Response Of Elevated Water Tank Research Articles

Response of Elevated Water Tanks Subjected to Lateral Loads

Abstract During previous earthquakes around the world, it was discovered that elevated water tanks were severely damaged or collapsed. As a result, structural engineers are concerned about the analysis of these structures to gain a better understanding of the effects of seismic loads on elevated water tanks. In the current study, E-Tabs software, which is based on finite elements, is used to model various shapes of elevated water tanks along with various staging patterns. The higher stiffness of the supports in cross staging tanks makes them better than normal staging tanks, according to the results of the analysis. Furthermore, circular tanks perform better than other tank shapes when subjected to seismic loads. The study looks at water tanks subjected to static seismic loads. More research is needed to determine the analysis results for the dynamic seismic loads applied to the structure. All the analysis results are derived from the software’s tank analysis results.

Seismic behavior of existing elevated water tanks resting on different type of foundations

It has been well recognized that heavy structures built on soft soils, experience significant impact on seismic response, because of considerable foundation movements and hence, the effect of Soil-Structure-Interaction (SSI) can be a major factor while analyzing important structures like; nuclear power plants, elevated water tanks, chimneys, etc. against seismic forces. In general, elevated water tanks that were constructed on different type of soils in seismic regions, prior to the revision of seismic codes, must be checked on behavior and safety of such structures against earthquake loads as per present codes.In this paper, two similar elevated R.C. circular water tanks, each of 4.0 lakh liters capacity supported by two types of foundations; one with circular ring raft below the columns of tank resting on sandy soils, and the other with circular ring raft supported by piles embedded in black cotton soils, are chosen for carrying out seismic analysis. In the analysis, the water tank is idealized as a system with three degrees of freedom, treating the staging of tank as one spring attached to the mass of the water tank and the soil is treated with two springs; one in horizontal and the other in rocking mode, both attached to the soil mass and the response parameters like; time periods, base shears and displacements are worked out against earthquake loads. Results indicate that, irrespective of type of foundation, the soil play important role on seismic response of elevated water tanks by virtue of their configuration with top heavy mass and slender staging; particularly displacements are found high when they rest on loose soils. According to the new guidelines provided in the revised IS 1893 (Part-1) 2016 code, SSI effect should be considered in seismic analysis when the structure rests on loose or soft soils.

Seismic vulnerability assessment of elevated water tanks with variable staging pattern incorporating the fluid-structure interaction

The damage suffered by elevated water tanks in previous seismic events can be generally attributed to poor performance of their frame-type supporting structure. It is pivotal to quantify the damage experienced by these tanks in damage states in order to ascertain their performance. In this study, the nonlinear response of frame-supported elevated water tanks is investigated using performance-based earthquake engineering method by utilizing the top drift of frame staging as the engineering demand parameter to evaluate its performance level. The influence of different patterns of reinforced concrete frame staging on the response of elevated water tanks was quantified using a fragility assessment. Finite element approach was employed and a total of nine models were developed representing the variation in staging patterns (basic, cross, and radial bracing configurations) and water-filling levels (empty, half-full, and full conditions) of the tanks and considering the fluid–structure interaction effect. Non-linear analyses were performed based on different seismic scenarios, and the seismic damage states from each staging pattern were evaluated. Fragility curves were generated according to three performance limit states specified in Vision 2000 and based on incremental dynamic analysis results for each staging pattern. Finally, the collapse margin ratios were quantified to evaluate the seismic safety margin against collapse of the elevated water tanks. From the analysis results, elevated water tanks having staging with cross and radial configurations showed better seismic performance compared to the basic configuration.

Effect of Supporting Soil on the Seismic Response of Elevated Water Tanks under Different Excitations

Effect of Supporting Soil on the Seismic Response of Elevated Water Tanks under Different Excitations

Experimental and numerical study of dynamic response of elevated water tank of AP1000 PCCWST considering FSI effect

AP1000 passive containment cooling system water storage tank (PCCWST) is set at the top of a shield building. Its function is to hold the water which will flow by gravity to help cool the containment vessel in the highly unlikely event of an emergency – one of the AP1000 plant’s innovative passive safety systems. The huge amount of water may pose a threat to the integrity of the shield building during an earthquake. In this paper, both modal characteristics and transient response of a scaled elevated water tank model were studied by a shaking table experiment. The acceleration of the supporting structure and displacement of water sloshing were recorded under transient loading. Four numerical models were built, including two-mass equivalent model, single lumped-mass model, and finite element models using Fluid30 and Fluid80 elements. The advantages and disadvantages of different numerical methods were discussed. Moreover, finite element (FE) models of AP1000 shield building were established considering the fluid–structure interaction (FSI) effect. The sloshing phenomenon in PCCWST under resonant three-cycle sine (RTCS) wave and seismic loading was studied. The response of shield building under seismic loading was also studied. The results showed that the maximum von Mises stress occurred at the corner of the air inlet. The shaking table experiment can provide a benchmark for seismic response of an elevated water tank. The FE model of shield building may help improve the design of the AP1000 and CAP1400 in the future.

Seismic response factors of reinforced concrete pedestal in elevated water tanks

Reinforced concrete (RC) elevated water tanks are critical structures that are expected to remain functional after severe earthquakes in order to serve the water system networks. Despite this significant role, the number of research studies which investigated the nonlinear seismic response of RC pedestals in elevated water tanks is very limited. In the current codes and standards, the seismic response factors are mainly based on engineering judgement. In this paper, a systematic approach is employed to establish the seismic response factors for a wide range of elevate water tank sizes and RC pedestal dimensions commonly built in industry. In total, forty-eight model configurations (prototypes) are selected and designed based on current codes and standards. The finite element (FE) method is then used for nonlinear static (pushover) analysis of the prototypes. The pushover curve of each prototype is developed and the seismic response factors are determined accordingly. The effect of various parameters such as fundamental period, height to diameter ratio, seismic design category, and tank size on the seismic response factors of elevated water tanks is evaluated. Furthermore, the cracking propagation pattern in RC pedestal is studied. The result of the study shows that the tank size is a critical parameter affecting the seismic response of elevated water tanks. It is recommended not to use the same seismic response factors for all RC elevated water tanks regardless of the tank size. In addition, two different patterns of cracking depending on the height to diameter ratio of the pedestal are detected and discussed.

The effect of seasonally frozen soil on stochastic response of elevated water tank under random excitation

Significant seismic events have occurred around the world during winter months in regions where cold temperatures cause ground freezing. Current seismic design practice does not address the effects of cold temperatures in the seasonally frozen areas. Since many elevated water tank structures in cold regions are located in seismic active zones, determining the effect of seasonally frozen soil on the stochastic response of elevated water tank structures subjected to random seismic excitation is an important structural consideration. A three dimensional finite element model, which considers viscous boundaries, was built up to obtain the stochastic seismic behavior of an elevated water tank–fluid–soil interaction system for frozen soil condition. For this model, the power spectral density function represents random ground motion applied to each support point of the three dimensional finite element model of the elevated water tank–fluid–soil interaction system. Numerical results show that the soil temperature affects the seismic response of the elevated water tank; whereas the variation in the thickness of the frozen soil causes insignificant changes on the response. In addition, the effect of the variation in water tank’s fullness on the stochastic response of the coupled system is investigated in the study. As a result, the seasonal frost changes the foundation soil stiffness and may impact seismic behavior of the water tank.

The dynamic behavior of water tanks

abstract During the Chilean earthquakes of May, 1960, a number of large elevated water tanks were severely damaged whereas others survived without damage. An analysis of the dynamic behavior of such tanks must take into account the motion of the water relative to the tank as well as the motion of the tank relative to the ground. Some simple expressions are given for the pertinent dynamic properties of tanks with free water surface. A simplified dynamic analysis is indicated for the response of elevated water tanks to earthquake ground motion.