A Hybrid Model to Predict Localised Cracks of Reinforced Concrete Slabs in Fire

This paper presents a robust hybrid finite element procedure for predicting the large individual cracks within reinforced concrete floor slabs at elevated temperatures. For modelling the cracks formations and propagations within the floor slabs, the smeared crack model is used for modelling early stages of crack evolution, and then the ‘delayed extended finite element method (D-XFEM) is proposed for capturing individual big cracks within the floor slabs. The new model has been validated against previous fire test results. A series of parametric studies has been conducted on a composite floor to understand the influences of different protection conditions of the support steel beams on both global responses and cracking patterns of the composite floor under fire conditions

Modelling localised fracture of reinforced concrete structures

This paper presents a robust finite element procedure for simulating the localised fracture of reinforced concrete members. In this new model the concrete member is modelled as an assembly of plain concrete, reinforcing steel bar and bond-link elements. The 4-node quadrilateral elements are used for 2D modelling of plain concrete elements, in which the extended finite element method is adopted to simulate the formation and growth of individual cracks. The reinforcing steel bars are modelled by using a 3-node beam-column element. 2-node bond-link elements are employed for modelling the interaction between plain concrete and reinforcing steel bar elements. It is evident that the nonlinear procedure proposed in this paper can properly model the formation and propagation of individual localised cracks within the reinforced concrete structures. The model presented in this paper enables the researchers and designers to access the integrity of reinforced concrete members under extreme loading conditions by using mesh independent extended finite element method.The support of the Engineering and Physical Sciences Research Council of Great Britain under Grant No. EP/I031553/1

Tests on sea sand concrete-filled stainless steel tubular stub columns

[EN] This paper presents a series of tests on sea sand concrete-filled stainless steel tubular (SSCFST) stub columns under axial compression, where the main test parameters include type of fine aggregates (river sand, desalted sea sand and sea sand), steel ratio, and concrete strength. The failure mode, axial load versus axial shorten response, cross-sectional strength of the SSCFST specimens are investigated and compared with those of traditional composite columns with normal concrete. The confinement effect between stainless tube and the sea sand concrete is also evaluated. High strength and good ductility was observed for the tested SSCFST stub columns. In general, when being used as the concrete core in a composite column, differences of confinement behaviour between sea sand concrete and normal concrete are not significant, indicating the potential adoption of SSCFST columns in practice.The study of this paper is financially supported by the National Natural Science Foundation of China (51578154) and International Collaborative Funding of Fujian Agriculture and Forestry University (KXGH1700A). The financial support is highly appreciated.Liao, F.; Hou, C.; Zhang, WJ.; Ren, J. (2018). Tests on sea sand concrete-filled stainless steel tubular stub columns. En Proceedings of the 12th International Conference on Advances in Steel-Concrete Composite Structures. ASCCS 2018. Editorial Universitat Politècnica de València. 379-384. https://doi.org/10.4995/ASCCS2018.2018.6937OCS37938

Factors influencing self-healing mechanisms of cementitious materials: A review

The increasing awareness of climate change and global warming has pushed industries to be more conscious of their environmental impact, especially in the construction industry with the main contributor being concrete. Concrete is a material that is in very high demand in the construction industry for structural applications. However, it’s a material with a major concern with the challenges of microcracking. New technology has seen the development of self-healing material, using novel techniques to bring cementitious materials back to its original state. This paper reviews and evaluates the novel techniques adopted by the researchers in the field to achieve a self-healing material, with the main focus being on the factors influencing the mechanisms of autogenous healing and bacteria-based healing. Various parameters including bacteria type, pH, temperature, nutrient, urea, and Ca2+ concentration, bacteria concentration and application, pre-cracking, healing condition, cement type, and crack width are all important for healing efficiency, although the use of water to facilitate both autogenous and ureolytic bacteria healing mechanism is paramount for the triggering of healing processes. This study thoroughly presents various factors and their correlation to the healing mechanisms of autogenous healing and ureolytic bacteria healing. Further studies are identified to better understand the exact mechanism taking place and which healing process contributed to how much of the healing, and this review could serve as an informative platform for these pursues

Critical review on the thermal conductivity modelling of silica aerogel composites

As a new generation of thermal insulation materials, the effective thermal conductivity of aerogel and its composites is extremely low. The nanoporous structure of aerogels demobilises the movement of gas molecules, and the nano-skeleton system restricts solid heat transfer because of the size effect. Numerous research and modelling works have been carried out to understand and predict heat transfers. This review thoroughly discusses the existing theories and models of silica aerogel composites in gas, solid and radiative heat transfers. It investigates the correlation of the pore size distribution and solid skeleton network of the composites with the thermal conductivity. The review then assesses the advances of the development and questions remaining for further development, including 1) some unexplainable performance of existing models and 2) improvements required for gas and solid thermal conductivity models. Bridging the identified research gaps shall lead researchers to understand existing models better, develop a more accurate model based on more realistic microstructure simulation and further innovate the models for other emerging composites

An extended finite element model for modelling localised fracture of reinforced concrete beams in fire

Open Access funded by Engineering and Physical Sciences Research Council under a Creative Commons license.A robust finite element procedure for modelling the localised fracture of reinforced concrete beams at elevated temperatures is developed. In this model a reinforced concrete beam is represented as an assembly of 4-node quadrilateral plain concrete, 3-node main reinforcing steel bar, and 2-node bond-link elements. The concrete element is subdivided into layers for considering the temperature distribution over the cross-section of a beam. An extended finite element method (XFEM) has been incorporated into the concrete elements in order to capture the localised cracks within the concrete. The model has been validated against previous fire test results on the concrete beams.The Engineering and Physical Sciences Research Council of Great Britain under Grant No. EP/I031553/1

Biodegradable Silk Fibroin Nanocarriers to Modulate Hypoxia Tumor Microenvironment Favoring Enhanced Chemotherapy

Biopolymer silk fibroin (SF) is a great candidate for drug carriers characterized by its tunable biodegradability, and excellent biocompatibility properties. Recently, we have constructed SF-based nano-enabled drug delivery carriers, in which doxorubicin (Dox) and atovaquone (Ato) were encapsulated with Arg-Gly-Asp-SF-Polylactic Acid (RSA) to form micellar-like nanoparticles (RSA-Dox-Ato NPs). The RGD peptide was decorated on micellar-like nanoparticles, promoting tumor accumulation of the drug. Meanwhile, Ato, as a mitochondrial complex III inhibitor inhibiting mitochondrial respiration, would reverse the hypoxia microenvironment and enhance chemotherapy in the tumor. In vitro, the biopolymer alone showed extremely low cytotoxicity to 4T1 cell lines, while the RSA-Dox-Ato demonstrated a higher inhibition rate than other groups. Most significantly, the ROS levels in cells were obviously improved after being treated with RSA-Dox-Ato, indicating that the hypoxic microenvironment was alleviated. Eventually, SF-based targeted drug carrier provides biocompatibility to reverse hypoxia microenvironment in vivo for enhancing chemotherapy, strikingly suppressing tumor development, and thereby suggesting a promising candidate for drug delivery system

A Hybrid Model to Predict Localised Cracks of Reinforced Concrete Slabs in Fire

This paper presents a robust hybrid finite element procedure for predicting the large individual cracks within reinforced concrete floor slabs at elevated temperatures. For modelling the cracks formations and propagations within the floor slabs, the smeared crack model is used for modelling early stages of crack evolution, and then the ‘delayed extended finite element method (D-XFEM) is proposed for capturing individual big cracks within the floor slabs. The new model has been validated against previous fire test results. A series of parametric studies has been conducted on a composite floor to understand the influences of different protection conditions of the support steel beams on both global responses and cracking patterns of the composite floor under fire conditions

Structural behavior of concrete-filled steel tubular (CFST) with spherical cap gap subjected to corrosion and long-term tensile loading

Concrete-filled steel tubes (CFSTs) are commonly used as structural specimens in construction. Gaps between the steel tube and enclosed concrete core can form during manufacture or repair procedures. This study developed a computational model to investigate the structural implications of spherical cap gaps in CFSTs subjected to sustained axial tension and chloride-induced corrosion. Finite element analysis (FEA) incorporated appropriate material constitutive laws and elements. Model predictions closely matched experiments for load-displacement response and ultimate capacity. Parametric comparisons between gap and no-gap geometries quantified performance impacts, including reduced stiffness, deteriorated load transfer, internal force redistribution, and diminished flexibility stemming from localized steel tube buckling adjacent to the unrestrained gap. Outcomes highlight the importance of quality control during CFST production and repair to minimize defects like uncoupled zones between the concrete infill and hollow tube. The validated simulation approach provides an efficient tool for exploring gap influences and informing structural design provisions

Design, Simulation, and Experimental Verification of a Destruction Mechanism of Transient Electronic Devices

To quickly destroy electronic devices and ensure information security, a destruction mechanism of transient electronic devices was designed in this paper. By placing the Ni-Cr film resistance and the energetic material between the chip and the package and heating the resistance by an electric current, the energetic material expanded and the chip cracked. The information on the chip was destroyed. The author simulated the temperature distribution and stress of the power-on structure in different sizes by ANSYS software. The simulation results indicate that the chip cracks within 50 ms under the trigger current of 0.5 A when a circular groove with an area of 1 mm2 and depth of 0.1 mm is filled with an expansion material with an expansion coefficient of 10−5°C−1. Then, the author prepared a sample for experimental verification. Experimental results show that the sample chip quickly cracks and fails within 10 ms under the trigger current of 1 A. The simulation and experimental results confirm the feasibility of the structure in quick destruction, which lays the foundation for developing instantaneous-failure integrated circuit products to meet information security applications