MECHANICAL BEHAVIOR OF HORIZONTAL SWIVEL SYSTEM WITH UHPC SPHERICAL HINGE UNDER SEISMIC ACTION

In the process of rotation, the total weight of the bridge structure is jointly supported by the spherical hinge and the supporting structure, and its lateral stability is poor. It is easy to lose stability under the action of dynamic loads such as seismic action effect. The present paper takes a 10,000-ton continuous rigid frame swivel bridge as the re-search object, analyzes the dynamic response of the seismic action to the horizontal swivel system, and establishes several structure simulation models. Eighteen seismic waves in three directions that meet the calculation requirements are screened for time history analysis and compared with the response spectrum method. Finally, an optimization algorithm for the seismic response of the bridge under horizontal swivel system is proposed based on the mode superposition method. The UHPC spherical hinge bears all the vertical forces and 20% of the bending moment caused by the seismic action, the support structure bearing the remaining 80% of the bending moment. The optimization algorithm proposed in this paper features high accuracy.

Dynamic Modeling and Frequency Characteristic Analysis of a Novel 3-PSS Flexible Parallel Micro-Manipulator

Dynamic modeling and frequency characteristic analysis of a novel 3-PSS (three-prismatic-spherical-spherical) flexible parallel micro-manipulator with three translational DOF in space were investigated in this paper. Firstly, the kinematics analysis was developed based on the pseudo-rigid body model. The Jacobian matrix and the relationship between the micro angular deformation of the flexible spherical hinge and the end pose of mobile platform were respectively obtained by employing vector closed-loop method and coordinate transformation method. Then, taking into account the elastic strain energy of the flexible spherical hinge, dynamic model of this mechanism was established via Lagrange equations, and the expression of natural frequency was further derived. Combined with a set of given parameters, natural frequencies of the system were calculated by using MATLAB software. For the comparison purpose, a simulated modal analysis of the mechanism with the same parameters was also performed by employing finite element ANSYS software. Results from numerical calculation and finite element simulation indicated that maximum error of their natural frequencies was 2.71%, which verified the correctness of the theoretical dynamic model. Finally, variations of natural frequencies with changes of the basic parameters were analyzed. Analysis results show that natural frequencies increase with the increase of the bending stiffness kbm of flexible spherical hinge and the difference in radius Er between static platform and mobile platform, while decrease with the increase of the length l of the link rod and the masses of the main components of mechanism. Besides, it can be further drawn from these obtained results that the natural frequencies increase with the increase of the angle θl between the link rod and the z axis of reference coordinate system. Considering that the increase of the stiffness kbm and the angle θl will reduce the scope of working space, it is recommended in designing the structure to choose a set of larger stiffness kbm and angle θl as much as possible under the premise of satisfying the working space.

On the subject of influence of dissipative and constant of moments on the stability of uniform rotations of non-free two elastically connected gyroscopes of Lagrange

The conditions for asymptotic stability of uniform rotations in a resisting medium of two heavy Lagrange gyroscopes connected by an elastic spherical hinge are obtained in the form of a system of three inequalities. The bottom gyroscope has a fixed point. The rotation of the gyroscopes is maintained by constant moments in the inertial coordinate system. The influence of the elasticity of the hinge on the stability conditions is estimated. It is shown that for a sufficiently high rigidity of the hinge, the asymptotic stability conditions are determined by only one inequality, which coincides with the inequality obtained for the case of a cylindrical hinge. When the angular velocities of the gyroscopes' own rotations coincide, this inequality coincides with the well--known condition for one gyroscope. Cases of degeneration of an elastic spherical hinge into a spherical inelastic, cylindrical and universal elastic hinge (Hooke's hinge) are considered. For the Hooke hinge, it is shown that there is no asymptotic stability at a sufficiently high angular velocity of gyroscopes rotation.

Study on Design of Concrete Box Girder of A Railway Swivel Cable-Stayed Bridge

A swivel cable-stayed bridge over the existing railway is a span across the existing railway. The recommended scheme for the main bridge is (128 + 388 + 128) m steel mixed composite beam swivel diagonal pull bridge with span. The cables of the diagonal pull bridge are arranged according to the fanshaped central double cable plane, taking into account the mechanical performance and aesthetics. The bridge structure adopts semi floating system. The concrete swivel diagonal pull bridge is adopted in the comparison scheme. The design of the bridge is three spans and (138 + 268 + 138) m prestressed concrete box girder is adopted. The cables are arranged according to the central double cable plane, and the bridge composition adopts the consolidation system. Considering the needs of bridge operation and maintenance in the later stage of the bridge, when the dead weight of concrete diagonal pull bridge is within the ideal range, the concrete swivel diagonal pull bridge can be preferred. In order to calculate the dead weight of the selected bridge, the author uses the finite element software to model the whole bridge and calculate the weight of the bridge. The results show that the dead weight of the concrete swivel diagonal pull bridge is too large, which has exceeded the maximum bearing capacity of the existing spherical hinge. In order to continue to use the concrete swivel diagonal pull bridge scheme, it is necessary to optimize the design of the concrete swivel diagonal pull bridge scheme.

Investigation on Moisture Damage Prevention of a Spherical Hinge Structure of a Swivel Bridge

As a key component of a swivel bridge, the spherical hinge is a steel-concrete structure, which is susceptible to moisture damage during waiting time. In this paper, spherical hinge moisture damage prevention is investigated comprehensively from two aspects of impermeable concrete and steel-concrete interface waterproof coating. Three impermeable concretes were prepared and tested by the compressive strength test, splitting tensile test, four-point bending test and the impermeability test. The test results illustrated that addition of cementitious capillary crystalline active masterbatch (CCCAM) and polypropylene fiber (PP) could improve the toughness and brittleness of concrete. The addition of CCCAM was an effective technique for improving the permeability of concrete. However, the incorporation of PP and CCCAM at the same time cannot improve the impermeability of concrete. This may be because the chaotic support structure formed by PP prevents the infiltration and uniform dispersion of CCCAM. A waterproof coating consolidation performance test was proposed to quantify the interface bond strength of waterproof coatings and assess the impact of temperature, moisture and freeze-thawing cycles on consolidation performance of waterproof coatings. The test results showed that temperature had a significant effect on the interface consolidation property of waterproof coatings and the optimal dosage of SBS modified asphalt (SBS), polyurethane (PLT) and unsaturated polyester resin (UPLS) waterproof coating is 1.18kg/m2, 0.95kg/m2 and 1.15kg/m2, respectively. Moreover, it was found that PLS waterproof coating maintained excellent properties in complex environment. This is because PLS has excellent shear strength and rubber characteristics, and it can form a hard–soft–hard transition layer between the concrete and steel, reducing the impact of environmental factors.

Experimental Study on Improving the Compressive Strength of UHPC Turntable

Purpose. In the recent years, horizontal rotation methods have been widely used for bridge construction, particularly for constructing overpass bridges on highways, railways, and shipping. However, bridges constructed using the swivel construction method bear several types of loads during the rotation process. Furthermore, the bridge turntable, which is the core force-bearing component of the structure, bears considerably large vertical pressure and horizontal frictional resistance. The present research proposes three strengthening methods when applying ultrahigh performance concrete (UHPC) materials to the turntable of a spherical hinge to improve structural reliability. Furthermore, the mechanical properties of the structure are evaluated using a unidirectional compressive strength test to provide a theoretical and experimental basis for the application of the UHPC material. Design/Methodology/Approach. To evaluate the mechanical performance of the turntable of a spherical hinge, scale models of six sets of UHPC turntables—steel tube-UHPC, stirrup-UHPC, and directional steel fiber UHPC—were constructed in the study. The compressive strengths of the turntable specimens were calculated after theoretical analysis. After obtaining the load-displacement curves of the cube specimens, the force characteristics of the turntable and the failure mechanism of the structure were analyzed by observing the failure mode of the specimens. Findings. The compressive strength of the steel tube-UHPC turntable was 207 MPa, which can completely replace the traditional steel turntable. In addition, the stirrup-UHPC turntable demonstrated a significant loading effect. However, the effect of the restraint radius of the stirrup needs to be considered during the design; otherwise, the loading effect is poor. Furthermore, a directional steel fiber UHPC turntable can improve the compressive strength to a certain extent. We summarize the failure mechanism of the spherical hinge turntable specimens that are expected to play a role in UHPC spherical hinge in engineering applications and construction monitoring. Originality/Value. To the best of our knowledge, this study is the first to employ the UHPC, steel tube-UHPC, stirrup-UHPC, and directional steel fiber spherical hinge turntables in the swivel construction of bridges. The compressive strength and mechanical characteristics of the UHPC structure meet the requirements of the turntable, and more importantly, the manufacturing process (on-site pouring) of the aforementioned UHPC turntable structures is relatively simple. Finally, the manufacturing cost of the turntables is expected to be reduced by more than 50% compared to those of traditional turntables.