Analysis of Shear-critical reinforced concrete columns under variable axial load

Older existing reinforced concrete (R/C) frame structures often contain shear-dominated vertical structural elements, which can experience loss of axial load-bearing capacity after a shear failure, hence initiating progressive collapse. An experimental investigation previously reported by the authors focused on the effect of increasing compressive axial load on the non-linear post-peak lateral response of shear, and flexure-shear, critical R/C columns. These results and findings are used here to verify key assumptions of a finite element model previously proposed by the authors, which is able to capture the full-range response of shear-dominated R/C columns up to the onset of axial failure. Additionally, numerically predicted responses using the proposed model are compared with the experimental ones of the tested column specimens under increasing axial load. Not only global, but also local response quantities are examined, which are difficult to capture in a phenomenological beam-column model. These comparisons also provide an opportunity for an independent verification of the predictive capabilities of the model, because these specimens were not part of the initial database that was used to develop it.

Stress Monitoring in a Real-Size Reinforced Concrete Column Using Torsional Resonance

Nondestructive detection and monitoring of stress in concrete structural members is highly coveted. Yet, there are still no efficient techniques capable of achieving that goal. The leading approach towards this goal has been based on acoustoelasticity, the relationship between mechanical properties, such as mechanical wave speed, and the stress state of the solid medium. In concrete materials, acoustoelasticity has been increasingly studied, mainly using wave propagation phenomena, and usually in small samples of plain concrete — without steel reinforcement — axially loaded. A less studied approach involves the use of resonance phenomena, which offers other benefits. In this study, we tested a real-size reinforced concrete column of cross section 20 cm × 20 cm and 2 m long, by applying three cycles of controlled compressive axial load, varying from 0 to 4 MPa, and measuring axial strains and torsional frequencies of vibration. Repeatable results show that the frequencies of vibration and applied compression are positively correlated. indicating a dominant elastic behavior. This study is an important step forward on the path to understanding and implementing a nondestructive technique for stress monitoring of real concrete structures.

Contribution of Transverse Reinforcement Configuration on Concrete Shear Capacity of RC Column

Proper design of transverse reinforcement in the RC column is needed to maintain its ability to deform under axial and shear load safely. Even though mandatory building codes for transverse support of the RC column exist, shear failure was still found in the last high earthquake in Pidie, Aceh, in 2016. Therefore, as an attempt to improve RC column strength and elasticity, the effect of transverse reinforcement configuration was evaluated experimentally to a column subjected to an axial and shear load. The experiment was conducted by using four-column specimens with a cross-section 200 x 200 mm. Four types of transverse reinforcement configurations were applied in each column. The test was carried out by loading an axial load always and shear load gradually until its failure. The test results show that the configuration of transverse reinforcement has a significant effect of maintaining column stiffness, which was subjected to compressive axial load and shear load. Furthermore, the arrangement of transverse reinforcement influences the compressive strength significantly and enhance the concrete shear capacity of a column due to its confinement effect.

Cross validation of analytical solutions against the computational model predictions of the response of end bearing energy pile

Predictions of responses of a single energy pile to a combined mechanical and thermal loading are presented. They were obtained from computational and analytical models. The former model provided predictions based on a coupled thermal hydro-mechanical finite element analysis while the predictions of the latter were obtained from the recently derived analytical solutions. The energy pile is surrounded by a single uniform soil layer underlain by a very stiff bedrock. Two scenarios of temperature history were considered. In the first scenario the pile remained in a net heated state while the second one induced a net cooled state. In both loading scenarios a compressive axial load was applied at the pile head prior to the thermal loading. The net heating induced an upward axial displacement, tensile strain and compressive stress while the net cooling induced a downward vertical pile displacement, compressive strain and tensile stress. In spite of different methods of obtaining the soil stiffness for computational and analytical models the predictions of the axial pile displacement, stress and strain show a very good agreement.

Structural stability enhancement by nonlinear geometry design and piezoelectric layers

Vibration and stability analysis of nonlinearly tapered cone beams coupled with a piezoelectric layer under compressive axial load is conducted using a new semi-theoretical model based on the Adomian decomposition method and a modified mathematical procedure. The method is applied to tapered structures with perfectly surface-bonded piezoelectric layers and general boundary conditions to analytically derive the natural frequencies and mode shape functions for flutter and buckling analysis. Furthermore, from the optimum structural design perspective, the effects of follower force, geometrical tapering ratio, boundary condition, and applied voltage on piezoelectric layers on the structural stability are thoroughly studied and presented. Simulation results show that the stability of the beam can be noticeably enhanced by the external voltage because of a pair of tensile loads locally induced by the piezoelectric effect. Moreover, for certain boundary conditions and applied voltages, the nonlinear tapered design has much greater buckling and flutter capacities than does the uniform beam. Consequently, the ideal structural design for effective stability enhancement can be reached efficiently.

Earthquake resistance of reinforced concrete corner beam-column joints with different column axial loads under bi-directional lateral loading

The seismic performance of a corner beam-column joint in reinforced concrete frames was studied by testing two three-dimensional corner beam-column subassemblage specimens without slabs under constant column axial load and bi-directional lateral cyclic load reversals. The column-to-beam flexural strength ratio was varied from 1.4 to 2.3 by changing the magnitude of column axial load. Although a sufficient margin to prevent shear failure was provided to a corner beam-column joint in the test, the subassemblage specimens failed in joint hinging after beam and column longitudinal bars and joint hoops yielded. The ultimate joint hinging capacity of a corner joint under bi-directional lateral loading was enhanced by an increase in column compressive axial load, and can be estimated based on the new mechanism proposed by Kusuhara and Shiohara.

Dynamic and Stability Analysis of the Rotating Nanobeam in a Nonuniform Magnetic Field Considering the Surface Energy

It is well-known that rotating nanobeams can have different dynamic and stability responses to various types of loadings. In this research, attention is focused on studying the effects of magnetic field, surface energy and compressive axial load on the dynamic and the stability behavior of the nanobeam. For this purpose, it is assumed that the rotating nanobeam is located in the nonuniform magnetic field and subjected to compressive axial load. The nonlocal elasticity theory and the Gurtin–Murdoch model are applied to consider the effects of inter atomic forces and surface energy effect on the vibration behavior of rotating nanobeam. The vibration frequencies and critical buckling loads of the nanobeam are computed by the differential quadrature method (DQM). Then, the numerical results are testified with those results are presented in the published works and a good correlation is obtained. Finally, the effects of angular velocity, magnetic field, boundary conditions, compressive axial load, small scale parameter and surface elastic constants on the dynamic and the stability behavior of the nanobeam are studied. The results show that the magnetic field, surface energy and the angular velocity have important roles in the dynamic and stability analysis of the nanobeams.