Papers by Ramin Yarmohammadian
Surrogate modelling is increasingly used in engineering to improve computational efficiency in co... more Surrogate modelling is increasingly used in engineering to improve computational efficiency in complex simulations. However, traditional data-driven surrogate models often face limitations in generalizability, physical consistency, and extrapolation-issues that are especially critical in safety-sensitive fields such as fire safety engineering (FSE). To address these concerns, physics-informed surrogate modelling (PISM) integrates physical laws into machine learning models, enhancing their accuracy, robustness, and interpretability. This systematic review synthesises existing applications of PISM in FSE, classifies the strategies used to embed physical knowledge, and outlines key research challenges. A comprehensive search was conducted across Google Scholar, ResearchGate, ScienceDirect, and arXiv up to May 2025, supported by backward and forward snowballing. Studies were screened against predefined criteria, and relevant data were analysed through narrative synthesis. A total of 100 studies were included, covering five core FSE domains: fire dynamics, wildfire behaviour, structural fire engineering, material response, and heat transfer. Four main strategies for embedding physics into machine learning were identified: feature engineering techniques (FETs), loss-constrained techniques (LCTs), architecture-constrained techniques (ACTs), and offline-constrained techniques (OCTs). While LCT and ACT offer strict enforcement of physical laws, hybrid approaches combining multiple strategies often produce better results. A stepwise framework is proposed to guide the development of PISM in FSE, aiming to balance computational efficiency with physical realism. Common challenges include handling nonlinear behaviour, improving data efficiency, quantifying uncertainty, and supporting multi-physics integration. Still, PISM shows strong potential to improve the reliability and transparency of machine learning in fire safety applications.
The experimental characterization of concrete's post-peak stress vs crack opening curve is a key ... more The experimental characterization of concrete's post-peak stress vs crack opening curve is a key aspect in many practical problems involving crack stability, like size-effect and explosive spalling of High-Performance concrete in the fire. The direct-tension test is recognized as the most straightforward solution, though the strain-softening material behaviour entails tricky issues concerning the axial and flexural stability of the test. Axial stability is impaired by the deformability of the loading frame since the traditional scheme of universal testing machines entails compression of rather long columns and bending of the crosshead and the table. The consequent deformation energy largely exceeds the dissipation capacity of the tested sample, requiring responsive closedloop control systems for smoothly driving the descending branch of the test. As regards flexural stability, several solutions have been proposed to improve the bending stiffness of the test rig, mostly based on ball bushing guiding systems or adjustable tie-rods secured to the loading platens. However, the transversal restraint to the sample may trigger parasitic shear stress, which translates into inclined fracture propagation paths and overlapping cracks. To address these multifaced issues, an innovative frameless test rig has been designed, based on three symmetrically arranged electro-mechanical jacks directly pushing the top of the sample up. The samples are short, notched cylinders (Ø=100mm, h=150mm) preliminarily glued to thick steel platens and then bolted to the bottom table and the moving head of the machine, speeding up their installation and later removal. The load is exerted through stiff load cells and pendular struts, preventing any transversal load component. The actuators are optimized for stiffness and promptness, and three parallel control loops are implemented to drive the mean opening and two orthogonal rotation components of the crack mouth. At the present stage, the prototype has been assembled and the control routines are being tested. A first series of experimental results will be included in the final presentation at the conference.
Explosive spalling keeps being one of the main open issues concerning the fire safety of concrete... more Explosive spalling keeps being one of the main open issues concerning the fire safety of concrete structures. Though it is recognized that cracks in the exposed cover can be triggered by the combined effect of thermal stress and pore pressure, the energy source and the mechanism behind the violent projection of fragments are not yet fully understood. Nonetheless, the huge thermal energy accumulated in the hot cover (in the order of 500kJ/m 2 in a 1mm thick layer) has a high potential to drive dynamic fracturing, provided that water vaporization could quickly convert it into mechanical work. To make this possible, flash vaporization of a significant amount of water should take place in a sub-millimetre layer facing the opening crack (since vapour diffusion time goes with the path length squared). To validate this new perspective, a special setup was developed where concrete disks (D=100mm, thickness=60mm) were heated on the two opposite faces, so to instate a thermo-hygral transient similar to the concrete cover exposed to fire, while keeping negligible the contribution of thermal stress. A crack is triggered in the sample mid-plane by the high thermal dilation of a polymeric insert (a PTFE ring) embedded in the sample. FEM analyses were performed to optimize the specimen shape and to adjust the insert thickness to control the temperature at which the crack develops a critical opening. Remarkably unstable blasts were observed in high-performance concrete samples, during which the relative acceleration of the two splitting halves was monitored via optical sensors. The results showed that pressure not far from the saturation value quickly develops in the opening crack. Continuous monitoring of the specimen mass also allowed assessing the amount of vaporized water entailed by the process. Tests on pre-dried samples exhibited a milder blast or even a stable propagation of the crack. In summary, this study is expected to cast new light on the fundamental mechanism behind the explosive spalling phenomenon.
Fast Vapour Migration Next to a Depressurizing Interface:A Possible Driving Mechanism of Explosive Spalling Revealed by Neutron Imaging
Fast transient analysis of spalling phenomenon using neutron radiography
In this paper the very quick vaporization of water in the pores of hot concrete next to an openin... more In this paper the very quick vaporization of water in the pores of hot concrete next to an opening crack is regarded as way to convert the considerable amount of thermal energy stored in the material into kinetic energy of the fractured splinters. To this purpose, a special setup has been developed in order to suddenly release the vapor pressure accumulated at a sealed edge of a heated sample. The quick local cooling observed confirmed that a sizeable loss of thermal energy occurs in a rather thin layer of concrete facing the depressurized surface. Fast sequences of Neutron Radiographic images allowed to recognize that the influenced zone doesn't exceed 1mm thickness. This has a direct impact on the time scale of thermal and hygral transients and corroborates the idea that a significant contribution to the explosive nature of spalling may be provided by water vaporization.
The experimental characterization of concrete's post-peak stress vs crack opening curve is a key ... more The experimental characterization of concrete's post-peak stress vs crack opening curve is a key aspect in many practical problems involving crack stability, like size-effect and explosive spalling of High-Performance concrete in the fire. The direct-tension test is recognized as the most straightforward solution, though the strain-softening material behaviour entails tricky issues concerning the axial and flexural stability of the test. Axial stability is impaired by the deformability of the loading frame since the traditional scheme of universal testing machines entails compression of rather long columns and bending of the crosshead and the table. The consequent deformation energy largely exceeds the dissipation capacity of the tested sample, requiring responsive closed-loop control systems for smoothly driving the descending branch of the test. As regards flexural stability, several solutions have been proposed to improve the bending stiffness of the test rig, mostly based on ball bushing guiding systems or adjustable tie-rods secured to the loading platens. However, the transversal restraint to the sample may trigger parasitic shear stress, which translates into inclined fracture propagation paths and overlapping cracks.
To address these multifaced issues, an innovative frameless test rig has been designed, based on three symmetrically arranged electro-mechanical jacks directly pushing the top of the sample up. The samples are short, notched cylinders (Ø=100mm, h=150mm) preliminarily glued to thick steel platens and then bolted to the bottom table and the moving head of the machine, speeding up their installation and later removal. The load is exerted through stiff load cells and pendular struts, preventing any transversal load component. The actuators are optimized for stiffness and promptness, and three parallel control loops are implemented to drive the mean opening and two orthogonal rotation components of the crack mouth.
At the present stage, the prototype has been assembled and the control routines are being tested. A first series of experimental results will be included in the final presentation at the conference.
Explosive spalling in concrete during fire incidents is a complex phenomenon, involving the detac... more Explosive spalling in concrete during fire incidents is a complex phenomenon, involving the detachment and projection of fragments from heated surfaces. While existing literature outlines pore pressure and thermal stress as primary driving mechanisms, their individual roles fail to explain the violent expulsion of concrete fragments. This paper proposes a new framework, combining these factors synergistically, to reassess the mechanism underlying spalling. The first stage involves incipient crack formation, where thermal gradients and external loads induce tensile stress in small convex samples or high compressive stress in large heated faces, interacting with hydrostatic tension ensuing from pore pressure. High-Performance Concrete (HPC) and Ultra-High-Performance Concrete (UHPC) exhibit diffuse cracking due to their homogeneous nature and low permeability which help assessing that interaction in small-scale tests. The second stage involves rapid crack propagation, leading to particle projection at high velocity, fuelled by accumulated thermal energy. A novel small-scale spalling test is developed to explore the influencing parameters, supporting spalling risk assessment and suggesting insights into mitigation strategies. The study provides a comprehensive understanding of spalling dynamics, highlighting factors such as concrete composition, element shape, and pore pressure effects. Future research lines are suggested for enhancing spalling prevention and mitigation strategies.
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Papers by Ramin Yarmohammadian
To address these multifaced issues, an innovative frameless test rig has been designed, based on three symmetrically arranged electro-mechanical jacks directly pushing the top of the sample up. The samples are short, notched cylinders (Ø=100mm, h=150mm) preliminarily glued to thick steel platens and then bolted to the bottom table and the moving head of the machine, speeding up their installation and later removal. The load is exerted through stiff load cells and pendular struts, preventing any transversal load component. The actuators are optimized for stiffness and promptness, and three parallel control loops are implemented to drive the mean opening and two orthogonal rotation components of the crack mouth.
At the present stage, the prototype has been assembled and the control routines are being tested. A first series of experimental results will be included in the final presentation at the conference.