Constructal Design for the ultimate buckling stress improvement of stiffened plates submitted to uniaxial compressive load

The ultimate compressive strengths of deck plates stiffened longitudinally by U-shaped stiffeners have been investigated by the nonlinear finite element analysis (FEA). A total of 112 hypothetical models with various combinations of slenderness parameters for the deck plates and column slenderness parameters for the stiffeners were modeled and analyzed. Both conventional and high performance steels were considered in models following elasto-plastic strain hardening constitutive relationships. Initial geometric imperfections and residual stresses were also incorporated in the FEA. Numerical results from FEA have been compared to compressive strengths from Eurocode 3 EN 1993-1-5, FHWA-TS-80–205, and other available formulas. Based on analysis results, new unified strength predictor equations have been developed for the stiffened plate systems with conventional steel and/or high performance steel (HPS). It has been found that use of Eurocode 3 EN 1993-1-5 and FHWA-TS-80–205 may lead to highly conservative design when large column slenderness parameters are encountered. The proposed equations have simple forms yet provide accurate strength predictions resulting in more economic design.

In-plane ultimate compressive strengths of HPS deck panel system stiffened with U-shaped ribs

The orthogrid-stiffened FRP panel (OSFP) is a generic structural element in weight-sensitive structure applications. Based on the variational asymptotic method, a 2D reduced-order plate model (2D-RPM) of OSFP was constructed through matching the strain energy of the original panel for static and dynamic analyses. The local field distributions were recovered using the recovery relationship and global response. The relative influences of select parameters on the effective performance of the OSFP were revealed by parametric studies. The comparative results showed that the effective performance of the OSFP predicted by the 2D-RPM were consistent with those predicted by the 3D finite element model, but the computational efficiency was greatly improved. The stiffener height had the greatest influence on the natural frequency of the panel. The layup configurations of laminates had significant influences on the equivalent stiffness and buckling load of the OSFP but had little effect on the vibration modes, which could be varied by adjusting the stiffening forms.

Estimating of the Static and Dynamic Behaviors of Orthogrid-Stiffened FRP Panel Using Reduced-Order Plate Model.

Orthogonal stiffened plates present in the ship deck are subjected to axial compression due to hogging and sagging bending moments and, lateral load due to cargo load. The main objective of this investigation is to determine the ultimate load carrying capacity and study the interactive behaviour of orthogonal stiffened plates under axial and lateral loads. Tests were conducted on six stiffened plates with plate slenderness ratios of 80 and 64, and corresponding column slenderness ratios of 24 and 26. Hydraulic jacks and inflatable air balloon with load control mechanism were fabricated to apply axial and lateral loads on the test specimens respectively. All the specimens were tested up to ultimate load and the mode of failure was determined based on the initial yielding observed in the plate and/or stiffener. Nonlinear finite element analysis of test specimens was performed using the general purpose FE software ANSYS®. Both material and geometric nonlinearities were considered in the FE analysis of test specimens. The ultimate loads obtained from the finite element analysis were compared with experimental data and found to be satisfactory. It was also observed that the mode of failure obtained from finite element analysis is similar as observed from experiments. It was concluded that the increase in lateral load beyond two thirds of ultimate lateral load significantly reduces the axial ultimate load carrying capacity of stiffened panels. The interactive effect of stiffened plates subjected to combined action of axial and lateral loads is determined as nonlinear.

C. Lavana Kumar

Papers

Ultimate strength of orthogonal stiffened plates subjected to axial and lateral loads