Increasing buildings’ resistance to earthquake forces is not always a desirable solution especially for the building contents that are irreplaceable or simply more valuable than the actual primary structure (e.g. museums, data storage Centre’s, etc.). Base isolation and seismic dampers can be employed to minimize inter-story drifts and floor accelerations via specially designed isolation and dampers system at the structural base, or at higher levels of the superstructure. In this research, we’ll examine the response of buildings isolated using isolation system hybrid consisting of Lead-Rubber Bearings (LRB), Flat Sliding Bearings (FSB), with the addition of Rotation Fiction Damper (FD) at the base, then compare the results with buildings that have traditional foundation, in terms of the (period, displacement and distribution shear force and height of the building). It conducts TIME HISTORY seismic analysis for some varying height buildings (eight, twelve, sixteen, and twenty stories), with help of SAP2000 using an earthquake acceleration-time history for (El- Centro). The results show that the use of insulation system Hybrid has had a significant impact on improving the performance of origin in terms of reducing displacements and base shear with in-creasing height of the building, but has had a negative impact on the drift, which leads to an in-crease in drift with the increased flexibility of the building.
The traditional design principle of the earthquake resistant structures is that each element of the structure is able to resist the applied seismic forces with enough plasticity to absorb vibration energy caused by the earthquake. In this case, you get a large plastic deformation in the structural elements that are difficult to repair and restore after the earthquake and might develop to an irreparable structure [
Therefore, the uses of the seismic isolation system in these structures have a major positive role for these buildings resistant to earthquakes [
The seismic isolation method is a creative seismic design method intended to protect the structure against the seismic risk and reduce the seismic energy and forces that structure suffer and not directly resist those forces [
Traditional structure without isolating seismic suffers important floor offsets during earthquakes, which could lead to the structure collapse. While isolated structure vibrates as a solid body by large deformation at the base, (
Characteristics of Well-Designed Seismic Isolation Systems (
・ Flexibility to increase period of vibration and thus reduce force response (
・ Energy dissipation to control the isolation system displacement (
Rigidity under low load levels such as wind and minor earthquakes.
The success of any seismic isolation system structure mainly on the quality of the bearings used in the system,
which is supposed to provide flexibility horizontal and damping required in addition to the return of power.
The modern seismic isolation systems for the base are classified into two categories [
ü Electrometric bearing system (
ü Bearing systems sliding (Figures 4-5).
Of the most important rubber bearings used in isolation structures are rubber bearings low or high damping or low damping natural rubber with lead core (LRB) [
Is based on lead-core generate hysterical damping and hence power dissipation, also depends on the rubber in the generation of forces returns (
Based system for power dissipation on the friction generated between the composite material which usually consists of high strength material soily or gummy known as “PTFE” (poly tetra fluoro ethylene), and sliding surfaces of steel (stainless steel) (Figures 4-5).
Insulation systems are classified slider turn into two types: [
・ Spherical Sliding Bearing (
・ Pure friction system (
Proven experience and expertise previous that slider isolation systems, which rely horizontal sliding surfaces (
Recall of these systems:
Is the frictional insulation system depends on the geometric shape and the forces of gravity in prolonging natural vibration period of the isolated structure and ingenerates returns the mechanics, and thus face seismic forces with high wrenches (
Sliding bearings provide an elastic-perfectly plastic hysteresis shape with no strain hardening after the applied force exceeds the coefficient of friction times the applied vertical load (
In practice, sliding bearings are not used as the sole isolation component for two reasons [
1) Displacements are unconstrained because of the lack of any centering force. The response will tend to have a bias in one direction and a structure on a sliding system would continue to move in the same direction as earthquake aftershocks occur [
2) A friction bearing will be likely to require a larger force to initiate sliding than the force required to maintain sliding. This is termed static friction, or “stickion”. If the sliders are the only component then this initial static friction at zero displacement will produce the governing design force [
Although the devices isolation seismic are manufactured typically with the ability to dissipate the energy and control to max move for device isolation, but there are situations we need to complementary mechanisms of the insulation system (dampers) to dissipate energy and to reduce the displacements [
Some of these cases [
-The location is close to seismic source dominant.
-To be under the soil layers insulation systems of tor weak.
-The isolation devices are prone to instability in the light both sides of the large deformation.
-Architectural considerations that limit the seismic interval allowed.
-The practical limitstostructureservicesandtheirtowithstandgreatmoveforisolationsystem.
-This device is designed to dissipate seismic energy and protect buildings from structural and structural damage during earthquakes moderate and severe (
-The damper has been tested at DTU in Denmark and later on experimental tests have also been carried out with the pure friction damper at Takenaka research center in Japan. The comparison of results obtained from the experimental and numerical models shows good agreement [
-Also uses rotational friction damper (FD) with other insulation systems such as (LRB) or (FPS) and others, as complementary dampers to control the Insulation deformation, and also for the formation of a hybrid insulation systems.
-The numerical studies have demonstrated that the overall response is mainly affected by damper properties as geometry, frictional sliding moment and viscoelastic properties combined with the structural natural frequencies [
-The device is easy to manufacture and implement in structures (
Types of dampers, friction dampers which are used to solve the problem of the nearby distance between buildings (
This also added to the insulation system as supplemental to control on the displacement (
-Study the effect of basement isolation system hybrid (LRB + FSB) on the response of isolated structures.
-Study combined effect the seismic isolation system hybrid (FSB, LRB) with rotational friction damper (FD) and its impact on structure response.
The characterised strength (Q) is effectively equal to the yield force (Fy), of the lead plug. The yield stress of the lead plug is usually taken as being around 10 MPa. The effective stiffness
The energy dissipated for one cycle of sliding, with amplitude (D) (
The effective percentage of critical damping provided by the isolator (
For Spherical Bearings:
Flat Bearings (
where:
µ: Coefficient of friction for the sliding.
W: Total seismic forces.
・ Bearings do NOT increase natural period of structure; rather they limit the shear force transferred into the superstructure (
・ Requires supplemental self-centering mechanism to prevent permanent isolation system displacement (Fig- ure 11) [
Modeling of friction damper as spring form (Plastic Wen link [
The force in the Rotation Friction Dampers (FD) are determined in
z: hysteretic variable where
F: forced, d: deformation, k: Stiffness, y: yield force, r: yield ratio.
The schematic as well as basic principle of the proposed damper are shown in
Combination of rotation friction dampers, rubber bearings and flat sliders (
The free vibration analysis, time history earthquake analysis is performed by using SAP 2000 software, the natural and mode shapes of the building are obtained from the free vibration analysis, from the time history analysis, the time dependent dynamic responses of the building for the whole duration of the earthquake excitation, the base shear, displacement, shears, moments and axial loads of the elements at various amounts of earthquake ground motions have been determined.
The understanding of seismic behavior of building structure by isolators has been done by four analysis methods such as―(without use of seismic isolation, structure foundations of traditional) (Fix), use isolation methods (rubber and sliding isolators) (LRB + FSB), (rubber, sliding with rotation friction dampers at the base of the building) (FD + FSB + LRB)
El Centro earthquake is selected for Time History analysis to understand the seismic performance of the case study building.
We will study the building several heights (eight-story, twelve-story, sixteen floors, and twenty-story).
The studied construction of reinforced concrete (
The required material properties like mass, weight density, modulus of elasticity shear modulus and design values of the material used can be modified as per requirements or default values can be adopted Beams and column members have been defined as “frame elements” with the appropriate dimensions and reinforcement. Soil structure interaction has not been considered. Slabs are defined as area elements having the properties of shell elements with the required thickness.
In our case, the slabs have been modeled as rigid diaphragms and in this connection, the center of rigidity (mass) and center of gravity of building is considered same in order to neglect the effect of torsion.
q T)Fixed) = 0.7 sec
q T)FSB + LRB) = 1.9 sec
q T)FD + LRB + FSB) = 0.9 sec
q T)FD1 + LRB + FSB (= 1.89 sec
Comparing the Displacements of cases isolation (
Comparing the floor drift of the structure height 8 floors (
Comparing Base shear of cases isolation (
We have the follow-up analysis of the structure of the higher (12-16-20) floor and compare the results in terms of period (
Comparing the results of the use of hybrid isolation system (LRB + FSB) with friction damper (FD) on the base shear (
Number of story | Fixed base | Rubber and sliding isolators (LRB, FSB) | Rubber, sliding with rotation friction dampers at the base of the building (FD, FSB, LRB) | Rubber, sliding with rotation friction dampers at the ground floor level (FD1, FSB, LRB) | The amount of reduction of base shear as a result of isolation structure % | The amount of reduction drift as a result of isolation structure % | ||||
---|---|---|---|---|---|---|---|---|---|---|
Time period (sec.) | Base shear (ton) | Time period (sec.) | Base shear (ton) | Time period (sec.) | Base shear (ton) | Time period (sec.) | Base shear (ton) | |||
8 | 0.7 | 655 | 1.9 | 350 | 0.9 | 324 | 1.89 | 351 | 47% | 65% |
12 | 1.1 | 883 | 2.37 | 341 | 1.41 | 311 | 2.36 | 345 | 61% | 74% |
16 | 1.5 | 497 | 2.94 | 466 | 1.83 | 325 | 2.93 | 458 | 6% | 28% |
20 | 2 | 564 | 3.31 | 582 | 2.3 | 390 | 3.31 | 581 | −3% | 13% |
Number of story | Rubber and sliding isolators (LRB, FSB) | Rubber, sliding with rotation friction dampers at the base of the building (FD, FSB, LRB) | Rubber, sliding with rotation friction dampers at the ground floor level (FD1, FSB, LRB) | Reduction displacements the result of adding rotation friction damp ers at the base of the building on isolated structure % | Reduction displacements the result of adding rotation friction dampers at the ground floor level on isolated structure % |
---|---|---|---|---|---|
Max, min displacements (mm) | Max, min displacements (mm) | Max, min displacements (mm) | |||
8 | 52 - 75 | 32 - 61 | 53 - 71 | 28% | Almost without change |
12 | 40 - 67 | 25 - 62 | 40 - 67 | 19% | Almost without change |
16 | 97 - 127 | 30 - 91 | 77 - 121 | 46% | 11% |
20 | 129 - 213 | 39 - 152 | 130 - 211 | 44% | Almost without change |
Number of story | Effect on drift as a result of adding rotation friction dampers at the base of the building on isolated structure % | Effect on drift as a result of adding rotation friction dampers at the ground floor level on isolated structure % | |
---|---|---|---|
8 | Increase (48%) | Almost without change | |
12 | Increase (18%) | Reduction (13%) | |
16 | Increase (27%) | Reduction (8%) | |
20 | Increase (15%) | Reduction (15%) |
1) The results of displacement show that the displacements are increased with the period and with the story height in the base isolated building.
2) The effectiveness of hybrid isolation system (LRB + FSB) in reducing the base shear and drift of the structure isolated decreases with increased flexibility of structure.
3) Using hybrid isolation system (LRB + FSB) with the addition of rotation friction dampers (FD) at the base of the structure, has had a significant impact on improving the performance of isolated structure by hybrid isolation system (LRB + FSB), in terms of reducing displacements, base shear with increased height, but has had a negative impact on the drift, which lead to an increase in the drift with the increased flexibility structure.
4) Using hybrid isolation system (LRB + FSB) with the addition of rotation friction dampers (FD) at the ground floor level is not effective, and does not lead to any improvement in the performance of structure isolated by (LRB + FSB), in terms of displacements or base shear, while it has a positive effect on reducing the drift with the increased flexibility structure.