Seismic tensions monitoring and control systems.

Serban, Viorel ; Mohora, Cristina ; Androne, Marian 等

1. INTRODUCTION

The pilot experimental installation of radioactive material separation at ICSI Ramnicu Valcea, is set-up in a hall consisting of four sections with different heights and spans.

There are no exceptional issues regarding the seismic behavior of the technological installations of Cold-box columns, because these have low weight so that the corresponding seismic forces are also low but cold-boxes 301 and 302, mounted on a metallic structure in section 2 of the hall are more vulnerable.

The section 2 of the hall has a 6m span and a 14,3m height. It is made of reinforced concrete beams, prefabricated poles and beams, with the exception of beams at quotations 5,500m and 10 300m made of monolithic reinforced concrete. At quotations +3,00; +5,500; +8,00; +10,300m there are metallic platforms as support for the equipments of the technological installation of mining and separation of radioactive materials.

The roof is built of prefabricated strips covered with bituminous concrete (CITON, 2008).

From seismic point of view the building is a homogeneous structure without dangerous torsion movements, but the weight of the relatively large equipments and metallic platforms only between certain axes, can generate torsion movements of the building and amplify the general seismic movement.

The evaluation of the seismic movement of the building relative to the seismic movement of the ground has been done conservatively according to current design indications Code P100/2006, considering during analysis the maximal amplification coefficient to be 3 times the height of the building.

The two cold-boxes are made of 3 rings, connected by screws, the upper ones having 2 diametrically opposed supports, resting on the metallic platform at quotation 10,300 m.

The fastening mechanism is conceived only for their own weight and induces a sizeable amplification of the seismic movement of the cold-boxes in horizontal plane, because their fixed point is on the upper platform and also because in both directions in the horizontal plane the columns have a pendulum movement with maximum effect on crosswise direction of the hall (C.Ispas et al., 2007).

In order to reduce the seismic movement of the cold-boxes and to obtain an efficient interaction between the cold-boxes and the metallic structure of the building, with results in the control, limitation and reduction of the seismic movements of the equipments, to avoid collisions, to obtain a higher damping to obtain the minimal possible amplification of the seismic movements, the a new technical solution was proposed for the cold-boxes in order to decrease the seismic movements.

[FIGURE 1 OMITTED]

For each column, at the lowest platform, 4 controlled stiffness and damping supports SERB CT140/10 are mounted, tightened between the column itself and the intermediary beams of the metallic platform, and joined one to another with flanges. (fig. 1)

To establish SERB support's stiffness and damping characteristics needed on the seismic qualification of the COLD-BOX-HYDROGEN for the control, limitation and damping of relative movements the following steps were taken:

* The force-deformation (hysterezis) and relative damping curves were obtained for the equipment, through elongations and compression testing cycles at different amplitudes of force and deformations.

* The relative damping was calculated based on the energy dissipated during one hysterezis cycle.

* The damping coefficient c, proportional with the deformation speed was calculated at maximal load.

* The stiffness characteristic was approximated by a bilinear strengthening curve with stiffness coefficients [k.sub.1] for deformations smaller than [+ or -] 1mm and [k.sub.2] for deformation between [+ or -] 1mm and [+ or -] 3mm.

The SERB support for the seismic qualification of the COLD-BOX-HYDROGEN must have a stiffness curve which can be approximated with a bilinear characteristic of stiffness based on stiffness characteristics from previous analysis of seismic qualification obtained by SITON (Panait et al., 2008).

The nonlinear medium characteristic of the equipment must have values between: [k.sub.1] =(0,5 / 8) x [10.sup.6]N/m, for deformations smaller than [+ or -] 1mm and [k.sub.2] =(3 / 48) x [10.sup.6]N/m, for deformations between [+ or -] 1mm and the maximum deformation.

The damping coefficient c is proportional with the deformation speed and it is: c [greater than or equal to] 0,3 x [10.sup.5]Ns/m.

2. MODELLING AND SIMULATION OF THE FABRICATION PROCESS

In order to determine the cinematic and dynamic behavior of the Cold-box during an earthquake, nonlinear direct integration analysis was conducted, and two calculation methods were applied, with and without telescopic devices, with input data being the synthetic and independent acceleration time-history, compatible with the Ground Response Spectrum (GRS).

The analysis was conducted using SAP2000 non-linear software, version 11.0.6 and the direct nonlinear integration method.

In the first step the seismic analysis of the equipment was conducted, without telescopic devices and the vibrations, relative movements and absolute accelerations were determined at main quotas and stresses in the fastening bolts. Dynamically, the device was in the maximal amplification margins of the GRS, having big values regarding relative movement and absolute accelerations at all main quotas and over-the-top stresses in the fastening bolts.

In order to decrease under the maximum admitted values, the telescopic devices, with nonlinear stiffness and large damping values were added. These were designed to meet safety demands at the Dead-weight [+ or -] Earthquake combined loads. Three types of devices were considered with stiffness characteristics ratios of 1:4 and 1:16.

The telescopic devices have a nonlinear behavior, modelable with GAP, HOOK and SPRING type elements in order to reach the reinforcement phenomena during the increase of the relative level deformation (Panait et al., 2008).

The damping values for the Cold-box assembly and telescopic devices are calculated by the software using the initial linear analysis. With the obtained values the nonlinear analysis was conducted using the direct integration method.

In the analysis the first 12 vibration modes were considered in order to obtain a realistic response of the cold-box.

A bilinear strengthening stiffness model [K.sub.1] - [K.sub.2] was obtained with the value Open for the point of change of the stiffness. Regarding nonlinear elements of GAP and HOOK types, material damping values were considered in order to model a realistic damping of the telescopic devices.

The modal damping calculation associated with the non-linear analyses of direct integration were previously achieved within a linear analysis for which SERB stiffness values equivalent with the value of the stiffness of the secant associated with the bilinear stiffness model were attributed to the telescopic devices (Serban &Mohora, 2008).

3. EARTHQUAKE SIMULATION

According to P100/2006 the acceleration time-history used were compatible with the ground response spectrum for the Ramnicu Valcea area, having the following parameters (Fig. 2):

* Maximum ground acceleration: A = 2.0 m/[s.sup.2] in horizontal plane and [A.sub.v] = 0.7 * A = 1.4 m/[s.sup.2] in vertical plane;

* Building importance coefficient: [gamma] = 1.4;

* Coefficient of the amplification of the acceleration for the fastening support (P100/2006) is within coverage, it was assumed that the fastening is done on top of the building;

* The simulated acceleration used in the analysis: A = 8.4 m/[s.sup.2] in horizontal plane and Av = 6 m/[s.sup.2] in vertical plane;

* [A.sub.max] = 8.4 m/[s.sup.2] and [T.sup.c] = 0.7s.

* Corner period: [T.sub.c] = 0.7 on horizontal direction, [T.sub.c] = 0.45 x TC = 0.32 s on vertical direction.

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

4. CONCLUSIONS

For the most accurate model of the reinforcement phenomena of the SERB telescopic devices nonlinear elements of GAP and HOOK types were used, elements which start to work when a given level of deformation is reached, Open.

For an initial stiffness around zero deformation up to the threshold value, Open, together with these nonlinear elements, linear elements of SPRING type were used, whose stiffness is equal to the initial stiffness of the telescopic devices.

After the data analysis we can reach the conclusion that mounting 4 SERB CT140/10 type supports, with stiffness values of [K.sub.1] = 8 x[10.sup.6] N/m and K2 = 48 x[10.sup.6] N/m reduces 350 times the maximum relative displacements, 12 times the maximum horizontal accelerations and 60 times capacity of the bolts during the bending and 26 times the cutting force.

This method can be a solution for the seismic qualification of the 301 and 302 type cold-boxes at ICSI Ramnicu-Valcea.

5. REFERENCES

CITON. (2008), "Proiect suporti calificare seismica COLD-BOX" (Project of seismic qualification), Research contract, Bucharest CITON

Ispas, C., Bausic, F., Zapciu, M., Parausanu, I. & Mohora, C. (2007). Dinamica masinilor si utilajelor (Machine tools dynamic's", Editura AGIR, ISBN 978-720-147-8, Bucuresti

Panait, A. & Serban, V. (2006), Isolation and damping of shocks, vibrations, impact load and seismic movements at buildings,equipment and pipe networks by SERB-SITON method, International Conference on Nuclear Engineering, 2006, July 17-20, Miami, Florida, USA

Serban, V. & Mohora, C. (2007). New devices to control, limit and damp the schocs and vibrations--The 18th International DAAAM Symposium "Intelligent Manufacturing &Automation: Focus on Creativity, Responsibility and Ethics of Engineers" 24- 27th October 2007, pag. 683-685

Serban, V., Mohora, C. & Lungu, B.. (2008). ExperimentsThrough elastic couplings which allow great deviations--Conferinta cercetare de Excelenta CEEX Brasov