Salma Mozaffari

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Mozaffari

First Name

Salma

ORCID

0000-0002-5364-3849

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Publications 1 - 10 of 11

Development of three-dimensional strut-and-tie models for structural concrete components
Mozaffari, Salma; Akbarzadeh, Masoud; Vogel, Thomas (2018)
Proceedings of the 12th fib International PhD Symposium in Civil Engineering
This paper presents a proposal for developing a procedure for the generation of 3D strut-and-tie models for structural concrete components, using the techniques of topology optimization and graphical statics. Extensive research has been carried out on the development of methodologies to generate strut-and-tie patterns based on the flow of stresses within a structural volume. Some focus on the various formulations of topology optimization algorithms. The goal of this research is to address the limitations of topology optimization in producing reasonable strut-and-tie patterns. This study will also investigate the potentials of graphic statics for the creation or refinement of such models. The arguments presented in this article demonstrate the possibilities for the further exploration of topology optimization and graphical statics in the production of suitable strut-and-tie models for three-dimensional scenarios.
An examination of some aspects of factor analysis in damage detection
Mozaffari, Salma; Bernal, Dionisio P. (2012)
Conference Proceedings of the Society for Experimental Mechanics Series ~ Topics in Modal Analysis II
It is well known that dynamic properties can be affected by environmental factors and this complicates the identification of damage. Among procedures explored to mitigate the fluctuations in dynamic features from environmental effects factor analysis is one of the simplest and has the merit that it operates without the need to measure the environmental variables. The method has been examined by several researchers in recent years but experience is limited and questions on some technical details remain open. This paper presents an investigation on three aspects that may affect the performance. The most important is the number of factors used in the analysis. The second relates to whether the diagonal nature on the covariance of random errors is enforced or not, and the third examines the influence of the criterion used to solve the over-determined set of equations that arise in the method. Results are obtained by simulating a system where the stiffness is cubically related to changes in temperature and where the temperature field, in each simulation, is a realization of a random process with a prescribed spatial correlation.
Linear Projection Techniques in Damage Detection Under a Changing Environment
Mozaffari, Salma; Döhler, Michael; Bernal, Dionisio P.; et al. (2014)
Conference Proceedings of the Society for Experimental Mechanics Series ~ Topics in Modal Analysis
The merit of linear projections as a way to improve the resolution in damage detection under changing environmental conditions is examined. It is contended that if the data from the reference condition is balanced, in the sense that the number of feature vectors available for the various temperatures is similar, then projections, such as those in Principal Component Analysis and Factor Analysis, will not improve performance. Projections, however, help to control the false positive rate when the reference data set is not balanced. Analysis and simulation results suggest that previous claims on the merit of projection as a way to improve damage detection resolution under environmental variability may be too optimistic.
Generation of strut-and-tie models and stress fields for structural concrete
Mozaffari, Salma; Akbarzadeh, Masoud; Vogel, Thomas (2019)
Strut-and-tie models are principally the discretized stress fields, which simplify the dimensioning and detailing of reinforced concrete members. The computational generation of stress fields currently relies on finite element analysis or optimization methods. This research addresses the limitations of optimization algorithms in producing reasonable strut-and-tie configurations. The computational procedure of this paper utilizes layout optimization and graphic statics cooperatively to create strut-and-tie models and stress fields for two-dimensional cases. The presented examples demonstrate the capabilities of the mentioned methods to produce some desired results for two-dimensional scenarios and suggest a similar approach to solve the strut-and-tie problem for three-dimensional cases.
First mode damping ratios for buildings
Bernal, Dionisio P.; Döhler, Michael; Mozaffari, Salma; et al. (2015)
Earthquake Spectra
Expressions for the expected value of the first mode damping ratio are derived by using 122 seismic responses from concrete buildings and 81 from steel. The results include dissipation at the soil-structure interface and are appropriate for situations in which this source of dissipation is not included in the model. Comparisons between models of different complexity indicate the appropriateness of using a single regressor, for which the building height is used. It is shown that the Fisher information about damping increases with the number of response cycles; this result is used to define weights for the residuals of the regression. The effective damping in steel buildings, with the exception of very tall structures, is found to be larger than the 2% typically used in practice, whereas the 5% assigned to concrete proves to be similar to the mean of the data set.
Computational Strut-and-Tie Modeling
Mozaffari, Salma (2021)
The research presented in this manuscript investigates computational methods and integrative approaches for planar and spatial strut-and-tie modeling. This study is formulated in response to the limitations of the existing computational techniques in generating practical truss models and the lack of useful developments and applications of computational graphical statics in the current structural engineering core research and practice. Stress-based methods like finite element analysis or topology optimization use detailed stress analysis to help create truss models. Since these methods focus on analysis rather than design, they deliver less freedom to create practical models or consider modification scenarios. Alternatively, geometry-based techniques like the load path method or graphic statics are design tools that aid in the procedural creation of strut-and-tie models. So, they provide more control and creativity, but at the same time, no pre-analysis of the structure is provided; therefore, more relevant expertise is required to create a model using these techniques. Furthermore, the latest advancements in graphic statics still require considerable improvements to find practical applications for computational strut-and-tie modeling. Three key research objectives are established by examining the potentials and limitations of the existing techniques: (i) exploring applications and extensions of algebraic graphic statics and layout optimization in creating truss models, (ii) investigating strategies to implement modifications to the initiated models using graphic statics, and (iii) addressing the challenges for spatial cases and develop required algorithmic extensions. Through the development of integrative algorithms and expansion of existing formulations, the methodologies of this research demonstrated the potential to bridge the gap between analytical and graphical approaches and contribute to the evolving nature of computational graphic statics in structural design. The presented algorithms of this study can be incorporated into the various parametric design, structural analysis, and digital fabrication workflows, proceeding one step further towards the materialization of the tension-compression networks.
Graphic statics in a continuum: Strut-and-tie models for reinforced concrete
Mozaffari, Salma; Akbarzadeh, Masoud; Vogel, Thomas (2020)
Computers & Structures
This research bridges the gap between the numerical layout optimization method and the geometry-based analysis and design method of graphic statics. The study connects the two methods for the application of strut-and-tie models in reinforced concrete design. It suggests a new algorithm for the algebraic graphic statics of indeterminate trusses inspired by the layout optimization method. This research also contributes to the field of graphic statics by providing a formulation that generates form and force diagrams in a continuum, where the topology for none of the diagrams is initially provided. The generation of strut-and-tie models for reinforced concrete has extensively relied on optimization methods, which are helpful techniques for the initiation of a load path inside a continuous domain. However, the resulting truss model is a single answer, and there exists limited control to methodically modify the topology or the force distribution of the model. Furthermore, the minimized-weight truss does not guarantee a practical strut-and-tie model or an optimized performance of a reinforcement design. In contrast to the conventional optimization techniques with a single solution, the intuitive method of graphic statics provides the designer with a vast design space. It also offers explicit control over the geometry and force distribution of the generated truss models. The algorithm provided in this paper is applied to various continuous domains to systematically generate a variety of strut-and-tie models, their force diagrams, and constant stress fields. The production of the optimized truss model and its force distribution allows the direct interactive manipulations of the design while observing the changes in the stress fields and the reinforcement arrangement. The open-source repository of the implemented integrated algorithm and the examples used in this paper are also provided.
Cocoon: 3D printed clay formwork for concrete casting
Bruce, Mackenzie; Clune, Gabrielle; Xie, Ruxin; et al. (2021)
ACADIA 2021: Realignments: Toward Critical Computation. Proceedings of the 41st Annual Conference of the Association for Computer Aided Design in Architecture
Concrete, a material widely used in the construction industry today for its low cost and considerable strength as a composite building material, allows designers to work with nearly any form imaginable; if the technology to build the formwork is possible. By combining two historic and widely used materials, clay and concrete, our proposed novel process, Cocoon, integrates robotic clay three-dimensional (3D) printing as the primary formwork and incrementally casting concrete into this formwork to fabricate nonstandard concrete elements. The incremental casting and printing process anchors the concrete and clay together, creating a symbiotic and harmonious relationship. The concrete’s fluidity takes shape from the 3D printed clay formwork, allowing the clay to gain structure from the concrete as it cures. As the clay loses moisture, the formwork begins to shrink, crack, and reveal the concrete below. This self-demolding process produces easily removable formwork that can then be recycled by adding water to rehydrate the clay creating a nearly zero-waste formwork. This technique outlines multiple novel design features for complex concrete structures, including extended height limit, integrated void space design, tolerable overhang, and practical solutions for clay deformation caused by the physical stress during the casting process. The novelty of the process created by 3D printing clay formwork using an industrial robotic arm allows for rapid and scalable production of nearly zero-waste customizable formwork. More significant research implications can impact the construction industry, integrating more sustainable ways to build, enabled by digital fabrication technologies.
Change detection under environmental variability
Mozaffari, Salma; Bernal, Dionisio P.; Döhler, Michael (2014)
5th International Operational Modal Analysis Conference (IOMAC 2013). Proceedings of a meeting held 13-15 May 2013, Guimaraes, Portugal
Change detection is the process of announcing, from inspection of the sequence of measured signals, if changes in a system have taken place. Change detection is tantamount to a hypothesis test on the likelihood of the aggregate of the data given a statistical model of reference state. A fundamental assumption in change detection is that the data points are independent and identically distributed (i.i.d) under the null hypothesis. When the data depends on environmental parameters, the i.i.d premise for a sequential stream of points is not justified. However, operations on the data can be performed, so the premise is reasonably satisfied, and the change detection scheme can then be applied. Among alternatives that do not require that the environmental parameters be measured, the one that has been most widely examined is Principal Component Analysis. In this case, the data is projected into a subspace where the variance from the environment is slight. The price paid is that the damage-related information on the principal directions is then discarded. There are (at least) two other possibilities: one is to decorrelate the data using an autoregressive model, and the other is to break the correlation by scrambling. In the latter case, the price is that detection must be carried out with some irreducible delay. This paper examines the relative merit of the alternatives noted.
Damping Identification in Buildings from Earthquake Records
Bernal, Dionisio P.; Mozaffari, Salma; Kwan, Kenny; et al. (2012)
SMIP12 Seminar on Utilization of Strong-Motion Data. Proceeding
It is shown that the Fisher information on damping contained in seismic response is small and, as a consequence, identified damping ratios are realizations from a distribution with high variance. Predictive expressions with reasonable confidence intervals can be generated, however, if sufficient data is available. In this study 122 responses from concrete buildings, 81 from steel, 26 for masonry and 10 from wood structures are used to identify damping ratios using a subspace algorithm.

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Salma Mozaffari

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