Showing papers on "Bending moment published in 2021"

Deformation limit for the ultimate strength of hollow section joints

Abstract: In order to determine the ultimate load capacity of hollow section joints with CHS or RHS chords, in cases the load - deformation diagrams or moment - rotation diagrams do not show a pronounced peak load, a deformation criterion has been discussed and evaluated. For this aim, various research activities have been carried out for the following types of connections: plate or I-beams to CHS connections, plate or I-beams to RHS connections, X-joints in CHS, X- and T-joints in RHS. From the previous research, it has been shown that the behaviour of hollow section joints is mainly dependent on the local plastification of the chord if the connection is designed in such way that the failure of the brace does not occur before connection failure. Therefore, the deformation limit criteria should be based on the local deformation of the chord face at the intersection between brace and chord. For the design of connections, it must be ensured that conditions with regard to the ultimate strength, deformation capacity and serviceability are satisfied. For this reason, the given deformation limit has been verified by checking the numerical results for the above mentioned types of connections loaded by axial compression or in-plane bending moment. Finally, the ultimate strengths at the deformation limit for connections with RHS chord have been compared with available design formulae from several references.

Experimental investigation on cold-formed steel lipped channel beams affected by local-distortional interaction under non-uniform bending

Abstract: This paper reports an experimental investigation, carried out at The University of Hong Kong, on the behaviour of cold-formed steel lipped channel beams affected by local-distortional (L-D) interaction under non-uniform bending – to the authors’ best knowledge, these are the first tests specifically devoted to this topic. This investigation consists of 16 non-conventional four-point simply supported bending tests involving twin lipped channel beams arranged in a “back-to-back” configuration and laterally restrained at the loading points. The 32 lipped channel specimens were brake-pressed from high-strength zinc-coated G450 grade structural steel sheets. Tensile coupon tests were performed to obtain the specimen material properties and initial geometrical imperfections were measured prior to testing. The beam geometries were carefully selected to enable testing beams that are prone to “true L-D interaction” (close critical distortional-to-local buckling moments) when acted by trapezoidal bending moment diagrams with four distinct gradients – all the tested specimens exhibited the sought L-D interactive nature. The output of the experimental investigation consists of (i) applied moment vs. displacement equilibrium paths, (ii) photos showing beam deformed configurations along those paths (including the failure modes) and (iii) the failure moment data. Lastly, the experimental failure moments obtained are compared with their predictions provided by the (i) current local and distortional Direct Strength Method (DSM) strength curves and (ii) available DSM-based approaches against L-D interactive failures, which were developed and calibrated exclusively in the context of beams subjected to uniform bending.

Deformation response of roof in solid backfilling coal mining based on viscoelastic properties of waste gangue

Abstract: Solid backfill mining (SBM) is a form of green mining, the core of which is to control and minimize the deformation and movement of strata above longwall coal mines. Establishing a mechanical model that can reliably describe roof deformation by considering the viscoelastic properties of waste gangue is important as it assists in improving mine designs and reducing the environmental impact on the surface. In this paper, the time-dependent deformation characteristics of gangue under different stress levels were obtained by using lateral confinement compression, that reliably represents the compaction of goaf. The viscoelastic foundation model for gangue mechanical response is different from the traditionally used elastic foundation model, as it considers the time factor and viscoelasticity. A mechanical model using a thin plate on a fractional viscoelastic foundation was established, and the roof deflection, bending moment, time-dependent, viscous and other characteristics of SBM were included and analyzed. Compared with the existing elastic foundation model, the proposed fractional order viscoelastic foundation model has higher accuracy with laboratory data. The plate deflection increases by 50.9% and the bending moment increases by 37.9% after 100 days, which the elastic model would not have been able to predict.

Temperature-dependent physical characteristics of the rotating nonlocal nanobeams subject to a varying heat source and a dynamic load

Abstract: In this article, the influence of thermal conductivity on the dynamics of a rotating nanobeam is established in the context of nonlocal thermoelasticity theory. To this end, the governing equations are derived using generalized heat conduction including phase lags on the basis of the Euler–Bernoulli beam theory. The thermal conductivity of the proposed model linearly changes with temperature and the considered nanobeam is excited with a variable harmonic heat source and exposed to a time-dependent load with exponential decay. The analytic solutions for bending moment, deflection and temperature of rotating nonlocal nanobeams are achieved by means of the Laplace transform procedure. A qualitative study is conducted to justify the soundness of the present analysis while the impact of nonlocal parameter and varying heat source are discussed in detail. It also shows the way in which the variations of physical properties due to temperature changes affect the static and dynamic behavior of rotating nanobeams. It is found that the physical fields strongly depend on the nonlocal parameter, the change of the thermal conductivity, rotation speed and the mechanical loads and, therefore, it is not possible to neglect their effects on the manufacturing process of precise/intelligent machines and devices.

Seismic behavior of thread-fixed one-side bolted endplate connection of steel beam to hollow square column

Abstract: Experimental studies were conducted to investigate the seismic behavior of the Thread-fixed One-side Bolts bolted Endplate Connection (TOBEC) of a steel beam to a Hollow Square Column (HSC). Three forms of strengthening methods were applied to the TOBECs, including the infilled concrete of HSC, the small facing plates, and the big facing plate outside of HSC. In addition, one TOBEC with no strengthening structures and one traditional Standard Nut-fixed Bolted Endplate Connection (SNBEC) were tested for comparative analysis. Presented test results included failure modes, bending moment strength, rotation ability, ductility, strength and stiffness degradation, and energy dissipation capability of connection. Test results indicated that these strengthening methods could effectively improve the mechanical performance of TOBECs. The initial stiffness and ultimate bending moment of the strengthened TOBECs could reach or even exceed those of SNBECs. The strengthened TOBECs could satisfy the rotation limitation requirements specified in both GB50011-2010 and FEMA-350, which proved the applicability of TOBECs in moment-resisting framed structures.

An experimental analysis of the end-notched flexure composite laminates beams with elastic couplings

Abstract: This paper presents an experimental study of the composite beams with elastic couplings subjected to the end-notched flexure (ENF) test. The object of research were carbon/epoxy composite laminates with specific stacking sequences exhibiting the bending–extension and the bending–twisting couplings. In addition, multidirectional laminates with different delamination interfaces were tested. Influence of elastic coupling phenomena on behavior of laminates subjected to the bending moment as well as on fracture toughness and delamination surfaces after the ENF tests was discussed. All experiments were performed according to the ASTM D7905 Standard. Determination of crack initiation was supported by the acoustic emission technique. Data analysis of the ENF test was performed by using both the direct beam theory and the corrected beam theory. Results obtained by using the classical data reduction schemes were compared with the compliance-based beam method (CBBM). Greater values of the fracture toughness obtained by using the non-standardized methods can be explained by the effect of the fracture process zone which was taken into account in the CBBM calculation scheme. Delamination surfaces of coupled laminates after the ENF tests were investigated by using the scanning electron microscopy. Results revealed that the effect of elastic couplings might influenced on intense bridging phenomena, more extensive fracture process zone and contribution of the mode III in total delamination resistance. Nevertheless, application of the standardized ENF procedure to determination of the fracture toughness of laminates exhibiting elastic couplings is still possible, provided assistance of additional data reduction schemes and techniques or numerical analysis.

Theoretical model of bending moment for the penetrated mortise-tenon joint involving gaps in traditional timber structure

Abstract: Mortise-tenon joints often have neighboring gaps due to initial manufacturing errors and accumulated damage over thousands of years. The looseness of joints can cause degradation of mechanical performance of joint, which might lead to the collapse or damage of the entire structure. In this study, the mechanical performances of penetrated mortise-tenon joint involving gaps were investigated. Working states and judging criteria for different working states were produced under positive and negative loading. A theoretical model of the bending moment for a loose mortise-tenon joint was proposed. Full-scale experiments were conducted to verify the proposed theoretical model. Transverse four-column wooden frames, characterizing the overall mechanical properties of a structure, were chosen to clarify the applicability of the proposed model. A simplified finite element model (FEM) with bar units and rotation springs was established and verified using solid FEM. The deformation characteristics and lateral resistance of wooden frame were then analyzed. The results showed that the theoretical model was in good agreement with test results and could be used to estimate the joint bending moment. Simplified models of joints were then applied in the establishment of a timber structure. The lateral behavior of the wood frame mainly contributed by column foot joints at the beginning of rotation and penetrated mortise-tenon joints at later rotation. This study provided important references on the protection and repair of existing traditional timber structures.

Cross-section effect on mechanics of nonlocal beams

Abstract: In the current practice, the one-dimensional nonlocal constitutive relations are always employed to model beam-type structures, regardless of the inherent three-dimensional interactions between atoms, resulting in inaccurately predicted nonlocal structural behaviors. To improve modeling, the present work first reveals and establishes how the nonlocal interactions in beams’ width and height directions substantially affect the bending behaviors of nanobeams. Based on the new concept of a general three-dimensional nonlocal constitutive relation, a three-dimensional nonlocal Euler–Bernoulli beam model is developed for bending analysis. Closed-form solutions for the deflections of simply supported and cantilevered beams are derived. The cross-section effect on the nonlocal stress, the bending moment and the deflection is explored. Moreover, an effective calibration method is proposed for the determination of the intrinsic characteristic length based on molecular dynamics simulations. It has been found that the actually nonlocal physical dimension of beam-type structures is not in agreement with that from the one-dimensional geometric direction of classical beam mechanics, and the beams’ width and height must be taken into consideration, instead of just employing the beam’s length, a practice which has been somewhat blindly undertaken in the current practice without indeed much theoretical support and understanding. A beam problem at nanoscale has to be viewed and treated as a “three-dimensional” geometric and physical problem due to its geometric dimension in length and its physical dimensions in both the thickness and the width. When its intrinsic characteristic length is comparable to its width or thickness, a rigidity-softening effect of a beam can be observed. Further, it is established that the nonlocal effect is more sensitive in the thickness direction, as compared with the width direction.

Effects of Monopile Installation on Subsequent Lateral Response in Sand. II: Lateral Loading

Abstract: Monopiles under in-service conditions are subjected to lateral forces and resultant bending moments from the offshore environment. The subsequent lateral response following installation is ...

Behavior of steel-reinforced composite concrete columns under combined axial and lateral cyclic loading

Abstract: This study presents the experimental and numerical investigations on structural steel-reinforced concrete (SRC) columns under combined axial and lateral cyclic loadings. The main parameters evaluated are the peak lateral strength, mode of failure, hysteretic response, stiffness degradation , and energy dissipation potential of SRC columns. A parametric study has been conducted using a finite element software ABAQUS to predict the flexural capacity of the SRC columns under varying axial load levels and to evaluate the reliability of the design guidelines of Eurocode 4 (2004) and AISC 360-16 (2016) in predicting the axial load (P) - bending moment (M) interaction behavior of SRC columns. In the tension damage regions, the experimental and numerical data points mostly lie within or on the unfactored P-M envelopes of both these standards. However, the data points are found to fall outside the P-M envelopes in the compression damage region. For the SRC columns designed to fail in the compression damage, the Eurocode 4 (2004) provisions showed a more reliable prediction of the failure loads under the uniaxial bending condition.