In the present study, the buckling problem of nonhomogeneous microbeams with a variable cross-section is analyzed. The microcolumn considered in this study is made of functionally graded materials in the longitudinal direction and the cross-section of the microcolumn varies continuously throughout the axial direction. The Bernoulli–Euler beam theory in conjunction with modified strain gradient theory are employed to model the structure by considering the size effect. The Rayleigh–Ritz numerical solution method is used to solve the eigenvalue problem for various conditions. The influences of changes in the cross-section and Young’s modulus, size dependency, and non-classical boundary conditions are examined in detail. It is observed that the size effect becomes more pronounced for smaller sizes and differences between the classical and non-classical buckling loads increase by increasing the taper ratios.

/pdf/buckling-analysis-of-functionally-graded-tapered-microbeams-3c5iqmcg.pdf

Buckling Analysis of Functionally Graded Tapered Microbeams via Rayleigh–Ritz Method

Compression-shear performance and failure criteria of seawater sea-sand engineered cementitious composites with polyethylene fibers

Mechanical performance and failure criterion of coral concrete under combined compression-shear stresses

Although the author is well aware that it is nothing special, presented here is the method that he uses to design the columns of a seismic resistant reinforced concrete structure, in hopes that this could be of use to someone. The method, which is directed at satisfying the capacity design requirements without excessively large sections, consists of proportioning the column so that the seismic action effects shall be resisted by the maximum of the bending moment–axial force interaction curve. That design condition is defined by two equations whose solution provides the optimal aspect ratio (or, alternatively, the optimal section side length) and the maximum feasible reinforcement ratio. The method can be used directly to determine the optimal column for given beam spans and vertical loads, or indirectly to determine the optimal beam spans and vertical loads for given cross-sectional dimensions. The paper presents the method, including its proof, and some applications together with the analysis on the optimality of the obtained solutions. The method is intended especially for the practicing structural engineer, though it may also be useful for educators, students, and building officials.

/pdf/optimal-design-of-seismic-resistant-rc-columns-1ritpblq3x.pdf

Optimal Design of Seismic Resistant RC Columns

Experimental and modeling research on compression-shear behavior of carbon fiber reinforced coral concrete

A series of multi-scale sandwich cantilever micro-beams are prepared to investigate the size-dependent phenomenon in this paper. The sandwich micro-beam samples consist of a titanium substrate with a thickness of 1.996μm and two symmetrical nickel coatings with thickness between 106.6 and 362.6 nm by employing a physical vapor deposition method. The vibration responses of these composite micro-beams are excited by an acoustic exciter and measured by a laser Doppler vibration measurement system. It is revealed that with the decreasing of coating thickness, the dimensionless bending rigidity of nickel coating increases, and the dimensionless natural frequency of micro-beam increases first then decreases. Based on the non-classical continuum theories, the theoretical model of the sandwich micro-beam is established. Then the material length scale parameters are derived. The applicability of the non-classical continuum theories is verified when the material characteristic size of the structure is smaller than the material length scale parameter. The results are of great significance to the design and optimization of micro-/nano-electro mechanical systems. 

Size-dependent vibration of multi-scale sandwich micro-beams: An experimental study and theoretical analysis

To investigate the combined compression-shear performance of self-compacting concrete (SCC), eight groups of concrete specimens under different axial compression ratios were designed, and the composite performance under different axial stresses was carried out by hydraulic servo machine. The uniaxial and tensile splitting strength of SCC were also included in the study. The failure modes of SCC were presented, discussed, and compared with normal concrete (NC). The characteristic points of stress-strain curves of SCC specimens from the experiments were extracted and analyzed under different axial compression stress. Based on the experimental results, the shear strength of compression-shear load was divided into cohesive stress and residual friction stress. The variation of residual stress and cohesive stress under the combined compression-shear stress was analyzed, and the relationship was obtained by numerical regression. Research results indicated that the residual stress increases linearly with the compression stress while the cohesive stress increased at first and then decreased. The research found that the friction coefficient of SCC was much smaller than NC due to the lack of interlocking effect. Utilizing the compression-shear strength of SCC, the material failure criteria of SCC were proposed from the view of shear failure strength and octahedral stress space, which could fit the experimental results confidently following the mathematical regression analysis. The comparison with data from other literature shows favorable consistence with the obtained criteria. The results of the study could be beneficial complement in engineering practices where SCC was applicable.

https://www.mdpi.com/1996-1944/13/3/713/pdf

Experimental Study and Failure Criterion Analysis on Combined Compression-Shear Performance of Self-Compacting Concrete.

Experimental study on the mechanical properties of internally cured concrete with super absorbent polymer under monotonic and cyclic loads

To investigate the relationships between the different mechanical strength of internally cured concrete with Super Absorbent Polymer (SAP concrete), the uniaxial mechanical properties of SAP concrete with different internal curing water-cement ratios were studied. Various SAP concrete specimens were prepared, and the uniaxial compressive, splitting tensile, as well as four-point bending tests, were carried out using the electro-hydraulic servo testing machine. The cubic compressive strength, splitting tensile strength, and flexural strength of SAP concrete with different internal curing water-cement ratios was obtained. The converting relationships between the internal curing water-cement ratio and different mechanical strengths were analyzed extensively. Based on the conversion formulas of different strength indexes proposed by different national standards and other researchers, the equations among the splitting tensile strength, cubic compressive strength, and flexural strength of SAP concrete were proposed and verified using the experimental data. According to the comparative analysis results, the proposed formulas in this study have significant applicability and can help achieve a practical application of SAP concrete.

/pdf/comparative-study-on-the-mechanical-strength-of-sap-8znfbfczlh.pdf

Comparative Study on the Mechanical Strength of SAP Internally Cured Concrete

The lift-off method is an effective method to detect the effective pre-stress under the bridge anchor, but the mechanism of the force when the clip is disengaged is unclear. When using this method to detect pre-stress, how to determine the bite force of the clips to obtain the effective pre-stress under the anchor is not reported in the literature. Firstly, this paper analyzed the stress characteristics of the anchor system when the lift-off method is used, and analyzed the cause of the sudden change of the lift-off curve. Secondly, a theoretical method for calculating the bite force between the clips and the anchor plates was established, and the influence of the friction coefficient and tensile force on the bite force was analyzed. Thirdly, an indoor model test of clip bite force was designed, and the lift-off method outdoor test of an actual pre-stressed beam was carried out. The theoretical calculations and experimental values were compared and analyzed, and the results were in good agreement. On the basis of calculations and testing, we proposed a theoretical model of the linear relationship between the bite force and tensile force of the liftoff method, and recommended a formula for bite force based on test results. At the same time, based on theoretical calculations, we proposed a rational function fitting model for the friction coefficient and the linear slope of the bite force between the steel strand and the clips. The analysis shows that the friction coefficient of the proposed theoretical model is reasonable.

A Novel Theoretical Model of Bite Force for Detecting Pre-Stress by Lift-Off Method

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