Positive Bending Research Articles

Three Dimensional Analysis of Raft Foundation Rest on Homogenous Soil Using Finite Element Method

The study includes analysis of Al – Samaraie Hospital raft foundation by the finite element method (FEM) using program package Fear 4.0. The analysis conducted on the foundation is resting on infinite, homogeneous, isotropic soil. In this study, effect of raft thickness, soil properties, modulus of elasticity and Poisson’s ratio of soil are investigated. The most dominant parameters such as thickness of raft foundation, modulus of elasticity and Poisson’s ratio of soil are graphically plotted against maximum displacements, maximum positive and negative bending moments (Mx, My and Mxy). The results showed that raft thickness and soil properties play a vital role in changing the values of maximum positive and negative moments (Mx, My) and maximum displacements, while their effect on maximum positive and negative moment (Mxy) can be considered as insignificant. Also, empirical equations have been developed to calculate maximum positive and negative bending moment (Mx, My) and maximum displacements beneath the raft. This is performed by the aid of statistical program (Statistic). The accuracy of the proposed equations was ranging between 92.7% and 99.9%.

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.

Study on the Mechanical Behavior of a Secondary Tunnel Lining with a Yielding Layer in Transversely Isotropic Rock Stratum

For tunnels excavated in soft layered rock strata, the secondary lining is susceptible to asymmetrical pressure and substantial concrete cracking. To solve this problem, a supporting system that combines a secondary lining with a highly deformable layer is proposed. First, field investigations were conducted to reveal the mechanical behaviors of the secondary lining of two typical tunnels situated in phyllite formation in China. Then, similarity model tests were used to analyze the mechanical responses of the secondary lining in layered rock stratum with different inclination angles. Finally, numerical simulation was adopted to systemically investigate the yielding mechanism of yielding layer in different cases. The results show that: (1) The distribution of inner force and deformation of lining is non-uniform due to the anisotropy of rock mass and geo-stress field, with the positive bending moment and larger axial force appearing mainly in the region where the tangent of the tunnel contour is parallel or vertical to the weak planes, respectively. (2) The existence of yielding layer has no influence on the distributed feature of inner force and displacement around tunnel perimeter, while it can significantly lower the magnitude of inner force and displacement of the lining. (3) The distinctly compressive zones of yielding layer coincide with the zones of positive bending moment, and the line connecting the central points of the evidently compressive zones on both sides will deflect towards the direction of minor principal stress to a certain extent. (4) The inner force and deformation of lining increase with the increase in the strength or decrease in the thickness of yielding layer, and this changing trend is related to the different supporting curves for linings with yielding layer of different strength and thickness.

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.

Rigid slab foundation subjected to strike–slip faulting: mechanisms and insights

In this paper, the interaction of rigid slab foundations with a strike–slip fault is studied. A three-dimensional finite-element model of the soil–foundation system is developed, employing a thoroughly validated constitutive model that incorporates strain softening. The widely used rigid box type boundaries are compared to periodic boundaries, demonstrating their superiority. Allowing the soil to deform freely, periodic boundaries allow realistic simulation of fault rupture propagation through soil and minimisation of parasitic boundary effects. An approximate dimensional formulation is presented and verified by comparing the response of two self-similar systems. A parametric study is conducted, revealing two distinct kinematic mechanisms: a rotational one, where the foundation mainly rotates; and a translational one, where the foundation either displaces parallel to the fault trace or remains almost stationary. It is shown that the response is controlled by the presence of the foundation, acting as a kinematic constraint, which can be quantified by its polar moment of inertia, Iz. The rotational mechanism leads to positive bending moments of larger magnitude, whereas the translational leads to negative moments of larger magnitude. The effect of key dimensionless parameters is parametrically investigated, including the fault rupture location, the surcharge load, the interface friction coefficient and the foundation aspect ratio. Shorter foundations (parallel to the fault trace) tend to rotate, whereas longer ones tend to displace. Fault rupture locations close to the foundation sides lead to translation, whereas locations close to its centreline lead to rotation. The development of the translation mechanism is facilitated by the increase of surcharge load and interface friction coefficient.

Static test study on precast concrete frame beams with large-diameter and high-strength steel bars

The paper is focused on the mechanical properties of precast concrete frame beams with large-diameter and high-strength steel bars. The full-scale static tests and nonlinear finite element analysis were carried out on the two proposed beams with steel bars of HRB500 Ø32-Ø25 and Ø40-Ø32 to study the load-carrying capacity, flexural capacity and plastic rotational capacity. The influence of steel bar diameter on mechanical properties were explored. On the basis of equal-strength principle of flexural capacity at the same time, the finite element model of the cast-in-place concrete frame beam with large-diameter of HRB500 and ordinary steel bars of HRB400 were compared. Results indicated the properties of the precast concrete frame beams with large-diameter and high-strength steel bar. The load-carrying capacity of the prefabricated concrete beam with steel bars of Ø40-Ø32 was higher. The coefficient of plastic rotational capacity was 3.41 and 2.88 of specimens with steel bars of HRB500 Ø32-Ø25 and Ø40-Ø32, respectively. The positive section yield bending moment could be calculated by the current concrete codes. The properties such as yield load, flexural bearing capacity and the plastic rotational capacity were similar to the cast-in-place concrete frame beam, and could be verified by the current standard.

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.

Prevalence of adolescent idiopathic scoliosis in Turkey: an epidemiological study

BACKGROUND CONTEXTStudies have shown that adolescent idiopathic scoliosis (AIS) prevalence varies between 0.35% and 5.2% and it is generally accepted as an average of 2%–3% in children under age 16. There are a few narrow-scope studies based on school screening performed on the epidemiology of AIS in Turkey. Prevalence rates reported by these studies are lower than reported in neighboring countries. Of note, they were conducted in single cities, generally based on small sample size, and are different from each other in terms of methodology and age groups. The present study was conducted based on a large population in 85 schools of 40 provinces in Turkey. PURPOSEThe aim of this study was to determine the prevalence of AIS in Turkey. Secondary outcomes were to determine age, gender, curve distribution, using standard tests, and radiological verification. STUDY DESIGNA cross-sectional epidemiological study. PATIENT SAMPLEThe sample size was calculated to estimate the prevalence of AIS in children aged 10–15 years in Turkey. OUTCOME MEASURESAdams’ forward bending test, angle of trunk rotation measurement, and posture analysis were used to screen. Students who had an angle of trunk rotation greater than or equal to five (≧5°) with scoliometer measurement or who had a positive forward bending test were referred to the mobile X-ray unit located in the school-yard on screening day. Their diagnosis was confirmed using Cobb angles of greater than or equal to 10 (≧10°). METHODSMedical personnel, mobile radiological tools, and logistical support needed during fieldwork were provided by the Directorate General for Health Research, Ministry of Health Republic of Turkey. Spine and posture were examined in upright standing position. Examiners looked for shoulder asymmetries, scapular prominence, unequal waist, and lower limb length discrepancy. Potential scoliosis diagnosis was verified with onsite radiographic examination. Cases with a Cobb angle of ≧10° detected in any region were accepted as scoliosis. The direction and location of scoliosis were determined according to the Scoliosis Research Society terminology criteria. RESULTSA total of 16,045 students were reached whose informed consent forms were signed by their parents. The prevalence of AIS was found to be 2.3% (female, 3.1%; male, 1.5%). Radiological confirmation rate was 98.8%; 256 (69.3%) of 369 adolescents with scoliosis had a single curvature and 108 (29.3%) had a double curvature. The most common single curve type was a lumbar curve. In all, 90.5% of cases with AIS had a mild (range of 10°–19°) Cobb angle. CONCLUSIONSThe prevalence of AIS was 2.3% in Turkey. This prevalence rate was considerably higher than the values in previous regional studies conducted in Turkey; however, it was close to generally accepted averages in the literature. One of the strongest aspects of the study was that radiologic confirmation of each suspected case was made during the screening.

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 analysis of the structural behavior of different types of shear connectors in steel-concrete composite beams

ABSTRACT: The present work aims to compare the structural behavior of steel-concrete composite-section beams for three types of shear connectors made of U hot rolled section and cold-formed sections of U and L. Experimental tests were performed with the three types of connectors associated with I section laminated steel beams and reinforced concrete slabs. For each type of connector, three push-out tests were performed, as well as six simple supported beam tests to evaluate the positive bending moment region. The results indicated that the direct shear behavior among the different types of connectors presents significant differences, however they do not significantly influence the average flexural strength of the composite beams. These, however, present considerable differences in deflections and deformations due to the stiffness differences of the connectors.

Computation of Impact Effect of Multi-span Beam Bridge under Light-Rail Vehicle

In this paper, the bending moment impact effect of a 7-span beam bridges under the single-carriage light-rail vehicle at different speeds is investigated. The 7-span composite box girder bridge is modelled using the shell element. The light-rail vehicle is modeled using the rigid beam and the spring-damper elements with 31 degrees-of-freedom. The vehicle-bridge interaction is modeled using the displacement contact method. The computed bending moment envelopes show that for the studied bridges under the concerned light-rail vehicle at the moving speeds from 80 km/h to 120 km/h, the impact effect on the positive bending moment of the first and the sixth span are the most notable: the impact factor will reach 1.742 for the first span and 1.508 for the sixth span.

Trial Production of Stainless Steel Cladding Rebar by Liquidsolid Casting and Hot Rolling Method

In the present investigation, liquid-solid casting and hot rolling method was successfully used to manufacture stainless steel cladding (SSC) rebar. Stainless square tube that was surface treated by pellet blasting treatment was preheated to 1100 °C, and then liquid carbon steel which was heating up by induction furnace to 1620 °C was filled into the tube to cast the SSC billet. SSC billet was rolled in a wire and rod plant successfully due to metallurgical bond state between the tube and carbon steel. Soaking temperature and starting rolling temperature as well as finishing rolling temperature were exhibited 1180C, 1130C and 1000C. Uniaxial tensile testing of SSC rebar at room temperature exhibited an extremely yield strength of 433 MPa and a tensile strength of 599 MPa, while the elongation reached 24%. Positive and negative bending experiment showed no cracks during the deformation. Through metallographic analysis, it was found that the base structure of stainless steel was ferrite, and heterogeneous phases such as martensite and ferrite was discovered near the interface of carbon steel and stainless steel.

Equivalent Stiffness Methods for Free Vibration and Bending of Bimodular Composite Laminated Thick Curved Beam

In this research work an attempt has been made to analyzed the bending and free vibration behavior of bimodular composite material laminated thick curved beam based on first order shear deformation theory (FSDT). The effect of coupling parameter is more severe in bimodular laminated beam as compare to unimodular laminated beam. Therefore, equivalent stiffness methods (VS and RC) are used to incorporate the effect of all the coupling parameters. In the present analysis uniformly distributed load in transverse direction is considered. Hamilton’s principle is applied to elaborate governing equations from energy functional, and the equations are solved by analytical method. The position of neutral axis, transverse deflection, through the thickness strain distribution and frequencies for positive and negative side bending are presented for different bimodular composite material laminated curved beam. The results are presented for different stacking sequence and geometric parameter of the beam. The non-dimensional neutral surface location, positive and negative side bending deflections and positive and negative half cycle frequencies are having same magnitude for [00]4 or [00/900]s laminated curved beam of Material 1 (Aramid Rubber), and for Material 2 (Polyester Rubber) they are not same.

Investigating partial tension field action in gable frame panel zones

Gable metal frames are popular, cost-efficient structural systems for commercial and industrial buildings. The use of relatively thin web material typically leads to shear buckling of the column panel zone when such frames are subjected to lateral loads. Previous experimental research has shown that the exterior corner of a panel zone in gable frame knee joints may not be stiff enough to fully develop tension field action (TFA), but that some post-buckling strength is developed. This paper presents a theoretical model for TFA in knee joints based on plastic analysis, and an accompanying equation for predicting the post-buckling panel zone strength for positive bending (wherein the tension field is oriented from the interior to the exterior corners). The TFA was found to primarily depend on three design parameters, namely, flange flexural strength, panel aspect ratio, and panel slenderness. To calibrate the proposed equation, a parametric analytical study was conducted using the finite element method. The modeling scheme accounted for material and geometric nonlinearity and was validated with experimental test data. The study involved 98 prototype gable frame configurations and allowed the investigation of the impact of the aforementioned three design parameters on the TFA. The proposed equation was found to predict the panel zone shear strength for the prototype frames with an average error of 1% and an error standard deviation of 5%. Therefore, the equation can be used to calculate the post-buckling shear strength of panel zones for the range of design parameters considered in the parametric study.

Research on Buckling and Post-buckling Characteristics of Composite Curved Stiffened Fuselage Panel under Hoop Bending load

In order to study the buckling, post-buckling and failure modes of composite fuselage structures under circumferential bending loads, innovative four-point bending tests technology was developed and performed on composite curved stiffened fuselage panel (CSFP) specimens with two frame configurations of C-section and Z-section. Meanwhile, the stability engineering analysis and estimation based on plate buckling theory and simplified boundary were carried out, and the finite element (FE) models based on Hashin failure criterion were established to simulate the buckling, post-buckling and failure modes of CSFP specimens. The tests and analysis results show that the buckling modes and failure modes of C-section and Z-section specimens are different under positive bending loads. Specifically, the buckling of C-section specimens firstly occurs in the middle of the frame, then local buckling occurs at both ends of the frame, leading to fracture. For Z-section specimens, only local buckling occurs in the middle of the frame, which directly leads to fracture. By comparing the three methods, the results of FE analysis and engineering calculation are in good agreement with the test results. Among them, the prediction of instability mode and failure mode by FE method is very accurate, and the buckling strain calculated by engineering method can provide a good reference for structural design.

THREE-DIMENSIONAL NUMERICAL MODELLING OF FIRE EXPOSED COMPOSITE SLABS WITH STEEL DECK

Composite slabs with reinforced concrete and cold-formed profiled steel deck are very popular and reduce the building construction time. The steel deck acts as a permanent formwork to the concrete topping. Usually, the concrete is reinforced with individual rebars placed within the ribs for positive bending, and a steel mesh on the top for negative bending and to prevent concrete cracking. The fire rating of these building elements involves the analysis of different criteria, namely load bearing (R), integrity (E) and insulation (I). The integrity is easily verified, due to the construction method. The other two metrics require the development of experimental fire tests, the application of simplified calculation methods or the development of advanced calculation models. This investigation introduces 3-D numerical validation models for load bearing (R) and insulation (I) criteria. Parametric analyses are developed to investigate the effect of the load into the fire resistance (R) and critical temperature of the steel components (deck, rebar and mesh), as well as the effect of the concrete thickness on the fire resistance from the insulation standpoint (I). The advanced calculation model consists of a non-linear analysis for the thermal and structural behaviour. Both thermal and mechanical models consider perfect contact between materials. For the thermal model, an alternative model is used, with an air gap included between the steel deck and concrete topping to simulate debonding effects. For the mechanical model, the live load level changes from 1.0 kN/m2 to 21.0 kN/m2, and the dead load presents a constant value of 2.8 kN/m2. The fire resistance is determined according to standards, based on the maximum displacement or the rate of displacement. The critical temperature of each steel component decreases with the load level. A new proposal is presented for the critical temperature of each steel component and for the fire resistance according to the insulation criterion.