A hybrid nonlinear rooftop isolated tuned mass damper-inerter system for seismic protection of building structures

In recent years, the passive tuned mass damper inerter (TMDI) has been widely considered in the literature for the seismic demand mitigation of building structures. Its effectiveness relies on careful design/tuning of the TMDI stiffness and damping properties, while its performance improves with the increase of the inertance property, which is readily scalable, as well as with spanning several floors when placed to the top of buildings. Nevertheless, TMDI configurations spanning several floors may be impractical for ordinary structures. This paper addresses the above issue by presenting a novel hybrid energy dissipation system, termed rooftop isolated tuned mass damper inerter (RI-TMDI). The RI-TMDI comprises an additional seismically isolated floor with a TMDI placed atop of buildings, making it applicable for seismically retrofitting of existing structures as well as for enhancing the seismic performance of new structures. The motivation of the RI-TMDI is based on the fact that the vibration control potential of TMDIs improve as the floor they are installed to is designed to be more flexible. Herein, a three degree of freedom (3-DOF) structural system is put forward to study the potential of RI-TMDI for seismic response mitigation of buildings, modelled as linear damped single degree of freedom structures, in which isolator bearings are modelled through the Bouc-Wen model. Statistical linearization is applied to expedite optimal RI-TMDI tuning such that the input energy dissipated by the TMDI is maximized under white noise excitation. A pilot parametric numerical investigation is undertaken to assess the influence of the isolator flexibility and damping properties and of the TMDI inertance to the tuning and performance of the RI-TMDI under white noise excitation. Further, results from nonlinear response history analyses for four recorded GMs applied to optimally tuned RI-TMDI systems are reported. It is found that the efficacy of RI-TMDI for suppressing seismic structural displacement demands improves as the effective post-yielding flexibility of the isolators increases, provided that the TMDI is equipped with sufficiently high inertance. However, this improvement comes at the cost of increased deflection of the isolators. To this end, it is shown that by increasing inertance both building and isolator displacements may be reduced

Lamb Wave Mode Selection for Increased Sensitivity ot Interfacial Weaknesses of Adhesive Bonds

Interface quality between layers in a layered structure is critical in fracture and fatigue analysis. A theoretical and quantitative solution to the problem from a NDE point of view would be desirable in both manufacturing and for in-service investigation of a variety of different structures. For example a great need exists to develop a reliable and efficient inspection program of adhesive bond delamination and interfacial weakness detection in aging aircraft noting that the bond degradation generally preceeds cracking in the aluminum skin, starting at the rivet holes

A wavelet-based approach for describing the mechanical behaviour of cellular beams

This paper describes how a wavelet model comprised of a linear combination of sine terms is capable of representing the cross-section inertia variation along the length of cellular beams. This allows the efficient computation of deflections of cellular beams when these are deployed as a part of steel-concrete composite flooring systems. This method does not involve purely statistical approaches or piece-wise integration of moment-curvature relationships that lead to cumbersome matrix approaches and complicate the assessment of deflections. Despite its simplicity, the proposed approach is found to be reliable as it successfully predicts displacements obtained through finite element model representations of more than 260 cases with errors smaller than ±5 %. Furthermore, the proposed analytical description of cross-section inertia along the beam length is defined by only three parameters that can be inferred through linear expressions considering the geometrical characteristics of a perforated beam, namely, the ratio of flange to web thickness, the second moment of inertia of the steel beam and the ratio between beam length and depth, making it easy for widespread application by practitioners

Optimal design and assessment of nonlinear inerter vibration absorbers for earthquake response mitigation of building structures

Considerable damages to structural and non-structural components in building structures are persistently observed in the aftermath of several recent major seismic events, incurring downtime and disproportionally high economic losses in well-populated areas. These earthquake consequences highlight the need for widening the use of passive seismic protective devices, such as viscous fluid dampers (FVDs) and dynamic vibration absorbers (DVAs), in newbuilt and in existing structures to enhance seismic building performance beyond the one achieved by ductility-based earthquake resistant design approaches adopted by current seismic codes of practice. To this end, in recent years, the concept of the inerter, a lightweight device resisting relative acceleration through the inertance property, has been heavily considered in the scientific literature to improve the seismic building response mitigation capacity of FVDs and DVAs, giving rise to new promising classes of inerter-based seismic protective devices, such as the linear tuned mass damper inerter (TMDI). This thesis makes significant contributions to this body of research through novel analytical and numerical work by proposing innovative practically advantageous TMDI-based device configurations, leveraging nonlinear device/component behavior for enhanced seismic response mitigation in buildings and underpinned by simplified, yet theoretically rigorous, optimal device tuning approaches accounting for nonlinear device behavior. First, the potential for seismic protection of buildings of a nonlinear TMDI (NTMDI) featuring a FVD with nonlinear power law force-velocity relationship, commonly encountered in commercial FVDs, is compared vis-à-vis the conventional linear TMDI. This is facilitated by a practicable and computationally efficient optimal NTMDI tuning approach which accounts for any NTMDI connectivity to the building structure, modelled as a linear single-mode dynamical system, and employs statistical linearization to treat the nonlinear damping term assuming stationary random ground acceleration excitation. Response history analysis results for a benchmark 9-storey steel building with optimally tuned NTMDI demonstrate that reduced NTMDI stroke and inerter force are achieved with negligible change in peak storey drifts and floor acceleration responses under recorded ground motions by lowering the FVD exponent, leading to practically advantageous NTMDI deployments. Next, an innovative top-floor (N)TMDI configuration in conjunction with top-storey seismic isolation, implemented by standard nonlinear elastomeric bearings, is introduced termed nonlinear isolated roof-top TMDI (IR-TMDI). The IR-TMDI leverages the localized top floor softening, enabled by the isolation layer, to potentially enhance the seismic vibrations mitigation capacity of the TMDI throughout the elevation of multi-storey buildings, applicable to new and existing building structures. A simplified statistical linearization-based approach is devised for optimal IR-TMDI tuning under stationary random colored seismic excitations compatible with a given design/response spectrum, accounting for the nonlinearity of the isolation layer, modelled through a Bouc-Wen force-deformation hysteretic law, and of the FVD. Different IR-TMDI tuning criteria are considered, and it is shown that maximization of energy dissipation by the FVD yields a well-balanced and practically advantageous performance vis-a-vis minimization of structural displacement and acceleration response criteria in terms of TMDI and isolation layer force and deformation demands. Comprehensive response history analysis results pertaining to a 3-storey and a 9-storey steel benchmark structures with optimally tuned IR-TMDIs of various nonlinear isolation layer and FVD properties, exposed to well-populated sets of far-field, near-fault non-pulse, and near-fault pulse-like recorded earthquakes are examined to assess the seismic response mitigation potential of the IR-TMDI. It is found that reduced storey drifts and floor acceleration demands along the buildings’ height are achieved by increasing the flexibility of the roof-top isolation layer (i.e. post-yielding period). Further, by lowering the nonlinear FVD exponent, reduced IR-TMDI displacement demands (i.e. TMDI stroke and isolators’ deflection) and improved robustness of seismic storey drifts and floor acceleration demands to record-to-record variability is achieved. Overall, the herein reported numerical data demonstrate a remarkable effectiveness of the herein conceived NTMDI and IR-TMDI configurations in controlling RMS and peak response along the full building height, even for the flexible 9-storey benchmark building under near-fault pulse-like excitations. This is despite the low fidelity modeling of the earthquake excitation description (i.e. stationary random excitation) of the structural behavior (i.e. single-mode and linear) and of the seismic performance quantification (i.e. second-order stationary response statistics) adopted in the optimal tuning of the absorbers, purposely assumed to promote practicable easy-to-use design tools, attractive to both practitioners and researchers. This consideration suggests that even more favorable seismic response mitigation performance of the proposed nonlinear inerter-based vibration absorbers may be anticipated by adopting more refined models in the optimal tuning of the absorbers as well as by extending both the optimization-driven design to include the properties of the isolation layer and the assessment to account for severe excitations leading to nonlinear structural behavior

A novel nonlinear isolated rooftop tuned mass damper-inerter (IR-TMDI) system for seismic response mitigation of buildings

This paper conceptualizes a novel passive vibration control system comprising a tuned mass damper inerter (TMDI) contained within a seismically isolated rooftop and investigates numerically its effectiveness for seismic response mitigation of building structures. The working principle of the proposed isolated rooftop tuned mass damper inerter (IR-TMDI) system relies on the yielding of typical elastomeric isolators (e.g. lead rubber bearings) under severe earthquake ground motions to create a flexible rooftop which, in turn, increases the efficacy of the TMDI for seismic vibrations suppression. Herein, a nonlinear mechanical model is considered to explore the potential of IR-TMDI whereby the primary building structure is taken as linear damped single-mode system while the Bouc-Wen model is used to capture the nonlinear/hysteretic behavior of the rooftop isolators. An equivalent linear system (ELS), derived through statistical linearization, is used to expedite the optimal IR-TMDI tuning for different isolated rooftop properties, inertance, and primary structure natural periods under white noise excitations with different intensities as well as Kanai-Tajimi excitations for different soil conditions. It is found that tuning for maximizing TMDI seismic energy dissipation is more advantageous than tuning for minimizing primary structure displacement or acceleration response since it lowers deflection and force demands to the isolators and to the inerter. Further, significant primary structure displacement and acceleration reductions are achieved as the effective rooftop flexibility increases through reduction of the nominal strength of the isolators, which verifies the intended working principle of the IR-TMDI. This is also confirmed through response history analyses to the nonlinear model under four benchmark recorded ground motions. Moreover, for IR-TMDI with sufficiently flexible isolators, improved seismic structural performance with concurrent reduced deflection and force demands at the isolators is shown for all considered stationary excitations as the inertance scales-up, which is readily achievable technologically. Thus, it is concluded that the IR-TMDI mitigates effectively structural seismic response without requiring the inerter to span several floors, as suggested in previous studies, thus extending the TMDI applicability to both existing and low-rise new-built structures

Development of sensitive polyclonal antibodies against dominant stored wheat grain fungus for its immunological detection: Presentation

Fungal infestation causes deterioration of stored food grains. Most fungal species produce secondary metabolites like aflatoxins which are highly toxic to animals and humans. Aspergillus flavus has been found to be the predominant contaminant in stored wheat grains collected from the godowns of Food Corporation of India, West Bengal. The present study focuses on the development of sensitive polyclonal antibodies (PAbs) for molecular immunological detection of dominant toxigenic fungus. Pure A. flavus isolate was cultured on coconut agar media and its spores were harvested and inactivated by 4% formaldehyde. The inactivated spores were injected into a rabbit along with Freund’s complete/incomplete adjuvant for the development of PAbs. Specificity of the raised antibodies in rabbit serum was examined by enzyme-linked immunosorbent assay (ELISA) using spore proteins as antigen obtained by bead beating method. Out of several proteins (ranging from 10 to 200 kDa present in spore, only two prominent proteins of around 76 kDa and 100 kDa were detected by western blot analysis using raised polyclonal antiserum. The PAbs were purified with protein A column followed by spore proteins conjugated CNBr activated sepharose column for its use in the detection of fungal antigens. This highly purified raised antibody can be used for the development of rapid, sensitive, and accurate techniques (such as dot blot/ELISA) for the detection of toxigenic fungi present in stored wheat grains.Fungal infestation causes deterioration of stored food grains. Most fungal species produce secondary metabolites like aflatoxins which are highly toxic to animals and humans. Aspergillus flavus has been found to be the predominant contaminant in stored wheat grains collected from the godowns of Food Corporation of India, West Bengal. The present study focuses on the development of sensitive polyclonal antibodies (PAbs) for molecular immunological detection of dominant toxigenic fungus. Pure A. flavus isolate was cultured on coconut agar media and its spores were harvested and inactivated by 4% formaldehyde. The inactivated spores were injected into a rabbit along with Freund’s complete/incomplete adjuvant for the development of PAbs. Specificity of the raised antibodies in rabbit serum was examined by enzyme-linked immunosorbent assay (ELISA) using spore proteins as antigen obtained by bead beating method. Out of several proteins (ranging from 10 to 200 kDa present in spore, only two prominent proteins of around 76 kDa and 100 kDa were detected by western blot analysis using raised polyclonal antiserum. The PAbs were purified with protein A column followed by spore proteins conjugated CNBr activated sepharose column for its use in the detection of fungal antigens. This highly purified raised antibody can be used for the development of rapid, sensitive, and accurate techniques (such as dot blot/ELISA) for the detection of toxigenic fungi present in stored wheat grains

Effect of Geometric Parameters and Initial Imperfection on Global Buckling of Perforated Beams

This paper presents an extensive parametric study of elastic and inelastic buckling of cellular beams subjected to strong axis bending in order to investigate the effect of a variety of geometric parameters, and further generate mass data to validate and train a neural network-based formula. Python was employed to automate mass finite element (FE) analyses and reliably examine the influence of the parameters. Overall, 102,060 FE analyses were performed. The effects of the initial geometric imperfection, material nonlinearity, manufacture-introduced residual stresses, web opening diameter, web-post width, web height, flange width, web and flange thickness, end web-post width, and span of the beams and their combinations were thoroughly examined. The results are also compared with the current state-of-the-art design guidelines used in the UK. It was concluded that the critical elastic buckling load of perforated beams corresponds to the lateral movement of the compression flange while the most critical parameters are the web thickness and the geometry of the flange. However, from the inelastic analysis, the geometry and position of the web opening influence the collapse load capacity in a similar fashion to the geometry of the flange and thickness of the web. It was also concluded that the effect of the initial conditions was insignificant

Optimal design and assessment of tuned mass damper inerter with nonlinear viscous damper in seismically excited multi-storey buildings

In recent years, the tuned mass damper inerter (TMDI) has been demonstrated in several theoretical studies to be an effective vibration absorber for the seismic protection of non-isolated buildings. Its effectiveness relies on careful tuning of the TMDI stiffness and damping properties, while its performance improves with the increase of the inertance property which is readily scalable. Nevertheless, in all previous studies, the energy dissipative TMDI element has been modelled by a linear viscous damper. Still, commercial viscous dampers display a nonlinear velocity-dependent power law behavior. In this regard, this paper investigates, for the first time in literature, the potential of the TMDI fitted with nonlinear viscous damper (NVD) for seismic response protection of multi-storey buildings. This is supported by an efficient optimal nonlinear TMDI (NTMDI) tuning approach which accounts for any absorber connectivity to the building structure and employs statistical linearization to treat the nonlinear damping term. For the special case of white-noise excited undamped buildings, optimal NTMDI tuning is derived analytically in closed-form which is shown to be sufficiently accurate for lightly damped structures. Comprehensive numerical data are presented to delineate trends of optimal NVD damping coefficient with the NVD power-law exponent and the inertance. Further, nonlinear response history analysis results pertaining to optimally tuned NTMDI application for a benchmark 9-storey steel structure demonstrate that reduced NTMDI stroke and inerter force can be achieved with negligible change in storey drifts and floor acceleration performance by adopting lower NVD exponent values, leading to practically beneficial NTMDI applications

Elastic and inelastic buckling of steel cellular beams under strong-axis bending

This paper presents an extensive parametric study of elastic and inelastic buckling of cellular beams subjected to strong axis bending in order to investigate the effect of a variety of geometric parameters, and further generate mass data to validate and train a neural network-based formula. Python was employed to automate mass finite element (FE) analyses and reliably examine the influence of the parameters. Overall, 102,060 FE analyses were performed. The effects of the initial geometric imperfection, material nonlinearity, manufacture-introduced residual stresses, web opening diameter, web-post width, web height, flange width, web and flange thickness, end web-post width, and span of the beams and their combinations were thoroughly examined. The results are also compared with the current state-of-the-art design guidelines used in the UK. It was concluded that the critical elastic buckling load of perforated beams corresponds to the lateral movement of the compression flange while the most critical parameters are the web thickness and the geometry of the flange. However, from the inelastic analysis, the geometry and position of the web opening influence the collapse load capacity in a similar fashion to the geometry of the flange and thickness of the web. It was also concluded that the effect of the initial conditions was insignificant

Automated Minimum-Weight Sizing Design Routine for Tall Self-Standing Modular Buildings Subjected to Multiple Performance Constraints Under Static and Dynamic Wind Loads

In recent decades, the shortage of affordable housing has become an endemic issue in many cities worldwide due to the ongoing urban population growth. Against this backdrop, volumetric steel modular building systems (MBSs) are becoming an increasingly compelling solution to the above challenge owing to their rapid construction speed and reduced upfront costs. Notwithstanding their success in low- to mid-rise projects, these assembled structures generally rely on a separate lateral load-resisting system (LLRS) for lateral stability and resistance to increased wind loads as the building altitude increases. However, additional LLRSs require on-site construction, thereby compromising the productivity boost offered by the MBSs. To this end, this paper proposes a novel optimisation-driven sizing design framework for tall self-standing modular buildings subjected to concurrent drift, floor acceleration, and member strength constraints under static and dynamic wind loads. A computationally efficient solution strategy is devised to facilitate a meaningful sizing solution by decomposing the constrained discrete sizing problem into the convex serviceability limit stage (SLS) and non-convex ultimate limit stage (ULS), which can be conveniently solved using preferred local and global optimisation methods, separately. The framework is implemented by integrating SAP2000 (for structural analysis) and MATLAB (for optimisation) through SAP2000’s open Application Programming Interface (API), and demonstrated using a 15-storey self-standing steel modular building exposed to three different levels of wind intensity. A comprehensive performance assessment is conducted on the optimally designed case-study building to investigate the elastic instability behaviour, geometric nonlinear effects on wind-induced response, and impacts of global sway imperfections on member utilisation ratios. It is concluded that tall self-standing modular buildings can be achieved economically using ordinary corner-supported modules without ad hoc structural provisions, while consuming steel at similar rates to conventional building structural systems. Furthermore, the proposed sizing framework and solution strategy have proven to be useful design tools for reconciling the structural resilience and material efficiency in wind-sensitive self-standing modular building