Keywords: rotational restraint, purlin, trapezoidal sheeting, non-linear analysis, cold-formed steel and FEM.

This research study is concerned about developing a numerical model to evaluate the rotational restraint provided by the trapezoidal sheeting to the attached purlins in cold-formed steel roofs using finite element analysis. It is well known that in the design of cold-formed steel purlins the influence of attached roof sheeting has a constructive role to play. The reason for this beneficial role is due to the additional stiffness provided by sheeting to purlin. The attached sheeting provides both lateral and rotational stiffness to purlin, and thus increases its strength. Evaluating these lateral and rotational stiffnesses has a major influence in the design of purlins. Though the numerical modelling of cold-formed steel purlin-sheeting system has been an active area of research study for several years, it is still not convincing and complete in predicting the rotational restraint provided by sheeting to purlin.

The difficulty in developing a numerical model for estimating the rotational restraint in the purlin-sheeting systems is due to the complexity of the problem. The amount of rotational restraint between purlin and sheeting varies with each purlin- sheeting combination and depends on the connection details. Since both purlin and sheeting undergo considerable local cross-sectional distortion and yielding, calculating the rotational restraint using analytical methods is a complex task, and hence it must be determined either by experimental methods or by finite element techniques. A brief overview of the purlin-sheeting system and an outline of the approaches that had previously been considered in its numerical modelling can be found in Lucas et al. [1].

Using non-linear finite element analysis, a new model is presented to predict the response of purlin-sheeting systems under gravity and uplift loads. In modelling the purlin-sheeting system using ABAQUS [2] finite element program, both purlin and sheeting are considered in the analysis along with screws and washers to include the effects of contact phenomena near connections. To verify the performance of the non-linear finite element model presented, experiments are conducted, known as Pekoz-tests in literature [3], on Z and section purlin-sheeting systems for gravity and uplift loads. It is found that the response of cold-formed steel purlin-sheeting systems obtained from both the experimental and numerical results are in good correlation.

Both purlin and sheeting are modelled using thin shell elements. Since the presence of the washer near the screw has a significant factor in reducing the stress concentration in its vicinity, this effect is included by taking washers in the model. Screws are assumed to be very stiff comparatively to other members, as our concern is not in the failure of the screws, and are modelled using beam elements. A linear elastic-plastic material model is used when modelling members except screws. Contact phenomena between top flange of the purlin and sheeting, washer and sheeting are modelled in the analysis.

The purpose of this paper is to demonstrate the performance of the present model in predicting the response of cold-formed steel purlin-sheeting systems by combining both experimental and finite element analyses. Experimental tests were conducted on different purlin-sheeting systems to see their response to both uplift and gravity loads. Using this finite element model in a parametric study on purlin- sheeting systems, understanding of the factors which influence the rotational restraint will be possible without rigorous experimental work. Furthermore, the collected results and data will assist in simplifying the calculation methods which are commonly used in design practice.

1

R.M. Lucas, G.A. Al-Bermani, S. Kitiporchai, "Modeling of Cold-Formed Purlin-Sheeting Systems - Part-1: Full Model", Thin-Walled Structures, 27 (3), 223-243, 1997. doi:10.1016/S0263-8231(96)00038-9

2

ABAQUS, Standard User's Manual - Version-6.4, Hibbitt, Karlsson and Sorenson, Inc.

3

EN 1993-1-3, Eurocode 3: "Design of Steel Structures Part 1-3, General Rules for Cold-Formed Thin Gauge Members and Sheeting", Belgisch Instituut voor Normalisatie, September 2002.

purchase the full-text of this paper (price £20)

go to the previous paper
go to the next paper
return to the table of contents
return to the book description
purchase this book (price £135 +P&P)