Negative Bending Research Articles

Experimental study of the performance of a stress-absorbing waterproof layer for use in asphalt pavements on bridge decks

The presence of negative bending moments at the top of a continuous beam bridge can facilitate the sawing of false seams. The concrete bridge deck and its asphalt pavement will therefore develop transverse fatigue cracks under long-term cyclic traffic loads. This paper aims at preventing reflective cracks from forming in such asphalt pavements. The structure and materials used in crack prevention based on a composite stress-absorbing layer (CSAL) consisting of a geotextile and an asphalt gravel seal coat were investigated. The properties of polypropylene (PP) geotextiles were evaluated by means of differential scanning calorimetry, thermogravimetric analysis, thermal shock tests, etc. Adhesion, shear, and tensile tests were used to study the influences of factors such as the type, amount of asphalt materials, and construction temperature on the bonding performance of the pavement interface. Texas overlay tests were also carried out to explore the anti-reflective cracking and anti-fatigue performance of different pavement structures including an asphalt rubber stress-absorbing membrane interlayer (ARSAMI) and a CSAL. The results show that the PP geotextile has a melting point of about 166 ℃, a glass-transition temperature in the range of –20 to –10 ℃, and a thermal decomposition temperature of about 400 ℃. In addition, it retains good strength and deformability when subjected to thermal shock at 180 ℃, and it has high thermal stability. The modified asphalt has the highest adhesion strength to concrete slabs, followed by ordinary asphalt and then emulsified asphalt. The temperature state of the bonding layer is not sensitive to the bond strength of the bridge deck paving structure. The asphalt mixture waterproofs the surface after paving. The adhesive stress-absorbing layer imparts a secondary heating effect, thereby ensuring interface adhesion. Using a pavement structure with a CSAL can enhance resistance to reflective cracking at a low temperature by more than 5 times compared to the case not taking preventative measures. Its resistance to reflective cracking under a deformation amplitude of 2 mm at the room temperature (20 ℃) is also slightly better than that of the ARSAMI. Hence, CSALs have promising prospects for use in crack prevention.

Experimental Study of Bridge Foundation Reinforced with Front and Back Rows of Anti-Slide Piles on Gravel Soil Slope under El Centro Waves

A shaking table test for a bridge foundation reinforced with the front and back rows of anti-slide piles on a gravel soil slope was designed. The test results were obtained by loading El Centro waves with different peak accelerations. It was not an advantage for the deformation of bridge pile foundation while the distance between the front-row anti-slide piles and pier was large. The back-row anti-slide piles played a major role in seismic reinforcement, and the peak bending moment of the pile shaft and the peak earth pressure behind the pile had a triangular distribution. The distance from the crack to the sliding surface of the anti-slide pile was approximately one fifth of the length of the anchoring section. As the crack propagated, the bearing capacity of the pile shaft decreased gradually. Since the influence of pier inertia force and soil horizontal thrust, a peak negative bending moment and a peak positive bending moment were observed near the pile top and the sliding surface respectively. The rate of attenuation of the bending moment from the top of the pile along its depth was related to the resistance of the soil around the pile. The stress-induced deformation of the pile foundation behind the pier was larger than that in front of the pier. The peak ground acceleration (PGA) amplification factor of the slope had a vertical amplification effect and a layered distribution. The acceleration responses of the sliding section and the steep slope section were strong, while the acceleration responses of the region between the bridge pier and the back-row anti-slide piles were weak. With the increase in the vibration intensity, the soil damping ratio increased and the PGA amplification factor decreased. The feasibility of analyzing the acceleration response of the slope model by the two-dimensional equipotential map was experimentally verified.

Design of 3D Printed Programmable Horseshoe Lattice Structures Based on a Phase-Evolution Model.

By 3D printing lattice structure with active materials, the structures can exhibit shape and functional changes under external stimulus. However, the programmable shape changes of the 3D printed lattice structures are limited due to the complex geometries, nonlinear behaviors of the active materials, and the diverse external stimuli. In this work, we propose a design framework combining experiments, theoretical modeling, and finite element simulations for the controllable shape changes of the 3D printed horseshoe under thermal stimulus. The theoretical model is based on a phase evolution model that combines the geometrical nonlinearity and the material nonlinearity. Results show that the shapes with positive or negative Poisson's ratio and bending intermediate shapes can be programmed by tuning the geometrical parameters and the temperature distribution. This work provides a method to aid the design of 3D printed functional lattice structures and have potential applications in soft robotics, biomedicine, and energy absorbing fields.

Experimental study on precast beam-column connections with continuity reinforcement for negative bending moments

Abstract In this paper, an experimental investigation is presented on semi-rigid interior beam-to-column connections constituted by precast concrete beams supported on precast concrete column corbels and bending continuity reinforcement bars for bending negative moments. The main purpose of this paper was to analyze the influence of vertical interface grout filling between the corbel and the beam and the position of the bending continuity reinforcement bars (crossing only the column or crossing only the slab) on the behavior of this type of connection. Tests on eight specimens were performed. It was noticed that the vertical interface grout filling contributed to increase both rotational flexural stiffness and flexural strength capacity of the connections when compared to the connections without grout filling. It was also noticed that in the specimens in which the continuity bars crossed only the column, the rotational flexural stiffness was higher. For these last ones, coefficients k and β for predicting the secant stiffness by simplified expression present in Brazilian Code NBR 9062 were evaluate from experimental results. These evaluated coefficients may be regarded as indicative values for structural designers and helpful for future researches.

Interface Characteristics and Properties of a High-Strength Corrosion-Resistant Stainless Steel Clad Rebar

This paper aims at manufacturing stainless steel clad (SSC) rebars by metal deposition and a hot rolling method as well as characterizing its interface features and mechanical properties. The interface of the SSC rebar is relatively flat and clean, exhibiting a metallurgical bonding state at the microscale. Decarburization occurred at the interface in the carbon steel side of the SSC rebar. The diffusion of C, Cr, as well as Mn was measured across the interface of the SSC rebar, and the diffusion distance of Cr and Mn was found at 32 µm and 25 µm, respectively. The Vickers hardness testing in the transition zone of the SSC rebar near the carbon side showed 545 HV0.2 due to the martensite phase formed by the diffusion of key elements C, Cr, and Mn. The microstructure in the transition zone near the stainless steel reveals the duplex structure of martensite and ferrite. The carbide precipitations were observed near the interface, both in the transition zone and in the base metal of the stainless steel zone. The yield strength, tensile strength, and elongation of the SSC rebar were found as 423 MPa, 602 MPa, and 22%. No macroscopic crack was observed after the positive or negative bending tests.

Long-term behavior of continuous composite slabs made with 100% fine and coarse recycled aggregate

A composite slab is an efficient modern structural member. Recycled fine and coarse aggregates are alternative green materials for the depleting natural sand and natural gravels in the composite slabs. In recent years, the nonuniform shrinkage occurring in single-side-exposed concrete has been discovered to significantly affect the long-term behaviors of composite slabs, which have been included in newly published codes. Applying recycled aggregate concrete (RAC) would further increase the effect of nonuniform shrinkage on the long-term behaviors of composite slabs. However, most studies, with RAC or not, have only focused on simply- supported composite slabs. For continuous composite slabs (CCSs), in addition to increasing deflections, a nonuniform shrinkage would induce a larger negative bending moment, which would further increase the crack width at the interior support region. Hitherto, no experiment has been conducted regarding the time-dependent crack width of CCSs and CCSs with RAC. Therefore, the aim of this study is to investigate the effects of nonuniform shrinkage and RAC on the deflections, strains, and cracks of CCSs. Hence, a 500-d experiment was conducted on three full-scale specimens. Finally, a finite element (FE) model was established and benchmarked against the test results of this study and those reported in the literature. The results indicated that (1) nonuniform shrinkage significantly increased the crack width at the negative bending moment region; (2) the use of RAC resulted in a more significant effect of the nonuniform, e.g. mid-span deflections, soffit strains, and crack widths increased by 40%, 64%, and 38%, respectively; and (3) the FE model can predict the long-term behaviors of CCSs well.

Experimental and analytical research on the flexural behaviour of steel–ECC composite beams under negative bending moments

Due to the strain-hardening and multi-cracking properties, engineered cementitious composite (ECC) is a new solution to the cracking issue in the negative bending moment region of steel–concrete composite beams. This paper presents an experimental and analytical study on the flexural performance of composite steel–ECC beams subjected to negative bending moments as well as the tension stiffening behaviour of reinforced ECC (R/ECC) flange slabs. Three beams with different slab materials and reinforcement ratios were tested under a hogging moment. Experimental results demonstrated significant enhancement in stiffness and crack resistance for the steel–ECC composite beams. A practical four-parameter fibre-bridging model was established to describe the strain-hardening behaviour of different ECC materials. Then, a modified analytical tension-stiffening model for R/ECC was formulated considering the strain-hardening behaviour of ECC and rebar–ECC bond–slip interaction based on the conventional tension-stiffening model for reinforced concrete. This modified model was verified by several direct tensile tests of R/ECC members. In addition, by applying the model to the traditional fibre beam–column element model, the mechanical performance and crack opening of general R/ECC structures were derived. The simulation results of the steel–ECC composite beams demonstrated satisfactory accuracy compared with the test results. Finally, a parametric study based on the new model was conducted to identify the influence of several important material and structural parameters on the flexural performance of steel–ECC composite beams under negative moments.

Stiffness and Cracking Behavior of New U-Shaped Steel and Concrete Composite Beam under Negative Bending

AbstractThis paper discussed the stiffness and cracking behavior of a new kind of reinforcement-stiffened cold-formed U-shaped steel and concrete composite beam (RCUCB) under negative bending. The ...

Timber-FRP composite beam subjected to negative bending

In the previous studies, the authors proposed the use of laminated veneer lumber – carbon fiber reinforced polymer (LVL-CFRP) composite beams for structural application. Bond strength of the LVL-to-CFRP interface and flexural strengthening schemes to increase the bending capacity subjected to positive and negative moment were discussed in the previous works. In this article, theoretical models are proposed to predict the moment capacity when the LVL-CFRP beams are subjected to negative moment. Two common failure modes – CFRP fracture and debonding of CFRP are considered. The non-linear model proposed for positive moment is modified for negative moment to determine the section moment capacity. For the debonding based failure, previously developed bond strength model for CFRP-to-LVL interface is implemented. The theoretical models are validated against the experimental results and then use to determine the moment-rotation behaviour and rotational rigidity to compare the efficacy of various strengthening techniques. It is found that combined use of bi- and uni-directional CFRP U-wrap at the joint performs well in terms of both moment capacity and rotational rigidity.

On Flexural Performance of Girder-To-Girder Wet Joint for Lightweight Steel-UHPC Composite Bridge

Joints are always the focus of the precast structure for accelerated bridge construction. In this paper, a girder-to-girder joint suitable for steel-ultra-high-performance concrete (UHPC) lightweight composite bridge (LWCB) is proposed. Two flexural tests were conducted to verify the effectiveness of the proposed T-shaped girder-to-girder joint. The test results indicated that: (1) The T-shaped joint has a better cracking resistance than the traditional I-shaped joint; (2) The weak interfaces of the T-shaped joint are set in the areas with relatively lower negative bending moment, and thus the cracking risk could be decreased drastically; (3) The natural curing scheme for the joint is feasible, and the reinforcement has a very large inhibitory effect on the UHPC material shrinkage; The joint interface is the weak region of the LWCB, which requires careful consideration in future designs. Based on the experimental test results, the design and calculation methods for the deflection, crack width, and ultimate flexural capacity in the negative moment region of LWCB were presented.

Numerical simulation and experimental investigations on a three-roller setting round process for thin-walled pipes

In order to reveal the process principle of three-roller setting round process and optimize the setting round strategy, the three-roller setting round process is simulated and experimented. The results show that there are three positive bending regions and three reverse bending regions in the cross section of pipe in the setting round process. The absolute value of equivalent stress and equivalent strain not only decreases from both ends to the geometric neutral layer along the thickness direction of pipe but also decreases from the center of each positive and negative bending region to both sides along the circumferential direction of pipe. The distribution of maximum stress and minimum stress conforms to the characteristics of pure bending deformation in the setting round process. The direction of tangential stress is the direction of main stress, and the direction of tangential strain is the direction of main strain. The geometrical dimensions of pipe do not change in axial and radial directions. The residual ovality of pipes with different initial ovality is basically the same, which proves that the uniform curvature theorem of reciprocating bending is correct. The residual ovality of pipes decreases with the increase of the reduction. With the increase of the relative thickness of pipes, the optimum reduction of pipes decreases gradually. Comparing experimental results with simulation results, the residual ovality of pipes can be less than 0.2%.

Experimental investigation on mechanical behavior of segmental joint under combined loading of compression-bending-shear

The non-circular tunnels, for example the quasi-rectangular tunnel, may generate a considerable shear force at their shoulder joints owing to the geometry effect. To investigate the shear force effect on the mechanical behavior (e.g., capacity, deformation and duality) of the segment joint, a series of full-scale mechanical loading tests were conducted and reported in this paper. The loading scenarios include the combined axis force and moment scenario (N-M), and the combined axis force, moment and shear force (N-M-Q) scenario. Both the positive bending moment and negative bending moment are considered. DIC technique is also adopted to capture the detailed cracking process in the N-M-Q loading test. The test results reveal that the mechanical response of the segmental joint under both N-M and N-M-Q loading scenarios can be divided into three stages, which are separated by the initial joint opening and the initiation of cracks. The shear force would lead to a larger deformation (e.g., deflection, joint opening and rotational angle) before the failure but result in a brittle failure of the segment joint. Moreover, the shear force could reduce the moment bearing capacity under the positive moment loading condition while has little effect under the negative moment loading condition. These shear force effects are thought to be caused by the shear induced dislocation and inclined cracks.

Partial Composite-Action and Durability Assessment of Slab-on-Girder Highway Bridge Decks in Negative Bending Using Long-Term Structural Monitoring Data

AbstractThis paper uses long-term bridge monitoring data to quantitatively assess the composite action exhibited in slab-on-girder highway bridges and investigates the potential relationship betwee...

A new protocol for testing RC beams in combined shear and tension loading conditions

The problem of the shear strength of reinforced concrete members which are simultaneously subjected to an axial tension occurs in a number of practical cases such as continuous beams rigidly connected to columns (where tension results from the restraint of the axial variation of length due to concrete shrinkage and temperature variation), columns or shear walls and foundation piles in beam-column or shear wall-slab frames subjected to high horizontal forces. An original protocol is proposed for testing in these loading conditions, where reaching shear failure represents the main difficulty for designing specimens. This protocol makes use of an original and reliable test setup, in which two horizontal forces are symmetrically applied apart the beam axis, making it possible to generate a constant axial force and a constant negative bending moment along span. The loading protocol is oriented towards a defined value of axial force, while shear at failure may be combined with a negative or positive moment. The loading path for bending moment and axial force is chosen as to remain inside the normal force-bending moment failure curve. The failure in shear occurs at constant axial force and increasing bending moment. The whole procedure was first implemented to perform three rather simple preliminary tests. Their results show the technical feasibility of this protocol. Some limitation of initial parameters was evidenced. So better parameters were chosen for carrying out the main experimental program (presented in another paper).

Experimental behaviour of steel-concrete composite box girders subject bending, shear and torsion

The results of two unique experimental campaigns carried out on composite box girder sections subjected to moment-shear interaction and moment-shear-torsion interaction are presented. They involve the behaviour of the box sections both in positive and negative bending. The effect of the flexibility of the connection is measured and accounted for. A finite element model is implemented to account for this effect, resulting in an improvement in the accuracy of the stiffness of the sectional behaviour. One of the main results is a significant over-resistance in relation to the shear capacity of the sections, which is very clear in the tests involving bending shear and torsion. This effect is attributed to the contribution to the shear capacity of the concrete slab.

Shear behavior and shear capacity prediction of precast concrete-encased steel beams

A novel precast concrete-encased steel composite beam, which can be abbreviated as PCES beam, is introduced in this paper. In order to investigate the shear behavior of this PCES beam, a test of eight full-scale PCES beam specimens was carried out, in which the specimens were subjected to positive bending moment or negative bending moment, respectively. The factors which affected the shear behavior, such as the shear span-to-depth aspect ratio and the existence of concrete flange, were taken into account. During the test, the load-deflection curves of the test specimens were recorded, while the crack propagation patterns together with the failure patterns were observed as well. From the test results, it could be concluded that the tested PCES beams could all exhibit ductile shear behavior, and the innovative shear connectors between the precast concrete and cast-in-place concrete, namely the precast concrete transverse diaphragms, were verified to be effective. Then, based on the shear deformation compatibility, a theoretical model for predicting the shear capacity of the proposed PCES beams was put forward and verified to be valid with the good agreement of the shear capacities calculated using the proposed method and those from the experiments. Finally, in order to facilitate the preliminary design in practical applications, a simplified calculation method for predicting the shear capacity of the proposed PCES beams was also put forward and validated using available test results.

Investigation of Traffic Loading Effects for Different Codes on Medium‐ and Small‐Span Girder Bridges in China

With increasing traffic volume, the traffic load grade given by design codes has gradually increased. For new bridges, there is no problem, and the traffic load can be met through the requirements of the new code. However, for existing bridges, there is a lack of uniform standards on whether they can continue to be used. It is not clear whether these bridges will be judged according to the new code or the original design code. The traffic loading effects of different codes on medium‐ and small‐span girder bridges in China are investigated in this study. Three codes are introduced: JTJ 021‐89, JTG D60‐2004, and JTG D60‐2015. Simply supported girder bridges and continuous girder bridges are discussed. The traffic loading effects calculated based on JTG D60‐2015 are significantly larger than those calculated based on JTJ 021‐89. For simply supported girder bridges, most of the differences range from 20% to 40%, and the maximum value is almost larger than 60%. For continuous girder bridges, most of the differences in the positive bending moments are concentrated in the 20%∼40% range, while the differences in the negative bending moments range from 10% to 20%. Therefore, the differences in traffic loading effects calculated based on various codes cannot be ignored in actual bridge engineering. The conclusion in this study can provide a basis for bridge structure evaluation and life prediction.

Experimental Study on Fatigue Performance of Negative Bending Moment of Steel‐Concrete Continuous Composite Box Girder

The experimental work presents results on the fatigue performance of composite beams in the negative moment region and the changes of stiffness and deformation of composite beams under repeated loads; fatigue tests were carried out on two double‐layer composite beams. The fatigue performance of composite beams with different reinforcement ratios under complete shear connection and the variation of deflection, strain of the reinforcement, strain of steel beam, and crack growth under fatigue load were obtained. The results showed that the fatigue resistance performance of concrete slab with low reinforcement ratio was much lower than that of concrete slab with high reinforcement ratio whereas, under the fatigue load, the stress of the welding nail in the negative moment region was small and the slip was almost negligible. The degradation of stiffness and the development of cracks were mainly due to the degradation of bond‐slip between the concrete and reinforcement. The fatigue failure mode was the fracture of the upper reinforcement in negative moment region. The results obtained in this study are helpful in the design of composite beam.

Measurement of deformation of the concrete sleepers under different support conditions using non-contact laser speckle imaging sensor

Prestressed concrete sleepers play a significant role in distributing wheel loads from the rails to the ballast layer. Cyclic wheel loads may cause local deterioration of the ballast layer which would affect the support conditions beneath the sleepers. Therefore, understanding the influence of different support conditions on the deformation of sleepers is necessary for maintaining safe railroad operations. In this study, a non-contact and non-destructive laser speckle imaging sensor (LSIS) was developed and successfully applied to investigate the flexural behaviour of concrete sleepers under various support conditions, including “full support”, “partial support” and “centre binding”. The results show that LSIS was in agreement with foil strain gauges of achieving high-resolution strain measurements with a maximum mean absolute error of 5.41±3.12με (equivalent to a mean absolute error of 7.15%) as the detection threshold (20 με) is exceeded. More than three times change in the negative bending moment was observed at the mid-span of the sleeper as the support condition was changed from “full support” to “centre binding”, which indicates the potential risks of voided ballast support and importance of ballast tamping in railway maintenance.

Statistical Prediction of Center Negative Bending Capacity of Pretensioned Concrete Crossties

AbstractWhen concrete railway crossties are installed in North American freight track and subjected to flexural loads, center negative bending is one of the most critical demands. However, the ulti...