Middle Span Research Articles

Dynamic responses of metal foam sandwich beam under repeated impacts considering impact location and face thickness distribution

Owing to the excellent mechanical performance, the metal foam sandwich structures have potential applications in the design of protective equipment, which can improve the impact resistance of engineering structures. In this paper, the nonlinear finite element model is employed to investigate the dynamic behaviors of metal foam sandwich beam (MFSB), and the accuracy of the finite element method is verified by repeated impact tests. In addition, the effects of impact location and face thickness on the dynamic behavior of the MFSB are examined. Results show that, as the distance from the impact position to the middle span of the beam increases, the deflections of face sheets decrease gradually, and the loading and unloading stiffness increases. The thickness of front face sheet affects the depth of indentation, while the total thickness of the front and back face sheets decides the overall deformation, loading and unloading stiffness. Overall, as the impact number increases, the influences of impact location and face thickness on the dynamic behavior of MFSB enhances gradually.

Application and Practice of Variable Axial Force Cable in Powerhouse Truss Reinforcement System

Long-span steel structure trusses are widely used in factory buildings. However, with the increase in service time and dynamic load fatigue, transverse cracks at the bottom of the middle span and oblique deformation of the abdomen during the operation process may appear in a considerable part of long-span trusses with dynamic load. The U-shaped cracks at the bottom and belly, as well as the mid-span down deflection of the main truss, can also reduce the functionality of the factory building truss structure and limit the original crane load, thus affecting the normal safety and durability of the structure. Therefore, the principle of variable axial force cable system in the long-span factory building truss structure and 3D3S software modelling were applied. Analysing and studying the reinforcement method of large-span powerhouse trusses can provide practical experience for subsequent similar projects. In view of the above phenomenon, the large-span powerhouse trusses of Hongcheng Powerhouse No. 1 and No. 2, located in Tonglu, Zhejiang Province, were used as the research objects, and the variable axial force cable method was proposed to strengthen and lift the load. Considering the span of the powerhouse truss, a cable system with 22 m and a controlling force of 400 kN was proposed for Powerhouse 1, and a cable system with a variable axial force of 24 m was proposed for Powerhouse 2. The force model of large-span trusses was established by using the finite element method, which is commonly used to analyse the force of the truss. The influence of the reinforcement effect was analysed under two working conditions and compared from three aspects: stiffness, bearing capacity and stability. Furthermore, the phenomenon of uneven stress distribution was analysed. The stress distribution characteristics of each node were understood by simulating the most disadvantageous node plates with the greatest internal force before and after reinforcement.

Multi-objective optimization of aerodynamic and erosion resistance performances of a high-pressure turbine

Focusing on a high-pressure turbine, this study conducts a multi-objective optimization aimed to improve its aerodynamic and erosion resistance performances. With a self-adaptive updated Kriging model first applied, the Latin hypercube sampling method and NSGA-II algorithm are then used to find trade-off solutions. The sensitivity analysis shows that the efficiency is mainly influenced by the flow angles near trailing edges of three selected blade spans, among which the flow angle near the trailing edge of middle span is the most significant, followed by the root span and tip span, while the dominant design parameters affecting the erosion are the flow angles near trailing edges of middle span and tip span. After optimization, the erosion around the middle span on pressure side and middle chord on suction side is significantly reduced due to the decrease of impact velocity and impact frequency, and the increase of impact angle. Besides, the low-velocity fluid regions near the pressure side of middle span and the trialing edge of tip are greatly reduced, which can relieve the blockage of flow passage. At all axial sections considered, the optimized blade is shown to significantly reduce losses near the tip and suction side, especially at 80% axial section.

Intelligent safety assessment method for demolition construction of closure segment of long-span continuous rigid frame bridges

In order to clarify the risk of demolition construction of large-span continuous rigid structure bridge and put forward an intelligent safety assessment method to ensure the safety of demolition construction of the closure segment. Taking a concrete continuous rigid bridge as an example, this paper uses the combination of finite element analysis, theoretical calculation and actual measurement verification to study the influencing parameters and construction safety assessment methods of the long-span continuous rigid bridge in the demolition construction stage of the closure segment. The results show that the parameters that have a great influence on the stress state of box girder and pier during the demolition stage of the closure segment are mainly the self-weight of the structure, tendon prestress state and construction temperature difference. Through the influence envelope analysis of each parameter, it is clear that the ultimate failure mode caused by the most unfavorable parameter combination in the demolition stage of the closure segment is the crushing of the bottom plate of the box girder in the middle span, and the cracking of the piers on the side span at the top and the variable section. In order to further accurately evaluate the construction safety in the demolition stage of the closure segment, based on the long-term down-warping state inversion analysis of the box girder, the identification method of cross-section damage and prestress loss of the box girder and the calculation results of engineering examples are given. Finally, a safety assessment method of the most unfavorable section based on the principle of influence matrix is proposed. Through the analysis of an example, the safety of the closure segment demolition construction is clarified, and the correctness of the analysis is verified by intelligent monitoring means.

Hybrid Test of Precast Concrete Frame with Energy-Dissipation Cladding Panel System

To investigate the influence of an energy-dissipation cladding panel system (EDCPS) on the dynamic responses of a precast concrete (PC) frame structure, a six-story, three-span planar frame structure with an EDCPS (called “damping structure”) and a counterpart planar bare frame structure (called “bare frame structure”) were designed. The middle span and bottom two stories of the frame were selected as the test substructures, whereas the rest were considered using the numerical substructure. Hybrid tests were conducted on the two structures under four earthquake levels. The test results indicated that the damage evolution characteristics of the PC frame were not affected by the introduction of EDCPS. The dampers in the EDCPS successfully yielded and dissipated seismic energy under the four earthquake levels. Moreover, the maximum inter-story drift ratio of the damping structure was reduced by 12.59%, 17.68%, and 10.34% under the design-basis earthquake, maximum considered earthquake, and very rare earthquake, respectively, exhibiting a satisfactory damage-control effect. The cladding panels remained intact under the four earthquake levels, indicating that this structure effectively prevents damage to the cladding panels. Finally, a numerical simulation method is recommended according to the damage characteristics of the damping structure and is validated against the test data.

Full-scale computational fluid dynamics study on wind condition of the long-span Queensferry Crossing Bridge

To date, the majority of numerical modelling [computational fluid dynamics (CFD)] studies on long-span bridges have been carried out on scaled physical models, and without field-data for validation. For the first time, a full-scale bridge aerodynamic CFD study was conducted in this paper. A full-scale three-dimensional CFD model of the middle span and central tower of the Queensferry Crossing, United Kingdom, was created. The aim of this work was accurately simulating the wind field around the bridge. The CFD simulations were developed in OpenFOAM with the k − ω SST turbulence model. Atmospheric boundary layer inflows were configured based on wind profiles provided by a full-scale Weather Research and Forecasting (WRF) model. CFD predictions were validated with field data which were collected from an on-site Structural Health Monitoring System. The simulated fluctuating wind field closely satisfied the characteristic of field data and demonstrated that the modelling approach had good potential to be used in practical bridge aerodynamic studies. Meanwhile, comparisons and sensitivity analyses on mesh density provided a reference modelling approach for any future works on full-scale bridge aerodynamic models. Additionally, a cylindrical-like domain was applied in bridge aerodynamics for the first time and verified as being a convenient and reliable way to be used in bridge studies that involve changes in yaw angle.

Calculation of capacity of spillway № 2 Boguchanskoye HPP with free water overflow

The article considers a variant with the operation of spillway No. 2 of the Boguchanskaya HPP as the main spillway structure for the period of temporary operation of the hydroelectric complex. In the process of developing options for skipping construction costs, a calculation was made of the throughput with a free overflow through a flat threshold at the level of 167.0m at the FSL=175m and forcing the UVB to the level of 185.0 m with the damping of the flow energy in the water well. The task of the calculations is to obtain the discharge characteristics of the considered spillway option with the calculated flood hydrograph with a probability of 0.2%. At the same time, based on the throughput capacity of the spillway No. 1, the dependence of the turbine flow rate and the water depth in the downstream, as well as the transformation of the flood of a given probability, the estimated flow rate is 5500 m3/s, the maximum head H=18 m (determining) at a minimum threshold level of 167.0 m. Weir refers to weirs with a wide threshold. The throughput capacity of the spillway No. 2, operating in the free overflow mode, was determined. The change in the lateral compression coefficient depending on the head for the middle and outer working spans is considered. The outlines of free-falling jets behind the culverts operating in the free overflow mode are obtained, which makes it possible to refine the outlines of the side walls of the spillway.

Structural Design and Mechanical Properties of a Plate-Shell Structure Bridge

PDF HTML XML Export Cite reminder Structural Design and Mechanical Properties of a Plate-Shell Structure Bridge DOI: 10.59238/j.pt.2023.01.006 Author: Affiliation: (1.Department of Bridge Engineering, Tongji University, Shanghai 200092, China;2.Tongji Architectural Design (Group) Co., Ltd., Shanghai 200092, China) Clc Number: Fund Project: Article | Figures | Metrics | Reference | Related | Cited by | Materials | Comments Abstract:The main bridge of Quzhou Academy Bridge is a V-shaped rigid frame bridge with a hanging hole, the span arrangement is 75 m+150 m+75 m=300 m, the middle span hanging hole was provided with a 60 m steel box girder, and the V-leg structure and the main beam are all prestressed concrete box girders with variable height. Due to the need for bridge landscapes and pedestrian viewing platforms, the large extension arc V-leg structure extends 6 m to each side of the bridge deck, and the total width is 41 m. It was necessary to consider the stress effect of the shell in the longitudinal and transverse directions. The stress and deformation of the shell in two directions are analyzed by using the finite element method solid model, and the difference between the solid model and the frame model is compared in detail. Finally, the overall structure was analyzed and checked in the modified simplified frame finite element model. Reference Related Cited by

Study on the Adaptability of Vehicle Loads in Special Lanes for Trucks on Highway Bridges

To study the adaptation of the current automobile design load of highway bridges in China in case of separation of passenger cars and trucks, a statistical method is proposed in this paper to study the load data of special lanes for trucks. Four typical truck‐based lanes were selected as the study object, from which information of continuous truck fleet was selected as the study of truck‐specific lane load flow samples, and technical parameters of truck vehicles were determined. Finally, the load flow was introduced into simply supported bridges and continuous bridges of different spans, and the load effect at the control section was calculated and compared with the effect of the design load at the control section according to the current code. The results show that under the operation mode of “passenger car and truck separation,” when the truck fleet passes through the simple support beam, the load effect at the control section generally does not exceed the effect of the vehicle load calculated according to the code design load. When the truck fleet passes through the continuous beam, the midspan bending moment of the continuous beam side span and the midspan bending moment of the middle span do not exceed the effect of the vehicle load calculated according to the code design load. However, the bending moment effect of the continuous beam support section exceeds the effect of the vehicle load calculated according to the design load of the code. To ensure the safety and durability of the bridge structure, the proposed lane load standard value is increased by 1.1 times and rounded up from the current Highway Bridge and Culvert Design Code.

Flexural design of restraining panels in buckling-restrained steel plate shear walls considering high-order buckling modes

Buckling-restrained steel plate shear wall (BRSPSW) is one kind of excellent energy dissipating member. The inner steel plate in BRSPSW usually works with high-order buckling modes to resist lateral force under the buckling restrained effect of outer restraining panels. However, current design of the restraining panels is commonly based on simplified uniform-loaded plates without considering the effect of the high-order buckling modes, which may result in unsafe designs. In this paper, the high-order buckling modes in BRSPSW and their influence on the flexural design of the restraining panels were studied. Finite element (FE) models that can accurately simulate the out-of-plane interaction behavior of BRSPSW were developed and verified by existing test results. The numerical results show that the high-order buckling of the steel plate leads to a series of inclined strip-shaped stress regions on restraining panels. When the parameters of BRSPSW are varied in common range, the positive and negative bending moments of the restraining panel under the strip-shaped force are 9.6 and 2.8 times those under the uniform force, respectively. The differences between the bending moment of the restraining panels under strip-shaped force and that under uniform force become larger as the spacings of the strip-shaped stress regions increase. Furthermore, the spacings of the strip-shaped stress regions increase with the decrease of the height-to-thickness ratio of the steel plate and the increase of the gap between the steel plate and the restraining panel. Two fitting formulas of the positive and negative moment amplification factors considering the effect of the high-order buckling modes are proposed to design the restraining panels safely. Additionally, a simplified model and bending moment equations of the restraining panels in BRSPSW are suggested. To avoid the excessive negative bending moments occurring at side supports of the restraining panel, the ratio of cantilever length to middle span is suggested to be not more than 0.4.

TESTING OF HOLLOW-CORE END NOTCHED FLOOR SLAB

This paper examines the test results of a hollow-core reinforced concrete prestressed end-notched floor slab of formwork formation subjected to uniformly distributed load.
 The research of the end-notched slab was carrying out in the testing hall of the State Enterprise "State Research Institute of Building Structures" according to the procedure of standard DSTU B B.2.6-7.
 Vertical uniformly distributed load was applied to the end-notched slab with cross-rails and support fixtures for loading, with hydraulic jacks and pumping station equipped with force meter.
 The end-notched slab was subjected to step-by-step loading with load steps of 100 kgf/m2.
 Inspection of the surface of the end-notched slab in the test area, with recording in the register of measurement results of displacements and potential damages was carried out after every loading step.
 Vertical displacements of the end-notched slab corners were measured with four clock type indicators ICH-10. Vertical displacements of the middle slab span were measured with two deflectometers 6PAO. The middle span deflection of the end-notched slab was calculated considering corner displacements.
 Based on the results of research, it was established that before applying the load of 800 kg/m2 there were not detected cracks the opening width of which exceeded the limit values.
 The loss of loadbearing capacity of the end-notched slab was detected after the load of 1280 kgf/m2, which which exceeded the design load by 1.6 times. The end-notched slab collapsed due to loss of shear resistance.
 According to the test results, it was established that hollow-core reinforced concrete prestressed end-notched floor slab meets the requirements of strength, stiffness and crack resistance.

Seismic response analysis of long-span continuous girder bridge considering fluctuating friction of bearing

Under the combined action of horizontal and vertical earthquakes, separation-pounding of bridge beam ends and bearings occurs, which adversely affects the overall mechanical behaviour of any bridge. Based on D'Alembert's principle, this study proposes a theoretical analysis method to verify the separation of bridge beam ends and bearings, which is substantiated by the measured data. A three-span continuous steel-box-girder bridge was selected as the research object, and finite element models (FEMs) using the bilinear bearing and friction bearing models were established. The numerical models were verified by comparing the simulation results with the theoretical calculations. A comparative study on the seismic response of continuous girder bridges with different bearing models was conducted, and it was found that the friction bearing model is better for simulating the whiplash effect of long-span continuous girder bridges. The results indicate that the peak pounding force generated by the separation of the beam end and bearing is 1.74 times the weight of the beam end. Moreover, the whiplash effect causes the tension and compression stress states of the side span of the main beam to reverse and drastically reduce the compressive stress of the middle span by 70%. Finally, it is recommended that the friction bearing model which is able to realistically simulate the seismic response of the bridge more accurately be used to simulate bearings with large axial force fluctuations.

Seismic performance of precast concrete frame with energy dissipative cladding panel system: Half-scale test and numerical analysis

An energy dissipative cladding panel system was proposed for large precast concrete cladding panels in multi-story buildings. A six-story, three-span planar prototype frame structure with energy dissipative cladding panel was designed to evaluate the seismic performance and damage control effects of the precast concrete frame with the proposed energy dissipative cladding panel system. The bottom two stories of the middle span were selected as the test substructure and were tested under cyclic loading. The damage evolution mode and seismic performance of this structure were identified. A numerical simulation method was recommended for such a structure based on the damage characteristics observed in the two-story substructure, and validated against the test results. The seismic responses of the six-story prototype frame structure with and without the energy dissipative cladding panel were then compared through nonlinear time-history analyses under near- and far-field ground motions. The analysis results indicated that the maximum inter-story drift ratios of the precast concrete frame with energy dissipative cladding panel were 23.8%–35.2% and 19.8%–41.6% lower than those of the bare precast concrete frame under far- and near-field ground motions, respectively. The maximum inter-story drift ratios of the precast concrete frame with energy dissipative cladding panel under near-field motions were 1.72 and 1.76 times those under far-field motions under the maximum considered and very rare earthquakes, respectively.

Optimization of vascular structure of self-healing concrete using deep neural network (DNN)

In this paper, optimization of vascular structure of self-healing concrete is performed with deep neural network (DNN). An input representation method is proposed to effectively represent the concrete beams with 6 round pores in the middle span as well as benefit the optimization process. To investigate the feasibility of using DNN for vascular structure optimization (i.e., optimization of the spatial arrangement of the vascular network), structure optimization improving peak load and toughness is first carried out. Afterwards, a hybrid target is defined and used to optimize vascular structure for self-healing concrete, which needs to be healable without significantly compromising its mechanical properties. Based on the results, we found it feasible to optimize vascular structure by fixing the weights of the DNN model and training inputs with the data representation method. The average peak load, toughness and hybrid target of the ML-recommended concrete structure increase by 17.31%, 34.16% and 9.51%. The largest peak load, toughness and hybrid target of the concrete beam after optimization increase by 0.17%, 14.13%, and 3.45% compared with the original dataset. This work shows that the DNN model has great potential to be used for optimizing the design of vascular system for self-healing concrete.

Flexural Behavior of RC Beams with an Abrupt Change in Depth: Experimental Work

The most crucial components in the case of roofs with two levels or a variable floor height are variable depth beams. In order to investigate the flexural behavior of reinforced concrete (RC) beams with varying depths under static loads, experimental research was conducted. Under the four-point bending flexural test, two reference beams with constant depth, six dapped beams at the soffit, and four dapped beams at the top were tested. For all beams with a 150 mm depth, a 100 mm increase in depth occurred at the middle span of the beams. The primary characteristics included the impact of increasing depth, the impact of stirrups’ absence and their various ratios, and the characteristics of the longitudinal bars at the locations of sudden depth changes in either the top or bottom bars. Both the cracks’ progression and the load-deflection relationship along the beam’s length were observed. The ultimate carrying load (Pu) was reduced by 23.56% and 27.35% as a result of the 100 mm increase in the half-span of the beam over the constant depth in case of changes at the top and soffit, respectively. The Pu was increased by a ratio ranging from 20.9% to 31.35% for the bottom dapped beams and by a ratio of 29.79% for the top dapped beams due to the various stirrup ratios in the dapped area. The ductility was significantly impacted by the elevated stirrup ratios in the dapped area. The predicted results and the experimental results matched when the Pu of the tested beams was evaluated using the strut and tie model.

Hub aspiration strategies and flow loss analysis of a shock-in type supersonic compressor rotor with negative inlet pre-whirl

Large-scale corner separation is one of the key factors that limit the performance improvement of high-load compressors. In this paper, the hub aspiration method was applied to a supersonic shock-in type compressor rotor with negative inlet pre-whirl to suppress the hub corner separation. Six suction schemes composed of aspiration slots with different locations and orientations have been designed and numerically tested. The results revealed that the aspiration location is better to be placed starting from the post-shock point and extending to the deep separation zone. The streamwise slot satisfying such conditions could effectively suppress corner separation but narrows the rotor stable mass flow range by increasing the pitchwise secondary flow. The circumferential skew slot could exactly remedy such defects. The streamwise slot combined with a downstream skew slot is the optimal aspiration strategy that effectively improves the rotor performance without reducing mass flow range. At the design and near-stall operating point, the rotor efficiency (EF) and total pressure ratio (TPR) could be improved by 1.3% and 5.0%, 3.3% and 7.2%, respectively. Consequently, the stall margin was increased by 2.0%. According to the flow loss analysis, the combined aspiration scheme mainly alleviated losses from hub to middle span by reducing the shock strength and the magnitude of separation as well as its radial migration. But in the tip region, it strengthened the leakage flow and its interaction with shock waves, thus increasing the flow losses.

Effects of parameters on vertical porosity distribution in pervious concrete

The vertical porosity profile of pervious concrete (PC) is dictated by various mix design parameters, including aggregate/cement (a/c) ratio, compaction type and effort. In the presented work, an attempt was made to reveal the profound impacts of these parameters on porosity and strength. Vertical profile analysis using image processing techniques revealed that a zone approximately 10–15 mm thick with high porosity was observed at the top and bottom ends of a cylindrical PC core (13–20% of total PC thickness in total). Total porosities in that zone were 20–42% and 35–60% for lower and higher a/c ratios, respectively. The middle span of 120–130 mm of the vertical profile showed porosity variations of 5–15% and 30–45% for low and high a/c ratios, respectively. Overall, the a/c ratio and compaction effort manifested a profound impact on the vertical porosity profile. Compaction types showed trivial impact on porosity and compressive strength properties of PC for a/c ratios from 3.0 to 5.0. The authors recommend that the findings of this study would help to obtain the required porosity profile in PC without compromising strength characteristics.

Influence of fiber dispersion and distribution on flexural tensile properties of asphalt mixture Based on finite element simulation

• Basalt fibers can improve the low temperature crack resistance of asphalt mixture. • The Weibull distribution can approximately describe the fiber distribution in basalt fiber asphalt mortar. • Better reinforcement can be achieved by well dispersed basalt fibers. • The spatial distribution of fibers truly influence the flexural tensile properties of asphalt mixture. This study aims to reveal the relationship between the uneven distribution characteristics of basalt fibers and the flexural tensile performance of asphalt mixture. Nano Computed Tomography(nano-CT) was used to explore the realistic distribution features of basalt fibers in asphalt mortar. In addition, the distribution fitting and goodness of fit tests were carried out to find out the distribution form that can well describe the distribution of basalt fibers. The three-dimensional fiber models with different distribution forms were established in finite element software ABAQUS. Then the three-point bending test was simulated to analyze the influence of fiber dispersion and distribution on the flexural tensile properties of the asphalt mixture. Simulation results show that the asphalt mixture beam model shows better tensile resistance when the fibers are better dispersed. Moreover, when more basalt fibers are at the bottom of the middle span, it is more conducive to reducing the peak stress at the bottom of the beam and delaying the cracking of the asphalt mixture.

The Analysis of Type L Joint Precast Beam Concretea

Research precast beam type L shape has produced strength of flexure where it was jointed at middle of span with L shape. Problem was about strength and deflection with joint of Type L shape. Aim of this research was determined strength of flexure such deflection and maximal load would be apllicated. Precast beam type L shape consist of two beam P1 and P2 were tested at two point load was applicated. This research have produced of data of precast beam P1 and P2. Precast beam P1 has deflection 28,44 mm at maximum load 11,21 Ton. Precast beam P2 has deflection 26,71 at maximum load 11,76 Ton. Except that data, has produced also chart of load versus deflection where precast beam type L shape has behavior less for ductility approximately du/dy 1,17, where deformation inelasticity was not seem. That occur because overlapping at joint of precast concrete at middle of span.

Parameter Optimization and Bending Performance Analysis of a Corrugated Steel Plate-UHPC Composite Bridge Deck with PZ Shear Connectors

Composite bridge decks consisting of steel plates and concrete are used to minimize fatigue cracking and damage of asphalt pavement of orthotropic steel bridge decks subjected to wheel loads. This paper presents a methodology to optimize the parameters and mechanical performance of a corrugated steel plate-ultrahigh-performance concrete (UHPC) composite bridge deck with panel zone (PZ) shear connectors using the improved non-dominated sorting genetic algorithm (NSGA-II). A 3-D finite element model is established in ANSYS Workbench software to conduct numerical parameter analysis, and ABAQUS software is used to analyze the optimized model’s mechanical performance. The results show a significant improvement in the mechanical performance of the optimized composite bridge deck, with a 27.66% decrease in the maximum stress in the UHPC layer. The vertical displacement of the optimized composite bridge deck increases sharply when the load reaches 90% of the ultimate load, and a significant change in the strain is caused by the sliding displacement between the UHPC layer and steel plate. The bottom part of the corrugation yields first in the middle span, followed by failures of the ribs. In addition, as the tensile stress increases, damage occurs first in the UHPC layer near the PZ shear connectors in the shear bending area and the bottom in the bending area, expanding significantly to the entire bending and loading areas. The results indicate that the parameter optimization of the corrugated steel plate-UHPC composite bridge deck using NSGA-II improves the structure’s bending performance.