Effect of Backstay on Tall Structure with Podium Structure

In a multi-functional tall building, generally the building has a more extensive plan area and higher lateral resistance at the lower story level than the above story levels. So, the scope of this study is to understand the realistic behavior of such structures under lateral loads considering the backstay effect as per IS: 16700(2017). A Sensitivity Analysis was performed as per IS: 16700(2017) provisions by considering the stiffness parameters given in code to understand the changes in the shear force distribution among structural elements when the tower and Podium are modeled together. The changes in the force distribution are compared with the structure without the backstay effect. At the podium-tower interface level, the amount of backstay forces developed is also presented in this paper, along with the impact on backstay forces with changes in the lateral resistances by changing floor diaphragm thickness and by changing the podium area.

Modelling of tall-structure lightning return-stroke current using the Electromagnetic Transients Program

The main aim of this PhD work is to advance tall-structure lightning return-stroke current modelling. The Alternative Transients Program (ATP), a version of the Electromagnetic Transients program (EMTP), is used to model the lightning current distribution within a tall structure and the attached lightning channel. The tall structure, namely the CN Tower, is modeled as three or five transmission line sections connected in series. The lightning channel is represented by a transmission line with a continuously expanding length. The presented model takes into account reflections within the tower and within the lightning channel. Locations of reflections, current reflection coefficients and the parameters of the current simulation function are calculated based on the time analysis of the current derivative signal, measured at the tower. The decay parameters of the simulation function are first determined by curve fitting the decaying part of the current obtained from measurement. The other parameters are determined by curve fitting the measured initial current derivative impulse with the derivative of the simulation function, before the arrival of reflections. The simulation results substantially succeeded in reproducing the fine structure of the measured current derivative signal. The model allows for the computation of the lightning current at any point along the current path (the tower and the attached channel), which is required for the calculation of the associated electromagnetic field. Using the three-section model of the tower, the presented return-stroke current model enables the determination of a discrete return-stroke velocity profile, demonstrating that the velocity generally decays with time. Furthermore, based on the five-section model, the proposed approach enables taking into account the existence of upward-connecting leaders, which allowed, for the first time, the determination of upward-connecting leader lengths and return-stroke velocity variation profiles with more details. The return-stroke velocity profile is found to initially increase rapidly with time, reaching a peak, and then decrease less rapidly. The proposed model is also experimentally verified based on the comparison between the computed and measured electromagnetic fields. The simulated electric and magnetic field waveforms are found to reproduce important details of the measured fields, including initial split peaks that appear due to channel-front reflections in the presence of upward-connecting leaders.

Modeling of the Lightning Return Stroke Current at a Tall Structure Using the Derivative of the Heidler Function

Traditionally tall structures have been modeled as simple lossless transmission lines. This model is inadequate for the CN Tower, which may be modeled as a series of transmission lines with different characteristic impedances resulting in a reflection coefficient at each discontinuity. Analysis shows that these vary significantly and are related to the ratio of the current derivative peak to the current derivative 10%-90% risetime, suggesting that they are frequency dependent. The magnitude of the reflection from the return stroke front, if it does exist, is much smaller that was previously proposed. An alternative approach to modeling, based on modeling the current derivative, is proposed and it is found to provide a better match with the measured waveforms. The CN Tower is modeled as a series of uniform lossless transmission lines and the channel is represented by the MTLL model. The features of the measured magnetic field waveform are well reproduced.

Modeling of the Lightning Return Stroke Current at a Tall Structure Using the Derivative of the Heidler Function

Traditionally tall structures have been modeled as simple lossless transmission lines. This model is inadequate for the CN Tower, which may be modeled as a series of transmission lines with different characteristic impedances resulting in a reflection coefficient at each discontinuity. Analysis shows that these vary significantly and are related to the ratio of the current derivative peak to the current derivative 10%-90% risetime, suggesting that they are frequency dependent. The magnitude of the reflection from the return stroke front, if it does exist, is much smaller that was previously proposed. An alternative approach to modeling, based on modeling the current derivative, is proposed and it is found to provide a better match with the measured waveforms. The CN Tower is modeled as a series of uniform lossless transmission lines and the channel is represented by the MTLL model. The features of the measured magnetic field waveform are well reproduced.

Modelling of tall-structure lightning return-stroke current using the Electromagnetic Transients Program

The main aim of this PhD work is to advance tall-structure lightning return-stroke current modelling. The Alternative Transients Program (ATP), a version of the Electromagnetic Transients program (EMTP), is used to model the lightning current distribution within a tall structure and the attached lightning channel. The tall structure, namely the CN Tower, is modeled as three or five transmission line sections connected in series. The lightning channel is represented by a transmission line with a continuously expanding length. The presented model takes into account reflections within the tower and within the lightning channel. Locations of reflections, current reflection coefficients and the parameters of the current simulation function are calculated based on the time analysis of the current derivative signal, measured at the tower. The decay parameters of the simulation function are first determined by curve fitting the decaying part of the current obtained from measurement. The other parameters are determined by curve fitting the measured initial current derivative impulse with the derivative of the simulation function, before the arrival of reflections. The simulation results substantially succeeded in reproducing the fine structure of the measured current derivative signal. The model allows for the computation of the lightning current at any point along the current path (the tower and the attached channel), which is required for the calculation of the associated electromagnetic field. Using the three-section model of the tower, the presented return-stroke current model enables the determination of a discrete return-stroke velocity profile, demonstrating that the velocity generally decays with time. Furthermore, based on the five-section model, the proposed approach enables taking into account the existence of upward-connecting leaders, which allowed, for the first time, the determination of upward-connecting leader lengths and return-stroke velocity variation profiles with more details. The return-stroke velocity profile is found to initially increase rapidly with time, reaching a peak, and then decrease less rapidly. The proposed model is also experimentally verified based on the comparison between the computed and measured electromagnetic fields. The simulated electric and magnetic field waveforms are found to reproduce important details of the measured fields, including initial split peaks that appear due to channel-front reflections in the presence of upward-connecting leaders.

Characteristics of lightning at and in the vicinity of the CN Tower

The CN Tower has been the center of tourism in Toronto since it first opened to the public on June 26, 1976. It is the world's tallest manmade freestanding structure as well as Canada's most recognizable icon standing at a height of 553 meters. However, like everything else, there could be a down to this incredible structure. Does it attract more lightning; potentially putting the surrounding area in its vicinity in harm's way, or does it provide lightning protection to this area? Although, extensive analysis have been performed concerning the characteristics of lightning strikes to the CN Tower, not much attention has been given to the characteristics of lightning strikes in the vicinity of the tower or the influence the tower has on the lightning environment around it. This thesis is believed to be the first to fill such a gap and tries to answer these questions. Using the 2005 North American Lightning Detection Network data for the area of up to 100 km from the tower, an extensive investigation of lightning activities in the vicinity of the tower is presented here. A comparison between the characteristics of CN Tower strikes and the characteristics of strikes occurring in its vicinity is also presented. Furthermore, the parameters of the lightning electromagnetic pulse (LEMP) generated by a strike to the tower are compared with those generated by a non-eN Tower strike. A substantial increase in the CN Tower LEMP peak in comparison with that resulting from non-CN Tower LEMP has been found. Therefore, electronic and communication systems located in the vicinity of a very tall structure must be specially protected from the lightning-generated electromagnetic pulse.

Characteristics of lightning at and in the vicinity of the CN Tower

The CN Tower has been the center of tourism in Toronto since it first opened to the public on June 26, 1976. It is the world's tallest manmade freestanding structure as well as Canada's most recognizable icon standing at a height of 553 meters. However, like everything else, there could be a down to this incredible structure. Does it attract more lightning; potentially putting the surrounding area in its vicinity in harm's way, or does it provide lightning protection to this area? Although, extensive analysis have been performed concerning the characteristics of lightning strikes to the CN Tower, not much attention has been given to the characteristics of lightning strikes in the vicinity of the tower or the influence the tower has on the lightning environment around it. This thesis is believed to be the first to fill such a gap and tries to answer these questions. Using the 2005 North American Lightning Detection Network data for the area of up to 100 km from the tower, an extensive investigation of lightning activities in the vicinity of the tower is presented here. A comparison between the characteristics of CN Tower strikes and the characteristics of strikes occurring in its vicinity is also presented. Furthermore, the parameters of the lightning electromagnetic pulse (LEMP) generated by a strike to the tower are compared with those generated by a non-eN Tower strike. A substantial increase in the CN Tower LEMP peak in comparison with that resulting from non-CN Tower LEMP has been found. Therefore, electronic and communication systems located in the vicinity of a very tall structure must be specially protected from the lightning-generated electromagnetic pulse.

Experimental Investigation on The Effect of Divergent Tower Solar Chimney on The Theoretical Power Potential

Solar chimney power plant is a sustainable alternative for electricity generation using solar as the source of energy. In general, the main body of a solar chimney plant requires a tall structure which is costly and challenging to construct. Thus, it is important to increase the performance of the solar chimney power plant and have a better energy-cost ratio. This study aims to experimentally investigate the influence of divergent solar chimney as opposed to a cylindrical chimney on solar chimney performance. Three divergent scaled-down solar chimney model at 1-meter, 1.5-meter and 2-meter were fabricated and tested for its performance at various simulated heat loads. The test results were compared with similar heights cylindrical solar chimney. The experiments show that divergent solar chimney increases the theoretical power generation potential and improves the stalk effect and have higher outlet velocity compared to a cylindrical solar chimney. The power potential of the divergent chimney is increased up to 18 times with the maximum theoretical power obtain at 0.183W on the 2-meter divergent chimney. Higher temperature was recorded on the 2-meter divergent chimney outlet at 341.3k compared to 330.4k on the cylindrical chimney indicates better stack effect. The highest average velocities in the divergent and cylindrical chimneys were recorded under the electric heat load of 2 kW at 0.994 m/s and 0.820 m/s respectively in the 1-meter configuration. It is also observed that the air velocity in a shorter divergent chimney is higher than taller divergent chimney models while better compared to all cylindrical height. This study finds that a shorter divergent solar chimney produces greater energy compared to a higher cylindrical solar chimney. Therefore, it is possible to reduce the overall cost of solar chimney by reducing the height of the main structure without sacrificing the performance of the solar chimney.