Bijan Samali

Optimization of tuned liquid column dampers

Abstract The effectiveness of a tuned liquid column damper (TLCD) in controlling structural vibration is studied. A numerical method is adopted to account for nonlinearity of the governing equation. Optimum parameters of the TLCD for maximum reduction of peak structural response to harmonic excitations in a wide frequency range are presented for a wide range of flexible structures. A variation of U-shaped TLCD with different cross-sectional areas in its vertical and horizontal sections is investigated. It is found that an increase in cross-sectional area ratio (vertical/horizontal) can greatly reduce the length requirement of a TLCD making it more attractive to flexible structures. A new type V-shaped TLCD is also investigated. This type of TLCD can suppress stronger vibrations such as those caused by strong wind. It is found that, like the tuned mass damper (TIVID), there is an optimum tuning ratio (damper frequency/structure frequency) for maximum reduction in response of a structure system which is independent of the excitation. The optimum coefficient of head loss will depend on the intensity of the excitation with smaller coefficient of head loss associated with stronger excitation.

Development and characterization of a magnetorheological elastomer based adaptive seismic isolator

One of the main shortcomings in current base isolation design/practice is lack of adaptability. As a result, a base isolation system that is effective for one type earthquake may become ineffective or may have adverse effect for other earthquakes. The vulnerability of traditional base isolation systems can be exaggerated by two types of earthquakes, i.e. near-field earthquakes and far-field earthquakes. This paper addresses the challenge facing current base isolation design/practice by proposing a new type of seismic isolator for the base isolation system, namely an adaptive seismic isolator. The novel adaptive seismic isolator utilizes magnetorheological elastomer (MRE) for its field-sensitive material property. Traditional seismic isolator design with a unique laminated structure of steel and MRE layers has been adopted in the novel MRE seismic isolator. To evaluate and characterize the behavior of the MRE seismic isolator, experimental testing was conducted on a shake table facility under harmonic cycling loading. Experimental results show that the proposed adaptive seismic isolator can successfully alter the lateral stiffness and damping force in real time up to 37% and 45% respectively. Based on the successful development of the novel adaptive seismic isolator, a discussion is also extended to the impact and potential applications of such a device in structural control applications in civil engineering.

Performance of tuned mass dampers under wind loads

The performance of both passive and active tuned mass damper (TMD) systems can be readily assessed by parametric studies which have been the subject of numerous research. The results of those parametric studies are invaluable in the selection of optimum TMD parameters. Few experimental verifications of TMD theory have been carried out, particularly those involving active control, but the results of those experiments generally compared well with those obtained by parametric studies. Despite some serious design constraints, a number of passive and active tuned mass damper systems have been successfully installed in tall buildings and other structures to reduce the dynamic response due to wind and earthquakes. The results of extensive full-scale measurement programs conducted on a significant number of these clearly show the effectiveness of the systems.

Use of viscoelastic dampers in reducing wind- and earthquake-induced motion of building structures

Viscoelastic (VE) dampers have been successfully incorporated in a number of tall buildings as a viable energy dissipating system to suppress wind- and earthquake-induced motion of building structures. This type of damper dissipates the buildings mechanical energy by converting it into heat. Several factors such as ambient temperature and the loading frequency will affect the performance and hence the effectiveness of the damper system. VE dampers have been able to increase the overall damping of the structure significantly, hence improving the overall performance of dynamically sensitive structures. The effectiveness of VE dampers has been demonstrated both experimentally and analytically by many researchers over the past 25 years. The twin towers of the World Trade Center Buildings in New York City and the Columbia SeaFirst Building in Seattle, Washington, are among the first buildings which benefited from the installation of VE dampers. In seismic applications, the VE dampers can be incorporated either into new construction or as a viable candidate for the retrofit of existing buildings which adds to the versatility of VE dampers.

Active control of along wind response of tall building using a fuzzy controller

Abstract This paper focuses on the benchmark problem application regarding the vibration control of tall buildings under along wind excitation. The building under consideration is the 76-story, 306 meter tall reinforced concrete office tower proposed for the city of Melbourne, Australia. The adopted control scheme consists of an Active Tuned Mass Damper (ATMD) where the control action is achieved by a Fuzzy Logic Controller (FLC). The main advantage of the fuzzy controller is its inherent robustness and ability to handle any non-linear behaviour of the structure. This benchmark study is based on specified design constraints for the ATMD to be considered in the design of the proposed control scheme. The robustness of the controller has been demonstrated through the uncertainty in stiffness (+15% and −15% variation from initial stiffness) of the building. The results of the simulation show a good performance by the fuzzy controller for all cases tested. Also the results show that the fuzzy controller performs slightly better than the LQG controller, while possessing several advantages over the LQG controller.

Seismic behavior of building frames considering dynamic soil-structure interaction

AbstractThe seismic excitation experienced by structures is a function of the earthquake source, travel path effects, local site effects, and soil-structure interaction (SSI) influences. The result of the first three of these factors is referred to as free-field ground motion. The structural response to free-field motion is influenced by the SSI. In particular, accelerations within structures are affected by the flexibility of the foundation support and variations between the foundation and free-field motions. Consequently, an accurate assessment of inertial forces and displacements in structures can require a rational treatment of SSI effects. In the current study, to depict these effects on the seismic response of moment-resisting building frames, a 10-story moment-resisting building frame resting on a shallow foundation was selected in conjunction with three soil types with shear-wave velocities of less than 600 m/s, representing Soil Classes Ce, De, and Ee according to an existing Australian Standard....

Characteristics of multiple tuned liquid column dampers in suppressing structural vibration

Abstract The characteristics of multiple tuned liquid column dampers (MTLCD) in suppressing structural vibration are investigated. A parametric study involving the effects of frequency range, coefficient of head loss, number of TLCDs and central frequency on the performance of MTLCD is carried out through a numerical procedure which reflects the non-linear character of the liquid motion. The advantages and disadvantage of MTLCD are discussed. It was found that the frequency range and the coefficient of head loss have significant effects on the performance of a MTLCD; increasing the number of TLCDs can enhance the efficiency of the MTLCD, but no further significant enhancement is observed when the number of TLCDs is over five. The investigation also confirmed that the sensitivity of an optimised MTLCD to its central frequency ratio is not much less than that of an optimised single TLCD to its frequency ratio, and an optimised MTLCD is even more sensitive to the coefficient of head loss (or damping). However, to maintain the same level of efficiency as an optimised single TLCD, a MTLCD offers much wider choices in both frequency ratio and coefficient of head loss. In this sense, a MTLCD is more robust than a single TLCD.

Performance of a five-storey benchmark model using an active tuned mass damper and a fuzzy controller

Abstract This paper focusses on the performance of a five-storey benchmark model using an active tuned mass damper (ATMD), where the control action is achieved by a Fuzzy logic controller (FLC) under earthquake excitations. The advantage of the Fuzzy controller is its inherent robustness and ability to handle any non-linear behaviour of the structure. The simulation analysis of the five-storey benchmark building for the uncontrolled building, the building with tuned mass damper (TMD), and the building with ATMD with Fuzzy and linear quadratic regulator (LQR) controllers is reported, and comparison between Fuzzy and LQR controllers is made. In addition, the simulation analysis of the benchmark building with different values of frequency ratio, β ( β =dominant earthquake frequency/fundamental building frequency) using a Fuzzy controller is conducted and the effect of mass ratio, μ ( μ =mass of the TMD/total mass of the model) on the five-storey benchmark model using the Fuzzy controller is studied.

Control of wind-induced tall building vibration by tuned mass dampers

Abstract Wind tunnel model tests and theoretical analyses were conducted to investigate the effectiveness of tuned mass dampers in suppressing wind-induced tall building motion. The tall building model was a 1:400 scale aeroelastic model of the CAARC Standard Tall Building. This model and the tuned mass damper models of different parameters were designed and tested in a wind tunnel with properly simulated atmospheric boundary layer flow. The aeroelastic test of the CAARC model demonstrated the effectiveness of the tuned mass damper system in suppressing the dynamic response of the building. The parametric study of passive tuned mass dampers, leading to theoretical analysis and design of an effective and efficient tuned mass damper system, was based on excitation spectra which were directly measured from the wind tunnel model tests. Semi-analytical results were in good agreement with the test results. The analytical results further indicated that the effectiveness of tuned mass dampers can be enhanced by the inclusion of an active control system.

Behaviour of concrete beam-column connections reinforced with hybrid FRP sheet

Abstract Modelling complex concrete column–beam connection with hybrid fibre reinforced plastic (FRP) reinforcement properly requires understanding of the behaviour of such component and supporting from some experimental data for model updating and refinement. This paper, through a comprehensive experimental work, investigates the behaviour of reinforced concrete frame specimens designed to represent the column–beam connections in plane frames. As a follow-up to the previous reported work, it focuses on details of experimental analyses, in particular, a comprehensive strain analysis. Results of the analysis show that designed hybrid FRP reinforcement greatly improve the stiffness and load carrying capacity of its concrete counterpart. It also delays the crack initiation at the joint through confinement due to FRP reinforcement.