EXAMPLE ANALYSIS OF BUILDING SEISMIC ISOLATION DESIGN

1.Design basis

According to (construction seismic design code)

 ( EN 15129, EN 1337,GB50011-2010),(regulations), “government no.3 hospital”  project seismic fortification criterion is 8 degree (0.3g), the designed basic seismic oscillation’s accelerated speed is 0.30g, The second group of design earthquake, II site.

 Seismic isolation structure is as an effective passive control mode, through adjusting the natural vibration period of original structure to keep it away from predominant period of ground motion, thereby reducing the earthquake response of structure observably. It has been through so much study at home and abroad and it has been widely used in actual project.

 Because the horizontal stiffness of seismic isolation system is small, the period of superstructure can be extended more than 3 seconds to reduce the earthquake produced structure’ acceleration responses greatly, the seismic isolation system can also absorb earthquake energy and the energy dissipation of additional adhesive tape damper by making use of seismic isolation bearing’s nonlinear deformation to increase damping ratio of system, thus it can reduce the earthquake’s acting force on buildings.

2 Earthquake shearing force’s Analysis of designed seismic oscillation

Through calculating and analysis, all bottom shearing force of elastic non-isolated structure calculated in each group time travel curve are greater 65% than the calculated result of response spectrum. The average of bottom shearing force in three group time travel curve is greater 80% than the calculated result of response spectrum, but each group time-histories result should be not great 135% than response spectrum result, three groups time-histories results aren’t greater 120% than response spectrum result, all meets standard requirements. The maximum earthquake response value under the action of three groups time travel curve is as the finally calculated value of time history analysis and the result is reliable, which can be used for project’s design. Figure 3.2-1 shows the each floor’s shearing force of non-isolated structure under 8 degree (0.3g) earthquake.

It can be seen in above table, the base shearing force under time history analysis of non-isolated structure meet the standard requirements for earthquake wave, The above three earthquake wave can be used for seismic isolation analysis and elastic-plastic analysis.

3. Design of isolation layer

 Through layout rubber bearing and lead rubber bearing reasonably in isolation layer, it can make isolation structure have larger vertical bearing capacity, changeable horizontal stiffness, horizontal elastic restoring force and make it meet anti-seismic and wind resistance’s requirements.

Through the calculating and analyzing, confirming to use base isolation and the isolation layer is located between main roof of structural elevation and ±0.000. Totally setting twenty seven isolation bearings, fourteen LRB600, two LNR600, eleven LRB500. Controlling the long time surface pressure of each isolation bearing no more than 12Mpa. The deployment diagram of isolation bearing reference figure4-1, all parameter of isolation bearing reference table 4-1.

The surface pressure analysis of isolation layer

surface pressure control, For long time surface pressure, it should consider the function of representative value of gravity load, For extremum surface pressure, it need to consider the gravity load representative value and the horizontal and vertical earthquake function under rare occurrence earthquake. Through calculating, the maximum value of long time surface pressure occur on number 8 isolation bearing and it is 3077KN (10.9 Mpa), The maximum extremum surface pressure occur on number 11 isolation bearing and it is 5330KN(18.9Mpa), the minimum extremum surface pressure occur on number 1 isolation bearing and it is 420KN (2.1Mpa), all meets the relevant provisions of (building aseismic design standards) (EN15129), It means that the isolation layer have enough stability and safety. Detailed analysis reference the sixth chapter.

4 Horizontal Resilience Character Of Isolation Layers

The isolation layers must meet the requirements of wind load and micro vibration, simplifying the stiffness of lead rubber bearing and laminated rubber bearing to bilinearity, the horizontal resilience character of isolation layer is consists of lead rubber bearing,

Eight degree (0.3g) under the effect of earthquake isolation effect recognition

Comparison of isolation structure and non isolated structure under seismic fortification response results, we can clearly see the isolation effect of vibration isolation system, the table 5.5-1 and table 5.5-2 respectively, are presented the isolation structure and the non isolated structure seismic shear and interlayer displacement angle of the comparison results.

Table 5.5-1 comparison of seismic shear forces of isolated and non isolated structures (unit: x10³kN)

5.Analysis conclusion of seismic isolation

Through the above through the example with higher than engineering construction, higher seismic level (8 degrees 0.3g) analysis shows that, in order to improve the seismic safety of the project and improve the seismic performance and reduce the seismic response, seismic isolation technology is applied to the engineering

This chapter evaluates and analyzes the seismic system . The conclusions are as follows:

Analyzing software reliability and calculating model rationality

We established a 3 d finite element model of isolated and non-isolated structure of and analyzed their characters of structure dynamics,  with the large finite element software EtabsV9.7.4. And the results show that The model can accurately characterize the dynamic characteristics of actual structure, and can provide a reliable benchmark model for the analysis of dynamic response.

(2)the seismic waves chosen is appropriate according the time procedure analysis.

The time procedure analysis consist of 2groups  of natural seismic oscillation and 1 group of artificial seismic oscillation,among them the natural seismic oscillation is the actual observation records of strong shock.the seismic shear force of elastic structure in each group time-history curve calculated by equivalent base shear method is more than 65% of the calculated date using  response spectrum method,among these 3 groups of  calculated date by equivalent base shear method is more than 80% of the date by response spectrum method. We used their maximum seismic response  and envelope value in the 3 groups as the final calculated value, and the result is reliable and can be used in project design.

(3) the design of isolation layer is reasonable and the isolation bearings is in good condition.

 The isolation bearings have the reasonable allocation . Under the action of wind load , smaller earthquakes or  other non-earthquake  horizontal loads ,the isolation layer can satisfy the stability with the enough initial stiffness. The isolation layer can provide the lower stiffness than initial shear

stiffness ,which ensures isolation layer can reduce earthquake response under the action of larger earthquake.

(4)the structure above the earthquake shear force greatly reduced, and you can design according to the standard decreasing a level .

Under the 8- degree (0.3g)earthquake resistance ,the earthquake shear force of each floor earthquake resistance is less than 0.40 times of the earthquake shear force of non-isolation structure and earthquake-reduction coefficient is 0.37. According to the  Explanatory 8 in<<Code for Seismic Design of Building>> (EN15129, EN1337,GB50011-2010),the structure above the earthquake shear force  can  be designed  according to the standard decreasing a level ,that is to say the maximum coefficient of seismic effect is 0.12.

the significantly additional value of  isolation project design and economic benefit.

Under the action of 8-degrees (0.3g) fortification intensity,the conventional anti-seismic technology cannot reach the code requirement-3 seismic fortification levels,while it can reduce the section size observably and enhance the seismic safety performance after adapting isolation technology and design according to the standard decreasing a level.the structure above the isolation layer is nearly translational state under the action of fortified earthquake intensity, and it can totally meet the target of No Collapsing in the Strong Earthquake .the isolation scheme has the obvious economic benefits in view of the costs of building repair and total costs during the period of use.

According to the analysis , the lead rubber bearings complying with the design parameters can meet the design requirement of this project.