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Cracks, faults, or damages are serious threat to the current and future performance of the system. For decades, research work is being carried out on the dynamic behavior of the structural elements for fault diagnosis. The modern types of damage detection methods use the dynamic response from the signals of the beams. In this article, a robust fault diagnostic tool based on clonal selection algorithm and fuzzy logic has been proposed. Theoretical and finite element analyses are done to model the crack and to find the effect of the presence of cracks changes on the vibrational characteristic (natural frequencies) of a fixed–fixed beam. The inputs to (Clonal Selection Algorithm-Fuzzy Logic) system are the first three relative natural frequencies and the outputs from the system are the relative crack depth and relative crack location. Experimental validations with the theoretical results have been carried out to check the robustness of the predicted algorithm. [ABSTRACT FROM AUTHOR]

Experimental study on thin-walled welded steel beam-to-column connections under cyclic large plastic strain loading was conducted. Severe shear buckling in panel zones was observed during the testing. The connections have stable and excellent seismic performance, and finally failed due to the post-buckling ductile fracture. This paper aims to numerically simulate the post-buckling ductile cracking process using a proposed micro-mechanism based ductile fracture model, and further investigate critical factors, such as equivalent panel zone width-to-thickness ratio, axial load ratio and initial geometrical imperfection, that affect cracking behaviors of the connections. The cyclic ductile fracture model is verified with the experimental data, and employed to conduct the parametric analyses. Deterioration of stress-carrying capacity is also considered, so the fracture model can successfully simulate the load decrease in the load-displacement curves of the experimental results. [ABSTRACT FROM AUTHOR]

Thin-walled cold-formed steel beams are investigated with existing experimental data and shell finite element simulations to characterize their in-plane moment-rotation behavior, up to and past peak strength, in local or distortional failure modes. Although ultimate strength prediction of cold-formed steel members is generally well addressed in design codes, pre- and post-peak member stiffness is only partially addressed; while member ductility and post-peak moment-rotation response suffers from a lack of any clear guidance. Without fundamental information on cold-formed steel moment-rotation/curvature response, i.e. the backbone curve, system modeling for cold-formed steel structures to collapse remains severely hampered. Existing data on cold-formed steel beams are used as the basis for the study conducted herein. Simplified moment-rotation models, motivated from ASCE 41 characterizations, defined with pre-peak flexural rigidity degradation, post-peak plateau and strength drop are explored by equating the area under the backbone moment-rotation response (energy) between the available data and simplified models. In-plane response of cold-formed steel beams is parametrized with new design expressions depending on local and distortional cross-section slenderness. This research provides work for potential incorporation into design standards such as ASCE 41 and AISI S100. Out-of-plane response of cold-formed steel beams, including lateral-torsional buckling, remains as needed future work. [ABSTRACT FROM AUTHOR]

In designing a steel beam, one of the limit states is lateral torsional buckling. The value of the bending moment limit is called the critical moment. AISC specification only provides formulas for calculating the critical moment in prismatic beams, but not for non-prismatic beams like castellated beams. The objective of this paper is to study the lateral torsional buckling of castellated beams. The method used for this study is the collapse analysis using the finite element method, analyzed by ADINA 8.9. In the collapse analysis, a geometrically imperfect beam is loaded with an increasing load. At a certain value of the load, the lateral displacement increases progressively. The value of the maximum load is considered to be the critical load. In this study, the imperfection is taken 1/1500 of the unbraced length of the beam. The critical moment of castellated beam obtained from the finite element analysis is up to 42.31% lower than the critical moment of full beams with the same dimension calculated by using the AISC formula. Therefore, the correction factor for AISC formula to calculate the critical moment of the castellated beam is established. [ABSTRACT FROM AUTHOR]

This paper presents the fracture characteristics of cracked wide-flange steel girders (W18-W40, W460-W1000 in metric) strengthened with carbon fiber-reinforced polymer (CFRP) sheets. A broad range of parameters are considered to study their effects on the crack-tip stress intensity of the girders: flange-to-web area ratios, crack depth-to-height ratios, CFRP-to-steel area ratios, CFRP-to-steel modular ratios, and CFRP-bond widths. A three-dimensional finite-element approach is proposed and validated with a previously conducted experimental program. A total of 1,240 models, i.e., 40 unstrengthened and 1,200 strengthened girders, are used to evaluate the crack-tip behavior of the W-shape girders. The response surface-regression analysis procedures (RSREGs) are used to develop correction factors for the stress intensity of the girders. Stochastic simulations are conducted to probabilistically understand the vulnerability of the cracked girders and evaluate the efficacy of CFRP strengthening in terms of reducing stress intensity. [ABSTRACT FROM AUTHOR]

The load carrying capacity in a damaged steel beam can be substantially increased through repairing by attaching Fiber-Reinforced-Polymer (FRP) plates to tension flange. Such a repaired beam is generally failed by either debonding of the FRP plates from the steel flange or FRP rupture at the damage location due to the stress concentration. In this case, the effectiveness of repair significantly depends on the repairing material properties, i.e. FRP and adhesive. This paper developed a Finite Element (FE) modeling of damaged steel beams repaired with FRP plates, and aimed to clarify the FRP and adhesive properties effects on beam recovery. The primary defect was simulated by inserting a notch through the tension flange at mid-span. To ensure the validity of the proposed numerical model, the results of numerical models were compared with those existing experimental works. A parametric study was performed to achieve a better understanding on the sensitivity of parameters which are responsible for flexural behavior of the repaired beams. Studies showed that the in fluence of the most investigated parameters on the response of the repaired beam is very notable, and considering influential parameters in choosing the material for a FRP-repair leads to promising results in design consideration. [ABSTRACT FROM AUTHOR]

Load structure, the maximum permissible load is usually determined by the strength calculation (bearing data. Yield stress or strength of the material), or the parameters of fracture mechanics. The paper analyzes the calculations lamellar cracks formed in the lower crane girders steel belts. These cracks are formed in rolled sheets of non-metallic inclusions. The determination of the cracks in the existing designs are extremely difficult. It requires testing metallographic, ultrasonic or acoustic methods. Based on typical images of metallographic steel plates specified place of occurrence of cracks lamellar and sampling, and has subsequently been adopted for the calculation of numerical models of material structure and distribution of artificial joints. In order to analyze the propagation of cracks and formation of lamellar phase slots and destruction was carried out modeling studies and numerical methods cracking process. [ABSTRACT FROM AUTHOR]

Reinforced concrete (RC) slabs on the steel girders of old highway bridges occasionally get damaged. Various repair methods for damaged deck slabs have been developed and adopted on site. A new method for repairing damaged RC slabs, deck restoration by adhesive panels (D-RAP), was developed, in which double layered prefabricated panels are glued on the top surface of the concrete by means of epoxy resin mortar. It is not clear how the system behaves under static and dynamic load. Various tests were performed on the mechanical behavior of beams and slabs reinforced by this method. Fatigue tests of full-scale model slabs were also carried out on two alternative points. It was found that the D-RAP method increased the load-carrying capacity and fatigue strength up to the level of newly constructed slabs. The test results show that the D-RAP method is an effective reinforcing method for deteriorated slabs. [ABSTRACT FROM AUTHOR]

The author discusses the problem faced by bridge owners due to cracking in bridges as caused by the distortion-induced fatigue in web gaps of steel girder bridges. Topics discussed include use of retrofit technique for creating load path between transverse connection plate and the flange of the girder, use of bolted angles on sides of the transverse connection plate and a backing plate, and use of autonomous robotic nondestructive evaluation platform for assessment of concrete bridge decks.