CTL Model Update for System Modifications

Model checking is a promising technology, which has been applied for verification of many hardware and software systems. In this paper, we introduce the concept of model update towards the development of an automatic system modification tool that extends model checking functions. We define primitive update operations on the models of Computation Tree Logic (CTL) and formalize the principle of minimal change for CTL model update. These primitive update operations, together with the underlying minimal change principle, serve as the foundation for CTL model update. Essential semantic and computational characterizations are provided for our CTL model update approach. We then describe a formal algorithm that implements this approach. We also illustrate two case studies of CTL model updates for the well-known microwave oven example and the Andrew File System 1, from which we further propose a method to optimize the update results in complex system modifications

Experimental investigation on the composite effect of steel rebars and macro fibers on the impact behavior of high performance self-compacting concrete

In this study, the impact behavior of ten types of high performance self-compacting concrete (HPSCC) was explored using the drop-weight method. The HPSCC specimens were reinforced with steel rebars and different fibers for comparison with plain concrete. The reinforcement mechanism of the influences of steel rebars and different fibers on failure impact energy was explained. The composite effects of hybrid use of steel rebars with different fibers on the failure impact energy were also compared. The penetration depth for each mixture was analyzed. Test results showed that the macro fibers could greatly improve the failure impact energy both in plain and reinforcement concrete. Moreover, the toughness, penetration depth, stress redistribution could be improved obviously due to the positive hybrid effect of rebars and macro fibers in reinforced concrete. The statistical analysis technique was introduced to evaluate the experimental data, and the goodness of fit tests showed that the distribution of the blow numbers to the first crack and up to the final failure followed the two-parameter Weibull distribution.The authors gratefully acknowledge the National Natural Science Foundation of China: Grants: 51578109 and 51121005.DUT and Fundação para a Ciência e a Tecnologia(SFRH/BPD/22680/2005).info:eu-repo/semantics/publishedVersio

Effect of steel fiber on the crack permeability evolution and crack surface topography of concrete subjected to freeze-thaw damage

This paper describes the steel fiber effect on the crack permeability and crack surface topography of concrete subjected to freeze-thaw damage. The sequential crack permeability of steel fiber reinforced concrete are investigated by a vacuum permeability set-up. The topographical analysis is applied on the crack surface by an invented 3-D laser scanning equipment. The results show that the crack permeability of concrete is less than the value predicted by the Poiseuille flow model and their difference decreases gradually with the crack widening. With increment of steel fiber dosage and freeze-thaw damage level, the effect of steel fiber on reducing the crack permeability becomes strong. Topographical analysis illustrates that both steel fiber and freeze-thaw damage enhance the roughness of concrete crack surface. The relationship between roughness number of crack surface and material permeability parameter α follows an exponential function, which can be employed to quickly estimate the crack permeability of concrete.National Natural Science Foundation of China (Grant: 527 51578109

Effect of macro polypropylene fiber and basalt fiber on impact resistance of basalt fiber‐reinforced polymer‐reinforced concrete

First published: 07 April 2020In this paper, the effect of macro non-metallic fibers (i.e. polypropylene fibers and basalt fibers) on the impact response of basalt FRP-reinforced concrete discs is experimentally investigated using a self-developed drop-weight impact test device. The plain concrete and conventional steel reinforced concrete samples are explored as references. The impact resistance and failure behaviors are analyzed. Statistical analyses for first-crack strength and failure strength are performed. The composite effect of basalt FRP bars and macro non-metallic fibers on the impact energy at failure is also compared. The results indicate that the behaviors under impact load, i.e. failure strength, crack number, the indent diameter and penetration depth of the shriveled area, are greatly improved by adding of macro non-metallic fibers, in particular macro polypropylene fibers. Additionally, the incorporation of these fibers into the basalt FRP-reinforced concrete transforms the brittle failure mode into a well ductile failure mode. Two-parameter Weibull models are fitted by graphical methods and used to characterize the first crack strength and failure strength distributions. Reliability functions for first crack strength and for failure strength are estimated and failure strength can be predicted from first-crack strength by using a linear regress model. The hybrid use of basalt FRP bars and macro non-metallic fibers demonstrates a positive synergetic effect on the impact energy at failure.The authors gratefully acknowledge the National NaturalScience Foundation of China (Grant: 51578109), the Por-tuguese Funds through FCT, within the Project UID/MAT/ 00013/2013

Experimental study and prediction model for flexural: behavior of reinforced SCC beam containing steel fibers

Seven full-scale steel fiber reinforced self-consolidating concrete (SFRSCC) beams were tested to study the effects of macro steel fibers on the flexural behavior of reinforced self-consolidating concrete beams. The major test variables are fiber contents and longitudinal reinforcement ratios. The ultimate load, midspan deflections, steel reinforcement strains, crack width and crack spacing were investigated. The enhanced ultimate flexural capacity and reduced midspan deflection due to the addition of steel fibers were observed. With the increasing of fiber contents, the strain in longitudinal reinforcement, crack width and crack spacing decreased significantly. The possibility of using steel fibers for partial replacement of the conventional longitudinal reinforcement is estimated, which is meaningful for extending the structural application of SFRSCC. A method incorporating fiber contribution to the post-cracking tensile strength of concrete in the flexural analysis of SFRSCC beam is also suggested. Comparisons are made between the suggested model and the fib Model Code 2010 model with experimental data. The results showed that the suggested model can estimate ultimate flexural capacity accurately.National Natural Science Foundation of China: Grants: 51078058 and 51121005

Effect of fibers on the temperature field and radialdeformation behavior of self-compacting concrete pipesunder cyclic fire condition

In this paper, the radial deformation of fiber reinforced self-compacting con-crete (SCC) pipes under cyclic fire conditions is studied. A series of experimen-tal study on the temperature fields and radial deformation properties of steelmesh, polypropylene fiber (PP fiber), and macro steel fiber (SF) reinforcedSCC pipes subjected to fire is carried out. A novel method for measuring thedeformation of pipes under high temperature has been proposed. The resultsindicate that both micro PP fiber and macro SF are effective in decreasing thetemperature difference and reducing the radial deformation in each thermalcycle. A significant positive synergistic effect on decreasing the residual radialdeformation can be achieved by combined use of macro SF and micro PP fiber.The elastic theory is used to estimate the elastic portion in the total radialdeformation, and the elastic radial deformation is about 22.3% of the maxi-mum radial deformation in the first thermal cycle. Based on the elastic calcula-tion and observed experimental results, a simplified method for estimating themaximum radial deformation in the first thermal cycle is proposed.National Natural Science Foundation of China, Grant/Award Number: 5157810

Topographical analysis of fractured surface roughness of macro fiber reinforced concrete and its correlation with flexural toughness

Macro fibers reinforcement is considered to be an effective way to improve the flexural toughness of the concrete. With growing public interest in the wide-spread use of fiber reinforced concrete (FRC), the need for understanding and evaluating micro fiber reinforcement mechanism is on the rise. In this study, concretes were reinforced by various dopant amounts of macro polypropylene (PP) fiber or steel fiber (SF) or their mixtures, topographical analysis was applied on a fractured concrete surface by using a custom-built 3-D laser scanning equipment, and the tested surface was fractured by using a three-point bending beam test. The topographical analysis results were evaluated quantitatively by roughness parameters of roughness number (RN), fractal dimension (D), standard deviation of height distribution (σz), and arithmetic mean deviation of the surface topography (Ha). Multivariate analysis suggests the most effective of roughness number (RN) for evaluating the roughness of fractured surface. Furthermore, the RN of fractured surface was further correlated to the flexural toughness of the concrete, the relation between the fractured concrete surface roughness (RN) and flexural toughness follows an exponential function, which can be employed to quickly estimate its roughness of fractured surface by flexural toughness of the FRC. In conclusion, from the developed topographical analysis method, the hybrid fibers reinforced concrete shows the most significant improvement of the flexural toughness of the concrete, which suggests hybrid fiber reinforcement shall be a future solution for commercialization of the FRC in terms of high toughness and high durability.National Natural Science Foundation of China (Grant: 51578109

Shear behaviour of steel fibre reinforced self-consolidating concrete beams based on the modified compression field theory

A series of steel fibre reinforced self-consolidating concrete (SFRSCC) beams have been tested to investigate the influence of steel fibres and the combined effect of fibres and stirrups on the deflection and cracking, ultimate loads and failure pattern. The experiment indicates that the shear strength increases clearly with the increasing of fibre content. The combination of steel fibres and stirrups demonstrates a positive composite effect on the ultimate load, ductility and failure pattern of concrete beam. This study also examines the feasibility of applying the modified compression field theory (MCFT) for the suitable assessment of shear resistance in fibre and steel rebar reinforced self-consolidating concrete beams. For fibre reinforced concrete member, a theoretical method is proposed based on the MCFT. The proposed ultimate shear capacity model was verified by the comparison with different test results.FCT and National Natural Science Foundation of China

Concrete with triphasic conductive materials for self-monitoring of cracking development subjected to flexure

In this study, the macro steel fiber (SF), carbon fiber (CF) and nano carbon black (NCB) as triphasic conductive materials were added into concrete, in order to improve the conductivity and ductility of concrete. The influence of NCB, SF and CF on the post crack behavior and conductivity of concrete was explored. The effect of the triphasic conductive materials on the self-diagnosing ability to the load–deflection property and crack widening of conductive concrete member subjected to bending were investigated. The relationship between the fractional change in surface impedance (FCR) and the crack opening displacement (COD) of concrete beams with conductive materials has been established. The results illustrated that there is a linear relationship between COD and FCR.National Natural Science Foundation of ChinaThe authors acknowledge the National Natural Science Foundation of China (Grant: 51578109), the National Natural Science Foundation of China (Grant: 51121005), and Fundaçãopara a Ciência e a Tecnologia (SFRH/BPD/22680/2005 ), the FEDER Funds through “Programa Operacional Factores de Competitividade - COMPETE" and by Portuguese Funds through FCT-within the Projects PEst-CMAT/UI0013/2011 and PTDC/MAT/112273/2009