Ultimate strength of dented steel plates under axial compressive loads

Abstract

In this paper the ultimate strength characteristics of dented steel plates under axial compressive loads are investigated using the ANSYS nonlinear finite element code. The effects of shape, size (depth, diameter), and location of the dent on the ultimate strength behavior of simply supported steel plates under axial thrust are studied. A closed-form formula for predicting the ultimate compressive strength of dented steel plates are empirically derived by curve fitting based on the computed results. The results and insights developed in the present study will be useful for damage tolerant design of steel plated structures with local denting.

Introduction

Steel structures can normally suffer various types of damages while in service. Some types of damage such as corrosion and fatigue cracking are related to age, but others are more likely to be mechanical damage caused by accidental loading or impact. Structural damage can reduce load-carrying capacity of the structure and lead to catastrophic failure. Once structural damage is detected the operator will need to judge if relevant repair and maintenance should be done. In fact, repair or renewal of damaged structural part is in general complex and costly.

It is therefore of importance to better understand the strength reduction characteristics of structural members due to damage so that cost-effective action plan for repair and maintenance can be established. Also, to develop the damage tolerant design scheme for steel structures, it is required to assess the ultimate limit state based risk or reliability taking account of the effect of structural damage. In this case, closed-form expressions for predicting the ultimate strength of damaged structural members are needed. The present paper is concerned with the effect of local denting on ultimate compressive strength of steel plates making up steel plated structures such as ships, deck structures of offshore platforms and other land-based structures (e.g., bins, bunkers).

Mechanical damage may occur in plate panels of steel plated structures in many ways depending upon where such plates are used. In inner bottom plates of cargo holds of bulk carriers, mechanical damage can take place by mishandled loading or unloading of cargoes; Inner bottom plates have mechanical damage during loading of iron ore, because iron ore cargo strikes the plates. In unloading of bulk cargoes such as iron ore or coal, excavator hits the inner bottom plates mechanically. Deck plates of offshore platforms may be subjected to impacts due to objects dropped from a crane. Such mechanical damage may normally show various features such as denting, cracking, residual stresses or strains due to plastic deformation, and coating damage. The present paper is focused on local denting, while pending as further study for other factors.

Numerous studies related to formation of local denting itself in steel cylinders or offshore tubular members and its influence on the structural behavior are found in the literature [1], [2], [3], [4], [5], [6], [7], [8]. However, to the authors’ knowledge, there are a few numbers of contributions to denting in steel plates [9], [10], [11] and its effect on the plate ultimate strength.

In this regard, the primary contribution of the present study is to investigate the ultimate compressive strength reduction characteristics for steel plates due to local denting. It is expected that the effect of denting on the plate buckling collapse behavior may vary from shape and size of the dent, and thus a series of ultimate strength analyses varying such parameters are in this paper carried out using ANSYS nonlinear finite element method [12]. A closed-form formula for the ultimate strength of dented steel plates under axial compressive loads is empirically derived by curve fitting based on the ANSYS computations. The results and insights developed in the present study are summarized.