Nunzio Scibilia

Strength and Ductility of Hollow Circular Steel Columns Filled with Fibre Reinforced Concrete

Publisher Summary This chapter investigates the behavior of hollow circular steel cross-sections filled with Fiber Reinforced Concrete (FRC), subjected to monotonic loads. The casting of different types of composite members—steel columns, steel columns filled with Normal Strength Concrete (NSC), and steel columns filled with Fiber Reinforced Concrete (FRC) was employed. The columns were tested in uniaxial compression utilizing a universal testing machine operating in displacement control. The maximum strength of composite members filled with FRC was 20% higher than that recorded for steel pipes filled with FRC. After the peak load was reached, failure was due to the crushing of concrete and due to local and global buckling of the steel pipes. The vertical loads of the composite members were obtained by considering of the steel pipes and concrete core to strength, without any reduction in the transverse cross-section of the concrete core, because of the effective confinement reached in concrete inside steel pipes. In the case of FRC, the buckling effects were reduced by the presence of fibers and failure was due to essentially plasticization of materials ensuring a good prevision of experimental results with the analytical model based on these concepts. In the case of steel pipes filled with plain concrete, the buckling effects reduced the bearing capacity of the columns in the softening branch.

Long-Term Structural Deficiencies in a Mat Foundation on Clay Soil

AbstractA 3-story building with a mat foundation consisting of a slab on a grid of grade beams performed poorly on clay soil. Cracking of the slab became progressively worse as a result of the incorrect design and fluctuations in the groundwater pressure under the foundation. The cyclic presence and absence of water rusted the steel reinforcement, and the sulfates in the clay soil caused formation of ettringite in the concrete. Plastic hinges formed in the slab and settlements occurred, causing damage to the beams. The situation is still in progress and may lead to the collapse of the structure under normal service conditions. The geotechnical and structural investigations performed to survey and assess the aforementioned problems are described in this paper. The causes and the consequences of the detected anomalies are analyzed, and a prediction of potential future structural problems is provided. A strengthening procedure is proposed, and an estimate of the cost to realize it is provided. Recommendation...

Retrofitting of existing steel MR-frames by encasing the columns

Summary The study concerns the behaviour of steel MR-frames subjected to vertical and lateral forces, not properly designed according to capacity design criteria, and upgraded by means of encasing the steel columns with concrete having different grade. The purpose of the paper is to examine if the proposed technique allows one to adequately increase the lateral stiffness and the resistance of the frames. Pushover analyses on multi-storey frames are performed trough a non-linear calculus program, able to take into account of the second order effects. The behaviour of frames with encased columns was compared with those of the bare frames, highlighting that with the proposed technique it is possible to locate the plastic hinges at the ends of the beams, out of the joint. Moreover, it is possible to ensure at the system enough lateral stiffness and strength for the requirements of the limit state damage and to achieve adequate global ductility for a good seismic behaviour. Keywords : steel frames, encased columns, strengthening techniques, push-over analysis, ductility.