Hussam Mahmoud

Hybrid Simulation for Earthquake Response of Semirigid Partial-Strength Steel Frames

AbstractThe behavior of semirigid partial-strength connections has been investigated through either experimental component testing or detailed three-dimensional (3D) finite-element (FE) models of beam-column subassemblies. Previous experiments on semirigid partial-strength connections were conducted under idealized loads and boundary conditions, which do not represent real situations. In addition, the developed 3D FE models are computationally expensive and have primarily been used under monotonic loadings. Evaluating the full potential of any connection requires a system-level investigation, whereby the effect of the local behavior of the connection on the global response of the structural system is considered. Moreover, the connection should be tested under realistic load and boundary conditions and/or analyzed using an accurate yet computationally affordable analytical model. This paper represents a new system-level hybrid simulation application aimed at investigating the seismic performance of semirig...

System-level biomechanical approach for the evaluation of term and preterm pregnancy maintenance

Preterm birth is the primary contributor to perinatal morbidity and mortality, with those born prior to 32 weeks disproportionately contributing compared to those born at 32-37 weeks. Outcomes for babies born prematurely can be devastating. Parturition is recognized as a mechanical process that involves the two processes that are required to initiate labor: rhythmic myometrial contractions and cervical remodeling with subsequent dilation. Studies of parturition tend to separate these two processes rather than evaluate them as a unified system. The mechanical property characterization of the cervix has been primarily performed on isolated cervical tissue, with an implied understanding of the contribution from the uterine corpus. Few studies have evaluated the function of the uterine corpus in the absence of myometrial contractions or in relationship to retaining the fetus. Therefore, the cervical-uterine interaction has largely been neglected in the literature. We suggest that a system-level biomechanical approach is needed to understand pregnancy maintenance. To that end, this paper has two main goals. One goal is to highlight the gaps in current knowledge that need to be addressed in order to develop any comprehensive and clinically relevant models of the system. The second goal is to illustrate the utility of finite element models in understanding pregnancy maintenance of the cervical-uterine system. The paper targets an audience that includes the reproductive biologist/clinician and the engineer/physical scientist interested in biomechanics and the system level behavior of tissues.

Seismic Performance of Semirigid Moment-Resisting Frames under Far and Near Field Records

The seismic performance of low-rise frames with energy dissipative semirigid connections is evaluated under far and near field artificial ground motion records. Four different connection capacities are employed in the frames and are characterized by two different moment-hardening ratios and two different hysteresis models. Nonlinear time-history and Fourier analyses are utilized to assess the seismic performance of 24 semirigid and 2 rigid frames. In the nonlinear time-history analyses, nine far field and nine near field artificial ground motion records generated from three different attenuation relations are used. Finally, the seismic performance of the rigid frames and the semirigid frames are compared, and the conditions under which the semirigid frames show better seismic performance than rigid frames are investigated. The results show that 25 of 26 sample frames satisfy all acceptance criteria and exhibit reliable seismic performance.

Hybrid Tuned Mass Damper and Isolation Floor Slab System Optimized for Vibration Control

Base isolation and tuned mass dampers are known to be highly effective for earthquake mitigation. However, their effectiveness is limited to a specific domain of cases and is confined by various constraints that have to be met. In this study, a hybrid floor slab tuned mass damper and isolation system is introduced whereby the floor slabs are allowed to move relative to the main frame. The floor slabs are resting on curved supports to allow for self-centering of the slabs upon the conclusion of the seismic event. An optimized design of the curved supports and friction between the supports and the slabs can reduce the response of the structure by up to 40%. The optimization strategy is employed over a range of frequencies in order to minimize the response for any input. The results show an improved system behavior with decreased displacement, acceleration, and inter-story drift. The proposed system is shown to not only be quite effective, but also much more robust than conventional isolation strategies. The floor slab mass is uncoupled from that of the main frame through isolation while emulating the function of a tuned mass damper system with inherently much higher mass ratio; hence the improved response.

Multihazard Assessment of Wind Turbine Towers under Simultaneous Application of Wind, Operation, and Seismic Loads

AbstractWind turbines are widely recognized as a renewable energy resource and as such, their safety and reliability must be ensured. Many studies have been completed on the blade rotor and nacelle components of wind turbines under wind and operation loads. While several studies have focused on idealized wind turbine models of the towers, significant advancements on the local behavior and global performance of these models under seismic loads in combination with other loads has been lacking. In this study, realistic numerical models are developed and used to evaluate the performance of wind turbines with various height under wind, operation, and seismic loads. Global performance parameters include drift ratios, normalized base shear, and turbine stability during operation. Localized behavior focuses on the welded connection at the base of the turbine and includes assessment of yielding at the tower base as well as the potential for the development of low-cycle fatigue failures. Several analyses indicated ...

Framework for Lifecycle Cost Assessment of Steel Buildings under Seismic and Wind Hazards

AbstractDespite the importance of considering multiple extreme events when designing structures, the current treatment of multiple hazard design in code provisions and assessment guidelines is rather vague. This is primarily because design and assessment of structures have traditionally been geared toward meeting the demand of a single hazard. In recent years, there has been a spike in interest by researchers and engineers in evaluating and designing structures for different hazard combinations. In this paper, a probabilistic framework is provided for assessing design alternatives based on estimating the lifecycle cost for two steel buildings with different heights subjected to different seismic and wind intensities. The intensities are specified based on probability of exceedance as per code standards. The total lifecycle cost is estimated using the initial cost and failure cost where the failure cost is a function of the probability of failure, which is calculated based on specified performance objectiv...

Using artificial neural networks to forecast economic impact of multi-hazard hurricane-based events

Abstract In multi-hazard events, it remains difficult to communicate the collective effect these hazards have on the envisioned outcome or impact to the public. Currently, there are multiple models in use by emergency management and other government personnel to predict effects of hazards that put emphasis on wind damage (just as the Saffir–Simpson scale does), which tend to leave out the non-wind driven precipitation hazard. Experts who work with hazard events consistently build a knowledge base over time from experience that accounts for the collective effects of these multiple hazards in relation to locational vulnerabilities. In this study, an original artificial neural network is developed and used in an effort to mimic the previously mentioned learned and experienced-based knowledge. The output from the neural network model is an Impact Level Ranking System that ranks hurricanes based on total economic damage. The use of population affected, landfall location(s), wind speed, pressure, storm surge, and precipitation for inputs with a final Bayesian Regulation training approach allows for an ability to forecast multi-hazard hurricane events in terms the public could comprehend while remaining thorough in all hazards.

Response of Steel Reduced Beam Section Connections Exposed to Fire

AbstractSteel structures may be vulnerable to fires; therefore, work is underway in several quarters to advance performance-based engineering (PBE) of steel frames for fire conditions. Both experimentation and finite-element simulations are necessary tools in PBE for assessing the behavior of structures under elevated temperatures. Numerical modeling of the overall structural system using line-element models fails to capture the localized behavior of connections due to the simplistic nature of such models. With advances in computation, attention is shifting to three-dimensional (3D) models, which are better able to capture the behavior of connections. Accurate predictions of structural response require the inclusion of realistic boundary conditions such that the interaction between the connections and the surrounding structure is properly captured. The study reported herein evaluates the response of steel frames with reduced beam section (RBS) connections under a typical compartment fire, with temperature...

Multi-Hazard Multi-Objective Optimization of Building Systems with Isolated Floors Under Seismic and Wind Demands

Traditionally, structural design standards or retrofit guidelines have been geared toward meeting the demand of individual hazards based on probability of exceedance of a certain event level. Performance requirements of the collective effects of individual hazards, however, acting simultaneously or spatially over time, may significantly increase the potential for substantial damage, collapse, and/or economic and life losses. In addition, performance-based earthquake engineering has recently evolved from its basic concept of defining performance objectives to prevent structural collapse, with acceptable high level of damage, to minimizing structural loss without compromising on performance. One way to achieve this objective is to make traditional seismic force-resisting systems stiffer (which also implies higher strength). However, it is neither effective nor economical to embrace such an approach. Moreover, while stiffening a structure may improve its performance under earthquake loading, the added stiffness may compromise the performance under wind loading. Therefore, it is necessary to create new seismic force-resisting systems that satisfy higher performance goals for multiple hazards and can be easily repaired, with minimal cost, after major events. Motivated by the mentioned objectives, the concept of sliding slab systems is introduced and discussed in this chapter where curved slabs are isolated from their respective bays and utilized to act as tuned mass dampers. The decision on which slab to optimize in order to achieve a superior performance under the multiple hazards of wind and earthquake is arrived at using a nested optimization approach. The optimization strategy and the modifications implemented are discussed in detail. Results of the study highlight the effectiveness of the proposed sliding slab system and the optimization scheme in configuring building systems that can withstand the multiple hazards.

Near-optimal planning using approximate dynamic programming to enhance post-hazard community resilience management

Abstract The lack of a comprehensive decision-making approach at the community level is an important problem that warrants immediate attention. Network-level decision-making algorithms need to solve large-scale optimization problems that pose computational challenges. The complexity of the optimization problems increases when various sources of uncertainty are considered. This research introduces a sequential discrete optimization approach, as a decision-making framework at the community level for recovery management. The proposed mathematical approach leverages approximate dynamic programming along with heuristics for the determination of recovery actions. Our methodology overcomes the curse of dimensionality and manages multi-state, large-scale infrastructure systems following disasters. We also provide computational results showing that our methodology not only incorporates recovery policies of responsible public and private entities within the community but also substantially enhances the performance of their underlying strategies with limited resources. The methodology can be implemented efficiently to identify near-optimal recovery decisions following a severe earthquake based on multiple objectives for an electrical power network of a testbed community coarsely modeled after Gilroy, California, United States. The proposed optimization method supports risk-informed community decision makers within chaotic post-hazard circumstances.