Aly Mousaad Aly

ABSTRACT During their lifetimes, high-rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which make the tuned mass damper (TMD) design challenging. In this paper, a proposed approach for the design of robust TMDs is presented and investigated. The approach accounts for structural uncertainties, optimization objectives and input excitation (wind or earthquake). For the use of TMDs in buildings, practical design parameters can be different from the optimum ones. However, predetermined optimal parameters for a primary structure with uncertainties are useful to attain design robustness. To illustrate the applicability of the proposed approach, an example of a very slender building with uncertain natural frequencies is presented. The building represents a case study of an engineered design that is instructive. Basically, due to its geometry, the building behaves differently in one lateral direction (cantilever building) than the other (shear building). The proposed approach showed its robustness and effectiveness in reducing the response of tall buildings under multidirectional wind loads. In addition, LQG and fuzzy logic controllers enhanced the performance of the TMD.

During their lifecycle, wind turbines can be subjected to multiple hazard loads, such as highintensity wind, earthquake, wave, and mechanical unbalance. Excessive vibrations, due to these loads, can have detrimental effects on energy production, structural lifecycle, and the initial cost of wind turbines. Vibration control by various means, such as passive, active, and semi-active control systems provide crucial solutions to these issues. We developed a novel control theory that enables semi-active controller tuning under the complex structural behavior and inherent system nonlinearity. The proposed theory enables the evaluation of semi-active controllers' performance of multi-degrees-of-freedom systems, without the need for time-consuming simulations. A wide range of controllers can be tested in a fraction of a second, and their parameters can be tuned to achieve system-level performance for different optimization objectives.

In recent years, as a result of significant climate change, stringent windstorms are becoming more frequent than before. Given the threat that windstorms bring to people and property, wind/structural engineering research is imperative to improve the resilience of existing and new infrastructure, for community safety and assets protection. The Windstorm Impact, Science and Engineering (WISE) research program at Louisiana State University (LSU) focuses on creating new knowledge applicable to the mitigation of existing and new infrastructure, to survive and perform optimally under natural hazards (Figure 1). To achieve our research goals, we address two imperious challenges: (i) characterization of realistic wind forces on buildings and other types of structures; and (ii) developing advanced control theory to accelerate the optimal tuning of smart structures, with the aim of developing novel probabilistic analytical methods to address the complex behavior and inherent nonlinearity in semi-active control, for multiple hazards.

This paper focuses on the processes of wind flow in the atmospheric boundary layer, to produce realistic full-scale pressures for the design of low-rise buildings. CFD with LES turbulence closure is implemented on a scale 1:1 prototype building. A proximity study was executed computationally in CFD with LES that suggests new recommendations on the computational domain size, in front of a building model, apart from common RANS-based guidelines (e.g. COST and AIJ). Our findings suggest a location of the test building, different from existing guidelines, and the inflow boundary proximity influences pressure correlation and reproduction of peak loads. The CFD LES results are compared to corresponding pressures obtained by open jet, full scale, wind tunnel, and the ASCE 7-10 standard for roof Component & Cladding design. The CFD LES shows its capability to produce peak pressures/loads on buildings, in agreement with field pressures, due to its capabilities of reproducing the spectral contents of the inflow at a 1:1 scale.

With the sustainability movement, vegetated building envelopes are gaining more popularity. This requires special wind effect investigations, both from sustainability and resiliency perspectives. The current paper focuses on wind load estimation on small-and full-scale trees used as part of green roofs and balconies. Small-scale wind load assessment was carried out using wind tunnel testing in a globaleffect study to understand the interference effects from surrounding structures. Full-scale trees were investigated at a large open-jet facility in a local-effect study to investigate the wind-tree interaction. The effect of Reynolds number combined with shape change on the overall loads measured at the base of the trees (near the roots) has been investigated by testing at different model scales and wind speeds. In addition, high-speed tests were conducted to examine the security of the trees in soil and to assess the effectiveness of a proposed structural mitigation system. Results of current research show that small-scale testing may overestimate wind loading on actual trees when the tests do not account fully for tree-wind interaction. On the other hand, the full-scale testing shows that at higher wind speeds the load coefficients tend to be reduced, limiting the wind loads on trees. No resonance or vortex shedding was visually observed.

Solar power can improve the quality of life and reduce dependency on traditional energies that are a significant source of pollution and global warming. Solar panels are common devices used for collecting solar energy. To balance between sustainability and resilience, it is essential to provide an accurate estimate of the design wind loads for the solar panels. Traditionally design wind loads for buildings and other structures are obtained using building codes and standards. The solar panels represent a relatively recent technology and indeed there is no complete guidance ready for codification of wind loads on these types of structures. Available wind tunnel data show discrepancies in wind loads on solar panels, owing to inconsistent model scales and test flows, among other factors. To eliminate such discrepancies in the test results and to allow for accurate wind load estimation, the current paper investigates the geometric scale and the inflow turbulence characteristics as potential causes of high uncertainties. Computational fluid dynamics (CFD) simulations are employed and results are compared with available wind tunnel data, as a complementary tool with a potential to simulate wind loads at full-scale. The results show that the geometric scale is a primary reason for the discrepancies in peak wind loads, which can be avoided by adapting the inflow turbulence and using a proper testing protocol. The results show an evidence of the correctness of a hypothesis that the lack of large-scale turbulence can dramatically affect peak wind loads on test objects. Consequently, recommendations are articulated regarding the best usage of the available wind load estimation tools. This is expected to lead to consistent and accurate results from wind tunnel testing and CFD simulations, a crucial step toward codification of wind loads on solar panels.

In recent years, high-rise buildings received a renewed interest as a means by which technical and economic advantages can be achieved, especially in areas of high population density. Taller and taller buildings are being built worldwide. These types of buildings present an asset and typically are built not to fail under wind loadings. The increase in a building\'s height results in increased flexibility, which can lead to significant vibrations, especially at top floors. Such oscillations can magnify the overall loads and can be annoying to the top floors\' occupants. This paper shows that increased stiffness in high-rise buildings may not be a feasible solution and may not be used for the design for comfort and serviceability. High-rise buildings are unique, and a vibration control system for a certain building may not be suitable for another. Even for the same building, its behavior in the two lateral directions can be different. For this reason, the current study addresses the application of hybrid tuned mass and magneto-rheological (TM/MR) dampers that can work for such types of buildings. The proposed control scheme shows its effectiveness in reducing floors\' accelerations for both comfort and serviceability concerns. Also, a dissipative analysis carried out shows that the MR dampers are working within the possible range of optimum performance. In addition, the design loads are dramatically reduced, creating more resilient and sustainable buildings. The purpose of this paper is to stimulate, shape, and communicate ideas for emerging control technologies that are essential for solving wind related problems in high-rise buildings, with the objective to build the more resilient and sustainable infrastructure and to optimally retrofit existing structures.

In the past few decades, high-rise buildings have received a renewed interest in many city business locations, where land is scarce, as per their economics, sustainability, and other benefits. Taller and taller towers are being built everywhere in the world. However, the increased frequency of multihazard disasters makes it challenging to balance between a resilient and sustainable construction. Accordingly, it is essential to understand the behavior of such structures under multihazard loadings, in order to apply such knowledge to design. The results obtained from the dynamic analysis of two different high-rise buildings (54-story and 76-story buildings) investigated in the current study indicate that earthquake loads excite higher modes that produce lower interstory drift, compared to wind loads, but higher accelerations that occur for a shorter time. Wind-induced accelerations may have comfort and serviceability concerns, while excessive interstory drifts can cause security issues. The results also show that high-rise and slender buildings designed for wind may be safe under moderate earthquake loads, regarding the main force resisting system. Nevertheless, nonstructural components may present a significant percentage of loss exposure of buildings to earthquakes due to higher floor acceleration. Consequently, appropriate damping/control techniques for tall buildings are recommended for mitigation under multihazard.

This paper summarizes the state-of-the-art techniques used to simulate hurricane winds in atmospheric boundary-layer (ABL) for wind engineering testing. The wind tunnel simulation concept is presented along with its potential applications, advantages and challenges. ABL simulation at open-jet simulators is presented along with an application example followed by a discussion on the advantages and challenges of testing at these facilities. Some of the challenges and advantages of using computational fluid dynamics (CFD) are presented with an application example. The paper show that the way the wind can be simulated is complex and matching one parameter at full-scale may lead to a mismatch of other parameters. For instance, while large-scale testing is expected to improve Reynolds number and hence approach the full-scale scenario, it is challenging to generate large-scale turbulence in an artificially created wind. New testing protocols for low-rise structures and small-size architectural features are presented as an answer to challenging questions associated with both wind tunnel and open-jet testing. Results show that it is the testing protocol that can be adapted to enhance the prediction of full-scale physics in nature. Thinking out of the box and accepting non-traditional ABL is necessary to compensate for Reynolds effects and to allow for convenient experimentation. New research directions with focus on wind, rain and waves as well as other types of non-synoptic winds are needed, in addition to a more focus on the flow physics in the lower part of the ABL, where the major part of the infrastructure exists.

Most boundary-layer wind tunnels (BLWTs) were built for testing models of large civil engineering structures that have geometric scales ranging from 1:500 to 1:100. However, producing aerodynamic models of the solar panels at such scales makes the modules too small, resulting in at least two technical problems. First, the resolution of pressure data on such small models becomes low. Second, the test model may be placed in the lower portion of the boundary-layer that is not a true representative of a real world scenario, due to high uncertainty in wind velocity. To alleviate these problems, development of a standardized testing protocol is very important. Such protocol should account for different time and geometric scales to design appropriate wind tunnel experiments that can allow accurate assessment of wind loads on the solar panels. The current paper systematically investigates the sensitivity of wind loads to testing ground-mounted solar panels, both experimentally (in a BLWT) and numerically (by computational fluid dynamics (CFD)), at different geometric scales. While mean loads are not significantly affected by the model size, peak loads are sensitive to both the geometric scale and the spectral content of the test flow. However, when the objective is to predict 3-s (three seconds) peak loads, large models can be tested in a flow that has reduced high-frequency turbulence.

The existing literature has limited aerodynamic data for the evaluation of design wind loads for solar panels. Furthermore, there are no provisions in building codes and standards to guide the design of these types of structures for wind. This paper presents a systematic wind tunnel study to evaluate wind loads on solar panels mounted on low-rise gable buildings. A preliminary geometric scale effect study using a simple isolated solar panel was carried out to permit design appropriate wind tunnel experiments. Following the scale effect study, wind loads on solar panels mounted on different critical zones of low-rise residential roof are systematically investigated. The results of the current paper provide useful information for the design of the solar panels.


Read More: http://ascelibrary.org/doi/abs/10.1061/9780784412848.137

In wind load calculations based on pressure measurements, the concept of 'tributary area' is usually used. The literature has less guidance for a systematic computational methodology for calculating tributary areas, in general, and for scattered pressure taps, in particular. To the best of the author's knowledge, there is no generic mathematical equation that helps calculate the tributary areas for irregular pressure taps. Traditionally, the drawing of tributary boundaries for scattered and intensively distributed taps may not be feasible (a time and resource consuming task). To alleviate this problem, this paper presents a proposed numerical approach for tributary area calculations on rectangular surfaces. The approach makes use of the available coordinates of the pressure taps and the dimensions of the surface. The proposed technique is illustrated by two application examples: first, quasi-regularly distributed pressure taps, and second, taps that have scattered distribution on a rectangular surface. The accuracy and the efficacy of the approach are assessed, and a comparison with a traditional method is presented.

With the sustainability movement, vegetated building envelopes are gaining more popularity. This requires special wind effect investigations, both from sustainability and resiliency perspectives. The current paper focuses on wind load estimation on small- and full-scale trees used as part of green roofs and balconies. Small-scale wind load assessment was carried out using a wind tunnel testing in a global-effect study to understand the interference effects from surrounding structures. Full-scale trees were investigated at a large open-jet facility in a local-effect study to account for the wind-tree interaction. The effect of Reynolds number combined with shape change on the overall loads measured at the base of the trees (near the roots) has been investigated by testing at different model-scales and wind speeds. In addition, high-speed tests were conducted to examine the security of the trees in soil and to assess the effectiveness of a proposed structural mitigation system. Results of the current research show that at relatively high wind speeds the load coefficients tend to be reduced, limiting the wind loads on trees. No resonance or vortex shedding was visually observed.

This paper presents wind-induced response reduction in a very slender building using smart dampers with proposed bracings-lever mechanism system. The building presents a case study of an engineered design that is instructive. The paper shows that shear response and flexural response of tall buildings present two very different cases for vibration suppression. Smart dampers are implemented optimally in the building to reduce its response in the lateral directions for both structural safety and occupant comfort concerns.

This research presents vibration control of buildings due to earthquake effect. The model is subjected to the horizontal component of the earthquake, which has a larger effect than the vertical component. Newton's second law of motion is applied to obtain the mathematical model of the structures. Magneto-Rheological (MR) dampers are placed between the stories. Several control algorithms including the decentralized bang-bang controller, the Lyapunov controller, the modulated homogeneous friction controller, the maximum energy dissipation controller, and the clipped-optimal controller are applied with the MR damper. The modified quasi-bang-bang control is proposed in this paper. The MR damper (depending on the control algorithm used) gives a better reduction in the maximum absolute acceleration, also an excellent reduction in the maximum inter-story displacement; also the maximum displacement of the top story is reduced.

... Contact person: AM Aly, Politecnico di Milano, Via G La Masa 34, Milano, Tel: (+39) 0223998023 Fax: (+39) 0223998081 E-mail: aly.mousaad@polimi.it ... AM Aly, A. Zasso, F. Resta Politecnico di Milano – aly.mousaad@polimi.it – Via G La Masa, 34, Milano, Italy ...

This paper presents vibration control of a building model under earthquake loads. A magnetorheological (MR) damper is placed in the building between the first floor and ground for seismic response reduction. A new control algorithm to command the MR damper is proposed. The approach is inspired by a quasi-bang-bang controller; however, the proposed technique gives weights to control commands in a fashion that is similar to a fuzzy logic controller. Several control algorithms including decentralized bang-bang controller, Lyapunov controller, modulated homogeneous friction controller, maximum energy dissipation controller, and clipped-optimal controller are used for comparison. The new controller achieved the best reduction in maximum interstory drifts and maximum absolute accelerations over all the control algorithms presented. This reveals that the proposed controller with the MR damper is promising and may provide the best protection to the building and its contents.

The paper presents an experimental study to assess wind induced pressure on full-scale loose concrete roof pavers by using Wall of Wind, a large-scale hurricane testing facility at Florida International University. Experimental tests were conducted on full-scale concrete pavers mounted on a test building to evaluate wind-induced external and underneath pressures acting on the pavers. The study shows that roof pavers could be subjected to significant uplifting wind forces due to negative pressures. In corner and edge areas of the roof, pressure differences produced net uplift on the pavers, at design wind speed, that was greater than the individual weight of the pavers. The study provides new insights by testing the actual roofing material at high wind speeds in a controlled environment and also showed that locking the pavers together can mitigate the issues at corners and edges by increasing the weight of the pavers that acts together to counterbalance the net uplift pressure. © 2012 Elsevier Ltd.

The most common device for control of tall buildings under wind loads is the tuned mass damper (TMD). However, during their lifetimes, high-rise and slender buildings may experience natural frequency changes under wind speed, ambient temperatures and relative humidity variations, among other factors, which make the TMD design challenging. In this paper, a proposed approach for the design of robust TMDs is presented and investigated. The approach accounts for structural uncertainties, optimization objectives and input excitation (wind or earthquake). For the use of TMDs in buildings, practical design parameters can be different from the optimum ones. Nevertheless, predetermined optimal parameters for a primary structure with uncertainties are useful to attain design robustness. To illustrate the applicability of the proposed approach, an example of a very slender building with uncertain natural frequencies is presented. The building represents a case study of an engineered design that is instructive. Basically, due to its geometry, the building behaves differently in one lateral direction (cantilever building) than the other (shear building). The proposed approach shows its robustness and effectiveness in reducing the response of tall buildings under multidirectional wind loads. In addition, linear-quadratic Gaussian and fuzzy logic controllers enhanced the performance of the TMD. Copyright © 2012 John Wiley & Sons, Ltd.

ABSTRACT: The reliable measurement of pressures on low-rise buildings in the atmospheric boundary layer (ABL) flow remains a challenge, as has been shown by the large discrepancies among results obtained in different wind tunnel facilities or even in the ...

Civil engineering structures are an integral part of our modern society. Traditionally, these structures are designed to resist static loads. However, they may be subjected to dynamic loads like earthquakes, winds, waves, and traffic. Such loads can cause severe and/or sustained vibratory motion, which can be detrimental to the structure and human occupants. Because of this, safer and more efficient designs are sought out to balance safety issues with the reality of limited resources. Wind-induced vibrations in buildings are of increasing ...

ABSTRACT Developments in structural materials have led to designs that satisfy strength requirements but are often very flexible. Wind loads and the associated structural responses are a governing factor in the design of the steel framing system of many high-rise buildings. Wind load capacity is also a key factor in determining the overall strength of towers and also for comfort reasons.

Smart damping technology has been proposed to protect civil structures from dynamic loads. Each application of smart damping control provides varying levels of performance relative to active and passive control strategies. Currently, researchers compare the relative efficacy of smart damping control to active and passive strategies by running numerous simulations. These simulations can require significant computation time and resources. Because of this, it is desirable to develop an approach to assess the applicability of smart damping technology which requires less computation time. This paper discusses and verifies a probabilistic approach to determine the efficacy of smart damping technology based on clipped optimal state feedback control theory.

ABSTRACT This paper presents a detailed study to investigate the influences of incident wind direction, upstream terrain conditions and interferences from the surroundings on the wind responses of a tall building. The building tower considered in this study has 209 m height, 57.6 m width, and 22.5 m depth. A 1: 100 scaled 3D rigid model of the tower has been constructed for different test cases at the Boundary Layer Wind Tunnel of Politecnico di Milano, Italy. Surface pressure and base load measurements have been conducted for ...

Hurricane winds are one of the governing design environmental loads for structures. In coastal regions such as Florida, hurricanes cause enormous loss to life and property. Research focusing on the complex interaction between hurricanes and the built environment is therefore needed for developing a cohesive approach to build hurricane resilient coastal communities. At the International Hurricane Research Center (IHRC), Florida International University (FIU), research is going in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility for potential full- and large-scale wind engineering testing. In this paper, a technique for simulating hurricane winds at the WoW is presented and investigated. Wind profiles were simulated using turning vanes, and/or adjustable planks mechanism with and without grids. Assessments of flow characteristics were performed in order to enhance the WoW's flow simulation capabilities. The full-scale testing facility will be capable of generating hurricane wind and wind-driven rain field with proper characteristics to allow better understanding of category 1 to 4 hurricane (using Saffir-Simpson scale) effects on structures. The facility will be large enough to engulf full- and large-scale models of single-story buildings built using actual construction materials. This will help improve code provisions, innovative hurricane mitigation development, and producing solutions which bridge the disciplines of wind engineering and structural engineering. Copyright © ASCE 2011.

ABSTRACT: To develop a cohesive and systemic approach to building hurricane resilient communities research is needed on the complex interaction between hurricanes and the built environment. Florida International University (FIU) is working in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility to support research in the area of wind engineering. Three different types of tests are envisioned:(i) aerodynamic (ii) hydro-aerodynamic, and (iii) destructive. This paper describes the new facility, provides ...

Researchers at the International Hurricane Research Center (IHRC), Florida International University (FIU), are working in stages on the construction of a large state-of-the-art Wall of Wind (WoW) facility to support research in the area of Wind Engineering. In this paper, the challenges of simulating hurricane winds for the WoW are presented and investigated based on a scale model study. Three wind profiles were simulated using airfoils, and/or adjustable planks mechanism with and without grids. Evaluations of flow characteristics were performed in order to enhance the WoW's flow simulation capabilities. Characteristics of the simulated wind fields are compared to the results obtained from a study using computational fluid dynamics (CFD) and also validated via pressure measurements on small-scale models of the Silsoe cube building. Optimal scale of the test model and its optimal distance from the WoW contraction exit are determined - which are two important aspects for testing using an open jet facility such as the WoW. The main objective of this study is to further the understanding of the WoW capabilities and the characteristics of its test section by means of intensive tests and validations at small scale in order to apply this knowledge to the design of the full-scale WoW and for future wind engineering testing.

ABSTRACT This thesis presents vibration control of two civil engineering structures (buildings and bridges) due to earthquake effect. For buildings, the model is subjected to EL-Centro and/or Takoshi-oki earthquake horizontal component, while the bridge is subjected to EL-Centro vertical component which has a larger effect than the horizontal component. Newton's second law of motion and the influence coefficient method are applied to obtain the mathematical model of the structures.

This paper presents wind-induced response reduction in a very slender building using magneto-rheological (MR) dampers with lever mechanism. The building presents a case study of an engineered design that is instructive. The paper shows that shear response and flexural response of tall buildings present two very different cases for vibration suppression. MR dampers are implemented optimally in the building to reduce its response in the lateral directions for both structural safety and occupant comfort concerns. A proposed lever mechanism is used with the dampers to improve their performance. The study shows how a lever mechanism can enable application to flexural response and scenarios where the inter-story drift is not enough for dampers to work effectively. Furthermore, the decentralized bang-bang controller produced additional improvement to the performance of the MR dampers. Copyright © 2010 John Wiley & Sons, Ltd.

"Active control of a tall building subjected to wind loads is presented in this paper. A 48-story high-rise building (209 m height) equipped with two active mass dampers is used in this research. The structure is subjected to both across-wind and along-wind loads obtained for a rigid model (scaled 1:100) that was tested in the wind tunnel of Politecnico di Milano for two different configurations of the surrounding. The building alone is modeled dynamically using three-dimensional model with a total degrees-of-freedom of 144 (each floor has three degrees-of-freedom: two lateral translations and one rotation about the vertical axis). The state reduced order technique is used for the control purposes. The lateral response of the building in the two directions is controlled simultaneously while the effect of the uncontrolled torsional response of the structure is considered instantaneously. Effects of the wind attackangle on the performance of the controlled system are studied. The results obtained show that both tuned mass dampers and active mass dampers have a great effect on the reduction of the displacement and acceleration responses of the building over a wide range of excitation inputs. However, it is found that controlling the responses in one lateral direction is more effective than that in the other direction due to the unequal effects of the vortex shedding and the torsional responses.

Abstract In this study two semiactive controllers are used for the Fast Hybrid Testing (FHT) of three physical largescale 200 kN Magneto-Rheological (MR) dampers implemented on the SAC three story nonlinear building designed for Los Angeles, US. Clipped-optimal and Lyapunov control algorithms are evaluated in this research with the MR dampers to control the response of the building. Both experimental and numerical simulations are conducted to examine the performance of the proposed controllers. The NEES FHT facility at the ...