Tall Chimneys Research Articles

THE USE OF TERRESTRIAL LASER SCANNING TECHNIQUES TO EVALUATE INDUSTRIAL MASONRY CHIMNEY VERTICALITY

Abstract. This paper presents a strategy to measure verticality deviations (i.e. inclination) of tall chimneys. The method uses laser scanning point clouds acquired around the chimney to estimate vertical deviations with millimeter-level precision. Horizontal slices derived from the point cloud allows us to inspect the geometry of the chimney at different heights. Two methods able to estimate the center at different levels are illustrated and discussed. A first solution is a manual approach that uses traditional CAD software, in which circle fitting is manually carried out through point cloud slices. The second method is instead automatic and provides not only center coordinates, but also statistics to evaluate metric quality. Two case studies are used to explain the procedures for the digital survey and the measurement of vertical deviations: the chimney in the old slaughterhouse of Piacenza (Italy), and the chimney in Leonardo Campus at Politecnico di Milano (Italy).

THE RESPONSE OF PILES UNDER TENSION LOADS BASED ON ANALYTICAL METHOD AND FINITE ELEMENT ANALYSIS

In the past, there were many research studies carried out on the response of single piles and pile groups under compression loads, but it was comparatively lesser for piles and pile groups under uplift loads. Uplift loads on piles usually occur in pile foundations supporting wind farm structures, tall chimneys, transmission towers and jetty structures. During recent decades, research studies on piles under uplift loads have progressed, and were mainly focused on the capacity, failure modes and load displacement performance of single piles, but no research has been done on the influence zone of a pile and its effects within a group. This paper presents the initial findings of research to investigate the stress distribution and influence zone of a single pile under uplift loads using a hybrid approach combining analytical theory and 2D Finite Element (FE) analysis. Finally, the effect of the estimated influence zone was successfully verified in 3D FE analysis which confirmed that group efficiency reduced when an adjacent pile was within the estimated influence zone and thus piles behave as a group.

Population trends and diversification of breeding habitats of Peregrine Falcon (Falco peregrinus) in the Czech Republic since 1990

Abstract The population of the Peregrine Falcon (Falco peregrinus) in the Czech Republic recovered from a nearly total extinction during the 1960s and 1980s (0­3 breeding pairs) and the first successful breeding after this interval was confirmed in 1995. The increase of the population size accelerated after 2000 and it is still growing despite the limited amount of suitable natural breeding opportunities. There were 89 known pairs in 2016, 70 of them were proven to breed with altogether at least 121 reared young. Several breeding attempts on historical buildings in city­centres were recorded up to 2002 (in Prague and Pilsen), but this breeding habitat was abandoned later. More and more pairs are nowadays breeding on industrial buildings. The first breeding on a power plant chimney, 300m above the ground was discovered in 2010. Moreover, 16 breeding pairs were found on industrial buildings in 2016 (mainly tall chimneys or cooling towers and power­plant buildings), all of them breeding in nest boxes. The colonization of industrial buildings started in western part of the Czech Republic and continues eastwards every year. Currently, the easternmost colonized building is in Mladá Boleslav. We have no recent tree­breeding pairs and all eight published historical cases are at least doubtful. Most of the observed Peregrines ringed abroad came from Germany, indicating a strong influence of German population on restoration of the population in the Czech Republic. Within these recoveries, some of Peregrines were released in the tree­breeding population restoration project in Germany and Poland, but all these birds bred on rocks.

Wind-induced responses of a tall chimney by aeroelastic wind tunnel test using a continuous model

This study aims to investigate wind-induced responses of a 300 m high chimney by using wind tunnel tests on an aeroelastic model. Due to the fact that it is unrealistic to simulate wind flow with a high Reynolds number as high as 1 × 108 for a chimney model in a wind tunnel, roughness paper strips were attached to the model surface to artificially achieve effective high Reynolds number flow in the full-scale condition. An optimal thickness of the roughness paper strips was determined via a series of pressure measurement tests on a rigid model of the chimney. To examine wind-induced responses of the chimney, a continuous aeroelastic chimney model was manufactured with the DEVCON plastic steel liquid. After roughening the aeroelastic model by the paper strips with the optimal thickness, a series of wind tunnel tests were conducted on the model to directly acquire the structural responses, for three different oncoming wind flow conditions. Results show that the response of the roughened model is much smaller than that for the model without roughness element, indicating that ignoring the Reynolds number effect will overestimate the response. The across-wind acceleration response of the chimney is more considerable than that in the along-wind direction, when the reduced wind velocity Vr is larger than 4. In addition, the across-wind acceleration response is usually larger in the more turbulent wind flow, although the lock-in phenomenon is more evident in uniform flow.

Efficiency enhancement of solar chimney power plant by use of waste heat from nuclear power plant

Abstract A solar chimney power plant (SCPP) offers an efficient method of converting solar irradiation to electrical power. It can be combined with a nuclear power plant to improve its efficiency and minimize its environmental impact. Rather than dumping the waste heat rejected by a nuclear power plant to a wet cooling tower, a better solution may be to connect it to an SCPP. This is particularly true in arid regions. The SCPP can serve the function of a dry cooling tower and produce additional electrical power. In a solar chimney power plant, the energy of buoyant hot air is converted to electrical energy. SCPP includes a collector at ground level covered with a transparent roof. The sun heats the air inside the collector and the ground underneath. A tall chimney is placed at the center of the collector, with a turbine located at the base of the chimney. In this investigation, the surplus heat from the nuclear cycle is used to increase the temperature of the air in the collector and therefore produce more electricity in the solar chimney power plant. The efficiency of the nuclear plant will be lowered due to the higher temperature of the condenser, but the loss can be made up by the increased power of the solar chimney. Heat from the sun is always free once the solar plant has been constructed and is not normally considered in the efficiency calculation. Computational fluid dynamics (CFD) and thermal analysis have been performed to apply the available surplus heat from the nuclear cycle and to measure the available kinetic energy of air for the turbine of the solar chimney power plant system. The feasibility of the system is evaluated, and the thermal efficiency of the combined power plant has been computed. By applying this idea to a typical 1000 MW nuclear power plant with a nominal 35.3% thermal efficiency, its efficiency can be increased to 42.0%. The combined cycle as presented is advantageous in environments where water is scarce. The cooling tower is replaced by the solar chimney power plant utilizing the surplus heat from the available warm steam in the secondary loop of the reactor.

Seismic Response and Safety Assessment of an Existing Concrete Chimney under Wind Load

A safety assessment of a chimney under the action of wind and earthquake is performed on one of the reinforced concrete chimneys in the Jinchuan company in China. The assessment is based on the linear filtering method, and wind loads of several heights on one field are simulated by MATLAB. The displacement of the structure under the action of wind load and earthquake is analyzed using maximum value superposition, and the stress on the chimney is calculated in four cases using the equal curvature criterion method. The time‐history responses of the tall chimney structure under linear and nonlinear elastic conditions are discussed. The results show that for a chimney under wind load or frequent earthquakes, the displacement limit can meet the code requirements; however, under the combined action of frequent earthquakes and wind load, the structural displacement is bigger than other conditions. When the chimney is acted upon by a wind load, frequent earthquake action, or the combined action of wind load and frequent earthquake action, the maximum compressive stress, maximum tensile stress, and maximum shear stress are concentrated at the bottom of the chimney. The ultimate bearing capacity of a reinforced concrete chimney under three conditions can meet the original design requirements, but the maximum compressive stress at the bottom approaches the designed tensile limit value under the action of rare earthquakes; under these conditions, the bottom of the chimney may experience partial damage.

Analysis of Foundation of Tall R/C Chimney Incorporating Flexibility of Soil

Three dimensional Finite Element (FE) analysis was carried out for 100 and 400 m high R/C chimneys having piled annular raft and annular raft foundations considering the flexibility of soil subjected to across-wind load. Stiffness of supporting soil and foundation were varied to evaluate the significance of Soil-Structure Interaction (SSI). The integrated chimney-foundation-soil system was analysed by finite element software ANSYS based on direct method of SSI assuming linear elastic material behaviour. FE analyses were carried out for two cases of SSI namely, (1) chimney with annular raft foundation and (2) chimney with piled annular raft foundation. The responses in raft such as bending moments and settlements were evaluated for both the cases and compared to those obtained from the conventional method of analysis of annular raft foundation. It is found that the responses in raft vary considerably depending on the stiffness of the underlying soil and the stiffness of foundation. Piled raft foundations are better suited for tall chimneys to be constructed in loose or medium sand.

Low-enrichment and long-life Scalable LIquid Metal cooled small Modular (SLIMM-1.2) reactor

The Scalable LIquid Metal cooled small Modular (SLIMM-1.0) reactor with uranium nitride fuel enrichment of 17.65% had been developed for generating 10–100MWth continuously, without refueling for ∼66 and 5.9 full power years, respectively. Natural circulation of in-vessel liquid sodium (Na) cools the core of this fast energy spectrum reactor during nominal operation and after shutdown, with the aid of a tall chimney and an annular Na/Na heat exchanger (HEX) of concentric helically coiled tubes. The HEX at the top of the downcomer maximizes the static pressure head for natural circulation. In addition to the independent emergency shutdown (RSS) and reactor control (RC), the core negative temperature reactivity feedback safely decreases the reactor thermal power, following modest increases in the temperatures of UN fuel and in-vessel liquid sodium. The decay heat is removed from the core by natural circulation of in-vessel liquid sodium, with aid of the liquid metal heat pipes laid along the reactor vessel wall, and the passive backup cooling system (BCS) using natural circulation of ambient air along the outer surface of the guard vessel wall. This paper investigates modifying the SLIMM-1.0 reactor design to lower the UN fuel enrichment. To arrive at a final reactor design (SLIMM-1.2), the performed neutronics and reactivity depletion analyses examined the effects of various design and material choices on both the cold-clean and the hot-clean excess reactivity, the reactivity shutdown margin, the full power operation life at 100MWth, the fissile production and depletion, the Beginning-Of-Life (BOL) spatial distributions of the fission power in the core at 100MWth, and the negative temperature reactivity feedback effects. Besides decreasing the UN fuel enrichment, other parameters examined are the materials of the followers to the B4C rods for RSS and RC, the rods in the radial blanket assemblies, and the thickness of the scalloped BeO walls of the UN fuel and radial blanket assemblies. Despite ∼13% lower fuel enrichment (15.35%) and ∼22% lower hot-clean excess reactivity ($6.29 versus $8.06 for SLIMM-1.0 at 100MWth), the operation life of the SLIMM-1.2 is ∼6.8% longer (6.3 versus 5.9 FPY for SLIMM-1.0), and the total negative temperature reactivity feedback is slightly smaller. At BOL, the radial blanket assemblies in ring 4, and the six UN fuel assembles in ring 1 of the SLIMM-1.2 core generate 2% and 23% of the total reactor thermal power, respectively. The twelve and eighteen UN fuel assemblies in rings 2 and 3 of the SLIMM-1.2 core generate 38% and 37% of the reactor thermal power, respectively. At EOL, the thermal power generation by the UN assemblies in rings 1 and 2 of the SLIMM-1.2 core decreases to 21.5% and 35.9%, respectively, while that by the assemblies in rings 3 and 4 increases to 37.6% and 5%, respectively.

Evolving ICA and HGAPSO algorithms for prediction of outlet temperatures of constructed solar chimney

A small-scale experimental solar chimney consisted of a 3 m diameter air collector and a 2 m tall chimney was built. The absorber and fluid temperatures were recorded based on the practical weather conditions, and the experimental data were evaluated by a hybrid of genetic algorithm with particle swarm optimization (HGAPSO). In next step, imperialist competitive algorithm (ICA) method was applied as an artificial intelligence approach to forecast the temperature changes due to radiation variations. In this case, a data set of 1000 condition parameters for 30 days operation of solar chimney was used, which include eight and four sensors for input and output variables, respectively. Finally, according to the value correlation coefficient (R2) and the mean square error, the results of the trained networks were reported and the temperature prediction was done with high accuracy. The results showed that the solar chimney's experimental data were qualified with no noise.

Comparison of P-Delta Effect on a Slender RCC Chimney by using Beam-Column Theory and STAAD PRO

Chimneys are very tall and slender structures. As per ISIS 4998 (Part 1): 1992, major loads considered for analysis of chimneys are wind loads and earthquake load. Each of them is combined with dead load to get the most critical load for designing a chimney. This paper presents the analysis of a slender RCC chimney with a combination of dead load and wind load. Firstly beam column theory is applied on a tall slender chimney and general equations are developed for bending moment with and without the consideration of second order analysis. Validation of same is done by a typical problem of a tall chimney. Dead load of the structure is calculated by using frustum of a cone method. Wind load is calculated as per IS 875 (part3)-1987. Analysis is carried out by the combination of dead load and wind load. The dynamic effect is ignored. Bending moments are calculated manually by using beam column theory for first and second order analysis of chimney. These results are later compared with STAAD PRO results.

SLIMM-Scalable LIquid Metal cooled small Modular Reactor: Preliminary design and performance analyses

This paper presents a preliminary design of the Scalable LIquid Metal cooled small Modular (SLIMM) reactor for generating 10–100 MWth. It has an estimated operation life of ∼5.8 full-power year (FPY) at 100 MWth and ∼33.3 FPY at 20 MWth and would be fabricated and sealed in the factory, installed below ground, to avoid direct impact by missiles or aircraft, and mounted onto seismic oscillation bearings to resist earthquakes. In-vessel natural circulation of liquid sodium cools the reactor during nominal operation and after shutdown, with the aid of in-vessel Na/Na heat exchanger (HEX) and a tall chimney, while limiting the sodium exit temperature from the core to ≤ 820 K. The design takes advantage of the high heavy metal ratio, high melting point and high thermal conductivity of the UN fuel, and uses HT-9 stainless steel for the UN fuel rods cladding, the core structure, and the reactor primary and guard vessels. The HT-9 is a strong and high corrosion resistant alloy that is compatible with UN and liquid Na at the SLIMM reactor operating temperatures. The active core is comprised of 36 hexagonal assemblies with scalloped-walls BeO shrouds. Each assembly is loaded with 37 UN fuel rods. The core has a negative temperature reactivity feedback, a hard-fast neuron energy spectrum, and independent reactor emergency shutdown (ESD) and control (RC) systems. In the unlikely event of a malfunction of the in-vessel Na/Na HEX, the large sodium mass in the reactor vessel would effectively store heat, until natural circulation of ambient air on the outer surface of the guard vessel can safely remove the decay heat generated in the reactor core. Variable conductance liquid-metal (LM) heat pipes, along the primary vessel wall, transport thermal energy to thermoelectric modules to generate 10 s of kWe of auxiliary power for maintaining the plant's vital functions during nominal reactor operation and in case of a total loss of conventional onsite and offsite powers.

Wind load analysis of tall chimneys with piled raft foundation considering the flexibility of soil

Soil–structure interaction (SSI) analysis was carried out for tall reinforced concrete chimneys with piled raft foundation subjected to wind loads. To understand the significance of SSI, four types of soil were considered based on different material properties. Chimneys of different elevations and different ratios of height to base diameter of chimney were selected for the parametric study. The thickness of raft of piled raft foundation was also varied based on different ratios of outer diameter to thickness of raft. The chimneys were assumed to be located in open terrain and subjected to a maximum wind speed of 50 m/s. The along-wind and across-wind loads were computed according to IS: 4998 (Part 1)-1992 and applied along the height of the chimney. The analysis was carried out using three-dimensional finite element technique based on the direct method of SSI. The linear elastic material behaviour was assumed for the integrated chimney–foundation–soil system. The radial and tangential moments, lateral deflection and base moment of chimney were evaluated through SSI analysis and compared with the response obtained from chimney with fixed base. The base moment of chimney considerably reduces due to the effect of SSI. It is found that the variation of different responses in chimney due to the effect of SSI depends significantly on the geometrical properties of chimney and foundations. The response variation at base for a distance of 1/40th of the height of chimney should be considered for a safe design.

Response in piled raft foundation of tall chimneys under along-wind load incorporating flexibility of soil

The present paper deals with the numerical analysis of tall reinforced concrete chimneys with piled raft foundation subjected to along-wind loads considering the flexibility of soil. The analysis was carried out using finite element method on the basis of direct method of soil-structure interaction (SSI). The linear elastic material behavior was assumed for chimney, piled raft and soil. Four different material properties of soil stratum were selected in order to study the effect of SSI. The chimney elevation and the thickness of raft of piled raft foundation were also varied for the parametric study. The chimneys were assumed to be located in terrain category 2 and subjected to a maximum wind speed of 50 m/s as per IS:875 (Part 3)-1987. The along-wind loads were computed according to IS:4998 (Part 1)-1992. The base moments of chimney evaluated from the SSI analysis were compared with those obtained as per IS:4998 (Part 1)-1992. The tangential and radial bending moments of raft of piled raft foundation were evaluated through SSI analysis and compared with those obtained from conventional analysis as per IS:11089-1984, assuming rigidity at the base of the raft foundation. The settlements of raft of piled raft foundation, deflection of pile and moments of the pile due to interaction with different soil stratum were also evaluated. From the analysis, considerable reduction in the base moment of chimney due to the effect of SSI is observed. Higher radial moments and lower tangential moments were obtained for lower elevation chimneys with piled raft resting on loose sand when compared with conventional analysis results. The effect of SSI in the response of the pile is more significant when the structure-foundation system interacts with loose sand.

BEHAVIOUR OF LATERALLY LOADED PILES IN COHESIONLESS SOILS

The response of an individual pile to externally applied lateral load is one of the most complex soil-structure interaction problems in the field of foundation engineering. Piles that are used under tall chimneys, television towers, high-rise high retaining walls, offshore structures etc. Several methods are available for predicting the ultimate lateral resistance to piles in cohesionless soils. However these methods often produce significantly differently ultimate resistance values. This makes it difficult for practicing engineers to efficiently select the method when designing laterally loaded piles in cohesionless soils. This paper gives a comparative study of the lateral load behaviour of piles in cohesionless soils based on Finite Difference Method and Matlock &Reese Method. Slope, deflection, shear and moments were calculated for a typical pile in both methods and their results were presented.

Effect of Dynamic Loads on Tall RCC Chimneys of Different Heights with Elliptical and Circular Cross sections

Tall RC chimneys form an important component of major industries and power plants. Since pollution control standards are getting stringent every passing day, the mandatory height requirements of chimneys are increasing. Such increased heights pose structural challenges for designing against dynamic loads such as wind gust and seismic forces. Arriving at an economic and efficient structural profile is one of the important aspects of the analysis and design of tall chimneys. Most of the chimneys constructed in industry are of circular cross section. With increase in heights, chimneys become more vulnerable to dynamic loads. In order to combat these loads and design an economical and efficient structural solution needs to be evolved. Elliptical cross-section provides one such possible alternate solution. Therefore evaluating the behavior of chimneys of varying heights with elliptical cross-section and comparing the same with that of circular cross-section assume significance. Chimneys with circular and elliptical cross sections of five different heights viz. 275m, 300m, 325m, 350m and 400m with two different profiles in elevation - one tapering from bottom to top and the other tapering from bottom to 2/3 H and straight afterwards - have been analyzed for seismic and vortex shedding effects caused by wind forces; further, analyses have been carried out for three R/t ratios - 15, 20 and 25. In total 120 models have been analyzed 60 for seismic forces and 60 for vortex shedding effects. Analytical results in terms of stresses induced on the structure, earthquake base shear, joint acceleration, joint displacements and vortex shedding base shear are evaluated. Maximum values of seismic forces induced base shear is only 1% of the self weight of the structure for all heights. It is interesting to note that chimneys with elliptical cross section experience less accelerations compared to that with circular cross section. Circular chimneys undergo higher displacement than the elliptical chimneys which is attributed to the higher accelerations they are subjected to by seismic forces. As the height of the chimneys is increased vortex shedding phenomenon induces increased forces compared to that due to earthquakes.

A MATLAB toolbox for soil–structure interaction analysis with finite and boundary elements

In this work the numerical model SSIFiBo developed in MATLAB to study dynamic soil-structure interaction problems is presented. The model is based on a three dimensional boundary element-finite element coupled formulation in time domain. This model allows computing structural forced-vibrations, as well as seismic responses. Two numerical examples are solved with the proposed technique: ground-borne isolation with open and filled trench, and the seismic response of a tall chimney.

Correlations between metals in tree-rings of Prosopis julifora as indicators of sources of heavy metal contamination

Heavy-metals (Cu, Pb and Zn) in tree-ring sequences of Prosopis juliflora, a tree species native to arid environments, were analyzed by ICP-MS. The tree-ring sequences were obtained from three specimens growing in an urban area previously reported as contaminated by the activity of a Cu smelter facility. The metal found in highest concentration in the wood was Zn, with concentrations up to 120mg/kg and an enrichment factor up to 26; followed by Cu (up to 9.6mg/kg, enrichment factor up to 8.6) and Pb (up to 1.4mg/kg, enrichment factor up to 3). By assessing the correlation between different metal concentration trends, it was possible to infer two main pollution sources: vehicle traffic and Cu smelter emissions. Vehicle traffic is indicated by a correlation between Pb and Zn over time within individual trees, whereas contamination from the Cu-smelting facility is indicated by a correlation of Cu over time between trees. In tree A there was a significant within-tree correlation between Pb and Zn concentration trends (r=0.856, P<0.001), whereas Cu showed no correlation with the other metals. For tree B, there were no within-tree correlations between these metals, but when comparing the concentration–time trends between trees A and B, there was a significant correlation for Cu (r=0.768, P<0.01). The tree-ring sequence from tree C showed significant within-tree correlation for Cu:Zn (r=0.430, P<0.01) and for Pb:Zn (r=0.753, P<0.001). The highest enrichment values were found in tree A, located along the path of the growing-season dominant wind direction from the smelter facility, and not in the tree growing closer to the smelter (tree C), suggesting that the smelter’s emissions are dispersed to longer distances through the tall chimneys, attenuating the impact to the area directly closest to the smelter facility. It is concluded that Prosopis juliflora appears as a good bioindicator based on its metal accumulation capacity and lack of metal mobility among tree rings, thus providing information on the chronology and sources of heavy-metal pollution in urban and industrial areas.

Effects of flow area changes on the potential of solar chimney power plants

The solar chimney power plant is a solar power plant for electricity generation by means of air flow induced through a tall chimney. Guided by a theoretical model, this paper uses CFD technology to investigate the changes in flow properties caused by the variations of flow area. It is found that the sloping collector roof affects the plant performance. The divergent-top chimney leads to augmentations in kinetic energy at the chimney base significantly. The proper combination between the sloping collector roof and the divergent-top chimney can produce the power as much as hundreds times that of the conventional solar chimney power plant.

New vibration control device and analytical method for slender structures

Since slender structures such as utility poles, radio masts, and chimneys, are essentially statically determinate structures, they often collapse during earthquakes. Although vibration control is the most logical method for improving the earthquake resistance of such structures, there are many practical problems with its implementation due to their very long natural vibration period. This paper proposes a new vibration control device to effectively prevent the collapse of slender structures subjected to strong earthquakes. The device consists of a pendulum, an elastic restraint and a lever, and is designed such that when it is attached to a slender structure, the second vibration mode of the structure corresponds to the first vibration mode of the same structure without the device attached. This is highly effective in causing the transverse motions of the device and the structure to oppose each other and so reduce the overall transverse vibration during an earthquake. In the present paper, the effectiveness of the vibration control device is first evaluated based on laboratory experiments and numerical studies. An example of applying the device to a tall chimney is then simulated. A new dynamic analytical method for slender structures with abrupt rigidity variations is then proposed.

Numerical Simulation for Achieving Optimum Dimensions of a Solar Chimney Power Plant

Renewable energies are playing a fundamental role in supplying energy, as these kinds of energies can be clean, low carbon and sustainable. Solar chimney power plant is a novel technology for electricity production from solar energy. A solar chimney power plant derives its mechanical power from the kinetic power of the hot air which rises through a tall chimney, the air being heated by solar energy through a transparent roof surrounding the chimney base. The performance evaluation of solar chimney power plant was done by FLUENT software by changing three parameters including collector slope, chimney diameter and entrance gap of collector. The results were validated with the solar chimney power plant which was constructed in Zanajn, Iran with 12 m height, 10 m collector radius and 10 degree Collector angle. By simulation and numerical optimization of many cases with dimensional variations, increasing 300 to 500 percent of chimney velocity and eventually increasing output power of system was observed in different cases.