A numerical analysis based on previous experiment has been carried out on T-shaped concrete-filled steel tubular columns subjected to constant axial compressive load and cyclic lateral loads. Tensile bar stiffeners were introduced to be welded on inside surfaces of steel tube to postpone its local buckling and to enhance the confinement of steel tube for concrete. A modified fiber-based method was developed to establish numerical modeling program of specimens' cyclic behavior, incorporating the effect of stiffeners on postponing steel tube's local buckling and the confinement for concrete. The reciprocating movement of inflection point along frame column is also considered in the numerical program. A simplified arc-length method was employed as iterative control algorithm of the numerical model. Horizontal load-displacement hysteretic curves of specimens were calculated with the numerical model and verified with test results. A restoring force model based on experimental investigation was proposed as simplified method for engineering practice.
A total of 11 L-shaped multi-cell concrete-filled steel tubular stub columns were fabricated and researched in axial compression test. The key factors of width-to-thickness ratio D/ t of steel plates in column limb and prism compressive strength of concrete fck were investigated to obtain influence on failure mode, bearing capacity, and ductility of the specimens. The test results show that the constraint effect for concrete provided by multi-cell steel tube cannot be ignored. The ductility decreases with the increase of width-to-thickness ratio D/ t of steel plates in column limb. The bearing capacity increases and the ductility decreases with the increase in prism compressive strength of concrete fck. A finite element program to calculate concentric load–displacement curves of L-shaped multi-cell concrete-filled steel tubular stub columns was proposed and verified by the test results. A parametric analysis with the finite element program was carried out to study the influence of the steel ratio α, steel yield strength fy, prism compressive strength of concrete fck, and width-to-thickness ratio D/ t of steel plates in column limb on the stiffness, bearing capacity and ductility. Furthermore, the design method of bearing capacity was determined based on mainstream concrete-filled steel tubular codes.
A new type of composite structure, the composite box girder with corrugated steel webs (CSWs) and trusses, is proposed recently. In order to investigate the structural behavior under positive and negative bending moments, flexural tests of the continuous girder were carried out, and the failure modes, deformation patterns, strain distribution, and development of the concrete cracks were investigated. Finite element analysis was conducted to investigate the effect of the range of concrete in the steel tube and the thickness of CSWs on the flexural behavior. The experimental and numerical results show that the test beam has a good ductility and integrity under flexural load. The contribution of CSWs to the flexural bearing capacity is very small and can be neglected. Besides, the plane section assumption is still valid when only top concrete slab and bottom steel tubes are concerned. The concrete filled in bottom steel tubes increases the stiffness and the bearing capacity of the girder. Equations to calculate the flexural bearing capacity under positive and negative bending moments were put forward and then verified with experimental results.
Corrosion products which occupy much greater volume accumulate, and generate expansive pressures on the surrounding concrete. The pressure builds up and eventually leads to the cover cracking of the structures. The cracking accelerates further corrosion and leads to the loss of the bond strength and the load carrying capacity. Corrosion cracking would reveal the reducing of the residual service life of the corrosion-affected structures. In this paper, an analytical model is proposed to predict the critical corrosion penetration at cover cracking in RC structures based on the crack process. An attempt has been made to develop the model by considering material properties of the surrounding concrete and expansive corrosion products. The problem is established as a boundary-value problem and the governing equations are expressed in terms of the radial displacement. The analytical predictions of the proposed model have also been in agreement with the available experimental data.
This paper analyzed the main interference sources and their influences on the operation of protection both in the smart substation and the traditional substation. The interferences could be suppressed by reducing radiation of the interference sources, blocking the coupling channel of common-mode interference, promoting the anti-electromagnetic interference ability of the sensitive circuit and designing the bleeder circuit rationally. A microcomputer protection has passed the EMC test successfully by adopting these measures.
The thermal stress field in the polysilicon was simulated and comparatively analyzed at different shapes of crucibes which have different types of a flat, a inverted-conical and concave bottom by COMSOL Multiphysics version 4.3a. The results indicated that: within the flat-bottomed crucible ,the isotherm in the crystal was slightly convex and the area of the maximum thermal stress was distributed in the bottom of the crystal edge and near the top of crystal edge; within the inverted-cone crucible, the isotherm in the crystal was straight and the area of the maximum thermal stress was only distributed in the bottom of the crystal edge; within the bottom of the concave crucible, the isotherm in the crystal was slightly concave and the area of the maximum thermal stress distributed in the bottom of the crystal edge was larger than that of the crystal within the first two kinds of crucibles. To sum up, the inverted-cone crucibe was beneficial to reduce the thermal stress distribution in the polysilicon which could provide theoretical guidance for improving the production process of the polysilicon.
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