Elyas Ghafoori

Last Name

Ghafoori

First Name

Elyas

ORCID

0000-0002-4924-0668

Organisational unit

01109 - Lehre Bau, Umwelt und Geomatik

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Publications 1 - 10 of 54

Strengthening of steel beams with adhesively bonded memory-steel strips
Wang, Sizhe; Li, Lingzhen; Su, Qingtian; et al. (2023)
Thin-Walled Structures
This study entails the development of a non-destructive prestressed strengthening solution for steel beams using adhesively bonded memory-steel (also known as iron-based shape memory alloy, Fe-SMA) strips. The Fe-SMA strip is activated via heating and subsequent cooling to generate prestress, while the two ends of the Fe-SMA strip are adhesively bonded as anchorages. The behavior of the Fe-SMA-to-steel bonded joints was investigated through lap-shear tests, from which an effective bond length of approximately 120 mm was determined. Subsequently, a strengthening solution for a 5.3 m span steel I-beam was designed based on finite element analysis. A 4200 mm × 100 mm × 1.5 mm Fe-SMA strip was bonded to the bottom of the steel beam with a bond length of three times the effective bond length, and a two-step activation strategy using torches was proposed. Furthermore, the designed strengthening solution was experimentally tested. With activation to the target temperature of 240 °C, the Fe-SMA developed a prestress level of approximately 280 MPa. A series of static and fatigue four-point bending tests were conducted. After 3 million cycles of fatigue loading, no debonding or degradation was observed for the adhesively bonded Fe-SMA-strengthened specimen; this demonstrated the reliable performance of the strengthening solution under service loads.
Arresting fatigue cracks in steel plates using prestressed bonded Fe-SMA strips: Analytical prediction and experimental validation
Li, Lingzhen; Wang, Sizhe; Chen, Tao; et al. (2025)
Thin-Walled Structures
Bonded iron-based shape memory alloy (Fe-SMA) strengthening has shown great potential in fatigue strengthening for steel structures. However, there is a lack of a comprehensive model for analysing the fatigue behaviour of systems strengthened with prestressed bonded Fe-SMA. This study proposes the first analytical model, integrating a prestress analysis and fatigue analysis, to predict fatigue crack arrest in steel plates strengthened with prestressed bonded Fe-SMA strips. Four steel plates, each featuring a central through-thickness crack, were strengthened using bonded Fe-SMA strips, and subsequently, tested under fatigue loading after generating prestress via heating and cooling. The proposed model succeeded in predicting (i) the fatigue crack arrest at certain load levels and (ii) onset of crack propagation at increased load levels.
Mixed-mode debonding mechanisms of Fe-SMA and CFRP bonded joints
Pichler, Niels; Wang, Wandong; Heydarinouri, Hossein; et al. (2025)
Engineering Fracture Mechanics
Adhesively bonding iron-based shape memory alloy (Fe-SMA) offers a solution to strengthen fatigue-prone metallic structures and prolong their service life. However, adhesive joints being susceptible to debonding failure, static failure was studied in Mode I, Mode II, and mixed-mode conditions, both experimentally and theoretically. The Fe-SMA material behaviour on the debonding mechanism was shown to be influential, reducing the bond capacity compared to carbon fibre reinforced composites (CFRP) strengthening material. So far the study of static joint failure was mainly confined to the debonding under the controlled lap-shear test conditions, a very common test for joint characterization and not on a component scale. The interaction between the structure end the repair was assumed negligible with the focus being on the interaction between the adhesive and adherend. In this manuscript, the static mixed-mode debonding is approached experimentally and theoretically at component scale. The residual tensile strength of a fully separated structural steel or aluminium element repaired with bonded Fe-SMA or CFRP strips of different width is measured. The repair eccentricity induced bending of the structural element is considered. Analytical and finite element modelling of the structural component are validated with the experiment and allow to perform the mode separation. It is shown that the deformation of the structural element affects the mode mixity. When the repair strip stiffness is high relative to the structural components stiffness, the Mode I contribution increased, negatively affecting the component residual strength. However, this effect was shown to be less important for Fe-SMA repair strips due to their material nonlinearity. These bonded repair were thus shown to be more resilient than their CFRP counterpart.
Analysis and design recommendations for structures strengthened by prestressed bonded Fe-SMA
Li, Lingzhen; Wang, Sizhe; Chatzi, Eleni; et al. (2024)
Engineering Structures
Previous studies have demonstrated a great potential of prestressed strengthening of structures employing iron-based shape memory alloys (Fe-SMAs). A bonded Fe-SMA strengthening solution with partial activation has been proposed. However, an analytical model for assessing the strengthening efficiency was lacking, due to the unique nature of the employed prestressing mechanism involving heating. In this study, a symmetric strengthening model and an asymmetric strengthening model are developed to analyze the prestress level in steel and glass beams and plates strengthened by bonded Fe-SMA strips. The asymmetric strengthening model is then modified to analyze reinforced concrete (RC) beams strengthened by embedded Fe-SMA rebars. Recovery stress at different activation temperatures, the influence of the activation temperature on the adhesive bond, as well as the prestress loss resulting from the deformation of substrate elements and adhesive joints are taken into account. The predicted strains and deflections in the parent structure closely approximate the experimental measurements that appear in current literature. A parametric study and a sensitivity analysis are then conducted to assess the impact of the four influential features on the final prestress level, and their impact is ranked in the following order: recovery stress ≈ Fe-SMA width > activation length > bonded anchorage length. Based on these findings, a design strategy, in line with Eurocode 0, for the bonded/embedded Fe-SMA strengthening system is proposed. Finally, some perspectives on potential areas for future research are offered.
Design criterion for fatigue strengthening of riveted beams in a 120-year-old railway metallic bridge using pre-stressed CFRP plates
Ghafoori, Elyas; Motavalli, M.; Nussbaumer, A.; et al. (2015)
Composites Part B: Engineering
Prestressed CFRP-strengthening and long-term wireless monitoring of an old roadway metallic bridge
Ghafoori, Elyas; Hosseini, Ardalan; Al-Mahaidi, Riadh; et al. (2018)
Engineering Structures
Irreversible cyclic cohesive zone model for prediction of mode I fatigue crack growth in CFRP-strengthened steel plates
Mohajer, Mana; Bocciarell, Massimiliano; Colombi, Pierluigi; et al. (2020)
Theoretical and Applied Fracture Mechanics
Experimental studies on various strengthening systems for steel elements under fatigue loading showed that the use of carbon fiber reinforced polymer (CFRP) strengthening system could significantly enhance the fatigue lifetime. Besides, more recently it was shown that the use of prestressed unbonded CFRP strengthening system results in an additional reduction of the fatigue crack propagation rate and promotes crack arrest. Different models have been proposed to evaluate the fatigue lifetime of CFRP-strengthened steel members (e.g. S-N curves and fracture mechanics-based models making use of Paris’ law or similar). As an alternative approach in this study, the numerical assessment of mode I (tensile mode) fatigue crack growth of an existing macrocrack in unstrengthened and CFRP-strengthened (both nonprestressed bonded and prestressed unbonded) tensile steel members is investigated by using a cyclic cohesive zone model (CZM). The key advantage, compared to the above-mentioned methods, is that it introduces a constitutive relationship of the material, capable of being calibrated for different materials and being used for any geometry and loading condition. In this way, the crack initiation, crack propagation, crack retardation as well as crack arrest are the natural outcomes of the model. It is shown that the finite element (FE) model can be readily coupled with an interface traction-separation law (TSL), to predict the damage evolution in the steel-CFRP interface. The comparison between the numerical and experimental results validated the proposed FE modelling, which has also been used to perform a parametric study with respect to the main design parameters. © 2020 Elsevier Ltd.
Normal, high and ultra-high modulus carbon fiber-reinforced polymer laminates for bonded and un-bonded strengthening of steel beams
Ghafoori, Elyas; Motavalli, Masoud (2015)
Materials & Design
Fatigue strengthening of cracked steel plates with bonded Fe‐SMA strips
Li, Lingzhen; Wang, Sizhe; Chen, Tao; et al. (2023)
ce/papers ~ EUROSTEEL 2023
Prestressed fatigue strengthening of steel structures has been proven effective by numerous investigations. Bonded iron-based shape memory alloy (Fe-SMA) strengthening has shown a great potential in this regard, however, with limited corroborating studies. Moreover, a proper model for fatigue analysis of systems that are retrofitted with bonded Fe-SMA strengthening is missing. In this study, an analytical model, coupling prestress analysis and fatigue analysis, is proposed. Four steel plates with central through-thickness cracks were strengthened with use of bonded Fe-SMA strips, and subsequently tested under fatigue loading after generating prestress via heating and cooling. The fatigue behavior predicted by the proposed model lies in excellent agreement with the fatigue testing results.
Interfacial stresses in beams strengthened with bonded prestressed plates
Ghafoori, Elyas (2013)
Engineering Structures

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