Showing papers by "Solomon Tesfamariam published in 2022"

Shake-Table Tests and Numerical Analysis of Steel Frames with Self-Centering Viscous-Hysteretic Devices under the Mainshock–Aftershock Sequences

Abstract: Shake-table tests, subjected to mainshock–aftershock sequences, were conducted on a 1/3-scaled 3-story steel frame equipped with self-centering viscous-hysteretic devices (SC-VHDs) and its primary frame to investigate the effect of the aftershock on seismic performance. It was found that the SC-VHD can effectively reduce 30%–50% of the peak drift and 50%–80% of the residual drift, respectively. Additionally, the peak and residual drifts of the 3-story primary frame under the mainshock–aftershock sequences were more than those under the mainshock-only sequences, while the peak and residual drifts of the 3-story SC-VHD frame under the mainshock-only and mainshock–aftershock sequences were basically the same. A numerical simulation method for the SC-VHD frame was further developed and validated, based on which 6-, 9-, and 12-story SC-VHD frames were analyzed to investigate the seismic performance of medium- high-rise SC-VHD frames. Both shake-table tests and numerical analysis indicate that the peak and residual drifts of the 3-, 6-, 9-, and 12-story SC-VHD frames can meet the design objective under the mainshock–aftershock sequences.

Multiobjective design optimization of multi-outrigger tall-timber building: Using SMA-based damper and Lagrangian model

Abstract: This study proposes a shape memory alloy (SMA)-based damped outrigger system for vibration control of tall timber buildings. In this study, the core of the structure is idealized as a cantilever beam, and each floor mass is considered as a discrete mass that acts at the junction between the floor and the core of the structure. The governing equations of motion of the combined system of shear core and outrigger are derived using the Lagrange formulation. The SMA spring is installed between the outrigger beam and the column to dissipate earthquake-induced energy and reduce excessive load demand on the column. Optimal performance of the proposed system requires optimizing the outriggers’ location and tuning the SMA properties in an uncertain environment. Two conflicting objective functions, minimization of acceleration and inter-storey drift ratio, are solved through a multi-objective optimization. Four different multi-objective meta-heuristic optimization algorithms (ant-lion, dragonfly, particle swarm optimization, and non-dominated sorting genetic algorithm II) are considered. Three different tall timber buildings (10-, 15-, and 20-storey) and up to two outrigger beams are considered for optimization. The seismicity of Vancouver, BC is used for the numerical simulation and vulnerability assessment. The optimum outrigger location for a one-outrigger system is found to be approximately 60%, while for a two-outrigger system, the same is obtained as 33% and 68%, respectively. Finally, the fragility analysis is carried out, which shows the superiority of this passive device in terms of minimizing the probability of failure exceeding a given threshold limit, which yields an improvement in the reliability of the structure.

State-of-the-Art Review of Design of Experiments for Physics-Informed Deep Learning

Abstract: This paper presents a comprehensive review of the design of experiments used in the surrogate models. In particular, this study demonstrates the necessity of the design of experiment schemes for the Physics-Informed Neural Network (PINN), which belongs to the supervised learning class. Many complex partial differential equations (PDEs) do not have any analytical solution; only numerical methods are used to solve the equations, which is computationally expensive. In recent decades, PINN has gained popularity as a replacement for numerical methods to reduce the computational budget. PINN uses physical information in the form of differential equations to enhance the performance of the neural networks. Though it works efficiently, the choice of the design of experiment scheme is important as the accuracy of the predicted responses using PINN depends on the training data. In this study, five different PDEs are used for numerical purposes, i.e., viscous Burger’s equation, Shrödinger equation, heat equation, Allen-Cahn equation, and Korteweg-de Vries equation. A comparative study is performed to establish the necessity of the selection of a DoE scheme. It is seen that the Hammersley sampling-based PINN performs better than other DoE sample strategies.

Performance-Based Design of Tall Timber Buildings Under Earthquake and Wind Multi-Hazard Loads: Past, Present, and Future

Abstract: The rapid growth of the urban population and associated environmental concerns are challenging city planners and developers to consider sustainable and cost-efficient building systems. Timber-based buildings, such as sustainable systems, are increasingly used. The timber buildings, however, being lighter and flexible, can be vulnerable to earthquakes and wind loads. This paper gives a state-of-the-art review on performance-based design (PBD) considerations and future direction for timber and timber-based hybrid buildings. The PBD review covered both earthquake and wind loads and multi-hazard design considerations. The review also provided 1) current practice and future direction in consideration of hazard, response, and loss assessment within the multi-hazard PBD, 2) damping and energy dissipation devices, 3) optimization under uncertainty, and 4) future of surrogate and multi-fidelity modeling in PBD.

Performance‐based design of tall‐coupled cross‐laminated timber wall building

Abstract: Growing demand in sustainable high‐rise timber structures is satisfied by proposing innovative structural systems that enhance the building's stiffness, strength, and energy‐dissipation capacity. This study propose and develop the performance‐based design (PBD) guideline for balloon type cross‐laminated timber (CLT) coupled wall (CLT‐CW) structure. In this system, the CLT shear‐walls are connected with energy dissipation coupling beams that comprise shear‐links and in return reduce the seismic demand of the system. To facilitate the desired rocking deformation mode of CLT shear‐wall panels, buckling‐restrained brace (BRB) hold‐downs are used. Utility of the proposed system and design is applied on a 20‐story balloon CLT‐CW system. To investigate the effect of coupling ratio ( CR$CR$ ) on the behavior of the system, five CR$CR$ values (10%–50%) are used. Nonlinear and incremental dynamic analyses (IDAs) are performed using suitable set of 30 ground motion (GM) records that reflects the seismicity of Vancouver, Canada. Fragility curves are developed and compared considering both the collapse and non‐collapse limit states. The results show that, for a given CLT‐CW system, a system with higher CR$CR$ value exhibits better seismic performance.

Experimental testing and system identification of the sliding bistable nonlinear energy sink implemented to a four-story structure model subjected to earthquake excitation

Abstract: Bistable nonlinear energy sink system has been explored as an efficient vibration absorber in many areas. This paper aims to experimentally validate the seismic mitigation performance of sliding bistable nonlinear energy sink (SBNES) for multi-story building structures. An SBNES device was designed and placed on top of a four-story building structure model. Earthquake ground motions were applied through a shake table as the base excitation input into the structure model. By matching the time history envelope curves between the experiment and numerical simulation, the structural parameters of the primary structure, as well as the constitutive model of the SBNES, were experimentally determined. The comparisons between mitigated and unmitigated structural responses, including inter-story drift, acceleration, base-shear force and base-overturning moment of the primary structure, show that substantial reduction of structural seismic responses can be achieved by the SBNES device. The 1:1 transient internal resonance is verified as the dominant scheme for highly efficient targeted energy transfer. With respect to variation of peak ground acceleration, a relatively optimal interval distributed near the borderline of intra-well and inter-well regime is proposed for robust SBNES design. The test validates the potential of the SBNES strategy for both acceleration and displacement control of multi-story building structures.

FRP-laminated Rubber Isolator: Theoretical Study and Shake Table Test on Isolated Building

Abstract: ABSTRACT Performance of fiber-reinforced polymer (FRP)-laminated rubber isolators has been investigated through theoretical and experimental analyses. Effective horizontal stiffness of FRP rubber isolator is analyzed by the cyclic quasi-static experiment. A 1/3 scale shake table tests have been carried out to assess the seismic behavior and the efficiency of the FRP-laminated rubber isolator under the ground motions in different site conditions. The effective horizontal stiffness of the isolator has been derived which has been compared with the experimental results. Experimental studies have shown that FRP-laminated rubber bearings with many advantages can be applied to building structures to enhance seismic capacity.

Seismic collapse risk of RC-timber hybrid building with different energy dissipation connections considering NBCC 2020 hazard

Abstract: The 2020 National Building Code of Canada (NBCC) seismic hazard model (SHM) marks a comprehensive update over its predecessor (NBCC 2015). For different regions in Canada, this will have an impact on the design of new buildings and performance assessment of existing ones. In the present study, a recently developed hybrid building system with reinforced concrete (RC) moment-resisting frames and cross-laminated timber (CLT) infills is assessed for its seismic performance against the latest SHM. The six-story RC-CLT hybrid system, designed using the direct displacement-based method, is located in Vancouver, Canada. Along with very high seismicity, southwestern British Columbia is characterized by complex seismotectonics, consisting of subduction, shallow crustal, and in-slab faulting mechanisms. A hazard-consistent set of 40 ground motion pairs is selected from the PEER and KiK-net databases, and used to estimate the building's seismic performance. The effects of using steel slit dampers (associated with large hysteresis loops) and flag-shaped energy dissipators (associated with the recentering capability) are investigated. The results indicate that the hybrid system has good seismic performance with a probability of collapse of 2-3% at the 2475-year return period shaking intensity. The hybrid building with steel slit dampers exhibits a collapse margin ratio of 2.8, which increases to 3.5-3.6 when flag-shaped dissipators are used. The flag-shaped dissipators are found to significantly reduce the residual drift of the hybrid building. Additionally, the seismic performance of the hybrid building equipped with flag-shaped dissipators is found to improve marginally when the recentering ratio is increased.

Data Augmentation Using conditional Generative Adversarial Network (cGAN): Application for Prediction of Corrosion Pit Depth and Testing Using Neural Network

Abstract: Machine learning (ML) based algorithms, due to their ability to model nonlinear and complex relationship, have been used in predicting corrosion pit depth in oil and gas pipelines. Class imbalance and data scarcity are the challenging problems while training ML models. This paper utilized a conditional generative adversarial network (cGAN) to handle class imbalance problem in a corrosion dataset by generating new samples. Utility of the cGAN data augmentation is evaluated by training an artificial neural network (ANN) model. In addition, random oversampling and Borderline-SMOTE data generating techniques are used for comparison with cGAN. The testing accuracy of the ANN model increased greatly when trained by the cGAN based augmented dataset and this model performance improvement can be useful for a pipeline integrity management.

Experimental investigation and numerical simulation of self-centering concrete frames with sliding infill walls

Abstract: The self-centering prestressed concrete (SCPC) frame has been developed and showed excellent seismic toughness; however, interaction between conventional infill wall and the SCPC frame weakened the seismic performance. In this study, an innovative SCPC frame with sliding infill walls (SCPC-SIW) frame is proposed and investigated. The structural configuration and working principle of the SCPC-SIW frame are introduced first, followed by the design, fabrication, and pseudo-static tests of a SCPC-SIW frame and a SCPC frame to compare their seismic performance. Finally, the simulation method of the SCPC-SIW frame is presented, and the simulation results are compared to the test results. The results show that both the self-centering frame and the sliding infill wall functioned normally during the tests. Furthermore, except for the local cracking in the wall panels, no damage was found in the beams and columns of the SCPC-SIW frame. The SCPC-SIW frame has similar mechanical properties to the SCPC frame in that it presents a stable, repeatable, and non-degraded "double flag-shape". Unlike the SCPC frame, its unloading stiffness was not significantly reduced when compared to its initial stiffness. The SCPC-SIW frame dissipated no less energy than the SCPC frame, and the final residual drift ratios of the SCPC frame in the positive and negative loading directions were 0.18% and 0.04%, respectively. Besides, the numerical results match well with the test results (e.g. with the error of peak base shear within 3%), and the opening and closing behavior of the connections, as well as the sliding of the frictional sliding devices can be reasonably simulated.

Probabilistic Seismic Risk Analysis of Buried Pipelines Due to Permanent Ground Deformation for Victoria, BC

Abstract: Buried continuous pipelines are prone to failure due to permanent ground deformation as a result of fault rupture. Since the failure mode is dependent on a number of factors, a probabilistic approach is necessary to correctly compute the seismic risk. In this study, a novel method to estimate regional seismic risk to buried continuous pipelines is presented. The seismic risk assessment method is thereafter illustrated for buried gas pipelines in the City of Victoria, British Columbia. The illustrated example considers seismic hazard from the Leech River Valley Fault Zone (LRVFZ). The risk assessment approach considers uncertainties of earthquake rupture, soil properties at the site concerned, geometric properties of pipes and operating conditions. Major improvements in this method over existing comparable studies include the use of stochastic earthquake source modeling and analytical Okada solutions to generate regional ground deformation, probabilistically. Previous studies used regression equations to define probabilistic ground deformations along a fault. Secondly, in the current study, experimentally evaluated 3D shell and continuum pipe–soil finite element models were used to compute pipeline responses. Earlier investigations used simple soil spring–beam element pipe models to evaluate the pipeline response. Finally, the current approach uses the multi-fidelity Gaussian process surrogate model to ensure efficiency and limit required computational resources. The developed multi-fidelity Gaussian process surrogate model was successfully cross-validated with high coefficients of determination of 0.92 and 0.96. A fragility curve was generated based on failure criteria from ALA strain limits. The seismic risks of pipeline failure due to compressive buckling and tensile rupture at the given site considered were computed to be 1.5 percent and 0.6 percent in 50 years, respectively.

Development of Ductility-related Modification Factor for CLT-Coupled Wall Buildings with Replaceable Shear Link Coupling Beams

Abstract: The desire of using sustainable materials has reignited the interest in timber-based construction. Researchers and practitioners are developing novel timber-based structural solutions. Cross-laminated timber (CLT) coupled-wall is a recently proposed system for potential use in mid- and high-rise timber construction. The National Building Code of Canada, however, does not include this system and consequently, the seismic force modification factors are not available. This study evaluates the ductility-related force modification factor (Rd=4) using the FEMA P-695 procedure. Nine archetype buildings are designed considering different design parameters: building storey height, CLT wall configuration, and coupling ratios. Using 30 ground motion records (bi-directional), rigorously selected for seismicity of Vancouver - Canada, incremental dynamic analyses are performed. Collapse margin ratios are calculated to assess the adequacy of the trial Rd factors. Using an over-strength factor of 1.5, Rd=4 is found to be acceptable for this system.

Editorial: Smart passive damper design for building structures with higher resilience under uncertain earthquake ground motions

Abstract: Existing and new building structures located in earthquake-prone areas are vulnerable to damage. One strategy to protect these structures is to incorporate supplemental energy dissipation devices, in the form of hysteretic, viscous, or inertial dampers. In the last few years, these devices demonstrated their capability to limit earthquake-induced damage, thus implying minimal downtime and affordable repair cost in both ordinary and strategic/critical building structures. However, the efficiency of such devices strongly relies on their appropriate placement in the building structure as well as in selecting their constitutive parameters. Another open issue is how to incorporate the uncertain nature of seismic excitation within a robust design framework. A smart design strategy using passive dampers should account for the peculiar characteristics of the structure and should aim at achieving multi-level performance requirements under different levels of excitation through robust multi-objective optimization. Based on these motivations, this Research Topic has collected seven papers after a detailed and rigorous peer-review process. The papers deal with smart passive damper design that explicitly incorporates the uncertainty of the seismic excitation or structure, simultaneous optimal design of main building structures and dampers under critical seismic excitation, innovative energy dissipation technologies, and hybrid dampers for an improved earthquake-resilient building design and smart damper optimization under long-period pulse-type ground motions of extremely large amplitudes. OPEN ACCESS