Performance-based Structural Design Research Articles

Fragility estimation for performance-based structural design of floating offshore wind turbine components

This study proposes a computational and mathematical framework aimed at assessing the reliability of structural components within Floating Offshore Wind Turbines (FOWT) that reflects the various sources of uncertainties coupled between structural analyses, hydrodynamics, and aerodynamics. The limit state functions are represented through structural capacity and environmental demand models for selected structural failure modes that incorporate fully coupled aero-hydro-servo-elastic analysis. The fragility surfaces are developed for a selected benchmark wind turbine for both operating and parking conditions. The fragilities are also estimated under 50-year and 100-year environmental conditions in the selected U.S. coastal regions. It is found that the wind speed variations largely affect the fragility during non-operation, while wave height variations are significant during operation. Increased uncertainties in environmental parameters raised failure probabilities, especially in lower fragility ranges targeted by design codes. Analyses in U.S. coastal environments show both parking and operating conditions can be critical, challenging the previous focus on parking. Sensitivity studies reveal that under mild conditions, structural reliability is influenced by moment of inertia and material strength, but as environmental loads increase, these parameters become equally significant. Increased uncertainties in parameters lead to higher failure risks, especially below 25 m/s wind speeds.

Predicting the shear strength of rectangular RC beams strengthened with externally-bonded FRP composites using constrained monotonic neural networks

Fiber-reinforced polymer (FRP) composites bonded externally to reinforced concrete beams have shown promise for increasing shear load-carrying capacity. However, accurately predicting the shear strength contribution of FRP remains challenging due to the complexity of the shear failure mechanisms and interactions between the contributing components. Existing design provisions have limitations in modeling this behavior. Recently, machine learning has shown promise for addressing such complex problems but lacks transparency. Therefore, this study developed a data-driven Constrained Monotonic Neural Network (CMNN) approach implemented using Python libraries Keras and Tensorflow, which integrates domain knowledge to provide reliable FRP shear-strength predictions. This framework directly encodes expected monotonic input-output relationships through constraints, harnessing both predictive power and monotonicity guarantees. A comprehensive database of 273 beam tests was used to train and evaluate the model. Bayesian optimization through the Optuna framework and 4-fold cross-validation were used to tune the hyperparameters of the CMNN model. Extensive evaluation demonstrated the CMNN model's superior accuracy, yielding an R² value over 0.9, a CI above 0.93 and a low MAE under 16 kN on both training and unseen test data. The model also outperformed existing design code provisions, achieving significantly optimal performance metrics across various strengthening configurations. The analysis of the predictions revealed logical sensitivity trends aligned with the principles of shear mechanics. Such physics-informed machine learning presents a next-generation technique for performance-based structural design, contributing an effective and interpretable tool to advance knowledge on quantifying the shear capacity contribution of externally bonded FRP reinforcement in concrete beams.

Performance-based design for structures in fire: Advances, challenges, and perspectives

The Performance-Based Design approach provides a goal-oriented process to support safe, innovative, and resilient structural fire designs. However, adoption of this approach requires both a rigorous framework and appropriate analysis tools to assess the expected performance of structures in fire. The objective of this paper is to provide an overview of the Performance-Based Design approach, including the process and its specific elements, applied to structures in fire. First, the value of the approach is illustrated through a review of case studies. Then, the process is described with identification of the role of the structural fire engineer. Recent research in methods to enable the evaluation of the structural fire performance, conducted within the author's group at Johns Hopkins University, is discussed. Issues addressed include the coupling between the fire and thermal-structural models, the characterization of the material behavior at elevated temperature, numerical modeling of structures subjected to fire, probabilistic risk assessment, and cost-benefit analyses. The paper concludes with a discussion of some challenges and perspectives for the future of performance-based structural fire design.

Practical application of multi-material topology optimization to performance-based architectural design of an iconic building

With the rapid development of architectural design methods and structural analysis techniques, structural performance-based design approaches have become increasingly important in architectural design. Among these approaches, topology optimization is a significant design method. However, most existing topology optimization research and related applications are based on single-material topology optimization techniques, which have limitations when applied to the design of complex and challenging structures. Building upon our previously proposed multi-material bi-directional evolutionary structural optimization (multi-material BESO) method, this paper presents the approaches for achieving diverse and competitive structural designs and then presents a practical application of the multi-material BESO method to the structural design of the core structure of a long-cantilevered building project called “Xiong’an Wings”. After an evolutionary design process based on the multi-material BESO method, an efficient frame with lower overall material costs, better static and dynamic performance compared to the initial design by experienced engineers is achieved. As the first practical application of the multi-material BESO method to a large-scale architectural design, the example of the “Xiong’an Wings” building demonstrates the tremendous prospects for the application of multi-material topology optimization technology to the generative design of innovative and efficient building structures.

Structural Performance-Based Design Optimisation of a Secondary Mirror for a Concentrated Solar Power (CSP) Plant

Concentrated Solar Power (CSP) plants use mirrors to reflect and concentrate sunlight onto a receiver, to heat a fluid and store thermal energy, at high temperature and energy density, to produce dispatchable heat and/or electricity. The secondary mirror is a critical component in the optical system of certain Solar Power Tower plants (SPT), as it redirects the concentrated sunlight from the primary mirror onto the receiver, which can be arranged at ground level. In this study, we propose a design optimisation for the secondary mirror of a CSP plant. The design optimisation method consists of two steps. The first step involves the use of the finite element simulation software Abaqus 2022 to analyse the structural performance of the secondary mirror under thermal loads and wind. The second step consists of the use of simulation results to identify the combination of design parameters and best performances, with respect to both design constraints and structural safety. This is carried out by developing an algorithm that selects those configurations which satisfy the constraints by using safety coefficients. The proposed optimisation method is applied to the design of a potential configuration of a secondary mirror for the beam-down of the CSP Magaldi STEM® technology, although the methodology can be extended to other components of CSP plants, such as primary mirrors and receivers, to further enhance the structural performance of these systems.

Human-Induced Vibration Serviceability: From Dynamic Load Measurement towards the Performance-Based Structural Design

Since the well-known Millennium bridge accident happened at the beginning of this century, both researchers and engineers realized that the human-induced vibration may lead to unaffordable consequences. Although such vibrations hardly threaten the safety of the structure, the large vibration may affect the functionalities of the structure, causing the serviceability problem. The first study on the human-induced vibration serviceability problem started from the measurement of human-induced load, with many mathematical models proposed. The strong randomness of the measured data led to the investigation on the randomness feature of the load. With the research going deeper, the phenomenon of human–structure interaction was found, which attracted the researchers to study the randomness of the human body dynamic properties that may affect the structural response. Once the interaction mechanism and the system parameters became available, random vibration analysis methods could be proposed to calculate human-induced random vibration, providing the foundation of the reliability analysis from the perspective of vibration serviceability. Such reliability is highly related to subjective feelings of the human body, which has also been deeply studied in the literature. Furthermore, the purpose of studying the dynamic reliability is to conduct the reliability-based structural design. This paper provides a review of the research on human-induced vibration serviceability following the above logic, from the first attempt on load measurement towards the modern techniques for performance-based vibration serviceability design.

Regional liquefaction-induced ground displacement predictions for Canada using 5th Generation NBCC Seismic Hazard Model

Significant regions of Canada are seismically active, and areas underlain by loose, saturated sediments in these regions are expected to experience liquefaction-induced lateral spread permanent ground displacements (PGDs) under earthquake shaking. The empirical predictive equations are commonly used for estimating the PGDs especially when detailed numerical analyses are not undertaken. The key input parameters for these equations comprise earthquake magnitude (M) and source distance (R), along with geotechnical and topographic parameters; however, there is ambiguity over choosing appropriate site-specific values of M and R. The current study predicts PGD probabilistic hazard curves that are applicable for locations in southwestern and southeastern regions of Canada using a probabilistic seismic hazard assessment (PSHA) framework. This was achieved by embedding two relevant empirical models for predicting lateral spread PGDs (replacing the ground motion prediction equations) within the 2015 National Building Code of Canada framework that is currently available in OpenQuake platform. Moreover, deaggregation analyses have been performed to understand the M and R contributions from different seismic sources on the predicted site-specific hazard. The developed PGD curves can be readily adopted for estimating site-specific lateral spread PGD demand as input to performance-based design of structures in seismically active areas of Canada.

Earthquake Performance Analysis of Steel Structures with A3 Plan Irregularities

In earthquake engineering, a performance-based design method is used to determine the level of the expected performance of the structures under the earthquake effect. The level of performance is related to the damage situation that could be occurred in the structure after the earthquake. In the performance-based structural design, it is predicted that more than one damage levels emerge under one certain earthquake effect. In this study, the seismic behavior of steel structures with plan irregularities in the Turkey Building Earthquake Code in the 2018 (TBEC-2018) is investigated by the nonlinear static analysis methods. The selected steel structures are located in İzmir, Turkey. The Turkey Earthquake Code in 2018 is considered for assessing seismic performance evaluation of the selected moment-resisting frame steel building. Four different A3 type irregularity was investigated. The steel building with no irregularity in its plan. was selected as the structure of the reference. The performance goals of the five different steel structures are evaluated by applying the pushover and procedures of the TBEC-2018. The steel structures were compared by obtaining pushover curves for both the X and Y directions. The results show that the effects of A3 type irregularity should be not considered in design and buildings without irregularities are safer.

Estimation of the Damage-Based Residual Displacement Spectrum for Simple Structures

ABSTRACT A statistical study aimed at estimating residual displacement spectrum (C r) of single-degree-of-freedom (SDOF) systems with a given damage index is developed. The C r are calculated with the Park-Ang damage model, which can be parameterized in terms of the ultimate ductility factor μ u and energy dissipation factor β, for SDOF systems subjected to 228 ground motions. The variation in C r with site conditions, damage model, postyield stiffness ratio and stiffness degradation is investigated. The results showed that μ u and β had moderate and negligible effects on C r, respectively. Reliable estimation of damage-based C r can facilitate the performance-based design of structures.

Límites de esbeltez basados en prestaciones para vigas de hormigón armado para el control de deformaciones y el control de tensiones en la armadura

Los procedimientos actuales de dimensionamiento a flexión de elementos de hormigón armado, basados ​​en la comprobación de estado límite último (ELU), proporcionan suficiente resistencia para soportar las cargas de diseño con un canto reducido. Sin embargo, las dimensiones estrictas de la sección transversal y la cantidad de armadura calculada para satisfacer el ELU pueden ser insuficientes para evitar deformaciones excesivas que pueden producir daños en los elementos no estructurales, o para garantizar el control de la fisuración y satisfacer así, los requisitos de durabilidad, funcionalidad o estética.Debido a la complejidad asociada a un cálculo riguroso de las deformaciones y el ancho de fisura en elementos de hormigón armado a lo largo de su vida útil, una forma efectiva de garantizar la satisfacción del estado límite de servicio es mediante la limitación de la relación de esbeltez l/d del elemento. En el presente estudio, el concepto de esbeltez límite, utilizado anteriormente para el control de la deformación, se generaliza para incorporar las limitaciones de la abertura de fisura, en el marco del diseño estructural basado en prestaciones. Por ello, se derivan las ecuaciones para la esbeltez límite que incorporan los parámetros principales que influyen en el comportamiento de servicio de los elementos de hormigón armado, que son válidos para secciones transversales rectangulares en forma de I o T y para elementos simplemente apoyados o continuos. La fisuración y los efectos a largo plazo se explican a través de coeficientes simplificados derivados de la mecánica estructural y las observaciones experimentales.Las esbelteces límite propuestas, tanto para una carga aplicada constante como para una deformación en la armadura constante, se comparan con las obtenidos utilizando el procedimiento EC2 para el cálculo de deformaciones, basado en la integración de curvaturas. Se han obtenido buenos resultados en términos de errores y dispersión, lo que demuestra que las esbelteces límite propuestas son una herramienta útil para el diseño basado en prestaciones de estructuras de hormigón armado. El carácter mecánico de la formulación facilita su modificación para situaciones diferentes a las utilizadas en su deducción, por ejemplo, diferentes tipos de carga, vigas parcialmente pretensadas o elementos de hormigón armado con FRP, entre otros.

Wind field generation for performance-based structural design of transmission lines in a mountainous area

The first step of performance-based design for transmission lines is the determination of wind fields as well as wind loads, which are largely depending on local wind climate and the surrounding terrain. Wind fields in a mountainous area are very different with that in a flat terrain. This paper firstly investigated both mean and fluctuating wind characteristics of a typical mountainous wind field by wind tunnel tests and computational fluid dynamics (CFD). The speedup effects of mean wind and specific turbulence properties, i.e., turbulence intensity, power spectral density (PSD) and coherence function, are highlighted. Then a hybrid simulation framework for generating three dimensional (3D) wind velocity field in the mountainous area was proposed by combining the CFD and proper orthogonal decomposition (POD) method given the properties of the target turbulence field. Finally, a practical 220 kV transmission line was employed to demonstrate the effectiveness of the proposed wind field generation framework and its role in the performance-based design. It was found that the terrain-induce turbulence effects dominate the performance-based structural design of transmission lines running through the mountainous area.

A Digitized Fuel Load Surveying Methodology Using Machine Vision

Fuel load is a crucial parameter for evaluating design fires for buildings. However, the availability of fuel load data is currently hindered by the lack of an efficient on-site data collection method. This research develops a new methodology for fuel load surveys that can facilitate the collection, storage, and analysis of fuel load data for a variety of building occupancies. The new survey method harnesses recent developments in mobile electronic devices, cloud storage, and machine vision to efficiently complete fuel load surveys in buildings. A four-step method is developed comprising digital inventory, data organization, item matching through computer vision, and fuel load estimation. The method is completed through an interactive electronic surveying form accessible on any mobile device with an internet connection, such as a tablet. The application allows taking digital measurements and pictures of the room and content, which are stored, and later searched through retail search engines using image recognition. Automatic matching of the picture with an online catalogue item gives access to further information about this item which are then used to evaluate the item fuel load, using a table of materials calorific values coded in the application. A wide adoption of this method could provide benefits by progressively populating such digital fuel load database. The results can then be used to provide design guidelines for fuel load density in codes and standards, for application in performance-based design of structures in fire.

Stability-based fire resistance duration of unbraced steel frames

PurposeThe collapse of a structure resulting from the instability of steel frames due to fire is the worst failure mode to consider in fire-structural engineering, and should be avoided. The purpose of this paper is to propose a new method for estimating the minimum possible duration of a fire event that could result in the instability of an unbraced steel frame.Design/methodology/approachThe proposed method is in the form of a constrained minimization problem that determines the worst case fire scenario that can cause instability of a structure, and is solved using nonlinear constrained mathematical programming algorithms. The formulation is demonstrated via a numerical example.FindingsFor frames subjected to fire events modelled with monotonically increasing fire curves, the worst case fire causing instability of a frame is always one where all of the compartments catch fire at the same time. For frames subjected to fire events where fire curves decay, the minimization problem must be solved rigorously. The results are significantly affected by the fire curves and amount of insulation applied to each member.Originality/valueThe proposed method is an extension of a method previously established by Xuet al.(2018) to assess the stability of unbraced steel frames subjected to elevated member temperatures. The previous method does not consider fire duration and heat transfer mechanics, which are included in the proposed method. The proposed method is potentially useful for designers in conducting fire scenario analysis in the performance-based design of structures.

The role of thermal loads in the performance-based design of energy piles

Over the past two decades, a substantial amount of research has investigated the effects of thermal loads associated with the geothermal operation of energy piles on their mechanical response. Based on this research, consensus about the need for considering the effects of thermal loads on the geotechnical and structural design of energy piles has been achieved. However, the understanding of the influence of thermal loads on the mechanical response of energy piles has prevented the determination of when the effects of these loads should be considered in performance-based design, e.g., only when addressing the deformation (at serviceability limit states) or also the failure (at ultimate limit states) of such foundations. Looking at this challenge, this paper presents an investigation of the role of thermal loads in the mechanical response of energy piles to provide a theoretically based approach for the geotechnical and structural performance-based design of such foundations. The main conclusion that can be drawn from this study and the discussed ductility-based design approach is that thermal loads cause negligible effects at ultimate limit states from both a geotechnical and a structural perspective, while they cause significant effects that should be considered at serviceability limit states.

Performance-based slenderness limits for deformations and crack control of reinforced concrete flexural members

The use of high strength materials allows flexural members to resist the design loads or to cover long spans with a reduced depth. However, the strict cross section dimensions and reinforcement amount required in ULS are often insufficient to satisfy the serviceability limit states. Due to the complexity associated to a rigorous computation of deflections and cracks width in cracked RC members along their service life, an effective way to ensure the satisfaction of the SLS is to limit the slenderness ratio l/d of the element. In the present study, the slenderness limit concept, previously used for deflection control, is generalized to incorporate the crack width limitations in the framework of structural performance-based design. Equations for slenderness limits incorporating the main parameters influencing the service behaviour of RC members are derived. Cracking and long-term effects are accounted for through simplified coefficients derived from structural concrete mechanics and experimental observations. The proposed slenderness limits are compared with those derived from a numerical non-linear time-dependent analysis for two case studies, and also with those obtained using the EC2 procedure for deflection calculation in terms of constant applied load and constant reinforcement strain. Very good results have been obtained in terms of low errors and scatter, showing that the proposed slenderness limits are a useful tool for performance-based design of RC structures.

Seismic Ductility Capacity Research of Integral Building-Bridge Station Structure

The performance-based structural design requires that the structure has a clear structural performance target under the specified set-up criteria, and the performance target is specifically reflected in the structural damage degree. This paper analyzes in detail the strength criteria of structural failure. Combined with the actual bridge-building project, the dynamic elasto-plastic analysis of the fiber unit is used to obtain the transverse and longitudinal ductility of the structure. Being destroyed, the displacement of the structure and the study of energy dissipation failures have been carried out. It is known from the research that the ductility of the analyzed engineering structures is good and meets the requirements of the current specifications, and can be used as a useful reference for structural seismic design.

An improved multi-objective optimization approach for performance-based design of structures using nonlinear time-history analyses

Performance-based design (PBD) of buildings can be properly addressed in a multi-objective optimization framework. However, computational costs of such an approach will be very expensive especially if nonlinear time-history analysis (NTHA) is used as the evaluation tool. In this paper, significant reductions in computational costs of solving structural multi-objective optimization problems is achieved by proposing a new metaheuristic surrogate model called Surrogate FC-MOPSO. In this method, which is an extension of FC-MOPSO algorithm, NTHA and pushover analysis (PA) are simultaneously employed for evaluating system responses. PAs are adopted as an approximation tool in the surrogate model while the responses corresponding to feasible solutions are always evaluated from NTHAs. The final Pareto optimal solutions, which yield tradeoffs between initial and life-cycle costs (LCCs), are already evaluated based on NTHAs. It is shown that application of the proposed method results in substantial reductions of runtime of the considered problems. It is also demonstrated that adopting PAs as the only evaluation tool in optimal performance-based design of structures can result in unreliable solutions.

An approach for synthesizing tri-component ground motions compatible with hazard-consistent target spectrum - Italian aseismic code application

A versatile approach for synthesizing non-stationary multicomponent ground motions compatible with a given target response spectrum is presented. In conjunction with performance-based structural design, the proposed approach combines a scenario-based procedure to select the target spectra of the three components of the motion, and a stochastic scheme, with an iterative wavelet-based method to generate the artificial time histories. In this context, the selection of an appropriate target spectrum is mandatory to synthesizing accelerograms with proper frequency content, input-energy, effective duration, and inelastic demand. In the scenario-based assessments, the target spectrum is derived directly from an earthquake scenario defined by seismic hazard disaggregation and strong ground-motion attenuation relationships. Firstly, the design spectrum specified by aseismic code provisions is replaced by a set of conditional mean spectra (CMS) for each of the ground motion components. Subsequently, an inverse stochastic dynamics problem, defined by a set of parametric evolutionary power spectra (EPS), is formulated and solved in a point-wise format for each CMS and for the three components of the motion. To improve the matching between the response spectrum of the simulated records and the CMS, an iterative procedure involving the family of harmonic wavelets is then employed. Post-processing for a proper baseline correction of the records is performed to synthesize ground-motions yielding realistic velocity and displacement traces. To illustrate the effectiveness of the approach, extensive numerical results pertaining to the Italian aseismic code provisions are included in this paper. In this regard, Monte Carlo simulations are undertaken to relate the CMSs to the evolutionary power spectrum. In particular, non-constant peak factor expressions via regression analysis are derived for various ground-motion durations. Finally, the nonlinear responses of elasto-plastic SDOF oscillators with different values of the yield strength reduction factor are considered. The oscillators subjected to artificially generated records and a set of natural unscaled and spectrum-compatible accelerograms, are examined in terms of ductility demand and equivalent number of yield cycles.

Evaluation of the EDR Performance in Seismic Control of Steel Structures Using Endurance Time Method

The Energy Dissipating Restraint (EDR) is a friction device which can be used to dissipate the energy introduced to a structure by a seismic event. In this paper, the performance of the structures which are outfitted with the EDR is investigated in several intensity levels by using a novel seismic analysis method, namely the Endurance Time (ET) method. By reasonably estimating the response of structures over the entire range of the desired intensity levels through each time-history analysis, this method can effectively reduce the computational cost, offering an appropriate procedure for performance-based design of structures. The EDR performance in the seismic control of steel frames is evaluated at low to high intensity levels through three case studies with various story numbers. Additionally, a comparison is made between the ET results and those of conventional time-history analysis, in which a good concordance between the two methods is observed.

Application of endurance time method in performance-based optimum design of structures

In this research, application of the Endurance Time (ET) method in performance-based design of structures with and without consideration of uncertainties is investigated and a practical optimum design procedure is proposed. The ET method is used as an analytical assessment tool because of its capabilities in response estimation with an affordable computational demand. In the first step of the proposed method, ET analysis is implemented in a multi-objective optimum design procedure in order to achieve a set of Pareto optimal designs. Optimization is conducted with respect to initial cost and expected life cycle cost using a deterministic approach. For each design alternative the median damages due to probable earthquakes in its life time is estimated by the ET method, and the expected cost of earthquake consequences is calculated using Life Cycle Cost Analysis (LCCA). In the next step, a comprehensive performance assessment is carried out on a candidate optimal design considering inherent uncertainties in the framework of FEMA-P-58. It is also proposed to use the ET method as the response assessment tool in this framework. Expected damage costs, fatalities and probability of collapse are estimated using a Monte Carlo approach to account for uncertainties. The candidate design can then be altered to another optimal design from the Pareto set in the case of undesirable performance. The advantages and shortcomings of the method are investigated by comparing the results from the ET method and recommended procedure using a suite of ground motions. The results provide a pathway towards practical use of the ET analysis method in state of the art performance-based design and probabilistic estimation of losses.