Papers by Keyword: Limit State

Abstract: There is a need to determine the stresses value for responsible designs in the oil and gas refining, petrochemical and chemical industries, at which the defect reaches its maximum size. This stress value can be taken as the limit state criterion for strength calculations of vessels and apparatus. The article presents a technique for determining the limit state criterion for carbonaceous and low-alloy steels using the example of steels C1020 and A 516-55 in the state of delivery. As a limit state criterion it is proposed to use the stress value corresponding to the microcrack formation moment. The studies are based on the uniaxial tension tests results at room temperature of flat samples with V-shaped stress concentrators of 2 mm deep, accompanied by an acoustic emission nondestructive testing method. Based on the obtained pulse amplitude and pulse energy dependences on time in the process of testing and fractographic studies, a technique for estimating acoustic emission signals was developed to determine the microcrack formation moment for test steels. Stress values that can be taken as the limit state criterion for steels C1020 and A 516-55 in the delivery state for strength calculations vessels and apparatus are determined using the developed experimentally technique based on the high-amplitude acoustic emission to low-amplitude signals ratio. With the help of specimen fractures fractographic analysis the legitimacy of using the developed technique is justified. Thus, at room temperature for steel C1020, the stress at which a microcrack begins to form is 420 MPa, for steel A 516-55 it is 455 MPa.

Abstract: Deformations of an I-section steel beam under equal end moments are studied in this article. Initial geometric imperfection of the beam axis was introduced according to the Eurocode standard. Numerical studies have shown that the lateral deflection of slender beams under major axis bending can be relatively high. The acceptability of high values of lateral deflections within the framework of the serviceability limit state is discussed. In the next part of the paper, the limit value of maximum deflection was introduced as a fuzzy number. Fuzzy analysis of the maximum moment, which causes maximum deflection, was performed. The slenderness values of beams for which the serviceability limit state is the limiting condition for design were identified.

Abstract: The presented paper deals with the load-carrying capacity analysis of compress steel members having the square closed (box) cross-section with non-dimensional slenderness 0.6, 0.8, 1.0 a 1.2. The axis of these beams is randomly three-dimensionally curved. Initial curvatures are modelled by random fields applying the LHS method. Load-carrying capacities are then calculated by the geometrically nonlinear solution using the ANSYS program. The results are presented both in form of histograms and of the table. The analysis of load-carrying capacity of beams with individual nonlinear slenderness is carried out, and the values are compared with the values of design load-carrying capacity according to the standard.

Abstract: Experimental verification of structural members can be the necessary part of the structural design of load-carrying civil structures, mainly in the period of last two decades. In some cases, the knowledge obtained from the tests is the sole source of the reliable information about actual behaviour of structural member in strain and failure process and about its objective load-carrying capacity. The paper is specifically aimed at the control experimental verification of roof decking based on thin-walled metal profiled sheets. Loading test has been performed during structure erection, as additional resource for the verification of actual behaviour and objective load-carrying capacity and for the confirmation or refinement of static design assumptions and results, within the ultimate and serviceability limit states. The subject of the control experimental verification was roof decking composed of thin-walled metal cassettes with thermal insulation at its upper side, used for the university lecture room roofing.

Abstract: Based on the limit equilibrium theory and the failure model of the soil nailing structure, used the circular slice method and the geometric relationship of circular sliding surface with the center of the circle to derive the stability coefficient formula. The most dangerous slip surface was searched by genetic algorithm. To establish the reliability analysis function through the stability coefficient formula. Finally, the reliability calculation of engineering examples, compared the results with the Monte Carlo method, the reliability analysis method was reasonable and valid.

Abstract: The probabilistic characteristics of the seismic performance indices for the compression-bending reinforced concrete columns were studied, which is important for the Performance-Based Seismic Design (PBSD) and seismic performance evaluation of civil engineering structures. First, five damage states with four limit states were defined for the seismic performance level of ductile reinforced concrete components, along with the strain limit definition for each limit state. Then, based on the mechanical behavior and statistical characteristics of reinforcement and concrete, the deformation characteristics of circular reinforced concrete ductile component were analyzed probabilistically for each performance level. Hereby the probabilistic distribution characteristics of the performance indices for each performance level were obtained, and the regression formula as well as its probability distribution model for the performance index of each performance level was proposed, which can be used in the probabilistic analysis of seismic performance of civil engineering structures.

Abstract: By using gray theory model, the problem with less data and poor information is easy to be solved. Thus, the grey theory and the reliability assessment method were connected to analyze the mechanism motion. At first, the concept and model of mechanism’s grey movement reliability were presented. And then, from the limit state equations of a mechanism’s moving function and kinematic accuracy, the gray reliability calculation formulas were deduced. Finally, combined with two examples the method was applied to the actual reliability analysis. The results show that the method is feasible and efficient, so it is practical to apply the grey reliability model in mechanism reliability analysis.

Abstract: A probabilistic model is used to assess the structural reliability of typical reinforced concrete masonry walls under combined shear and compression. Factors such as model error, shear strength of concrete masonry, wall aspect ratio, horizontal and vertical reinforcement ratios, structural safety class, axial load-to-dead ratio, height and thickness radio of the wall, and load effect combination will be considered. Based on a relatively large number of test results and theoretical analysis from the literature, the limit state equation for shear bearing capacity was established. A sensitivity analysis will be performed to identify the key contributors to the reliability of the masonry walls under the combination of gravity and earthquake. The results will provide a base to evaluate whether consistent safety is achieved for masonry walls that are subjected to different load combinations. The counteracting load factors in current design codes for masonry structure will be investigated.

Abstract: According to risk analysis theory, a model of analysis for failure risk of upstream revetment of existing levees is proposed in this paper. Based on the model, the load effect and generalized resistance for the failure risk of upstream revetment of existing levees are analyzed, and then the influencing factors of the failure risk of upstream revetment are studied. The calculation results show that the proposed model is workable and effective for analysis of the failure risk of upstream revetment of existing levees, and the main factors influencing failure risk of existing upstream revetment are the randomness of the existing effective thickness of upstream revetment and ratio mean of upstream slope of the existing levees.

Abstract: The performance of resisting foundation displacement of a typical single return circuit transmission tower under all kinds of load conditions including foundation horizontal displacement, foundation vertical uneven downward displacement was analyzed by finite element modeling. Results showed that stability failure of single steel angle represents tower’s limit state under foundation displacement. And the corresponding foundation displacement limits were calculated. Results indicate that foundation pull condition is more dangerous than press condition. Under complex foundation displacement conditions, foundation horizontal displacement is primary factor leading to stability failure of towers. Under foundation press condition and pull condition, wind load is primary factor. Result also indicates that, tower does not fail when foundation displacements are smaller than 1.25% (under foundation press condition and pull condition) or 0.5% (under single foundation sink condition) of tower root distance.