Negative Moment Research Articles

Comparative study on flexural behavior of steel-UHPC composite beams and steel-ordinary concrete composite beams in the negative moment zone

To compare the flexural behavior of steel-UHPC (ultra-high performance concrete) composite beams and steel-ordinary concrete composite beams under a negative bending moment, 4 steel–concrete composite beams were tested under a negative bending moment. The effects of slab materials and stud number on flexural failure mode, crack development, stiffness ductility, cracking load and ultimate flexural capacity of composite beams were investigated. The results show that the UHPC can significantly improve the flexural behavior of steel–concrete composite beams under a negative bending moment. For the steel-UHPC composite beams with a single row, the cracking load is 135 % higher than that of steel-ordinary concrete composite beams, and the overall stiffness increased by 108 %, the yield stiffness increased by 40 %, the ultimate flexural capacity increased by 9 %, and the ductility increased by 133 %; for the steel-UHPC composite beams with double row, the cracking load is 102 % higher than that of the steel-normal concrete composite beam, the overall stiffness is increased by 34 %, the yield stiffness is increased by 44 %, the ultimate flexural capacity is increased by 6 %, and the ductility is increased by 75 %. Increasing the number of studs can significantly improve the overall ductility of composite beams, while the improvement of cracking load, overall stiffness, and ultimate flexural capacity of composite beams is not significant. The cracking load, overall stiffness, yield stiffness, ultimate load, and ductility of double-row stud steel–concrete composite beams are 23 %, 53 %, 13.2 %, 12 %, and 115 % higher than those of single-row stud steel–concrete composite beams, respectively; while those of double-row steel-UHPC composite beams increases by 6 %, 8 %, 16 %, 8 % and 62 % higher than those of single-row stud steel–concrete composite beams, respectively. A simplified calculation model for the flexural capacity of steel-UHPC composite beams in a negative moment zone was established.

Seismic performance of full-scale prefabricated semi-rigid bolted connection between RC column and composite beam

This paper presents a novel proposal for an assembled bolted joint between precast reinforced concrete (RC) column and steel-concrete composite beams, focusing on its seismic performance. To evaluate the joint's behavior, a comprehensive experimental investigation was conducted on a full-scale RC column to composite beam joint specimen subjected to pseudo-static loading. The study aimed to analyze the joint's failure mode, bearing capacity, ductility, and energy dissipation characteristics. The joint stiffness was assessed by analyzing the bending moment-rotation (M-θ) curve of the beam in accordance with the European standard BS EN 1993-1-8:2005. The experimental results demonstrate that the proposed assembled bolted joint exhibits semi-rigid behavior under positive moments and approaches rigidity under negative moments. To further enhance our understanding of the joint's performance, a finite element model was developed using ABAQUS. The stress distribution in each joint component, as well as the failure mode and ultimate bearing capacity, were analyzed in conjunction with the experimental results. Based on the findings from both the experimental and finite element analyses, an improved joint design is proposed. Additionally, parametric analysis was conducted on the enhanced joint configuration. The study findings indicate that the improved joint exhibits superior damage resistance, seismic performance, and enhanced assembly efficiency compared to the original design. This research contributes to the advancement of assembled bolted joints between precast RC columns and steel-concrete composite beams, offering valuable insights for practical applications in seismic regions.

Experimental study on fatigue behavior of UHPC joint in negative moment region of π-shaped steel–concrete composite beams

To improve the crack resistance of concrete bridge decks in the negative moment region of π-shaped steel–concrete composite beam, a novel ultra-high performance concrete (UHPC) joint was first proposed. Based on an actual bridge, a 1:2 scale model was then designed as the specimen. A fatigue test was conducted to investigate the variation of its structural properties during fatigue loading, and a static test was performed to evaluate its residual bearing capacity. The test results show that the new UHPC joint has good crack resistance under fatigue loading and can meet the engineering requirements. The stiffness of the specimen significantly decreases after 3 million fatigue cycles. However, without significant fatigue damage on the surface of specimen, plenty of stiffness is reserved. It is found that there is no significant slip between the concrete deck and steel girder, and between the UHPC and normal concrete in the static test after fatigue, indicating that the studs inside the π-shaped steel–concrete composite beam are arranged reasonably and the interaction of the overall structure is reliable. Furthermore, the ultimate bearing capacity of the specimen decreased by only 9.4% from its design value after being subjected to 3 million fatigue cycles. It is revealed that the application of UHPC in the composite beam effectively improves its crack resistance, resulting in a smaller reduction in bearing capacity. This paper can provide theoretical foundation for the preparation and application of the π-shaped steel–concrete composite beams with UHPC joints.

Fire and post-fire performance of blind-bolted concrete-filled steel tubular joints with restrained steel beams: Experiment and simulation

Blind-bolted connection is a type of new developed prefabricated beam-column connection, which can be used to connect the concrete filled steel tubular (CFST) columns and the steel beams easily. The static and dynamic performance of CFST column to steel beam joints with blind-bolted connections have been well explored, but limited research has been conducted to investigate the fire and post-fire performance of this type of composite joint. In this paper, a series of reversed T-shaped joint fire tests were conducted to investigate the fire and post-fire performance of blind-bolted CFST joints with axially restrained steel beams. The influence of restrained effect from adjacent members in the entire frame structure on the response of blind-bolted joints in and after fire could be reasonably considered by the reversed T-shaped joint fire test. The joint temperature, failure modes, beam and column displacements and temperature internal force development during the entire loading and fire stage were recorded and discussed. The test results indicated that the blind-bolted connections showed very good working performance in and after fire, and no bolt shank fracture or bolt pull-out failure was observed. Finite element analysis (FEA) models were established to simulate the fire and post-fire performance of blind-bolted CFST T-shaped joints with axially restrained steel beams, and the joint moment versus relative rotation angle relationship curves of the blind-bolted joints during the entire fire and loading process were extracted and discussed based on the FEA models. The results indicated that the joint negative moment generated by the axially restrained beam boundary in the heating and cooling phases could go up to around 1.4 times the joint negative moment at ambient temperature.

Cracking control technique for continuous steel-concrete composite girders under negative bending moment

Cracking control technique for continuous steel-concrete composite girders under negative bending moment

Finite element analysis of RC moment-resisting frames to assess effective slab width; a parametric study

In reinforced concrete (RC) moment-resisting frames (MRFs) with cast-in-situ slabs, the slab action as tension flange during lateral loading enhances the flexural capacity of beams in negative moments. This enhancement may lead to strong beam-weak column unfavorable failure mode in these structures. Field observations of RC MRFs during strong ground motion indicated that the effective slab width values considered by the seismic provisions of the design codes are not adequate to guarantee the achievement of the design method of weak beam-strong column. An accurate estimation of effective slab width needs to assess factors such as geometrical characteristics of connection, continuity of models, and imposed story drift level. A 3D spatial two-story RC MRF was developed using finite element analysis (FEA) to explore the effect of mentioned factors on effective slab width. For finite element (FE) modeling of RC MRF, the concrete damaged plasticity (CDP) model is applied. The CDP model parameters are defined using a mesh-independent methodology introduced in the literature. Comparing the FEA results and results obtained from three half-scale RC MRFs, tested under reversed cyclic loading conditions showed an excellent correlation. The results predicted by the FE model in terms of lateral load–displacement response, reinforcement yielding sequence, crack patterns, and failure modes had a considerable agreement with test observations. The validated FE model was used to develop the other models to conduct a parametric study in the next step. Geometric parameters studied in this paper through numerical modeling were longitudinal and transverse beam length and height, and cross-sectional column dimension. Results of the parametric study showed that the effect of the ratio of transverse beam length to height is significantly more than the ratio of longitudinal beam length to height. The trend of effective slab width versus story drift depends on connection geometry, especially the ratio of transverse beam length to transverse beam height. Finally, an equation was driven to predict the effective slab width using linear regression analysis.

Behavior and design of steel-UHPC composite beams subjected to negative moment

To improve the crack resistance of concrete deck slabs of steel–concrete composite beams in the negative moment regions, Normal Concrete (NC) and Ultra-high Performance Concrete (UHPC) were respectively used to cast the deck slab to investigate the effects of different slab materials on the failure modes, crack characteristics and flexural performance. The flexural performance tests under negative bending moment were conducted, and the impact of different slab materials on the mechanical performance of the composite beams were analyzed using the numerical simulation method verified by the tests. The method of calculating the ultimate flexural capacity of steel-UHPC composite beam, which considered the material micromechanics mechanism such as fiber distribution, orientation, burial depth and interfacial bond strength, was proposed based on the simplified plasticity theory and were verified with existing method by the test results of related literature. The results show that the force characteristics of the two composite beams were similar, and the failure modes were both flexural failures. Compared with the steel–concrete composite beam, the cracks of the steel-UHPC composite beam were more evenly distributed and narrower, with larger crack distribution spacing and fewer secondary cracks. The cracking resistance of composite beam can be effectively improved by using UHPC slab, and the flexural capacity improved slightly. The cracking load of the deck slab of the steel-UHPC composite beam was improved by 500%, the corresponding load when the crack width reached 0.2 mm was improved by 37.5%, and the ductility and ultimate flexural capacity were improved by 30% and 5 %. In addition, the ultimate flexural capacity of steel-UHPC composite beam should consider the tensile contribution of UHPC, and the proposed calculation method is suitable for steel-UHPC composite beam with different UHPC mix ratios.

Study on the Effect of Large Cross-Section Quasi-Rectangular Pipe Jacking near Side Crossing Viaduct Piles in Soft Soil Areas

Due to its high section use rate and minimal environmental impact, pipe jacking technology is frequently utilized in the building of urban rail transit and other municipal projects. This paper develops a three-dimensional numerical model for the gradual construction of rectangular pipe jacking based on the quasi-rectangular pipe jacking metro station project on Shanghai Line 14 and examines the interaction between the subsequent construction of double line pipe jacking and pile foundation. To analyze the deformation pattern of the tunnel section and the ground surface during the construction period and to confirm the applicability and accuracy of the model, the simulation results are compared with the monitoring data. The findings demonstrate that although the bending moment of the pipe jacking section is distributed as a “butterfly” under the influence of the viaduct piles, the maximum positive and negative bending moments as well as the lateral and vertical radial deformations of the pipe section cross-section are all somewhat diminished. The ground surface settlement curve in the vicinity of the bearing platform exhibits a more pronounced non-uniform settlement when the two pipe jackings pass through the pile foundation in close proximity, one after the other. The largest horizontal displacement of the pile foundation is found inside the jacking pipe tunnel at a depth of roughly 17 m below ground, where pipe jacking II has a greater influence on the lateral displacement of the pile foundation than pipe jacking I. The study’s findings line up with the monitoring data, which can serve as a guide and aid in the development of initiatives of a similar nature.

Study of U-shape steel-encased composite beams with variable sections under negative bending moments

To reduce steel consumption and improve the negative moment bearing capacity of composite beams, a new type of composite beam with an external U-shaped steel plate was proposed in this paper. Static load tests of three scaled simply supported composite beams were completed, and the failure patterns, load–displacement curves, strain distributions, and slip of the new composite beams under negative bending moments were researched. The results showed that the new composite beam under negative bending moments underwent typical flexural failure with excellent ductility (ductility coefficient of 6.2), wherein the embedded steel plate played a key role in the loading process of the composite beams, contributing more than 50% of the flexural load capacity. On the basis of the experiments, finite element models were established in ABAQUS to investigate the influence of different construction parameters, including the material strength, thicknesses of the external steel plate and the embedded steel plate, and reinforcement ratio. Finally, design formulas were derived according to the simplified plasticity theory to calculate the flexural capacity of the proposed composite beam for engineering practice, which achieved close agreement with the experiments, with an average relative error of 3.5%.

Influence of longitudinal prestress on the shear resistance of prefabricated shear stud connectors

In order to meet the requirements of accelerated bridge construction (ABC), the structure of steel–concrete composite bridges presents a development trend of the entire assembly. A Prefabricated Composite Shear Studs (PCSS) is proposed to speed up the assembly efficiency of traditional steel–concrete composite beams and improve the effectiveness of the prestress of prefabricated concrete decks in the negative moment zone. A finite element model (FEM) of the PCSS shear connector is established by considering the stress characteristics of different assemblies, thirty different steel tendon quantities, and relative arrangements are selected to analyse the impact of longitudinal prestress on the shear resistance of PCSS, the effectiveness of finite element model is verified this through test results. It is revealed that the steel tendon arrangement and quantity will change the shear resistance of the PCSS shear connectors. However, the magnitude, positive and negative effects are related to the position of the steel tendon along the deck height. When the steel tendon deviates downward from the neutral axis of the deck, the shear bearing capacity and shear stiffness increase; in addition, its force transfer mechanism is that the longitudinal prestress changes the lateral restraint effect of the PCSS on the concrete. Under the combined action of prestressing and transverse restraint of steel plate, the cooperative working ability of the stud and surrounding concrete can be enhanced or weakened. Thus, the yielding of stud and concrete damage can be delayed or accelerated, significantly affecting the shear bearing capacity and stiffness.

Experimental study of continuous T-beams with negative bending moment using UHPC instead of prestressed tendons under flexure

In order to explore the flexural performance of the two-span simply supported to continuous T-beam using UHPC material instead of prestressed tendons in the negative bending moment zone and the effect of the UHPC material connection length on the bearing capacity of the test beam, the flexural tests of three beams with different UHPC connection lengths were carried out. The results show that by using UHPC material instead of prestressed tendons to make continuous beams in the negative bending moment region, the tensile properties and high elastic modulus characteristics of UHPC material can be better exerted. The three test beams were all resistant to bending failure, and the cracks were distributed in the two positive and negative bending moment sections. Increasing the connection length of the UHPC material will increase the distribution range of cracks and the number of cracks in the positive moment section and the cracking load in the negative moment section. The ductility was reduced. When the connection length was increased from 300 mm to 2200 mm and 2300 mm, respectively, the bearing capacity of the test beam was increased by 4% and 6%, respectively, and the mid-span ultimate displacement was reduced by 7% and 12%, respectively. The flexural performance of the test beam was improved.

Design and Optimization of the Bi-Directional U-Ribbed Stiffening Plate–Concrete Composite Bridge Deck Structure

The steel–concrete composite structure is widely used in civil engineering for large-span bridges. Orthotropic steel bridge decks (OSDs) have particularly gained popularity due to their excellent mechanical performance. To address cracking issues in OSDs and concrete in negative moment regions, a novel bi-directional U-ribbed stiffening plate (BUSP)–concrete composite bridge deck is proposed. By using finite element analysis, the mechanical performance is evaluated based on maximum tensile stress and vertical displacement of concrete overlays. Results show that the BUSP–concrete deck outperformed conventional flat decks. It is also found that increasing the height, thickness, and opening width of U-ribs reduced tensile stress and maximum displacement. Adjusting height had the most significant effect on displacement while opening width affected tensile stress the most. Considering material usage, optimizing height is proved to be more effective than adjusting thickness and opening width. Decreasing spacing parameters improved performance but added complexity and reduced construction convenience. These findings will guide the design and optimization of steel–concrete composite bridge deck structures.

Analysis of Structural Parameters of Steel-NC-UHPC Composite Beams.

The cracking of the negative moment area of steel-normal concrete (NC) composite bridges is common owning to the low tensile strength of concrete. In order to solve the problem, Ultra High Performance Concrete (UHPC) is used to enhance the tensile performance of the negative moment area. This paper conducted interface experiments to study the bonding behaviour of the UHPC-NC interface. The design parametric analysis of steel-NC-UHPC composite bridges was carried out based on the interface experimental results. Firstly, slant shear tests and flexural shear tests were carried out to study the rationality of the interface handling methods. Then, the finite element model was used to analyze the state of every component in the composite beams based on experimental results, such as the stress of UHPC, concrete and steel plate. Finally, the calculation results of finite analysis were compared and summarized. It is concluded that (1) the chiseling interface can meet the utilization requirements of physical bridges. The average shear stress and flexural tensile strength of the chiseling interface are 10.29 MPa and 1.93 MPa, respectively. In the failure state, a slight interface damage occurs for specimens with a chiseling interface. (2) The influence on overall performance is different for changes in different design parameters. The thickness of concrete has a significant influence on the stress distribution of composite slabs. (3) Reliable interface simulation is conducted in the finite element models based on interface test results. The stress variation patterns are reflected in the change of design parameters.

Characterizing the Spatio-Temporal Variations of Urban Growth with Multifractal Spectra.

Urban morphology exhibits fractal characteristics, which can be described by multifractal scaling. Multifractal parameters under positive moment orders primarily capture information about central areas characterized by relatively stable growth, while those under negative moment orders mainly reflect information about marginal areas that experience more active growth. However, effectively utilizing multifractal spectra to uncover the spatio-temporal variations of urban growth remains a challenge. To addresses this issue, this paper proposes a multifractal measurement by combining theoretical principles and empirical analysis. To capture the difference between growth stability in central areas and growth activity in marginal areas, an index based on generalized correlation dimension Dq is defined. This index takes the growth rate of Dq at extreme negative moment order as the numerator and that at extreme positive moment order as the denominator. During the stable stage of urban growth, the index demonstrates a consistent pattern over time, while during the active stage, the index may exhibit abnormal fluctuations or even jumps. This indicates that the index can reveal spatio-temporal information about urban evolution that cannot be directly observed through multifractal spectra alone. By integrating this index with multifractal spectra, we can more comprehensively characterize the evolutionary characteristics of urban spatial structure.

Investigation on the Stress and Deformation Evolution Laws of Shield Tunnelling through a Mining Tunnel Structure

In the construction of a shield crossing an existing mined tunnel without load, it is imperative to develop corresponding design standards that reflect actual engineering force characteristics to ensure the successful completion of the tunnel construction. This study uses the MIDAS-GTS NX 2022 finite element software to facilitate the creation of a numerical model of a shield structure for an air-push-over mine tunnel project in Changsha, China while investigating the stress field’s evolution during shield construction and calculating the maximum positive and negative bending moments and maximum axial forces for different structures and other force states under various construction conditions. This study’s findings informed the design and construction optimisation of a shield tunnelling empty-push method. The outcomes of this numerical simulation led to several key findings: (1) The soil density exerted a significantly greater impact on the internal forces of the initial support structure than both the tunnel depth and soil Poisson’s ratio. Additionally, a sudden shift in internal forces occurred within the 300–350 mm range when the lining thickness was altered. (2) Factors such as the tunnel depth, soil density, soil Poisson’s ratio μ, and lining thickness similarly influenced the internal forces of the segment and the initial support. Notably, the backfill layer thickness significantly affected the segment’s maximum axial force, causing an abrupt change of approximately 300 mm. (3) It is essential to control the guide rail’s thickness under the shield machine equipment’s weight constraint to prevent it from becoming overly large.

Analysis of negative skin friction and bending moment on batter rock-socketed pile

A theoretical model is proposed to analyze the soil settlement-induced negative skin friction and bending moment on a batter rock-socketed pile (BRSP). A series of model tests were conducted to verify the accuracy of the proposed theoretical model. Parametric studies are conducted to investigate the effects of the inclined angle and diameter of BRSP, and the consolidation settlement of surrounding soil on the bending moment and skin friction on the BRSP. Under the settlement of surrounding soil, the axial forces and the bending moments of BRSP nonlinearly distribute in the clay layer and reach their maximum magnitudes at the rock-soil surface and rapidly attenuated to zero in the rock layer. The deflections of BRSPs decrease linearly along the pile embedded in the clay layer and decrease to zero at the rock-soil interface.

Flexural tests on composite basement walls with socket-type shear connectors

The effect of a recently developed socket-type shear connector (SSC) on the flexural behaviour of a composite basement wall (CBW) was examined in this work. To this end, 12 CBWs composed of cast-in-place (CIP) piles fabricated with H-shaped steel beams or reinforcing steel plates were prepared by varying the arrangement and amount of SSCs. Two-point loading was applied to simply supported CBW specimens. The CBW specimens with more SSCs had a higher effective stiffness in the elastic state and higher moment capacity in the ultimate state, irrespective of the cross-sectional details of the CIP piles. These trends were particularly prominent when a reinforcing steel plate was used in the SSCs. The post-peak behaviour of the CBW specimens subjected to a simulated load with a negative external moment tended to be more ductile. Consequently, a higher degree of composite action was fully exerted on the CBWs with greater numbers of SSCs. Using established equations for the sectional details of CBWs with SSCs, the nominal partially composite to full composite flexural capacity ratios of the CBW specimens subjected to simulated loads with positive and negative external moments were calculated to be, respectively, 0.83 and 0.91 for 0.5ηsc and 0.79 and 0.90 for 0.75ηsc, where ηsc is the normalised shear connector capacity specified in ANSI/AISC 360-16.

Quasiprobability distribution of work in the quantum Ising model.

A complete understanding of the statistics of the work done by quenching a parameter of a quantum many-body system is still lacking in the presence of an initial quantum coherence in the energy basis. In this case, the work can be represented by a class of quasiprobability distributions. Here, we try to clarify the genuinely quantum features of the process by studying the work quasiprobability for an Ising model in a transverse field. We consider both a global and local quench by focusing mainly on the thermodynamic limit. We find that, while for a global quench there is a symmetric noncontextual representation with a Gaussian probability distribution of work, for a local quench we can get quantum contextuality as signaled by a negative fourth moment of the work. Furthermore, we examine the critical features related to a quantum phase transition and the role of the initial quantum coherence as a useful resource.

Structural analysis of shield machine cutting monopile using p-y curve based finite element method

In this study, the structural response of piles during shield machine cutting is analyzed using p-y curves based on the finite element method (FEM). In the FEM program, the tangent stiffness matrix of the nonlinear soil-pile spring is derived from the tangent modulus of the p-y curve. The nonlinear finite element equation is solved using the Newton-Raphson iterative method. The program can consider the influence of the shield thrust force, the soil reinforcement, and the cross-sectional area decrease during shield cutting. The program output comprises the lateral displacement, internal force, and bending moment of the laterally loaded monopile. The correctness and accuracy of this method are validated with both field test data and commercial finite difference method (FDM) program. The results show that shield thrust force is the main factor affecting the lateral displacement and bending moment of the pile; as the cutting section area of the pile is decreasing, the maximum negative moment increases while the maximum positive moment decreases; soil reinforcement has a negligible effect on the internal force but can effectively reduce the lateral displacement of the pile head.

Investigation of Load Environment and Bending Load Capacities of Aged Prestressed Concrete Sleepers

In this study, field measurements of the bending moments of prestressed concrete (PC) sleepers installed on commercial lines were obtained, and numerical analyses to identify the effects of different parameters on their bending moments were conducted. The bending load capacities of aged PC sleepers collected from commercial lines via bending tests were also determined. According to the field measurement results of the wheel loads and bending moments of the PC sleepers, the measured values were smaller than the design values. In addition, neither the wheel load nor the bending moment depended on train speed. The numerical analysis results indicate that the positive bending moment at the rail seat section is unlikely to exceed the design decompression moment (DDM). However, the negative bending moment at the center section may exceed the DDM if center support is provided with a reduced spring constant under the rail (the “hanging” rail seat section). In addition, the bending moment increased with the rail surface roughness, so the rail should be kept smooth. Moreover, the results of the JIS E 1201 bending tests on the aged PC sleepers showed that the crack generation load and ultimate load decreased gradually with increases in age and passing tonnage. However, all samples satisfied the JIS standard values. Furthermore, the bending moments generated in the PC sleepers during train passage were considerably smaller than the crack generation load and ultimate load during the bending test. Thus, Japanese PC sleepers aged more than 50 years currently satisfy the standard flexural fracture values specified by the JIS, and safety is not immediately compromised.