Analysis and Design of Cold-Formed Z Purlins

Abstract

Structures built by cold-formed segments of primary members secondary members and roof panels provide a different solution for a great variety of areas such as housing, storage, education, etc The design of cold-formed sections has obvious complexity in view of the buckling of sections vis-à-vis stress in the compression element, especially in flexure. In this study, effective section properties of the Z section are calculated for a wide range of configurations with different b/t ratios for flange subjected to maximum allowable stress. The section properties are being used to develop the optimum section configurations for constructing a structure in different regions. . The study gives different formulae for quick assessment of parameters and also presents simple design tools and a few standard cold-formed sections having similar configuration but for thickness to be used for residential or community shelters for different zones. Recourse is made to compare the results with similar studies using AISI code and compare the results of lapped purlin and purlin without laps design. The whole course is mainly focused on analyzing and designing cold-formed section purlin.

Introduction

I. INTRODUCTION

Two core types of steel segments arc presently used in building construction, explicitly, the hot-rolled and cold-formed sections. The use of cold-formed steel segments has increased considerably as the world steel industry moves from the production of hot-rolled segments and hot-rolled plates to coil and strip, often with galvanized and painted coaling. Compared with conventional hot-rolled steel members, the cold-formed steel members gain enhancement of tensile properties after cold-forming, decrease weight (higher strength to weight ratio), and quicker and easier installation. Unlike hot-rolled steel sections, the cold-formed steel sections arc usually slender and not doubly symmetric and subsequently, they're prone to a range of complex buckling modes and their interactions

Cold form sections have primary members and secondary members that provide a broad range of implementation in different sectors like health, education, housing, etc. The cold-formed section has large flat width to thickness ratio and it leads to buckling of the element still, Cold-formed steel has the following intrinsic characteristics

1. Flexibility in designs.
2. Easy and fast manufacturing and erection.
3. Ease in transportation and handling.
4. Economical and light in weight.
5. Low maintenance.
6. Easy future expansion.

TABLE 1

Merits of cold-formed steel over hot-rolled steel

Cold-formed section forming methods

Three methods are generally used in the manufacture of cold-formed sections are

• Cold roll forming
• Press brake operation
• Bending brake operation

II. PURLINS

[2][5] Purlins are used as secondary roof members which must support the cladding against the action of the wind and the snow load. cold-formed steel (CFS) Z-shaped purlins have been extensively used as a primary component in metal roof systems for low-rise industrial and commercial buildings around the world. Lapped joints with bolted connections are one of the most popular design solutions for providing the continuity of purlins in the multi-span roof system.

Cold-formed steel purlins are generally utilized in roof systems because of their high structural efficiency. cold-framed steel purlins C and Z sections, and the part normally ranges from 100 to 350 mm while the thicknesses range from 1.2 to 3.0 mm. yield strength is between 280 and 350 N/mm2, however, nowadays segments with yield strength up to 450 N/mm2 might be viewed as some respectability purlin frameworks giving superior load-carrying capacities. As of now, four various kinds of purlin frameworks are generally found with various levels of continuity (i) single-span, (ii) Double span, (iii) multi-span with sleeves (iv) multi-span with overlaps

A. Plan for Continuity of purlin

To accomplish some level of continuity, cold-formed members are lapped and anchored together for a distance of not less than 600 mm; i.e., every section extends out somewhere around 300 mm. (Hypothetically 609.6mm and 304.8mm, and Standard Indian practice 706mm and 353mm). The level of continuity might be expanded with a more extended (long) lap distance, though at an expense of the additional material utilized in the lap. Continuous purlins are subject to varying bending moments at different spans, even from uniform loads. The most critical bending stress is a continuous beam that occurs at the end spans. It follows that the end purlins must have stronger sections than the inner ones. Some producers select to make use of the equal purlins all through the construction and offer extra splice lengths for end bay purlins. But it can suggest a few value performances have been forgone and all of the purlins saved to the dimensions managed via way of means of the end span. 

III. DESIGN METHODOLOGY

The gross sectional properties and effective sectional properties of the following sectional configuration are calculated and compared,

TABLE 2

Sectional configuration used for theoretical investigation

[11] In the analysis, the effective section properties were calculated by using the effective widths of single members. For example from the below fig 3, let us consider the abcdef compression element. Effective parts are highlighted. Section A1, the parts A-1, 2-3, 4-5, 6-7, and 8-F are regarded as being ineffective in resisting compression. As a general rule, the portions located close to the supported edges are effective. Note That in the case of compression members, all elements are subject to reductions in width.

In the case of flexural members, in most cases, only the compression elements are considered to have effective widths  

IV. THEORETICAL ANALYSIS 

The theoretical study involves the analysis and design ‘Z’ shaped purlin section. Calculations are done as per codal provisions of Indian standard IS 801-1975 and American standard AISI 2008 for effective width, for designing IS 801-1975 is taken.

VI. ACKNOWLEDGMENT

The author conveys gratitude to guide Dr. Tushar G. Shende Professor, Civil Engineering Department, and co-guide Dr. R. V. Megharajani, Neo Infrastructure Consultants, Nagpur for providing valuable guidance without which this Project Work would not have been possible.

Conclusion

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Copyright

Copyright © 2022 Rashmi Shambharkar, Dr. Tushar Shende , Dr. Ramesh Meghrajani. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.