Negative Bending Moment Research Articles

Computational modeling and dynamic response of reinforced concrete shear wall under out-of-plane impact loading

The purpose of the present work is to study the impact performance of the reinforced concrete shear wall. Considering the bond-slip and strain rate enhancement effects of steel and concrete, a numerical model for the study of the impact resistance of reinforced concrete shear walls was established. The numerical model was validated by comparing the simulation results with those observed during the drop hammer impact test. Based on the simulation results, the failure mechanism of reinforced concrete shear walls under impact loading was analyzed. The influence of impact velocity and edge members on the impact resistance of reinforced concrete shear walls was revealed. The results show that the dynamic response of the wall changes most obviously from the instant of peak impact force to the peak reaction force. The damage on the rear surface of the wall is more serious than the impact surface. The local damage of reinforced concrete shear walls is more serious for higher impact velocity. The maximum and residual displacement in the middle of the wall shows a quadratic growth relationship with the impact velocity and a linear growth relationship with the impact energy. With the increase in impact velocity, the peak and platform value of impact force first increase linearly, and then does not change remarkably while the duration increases linearly. The peak reverse reaction force varies irregularly with the increase in impact velocity due to the inertia of the wall. The influences of impact velocity and edge members on the value and duration of reaction force are similar to those on the impact force. Under impact loading, both the maximum positive and negative bending moment appear in the area near the impact location. The increase in impact velocity can elevate the internal force while edge members affect the shear force more than the bending moment. The change in impact velocity affects the energy distribution in steel and concrete during impact. Configuration of edge members can effectively enhance the impact resistance of the wall due to the improvement in global stiffness. The mid-span displacement of the wall and the duration of impact force are reduced and the energy dissipation capacity of concrete is improved.

Study on mechanical behavior of steel-UHPC-NC composite beams under negative bending moment

To investigate the negative moment region flexural performance of a steel-ultrahigh performance concrete (UHPC)-normal concrete (NC) composite beam, steel-UHPC-NC composite beams with a uniform and cluster arrangement of studs and three push-out specimens were designed and fabricated. Based on the test results, the finite element model of steel-UHPC-NC composite beams was established and verified. The results of the study show that in the push-out test, the failure mode of the specimens is the shear failure of the stud, and the specimens with the NC-UHPC composite slab and UHPC slab are crushed and spalled at the root of the studs, but the damage extent and damage range of the specimens with UHPC slabs were significantly smaller than the NC-UHPC composite slab specimens. The load-slip response of the push-out specimen is obviously affected by the concrete slab material. The ultimate bearing capacity of the single stud of the steel-UHPC specimen, the steel-UHPC-NC stud single layer arrangement and the double-layer arrangement specimens were 249 kN, 158 kN and 192 kN, respectively. In the negative bending moment zone loading test, the development trend of the mid-span load–displacement curves of steel-UHPC-NC composite beams with uniform and cluster studs is consistent, with the cracks in the former concentrated at the mid-span position and the cracks in the latter concentrated near the nearest group of shear studs in the mid-span. The load–displacement curves of composite beams that studs are evenly distributed and studs are cluster type are consistent, with ultimate displacements in the span of 65.8 mm and 68.5 mm, respectively, and ultimate bearing capacities of 723.8 kN and 712.3 kN, respectively. The calculation results obtained by the simulation method are in good agreement with the test results, which could effectively predict the load–displacement response of the steel-UHPC-NC composite beam.

Full-scale loading experiments on performance of UHPC joints for prefabricated mountain tunnel

This study used ultra-high performance concrete (UHPC) to design joints reinforced by various bolt types: straight, inclined, and curved bolts. Full-scale samples were prepared in the laboratory. Loading tests on these joints and the unbolted one were carried out based the actual stress state of the tunnel, and various axial force magnitudes and bending moments were combined to obtain the deformation characteristics. The fitting law of the bending stiffness of joints was presented. It is found that axial force increases the bending stiffness of the joint with better elastic performance. The bending stiffness of the straight bolt joint is the highest under positive bending moment during the first loading process, while that of the curved bolt joint is the greatest under negative bending moment during the second loading process. The test results indicate that joints made using UHPC (especially the curved bolt joint) can be used to build a more resilient prefabricated tunneling system.

Experimental investigation into the structural behaviour of ultra-high performance fibre-reinforced concrete box-celled composite panels

The present study investigates and advances on existing research on the structural performance of box-celled composite structures for its use as a wind-resistant roof system. The box-celled panel system is produced by casting ultra-high performance fibre-reinforced concrete (UHPFRC) into galvanised steel roofing profiled sheets with anchor screws and expanded polystyrene foam (EPS) placed in-situ to produce a light-weight system. Three reinforcement-based variations of the design are investigated and two panels for each variation are cast to produce six specimens. The structural responses of the variations as one-way panels under three-point flexure are experimentally studied for both positive and negative bending moment capacities. Test specimens showed flexural failure with significantly ductility and post-failure load capacity, and anchor screws preventing full delamination of steel profile and shear failure. Analysis based on the test results confirmed that the proposed system is compliant to various design standards based on upper limits for combined loading actions, and permissible deflections, highlighting its optimal performance.

Effect of support conditions on the performance of B70 sleeper overlying reinforced ballast and sub-ballast layer: Experimental and analytical investigation

It is well known that the moment distribution on the sleepers is very sensitive to deformations of the ballast caused by cyclic axle load over time and other environmental factors. To limit the non-uniform deformations of the ballast, reinforcement of the ballast or sub-ballast with geosynthetics can be a cost-effective solution. In this study, B70 prestressed concrete sleepers were tested under static loading conditions in a special test box developed to simulate the in-situ condition of a railroad track in the laboratory. The main test parameters were the degree of settlement of the ballast and the type of geosynthetics used. Four different settlement levels and two reinforcement types (sub ballast with geonet and ballast with geocells) were considered. The deflections and surface strain maps of the concrete sleepers were measured using the two-dimensional digital image correlation (2D-DIC) method. Following the experimental part, an analytical study was also carried out to investigate the ballast pressure distribution and consequently the moment distribution on the concrete sleeper. Based on the vertical deflection shape of the sleeper, a new algorithm was developed to derive the ballast pressure distribution under the sleeper by back calculation. The experimental results showed that using geocells to reinforce the ballast layer increased the stiffness of the ballast against the vertical deflection of the sleeper. From the analytical results, the magnitude of the negative bending moment increased significantly with increasing settlement level.

Assessing Dynamic Load Allowance of the Negative Bending Moment in Continuous Girder Bridges by Weighted Average Method

Accurate acquisition of dynamic load allowance (DLA) based on measurement data is essential to the safety assessment of a bridge. When static load tests cannot be achieved, and filtering fails, the estimated DLAs from the experimental method vary widely due to the choice of a left or right band. In this paper, the proposed weighted average method (WAM) is used to possibly solve the above problem in continuous gird bridges. Two-span and three-span precast concrete box-gird bridges were selected to optimize intercepted segments of WAM for the first time with the assistance of standard deviation and coefficient of variation in statistics. Then, a DLA measurement case of the negative bending moment was utilized to verify the validity of the WAM. The results show that the intercepted segments of 10/16 to 1 times the span length were suitable for the WAM to calculate the DLA of the negative bending moment due to small offset moments and stable variation coefficients. The WAM had a strong anti-interference ability of outliers filtering in “bad data,” which differed significantly from the experimental method. In three measurements of a field bridge, DLAs obtained by the WAM had less dispersion than the experimental and low-pass filtering methods.

Mechanical behavior of concrete pipes with erosion voids and the effectiveness evaluation of the polyurethane grouting

Research on pipes ringed by erosion voids is mainly concerned with circumferential mechanical behavior but ignores longitudinal bending responses induced by the relative motion of the pipe joints at voids. There has been limited innovative experimental investigation into pipe behavior that assesses the effectiveness of polyurethane (PU) grouting in rehabilitating erosion voids. Mechanical behavior tests of concrete pipes of intact, with an erosion void at the invert, and PU grouted were performed using a self-developed large-scale disaster testing system, and the measured results were numerically verified. Results show that the peaks of the positive and negative longitudinal bending moments of the intact pipes and pipes with a void at the invert appear at SgL2 and SgR2, SgL3 and SgR3, respectively, and the positive longitudinal bending moment is about 1.6–3.0 times higher than the negative ones. Voids at the invert have a significant effect on the longitudinal bending moments of the pipe segments located on the adjacent sides of the void. The longitudinal bending moments of the pipes with different void widths decrease with the increase of void width at SgL1 and SgR1 and increase with the increase of void width at SgL2 and SgR2, SgL3 and SgR3. The longitudinal bending moments of the pipes with different void lengths increase with the increase of void length in the whole longitudinal length. The circumferential bending moments at the bell-and-spigot decrease as the void width and void length increase. The maximum increases in the vertical displacements and maximum shear displacements of the pipes with different void widths and void lengths are 63–150% and 150–221%, 225–325%, and 325–550%, respectively, compared with the intact pipes. The rehabilitation efficiencies of the longitudinal and circumferential bending moments and the vertical displacement ranged from 85–93% and 85–94%.

Laser bending angle and deformation mechanism under different auxiliary loads

Auxiliary load laser forming is a new direction developed based on laser forming. This direction has the advantages of a large forming angle and high surface quality of the workpiece and achieves the effect of traditional mechanical forming. Currently, the auxiliary load is applied in a single way, which will not be conducive to the enrichment and development of this direction. Accordingly, four auxiliary methods are proposed, and these different approaches are modelled. The bending angles of these different methods are compared, and the deformation mechanism is discussed. Results showed that the four methods can effectively increase the bending angle. Amongst them, method 3 can effectively increase the bending angle by 4.51 times because the positive bending moment effect formed by the line load and the negative bending moment effect formed by the surface load are conducive to the increase in bending angle. The bending angles under the four methods linearly increase with the increase in load value. The larger the high-temperature distribution area is at the same temperature value, the larger the bending angle will be.

Mechanical response of horseshoe-shaped tunnel lining to undercrossing construction of a new subway station

This paper proposed a calculation model for the internal force around a horseshoe tunnel based on the principle of force method. A method is proposed for computing the lateral elastic resistance of the non-circular closed ring structure. The influence of the newly constructed station of Beijing Subway Line 12 approach crossing the existing Subway Line 5 was studied with the upper and the lower pilot tunnel excavation considered. The study denotes that the maximum positive and negative bending moments of the existing tunnel increased are due to the upper pilot tunnel construction, but the influence is limited. The influence on the existing tunnel is studied by a step-by-step excavation unloading method, with each unloading width assumed to be the same as the spacing of one steel arch frame in the lower pilot tunnel excavation stage. Lastly, the construction parameters affecting the internal forces of the existing tunnel are analyzed, including the distance between the unloading surface and the existing tunnel, the unloading area, and the total excavation steps of the lower pilot tunnel.

Deformation recoverability of longitudinal joints in segmental tunnel linings: An experimental study

The shield-driven tunnel is a fabricated lining structure. The existence of longitudinal joints between segments in a ring makes the entire tunnel lining vulnerable to deformations, because the rigidity of longitudinal joints is lower than that of the main concrete segments. Large transverse deformation, accompanied by joint opening, is a common disease of shield tunnels. The aim of this work is to explore the deformational behaviors and mechanical properties of tunnel longitudinal joints under overloading, unloading, and soil grouting conditions, with emphasis on the recoverability of joint deformation. For this purpose, a series of laboratory tests have been carried out on the full-scale longitudinal joints at tunnel crown adopted in Shanghai metro tunnels, including three parallel tests with different overload levels and one cyclic overloading and unloading test. The full-scale testing considers the actual stress state of the longitudinal joint under different working conditions in real environments. The specimen of the longitudinal joint at tunnel crown adopts the actual three-segment-two-oblique-seam structure, which is different from the simplified two-segment-one-straight-seam form used in previous studies. Multiple deformation indicators, including joint opening, concrete strain, and bolt strain, are monitored and analyzed. Based on the test results, the effects of restoration actions, i.e., unloading and soil grouting, on joint deformation recovery under different overload levels are discussed. The change of recovery efficiency with the degree of joint deformation is also obtained. In addition, the deformation recoverability and rotational stiffness are compared between the longitudinal joint at tunnel crown which is subjected to positive bending moment and the longitudinal joint at tunnel springline which is subjected to negative bending moment. The test results show that the larger the joint deformation caused by overload, the lower the recovery efficiency. From a mechanical perspective, soil grouting is an effective measure to recover the large deformation of shield tunnels.

Interface stress analysis and fatigue design method of steel-ultra high performance concrete composite bridge deck

Orthotropic steel-UHPC composite deck consists of orthotropic steel deck and ultra-high performance concrete (UHPC) layer. The shear force transferred by shear studs at the interface between steel deck and the UHPC layer is a key in fatigue design. Based on the finite element (FE) whole model analysis of composite deck, the detailed submodels of composite deck segments with single stud and single row studs were established respectively. It aimed to investigate the interface stress distribution and slip behavior of steel-UHPC composite deck under negative bending moment, and explore the failure mechanism of short headed stud. In term of shear force relationship, considering likely influences such as location and pattern of loading, flexural stiffness of the composite deck and stud arrangement, the whole model analysis results were compared with the submodel analysis results, and a fitting formula of shear relationship between the two models was proposed. A formula for fatigue design of short headed stud in orthotropic steel-UHPC composite deck was also proposed. In respect to the longitudinal and transverse shear force distribution of studs, composite deck stiffness, hot spot stress of fatigue-prone details of steel bridge deck and the maximum stress level of UHPC layer, the evaluation method of stud arrangement was proposed. The calculation results were assessed and compared with the stud layout schemes of three actual steel-UHPC composite decks, and the effectiveness of the design formula was validated.

Vehicle-SFT-current coupling vibration of multi-span submerged floating tunnel, Part II: comparative analysis of finite difference method and parametric study

An analytical method based on the mode superposition and Galerkin hybrid method (MSGHM) has been proposed for vehicle-SFT-current coupling vibration in Part I of the two-part paper. This Part II also puts forward the finite difference method (FDM) for solving the differential equations of vehicle-SFT-current coupling vibration. Taking the design parameters of a typical SFT as the engineering background, the correctness of the two methods are mutually verified. Subsequently, the influences of several structural parameters on the vehicle-SFT-current coupling vibration are discussed. The results show that the peaks of displacements appear near five eighths of the tube, whereas the peaks of bending moments appear at midpoint of each segment. When the current acts on the tube with large-diameter section, the vortex-induced vibration is difficult to be excited, making the current-SFT coupling vibration inconspicuous. Moreover, the boundary condition will significantly affect the dynamic response of the side segments. The flexible segment joint can effectively decrease the negative bending moment of the tube, while the shear keys with reasonable setting will avoid the abrupt change of the displacement. Furthermore, the variation in the layout of the cable will change the anchoring stiffness, and consequently influence the displacements of the tube.

Behavior of Multispan Extradosed Bridge Subjected to Variation of Cable-Free Segment Length

Based on the main bridge of the Paira Bridge in Bangladesh, this paper studies the behavior of multispan extradosed bridge subjected to variation of cable-free segment length. First, a finite element simulation model was established, and linear analysis was performed. The accuracy of the finite element model was verified by comparing the measured data with the finite element analysis. Then the influences of the cable-free segment length in the midspan and the pylon root on the horizontal displacement of the pylon top, the vertical deflection of the midspan, and the bending moment of the main girder were analyzed, respectively. The results showed that the variation of the cable-free segment length put a significant impact on the horizontal displacement of the pylon top and the vertical displacement of the middle of each span. The increase of positive moment was greater than negative moment when the cable-free segment length in the middle of the span increased. However, when the cable-free segment length of the pylon root increased, the negative bending moment of the main girder increased more than the positive bending moment.

Experimental investigation on the behavior of the steel–concrete composite frames with uplift-restricted and slip-permitted screw-type (URSP-S) connectors

The uplift-restricted and slip-permitted screw-type (URSP-S) connector is proved be very useful to improve the crack resistance of the concrete decks in the negative bending moment areas in steel–concrete composite bridges, thus it has been widely used recently in China. However, its application in building structures is very limited. In this paper, the structural behavior of steel–concrete composite frames with URSP-S connectors was experimentally investigated. A total of three composite frame specimens with different connector types and arrangements of the interface of composite beams were designed and tested. The load–deflection curves, hysteresis behavior, slab crack, strain, and interface slip under vertical and lateral cyclic loading cases were analyzed. The results indicated that compared with full-span stud connectors, after applying URSP-S connectors, the crack number and width of the concrete slab was effectively reduced, as well as the tensile strain of the concrete and rebar of the slab, while the interface slip of composite frame beam was notably enhanced, the stiffness of the composite frame with URSP-S connectors became slightly lower under vertical and lateral loading cases. Moreover, the composite frame with URSP-S connectors exhibited good seismic behavior under lateral cyclic loads, and the use of URSP-S connectors rarely affected the bearing capacity of the structures.

Effect of Ground Motion Orientation on Seismic Responses of an Asymmetric Stress Ribbon Pedestrian Bridge

The stress ribbon bridge uses ribbon in high tension to transfer loads and exhibits geometric nonlinearity under dynamic earthquake excitations. A typical double‐span asymmetric stress ribbon pedestrian bridge was introduced as a prototype, and nonlinear time history analysis was performed to investigate the effect of ground motion orientation on the structural responses. Non‐pulse‐type and pulse‐type ground motions were considered, and the influence of vertical ground motions was investigated. Numerical results showed that the stress ribbon bridge’s vertical and transverse displacements were sensitive to the excitation of the vertical ground motion. No single orientation led to the most critical values in all response indexes, and the critical orientation was approximately independent of the vertical ground motion. The negative bending moment of the ribbons, the pier top displacement, and the pier base moment at the transverse direction were sensitive to the ground motion orientation. Checking the responses resulting from different directions is necessary for a comprehensive estimation of the seismic performance of the stress ribbon bridge.

Numerical Analysis of the Influence of Deep Foundation Pit Construction on Adjacent Subway Stations in Soft Soil Areas

Deep foundation pit construction adjacent to a subway station in a soft soil area was numerically simulated with Midas GTS NX calculation software. The influence of the deep foundation pit construction on the deformation and stress of the subway station structure was studied, and the influence of the foundation pit retaining structure on the station was analyzed. The results show that during the foundation pit excavation process, the subway station slab rose as a whole and was greatly affected by the deformation of the common ground connecting wall, with the most unfavorable position changing as the excavation area changed. The excavation of foundation pits in different zones had a considerable influence on the east‐to‐west displacement of the common diaphragm wall outside the foundation pit. The maximum positive bending moment of the common diaphragm wall changed little, while the negative bending moment increased greatly during construction. Overall, the foundation pit excavation had a great impact on the negative moment of the common diaphragm wall. During the foundation pit excavation process, the subway station column lifted upward, and the maximum displacement, which was located at the west end of the station near the foundation pit, gradually weakened from west to east. As the foundation pit excavation process continued, the maximum axial force of the station column increased by 10.38%, and the pressure was the largest in the middle column. As the thickness of the diaphragm wall increased, the stiffness of the foundation pit retaining structure increased. After earthwork excavation and unloading, the locations in the retaining structure with high stiffnesses could resist deformations. The whole foundation pit was offset due to the high stiffness of the foundation pit retaining structure, which increased the horizontal deformation of the existing station structure. With increasing thickness, the relative horizontal deformation of the station slab gradually increased, mainly because the difference between the depths of the old and new diaphragm walls caused the embedded soil of the two same deep foundation pits to differ. Furthermore, there were great differences in the Earth pressure behind the wall. As the depth of the diaphragm wall increased, the active Earth pressure behind the diaphragm wall increased.

Full-scale testing and numerical modelling of segmental-joint performance with corroded bolt

Water leakage through segmental joints often occurs for shield tunnels built under groundwater. Chloride ions in groundwater can cause the corrosion of steel bolts in segmental joints, reducing the rigidity of the tunnel lining and endanger the operation safety of tunnels. In this paper, the impact of the corrosion of the steel bolt on the structural performance of segmental joint was investigated using six full-scale segmental joint tests and a series of numerical simulation. Both the experimental and numerical results indicate that the segmental-joint performance can be divided into three stages under different loading and corrosion states. The bolt corrosion can reduce the waterproof ability, bending stiffness, and ultimate bearing capacity of the segmental joint. The impact of the bolt corrosion is most significant in the second stage. Furthermore, the bolt corrosion has a larger impact on segmental-joint performance under a positive bending moment than under a negative bending moment, owing to the configuration of the joint. The impact of the bolt corrosion is strongly dependent on the loading state of the tunnel joint and the corrosion ratio of the bolt.

Analysis on the mechanical properties of the crossbeam of a new ground anchor counterfort grille dam considering bearings displacement

Aiming at the problem that the uneven deformation of the crossbeam of the new ground anchor counterfort grille dam under the impact of debris flow is easy to cause the overall damage of the structure, the crossbeam is simplified as a mechanics model of multi − span continuous beam supported on the grille columns, and the internal force calculation formulas of the crossbeam under the displacement and the local failure of the bearings are deduced. Combined with an example, during the process of bearings from the displacement to local failure, the internal force variation of the crossbeam are analyzed. The results show that when the single bearing is displaced, the mid − span bearing has the greatest impact on the internal force of the crossbeam. When the two bearings are displaced at the same time, the two side − span bearings have a greater influence on the internal force of the crossbeam. When three bearings are displaced at the same time, the influence on the internal force of the crossbeam is the smallest. When the single bearing fails, the failure of side − span bearing has the greatest influence on the internal force of the crossbeam, the mid − span bearing failure is second. Therefore, the reinforcement at each bearing of the crossbeam should be considered to meet the force requirements after the internal force redistribution in the design, so as to ensure the safety of the structure after the positive and negative bending moment of bearing are converted. In addition, when displacement or failure of bearings occur, attention should be paid to meet the limit requirements of structural deformation and stability. The research results can provide a theoretical basis for the reliability analysis of the new ground anchor counterfort grille dam.

Experimental investigation on reinforced concrete beams subjected to axial compressive and shear forces

AbstractThis paper presents two experimental campaigns carried out on 36 reinforced concrete (RC) beams (with and without shear reinforcement) subjected to a three‐point bending loading with a shear force on the one hand, an axial compressive load and a negative bending moment applied at each end of the beams on the other hand. Such a loading configuration makes it possible to investigate the influence of both axial compression and negative bending moment on the shear capacity of RC beams. For each campaign, three values of axial compressive force were studied, and the test beams were divided into two series with low and high negative bending moment. During the tests, Digital Image Correlation technique was used to capture the cracking evolution of the specimens. Besides, the experimental shear strengths of the beams are confronted to the predictions of Eurocode 2 in order to assess its practical validity. Finally, a semi‐analytical method proposed by Wahbi et al. 2021 (A failure criterion for RC beams subjected to axial and transverse loadings) for evaluating the resistance domain of RC elements subjected to transverse and axial loads, is extended in this paper to take into account the negative bending moment and compared to the experimental results.

Moving-wheel fatigue durability of cantilever bridge deck slab strengthened with high-modulus CFRP rods

Reinforced concrete (RC) slabs of highway bridge decks are gradually deteriorated due to the traffic vehicle wheel-loading. Fatigue is one of a number of possible causes for the deterioration. Cantilever RC slabs of the bridge are also damaged by fatigue loading. To increase the fatigue durability of the bridge deck slab, the near-surface mounted (NSM) technique is used with carbon fiber reinforced polymer (CFRP) rods embedded in the RC slab as an effective strengthening method. This study presents the fatigue characteristics of cantilever RC slabs strengthened with CFRP rods with a high-modulus of elasticity. A cantilever RC slab specimen with embedded CFRP rods with high moduli was constructed on a moving-wheel load testing machine and tested for approximately 11 months. The slab had a minimum thickness of 160 mm (as stipulated by the Japanese design code), and the minimum number of steel reinforcements was embedded to ensure (negative) flexural failure of the RC slab where CFRP rods were not used. During the test, the CFRP strengthened slab specimen was subjected to a negative bending moment from repeated moving-wheel loads. Very limited experimental data are available for the evaluation of the structural behavior of cantilever bridge decks subjected to wheel loads. Therefore, the moving-wheel fatigue experiment of the cantilever RC slab with NSM CFRP rods would be useful information for strengthening. The moving-wheel loading test confirmed the increase in fatigue durability of the CFRP strengthened slab as the slab specimen endured approximately 3.56 million equivalent-cycles at an initial load of 60 kN, which was 32% higher than the designed service load. The experimental investigation revealed that the ultimate failure of the cantilever slab was punching shear failure attributed to the rupture of the CFRP rods.