Portal frame

About: Portal frame is a research topic. Over the lifetime, 1778 publications have been published within this topic receiving 7210 citations.

Application of Fracture Mechanics to Concrete Bridges. Finite element analyses and experiments

Abstract: Material models based on fracture mechanics together with non-linear finite element analyses have been used in combination with experiments to study the behaviour of reinforced concrete bridges. The work covers two aspects of interest in the design of concrete bridges. * The shear behaviour was studied in full-scale tests on two highway bridges. The capacities of the bridges were compared with the shear capacities according to the design model in the Swedish concrete code. Non-linear finite element analyses were performed on one of the bridges tested. * The reinforcement detailing in frame corners was studied and the alternative of splicing the reinforcement within the corners of a frame bridge was examined in three test series. Non-linear finite element analyses were performed for some of the specimens tested. The objective of the study was to obtain greater knowledge of the behaviour of concrete bridges for these two aspects, as well as to find out how analyses based on fracture mechanics can be used to improve understanding of this behaviour. A background to the fracture mechanics for concrete and to the models used in the analyses is given. The results of the full-scale shear tests indicate that the design model for shear can predict the capacity for typical shear failures. However, when a combination of shear and moment actions leads to failure, the test results revealed shortcomings in the design models in the Swedish concrete code. A finite element analysis based on the discrete crack approach was performe d successfully up to initiation of the final failure; the analysis showed that the inclined crack leading to failure was initiated at mid-height of the bridge slab. The tests on frames and frame corners included both monotonic and cyclic loading. Reinforcement detailing suitable for portal frame bridges, and also detailing suitable for civil defence shelters, was studied. The test results did not uncover any drawbacks related to splicing of the reinforcement in the frame corners. Some of the test specimens were analysed using a material model for concrete based on fracture mechanics and the smeared crack approach. The finite element analyses were found to reflect the mechanical behaviour of the specimens tested throughout the failure process; the analysis results were in good agreement with the test results. The results from both the analyses and the tests support the idea that it should be feasible to splice the reinforcement within the corner area of a frame bridge. The use of fracture mechanics and non-linear finite element analyses has been shown to be a most powerful tool which, together with a limited number of tests, can increase understanding of the failure process in reinforced concrete structures.

Eccentric steel brace retrofit for seismic upgrading of deficient reinforced concrete frames

Abstract: The paper presents a simplified static force-based procedure for seismic retrofit design of RC frames using internal eccentric steel braces (ESBs), connected to long beam at distance of L/8 from beam ends, to enhance seismic resistance of the frame. The technique uses the linear static procedure given in ASCE 7-16 for calculation of appropriate design base shear for frame analysis, and the AISC 360-16 seismic provisions for preliminary design of steel braces. Response modification factor R was derived based on simplified kinematics of rigid frame response and flexure hinging of link beam, to reduce the elastic base shear force for lateral load analysis of frame and design of steel braces. This shifts plastic hinges from columns, and reduces joint shear deformation, by means of capacity protected braces and beam shear. The procedure was used for the preliminary design of ESB retrofitting technique for a two-story RC frame, employing hollow box steel sections. Quasi-static cyclic tests were performed on both as-built and ESB retrofitted portal frame panels under multiple-levels of lateral displacements demands. The tests performed on frames were analysed to understand the damage mechanism and retrieve the essential seismic response properties: force–displacement capacity curves, hysteretic cyclic response and hysteretic damping, and to establish performance-based story drift limits. The experimental data was used to calibrate finite element based nonlinear numerical models in SeismoStruct. Nonlinear static pushover analysis of considered two-story ESB retrofitted frame was carried to quantify structure ductility and response modification factors. The preliminary design was verified through nonlinear time history analysis (NLTHA) for both design base earthquakes and maximum considered earthquakes. Proposed seismic design of ESB retrofit for multi-stories RC frames having three to six stories has been presented and verified through NLTHA. It indicates the promising behaviour of ESB retrofit technique as well as the efficiency of the proposed simplified design procedure.

Three-Dimensional Modeling of Steel Portal Frame Buildings

Abstract: The realistic strength and deflection behavior of industrial and commercial steel portal frame buildings are understood only if the effects of rigidity of end frames and profiled steel claddings are included. The conventional designs ignore these effects and are very much based on idealized two-dimensional (2D) frame behavior. Full-scale tests of a 12×12 m steel portal frame building under a range of design load cases indicated that the observed deflections and bending moments in the portal frame were considerably different from those obtained from a 2D analysis of frames ignoring these effects. Three dimensional (3D) analyses of the same building, including the effects of end frames and cladding, were carried out, and the results agreed well with full-scale test results. Results clearly indicated the need for such an analysis and for testing to study the true behavior of steel portal frame buildings. It is expected that such a 3D analysis will lead to lighter steel frames as the maximum moments and deflections are reduced.