Effects of soil-structure interaction in seismic analysis of buildings with multiple pressurized tuned liquid column dampers

In this paper soil-structure interaction (SSI) effects are investigated while an array of Pressurized Tuned Liquid Column Dampers (PTLCD) is employed for seismic vibration control of buildings. This device represents the most general case of a passive damper, with different reduction options to other control devices obtained by simplifying the involved parameters. Soil conditions considerably affect the control device functioning, because dynamic parameters such as natural frequency, damping factor, and natural modes depend on the soil properties. A simplified mathematical model is developed for the building with multiple degrees of freedom connected to a flexible base. For the time-domain analysis, a computational routine is developed for the linearization of the equilibrium equations of the PTLCD, as well as details for the reduction to the other types of passive dampers. Several numerical examples are selected for the analysis of the damper efficiency in reducing seismic vibration considering SSI. These simulations include Kobe earthquake data, which is applied to the model to evaluate the device performance under different scenarios. It is verified the influence of SSI in the natural frequency and structural response, which is related to the earthquake frequency components. Results confirm that the array of PTLCD’s can reduce the vibration amplitudes, being more effective for soils with higher stiffness values

Adaptive Tracking Controller for Real-Time Hybrid Simulation

Real-time hybrid simulation (RTHS) is a versatile and cost-effective testing method for studying the performance of structures subjected to dynamic loading. RTHS decomposes a structure into partitioned physical and numerical sub-structures that are coupled together through actuation systems. The sub-structuring approach is particularly attractive for studying large-scale problems since it allows for setting up large-scale structures with thousands of degrees of freedom in numerical simulations while specific components can be studied experimentally.The actuator dynamics generate an inevitable time delay in the overall system that affects the accuracy and stability of the simulation. Therefore, developing robust tracking control methodologies are necessary to mitigate these adverse effects. This research presents a state of the art review of tracking controllers for RTHS, and proposes a Conditional Adaptive Time Series (CATS) compensator based on the principles of the Adaptive Time Series compensator (ATS). The accuracy of the proposed controller is evaluated with a benchmark problem of a three-story building with a single degree of freedom (SDOF) in a realistic virtual RTHS (vRTHS). In addition, the accuracy of the proposed method is evaluated for seven numerical integration algorithms suitable for RTHS

Magnetic Fields to Enhance Tuned Liquid Damper Performance for Vibration Control: A Review

Tuned Liquid Dampers (TLDs) are dissipative devices whose distinguished features like low cost in installation and maintenance or their multidirectional and multifrequency application to new and already existing structures make them an attractive damping option. Their working principle is similar to that of a Tuned Mass Damper but in this case the relative movement comes from a fluid that provides with mass, damping and stiffness. Moreover, TLDs can mitigate both horizontal and vertical vibrations. All these make TLDs worth deeply studying. TLD utilization in civil vibration control arose in the 1980s. From early years, different improvements have been implemented to achieve a better performance. Some of these modifications include passive variations in the geometry or the fluid. The use of smart materials applied on TLDs has also been of great interest since the 1990s and comprehends different configurations in which magnetic fields are used to passively or semi-actively improve the TLD performance. A lack of review is detected in this field. For this reason, a state-of-the-art review is presented in this paper. Its aim is to help researchers find a thorough, up-to-date classification of the different possibilities, configurations, numerical evaluation, materials used and also found limitations and future development in the application of magnetic fields on TLDs

Effectiveness of Suspended Lead Dampers in Steel Buildings Under Localized Lateral Impact and Vertical Pulsating Load

Presented herein is a study of the effectiveness of suspended lead dampers for use in steel buildings under a localized impact load and a vertical pulsating load. A series of lead spheres mounted on a string are suspended inside the building columns or damping panels to absorb the energy of vibration through a collision between the lead dampers and internal surfaces of the members. Experiments are conducted on a three-story steel building model and a cantilever member with suspended lead dampers and subjected to localized impact loading. The cantilever under impact load is analyzed with a partial differential equation of dynamic equilibrium using a central finite-difference scheme. The numerical scheme is also used to unveil the dynamic stability characteristics of a typical building column under lateral impact and vertical pulsating load. The building model and a full-scale building frame with damping characteristics of the suspended lead dampers are then analyzed using SAP-2000 program with localized impact and a vertical pulsating load. The study shows a substantial reduction in building vibration when suspended lead dampers are used. The elastic-plastic transient dynamic analysis of the full-scale steel building reveals that the impacted column does not develop a plastic hinge at its top when bolted panels with suspended lead dampers are used. In the absence of such damping panels, the impacted column develops three plastic hinges thereby turning into a collapse mechanism

Structural systems with suspended and self-centered floor slabs for earthquake resistance

2013 Summer.Includes bibliographical references.The purpose of this study is to develop a novel structural system for mitigating the effects of earthquakes on building systems by suspending the concrete floor slabs of a steel building. The slab is suspended using hanger rods and act as Tune Mass Dampers (TMDs) to reduce the response of the structural system. In addition, steel links are added between the bottom face of the suspended slab and the beam below the slab and are used as energy dissipaters during an earthquake. Moreover, post-tensioned cables are installed adjacent to the steel links to provide a self-centering capability to the floor slab and eliminate residual drift after a seismic event. The Suspended Slab (SS) system is analyzed by constructing suitable theoretical models, from which mathematical equations describing the response of the system are developed and analyzed The location and number of suspended slabs and energy dissipation links needs to be carefully chosen for optimum performance of the system. To find the optimized condition, the simple optimization approach of Numerical Search is used. The optimization identifies the best locations, damping ratio and the frequency ratio of the slabs. The approach is suitable for short structures, however with increase in number of floors the algorithm becomes time costly. A new combinatorial approach of optimization is implemented that uses Nelder Mead algorithm and Covariance Matrix Adaptation Evolution Strategy. The new optimization is modified and tested to assess its effectiveness. Finally, three test structures are utilized to evaluate the effectiveness of the suspended slab system using the combinatorial optimization approach. The earthquake is modeled as a stationary white noise and Kanai Tajimi Spectrum is used as excitation input to obtain the Root Mean Square response, which is considered as the performance evaluation parameter. From the results of this study it is concluded that the suspended slab system can be quite an effective strategy for earthquake mitigation

Seismic Loading Effects within Orthogonally Connected Steel Lateral Force Resisting Systems

Steel buildings located within seismically active regions require special design considerations to ensure public safety and prevent collapse during an extreme seismic event. Two commonly used steel systems are special moment frames (SMFs) and buckling-restrained braced frames (BRBFs). When two seismic systems share a common column in an orthogonal configuration (such as at a building corner), design specifications currently consider a 100+30 rule wherein the shared column is designed for 100% fuse demand in one direction, plus 30% fuse demand from the other direction. While this rule has been shown to be reasonable for elastic building response, a few studies performed on inelastic systems suggest that the 100+30 rule may not be reasonable for systems expected to experience significant inelastic response. This study investigated nonlinear effects resulting from simultaneous earthquake loading of orthogonally oriented seismic systems. Detailed nonlinear time-history analysis of three-dimensional frame configurations was considered, addressing coupled and non-coupled orthogonal system effects on resulting shared column demands. Various seismic system pairs (sharing a column) are considered, including both moment frames and braced frames. Results indicate that the current 100+30 rule is non-conservative for some frame-type combinations. Bidirectional seismic effects in coupled steel systems showed increased column axial demands over independent demand additions from un-coupled (unidirectional loading) analyses. Braced-frame-to–moment-frame configurations were more affected by bidirectional lateral forces than braced-frame-to-braced-frame orthogonal configurations. Additionally uncoupled steel systems experienced higher inter-story drift demands than the coupled frame configurations of the same geometry. A new approach to estimating shared column demands in orthogonal seismic systems was proposed herein

Composite confinement systems for RC column repair and construction under seismic loads: Concept, characterization and performance

This study aims at developing, characterizing and validating an integrated composite confinement system of conventional jackets for: (1) repair and retrofit of existing bridge columns; and (2) construction of new bridge columns, subjected to earthquake excitations. A new composite steel confinement jacket was proposed by combining a thin steel sheet and prestressing strands as a hybrid jacket, incorporating active and passive confining pressure on damaged RC columns. Both experimental and analytical studies were conducted to understand the performance and effectiveness of the proposed repair method. The experimental study involved two 1/2-scale lap-spliced deficient RC bridge columns originally tested to failure under reversed cyclic loading. The proposed jacket was designed and implemented to repair the damaged columns to achieve the required performance level after repair intervention for service and ultimate limit states. Experimental results indicated that both repaired columns exceeded the strength and ductility of their as-built columns. The stiffness of the second column designed for ultimate limit state was completely restored. Analytical studies and collapse analyses on the seismic performance of post-mainshock repaired bridges subjected to mainshock-aftershock sequences demonstrated the efficacy of the proposed technique under severe mainshock-severe aftershock attacks. Another new composite confinement system of a fiber reinforced polymer (FRP) sheet wrapped around a polyvinyl chloride (PVC) tube with energy dissipation medium in between was developed for new bridge columns construction. This composite system is essentially a FRP-confined concrete-filled PVC tube, featuring exceptional durability properties of PVC materials in addition to high strength of the FRP fabrics. Experimental tests under uniaxial compression and flexural loading were undertaken to establish the representative stress-strain behavior of confined concrete filled PVC tubes (CCFPT). Experimental studies clearly demonstrated that the CCFPT system outperforms conventional FRP jacket. The intermediate energy dissipation medium is critical to make the post-peak behavior more ductile. Analytical studies were conducted and equations were derived for the prediction of the ultimate strength and strain of a CCFPT system --Abstract, page iv