Steady-State Response Analysis of the Incompressible Nonlocal Saturated Poroelastic Beam under a Vertical Harmonic Load

Based on the nonlocal theory and the theory of saturated porous media, the mathematical and physical model and governing equations of the steady-state response of the incompressible nonlocal saturated poroelastic beam under vertical harmonic loading are established with assumption of the movement of the liquid-phase fluid only in the axial direction of the beam and considering the nonlocal effects such as particle size, pore size, and pore dynamic stress. The dynamic response of a saturated poroelastic cantilever beam with permeability at both ends under a vertical harmonic concentrated force at the free end is studied. In the frequency domain, the analytical expressions of deflection amplification factor and equivalent couple amplification factor of liquid fluid pressure are given. The effects of nonlocal coefficient τ, mechanical parameter α, and geometric parameter β on the deflection amplification factor and equivalent couple amplification factor at the midpoint of the nonlocal saturated poroelastic cantilever beam are studied. The results show that the steady-state vibration of the incompressible nonlocal saturated poroelastic cantilever beam has resonance. When the nonlocal effect is considered, the deflection amplification factor and the equivalent couple amplification factor are larger, so the influence of the nonlocal effect on the steady-state response of the beam should not be ignored. The geometric parameter β has significant effect on the peak positions of the curves of the deflection amplification factor and the equivalent couple amplification factor varying with frequency.

Assessment on the deflection amplification factor of steel buckling-restrained bracing frames

Researchers in the field of earthquake engineering are always looking for new ways to improve the seismic behavior of structures. The buckling-restrained brace (BRB) is one of these exciting innovations that are employed to increase the ductility capacity of traditional steel braced frames. Understanding the nonlinear response of these novel systems in estimating maximum displacements due to an earthquake has been of significant importance for structural designers. Accordingly, this research is carried out to study of deflection amplification factor ( C d) in BRBs, which have recently been presented in seismic design provisions as one of the seismic lateral-resisting systems. To this end, five 3-, 5-, 7-, 10-, and 15-story BRBs are modeled in the software framework of OpenSees. Ground motion simulation is performed by selecting several scaled earthquake records, and the values of elastic and ultimate displacements of structural systems are computed through pushover and nonlinear time-history analyses. The results showed that the deflection amplification factor suggested within famous building codes (such as ASCE-7-16) compared to the obtained values is, in some cases, for certainty; conversely, it is underestimated under some conditions. In fact, the findings indicate that the magnitude of C d in these systems is strongly related to the height of the building.

Modification of Buckling Restrained Braces and Evaluating the Deflection Amplification Factor

Buckling is a main problem in every structure. It is a sudden change in shape or deformation of a structural component under load. Under moderate to severe earthquakes, buckling of compressive braces may cause damage to the joints and connections. So Buckling-Restrained Braces (BRBs) have been widely implemented in framed structures to reduce damage during severe earthquakes. Unlike conventional braces that buckle under compression, the core of BRBs yields both in tension and compression under the restraining effect of the casing. A typical buckling-restrained brace (BRB) is composed of a ductile steel core, which is designed to yield in both tension and compression. To avoid global buckling in compression, the steel core is usually wrapped with a steel casing, which is subsequently filled with mortar or concrete. So in this work the deflection amplification factor of these braces are found out. As DAF predicts the maximum capacity of the structure, so a deep study in this field is necessary. DAF is the ratio of in-elastic deformations to elastic deformation. So after finding the DAF of these BRBs and by knowing the elastic deformation of the structure we can easily find the in-elastic deformation. For this works the analysis are carried out using etabs and abaqus software.

Estimation of Inelastic Interstorey Drift for OSB/Gypsum Sheathed Cold-Formed Steel Structures under Collapse Level Earthquakes

In order to estimate the inelastic interstorey drift of cold-formed steel (CFS) framed structures under collapse level earthquakes, the deflection amplification factor ηp is employed in this paper to compute the maximum interstorey drift ratio (IDRmax) from an elastic analysis. For this purpose, a series of CFS wall specimens were tested under cyclic horizontal loads, and then the hysteresis model of the walls was put forward by test results. In terms of the hysteresis model, a large quantity of elastic-plastic time-history analysis of CFS building structures was conducted based on the storey shear-type model. Furthermore, the deflection amplification factor ηp for estimating IDRmax and the parameters were analyzed. The results indicate that the deflection amplification factor ηp is highly dependent on yielding coefficient of storey shear force ξy, storey number N, period of structure T, and ground acceleration records GA. Eventually, an approximate ξy-N-ηp relationship for estimating the deflection amplification factor ηp is proposed in this paper, which can be used for seismic design in practices.

Evaluation of Seismic Response Factors for Eccentrically Braced Frames Using FEMA P695 Methodology

This paper reports details of a numerical study undertaken to evaluate seismic response factors for steel eccentrically braced frames (EBFs) using the FEMA P695 methodology. Six archetypes were designed by making use of the current U.S. specifications, and their behavior was assessed by making use of nonsimulated collapse models. Results indicate that the current values of response factors result in designs with higher collapse probabilities than expected. Two modifications were developed to bring the collapse probability of these archetypes to acceptable levels. The first modification is on the deflection amplification factor while the second one is on the response modification coefficient. Six archetypes were redesigned using the proposed modifications and reevaluated using the FEMA P695 methodology. The results indicate that the proposed modifications are adequate to satisfy the target collapse probability. Maximum and cumulative link rotation angles were observed to be less than the predefined limits.

The Analysis of Stiffness and Stability of Luffing Jib Cranes Based on Theory of Second Order

Luffing jib cranes are large flexible complex truss structure, and their mechanical property is nonlinearity. So the Precise analysis method for the stiffness and stability problem has been paid attention to by the researchers. To solve this problem, the equivalent mechanical model of luffing jib crane was established by taking the lifting load, counter weight and dead weight into consideration. The stiffness and stability of luffing jib crane was analyzed by using the differential equation of deflection based on second-order effect. The calculating formulas of lateral deflection, amplification factor of deflection and stability was derived. Taking a luffing jib tower crane for example, the lateral stiffness was calculated respectively by the formula given by this paper, the traditional linear method and the finite element method, and show that the result calculated by the formula given by this paper is identical to that by finite element software ANSYS, the error is 1.8%. and the error of traditional method is 7.6%, It is clear that calculation expression of lateral deflection, deflection amplification factor and the stability in this paper are accuracy. This method can be applied to the analysis of calculation of luffing jib tower crane stiffness and stability.