Geometric nonlinear formulation of plate buckling structure

The analytical or exact mathematical formulation of stresses and displacements for plate buckling structure become impossible to develop if the plate geometry is so complicated. Numerical technique is one another approach to solve this problem and it is chosen in this study for plate structure under in-plane and out-plane load. The formulation of elastic stiffness matrix (ke) and geometric nonlinear stiffness matrix (kg) of the plate structure due to buckling is presented and based on virtual displacement principle. The geometric nonlinear stiffness matrix (kg) is found function of internal stresses. The direct iteration technique is applied to find nodal displacements. Under this technique, the Gauss points stresses are initialized as zeros, then the kg matrix is updated, and then a new nodal displacement vector is found for the next approximation of internal stresses. Iterative process is done until convergence of displacement is satisfied. The rectangular plate with one fixed edge supported is used to test the proposed nonlinear formulation and procedure. The compressive in-plane load and moment is considered and applied for the tested plate. The plate is discretized with appropriate number of triangular finite element mesh. It is found that, the convergence of displacement is satisfied by using direct iteration technique. The load - deflection curve shows nonlinear relationship and approach to critical load. This finding shows that the direct iteration method can be accepted for the analyzing of plate buckling by considering geometric nonlinear assumption

Comparative structural performance of diagrid and bracing system in mitigation of lateral displacement

The design of high rise building with more than 10 stories is controlled by lateral drift which increases the cost rapidly with the number of stories. Recently, the diagrid structural system has emerged and in fact has been widely used for high rise buildings. How effective is a diagrid system in mitigating the lateral displacement of a high rise building? Thus, the objective of this research is to compare the lateral displacement of high rise building that adopts diagrid system with those that use X-bracing and frame system, due to wind. This research also explored the effect of using diagrid, X-bracing and frame system to the natural frequency of high rise building. Two diagrid systems which are 60°-diagrid and 80°-diagrid that has an angle of inclination of 60 degrees and 80 degrees, respectively, were studied. STAAD Pro software was used to analyse twelve building models to determine the lateral displacement due to wind load and the natural frequency in the along wind, across wind and torsional directions. Building with 80°-diagrid has the least lateral displacement, followed by buildings with the X-bracing, 60°-diagrid and frame for 40 and 60 storey buildings. Further study showed that X-bracing became the most effective system to lower the lateral displacement compared with the diagrid and frame when the number of storey of the building exceeds 71 storeys. Natural frequency was not affected by the different systems used except for torsional natural frequency that increased substantially by the use of 60°-diagrid

Diagnostic utility of electrocardiogram in screening patients post-COVID-19: a prospective multicentre follow-up study

BackgroundThe role of ECG in ruling out myocardial complications on cardiac magnetic resonance (CMR) is unclear. We examined the clinical utility of ECG in screening for cardiac abnormalities on CMR among post-hospitalised COVID-19 patients.MethodsPost-hospitalised patients (n = 212) and age, sex and comorbidity-matched controls (n = 38) underwent CMR and 12‑lead ECG in a prospective multicenter follow-up study. Participants were screened for routinely reported ECG abnormalities, including arrhythmia, conduction and R wave abnormalities and ST-T changes (excluding repolarisation intervals). Quantitative repolarisation analyses included corrected QT (QTc), corrected QT dispersion (QTc disp), corrected JT (JTc) and corrected T peak-end (cTPe) intervals.ResultsAt a median of 5.6 months, patients had a higher burden of ECG abnormalities (72.2% vs controls 42.1%, p = 0.001) and lower LVEF but a comparable cumulative burden of CMR abnormalities than controls. Patients with CMR abnormalities had more ECG abnormalities and longer repolarisation intervals than those with normal CMR and controls (82% vs 69% vs 42%, p ConclusionPost-hospitalised COVID-19 patients have more ECG abnormalities than controls. Normal ECGs, including normal repolarisation intervals, reliably exclude CMR abnormalities in male and female patients