" is the contact area with the liquid

N = G - L = (m- phS)(g+/-av) B.10. where "N" is the total compression force at the contact where the liquid is not present.

The formula B.10. leads to the conclusion that the structure will never be lifted, as long as the vertical acceleration "av" is smaller than gravity acceleration "g", which is the most frequent case. Even in the case when "av">"g", it is a very short time expressed in milliseconds. So, the liquid in the lifting system is preserved and the ALSC system remains reliable. c. The attention should be paid to the fact that the horizontal acceleration "ah" of the ground motion is acting on the liquid/s of the lifting system(LS), too. Therefore the long horizontal channels and big dishes should be obligatory located in the main structure(MS). If not, the horizontal ground acceleration may produce lifting of one or other side of the structure and lead to considerable loss of the liquid in the lifting system. d. The attention should be paid to the "wind effect" also. The "wind effect" may present the limits for the said friction force(Fr), when select the minimum value to reduce the earthquake effects. Three solutions are possible with the claimed

ALSC system: dl . - To keep permanently the total compression force "N" at the contact surface to a level at which the said friction force(Fr) is big enough to prevent the sliding caused by wind forces. d2.- To adjust the change of pressure in the lifting system(LS) of the ALSC in accordance with the event(wind or earthquake), eventually by computer control, or d3.- To prevent the unwanted sliding by adjusting of the horizontal displacement limiters (DS) e. The attention should be paid to the possibility of freezing of the liquid in the lifting system. This problem is to be solved by any conventional means. f. By planning the ALSC for a specific structure, endeavor should be made to prevent any damage of the structure which could provoke lose of liquid in the lifting svstem. g. Sometimes, when the height of the structure is not sufficient "to hide" the vertical tube of the lifting system, in order to increase the pressure, a heavy- piston at the top of tube which could slide in it , should be considered. C. Advantages of the ALSC system The "ALSC" system has many advantages comparing to the classical structural systems as well as the other base isolation systems, particularly because:

• It is reliable for any earthquake intensity, as long as the supporting structure remains intact.

• The technical solution is very simple • The repairing/replacing of the particular component of the system is very cheap and simple

• The ALSC system offers maximum reduction of energy transmission from supporting to the main structure, regardless the intensity of ground shaking. The bending and shear forces in the main structure, and consequently, relative storey drifts, are thus almost eliminated.

• The ALSC system offers a possibility for easy displacement and /or rotation of the main structure, if required.

• It is very cheap and long-life system

• The new structures with ALSC system should be cheaper than with other techniques because the main and supporting structures will have more rational dimensions.

• If the claimed ALSC system is designed and built-in properly, and in accordance to the above mentioned criteria, the performance of the structure during an earthquake will be more favorable than with any other known system. The human protection and safety will be of high level. D) Examples of the "ALSC" system

Example 1: (Almost) lifted building with "suspended weight displacement limiters" The "ALSC" system presented in Fig.l , consists of the following elements:

• MS - Main structure

• SS - Supporting structure • LS - Lifting system

• VT - Vertical tube R - Reservoir SPT - Soft plastic tube 4 - Metalic ring LFM - Low friction material DL - Displacement limiter (suspended weight type) Example 2: (Almost) lifted building with "spherical bearing displacement limiters" The "ALSC" system presented in Fig.2, consists of the following elements: MS - Main structure SS - Supporting structure LS - Lifing system VT - Vertical tube R - Reservoir SP - Soft plastic HP - Heavy piston SPT - Soft plastic tube 4 - Metalic ring LFM - Low friction material DL - Displacement limiter (spherical bearing type) P - Pump

Example 3: (Almost) lifted wall/ column with "spherical bearing displacement limiter"

The "ALSC" system presented in Fig.3, consists of the following elements: MS - Main structure SS - Supporting structure LS - Lifting system VT - Vertical tube SPT - Soft plastic tube 4 - Metalic ring LFM - Low friction material (1+2) - Displacement limiter (spherical bearing type) • P - Pump

• 3 - Hole for liquid flow

Example 4: (Almost) lifted column with "spherical bearing displacement limiter" ( applicable for modification of the existing classical structure)

The "ALSC" system presented in Fig.4, consists of the following elements: MS - Main structure SS - Supporting structure LS - Lifting system SPT - Soft plastic tube

4 - Metalic ring (1+2) - Displacement limiter (spherical bearing type)

6 - Metalic ring

5 - New concrete

7 - SPT holder

Example 5: (Almost) lifted liquid storage tank

The "ALSC" system presented in Fig.5, consists of the following elements:

• MS - Main structure (liquid storage tank)

• SS - Supporting structure

• LS - Lifting system

• PT - Flexible plastic tube

• SPT - Soft plastic tube

• 4 - Metalic ring

• LFM - Low friction material

• DL - Displacement limiter (suspended weight type) E) References:

1. Wiliam H. Robinson, " Latest Advances in Seismic Isolation". 1 1 WCEE. 1996. Acapulco, Mexico

2. R. Duarte. F. Emilio. F.J. Carvalhal, Felicita Pires." A New High- Performance system of Base Isolation". 11 ECEE, 1998. Paris, France 3. Arya.A.S." Sliding Concept for Mitigation of Earthquake Disaster to Masonry Buildings", University of Roorkee, India

4. F. Mhammadi Tehrani, A. Hasani, "Behavior of Iranian Low Rise Buildings on Sliding Base to Earthquake Excitation", 1 1 WCEE, 1996, Acapulco, Mexico 5. M. Qamaruddin, S.K. Al- Oraimi, K.S. Al-Jabri," Worldwide Development of Friction

Seismic Isolation Scheme for Masonry Buildings, 1 1 WCEE, 1996, Acapulco, Mexico

6. Xiyuan Zhou, Miao Han," Optimum Design of Resilience- Friction-Slide Base Isolation System for Low Cost Buildings", 11 WCEE, 1996, Acapulco, Mexico

7. R. Zaamorano, M. Sarazin, G. Toro." Development and Testing of Teflon Sliding Bearings", 1 1 WCEE, 1996, Acapulco, Mexico

8. J.M. Kelly," Seismic Isolation as an Innovative Approach for the Protection of Engineered Structures", 11 ECEE, 1998. Paris, France

9. A.S. Ikonomou," Alexisismon Seismic Isolation Levels for Translational and Rotational Seismic Input", University of Patras, Greece 10. K. Kitazawa, A. Ikeda, S. Kavamura," Study on a Base isolation System", Taisei

Corporation, Japan

Claims

1. " (Almost) lifted structure concept" is a specific solution of problems related to earthquakes and similar disturbances, which belongs to the well known "sliding concept", where the main structure(MS) is split from the supporting structure(SS) by a low friction material(LFM), thus allowing the main structure to slide when forced, characterized by that, a system for lifting the main structure(LS), as well as. when necessary, a number of horizontal displacement limiters (DL) are provided, in addition.

2. " (Almost) lifted structure concept" as in claim 1 , characterized by that, the said lifting system(LS) consists of channel/s. or dish/es, or combined, "located" preferably in the main structure(MS) and filled with liquid, eventually with additives, which is put under pressure, this pressure being such as to keep the main structure(MS) in a status of (almost) lifted and the licking of the said liquid being prevented, for example, by loop/s of soft plastic tube(SPT), the shape of which is presented in Fig.l, provided with inlet s for its pressurization with air, in order to carry also a portion of the weight of the main structure(MS).

3. " (Almost) lifted structure concept" as in claim 1. characterized by that, a significant portion of the contact surface between the main structure(MS) and the supporting structure(SS) is in the form of channel/s, or dish/es, or combined, "located" preferably in the main structure(MS) and filled with liquid, mud, powder etc., which is put under pressure by any conventional means, for example by vertical tube(VT). eventually with a reservoir on top, filled with liquid, presented in Fig.l and Fig.2., the pressure at the said contact being such as to keep the main structure(MS) in a status of (almost) lifted, permanently or programmed, in which case the said pressure is, eventually, computer controlled.

4. " (Almost) lifted structure concept", as in claim 3, characterized by that, the said computer control is for an individual structure or, common for a town or so.

5. " (Almost) lifted structure concept" as in claim 1. characterized by that, the said horizontal displacement limiters (DL) such as: suspended weights, presented in Fig. l , spherical or conical bearings, presented in Fig.2 and Fig.3. hydraulic cushions, springs, etc., are for the individual structures, or common for a group of near-by structures, in which case the main structures(MS) are interconnected and the said limiters are made intelligent, eventually.

6. " (Almost) lifted structure concept" as in claim 2 and 3, intended for protection of liquid storage tanks(LST), characterized by that, the said vertical tube(VT) with a reservoir on top is flexible, presented in Fig.5, so that the said reservoir is permanently floating in the liquid of the storage tank.

7. " (Almost) lifted structure concept" as in claim 1 and 2, intended for protection of a group of near-by structures, characterized by that, the lifting system of the individual structures are adequately interconnected. °

8. " (Almost) lifted structure concept" as in claim 7, intended for protection of liquid storage tanks(LST), characterized by that, not only the individual lifting systems but the liquids of the said tanks are also adequately interconnected, in which case the filling and the emptying of the said tanks is common.

9. " (Almost) lifted structure concept" as in claim 1 ,2 and 3, for structures intended to be ⁵ willingly displaced and/or rotated, characterized by that, the lifting system is provided with an inlet for an external pressure source, a pump for example, to be added temporally to the said lifting system.