Research on Crushing Concrete Members by High-Voltage Pulse Discharge Technology

High-voltage pulse discharge (HVPD) is an energy-saving, efficient, and green technique, which has broad prospects in concrete crushing. The finite element models of the concrete beam, slab, and column segments were established with ANSYS/LS-DYNA finite element software. Based on the principle of equal impact pressure, the shock wave generated by the fuse explosion caused by HVPD of 50 kJ is equivalent to the impact load of explosive blasting, and the stress of concrete beam segment was analyzed. The finite element models of the concrete beam sections were established to investigate the influence of diameter and spacing of the holes on the crushing effect of concrete beam segments. The width × height of each beam segment is 400 mm × 800 mm, and there are six types of beam segment length: 600 mm, 700 mm, 800 mm, 900 mm, 1000 mm, and 1100 mm. Two holes are drilled vertically on the surface of the width × length of each beam segment. The spacing of holes corresponding to beam segments of each length type is 200 mm, 300 mm, 400 mm, 500 mm, 600 mm, and 700 mm, respectively. The hole depth of each beam segment is 650 mm, and there are three types of aperture: 30 mm, 50 mm, and 70 mm. The analysis results show that the crushing effect of concrete beam segments increases with the increase of aperture and the decrease of hole spacing. According to the crushing effect of the beam segments, the aperture of 50 mm, the spacing of 400 mm, and the hole end (edge) spacing of 250 mm were determined as the optimal hole layout scheme. The finite element models of concrete slabs and columns were established. The square concrete slab thickness is 140 mm and side length is 700 mm, 800 mm, and 900 mm, respectively. Double-row holes were arranged in the slabs and the aperture is 50 mm and the hole spacing is 200 mm, 300 mm, and 400 mm, respectively. The section sizes of concrete columns are 500 mm × 500 mm, 600 mm × 600 mm, and 700 mm × 700 mm, respectively, and the aperture is 50 mm and the hole distance is 400 mm. According to the results of analysis, the optimal hole distribution scheme of concrete slab and column is chosen as the aperture of 50 mm and hole distance of 400 mm. The principle of the layout of multirow holes is that the spacing of row is not more than 400 mm, and the margin is not more than 250 mm.

Discussion on the Measurements in Cantilever Construction with Guyed Hanging Basket

Guyed hanging basket is qualified with reasonable structure , great carrying ability and clear construction process, and also can provide a good operating space for beam segment construction. Applying cantilever pouring construction with guyed hanging basket should be the development direction of the construction of large-span reinforced concrete cable-stayed bridge. By taking the girder construction of the grand bridge over Beijing-Hangzhou Canal as an example, this paper introduces the measurements in cantilever construction with guyed hanging basket, aiming at providing reference for other similar projects.

DYNAMIC ANALYSIS OF PRESTRESSED CONCRETE BOX-GIRDER BRIDGES BY USING THE BEAM SEGMENT FINITE ELEMENT METHOD

A beam segment element formulation is presented for the dynamic analysis of prestressed concrete box-girder bridges, which can conveniently takes into account the effects of the restrained torsion, distortion, transverse local deformation, diaphragms, and prestressing tendons of prestressed concrete box-girder bridges. The spatial displacement field of the beam segment element is directly represented by the nodal degrees of freedom of the corner points. The stiffness matrix and mass matrix of such a segment element are formulated based on the principle of stationary total potential energy in elastic system dynamics. The proposed beam segment element formulation is then implemented to carry out the free vibration analysis of a real case prestressed concrete box-girder bridge. In terms of both natural frequencies and mode shapes, the formulation is verified by the three-dimensional (3D) finite element analysis using a commercial package. It is demonstrated that the proposed beam segment element formulation is suitable and efficient for the dynamic analysis of prestressed concrete box-girder bridges with the advantages of less element numbers and enough accuracy. It is expected that this methodology can be an effective approach for the further dynamic response analysis under all kinds of dynamic loads such as earthquakes, winds, vehicles, and their interaction.